Vertebrate Pesticide Toxicology Manual (Poisons)Information on Poisons Used in New Zealand as Vertebrate Pesticides

2nd Edition (formerly the ‘Toxins Manual’)

Charles T. Eason and Mark Wickstrom

AcknowledgementsThis nomination has the endorsement of the New Zealand Conservation Authority and the Royal Forest and Bird Protection Society.

© Crown copyright

Department of Conservation

PO Box 10-420

Wellington

New Zealand

ForewordThis manual was first compiled in 1997 and published by the Department of Conservation as a scientific reference document designed to assist all those involved in the planning, and use of, registered poisons for the control of animal pests in New Zealand. It is appropriate that a second edition has been produced as the use of pest control products for conservation is a rapidly evolving field with numerous publications relating to their efficacy, advantages, and disadvantages appearing in the last 3 years. Please note that other documents will need to be referred to for details of the Health and Safety aspects of working with toxic substances.

The Department recognises that the use of vertebrate pesticides to control animal pests will always be difficult for some members of the wider community to accept, especially the concept that the benefits of their use may outweigh any perceived or real deleterious environmental effects.

New Zealand’s animal pest problems are unique. Unlike in Australia, where many native plants contain natural toxins (including monofluoroacetate, the active chemical for 1080) as defence against browsing animals, the New Zealand forests evolved in the absence of mammals and without a need for such chemical defences. Our forests are, therefore, extremely vulnerable to mammalian browsers. The application of toxic baits has been developed as one effective means of controlling animal pests. Continued access to, and acceptability of, poisons is essential if we are to maintain our economic health and meet our international obligations for biodiversity protection, to say nothing of maintaining the natural heritage of our forest landscapes. The maintenance of this access depends upon the continued responsible use of poisons by all who are required to use them. It must be appreciated that all poisons have advantages and disadvantages, which make them more or less appropriate for different use patterns.

The information included in this manual is specifically relevant to the use of toxic baits for pest control as part of the management of conservation lands and protected species. It is, however, likely to be useful to all land managers who currently use or would consider the use of toxic baits to deal with animal pests; the Department expects, and welcomes its use by a wide range of agencies and individuals who have similar pest problems, or a need to understand the toxicology and safety issues associated with the use of vertebrate pesticides.

The Vertebrate Pesticide Toxicology Manual (Poisons) contains details from the most recently published scientific data on the effects and impacts of specific poisons on the environment, target, and non-target species. This document should be used in conjunction with other documents such as the Department of Conservation’s National Possum Control Plan. We urge all users to acknowledge, however, that it can only be their personal responsibility to remain up-to-date in all aspects of law and current best practice in the use of these tools. If in any doubt, seek advice!

Please note that this manual has been compiled independently of the Department of Conservation’s Quality Conservation Management (QCM) process, but should be used in conjunction with the proposed Animal Pest QCM. The emphasis in this edition is similar to that in the first edition. Those poisons used widely are reviewed in considerable depth, e.g. 1080, cyanide, brodifacoum, and cholecalciferol. Some, but

1

less complete, information is provided on other poisons and those no longer used in New Zealand.

We trust that this manual when used in conjunction with the Animal Pest QCM will provide clear and concise information on the planning, use, and effects of poisons for animal pest control. Suggestions for the improvement of this manual are welcome.

Murray HoskingGeneral Manager, Conservation Policy

2

Contents

Foreword.....................................................................................................................1

Contents......................................................................................................................3

Introduction.................................................................................................................7

SECTION 1: ACUTE POISONS 9

1.1 Sodium monofluoroacetate (1080).......................................................................91.1.1 Physical and chemical properties....................................................91.1.2 Historical development, use, and occurrence in nature..................91.1.3 Fate in the environment................................................................101.1.4 Toxicology and pathology............................................................161.1.5 Diagnosis and treatment of 1080 poisoning.................................241.1.6 Non-target effects.........................................................................261.1.7 Summary.......................................................................................29

1.2 Cyanide (Feratox®)...........................................................................................301.2.1 Physical and chemical properties..................................................301.2.2 Historical development, use, and occurrence in nature................301.2.3 Fate in the environment................................................................321.2.4 Toxicology and pathology............................................................321.2.5 Diagnosis and treatment of cyanide poisoning.............................361.2.6 Non-target effects.........................................................................381.2.7 Summary.......................................................................................39

1.3 Cholecalciferol (Campaign®, FeraCol®)..........................................................401.3.1 Physical and chemical properties..................................................401.3.2 Historical development, use, and occurrence in nature................401.3.3 Fate in the environment................................................................411.3.4 Toxicology and pathology............................................................411.3.5 Diagnosis and treatment of cholecalciferol poisoning..................441.3.6 Non-target effects.........................................................................461.3.7 Summary.......................................................................................47

SECTION 2: ANTICOAGULANT POISONS 49

2.1 Brodifacoum (Talon®, Pestoff®)......................................................................492.1.1 Physical and chemical properties..................................................492.1.2 Historical development and use....................................................492.1.3 Fate in the environment................................................................502.1.4 Toxicology and pathology............................................................502.1.5 Diagnosis and treatment of anticoagulant poisoning....................572.1.6 Non-target effects.........................................................................612.1.7 Summary.......................................................................................65

2.2 Flocoumafen.......................................................................................................662.2.1 Physical and chemical properties..................................................662.2.2 Historical development and use....................................................662.2.3 Fate in the environment................................................................66

3

2.2.4 Toxicology and pathology............................................................662.2.5 Diagnosis and treatment of poisoning (see 2.1.5).........................692.2.6 Non-target effects.........................................................................692.2.7 Summary.......................................................................................69

2.3 Bromadiolone (Rid Rat).....................................................................................702.3.1 Physical and chemical properties..................................................702.3.2 Historical development and use....................................................702.3.3 Fate in the environment................................................................712.3.4 Toxicology and pathology............................................................712.3.5 Diagnosis and treatment of poisoning (see 2.1.5).........................722.3.6 Non-target effects.........................................................................722.3.7 Summary.......................................................................................73

2.4 Coumatetralyl (Racumin®)................................................................................732.4.1 Physical and chemical properties..................................................732.4.2 Historical development and use....................................................742.4.3 Fate in the environment................................................................742.4.4 Toxicology and pathology............................................................742.4.5 Diagnosis and treatment of poisoning (see 2.1.5).........................752.4.6 Non-target effects.........................................................................752.4.7 Summary.......................................................................................75

2.5 Diphacinone (Ditrac®)......................................................................................752.5.1 Physical and chemical properties..................................................752.5.2 Historical development and use....................................................762.5.3 Fate in the environment................................................................762.5.4 Toxicology and pathology............................................................762.5.5 Diagnosis and treatment of poisoning (see 2.1.5).........................782.5.6 Non-target effects.........................................................................782.5.7 Summary.......................................................................................79

2.6 Pindone...............................................................................................................792.6.1 Physical and chemical properties..................................................792.6.2 Historical development and use....................................................792.6.3 Fate in the environment................................................................802.6.4 Toxicology and pathology............................................................802.6.5 Diagnosis and treatment of poisoning (see 2.1.5).........................822.6.6 Non-target effects.........................................................................822.6.7 Summary.......................................................................................83

2.7 Warfarin.............................................................................................................832.7.1 Physical and chemical properties..................................................832.7.2 Historical development and use....................................................842.7.3 Fate in the environment................................................................842.7.4 Toxicology and pathology............................................................842.7.5 Diagnosis and treatment of poisoning (see 2.1.5).........................862.7.6 Non-target effects.........................................................................862.7.7 Summary.......................................................................................86

4

SECTION 3: TOXINS NO LONGER USED BY THE DEPARTMENT 87

3.1 Phosphorus ......................................................................................................873.1.1 Physical and chemical properties..................................................873.1.2 Historical development and use....................................................873.1.3 Fate in the environment................................................................873.1.4 Toxicology and pathology............................................................883.1.5 Current use....................................................................................89

3.2 Arsenic ......................................................................................................903.2.1 Physical and chemical properties..................................................903.2.2 Historical development and use....................................................903.2.3 Fate in the environment................................................................903.2.4 Toxicology and pathology............................................................903.2.5 Current use....................................................................................91

3.3 Strychnine ......................................................................................................913.3.1 Physical and chemical properties..................................................913.3.2 Historical development and use....................................................923.3.3 Fate in the environment................................................................923.3.4 Toxicology and pathology............................................................923.3.5 Current use....................................................................................93

SECTION 4: COMPARATIVE RISK ASSESSMENT FOR COMMONLYUSED VERTEBRATE PESTICIDES 94

4.1 What and where are the exposure and non-target risks.....................................944.1.1 Persistence in water, soil, plants.....................................................944.1.2 Susceptibility and risk reduction for pets and livestock.................974.1.3 Risk of exposure and toxicity to non-target vertebrates (wildlife). 984.1.4 Risk of exposure and toxicity to invertebrates..............................1004.1.5 Risk of exposure to humans..........................................................1014.1.6 Toxic effects and humaneness in non-target species....................1044.1.7 Humaneness in target species.......................................................1064.1.8 Summary of characteristics of poisons used for possum control..108

Acknowledgements.................................................................................................109

References...............................................................................................................110

Address list for suppliers of pest control products..................................................135

APPENDICES 135

Appendix 1 Glossary of terms.........................................................................135

Appendix 2 Quality specifications for 1080 pellet baits..................................139

Appendix 3 Quality specifications for 1080 carrot baits.................................141

Appendix 4 Possum baits per lethal dose (LD)...............................................144

5

LIST OF TABLES

Table 1: Water analysis after major 1080 operations............................................13

Table 2: Toxicology studies on 1080 relevant to human health: current status....19

Table 3: Acute oral toxicity (LD50 mg/kg) of sodium monofluoroacetate.............22

Table 4: Plants with cyanogenic potential ............................................................31

Table 5: Acute oral toxicity (LD50mg/kg) of cyanide............................................35

Table 6: Acute toxicity (96-hour LD50) of cyanide to daphnia and fishfrom aquaria............................................................................................35

Table 7: Acute oral toxicity (LD50mg/kg) of cholecalciferol................................43

Table 8: Summary of secondary poisoning studies...............................................47

Table 9: Acute toxicity (LD50mg/kg) of brodifacoum in rats................................52

Table 10: Persistence of first-generation anticoagulants.........................................54

Table 11: Persistence of second-generation anticoagulants....................................54

Table 12: Acute oral toxicity (LD50mg/kg) of brodifacoum for mammal species...56

Table 13: Acute oral toxicity (LD50mg/kg) of brodifacoum for bird species..........57

Table 14: Acute oral toxicity (LD50mg/kg) of flocoumafen....................................67

Table 15: Occurrence of peak plasma concentrations in animals after oralingestion of anticoagulants......................................................................68

Table 16: Acute oral toxicity (LD50mg/kg) of bromadiolone..................................72

Table 17: Acute oral toxicity (LD50mg/kg) of coumatetralyl..................................74

Table 18: Radioactivity in the tissue of female rats 8 days after oraladministration of a single dose of 14C-diphacinone................................77

Table 19: Detectable diphacinone residues in tissue of cattle.................................77

Table 20: Acute oral toxicity (LD50mg/kg) of diphacinone ....................................78

Table 21: Acute oral toxicity (LD50mg/kg) of pindone...........................................82

Table 22: Acute oral toxicity (LD50mg/kg) of warfarin...........................................85

Table 23: Acute oral toxicity (LD50mg/kg) of phosphorus......................................89

Table 24: Acute oral toxicity (LD50mg/kg) of arsenic.............................................91

Table 25: Acute oral toxicity (LD50mg/kg) of strychnine........................................93

Table 26: Summary of mean times to onset of clinical signs of toxicosis............107

FIGURE

Figure 1: Relationships of aspects of the science of ecotoxicology and

toxicology and the different levels of biological organisation..............104

6

IntroductionThe focus of this manual is on the properties of poisons used for mammalian pest control. Intensive measures have been devised, and implemented on an unprecedented scale in New Zealand, to control a wide variety of introduced mammals. These include aerial application of 1080 bait on mainland New Zealand, and baits containing brodifacoum to kill rodents on islands. Such measures are amongst the most aggressive taken worldwide to control introduced mammals.

The risk to non-target species, from the compounds, will be determined by their intrinsic susceptibility, the properties of the poisons used, such as the toxicokinetics of these chemicals, as well as bait design and the way in which toxic baits are used in the field, which may limit or exacerbate the exposure of non-target species. The manual documents in detail the different properties of the different poisons. All have advantages and disadvantages, which make them more or less effective or appropriate for different use patterns. There is a massive literature on these compounds generated around the world, which is complemented by New Zealand-based research. A review was undertaken of the first edition of this manual and additional details with regard to the treatment of poisoning incidents were requested (Moffat 1999). In response to this review, the second edition contains more details on symptoms, diagnosis, and treatment for those poisons extensively used: 1080, cyanide, cholecalciferol, and brodifacoum. There is a greater emphasis on comparative toxicokinetics, and a new section at the end of the manual on the comparative risks associated with different poisons.

The first edition of this manual has frequently been referred to as the ‘Toxins Manual’ (Haydock & Eason 1997). This reflects some confusion with regard to the following terms: toxins, toxicants, poisons, and vertebrate pesticides. Toxic substances of natural biological origin, principally derived from microbes, plants, and animals are usually described as toxins (e.g. cholecalciferol (vitamin D3), cyanide, and 1080). Toxicants are considered to be substances that are toxic in relatively small doses and do not originate from microbes, animals, and plants (e.g. brodifacoum, phosphorus, and pindone). The term ‘poison’ or ‘vertebrate pesticide’ can be used to cover both toxins and toxicants. In the context of this manual, compounds such as cholecalciferol and warfarin are considered as vertebrate pesticides, whereas the former is commonly regarded as a vitamin and the latter as a drug used to treat blood clotting disorders in humans. This should not be that surprising since ‘All substances are poison and it is only the dose that makes a distinction between one which is a poison and one which is a remedy.’ (Paracelsus c. 1500) Vertebrate pesticides (sometimes referred to as rodenticides) are distinguished from insecticides (toxic to insects), herbicides (toxic to plants), and fungicides (toxic to fungi). In this regard 1080 is unusual as it is known to be toxic to both insects and mammals and could therefore be classified as an insecticide, a vertebrate pesticide, or a rodenticide.

We1 hope that compiling the significant toxicological features of these vertebrate pesticides in one document will assist all those directly or indirectly involved in the application of toxic baits for wildlife management. The focus of the document is the

1 Dr C.T. Eason is a Wildlife and Environmental Toxicologist Dr M. Wickstrom is a Veterinary Toxicologist formerly working for Landcare Research, currently at the University of Saskatchewan, Canada

7

toxins and toxicants commonly used by the Department of Conservation (DOC) in New Zealand, e.g. 1080, brodifacoum, cyanide and cholecalciferol. Other, less widely used, anticoagulants and poisons no longer used by the Department are covered only briefly. Toxicology is the study of the fate and effects of compounds with a toxic potential. The manual follows the same general structure as that requested by the Department of Conservation in the first edition. However, a new section has been added to assist with the comparison of the key features of the different toxins and toxicants. A glossary of terms is provided in Appendix 1. Note that many common names for animals are used throughout the manual. Those interested are referred to the original research for the scientific names where these are not cited.

Dr Charles T. EasonCENTOX Centre for Environmental ToxicologyLandcare Research, Lincoln

8

While every care has been taken to ensure its accuracy, the information obtained in this report is not intended as a substitute for specific specialist advice. Landcare Research accepts no liability for any loss or damage suffered as a result of relying on the information, or applying it either directly or indirectly.

SECTION 1 : ACUTE POISONS

1.1 Sodium monofluoroacetate (1080)

Chemical Name: Sodium monofluoroacetate.

Synonyms: monofluoroacetate or Compound-1080 or 1080 (“ten-eighty”)

Sodium monofluoroacetate (1080) is still the most widely used poison for possum control in New Zealand (in carrot, cereal, paste, and gel baits) for situations where possum numbers need to be reduced rapidly over large areas. Carrot baits are screened to remove small pieces so that the risks of birds eating baits is reduced. Cereal baits are used for both aerial and bait station control. Paste baits, and more recently gel bait, are used for ground-based follow-up maintenance control. Cinnamon is usually added to baits to mask the taste of 1080, and may be a partial deterrent to birds. Sodium monofluoroacetate can only be used by licensed operators.

1.1.1 Physical and chemical propertiesThe empirical formula for 1080 is C2H2FNaO2 and the molecular weight is 100.3. It forms an odourless, white, non-volatile powder that decomposes at about 200ºC. Although the compound is often said to be tasteless, dilute solutions are thought to taste like weak vinegar. Sodium monofluoroacetate is very water-soluble but has low solubility in organic solvents such as ethanol and oils. Monofluoroacetates are chemically stable, hence 1080 as a pure compound in powder form—or when prepared in an aqueous stock solution—will not readily decompose.

1.1.2 Historical development, use, and occurrence in natureSodium monofluoroacetate was first used in the United States about 50 years ago to control gophers, ground squirrels, prairie dogs, field mice, and commensal rodents. In New Zealand it is a pivotal component of pest control and has been developed specifically for aerial control of possums (Morgan 1994a,b), though it is increasingly being used for predator control through primary (pers. comm. E.B. Spurr) and secondary poisoning (Alterio 2000). Currently in New Zealand the principal target species are possums (Thomas 1994) and rabbits. Overuse of 1080 baits may result in bait shyness, but this may be avoided or mitigated by adherence to high-quality baiting practices and use of different bait types (Morgan et al. 1996b; Ogilvie et al. 2000; Ross et al. 2000) or additives to the baits (Cook 1999; Cook et al. 2000) Despite this risk of ‘shyness’ 1080 remains a highly effective tool for possum control. Manufactured 1080 for use in toxic baits has been shown to be chemically identical to the toxic compounds found in a poisonous plant; naturally produced 1080 induces the same signs and symptoms in animals (de Moraes-Moreau et al. 1995). Highly toxic fluoroacetate-producing plants are globally distributed with species on several major continents. Research in the 1940s identified monofluoroacetate, the active toxin in 1080, as the toxicant in the South African plant gifblaar (Dichapetalum cymosum), long recognised as a hazard to livestock. Since this discovery, monofluoroacetate has

9

been identified as the toxic agent in many other poisonous plants, such as rat weed (Palicourea margravii), native to Brazil (de Moraes-Moreau et al. 1995); and ratsbane (Dichapetalum toxicarium), native to West Africa (Atzert 1971).

Monofluoroacetate also occurs naturally in some 40 plant species in Australia. Air-dried leaves of Gastrolobium bilobum (heart-leaf poison) and G. parviflorum (box poison), for example, can contain up to 2600 mg/g of monofluoroacetate, and seeds of G. bilobum can have in excess of 6500 mg/kg of monofluoroacetate (Twigg 1994; Twigg et al. 1996a,b; 1999). The highest monofluoroacetate concentration so far reported from a living source is 8000 mg/g in the seeds of Dichapetalum braunii (Meyer 1994).

Monofluoroacetate would appear to be one of the many secondary plant compounds that have evolved at high concentrations as a defence mechanism against browsing invertebrates and vertebrates. Most studies assessing monofluoroacetate concentrations in plants have focused on those species that are overtly toxic to mammals. However, it would appear that the ability of plants to synthesise monofluoroacetate is more widespread than generally supposed, since monofluoroacetate occurs at extremely low concentrations in some Finnish plants (Vartiainen & Kauranen 1980), in tea leaves (Vartiainen & Kauranen 1984), and guar gum (Vartiainen & Gynther 1984; Twigg et al. 1996b). In addition some plants, when exposed to fluoride ion, can biosynthesise fluoroacetate, albeit at very low levels. Fluorocitrate, the toxic metabolite of monofluoroacetate, has also been detected in tea leaves (Peters & Shorthouse 1972). Fluoroacetate biosynthesis can also occur in some bacteria, notably Streptomyces cattleya (O’Hagan & Harper 1999). Resistance in mammals, birds, and insects occurs in areas where there is continued exposure to the toxin. Interestingly, the caterpillar moth, Sindrus albimaculatus, which feeds on Dichapetalum cymosum, can not only detoxify fluoroacetate, but also accumulate it (probably in vacuoles) and uses it as a defence against predation (Meyer & O’Hagan 1992).

1.1.3 Fate in the environmentPersistence in soilPresumably, naturally occurring monofluoroacetate is diluted by rainwater and breaks down in soil after leaves and seeds drop to the ground or when the plants die. Not all micro-organisms can readily defluorinate monofluoroacetate and the rate of metabolism differs with different species of soil bacteria and fungi (King et al. 1994). Sodium monofluoroacetate, the sodium salt of this natural toxin, can certainly be metabolised by some soil micro-organisms, such as Pseudomonas and Fusarium species (Walker & Bong 1981; King et al. 1994). Enzymes capable of defluorinating fluoroacetate have been isolated from several micro-organisms. The active site of the enzyme attacks fluoroacetate. The fluoride carbon bond is cleaved and ultimately enzyme-bound intermediates form non-toxic metabolites such as glycolate (O’Hagan & Harper 1999).

Sodium monofluoroacetate derived from baits will also be dispersed by water since it is highly water soluble and mobile (Parfitt et al. 1995). In older literature, it was suggested that 1080 is retained in solid particles and does not leach. This conclusion was based on the mistaken assumption that 1080 would not be held on cation-exchange sites in soil. However, monofluoroacetate is an anion and New Zealand-

10

based research has demonstrated that it could potentially be leached through soil by water (Parfitt et al. 1995). If heavy rainfall follows the use of 1080 baits, dilution to unmeasurable concentrations (<0.0001 ppm) may precede biodegradation. In comparison to cereal bait, 1080 is retained in carrot baits and will only slowly leach from carrots into the soil (Bowen et al. 1995). However, control operations are planned to coincide with periods of dry weather, and some defluorination by micro-organisms on the decaying baits and in the soil around baits is probable, particularly if the baits become moist. Under favourable conditions, such as 11–20ºC and 8–15% moisture (King et al. 1994), 1080 may be significantly defluorinated in 1–2 weeks. In less favourable conditions breakdown might take several weeks and, in extreme cold and drought, 1080 residues might persist in baits or in the soil for several months.

Sodium monofluoroacetate that has leached into soil may be absorbed by plants (Atzert 1971; Rammell & Fleming 1978). Cabbage (Brassica oleracea capitata) has been shown to systematically accumulate 1080 through its roots, and subsequently become toxic to aphids (Negherbon 1959). To investigate whether herbivores may be at risk of secondary poisoning if they consume plants that have taken up 1080 leached from bait, concentrations of 1080 have been assessed in broadleaf (Griselinia littoralis) and perennial ryegrass (Lolium perenne) following simulated baiting (Ogilvie et al. 1998). The observation in both species that 1080 was absorbed, reached a peak, and then decreased to near the limits of detection, supports previous findings that plants can degrade 1080 (Preuss & Weinstein 1969; Ward & Huskisson 1969). The concentration achieved in broadleaf and ryegrass would be most unlikely to cause poisoning (Ogilvie et al. 1998).

Monofluoroacetate appears to be defluorinated by plants (Preuss & Weinstein 1969; Ward & Huskisson 1972) and animals (Eason et al. 1993a), which may make a small contribution to the removal of monofluoroacetate from the environment following the use of baits containing 1080.

The gene encoding for the bacterial enzyme capable of defluorinating fluoroacetate in soil has been cloned and expressed in the rumen bacteria, Butyrivibros fibriscolens. This organism has then, in an experimental setting, been employed to infect the gut of sheep in an attempt to protect against dietary poisoning by fluoroacetate-containing plants. Early indications are that the genetically modified organisms become established sufficently well to give the sheep a degree of resistance to fluoroacetate (Annison & Bryden 1998; Gregg et al. 1998). Currently there are no plans to introduce genetically modified organisms into New Zealand livestock to protect them from 1080 baits.

Water and 1080Communities in New Zealand have expressed considerable concern with regard to their potential exposure to 1080 after aerial application of 1080 bait. Between 1990 and 2000, field monitoring programmes of 1080 were undertaken after more than 25 possum and one rabbit large-scale control operations using aerially sown 1080 baits. These recent surveys are summarised in Table 1. There has been no evidence of 1080 presence in reticulated water and no evidence of significant or prolonged 1080 contamination in surface or ground waters (Eason et al. 1992; Hamilton & Eason 1994; Parfitt et al. 1994; Meenken & Eason 1995; Booth et al. 1997; Eason 1997; Eason et al. 1999b).

11

Trace amounts of 1080 have been found close to the limit of detection (of 0.0003 mg/L) in approximately 5% of over 1000 water samples. The occurrence is transient and has frequently been associated with the visible presence of baits in small streams. Further surveys in New Zealand continue to show that significant contamination of waterways is unlikely after carefully conducted control operations.

A series of laboratory studies have shown that 1080 would be biodegraded by aquatic plants and micro-organisms if small amounts entered waterways. The rate of breakdown would be temperature-dependent, and in fast-running streams dilution of the toxin would be more important in reducing the presence of 1080 to toxicologically insignificant concentrations. The breakdown of this toxin has been found to occur more rapidly at higher temperatures, but still occurs at <7ºC within 1–2 weeks (Ogilvie et al. 1996). Fluorocitrate (the active metabolite of 1080) has been detected in aquaria spiked with 1080. Its disappearance paralleled that of 1080, hence absence of 1080 in environmental samples would indicate that there would be a very low risk of fluorocitrate being present (Booth et al. 1999b).

12

Table 1. Water analysis after major 1080 operations. Further water sampling and residue analyses are anticipated as part of standard operating procedures enforced by Medical Officers of Health when granting approvals for aerial 1080 operations. (Adapted from Eason et al. 1999b with some recent results spanning 1998–99 added)

Location Date Total no. of samples taken in operation area

No. with residues

Highest concentrations (µg/L or ppb)

Waipoua

Rangitoto

Blackstone Hill

Mt Taranaki

Woodside

Hunua Range

Mt Taranaki

Marlborough Sounds

Wairarapa

Hawke’s Bay

Ohakune

Whangarei

Karioi

Manawatu

Waimakariri

Manawatu

Hawke’s Bay

Ohakune Erua Forest

Tongariro National Park

Northland

Tararua Ranges

Hawke’s Bay

Waimarino Forest

Wairarapa

Pirongia

Raukumara Ranges

Waikato

Levin Buffer

Erua State Forest

Waitohu Stream

Wairokau Stream

Raukumara Ranges

Ohakune

Pareora River, Timaru

Rangataua Forest

Te Whaiau Spillway

Raukumara Ranges

East Cape

Warawara Forest

Mt Bruce/Mikimiki

1990

1991

1992

1993

1993

1994

1994

1994

1994

1994

1994

1994

1994

1994

1995

1995

1995

1995

1995

1995

1995

1995

1995

1996

1996

1996

1996

1996

1996

1996

1997

1997

1997

1997

1997

1997

1997

1997

1997

1998

36

20

23

125

55

136

63

26

31

15

6

18

10

21

4

48

8

3

8

11

11

9

4

7

7

37

4

8

3

4

4

12

10

2

40

3

9

12

4

10

0

0

11

15

0

7

0

5

0

0

1

0

1

0

1

0

1

0

0

0

0

0

0

0

0

1

0

0

1

0

0

0

0

0

0

1

1

0

0

0

-

-

0.6

<0.3

-

0.7

-

3.4

-

-

0.2

-

0.8

-

0.2

-

0.3

-

-

-

-

-

-

-

-

0.2

-

-

3.5

-

-

-

-

-

-

2.4

0.5

-

-

-

13

Location Date Total no. of samples taken in operation area

No. with residues

Highest concentrations (µg/L or ppb)

Mawheraiti, West Coast

Kuharua Tb

Manawatu-Wanganui

Toko

Wairarapa

Manawatu-Wanganui

West Taieri Stream

Hook Bush, Timaru

Haurangi Crown

Northland

Otorohanga, Te Tahi

Ahuroa/Maungatoroto

Levin Buffer

Lawrence/Waitahuna

Northland

Masterton

Richmond

Porangahau

Northland

Waipoua Forest

Waipa River

Holdsworth/Woodside

Manawatu–Wanganui

Hawke Hills

Warawara Forest

Waima

Riwaka Forest

Eastern Tararua R.

Takaka

Amuri Range

Hawkins River

Wakamarama

Northland

Wainuiomata

Aorere

Hauturu/Honikiwi

Otorohanga

Wainuiomata

Pembroke Wilderness

Aorere

Rotomanu

Kaiiwi

Inland Paparoa

1998

1998

1998

1998

1998

1998

1998

1998

1998

1998

1998

1998

1998

1998

1998

1998

1998

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1

1

6

3

8

8

4

2

6

9

3

2

2

8

5

6

9

3

7

1

2

3

2

2

1

2

2

7

6

1

1

15

8

26

2

2

1

25

6

6

2

4

12

0

0

0

2

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

-

-

-

9.0*

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

14

Location Date Total no. of samples taken in operation area

No. with residues

Highest concentrations (µg/L or ppb)

Te Kopia Scenic Res.

Marlborough

Tapu River/Te Mata Str.

Te Kopia Scenic Res.

Benhopai

Eastern Tararua R.

Hauhungaroa Range

Hampden, Herbert

Manawatu–Wanganui

Waingawa

Tapanui

Murupara

Manawatu–Wanganui

Wairarapa

Totals

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

1999

10

1

7

1

1

4

8

14

2

1

1

1

1

2

1153

2

1

0

0

0

0

0

0

0

0

0

0

0

0

51

4.0

0.2

-

-

-

-

-

-

-

-

-

-

-

-

* This sample is included in the table but not included with regard to our risk assessment extrapolations on p.15. Enquiries from Landcare Research’s senior chemist identified that the sample had been collected by a worker with 1080 dust on his overalls and hands.

When considering the risks posed to humans from exposure to 1080 through drinking water it is worth exploring the process of risk assessment, which typically involves hazard identification and exposure assessment. The risks associated with 1080 to human health (or livestock or non-target wildlife) is determined by the innate toxicity of 1080 and the potential for exposure:

Risk = Hazard Exposure.

In a recent review Beasley (1996) pointed out that human exposure to 1080 might arise from drinking contaminated water, ingestion of toxic baits, consumption of food contaminated by contact with bait, or by inhalation of bait dust or contact with 1080 solution by pest control operators and bait manufacturers. Potentially the most significant source of general public exposure was considered to be contamination of surface water in public-water-supply catchments by aerially sown 1080 baits.

As indicated above, 1080 has never been detected in reticulated water at the point of consumption. The highest concentrations measured in surface water within the boundaries of pest control areas following aerial 1080 bait distribution are between 3.5 and 4.0 µg/L (ppb) (Table 1). If this concentration is chosen as a worst-case exposure scenario, the potential risk of adverse developmental effects from exposure of pregnant women to drinking water following possum control operations can be crudely assessed, based on recent observations in rats (Eason et al. 1999b). (For further details of recent regulatory toxicology studies on 1080, see the pathology section 1.1.4.)

15

The assumptions used in these calculations are those recommended by the Ministry of Health (Drs G. Durham and N. Foronda, pers. comm.), and are intended to be very conservative (i.e. protective). If a 50-kg woman consumed water containing 1080 at 3.5–4.0 g/L to provide all of her 2-litre daily intake during the first 90 days of pregnancy (the approximate period of organogenesis during which the foetus is most sensitive to toxic insult), she would receive a daily 1080 dose of 0.14–0.16 g/kg. The ‘safe human exposure’ for developmental end points is derived by applying a 1000-fold safety factor to the no-observable-effect level (NOEL) from the developmental toxicity study in rats: 0.1 mg/kg/day 1000 = 0.1 g/kg/day. Therefore, the potential dose received under this worst-case scenario is slightly greater than the ‘safe human exposure’ derived from the developmental toxicity study (after application of the 1000-fold safety factor).

In light of these findings, the Ministry of Health (MOH) recommended in 1998 that potable water from catchments treated with 1080 monitored to confirm that concentrations do not exceed 2 g/L. The likelihood of exceeding this value in drinking water is very small, since it has only rarely (i.e. in five samples out of 1153) been exceeded in small water bodies within the operational area immediately after aerial 1080 bait distribution (see Table 1). Further, these reported levels were only detected for short periods of time (days). Continuous exposure for the 90 days of the first trimester of pregnancy would be the comparable length of exposure to that experienced by the pregnant rats in recently completed regulatory toxicology studies (Eason et al. 1999b). The current provisional maximal acceptable value in the New Zealand Drinking Water Standards is 5 g/L (ppb).

In 1996–97, the Southland Regional Council monitored the fate of 1080 when 12 000 kg of 1080 bait were disposed of in a landfill. Bore water samples taken adjacent to the disposal pit contained 1080 concentrations either below or close to MOH guidelines. No 1080 was detected after 10 months. In situ samples of the residual waste material indicated that the 1080 concentration in the landfill decreased to less than its original level in 12 months (Bowman 1999).

1.1.4 Toxicology and pathologyOnset of symptomsThe latent period between the time monofluoroacetate is ingested and the appearance of clinical signs in mammals is between 0.5 and 3 hours. Peak plasma concentrations of monofluoroacetate occurred in possums and rabbits 0.5 hours after ingestion, 0.75 hours in goats, and 2.5 hours in sheep. This correlates with the latent period between ingestion and clinical signs and reflects the time taken for absorption and distribution of monofluoroacetate, and the conversion of monofluoroacetate to fluorocitrate. Animals receiving small sub-lethal doses of 1080 show mild clinical signs of poisoning, metabolise and excrete 1080 within 1–4 days, and then recover. Animals receiving a lethal dose usually show more severe signs of poisoning in addition to non-specific clinical signs such as nausea and vomiting. Specific signs include cyanosis, drowsiness, tremors, staggering, and death from ventricular fibrillation or respiratory failure. In general, herbivores experience cardiac failure, whereas carnivores experience central nervous system disturbances and convulsions then die of respiratory failure (Egekeze & Oehme 1979). Possums usually die within 6–18 hours (Eason et al. 1997). The clinical signs of 1080 poisoning in birds will vary

16

according to the species. Common signs may be lack of balance, slowness, ruffled feathers, and salivation. Vomiting will occur in some species such as raptors. In the terminal phase of poisoning, birds and mammals may exhibit convulsions and coma.

Mode of actionMonofluoroacetate is converted within the animal to fluorocitrate, which inhibits the tricarboxylic acid cycle. This results in accumulation of citrate in the tissues and plasma, energy deprivation, and death. Synthesis of fluorocitrate occurs in the mitochondria, and the fluorocitrate formed inhibits mitochondrial aconitate hydratase. There is also evidence to suggest that fluorocitrate inhibits citrate transport into and out of mitochondria, and that fluorocitrate has an inhibitory effect on succinate dehydrogenase. The high levels of citrate concentration that occur during monofluoroacetate intoxication can also have an inhibitory effect on the glycolytic enzyme, phosphofructokinase.

Death from monofluoroacetate poisoning is caused by the inhibition of energy production which, in turn, results in either cardiac or respiratory failure. Fluorocitrate is commonly described as a specific metabolic inhibitor of glial cells in the brain. Glial cells are thought to be important for extracellular fluid ion and pH regulation, and the control of breathing (Erlichman et al. 1998).

Pathology and regulatory toxicologyKnown target organs in animals following 1080 exposure include the heart, lungs, liver, kidney, testes, and foetus (Annison et al. 1960; McTaggart 1970; Buffa et al. 1977; Sullivan et al. 1979; Schultz et al. 1982; Trabes et al. 1983; Chung 1984; Savarie 1984; Chi et al. 1996; Gregg et al. 1998; Twigg et al. 1988; Eason et al. 1999b). The pathological changes observed at post-mortem appear to be largely the result of progressive cardiac failure with congestion of the abdominal viscera and lungs. Examination of monofluoroacetate-poisoned mammals usually reveals cyanosis of mucous membranes and other tissues. Diffuse visceral haemorrhage has been described in some animals, particularly cattle. Subepicardial haemorrhages on the epicardium and endocardium as well as on the epiglottis and trachea have been observed in sheep and possums poisoned with monofluoroacetate. The presence or absence of tissue damage is likely to be dose-related, and subepicardial haemorrhages have been observed in rabbits receiving a lethal dose of monofluoroacetate but not in those receiving a sub-lethal dose. It is apparent that the target organs vary to some extent in different species, which may relate to the citrate response in different species, or the metabolic activity in different tissue. In birds a target organ appears to be wing muscle (Ataria et al. 2000) as well as the heart, which is a more common target in other species.

Repeated exposure of rats to small doses of monofluoroacetate appears to afford some protection to subsequent challenge (Atzert 1971). However, at a histopathological level, this is not the case in sheep, probably because even small doses of monofluoroacetate result in myocardial damage in this species, and this damage will be cumulative with subsequent exposure (Annison et al. 1960). In sheep that had received multiple sub-lethal doses of 1080, myocardial degeneration has been reported as well as necrosis of individual or small groups of myocardial fibres (Schultz et al. 1982). Researchers in Australia noted macroscopic lesions in the heart of sheep, described as acute multifocal injury to the myocardium, after doses as low as 0.11 mg/kg/day for 3–7 days. A dose of 0.1 mg/kg is approximately equivalent to a

17

30-kg sheep eating one 4-g 1080 possum bait containing 0.08% 1080 w/w. Mild cardiac histopathology at doses of 0.055 mg/kg/day has been reported, but the duration of treatment was not specified (Whitten & Murray 1963). Although 1080 itself is not cumulative (Rammell 1993; Eason et al. 1994c), these reports in sheep clearly demonstrate that cumulative damage to the heart or other organs from repeated exposure to large sub-lethal doses of 1080 can occur.

A recent study demonstrated that ewes surviving a single exposure to 1080 did not experience any adverse long-term effects (Wickstrom et al. 1997b). Nevertheless, pathological abnormalities related to 1080 exposure were found in the heart and brain. Glial cells in the brain are particularly sensitive to fluorocitrate (Erlichman et al. 1998; Hulsmann et al. 2000). Obviously livestock must not be allowed access to toxic baits, and even partially degraded baits should be regarded as hazardous. Pregnant ewes are more susceptible to the acute toxic effects of 1080 than non-pregnant animals (O’Connor et al. 1999).

Many regulatory toxicology studies were completed in the USA before 1995, as 1080 is still used there in livestock protection collars. They included 17 studies on product chemistry, six studies on wildlife hazards, and four studies relevant to human health. The results from these studies were summarised in the Science Workshop Proceedings on 1080 (Fagerstone et al. 1994) (Table 2).

The most important of these studies to the health of those involved in pest control in New Zealand was on acute dermal toxicity of 1080 in rabbits. In this test, five male and five female rabbits for each of four dose levels were treated dermally with 1080 paste. The estimated LD50 was 324 mg/kg for females and 277 mg/kg for males. It had long been known that 1080 can be absorbed through the gastrointestinal and respiratory tracts, open wounds, and mucous membranes, but is less readily absorbed through intact skin (Atzert 1971). However, the results of this study demonstrated that poor dermal absorption of 1080 (Atzert 1971) does not imply no absorption, and there are obviously implications with regard to enforcing strict codes of practice and appropriate protective clothing for those involved in the manufacture or handling of 1080 baits.

Regulatory (laboratory-based) toxicology studies of this type are usually conducted before the launch of new drugs or pesticides, and are used to proactively assess the risk of these compounds to humans, pets, livestock, and wildlife. Alternatively, they may be conducted on older products, such as 1080, to provide an update to the toxicology data generated to meet new standards and data requirements that are now commonplace internationally.

The new regulatory toxicology studies (targeting human health concerns) listed in Table 2 were conducted following internationally recognised protocols. The methods are routine (Wilson 1965; Ames et al. 1975; Hoddle et al. 1983; Blazak et al. 1989). These data provide answers to the following general questions: does 1080 alter genetic material (mutagenic) and therefore have the potential to cause cancer; and does it cause birth defects (developmental toxicant)?

Results from a series of in vitro (cell culture) and laboratory animal studies (in rats and mice) to update the regulatory toxicology database for 1080 provided information

18

on mutagenicity and teratogenicity. Results of three different, complementary tests indicate that 1080 is not mutagenic, and therefore unlikely to cause cancer. Results of a developmental toxicity study in rats indicate that 1080 causes developmental defects in rats when pregnant females are exposed to relatively high doses (0.33 and 0.75 mg/kg) on a daily basis during the period of organogenesis (from days 6 through to 17 of gestation). The developmental abnormalities observed were mild skeletal effects: slightly curved forelimbs, and bent or ‘wavy’ ribs. These results highlight the highly toxic nature of 1080 and the need for extreme care when handling this pesticide during the manufacture and distribution of bait, but do not preclude its proper use (Eason et al. 1999b). Spielman et al. (1973) reported that 1080 at a dose just below the maternal LD50 was not teratogenic to rats. The embryos in this study showed no macroscopic or skeletal abnormalities. Spielman et al.’s work involved only a single dose and the results contrast with our investigation following current international guidelines that require dosing rats from day 6–17 of gestation at three dose levels.

Comparison of the study by Spielman et al. (1973) and Eason et al. (1999b) is relevant to human risk assessment in New Zealand. It is noteworthy that the NOEL derived from the present multi-dose study (0.1 mg/kg/day) was 10-fold less than the single dose NOEL (1 mg/kg) reported by Spielman et al. (1973). In the most recent 90-day exposure study in rats, the NOEL for effects on testes was 0.075 mg/kg/day. In the high-dose group (0.75 mg/kg) gross examination revealed small testes and microscopic examination at necropsy revealed damaged sperm. Effects occurred in only one out of three dose groups and they were partially reversible on cessation of dosing. At the time of completing this edition of the manual (March 2000) the histopathology is incomplete. Possible heart defects are being reported in the males of the top-dose group, but this requires confirmation. The effects on these target organs are consistent with earlier work. The difference between these current regulatory toxicology studies and earlier animal studies are that no effect levels have been defined.

Table 2. Toxicology studies on 1080 relevant to human health: current status (* = new studies)

Study types Status

Acute toxicity

Skin and eye irritation

Skin sensitisation

Ames assay

Mouse lymphoma assay

Mouse micronucleus test

Developmental toxicity in rats (including pilot study)

3-month feeding study in rats* (including pilot study)

Metabolism/pharmacology studies

Extensive database in the literature (see Rammell & Fleming 1978; Seawright & Eason 1994; Eisler 1995)

Completed (see Fagerstone et al. 1994)

Completed (see Fagerstone et al. 1994)

Completed January 1998

Completed January 1998

Completed January 1998

Completed January 1998

Scheduled for completion (report in 2000)

Extensive published database (see Eason et al. 1994c)* This core component of the study was completed in December 1999. Histopathological assessment and a full report will be prepared prior to July 2000.

19

Fate in animals

Absorption, metabolism, and excretionSodium monofluoroacetate (1080) is absorbed through the gastrointestinal tract or via the lungs if inhaled. (While it is not volatile, the inhalation of 1080 powder must be avoided). Monofluoroacetate is not readily absorbed through intact skin, but it can be absorbed more readily through cuts and abrasions.

Studies of laboratory animals since the 1950s have shown that sub-lethal amounts of 1080 are excreted both unchanged and as a range of non-toxic metabolites. After oral or intravenous dosing of laboratory rodents, 1080 is rapidly absorbed and distributed through the soft tissues and organs (Hagan et al. 1950; Egeheze & Oehme 1979; Sykes et al. 1987). This contrasts with the action of commonly used anticoagulant rodenticides, such as brodifacoum, which preferentially bind to liver cells (Bachman & Sullivan 1983). Sodium monofluoroacetate is excreted as unchanged fluoroacetate and a range of metabolites (Gal et al. 1961; Schaefer & Machleidt 1971). Approximately 30% of a dose of 1080 administered to rats was excreted unchanged in the urine over 4 days (Gal et al. 1961). At least seven unidentified metabolites other than fluoroacetate and fluorocitrate, the toxic metabolite of 1080, were also detected in rat urine (Gal et al. 1961).

Administration of 14C-labelled fluoroacetate to rats showed that fluorocitrate, the toxic metabolite of 1080, accounted for only 3% of the radioactivity (Gal et al. 1961), and this was confirmed by Schafer & Machleidt (1971). The major metabolite, unlike fluorocitrate, does not inhibit the activity of aconitase (Gal et al. 1961). Phillips & Langdon (1955) suggested that the unidentified metabolites include non-saponifiable lipids that probably serve as intermediates for cholesterol, and some radioactivity was found in fatty acids and cholesterol in the liver. Up to 3% of the radioactivity appeared as respiratory CO2, which implied cleavage of the C-F bond (Gal et al. 1961).

Defluorination of 1080 or its metabolites, including fluorocitrate, has been demonstrated in animals and other living organisms (Kirk & Goldman 1970; Smith et al. 1977; Egekeze & Oehme 1979; Soifer & Kostyniak 1983, 1984; Twigg et al. 1986; Tecle & Casida 1989). Although fluoride is extensively excreted, primarily in urine, some deposition occurs in bone (Sykes et al. 1987; Eason et al. 1993a,b; Rammell 1993; Eason et al. 1994b).

The earliest reports on rats suggested that some 1080 is retained for 1–4 days. In a study using mice, 1080 concentrations in plasma, muscle, and liver decreased by half in less than 2 hours. Prolonged persistence of 1080 in animals after sub-lethal exposure therefore seems unlikely, and this has been confirmed for larger animals such as rabbits, goats, possums, and sheep (Gooneratne et al. 1994; Eason et al. 1994c). Sodium monofluoroacetate was readily absorbed and excreted. The highest concentrations occurred in the blood, with moderate levels in the muscle and kidneys, and the lowest concentration in the liver. In sheep, the highest concentrations in blood occurred 2.5 hours after dosing and there were negligible amounts in tissue and plasma 4 days after dosing. All traces of the toxin are, therefore, likely to be eliminated within 1 week.

20

If recommended practices are followed in possum control operations, 1080 is unlikely to be present in meat for human consumption. Where any contact of livestock (farm animals or animals intended for slaughter) with 1080 is suspected, an adequate margin of safety should be achieved by imposing a minimum withholding period of 5 days. Should a death in a flock or herd be attributed to 1080, the withholding period should be doubled to 10 days for the surviving stock, which should be removed to a 1080-free pasture (Rammell 1993; Eason et al. 1994c).

Whilst 1080 is comparatively rapidly eliminated from living animals it can persist in carcasses for many months where it will break down more slowly and will pose a risk to dogs (Meenken & Booth 1997).

Limited research has been conducted on the pharmacokinetics of monofluoroacetate in invertebrates. In a laboratory study weta were dosed with 1080 and the persistence of 1080 residues at specified times after dosing was determined. In this experiment 1080 was eliminated from weta 6–10 days after exposure, and all weta survived dose levels of 15 mg/kg (Eason et al. 1993a,b). Similar results were obtained from a native ant (Booth & Wickstrom 1999). Insects have been monitored in forests for 1080 residues after toxic baits were aerially sown for possum control. No 1080 was found in living earthworms, spiders, beetles, millipedes, or centipedes. Although 1080 was found in some cockroaches, bush weta, and cave weta during the period the baits were on the ground, after 3–4 weeks all invertebrate samples were free from 1080 residues. Field and laboratory results for invertebrates do show that 1080 is taken up by some of the terrestrial invertebrate species. Its persistence in invertebrates is short-lived and the risk to insectivorous birds or other predators is therefore also confined to a short period after sowing baits for possum or rabbit control. However, large invertebrates frequently eat bait (Spurr & Drew 1999) and, since species like weta can contain large amounts of bait, the concerns regarding secondary poisoning via this route remain unresolved.

Species variation in response to monofluoroacetateWhilst monofluoroacetate is a broad-spectrum toxin, there are some marked differences in susceptibility (Table 3). There is an extensive database on the acute toxicity of 1080 in a diverse spectrum of species, including birds, mammals, and reptiles (Atzert 1971; Harrison 1978; Rammell & Fleming 1978; Eisler 1995). Unlike most other vertebrate pesticides, 1080 also has insecticidal properties (Negherbon 1959; Notman 1989; Booth & Wickstrom 1999). As with other poisons, the relative susceptibility and LD50 values can be influenced by the vehicle used to deliver the poison, and environmental conditions (Henderson et al. 1999). Dogs are extremely susceptible, and most other carnivores are highly sensitive to poisoning. Herbivores are less sensitive, and birds and reptiles are increasingly resistant (Atzert 1971; Rammell & Fleming 1978; Eisler 1995). Several studies have revealed that animals that forage in areas where fluoroacetate-producing plants are common have evolved an increasing resistance to fluoroacetate compared to animals from areas where plants containing the toxin are not indigenous. This phenomenon is well-documented in Australia where the effect is most dramatic in herbivores and seed eaters, which are more directly exposed to the toxin than carnivores. The emu (Dromaius novaehollandiae) is the oldest seed-eating bird species in Australia, and has a very high level of resistance with an LD50 of 100–200 mg/kg. In contrast, seed-eating birds from regions outside the range of fluoroacetate-producing plant species have an LD50

21

in the range of 0.2 to 20 mg/kg. Similarly the brushtail possum of south-western Australia is 150 times less susceptible to fluoroacetate poisoning than the same species in eastern Australia where plant species containing the toxin are not present. The biochemical basis for tolerance and species variation is not clear. This species variation in mammals in response to monofluoroacetate poisoning may in part be due to differences in the biochemical response of different organs to the toxin, which may be linked to difference in glutathione level and a glutathione-requiring defluorinating enzyme. For example, 1080-induced changes in citrate content of the heart are more pronounced than in any other organs in sheep, and for this reason citrate concentrations in sheep hearts may have diagnostic value (Annison et al. 1960; Schultz et al. 1982). Guinea pigs and rabbits, like sheep, are sensitive to myocardial damage. In rats there is some short-lived elevation of citrate in the heart and, by contrast, in dogs elevation of citrate concentrations in heart tissue is reported to be minimal (Bowsakowski & Levin 1986). Furthermore, dogs do not show the ECG changes seen in sheep that are suggestive of cardiac ischaemia (Matsubara et al. 1986). In comparison with dogs the clinical signs in cats are less severe (Eason & Frampton 1991). In birds, damage to wing muscle is a unique feature that occurs at sub-lethal dose levels (Ataria et al. 2000). Most deaths in mammals generally occur 8–48 hours after ingestion of a lethal dose.

Table 3. Acute oral toxicity (LD50 mg/kg) for sodium monofluoroacetate. N.B. These results represent a very small proportion of the LD50 data available in the literature. (Rammell & Fleming 1978; Hone & Mulligan 1982; Eisler 1995)

Species LD50mg/kg

Dog 0.07

Cat 0.3

Pig 0.3

Rabbit 0.4

Sheep 0.4

Cow 0.4

Deer 0.5

Goat 0.6

Wallaby <1.0

Rat 1.2

Possum 1.2

Human 2.5

Duck 9.0

Weka 8.0

Clawed toad (South Africa) 500

22

A recent review paper has highlighted the effects of ambient temperature on possum mortality, specifically how the acute toxicity of 1080 is reduced at low temperatures, and the importance of conducted aerial control in months with coldest average temperatures (Veltman & Pinder in press).

Aquatic toxicology:Historical data indicate that fish are relatively resistant to 1080. Fingerling bream and bass (species unidentified) survived indefinitely, without any signs of toxicity, in water containing 370 mg 1080/L (King & Penfound 1946). In New Zealand, fingerling trout were subjected to 1080 concentrations of 500 mg/L and 1000 mg/L without any visible effect on the fish. Force-feeding pellets containing a total of about 4 mg of 1080 (two fingerling trout and five adult trout) or about 8 mg of 1080 (two adult trout) also had no visible effect (Rammell & Fleming 1978). Fluoroacetamide (a compound related to 1080) at a concentration of 3500 mg/L killed only 50% of a harlequin fish (Rasbara heteromorpha) population in 48 hours. The LD50 of 1080 after intraperitoneal injection was approximately 500 mg/kg (Bauermeister et al. 1977). No explanation of the high resistance of fish to 1080 has been published but it is presumably associated with differences in the pathways or relative importance of the Krebs cycle in fish metabolism (Rammell & Fleming 1978).

During 1993, three aquatic toxicity tests were completed in the USA. The first estimated the acute toxicity of 1080 to bluegill sunfish (Lepomis macrochirus). No mortality or sub-lethal effects were observed at any concentration tested, with a highest NOEC (the no-observed-effect concentration) of 970 mg/L. Based on the results of this study and criteria established by the US Environmental Protection Agency (EPA), 1080 would be classified as practically non-toxic to bluegill sunfish. The second test, on rainbow trout (Oncorhynchus mykiss), used the same test conditions as the bluegill sunfish studies. Mortality ranged from 50% to 90% in four treatment levels ranging from 39 to 170 mg/L. In addition, mortality was 10% at the 23 mg/L treatment level, and sub-lethal effects were observed at levels over 23 mg/L. No mortality or sub-lethal effects were observed at the 13 mg/L level. The NOEC was 13 mg/L, which the US EPA classifies as slightly toxic to rainbow trout.

The third test estimated the acute toxicity (EC50) of 1080 to the small fresh water invertebrate Daphnia magna. The EC50 is defined as the concentration in water that immobilises 50% of the exposed daphnids. Of daphnids exposed to levels of 350 to 980 mg/L (ppm), 70 to 100% respectively were immobilised. Immobilisation of 5% was observed among daphnids exposed to 220 mg/L. Sub-lethal effects were observed among all the mobile daphnids exposed to 220–590 mg/L, but not among those exposed to 130 mg/L. The 48-hour EC50 value for daphnids exposed to 1080 was 350 mg/L and the NOEC was 130 mg/L, making 1080 practically non-toxic to Daphnia magna by US EPA classification standards (Fagerstone et al. 1994). An early experiment reported that mosquito larvae (Anopheles quadrimaculatus) were comparatively sensitive to 1080 (Deonier et al. 1946). In 48 hours, 1080 concentrations of 0.025 mg/L were fatal to 15%, 0.5 mg/L to 40%, and 0.1 mg/L to 65% of fourth-instar larvae. Since the concentrations of 1080 described above are many times higher than the residue concentrations rarely associated with 1080 use (<0.001 mg/L or ppm), adverse effect on aquatic animals is unlikely (see Table 1). In practice this data would only be of value in risk assessment relating to a large amount

23

of 1080 bait or stock solutions being deliberately or accidently tipped into a waterway.

1.1.5 Diagnosis and treatment of 1080 poisoningDiagnosis of non-target poisoning in domestic animalsDiagnosis of 1080 toxicosis is based on exposure history, clinical signs, laboratory analyses, and in lethal cases, lesions. Differential diagnoses (varies with species) include hypomagnesemia, hypocalcaemia, acute lead poisoning, cardiac glycoside toxicosis, strychnine, organochlorine insecticide or methyxanthine toxicosis, traumatic brain injury, epilepsy, and infectious central nervous system diseases such as distemper and rabies.

Clinical signsClinical signs of 1080 toxicosis vary with the species involved. In general, neurotoxic signs predominate in carnivores, while herbivores manifest signs of cardiotoxicity. However, there are exceptions and overlapping effects in some cases. The onset of clinical signs usually ranges from 30 minutes to 2–3 hours after oral exposure. Humans may experience nausea, vomiting, and abdominal pain initially, followed by respiratory distress, anxiety, agitation, muscle spasms, stupor, seizures, and coma. Hypertension is thought to be one of the more important predictors of mortality in 1080 intoxication (Chi et al. 1996, 1999).

Primary poisoning in sheep and cattle exposed to 1080 cereal bait is characterised initially by anorexia and depression, followed by staggering, muscle tremors, cardiovascular and pulmonary abnormalities (e.g. arrhythmias, ventricular fibrillation, tachypnoea, dyspnoea), terminal tonic convulsions, coma, and death from cardiac and/or respiratory failure. Severe trembling and sweating have been reported in horses (Beasley et al. 1997c). Death may occur within 12–24 hours. Animals alive 4 days after acute oral exposure are expected to make a complete recovery (Wickstrom et al. 1997b; O’Connor et al. 1999).

Secondary (or primary) poisoning in domestic dogs is characterised by rapid onset of anxiety, nausea, and vomiting (usually too late to prevent absorption of a lethal dose, given the extreme sensitivity of this species to 1080). These signs are followed by fits of wild barking and frenzied running (in a straight line or around the perimeter of an enclosure), with repeated urination, defecation, convulsions and paddling. Affected dogs appear to be oblivious to their surroundings. Seizures increase in frequency and severity with time until animals become exhausted. Death may occur during an extended tonic seizure, or from subsequent respiratory paralysis, usually 2–12 hours after ingestion (Lloyd 1983; Beasley et al. 1997c).

Neurological signs associated with 1080 exposure are generally less severe in domestic or feral cats than in dogs. Signs reported include depression or excitation, vocalisation, salivation, diarrhoea, and cardiac arrhythmias (Lloyd 1983; Eason & Frampton 1991; Beasley et al. 1997c).

Laboratory diagnosisThe most reliable diagnostic indicators of 1080 exposure are measurement of 1080 residues in blood, skeletal or cardiac muscle tissue, or stomach/rumen contents or

24

vomitus. Analytical laboratories require at least 1 mL of serum or plasma, or 10 g of tissue, for residue determination. Samples should be stored at <4C and analysed promptly2 (Wickstrom & Eason 1997).

Ante-mortem clinical pathology changes consistent with 1080 toxicosis include increased serum citrate concentration (the most specific and reliable biomarker), hyperglycaemia, azotemia (increased serum urea nitrogen), lactic acidosis (secondary to seizure activity), and hypocalcaemia. In animals that survive, clinical pathology parameters return to baseline levels by day 3–4 after exposure (Beasley et al. 1997c; Wickstrom et al. 1997b; O’Connor et al. 1999; Ataria et al. 2000).

LesionsRigor mortis occurs rapidly in animals poisoned with 1080, but distinctive, specific post-mortem lesions have not been described. Grossly, there is generalised cyanosis. The heart is usually observed in diastole with petechial subepicardial haemorrhages. Petechial haemorrhages are also often observed on the epiglottis, trachea, and abdominal viscera, and the lungs, liver, and kidney may be congested secondary to progressive cardiac failure. The stomach, colon, and urinary bladder of dogs and cats will invariably be empty (Lloyd 1983; Beasley et al. 1997c). Histopathological lesions observed in sheep that died from acute 1080 exposure included multifocal or diffuse, severe, pulmonary oedema, and scattered foci of myocardial degeneration and necrosis (Wickstrom et al. 1997b; O’Connor et al. 1999). Cerebral oedema and lymphocytic infiltration of the Virchow-Robin space have also been described.

Treatment of 1080 toxicosis in domestic animalsSodium monofluoroacetate poisoning is an urgent medical emergency, and veterinary treatment should be initiated rapidly in order to maximise the probability of survival. Although research continues, no specific antidote for 1080 poisoning has been identified, and treatment is largely symptomatic and supportive. Most animals that present with severe signs will die in spite of treatment, but veterinary intervention will increase the chance of survival in individuals that receive less than an LD50 dose.

Therapeutic goals for veterinarians are (1) to decrease 1080 absorption and facilitate toxin excretion; (2) to control seizures; and (3) to support respiration and cardiac function. Recommendations for the treatment of 1080 toxicosis in companion animals are as follows (Tourtellotte & Coon 1950; Chenoweth et al. 1951; Lloyd 1983; Beasley et al. 1997c): Where an owner sees the dog scavenging 1080-poisoned carcasses, giving a

simple emetic like supersaturated household salt solution or washing soda within approximately an hour can help save dogs.

Rapid onset of severe neurological signs precludes the induction of emesis as a means of decontamination in some cases.

Induce anaesthesia and perform enterogastric lavage (after endotracheal intubation) if there is any likelihood of continued toxin absorption.

Administer activated charcoal (1–2 g/kg) with a saline cathartic (magnesium sulphate at 250 mg/kg in 5–10 times as much water). (However, data from rodent studies indicate that activated charcoal is ineffective at reducing 1080 uptake from

2 contact Geoff Wright (03) 325 6700; wrightg@landcare.cri.nz

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the gastrointestinal tract.) Control seizures with barbiturates (phenobarbitone or pentobarbitone as needed). Intravenous fluid therapy to enhance renal excretion of 1080 (proposed), treat

hypotension/shock, lactic acidosis, and electrolyte imbalances (e.g. hypocalcaemia).

Calcium gluconate at 0.2–0.5 mL/kg IV (5% solution, slowly, in fluids) to control tetany.

Glycerol monoacetate (monacetin) at 0.55 g/kg IM has been recommended as a source of acetate (competitive inhibitor of fluoroacetate). However, it is difficult to obtain, and ineffective except when administered early to dogs with relatively low dose exposures.

Ethanol at 1.5–8.0 mL/kg (50% solution) orally has also been recommended as an acetate donor. However, combined therapy with ethanol and barbiturates produces profound depression of the central nervous system and prolonged (days) anaesthesia, with high risk of pneumonia and other complications. Use of acetate donors does not appear to be more effective than supportive treatment alone.

Antiarrhythmics for treatment of cardiac arrhythmias. Maintain normal core body temperature. Other symptomatic treatment, such as respiratory support, as needed.

1.1.6 Non-target effectsNon-target effects of 1080 used for possum control have been studied extensively during the last 20 years in New Zealand (Spurr 1991, 1994a,b; Eason et al. 1998a; Innes & Barker 1999; Powlesland et al. 1999). Dead birds may be found after aerial application of 1080 baits (Caithness & Williams 1970). However, cold-blooded animals such as reptiles are less susceptible than birds (Atzert 1971). Spurr has noted that fewer and fewer species of birds have been reported dead after 1080 poisoning operations since 1978. Most dead birds were found after large-scale control operations and trials using undyed, raspberry-lured, unscreened carrot bait that had a high percentage of small fragments or ‘chaff’. Reductions in bird deaths can be attributed to the screening of carrot baits to remove small fragments, the banning of raspberry lure, the use of cinnamon oil as a deterrent, the reduced rates of bait application, and the increased use of cereal-based baits. Bait specifications now minimise the amount of fragments and chaff (likely to be eaten by birds and insects) in bait consignments, which in turn minimises the effects on non-target species. It is imperative that only high-quality baits (carrot or cereal baits) are used in control operations. Carrot or cereal baits containing substantial amounts of fragments or chaff will result in substantial bird deaths. For carrot and cereal-pellet bait specifications see Appendices 2 and 3. However, improvements in quality will not reduce the secondary poisoning risk for forest insectivores, such as tomtit, hedge sparrow, and short-tailed bats, which may be exposed to concentrations of 130 mg/kg in some invertebrates (Lloyd & McQueen 2000).

Regardless of the route of exposure, extensive monitoring indicates that populations of common birds are not adversely affected (Spurr 1994a). The impacts on non-target species of 70 aerial 1080 operations or trials carried out between 1978 and 1993 were reviewed by Spurr. Dead birds were reported from six of the 11 operations where systematic searches were made and from nine of the 59 operations where only incidental observations were made. Most birds found dead were introduced species (blackbirds and chaffinches), but some native birds were also killed. These losses

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were insignificant in population terms as no population reductions were detected for any of the more common bird species in the 35 operations where bird populations were monitored both before and after poisoning (Spurr 1994a). However, less common bird species (e.g. kiwi and kokako) have been less frequently monitored, at least for some bait types. And the sub-lethal effects of 1080 in birds have received limited attention (Ataria et al. 2000). In contrast, Powlesland et al. (1999) have produced recent data to show that there can be very significant mortality of robins (43–55%) after aerial operations, even when quality control standards of bait are met. However, their data indicate that robin populations benefit in the longer term. They argue that the results suggest that as long as carrot protocols are strictly adhered to, and baits are distributed over large blocks of forest so that mammalian predator populations remain low during the next robin nesting season, robin populations will benefit from aerial 1080-carrot possum control operations (Powlesland et al. 1999).

Since 1993, radio transmitters have been increasingly used to monitor less common bird species. For example, in the Hauhungaroa 1080 poisoning operation in 1994, radio transmitters were fitted to 21 kaka and 19 blue ducks. All the radio-tagged birds survived for at least 4 weeks after the poison operation. Radio transmitters were also fitted to nine great spotted kiwi, five weka, and six moreporks on the Gouland Downs; 16 weka and one morepork in Tennyson Inlet; seven great spotted kiwi at Karamea; and eight weka at Rotomanu. One radio-tagged weka died from 1080 poisoning, but all other birds survived for at least 4 weeks after the operations. In 1995, radio transmitters were fitted to 24 North Island brown kiwi in Aponga Scenic Reserve, Northland, and all birds survived at least 6 weeks after 1080 baits were distributed in their territories (Fraser et al. 1995).

Lizards and frogs were not monitored in any 1080 poisoning operations prior to 1994; however, none have been reported killed by 1080. Hochstetters frog populations were monitored after possum control in the Hunua Ranges in 1994, and no short-term detrimental effect was observed. Whilst the primary focus on non-target species monitoring has been on birds, selected invertebrate populations were also monitored in five 1080 poisoning operations. No impact was detected on populations of weta in Waipoua Forest, a range of invertebrate species on Rangitoto Island, predatory insects in Mapara Reserve, or ground-dwelling invertebrates in Puketi Forest and Titirangi Reserve (Spurr 1994a). Recent observations of the numbers of species and number of individual invertebrates found feeding on 1080 baits has led to the prediction that vertebrate pest control operations are unlikely to have any long-term deleterious impacts on invertebrate populations (Sherley et al. 1999; Spurr & Drew 1999). However, concerns remain because of the number of taxa identified on baits, and changes in the number of invertebrates interfering with baits containing 1080. Sherley et al. (1999) suggested that the risk from carrot bait is small when compared with cereal bait. This conclusion is based on the mistaken assumption that ‘rain washes 1080 from carrots faster than from pollard’ and is incorrect as 1080 leaches more slowly from carrot bait than it does from cereal bait (Bowen et al. 1995). Regardless of these findings, efforts to reduce non-target exposure through the use of new bait materials, repellents, and colour continue (Morgan & Goodwin 1995; Hartley et al. 1999; Morgan 1999).

It has recently been suggested that a food-web approach may be a more rational way to evaluate 1080 movement and impact in ecosystems. Priorities suggested include

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measuring net ecological outcomes at the community level (Innes & Barker 1999) to provide a clearer assessment of risk versus benefit.

Dogs are extremely susceptible to 1080 and must be kept away from toxic baits and possum carcasses which can remain toxic for many months (Meenken & Booth 1997). Predators, such as stoats, ferrets, and cats, are also susceptible to secondary poisoning (Heyward & Norbury 1999; Murphy et al. 1999). Livestock must also be kept well away from baits, and even partially degraded baits should be regarded as hazardous to sheep and cattle. Although possum kills are routinely monitored, particularly for large-scale aerial 1080 operations, there have been few scientific studies of any associated deer mortality. One study in the northern part of Pureora Conservation Park in 1988 found that 43% of the red deer population were killed. Simultaneous carcass searches over the poisoned area confirmed the pellet-count result. The other study in the Hauhungaroa Range in 1994 gave deer kills in three areas of 30–40% of the population (Fraser et al. 1995). However, in a recent report 1080 carrot baits are reported to have reduced deer populations by >90% (Fraser & Sweetapple 2000). Pig mortality might also be expected but has not been reported.

There has been a sustained international trend to increase target specificity and reduce bait application rates when using any pesticide (Greig-Smith 1993; Morgan 1994a,b; Veltman & Pinder 2000) and minimum bait application rates (e.g. 5kg/ha) should be used. Pest control operators should guard against the careless use of 1080, poor-quality control operations, or use of poor-quality baits. Non-target mortality can be minimised by well-planned operations using high-quality baits and by the increased use of bait stations. Provided that control operations are well planned and carefully executed by trained professionals using high-quality baits, adverse effects on ecosystems, water quality and safety, livestock, and human health can be minimised. No significant hazards exist to people drinking water from poisoned areas unless substantial amounts of 1080 have been dropped into a small stream. Nevertheless, the continued use of aerial sowing techniques is bound to cause community concern. Greater use of ground control including trapping, cyanide, and 1080 bait enclosed within bait stations has reduced the conflict between communities and pest control operators. When conducting aerial control, operators should be aware of a recent review of aerial control operations that indicate they will be significantly more successful when conducted in cold conditions. These observations are consistent with acute toxicity studies in possums that have demonstrated that the toxicity of 1080 is temperature-dependent (Veltman & Pinder 2000).

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1.1.7 Summary

Advantages Disadvantages

Highly effective for achieving a rapid reduction in possum numbers

Controversial, especially aerial operations

The only poison available for aerial application Secondary-poison risk from possum carcasses (especially to dogs)

Cheap compared to most other poisons No effective antidote

Biodegradable in the environment Generates bait shyness if target animal gets sub-lethal dose

Can achieve consistently high kills Poor-quality bait causes bird deaths

High-quality efficacy data and extensive field experience underpin both aerial and ground-baiting techniques

Ten-eighty is the main poison currently used for possum and rabbit control, either aerial application or ground-based operations.

Monofluoroacetate, the active ingredient of 1080, occurs naturally in toxic plants in Australia, South Africa, and South America.

Since 1080 is highly water-soluble, it will be dispensed in the environment by rain and stream water. Some micro-organisms, such as Pseudomonas species, in the soil will defluorinate 1080.

Sodium monofluoroacetate is a relatively stable molecule that will not break down in water unless living organisms, such as aquatic plants or micro-organisms, are present. Water-monitoring surveys, conducted during the 1990s, have confirmed that significant contamination of waterways following aerial application of 1080 bait is unlikely.

Sodium monofluoroacetate is a broad-spectrum poison that acts by interfering with the energy-producing tricarboxylic acid cycle in the mitochondria.

Dogs are extremely susceptible to poisoning.

If an animal has ingested a sub-lethal dose of 1080, toxin residues will not persist in meat, blood, the liver, or fat (in contrast with brodifacoum – Talon® or Pestoff®).

Cellular and organ damage from multiple exposure to sub-lethal doses (e.g. myocardial necrosis) could be cumulative.

If livestock become exposed to 1080 bait, a minimum withholding period of 5–10 days should be enforced to allow for excretion of 1080, so that residues will not occur in meat.

High-quality baits reduce non-target impacts on birds. Current evidence suggests that populations of common bird species and invertebrates are not adversely affected, but further monitoring of rarer species after aerial application of baits is still underway.

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1.2 Cyanide

Chemical Name: Sodium cyanide

Synonyms: Cyanide

Cyanide paste and pellets are favoured by commercial hunters. Because it kills so quickly, animals die no more than a few feet from where the poison was laid so recovery of carcasses and skins is easy. Cyanide can only be purchased and used by licensed operators.

Pea-sized pieces of paste are placed with a little flour and icing sugar (or other lures such as cinnamon or eucalyptus oil) on a rock, leaf, or stick. However, cyanide paste rapidly loses its toxicity in wet conditions and possums that receive a sub-lethal dose become bait shy. This shyness problem may be compounded by the hydrogen cyanide gas (also hazardous for hunters) emitted by the paste. Bait and poison shyness is a problem in many areas where cyanide paste has been used intensively.

Feratox® (a pea-sized encapsulated cyanide pellet) was developed to increase the effectiveness of cyanide and reduce the risk of exposure of operators to hydrogen cyanide gas. The pellets are placed in a bait station with either similar-sized cereal feed pellets, or in a peanut-butter paste.

1.2.1 Physical and chemical propertiesThe empirical formula for sodium cyanide is NaCN and the molecular weight is 49. It is a white powder with a melting point of 563ºC. Potassium cyanide (KCN) is also available in New Zealand. Both compounds have similar properties. They are both highly soluble in water. KCN has a melting point of 623ºC, molecular weight.

1.2.2 Historical development, use, and occurrence in natureCyanide has been used in New Zealand for several decades for killing possums, but has limited use in other countries. Because of its fast action, cyanide is considered in a number of countries to be too hazardous for pest control. Cyanides are used widely and extensively in the manufacture of synthetic fabric and plastics, in electroplating baths, and metal-mining operations. Other sources of cyanide in the environment include fumigation operations, cyanogenic drugs, fires, cigarette smoke, and chemical warfare agents. Although the natural occurrence of cyanide is widespread in the environment, levels tend to be elevated in the vicinity of metal-processing operations, electroplaters, gold-mining facilities, oil refineries, power plants, and solid-waste combustion.

Cyanogenic (cyanide-containing) compounds occur in plants (see Table 4) and also in some fungi and bacteria. More than 2000 plants are known to be cyanogenic, including food plants and forage crops.

Some common sources for humans include cassava, sweet potatoes, yams, maize, millet, bamboo, sugar cane, peas, beans, almond kernels, lemons, limes, apples, pears, cherries, apricots, prunes, and plums. There are reports from overseas that yields of hydrogen cyanide (HCN) from common food and feed sources range from 0 to

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912 mg/100 g. There are also numerous overseas reports of livestock that have been acutely poisoned by young sorghum and sugar gums (Towill et al. 1978; Webber et al. 1984). Young bamboo shoots and peach leaf ‘tea’ are examples of dietary sources of HCN poisoning in children (Hayes 1994). Cyanogenic lipids are another group of precursors from plants that contain, instead of sugars, long-chain fatty acids and yield carbonyl compound and hydrogen cyanide upon hydrolysis. Like fluoroacetate, cyanogenic glycosides are considered to be a chemical plant-defence to deter browsing animals.

Table 4. Examples of plants with cyanogenic potential (Osweiler et al. 1985)

Botanical name Common name

Holcus lanatus velvet grass

Hydrangea spp. hydrangea

Linum spp. flax

Lotus corniculatus birdsfoot trefoil

Phaseolus lunatus lima bean

Prunus spp. cherry, apricot, peach

Malus spp. apple

Pyrus spp. pear

Sambucus canadensis elderberry

Sorghum spp. Sudan grass, Johnson grass

Suckleya suckleyana poison suckleya

Trifolium repens white clover

Triglochin maritima arrow grass

Vicia sativa vetch seed

Zea mays maize

Under natural conditions the hydrolysis of cyanogenic glycosides in plants is inhibited, since the degradative enzymes of plants that can cause release of cyanide from the glycoside are kept spatially separated from the glycoside in intact plant cells. Upon wilting, frosting, or stunting of the plant, free HCN may be released as a result of plant cellular damage, which allows enzymatic degradation of the glycoside.

Rapid hydrolysis and release of HCN occurs only when plant cell structure is disrupted. Thus when the leaves of cyanogen-containing plants that possess glycosidase enzyme are eaten or damaged by herbivores, HCN will be released.

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Cyanide has been recognised as a poison since very early times, having been used by the ancient Egyptians and early Romans. In the USA and Australia it is used in predator control devices and in New Zealand it is used in pastes or in a pellet (Feratox®) for controlling possums. The pastes contain oil, which protects the cyanide from exposure to air and hence slow down the release of hydrogen cyanide gas. Nevertheless, cyanide paste has a characteristic smell produced by the hydrogen cyanide gas liberated on hydrolysis. It is thought that ‘shy’ possums avoid cyanide paste because of this smell. The paste contains 55% NaCN and Feratox® pellets contain 80 mg. Cyanide has not been the toxicant of choice in the past, because cyanide pastes are only moderately effective and some possums have an innate aversion to the smell (Warburton & Drew 1994). Feratox® became available in 1997 and has become increasingly popular as field experience with the product has been gained. Feratox® products for other species (e.g. ferrets) are being developed, but at present these are still at the prototype phase (Spurr et al. 1999). A rodent repellent has been added to the Feratox® delivery system to increase its specificity for possum control (Morgan & Rhodes 2000).

1.2.3 Fate in the environmentThere are no formally published data on the fate of cyanide from possum pastes used in New Zealand. However, cyanide paste is fairly unstable. It is thought that the cyanide dissipates into the environment by gaseous diffusion as hydrogen cyanide. The stability of the cyanide is increased by the oil present in the paste bait. The length of time that baits remain toxic depends on rainfall and on how well they are protected from the rain. The baits are not considered safe until they are broken down and unrecognisable (Rammell & Fleming 1978). Feratox® pellets that fall from bait stations will disintegrate slowly over a period of 2–4 months.

Cyanide ions are not strongly absorbed or retained in soils. Leaching into water will occur. Cyanide salts may also be degraded by some soil micro-organisms (Eisler 1991). Bacteria exposed to high concentrations of cyanide can be adversely affected, but acclimatised populations can degrade cyanide to yield a variety of products, including carbon dioxide and ammonia (Towill et al. 1978).

1.2.4 Toxicology and pathologyOnset of symptomsCyanide is a potent and rapid-acting asphyxiant. At lethal doses inhalation or ingestion of cyanide produces adverse reactions within seconds and death within minutes. Of all the poisons currently used for possum control, cyanide is considered the most humane (Gregory et al. 1996, 1998). However, death from lower doses can in some cases take from 1 to 4 hours, hence the importance of using high-quality baits and baiting practices to ensure maximum efficacy.

The minimal lethal dose of HCN in humans is 0.5–3.5 mg/kg. Information on the LD50

values of specific species is detailed in Tables 5 and 6. Signs of acute poisoning in humans are hyperventilation, headache, nausea and vomiting, generalised weakness and coma, followed by respiratory depression and death (Hayes 1994). In animals, clinical effects also occur in rapid succession. Initially there can be excitement and generalised muscle tremor. Animals may salivate, void faeces and urine, and gasp for

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breath. Convulsions will follow due to anoxia. In possums there appears to be minimal signs of distress, and convulsions occur after unconsciousness (Gregory et al. 1998).

The first signs of cyanide toxicosis in birds appear between 0.5 and 5 minutes after exposure, and include panting, eye blinking, salivation, and lethargy (Wiemeyer et al. 1986). Breathing becomes laboured and intermittent prior to death.

Mode of actionCyanide disrupts energy metabolism by preventing the use of oxygen in the production of energy. Cyanide’s toxic effect is due to its affinity for the ferric haem form of cytochrome a3 (also known as cytochrome c oxidase), the terminal oxidase of the mitochondrial respiratory chain. Formation of a stable cytochrome c oxidase – CN complex in the mitochondria produces a blockage of electron transfer from cytochrome oxidase to molecular oxygen and cessation of cellular respiration, causing cytotoxic hypoxia in the presence of normal haemoglobin oxygenation. Tissue anoxia induced by the inactivation of cytochrome oxidase causes a shift from aerobic to anaerobic metabolism, resulting in the depletion of energy-rich compounds such as glycogen, phosphocreatine, and adenosine triphosphate, and the accumulation of lactic acid with decreased blood pH.

The combination of cytotoxic hypoxia with lactate acidosis depresses the central nervous system, the most sensitive site of anoxia, resulting in respiratory arrest and death (Eisler 1991). Cyanide is known to produce a range of biochemical changes in the brain associated with poisoning. Some of these changes will be associated with acute toxicity, anoxia, and death. Others, such as the depletion of dopamine (a central nervous system neurotransmitter), may be associated with chronic toxicity, such as the development of delayed progressive Parkinsonism and dystonia in humans following sub-lethal cyanide intoxication (Kanthasamy et al. 1994).

Pathology and regulatory toxicologyCyanide causes subendocardial and subepicardial haemorrhage and petechial haemorrhage in the intestine. However, the only consistent post-mortem changes are those related to the oxygenation of the blood. Mucous membranes are pink and appear well oxygenated. The blood is usually a bright cherry-red colour. Chronic exposure to sub-lethal doses may lead to multiple foci of degeneration in the central nervous system (Osweiler et al. 1985), and histological examination of the brain has associated extensive destruction of dopaminergic neurones in the basal ganglia with neurotoxicity associated with acute cyanide intoxication (Kanthasamy et al. 1994).

The authors were unable to access regulatory toxicology studies on cyanide, which are conducted in in vitro test systems and laboratory animals to assess risk to humans with regard to issues such as mutagenicity, teratogenicity, and to define no-effect levels.

Fate in animals

Absorption, metabolism, and excretionCyanide is rapidly absorbed through the lungs by inhalation or through the gastrointestinal tract following ingestion. It is less readily absorbed through the skin.

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However, it should be noted that the LD50 for a solution of KCN on intact skin in rabbits is as low as 22.3 mg/kg (Eisler 1991). Free cyanide is rapidly distributed in tissue and body fluids, resulting in the prompt onset of the signs of acute cyanide poisoning.

In animals surviving a sub-lethal dose, the great majority of the absorbed cyanide reacts with sulphane sulphur in the presence of enzymes to produce thiocyanate, which is excreted in the urine for several days afterwards. Owing to this rapid detoxification, animals can ingest sub-lethal doses of cyanide over extended periods without apparent harm (Mengel et al. 1989). Species vary considerably in both the extent to which thiocyanate is formed and the rate at which it is eliminated from the body. Thiocyanate metabolites resulting from the transulphuration process are about 120 times less toxic than the parent cyanide compound. However, thiocyanate may accumulate in tissues, and has been associated with developmental abnormalities and other adverse effects. The development of delayed progressive central nervous system disorders, including Parkinsons disease in humans, following acute cyanide intoxication (Kanthasamy et al. 1994) suggests that there is a risk of permanent brain damage in animals and humans after apparent recovery from acute exposure. Although cyanide is not cumulative, as with other toxic materials, the damage caused from repeated exposure could be cumulative.

Minor detoxification pathways for cyanide include exhalation in breath as HCN and as CO2 from oxidative metabolism of formic acid; conjugation with cystine to form 2-aminothiazolidene-4-carboxylic acid or 2-aminothiazoline-4-carboxylic acid; combining with hydroxocobalamin (B12) to form cyanocobalamin, which is excreted in urine and bile; and binding by methaemoglobin in the blood.

Inhalation and skin absorption are the primary hazardous routes in cyanide toxicity in relation to occupational exposure. Skin absorption is most rapid when the skin is cut, abraded, or moist. Inhalation of cyanide salts is also particularly hazardous because the cyanide dissolves readily on contact with moist mucous membranes. Regardless of route of exposure, cyanide is readily absorbed into the bloodstream and distributed throughout the body. Cyanide concentrates in erythrocytes through binding to methaemoglobin. Because of the affinity of cyanide for the mammalian erythrocyte, the spleen may contain elevated cyanide concentrations when compared to blood. Accordingly, the spleen should always be taken for analysis in cases of suspected cyanide poisoning (Eisler 1991). The brain is the major target organ of cytotoxic hypoxia, and brain cytochrome oxidase may be the most active site of lethal cyanide action, as judged by distribution of cyanide.

Species variation in response to cyanideCyanide is a broad-spectrum toxin and is likely to be toxic to a range of vertebrates and invertebrates. The LD50s on a mg/kg basis are similar for a range of mammals and birds (see Table 5). The insecticidal properties are utilised when HCN is used as a fumigant (e.g. to kill weevils in grain warehouses).

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Table 5. Acute oral toxicity (LD50mg/kg) of cyanide (Hone & Mulligan 1982; Marks & Gigliotti 1996)

Species LD50

(mg/kg)

Duck 1.43

American kestrel 2.12

Cattle 2.00

Sheep 2.30

Deer Approx. 3.5–4.5

Pig Approx. 3.5–4.5

Goat Approx. 3.5–4.5

Rabbit Approx. 3.5–4.5

Hare Approx. 3.5–4.5

Japanese quail 4–5

Rodents 6.40

Possum 8.70

European starling 9.00

It has been suggested that the rapid recovery of some birds exposed to sub-lethal doses of cyanide may be due to the rapid metabolism of cyanide to thiocyanate and its subsequent excretion. Species sensitivity to cyanide is not related to body size, but may be associated with diet. For example, raptors are more sensitive to cyanide than are species that feed mainly on plant material, with the exception of mallard duck (Eisler 1991).

There are limited data on the toxicity of cyanide to reptiles, though it would appear that cold-blooded animals such as frogs are less susceptible. The lethal dose in frogs is approximately 60 mg/kg (Hone & Mulligan 1982).

Aquatic toxicologyThere are numerous publications on the toxicity of cyanide to aquatic invertebrates and fish, and some examples of these are given below (Table 6).

Table 6. Acute toxicity (96-hour LD50) of cyanide to daphnia and fish from aquaria (Hone & Mulligan 1982)

Species Cyanide concentration (ppb)

Rainbow trout 28 at 6ºC

Yellow perch 76–108

Fat minnow 82–113

Daphnia magna 160

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However, these data are principally relevant to accidental spills of large quantities of sodium or potassium cyanide into rivers and streams (Eisler 1991) and are of very limited relevance to the use of cyanide baits for possum control in New Zealand.

1.2.5 Diagnosis and treatment of cyanide poisoningFirst aid for human exposureLethal exposures to cyanide can cause unconsciousness in 10 seconds and death within a few minutes. Symptoms in humans include hot flushes with diaphoresis (perspiration), headache, nausea, vomiting, lethargy/weakness, anxiety, confusion, coma, convulsions, increased respiratory rate at low doses, but rapid onset of apnea (respiratory arrest) at high doses, tachycardia (increased heart rate) early, which progresses to bradycardia (decreased heart rate) with hypotension, arrhythmias, and asystole (cardiac arrest).

Fatalities usually result from intentional ingestion of bait or cyanide salts. By contrast, pest managers are most likely to be exposed to inhalation of hydrogen cyanide (HCN) fumes in an enclosed space, such as a storeroom or vehicle. Serious risks to health are rare under these circumstances, but prompt treatment is essential if any of the above symptoms are observed in the presence of cyanide baits.First aid for persons who have inhaled HCN gas includes (Meredith et al. 1993):$ Move the victim to a safe environment, being careful to avoid exposing the

rescuers.$ Ensure adequate ventilation.$ Establish clear airway and provide 100% oxygen, if possible.$ If victim is still breathing, break a capsule of amyl nitrite in a handkerchief

and hold it under the nose and mouth for 30 seconds of every minute until the condition stabilises. Note that inhalation of amyl nitrite is rather ineffective at producing methaemoglobinemia, and is meant to be a temporising measure until intravenous sodium nitrite can be administered. In the field, it is far more important to adequately ventilate and oxygenate the victim than to administer amyl nitrite (Chen & Rose 1952).

$ If breathing has ceased, begin artificial respiration, preferably with an endotracheal tube and bag, or bag-mask-valve ventilation. Hold a crushed capsule of amyl nitrite in front of the intake valve of the ventilation bag for 30 seconds of every minute. Direct mouth-to-mouth resuscitation should be avoided because of risk to the rescuers.

$ Initiate cardiopulmonary resuscitation if there is no pulse.$ Remove any contaminated clothing and wash cyanide from the skin.$ Keep victim warm and transport to hospital immediately.

It is important to note that a person who has only inhaled HCN gas but has escaped to a safe environment without becoming seriously ill is unlikely to develop delayed adverse health effects (Peden et al. 1986).

Diagnosis of non-target poisoning in domestic animalsCyanide poisoning is an extremely acute syndrome, and non-target animals that receive a lethal dose are usually found dead close to the source of the toxin. However, in cases where exposure is observed directly, and the dose is not immediately fatal, veterinary intervention may increase the chance of survival.

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Diagnosis of cyanide toxicosis is based on exposure history, clinical signs, laboratory analysis of appropriate specimens, and in lethal cases, lesions. Differential diagnoses in livestock include nitrate and urea poisoning.

Clinical signsClinical signs generally begin within 5B10 minutes of oral exposure to toxic levels of cyanide, and are characterised by anxiety, salivation, lacrimation (flow of tears), and tachypnoea (rapid respiratory rate), progressing rapidly to dyspnoea (difficult breathing), weakness, pink-coloured mucous membranes, muscle fasciculations and tremors, urination, defaecation, pupillary dilatation, staggering, and tachycardia (rapid heart rate). Terminal signs include lateral recumbency, cardiac arrhythmias, opisthotonus (spasm in which the head and hind legs are bowed backward), clonic/tonic convulsions, and death from respiratory paralysis. Death can occur in as little as 10B20 minutes, or more swiftly if large doses are absorbed, or up to 3B4 hours after exposure. However, most animals that survive 2 hours after exposure will recover completely without treatment (Radostits et al. 1994; Osweiler 1996a; Beasley et al. 1997b).

Laboratory diagnosisSince cyanide exposure causes no specific, definitive pathologic changes, and many animals are found dead (rather than sub-lethally exposed), it is difficult to confirm a diagnosis of cyanide poisoning without demonstrating cyanide residues in stomach contents or blood or other tissue (Osweiler et al. 1985; Beasley et al. 1997b). Stomach or rumen contents, liver, or skeletal muscle samples should be collected and immediately frozen in airtight containers. Samples should be shipped frozen to an appropriate laboratory. Low concentrations of cyanide in tissues are indicative of intoxication. Whole, heparinised blood samples collected in airtight containers with no head space (submitted immediately or frozen) can also be analysed for cyanohaemoglobin concentration.

LesionsBlood and mucous membranes may be bright red in colour, especially in cases of rapid death, and when post-mortem examination is performed promptly. This distinct colouration is caused by high oxygen levels in the venous blood secondary to cyanide inhibition of mitochondrial cytochrome c oxidase, with resultant inability to utilise molecular oxygen at the cellular level. Peripheral tissue oxygen rises, preventing unloading of arterial oxygen, and the consequent increase in oxyhaemoglobin in the venous return (Smith 1996). However, this clinical sign is not consistently present. In the terminal stages, many poisoned animals become cyanotic (bluish or purple discolouration of skin and mucous membranes resulting from the accumulation of deoxyhaemoglobin in peripheral blood), as a result of respiratory paralysis, low cardiac output, and shock (Curry 1992).

Because death associated with cyanide exposure is so rapid, gross and microscopic lesions induced by the toxin are frequently absent (Jones et al. 1997). Many of the gross post-mortem changes that may be observed are attributable to death from anoxia, often accompanied by terminal seizures, and are not specific for cyanide. Subepicardial and subendocardial haemorrhage are often observed, as is congestion with petechial haemorrhages in the lungs, trachea, abomasum, and intestine. If death is somewhat delayed, or animals have been repeatedly exposed to cyanide, focal

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lesions of gray and white matter may be seen in the brain (Jones et al. 1997). A bitter-almond smell may be detectable in the rumen contents in some cases (Osweiler et al. 1985; Radostits et al. 1994).Treatment of cyanide toxicosis in domestic animalsCyanide poisoning is an urgent medical emergency, and veterinary treatment should be initiated rapidly in order to maximise the probability of survival. Therapeutic goals are (1) to decrease toxin absorption; (2) to split the cyanide-cytochrome oxidase bond and facilitate cyanide excretion; and (3) to support respiration and cardiac function. Recommendations for the treatment of cyanide toxicosis in animals are as follows (Osweiler 1996a; Beasley et al. 1997b):$ Peracute onset of signs precludes the induction of emesis as a means of

decontamination.$ Administer activated charcoal (1B2 g/kg).$ Livestock

$ Sodium nitrite at 10B20 mg/kg IV (as a 20% solution) to induce measured methaemoglobinemia. The Fe+3 in methaemoglobin binds cyanide (forming cyanomethaemoglobin) and reduces the amount of toxin available and bound to Fe+3 in cytochrome oxidase. Nitrite may also act as a vasodilator.

$ Sodium thiosulphate at 30B40 mg/kg IV (as a 20% solution), to provide a sulphur substrate to enable rhodanase-catalysed conversion of cyanomethaemoglobin to hydrogen thiocyanate, which is excreted in the urine. Repeat at half the initial dose in 30 minutes if no clinical response.

$ Recent reports indicate that high doses of sodium thiosulphate (660 mg/kg IV) may be effective without the use of nitrites (and the attendant risk of excessive methaemoglobinemia).

$ Small animals$ Administer 1.65 mL of a 25% solution of sodium thiosulphate per

kilogram, and 16 mg of sodium nitrite per kilogram body weight IV over several minutes. Repeat at half the initial dose in 30 minutes if no clinical response.

1.2.6 Non-target effectsIn general it is perceived that fewer land-bird species have been reportedly killed by cyanide than by trapping or 1080. Smaller numbers of individual birds have been killed by cyanide than caught in traps. The most commonly poisoned native bird species have been weka and kiwi. For example, in 1947/48, extensive use of cyanide in Poverty Bay killed thousands of possums, but only a small number of native birds, mainly weka. However, in 1984, 66 hunters reported 37 kiwi poisoned by cyanide, about a quarter of the number caught in traps (Spurr 1991). No kiwi have been reported poisoned after 1080 operations. A short-tailed bat has been found dead, presumably poisoned on a cyanide bait laid for possums (Daniel & Williams 1984). The use of Feratox® baits and improved delivery systems should limit non-target mortality. The risks of secondary poisoning are low, but freshly killed carcasses are likely to be hazardous to non-target species.

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1.2.7 Summary

Advantages Disadvantages

Cheap (1–2 cents per bait) Hazardous to users

Humane (very rapid action) Toxicity of paste deteriorates rapidly in wet weather

Suitable for skin/carcass recovery Paste can result in very poor kills if possums are cyanide-shy, hence not favoured by pest control agencies

Low secondary-poisoning risk Can induce poison aversion

Achieves moderate to high kills (70–90%) Antidotes are available but their use is controversial

Encapsulated cyanide does not produce HCN gas so is safer for hunters to use and is suitable for cyanide-shy possums

Encapsulated cyanide pellets can be recovered and reused

Encapsulated cyanide is not adversely affected by wet weather as cyanide paste is

Biodegradable in the environment

Cyanide has been used since ancient times. It is used in New Zealand in a concentrated paste bait or pellet for controlling possums.

Cyanide is the most humane poison available for vertebrate pest control.

Naturally occurring cyanogenic compounds are considered to be a plant defence mechanism to deter browsing animals. When animals eat the leaves of cyanogen-containing plants, hydrogen cyanide gas is released.

Cyanide in paste bait is fairly unstable and has low persistence in the environment. Cyanide dissipates by gaseous diffusion. The length of time that a bait remains toxic will depend on rainfall. Some cyanide may be washed into the ground, but it will not be strongly absorbed or retained in soil, and cyanide salts can be degraded by micro-organisms.

Cyanide is toxic to a wide range of aquatic organisms; however, significant contamination of waterways after ground use of cyanide paste is most unlikely.

Cyanide is a fast-acting broad-spectrum toxin and in both birds and mammals it causes tissue anoxia through inactivation of cytochrome oxidase and death due to respiratory failure.

Sub-lethal doses of cyanide will be metabolised to less toxic thiocyanides and excreted in the urine over a period of several days.

Cyanide biomagnification in food webs is most unlikely and has not been reported, possibly due to rapid detoxification of sub-lethal doses by most species and death at higher doses.

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Cyanide baits have been reported to kill non-target species, including kiwi, weka, and short-tailed bats.

Cyanide bait is a potential hazard to users and the public if not handled, dispensed, and disposed of with diligence.

Cyanide in paste can change into a gaseous state (HCN). Risk of inhalation of HCN is perhaps the greatest risk associated with cyanide. One or two cyanide capsules (Feratox®) contain enough cyanide to be lethal to humans.

1.3 Cholecalciferol (Campaign®, FeraCol®)

Chemical Name: 9,10-Secocholesta-5,7,10 (19)-trien-3-ol.

Synonyms: Vitamin D3

This is a relatively new poison and was introduced in New Zealand in 1995. It poses a low risk of secondary poisoning. Introduced initially for possum control, it is also a rodenticide.

1.3.1 Physical and chemical propertiesThe empirical formula is C27H44O and the molecular weight is 384.62. The melting point is 84–85ºC. It is practically insoluble in water, soluble in the usual organic solvents, and only slightly soluble in vegetable oils. Pure cholecalciferol is oxidised and inactivated by moist air within a few days. Commercially produced cholecalciferol concentrate and baits are formulated to overcome oxidation and ensure stability.

1.3.2 Historical development, use, and occurrence in natureCholecalciferol (vitamin D3) was developed in the 1980s as a rodenticide (Marshall 1984; Tobin et al. 1993). It is registered under the trade name of Quintox® (0.075% cholecalciferol) in the USA, and in Europe it has been added to baits (Racumin® plus) to overcome anticoagulant resistance in rats and mice (Pospischil & Schnorbach 1994). In 1995 a cereal bait containing 0.8% cholecalciferol (Campaign®) was registered for possum control in New Zealand. This was followed in 1999 by the development of a paste bait containing 0.8% cholecalciferol (FeraCol®). Two strengths of FeraCol® paste will be available from 2000, 0.8% for possums and 0.08% for rats and mice. Cholecalciferol is synthesised in animal skin by the action of sunlight on its precursor, 7-dehydrocholesterol. Natural dietary sources of vitamin D3

include liver, fish oils, egg yolk, and milk fat. Vitamin D exists in two forms, vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol), each sharing the same steroid nucleus, but having different side chains. Both forms of vitamin D appear to be identically metabolised and express similar biological activity in mammalian species. Cholecalciferol seems to be more widely used as toxin, probably because it is more readily available and less expensive than ergocalciferol.

Because Vitamin D3 is naturally occurring and is involved in calcium homeostasis, there has on occasion been a tendency to consider baits containing cholecalciferol as

40

safe to non-target species. However, the relatively lower sensitivity of cats and dogs compared with rodents does not make this product ‘safe’ for pets. Inappropriate marketing of cholecalciferol-containing rodenticides in Australia in the late 1980s produced a spate of poisoning incidents and subsequent backlash against its use. While target species for cholecalciferol are amongst the most sensitive, all bait containing cholecalciferol must be treated as potentially poisonous to non-target species, and must be handled and dispensed as carefully as other types of toxic bait.

1.3.3 Fate in the environmentThere are no published data on the fate of cholecalciferol in soil and water. The manufacturers of Campaign® (Aventis) have suggested that cholecalciferol residues will be degraded by sunlight. Proper use of cholecalciferol-containing baits will limit the contamination of soil. Some baits may be spilt from bait stations. Cholecalciferol leaches from cereal baits very slowly and trace amounts will be found in soil immediately underneath disintegrating baits (Booth et al. 1999a). Once cereal baits have disintegrated, low-level residues of cholecalciferol in soil are unlikely to present a significant hazard. Since cholecalciferol is licensed for use only in bait stations, any contamination will be localised. Cholecalciferol is most unlikely to be found in waterways when used in a proper manner in appropriately designed bait stations.

1.3.4 Toxicology and pathologyOnset of symptomsPossums that receive a lethal dose of cholecalciferol bait usually die within 4–7 days. Clinical signs commonly expressed include loss of appetite, constipation, lethargy, tachypnea (rapid and shallow breathing), and death. Death is thought to result from hypercalcaemia, tissue calcification, and renal or cardiac failure (Jolly et al. 1993; Beasley et al. 1997a).

The occurrence, speed of onset, and severity of signs is dose-dependent. There appears to be some species variation in the clinical signs of poisoning and target organs affected by cholecalciferol (Jolly et al. 1993). The clinical signs reported in cats and dogs include nausea, vomiting, and diarrhoea, but these do not occur in possums.

Mode of actionIn order to gain biological and toxicological activity, cholecalciferol must undergo metabolic conversion to 25-hydroxycholecalciferol. At toxic doses, this active metabolite mobilises calcium stores from bones into the bloodstream, and decreases calcium excretion by the kidneys. The net result is dangerously high concentrations of blood calcium (hypercalcaemia) and tissue calcification. Tissue calcification can occur in the cardiovascular system, kidneys, stomach, lungs, and muscles. Mineralisation and blockage of blood vessels, with death probably from heart failure, appears to be the mode of action of cholecalciferol in the possum, as in rodents. In other species, including cats and dogs, renal failure (caused by vessel blockage and nephrocalcinosis) and gastrointestinal haemorrhage appear more prominent (Gunther et al. 1988; Moore et al. 1988; Jolly et al. 1993).

Sub-lethal poisoning of target species can cause prolonged anorexia and wasting, which creates ethical and animal welfare concerns. Therefore, current baits are

41

designed with the appropriate concentration of cholecalciferol to ensure maximum potency. Calcium has been added to cereal baits in New Zealand to increase their effectiveness (Jolly et al. 1995). To avoid sub-lethal poisoning, it is particularly important for cholecalciferol baits that adequate palatability and efficacy of any new formulations are established using reliable quality assurance procedures.

Pathology and regulatory toxicologyPost-mortem examination of possums poisoned with cholecalciferol-containing bait has revealed pale, mottled hearts, oedema, and lung congestion. Histological examination has revealed widespread mineralisation of cardiac muscle fibres and calcification of blood vessel walls in the heart, kidneys, and lungs. In other species (cats and dogs) nephrocalcinosis and gastrointestinal haemorrhage appear more prominent. Necropsy shows a swollen liver with patchy congestion, pale enlarged kidneys with congested cortical vessels, pale blotching of the intestines, areas of gritty mucosa in the stomach, and pallid heart musculature. Histopathology shows widespread metastatic calcification of soft tissue e.g. renal tubules, submucosal and mucosal regions of stomach and small intestine, heart, and arterial walls of viscera.

The authors were unable to access data from regulatory toxicology studies on cholecalciferol. Regulatory toxicology studies are conducted in in vitro test systems and laboratory animals to assess risk to humans with regard to issues such as mutagenicity, teratogenicity, and define to no-effect levels.

Fate in animals

Absorption, metabolism, and excretionCholecalciferol after absorption from the intestine is transported to the liver, where it is metabolised to 25-hydroxycholecalciferol (25OHD). This metabolite is then transferred to the kidney and converted to 24,25-, or 1,25-dihydroxycholecaliferol. The latter metabolite is the most biologically active form of the vitamin.

Half-lives of cholecalciferol of 0.8–7.9 days have been observed in vitamin D-deficient humans and rats and 3–36 days in normal humans. The half-lives of the active metabolite 25OHD are 10.5–12 days in vitamin D-deficient humans, 15–36 days in humans when vitamin D status was normal, and 25–68 days in humans and cattle during vitamin D toxicity. Interestingly the half-life of 25OHD is shorter in seals than in other mammals, which probably explains the resistance of this species to cholecalciferol toxicity (Keiver et al. 1988). The fate of the 25OHD has been studied in a dog undergoing treatment for poisoning. Levels of 25OHD decreased from >250 ng/mL to normal (i.e. <50 ng/mL) within 30 days (Dougherty et al. 1990). After possums have received a lethal dose (20 mg/kg) of 0.8% cholecalciferol, the mean concentrations of the active metabolite in the blood increased from <50 to between 600 and 1000 ng/mL (Eason et al. 1996c).

Persistence studies in possums with cholecalciferol indicated that elevated concentrations of 25OHD are likely to persist for several weeks in animals that had received sub-lethal doses. In comparison to other examples of cholecalciferol excretion in the literature, the clearance of elevated 25OHD in poisoned possums appeared to be quite slow. This is perhaps not surprising since it has been shown in other animals that clearance of 25OHD is dose-dependent (Keiver et al. 1988) and

42

target animals poisoned with cholecalciferol receive extremely high near-lethal doses. Clearly 25OHD is more persistent than rapidly eliminated poisons like 1080 (Eason et al. 1996a), but is less persistent than second-generation anticoagulants (Eason et al. 1996b).

Species variation in response to cholecalciferolThe single-dose LD50 for cholecalciferol in Norway rats and house mice is very similar but there is considerable species variation in susceptibility amongst other mammals and birds (Table 7). Possums and rabbits appear to be particularly sensitive to cholecalciferol (Eason 1993; Eason et al. 1994a; Henderson et al. 1994; Jolly et al. 1995; Henderson & Eason 2000) and recent studies overseas have shown cholecalciferol to be effective in controlling rock squirrels, gophers, and ground squirrels (Beard et al. 1988; Tobin et al. 1993). Cats appear to be less susceptible than possums, but toxicity was less consistent with some cats surviving doses up to 200 mg/kg, while others died at 50 mg/kg (Eason 1991).

Table 7. Acute oral toxicity (LD50 mg/kg) of cholecalciferol (Eason 1993; Eason et al. 1994a; Jolly et al. 1995)

Species LD50

(mg/kg)

Rabbit 9.0

Possum 16.8 (reduced to 9.8 when administered with calcium)

Rat (Norway) 42.5

Mouse 43.6

Dog 80.0

Duck 2000.0

The relatively high LD50 in ducks suggests that cholecalciferol is less toxic to birds than the other toxins used for possum control. If the LD50 in ducks were applicable to other species, then a 500-g bird would need to eat approximately 100–150 g of bait to receive a lethal dose. However, mortalities in canaries and chickens at 2000 mg/kg indicate that some species may succumb to toxicosis after eating <100 g of bait containing cholecalciferol (Eason et al. 2000), and there are reports that calciferol (Vit D2), which is closely related to cholecalciferol, has killed song birds when used in bait for rodent control (Quy et al. 1995). These articles suggest some level of vulnerability of non-target birds to cholecalciferol.

Aquatic toxicologyThere are no published data on the aquatic toxicity of cholecalciferol. In the unlikely event of significant amounts of cholecalciferol bait being applied directly to a small stream, poisoning of some aquatic organisms might result. However, fish are naturally rich in cholecalciferol and animals that exclusively eat fish (e.g. seals) appear to be able to cope with levels of vitamin D that would be toxic to most mammals (Keiver et al. 1988).

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1.3.5 Diagnosis and treatment of cholecalciferol poisoningDiagnosis of non-target poisoning in domestic animalsDiagnosis of cholecalciferol toxicosis is based on exposure history, clinical signs, development of hypercalcaemia, and in lethal cases, lesions. Veterinarians should note that differential diagnoses in dogs include hypercalcaemia secondary to paraneoplastic syndrome (especially with lymphosarcoma), juvenile hypercalcaemia, and hyperparathyroidism.

Clinical signsClinical signs in companion animals can be divided into neurologic, cardiovascular, gastrointestinal, and renal effects (Beasley et al. 1997a). Signs of poisoning usually develop within 12B36 hours after consumption of a toxic dose. Initial signs may be non-specific and moderate, and include anorexia, lethargy, weakness, nausea, vomiting ( blood), diarrhoea ( blood), polyuria (increased urination), polydipsia (increased water consumption), and rarely neurological abnormalities (e.g. seizures). Clinical signs become more severe 24B36 hours after onset, as serum calcium levels increase. Renal effects, including polyuria, hyposthenuria (decreased urine specific gravity), and azotemia (increased blood urea nitrogen (BUN) and creatinine) become more pronounced. Hypercalcaemia can result in electrocardiogram (ECG) changes, (Dorman & Beasley 1989). Heart sounds are slowed and prominent, and animals become progressively more depressed. Death usually occurs in 2 to 5 days from the onset of clinical signs.

Laboratory diagnosisThe most significant and specific clinical pathology alteration is hypercalcaemia. Serum calcium concentration begins to increase about 24 hours after exposure, and values of >11.5 mg/dL in adult dogs are highly suggestive of cholecalciferol poisoning. Elevations of serum phosphate may proceed hypercalcaemia by 12 hours, and may serve as a non-specific indicator of exposure. Renal azotemia and hyposthenuria (urine specific gravity in the 1.002B1.006 range) are common, and proteinuria and glucosuria may be seen in some acute cases. Increased tissue 1, 25-dihydroxycholecalciferol is a sensitive indicator. Kidney calcium concentrations may reach 1000 ppm in poisoned animals, compared with about 100 ppm in normal dogs (Osweiler 1996a; Beasley et al. 1997a).

LesionsGross lesions include roughened, raised plaques in the intima of large vessels, petechial haemorrhages in various tissues; enlarged, pale thyroid glands; and pale, mineralised streaks in renal cortical surfaces. Histopathologically, calcification and necrosis of intramural coronary arteries, gastric mucosa, intestinal wall, parietal pleura, pulmonary bronchioles, pancreas, thyroid, muscles, and bladder have been observed. Degeneration, necrosis, and mineralisation may occur in the myocardium and especially the renal tubular epithelium (Beasley et al. 1997a; Jones et al. 1997).

Treatment of cholecalciferol toxicosis in domestic animalsCholecalciferol poisoning is a medical emergency. Treatment of animals presented with severe or advanced clinical signs is difficult and prolonged, and the prognosis is guarded. Therefore, treatment should be initiated rapidly in order to maximise the probability of survival. Therapeutic goals are (1) to decrease cholecalciferol absorption; (2) to correct fluid and electrolyte imbalances; and (3) to prevent or

44

reduce hypercalcaemia. Current recommendations for the treatment of cholecalciferol toxicosis in companion animals are as follows (treatment should be followed in order) (Dorman & Beasley 1989; Beasley et al. 1997a):$ If ingestion was recent (< 3 hours), induce emesis with household salt solution

or washing soda crystals, or perform gastric lavage.$ Administer activated charcoal (1B2 g/kg) with a saline cathartic (magnesium

sulphate at 250 mg/kg in 5–10 times as much water).$ Continue activated charcoal (at 0.5B1.0 g/kg t.i.d.) for 1B2 days to reduce

enterohepatic recirculation of vitamin D and its active metabolites.$ Determine baseline serum calcium as soon as the animal is presented (to rule

out normally occurring juvenile hypercalcaemia — values up to 14 mg/dL reported in some puppies), and continue to monitor serum calcium levels every 24 hours to determine if specific therapy to reduce serum calcium is required.

$ Monitor BUN and creatinine, urine specific gravity, heart sounds, and ECG parameters, beginning 24 hours after exposure.

$ Hypercalcaemia is treated with:$ Diuresis with IV normal saline and frusemide (5 mg/kg initial IV

bolus, followed by 3B4 mg/kg orally t.i.d.) to enhance renal calcium excretion. Thiazide diuretics are contraindicated since they may decrease urinary calcium. Early diuresis (initiate within the first 24 hours) is highly recommended in all animals with potentially serious exposures.

$ Corticosteroid administration (prednisone at 2B4 mg/kg, divided, b.i.d.) to inhibit the release of osteoclast-activating factors, reduce intestinal calcium absorption, and promote renal calcium excretion.

$ If serum calcium is excessive (>14 mg/kg), or hypercalcaemia is prolonged and unresponsive, administer salmon calcitonin to inhibit osteoclast activity at 4B6 IU/kg subcutaneously every 2B3 hours initially, until serum calcium levels stabilise (may be increased to 10B20 IU/kg if needed). Long-term administration at increased doses may be required, and some animals become refractory to treatment. Animals should be monitored for foreign protein reactions.

$ Life-threatening (> 20 mg/dL) hypercalcaemia may be treated with IV sodium EDTA at 25B75 mg/kg/h (human doses), although EDTA is potentially nephrotoxic. Severely hypercalcaemic or uremic animals may also benefit from peritoneal dialysis with calcium-free dialysate solutions.

$ Treatment with diuretics (frusemide at 2B4 mg/kg PO b.i.d.) and corticosteroids (prednisone at 2B4 mg/kg divided b.i.d.) should continue until serum calcium concentrations stabilise in the normal range. It is also valuable to continue to monitor BUN as an indicator of renal function. Often treatment is administered for 2B4 weeks, followed by withdrawal of therapy, and retesting serum calcium after 24 hours. Continue treatment until serum calcium remains normal at 24, 48, and 72 hours after withdrawal.

1.3.6 Non-target effectsThe use of cholecalciferol baits in bait stations should limit non-target effects. Baits in bait stations are likely to be less accessible to non-target species than baits on the

45

ground. A reassessment of the non-target hazards associated with toxic bait containing cholecalciferol has been recently completed by Eason & Wickstrom (2000). Current and future research questions for cholecalciferol relate to further investigation of primary and secondary poisoning risks to non-target species, its relative humaneness, and its persistence in the environment and animals.

Acute toxicityIn comparison with 1080 or brodifacoum, there is limited information on the susceptibility of non-target species to cholecalciferol. Primary poisoning assessments to gauge non-target susceptibility were undertaken with weta, ducks, chickens, canaries, and weka. Following oral gavage of cholecalciferol concentrate at 2000 mg/kg, there were no adverse effects in ducks. Chickens and canaries were more sensitive and some deaths occurred at 2000 mg/kg. Weka ate over 50 g of (0.1%) cholecalciferol without ill effects. Weta were not affected by oral administration of a single dose of cholecalciferol. Campaign® baits are dyed green and contain a high concentration of cinnamon (0.5%) to deter birds. Domestic cats or farm dogs allowed access to baits containing cholecalciferol may be killed or exhibit symptoms of cholecalciferol toxicosis. Treatment of cholecalciferol toxicosis is difficult (see section 1.3.5) (Hatch & Laflamme 1989) and prevention of exposure is critical.

Secondary poisoningThree secondary-poisoning studies are summarised in Table 8. These assessments involved the feeding of carcasses of poisoned animals to cats or dogs as their only food source for consecutive days. Dogs and cats fed these carcasses were therefore exposed to concentrations of 25OHD residues usually encountered by scavengers after poisoning operations. In addition, in order to create a worst-case secondary-poisoning scenario, some dogs were fed possums 48 hours after dosing with cholecalciferol (Eason & Wickstrom 2000). The feeding study in cats appeared to confirm earlier work with dogs (Marshall 1984), which indicated that the risk of secondary poisoning with cholecalciferol is low. This is despite the presence of elevated concentrations of 25OHD in possum carcasses. Research in rats has previously demonstrated that 25OHD is active when administered orally (Rambeck et al. 1990), but is partially degraded in the intestinal tract (Frolick & Deluca 1973). Hence not all the 25OHD present in poisoned carcasses will be bioavailable to cats and dogs. The study by Eason & Wickstrom (2000) demonstrated repeated consumption of poisoned carcasses by dogs over 5 days induced hypercalcaemia and calcium deposition in the kidney. This was accompanied by partial anorexia and lethargy. Nevertheless, all affected dogs began to recover without veterinary intervention by about 14 days after exposure.

Low risks of secondary poisoning with cholecalciferol does not imply no risk, and all pets and farm dogs should be discouraged from eating animals that have been poisoned with cholecalciferol. Given that mild toxicosis can occur in dogs eating possum meat, a precautionary approach should be followed, and it would be extremely unwise for hunters to take game from areas where cholecalciferol has been used in the previous 1–3 months. Game species, particularly if they have gained direct access to bait, would be potentially hazardous to humans since they would be likely to contain abnormal levels of 25OHD for 1–2 months.

Table 8. Summary of secondary poisoning studies

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Non-target species Treatment Result Author

Dog Dogs fed rat carcasses for 14 days (after poisoning with 0.08% cholecalciferol baits)

No clinical signs of toxicosis

No pathological abnormalities

Marshall 1984

Cat Cats fed possum carcasses for 5 days (after poisoning with 0.8% cholecalciferol baits)

No toxicosis

Non-significant increase in plasma Ca++

Eason et al. 1996a,c

Dog Variable from single to multiple feeding of dogs with possum carcasses (after poisoning with 0.8% cholecalciferol baits)

No toxicosis in dogs receiving 1 or 2 carcasses.Exposure to 5 carcasses resulted in moderate, sub-lethal toxicosis.

Eason & Wickstrom 2000

1.3.7 Summary

Advantages Disadvantages

Available to general public Expensive compared to 1080 and cyanide

Can rapidly reduce possum numbers (an acute toxin) Not registered for aerial application

Low risk of secondary poisoning Treatment for accidental poisoning of pets is available, but is complex – use of secure bait stations is essential

Less toxic to birds than 1080

A useful single-dose alternative to 1080

No long-term residue risks in sub-lethally exposed animals

The active ingredient of cholecalciferol is vitamin D3.

Cholecalciferol occurs in fish, liver, eggs, and milk.

Cholecalciferol is practically insoluble in water.

Possums and rodents that receive a lethal dose of cholecalciferol usually die within 4–7 days after ingestion.

Possums, rats, and rabbits are particularly susceptible to cholecalciferol; however, cholecalciferol will be toxic to all mammals that eat baits intended to kill possums or rodents. Post-mortem pathological changes in possums are consistent with heart failure. In other species kidney damage and gastrointestinal haemorrhage are more prominent.

After ingestion, cholecalciferol is converted to 25-hydroxycholecalciferol (25OHD), which acts to increase serum calcium concentrations by multiple mechanisms. The persistence of the active metabolite increases with increasing dose levels. For example, in humans the half-life of 25OHD is normally 15–36 days, but this increases to 25–68 days in humans during vitamin D toxicity. Elevated levels of 25OHD are likely in possum carcasses. Cholecalciferol

47

poisoning can be diagnosed by elevated blood 25OHD and calcium concentration, and at post-mortem by evidence of calcification.

The risk of secondary poisoning would appear to be low; however, poisoned carcasses are likely to contain active metabolites of cholecalciferol. These metabolites will be partially degraded in the intestine of an animal eating poisoned possums. Domestic pets and farm dogs should always be discouraged from eating poisoned carcasses.

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SECTION 2 : ANTICOAGULANT POISONS

2.1 Brodifacoum (Talon®, Pestoff®)

Chemical Name: 3-[3-(4'-bromo-[1,1'-biphenyl]-4-yl)-1,2,3,4-tetrahydro-1-naphthalenyl]-4-hydroxy-2H-1-benzopyran-2-one.

Synonyms: Brodifacoum is the approved common name. Talon® and PESTOFF® are trade names

Brodifacoum is one of the most widely used rodenticides worldwide. It has been used in New Zealand to control possums since the early 1990s. On islands, aerial application techniques are used. On mainland New Zealand it is used in cereal baits in bait stations. In January 2000 the Department of Conservation announced plans to reduce the field use of brodifacoum on the mainland.

It is essential that wildlife or livestock do not gain access to areas where brodifacoum is being used. Brodifacoum can persist (>1 year) in the liver and kidneys of sub-lethally poisoned wildlife or livestock. Hence it is important that the risk of contamination of wildlife or livestock is recognised and the product is used carefully to minimise non-target contamination.##

2.1.1 Physical and chemical propertiesThe empirical formula for brodifacoum is C31H23BrO3 and the molecular weight is 523.4. It is an off-white to fawn-coloured odourless powder with a melting point of 228–232ºC. It is of very low solubility in water (less than 10 mg/L at 20ºC and pH 7). Brodifacoum is slightly soluble in alcohols and benzene, and soluble in acetone. It is stable at room temperature. Commercial concentrated solutions of brodifacoum are available for bait manufacturers.

2.1.2 Historical development and useBrodifacoum is a synthetic compound that was developed a few decades ago. It is structurally related to a naturally occurring coumarin that causes haemorrhagic syndrome in cattle eating improperly cured or mouldy sweet clover. The rodenticidal properties of brodifacoum were described in the early 1970s. It is a very potent anticoagulant active against rats and mice, including strains resistant to warfarin and other anticoagulants (Rennison & Hadler 1975). A single ingestion of 1 mg/kg is usually sufficient to kill. In New Zealand it is used principally to control possums and rats, though it has also been used for rabbits (Williams et al. 1986a,b). In January 2000 the Department of Conservation took steps to reduce the mainland field use of brodifacoum because of concerns relating to contamination of birds and game (Eason et al. 1999c). Because of the tendancy for uncontrolled exposure of non-targets through secondary poisoning (Eason et al. 1999c), the suggested practice of secondary

49

poisoning of stoats (Brown et al. 1998) is not recommended, particularly in areas where game may be hunted for human consumption.

Brodifacoum has been used successfully in recent rodent eradication programmes on New Zealand’s offshore islands to protect populations of endangered indigenous birds (Taylor & Thomas 1989, 1993; Buckle & Fenn 1992; Robertson et al. 1993; Towns et al. 1993). In addition to its use to control and eradicate rats, brodifacoum has been successfully used in ground-laid baits or in baits placed in bait stations to eradicate rabbits (Merton 1987; Towns et al. 1993), to control wallabies (D. Moore pers. comm.) and brushtail possums (Eason et al. 1993b). Field use of brodifacoum-containing baits for rabbit or wallaby control has been discontinued in New Zealand.

Cereal baits (Talon®, PESTOFF®) containing brodifacoum are used for rodent and possum control. For possum control the baits are best used to further reduce low possum numbers following use of fast-acting poisons (such as cyanide, 1080, or cholecalciferol) for the initial population reduction. The slow action of this poison overcomes the problems associated with bait shyness in areas where possum control has been sustained for many years.

2.1.3 Fate in the environmentBrodifacoum is most unlikely to be found in water even after aerial application of baits for rodent control on offshore islands. Brodifacoum is not mobile in soil and is extremely insoluble in water (<10 mg/L water at pH 7). When baits disintegrate, brodifacoum will be likely to remain in the soil, where it will be slowly degraded by soil micro-organisms. The half-life in soil varies from 12 to 25 weeks depending on the soil type. Microbial degradation will be dependent on climatic factors such as temperature, and the presence of species able to degrade brodifacoum. In leaching studies, 2% of brodifacoum added to soil leached more than 2 cm in four soil types tested (World Health Organisation 1995).

Since brodifacoum remains absorbed in soil when baits disintegrate, only the erosion of soil itself would see any brodifacoum reaching water, and even then brodifacoum would be likely to remain bound to organic material and settle out in the sediment. If baits were sown directly into streams or rivers, localised short-term contamination might occur.

2.1.4 Toxicology and pathologyOnset of symptomsThe latent period between the time of ingestion and the onset of clinical signs varies considerably and in possums may take as long as 1–4 weeks (Littin et al. 2000). In rats the onset of symptoms and death usually occur within a week. Clinical signs reflect some manifestations of haemorrhage. Onset of signs may occur suddenly; this is especially true when haemorrhage of the cerebral vasculature or pericardial sac occurs. Clinical signs commonly include anaemia and weakness. Haemorrhaging may be visible around the nose, mouth, eyes, and anus of mammals. When pulmonary haemorrhage has occurred, blood-tinged froth may be visible around the nose and mouth. Swollen, tender joints are common and if haemorrhage involves the brain or central nervous system, ataxia or convulsions can occur. Poisoned animals die of multiple causes related to anaemia or hypovolemic shock. Possums respond significantly more slowly with onset of toxicosis occurring between 2 and 3 weeks

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after dosing. In general, possums appear to be less sensitive to anticoagulants, which may be due to species differences in the ability to metabolise xenobiotics (Olkowski et al. 1998) or difference in the half-lives of vitamin K-dependent clotting factors, or vitamin K epoxide reductase receptor binding.

Mode of actionBrodifacoum, like other anticoagulant toxicants, acts by interfering with the normal synthesis of vitamin K-dependent clotting factors in the liver of vertebrates (Hadler & Shadbolt 1975). In the liver cells the biologically inactive vitamin K1-2,3 epoxide is reduced by a microsomal enzyme into biologically active vitamin K, which is essential for the synthesis of prothrombin and other clotting factors (VII, IX, and X). Brodifacoum antagonism of the enzyme vitamin K1-epoxide reductase in the liver causes a gradual depletion of the active form of the vitamin, and consequently of vitamin K-dependent clotting factors, which results in an increase in blood-clotting time until the point where no clotting occurs.

The greater potency of second-generation anticoagulants such as brodifacoum compared to first-generation anticoagulants such as warfarin and pindone is likely to be related to their greater affinity for vitamin K-epoxide reductase and subsequent accumulation and persistence in the liver and kidneys after absorption (Huckle et al. 1988). Anticoagulants share this common binding site, but the second-generation anticoagulants have a greater binding affinity than the first-generation compounds (Parmar et al. 1987). All tissues that contain vitamin K-epoxide reductase (e.g. liver, kidney, and pancreas) are target organs for accumulating these toxicants.

Pathology and regulatory toxicologyGeneralised haemorrhage is frequently evident at post-mortem. Areas commonly affected are the thoracic cavity, subcutaneous tissue, stomach, and intestine. The heart is sometimes rounded and flaccid with subepicardial and subendocardial haemorrhages. Histomorphological analysis of the liver may reveal centrilobular necrosis as a result of anaemia and hypoxia. In possums, post-mortem findings range from mild to moderate haemorrhage in some limbs and in the gastrointestinal tract, to extensive haemorrhage throughout the body and major organs.

Brodifacoum is a slight skin irritant and a mild eye irritant in the rabbit. Various in vitro and in vivo studies (including the Salmonella reverse mutation assay, the forward mutation assay using mouse lymphoma cells, and the micronucleus test in mice) have been undertaken to assess the genotoxic potential of brodifacoum. No mutagenic activity was detected. Brodifacoum, when given by oral gavage to female rats at daily dose levels of 0.001, 0.01, or 0.02 mg/kg body weight during days 6–15 of pregnancy, caused no evidence of adverse developmental effects on the foetuses. Higher daily doses (above 0.05 mg/kg) caused an anticoagulant effect in the dams, which resulted in a high incidence of abortion.

Pregnant female rabbits were given oral gavage doses of 0.001, 0.002, or 0.005 mg brodifacoum/kg body weight per day from days 6–18 of pregnancy. At the highest dose level a high proportion of maternal deaths occurred as a result of haemorrhage. Although the survivors showed signs of haemorrhage, there were no effects on the developing foetuses.

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On the basis of these studies, brodifacoum can be classified as non-mutagenic and lacking in tetratogenic potential. In a 5-day study in rats, a no-observed-effect level for brodifacoum was 0.02 mg/kg/day (WHO 1995).

Fate in Animals

Absorption, metabolism and excretion of brodifacoum compared with other anticoagulant toxicants 3

Brodifacoum is absorbed through the gastrointestinal tract. It can also be absorbed through the skin (Table 9).

Table 9. Acute toxicity (LD50 mg/kg) of brodifacoum in rats (Hone & Mulligan 1982)

Species Route LD50 (mg/kg)

Rat (oral) 0.27

Rat (dermal) 50.00

After absorption, high concentrations in the liver are rapidly established and remain relatively constant. Disappearance from serum is slow with a half-life in rats of 156 hours or longer. The slow disappearance from the plasma and liver and the large liver:serum ratio probably contribute to the higher toxicity of brodifacoum when compared with warfarin or pindone (Bachmann & Sullivan 1983). It is apparent that a proportion of any ingested dose of brodifacoum bound in the liver, kidney, or pancreas remains in a stable form for some time and is only very slowly excreted.

In contrast to brodifacoum, warfarin will undergo relatively extensive metabolism. The metabolites will be more polar (water soluble) than the parent compounds and therefore more readily excreted in the urine.

Brodifacoum, like other second-generation metabolites, is not readily metabolised and the major route of excretion of unbound compound is through the faeces. Enterohepatic recirculation, the process that allows drugs and pesticides that have been absorbed to return to the gastrointestinal tract from the liver via the biliary tract, undoubtedly plays an important role.

Tables 10 and 11 present comparative data on the persistence of anticoagulants. Kelly & O’Malley (1979) reported the mean half-life for disappearance of warfarin from the plasma of human volunteers given a single oral dose of 0.5–100 mg/kg body weight varied from 24 to 58 hours. No dose-level effect on half-life was apparent even over

3 In this section the metabolism fate of brodifacoum in animals is compared with that for other anticoagulants to avoid repetition in the following sections. First-generation anticoagulants (developed c. 1950–70) are listed in Table 10 and second-generation anticoagulants (developed c. 1970–2000) in Table 11.

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this large range of doses. Second-generation anticoagulants are much more slowly cleared from the bloodstream.

In a comparative study in rabbits Breckenridge et al. (1985) reported plasma elimination half-lives of 5.6 hours for warfarin, 83.1 hours for difenacoum, and 60.8 hours for brodifacoum. There are very limited data on the influence of dosage on elimination. However, in the case of bromadiolone, a dose-dependent increase in plasma elimination half-life from 25.7 to 57.5 hours was reported after the oral dosage was increased from 0.8 to 3 mg/kg in rats (Kamil 1987).

Woody et al. (1992) observed an elimination half-life for brodifacoum in serum of 6 4 days in four dogs. The plasma half-life of brodifacoum determined in three patients with severe bleeding disorders was found to be approximately 16–36 days (Weitzel et al. 1990).

There are very limited data on the persistence of warfarin or pindone in the liver of animals. Two studies in non-rodent species indicate comparatively rapid clearance from the liver. Warfarin concentrations declined in pigs to very low concentrations after approximately 30 days, and concentrations were declining in those that received a lethal dose and those that survived (O’Brien et al. 1987).

In sheep receiving sub-lethal doses of bromadiolone (2 mg/kg), flocoumafen (0.2 mg/kg), and pindone (10 mg/kg), bromadiolone was detectable in the liver for 256 days and flocoumafen for 128 days. In contrast pindone was undetectable in the liver after 16 days (Nelson & Hickling 1994). Diphacinone, which is a close relative to pindone, appears to have a hepatic persistence profile more akin to that of second-generation anticoagulants. In cattle receiving a single injection of 1 mg/kg, almost constant residue concentrations were found in liver and kidney, 30, 60, and 90 days after dosing (Bullard et al. 1976). It is noteworthy that in persistence studies, and in risk assessment, limited consideration has been given to organs other than the liver. This is surprising considering that quite high concentrations of anticoagulants are found in the kidneys and lungs relative to other tissues some time after dosing.

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Table 10. Persistence of first-generation anticoagulants

Species Blood t½ †

(hours)

Liver retention ‡

(days)

Reference

Warfarin Rat , Rat

Rabbit

Possum

Human

Pig

18, 28

6

12

15–58

-

-

-

30–40

Pyrola 1968

Breckenridge et al. 1985

Eason et al. 1999b

O’Reilly et al. 1963

O’Brien et al. 1987

Pindone Dog

Sheep

120

-

-

8–16

Fitzek 1978

Nelson & Hickling 1994

Coumatetralyl Rat - t½ 55 Parmar et al. 1987

Diphacinone Cattle - >90 Bullard et al. 1976

† t½ for plasma or liver is the elimination half-life. It is convention to report the elimination t½ (-phase) rather than the -phase.

‡ Liver retention is expressed as the time period for which residues are reported to persist in the liver unless the value is preceded by t½. Plasma is t½ unless otherwise specified.

Table 11. Persistence of second-generation anticoagulants

Species Blood t½ (hours)†(except where specified)

Liver retention‡ (days)

References

Difenacoum Rat

Rat

Rabbit

-

83

t½ 118

t½ 120

-

Bratt 1987

Parmar et al. 1987

Breckenridge et al. 1985

Bromadiolone Rat

Rat

Sheep

26–57

25–26

-

t½ 170

256

Kamil 1987

Parmar et al. 1987

Nelson & Hickling 1994

Flocoumafen Rat

Sheep

Quail

Barn owl

Dog

-

-

-

-

-

t½ 220

>128

t½ 155

>100

>300

Huckle et al. 1989

Nelson & Hickling 1994

Huckle & Warburton 1989

Newton et al. 1990

Veenstra et al. 1991

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Species Blood t½ (hours)†(except where specified)

Liver retention‡ (days)

References

Brodifacoum Rat

Rat

Rabbit

Dog

Dog

Possum

Sheep

Human

156

-

60

6 days

0.9–4.7 days

(mean 2.8)

20–30 days

-

16–36

>80

t½ 130

-

-

-

>252

>250

Bachmann & Sullivan 1983

Parmar et al. 1987

Breckenridge et al. 1985

Woody et al. 1992

Robben et al. 1998

Eason et al. 1996c,d

Laas et al. 1985

Weitzel et al. 1990

Difethialone Rat

Dog

2.3 days

2.2–3.2 days

t½ 108 § Lechevin & Poche 1988

Robben et al. 1998

† t½ for plasma or liver is the elimination half-life. It is standard convention to report the elimination t½ (-phase) rather than the -phase.

‡ Liver retention is expressed as the time period for which residues are reported to persist in the liver unless the value is preceded by t½. Plasma is t½ unless otherwise specified.

§ The half-life hepatic elimination for difethialone reported by Lechevin & Poche (1988) is unusually short for a second-generation anticoagulant, which suggests that difethialone may be unique.

Brodifacoum was detected in the liver of sheep 128 days after oral administration (0.2 and 2.0 mg/kg body weight) in concentrations of 0.64 and 1.07 mg/kg dry weight (equivalent to 0.22 and 0.36 mg/kg wet weight), respectively. The peak levels which occurred at 2 days in the high-dose group and at 8 days in the low-dose group, were 6.50 and 1.87 mg/kg dry weight (2.21 and 0.64 mg/kg wet weight), respectively (Laas et al. 1985).

Parmar et al. (1987) found that elimination of radio-labelled brodifacoum, bromadiolone, and difenacoum from rat liver was biphasic, consisting of a rapid initial phase lasting from days 2 to 8 after dosing and a slower terminal phase when the elimination half-lives were 130, 170, and 120 days, respectively. Elimination of coumatetralyl was more rapid, with a half-life of 55 days.

Similar results for difenacoum were found by Bratt (1987). After a single oral 14C-difenacoum dose of 1.2 mg/kg body weight, the highest concentration of radioactivity (41.5% of the dose) was found in the rat liver 24 hours after dosing. The elimination from the liver was biphasic. The half-life of elimination of the radioactivity during the first rapid phase was 3 days, and for the slower phase was 118 days. A similar biphasic elimination was also apparent in the kidney. In the pancreas the concentration declined more slowly than in any of the other tissues (182 days). The parent compound was the major component in the liver 24 hours after dosing (42%).

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Unchanged flocoumafen comprised the major proportion of the hepatic radioactivity in rats and was eliminated with a half-life of 220 days (Huckle et al. 1989). Veenstra et al. (1991) found retention of about 8% of an administered flocoumafen dose of 0.4 mg/kg in the liver of beagle dogs 300 days after dosing. Despite the more rapid metabolism of flocoumafen in Japanese quail, a proportion of the administered dose is retained in the liver, with a elimination half-life of 155 days after oral dosing (Huckle & Warburton 1989).

There are limited data on the persistence of anticoagulants in New Zealand native species. In a study in weta, brodifacoum persisted for approximately 1 week after dosing (Morgan et al. 1996a).

Species variation in response to brodifacoumFor second-generation anticoagulants like brodifacoum only a single dose is needed to induce death, if sufficient toxicant is ingested, and brodifacoum is extremely toxic in a number of animal species. The toxicity of brodifacoum varies between mammal species (Table 12) and bird species (Table 13).

In most mammals LD50 values are 1 mg/kg or less. Some higher values are reported in sheep and dogs, but there is considerable variability in these reports (LD50 in sheep 5–25 mg/kg and in dogs 0.25–3.56 mg/kg).

It has been suggested that anticoagulants are unlikely to affect invertebrates, which have different blood-clotting systems from vertebrates (Shirer 1992) and a New Zealand-based study has shown that brodifacoum lacks insecticidal properties in weta (Morgan et al. 1996a).

Table 12. Acute oral toxicity (LD50mg/kg) of brodifacoum for mammal species (Godfrey 1985; Eason et al. 1994a, Eason & Spurr 1995)

Species LD50

(mg/kg)

Pig 0.1

Possum 0.17

Rabbit 0.2

Cat 0.25–25

Dog 0.25–3.56

Rat 0.27

Mouse 0.4

Bennett’s wallaby 1.3

Sheep 5–25

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Table 13: Acute oral toxicity (LD50mg/kg) of brodifacoum for bird species (Godfrey 1985)

Bird species LD50 (mg/kg)

Southern black-backed gull <0.75†

Canada goose <0.75†

Pkeko 0.95

Blackbird >3.0‡

Hedge sparrow >3.0‡

California quail 3.3

Mallard duck 4.6

Black-billed gull <5.0†

House sparrow >6.0‡

Silvereye >6.0‡

Australasian harrier 10.0

Ring-necked pheasant 10.0

Paradise shelduck >20.0‡

† Lowest dose tested ‡ Highest dose tested

Small birds such as silvereyes, sparrows, blackbirds, and California quail are considered more resistant to brodifacoum than some larger birds such as southern black-backed gulls, Canada geese, and pukeko (Godfrey 1985). However, some large birds, including Australasian harriers, ring-necked pheasants, and paradise shelducks, are also relatively resistant.

Aquatic toxicologyThere are limited data on the aquatic toxicology of brodifacoum. In the unlikely event of a significant amount of brodifacoum bait being applied directly to a small stream, poisoning of aquatic invertebrates and fish could result. The EC50 from Daphnia magna (first instar) was 1.0 mg/kg after 24 hours of exposure and 0.34 mg/kg after 48 hours using 50 ppm pelleted baits. The LC50 (24 hours) for rainbow trout is 0.155 mg/L. The LC50s (96 hours) for rainbow trout and bluegill are 0.05 and 0.165 mg/L, respectively (World Health Organisation 1995.

2.1.5 Diagnosis and treatment of anticoagulant poisoning

Diagnosis of non-target poisoning in domestic animalsDiagnosis of anticoagulant toxicosis is based on exposure history, clinical signs, response to treatment, laboratory analyses, and in lethal cases, lesions. Differential diagnoses vary with the species involved, and include other causes of coagulopathy (clotting disorders) such as autoimmune thrombocytopenia (reduced platelet numbers), liver disease, and hereditary clotting factor deficiencies like Von Willebrand’s disease or Haemophilia A (Beasley et al. 1997d).

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Clinical signsAlthough in some cases signs have been observed within 24 hours of ingestion, there is usually a lag period of 3–5 days between exposure and the onset of clinical signs of anticoagulant toxicosis. This delayed onset represents the time required to deplete hepatic stores of vitamin K, and reduce preformed vitamin K-dependent, clotting factor concentration in the plasma to the point of functional deficiency.

Initial clinical signs of anticoagulant poisoning are usually characterised by depression/lethargy and anorexia, followed shortly by anaemia with pale mucous membranes, dyspnoea, exercise intolerance, and haemorrhaging from numerous sites, as evidenced by haematemesis (vomiting blood), epistaxis (blood from the nose), haemoptysis (bronchial or pulmonary bleeding), melaena (‘tarry’ faeces), and haematomas in various locations. Periarticular or intraarticular haemorrhage causing swollen joints and lameness is especially common in pigs, and abortion induced by placental haemorrhaging has been reported in cattle. Convulsions indicate bleeding into the central nervous system. Animals experiencing prolonged toxicosis may be icteric (jaundiced). Similar clinical signs occur in humans and include haematuria, bleeding gums, and easy or spontaneous bruising (Park et al. 1986).

As blood loss continues, cardiac murmurs, irregular heart beat, weak peripheral pulses, ataxia, recumbency, and coma will be observed. Death due to hypoxia and hypovolemic shock may occur from 48 hours to several weeks after exposure. Animals may occasionally be found dead with no premonitory signs, especially if severe haemorrhage occurs in the cerebral vasculature, pericardial sac, abdominal cavity, mediastinum, or thorax (Murphy & Gerken 1989; Felice & Murphy 1995).

Laboratory diagnosisLaboratory evaluation of suspect anticoagulant exposures in domestic animals includes measurement of packed cell volume (haematocrit), clotting parameters, and residue analysis.

The activity of vitamin K-dependent clotting factors (II, VII, IX, and X) is commonly measured using a suite of tests, including prothrombin time (PT), activated coagulation time (ACT), and activated partial thromboplastin time (APTT). Abnormal prolongation of PT is usually the earliest indicator of anticoagulant-induced coagulopathies, due to the involvement of factor VII in the coagulation pathway assessed by this clotting parameter. Factor VII has the shortest half-life of the vitamin K-dependent factors (6.2 hours in dogs), and is therefore the first to be depleted in plasma (Murphy & Gerken 1989). Elevations of PT from 2–6 times normal may occur within 24–48 hours of ingestion of a toxic dose. This is followed several hours later by elevation in APTT to 2–4 times normal values in cases of significant exposure. In general, changes in clotting parameter times are suggestive of anticoagulant exposure if they are prolonged beyond 25% of normal values. Assessment of coagulation parameters requires a sample of fresh, non-haemolysed blood collected in a sodium citrate (Blue Top) tube, stored at 4C, and submitted immediately. The diagnostic laboratory may require submission of a parallel sample from a ‘normal’, unexposed animal of the same species to serve as a control.

The onset and severity of clinical signs of anticoagulant toxicosis are usually linked with declines in packed cell volume, except in cases of massive, acute haemorrhage.

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Therefore, regular assessment of this end point is a useful tool to determine the appropriate course of treatment and to monitor progress.

Suspect anticoagulant exposures can often be confirmed by laboratory identification of toxicant residues in vomitus (only in cases of very recent ingestion, prior to the onset of clinical signs) or tissue. The antemortem sample of choice is whole blood or serum (residues are protein-bound), while liver is the best post-mortem sample. Blood samples should be stored at 4C. Liver specimens should be wrapped in foil, sealed in plastic, and shipped frozen.

Response to treatmentAnticoagulant-induced coagulopathies (clotting disorders) can be distinguished from other types of coagulopathies by clinical response to treatment with the specific antidote, vitamin K1. Tests used to assess coagulation time should indicate significant improvement in clotting ability within 12–24 hours of initiation of treatment, and should return to normal within 36–48 hours (Murphy 1999).

LesionsPost-mortem lesions resulting from anticoagulant rodenticide exposure are characterised grossly by generalised haemorrhage, especially in the thoracic or abdominal cavities, mediastinal space, periarticular tissues, subcutaneous tissues, subdural space, and gastrointestinal tract. Sudden deaths are often marked by massive haemothorax, haemopericardium, and pulmonary oedema or haemorrhage. The heart is often flaccid, with subepicardial and subendocardial ecchymoses. Centrilobular hepatic necrosis secondary to anaemia and hepatocellular hypoxia may be observed histologically (Osweiler 1996b; Beasley et al. 1997d).

Treatment of anticoagulant toxicosis in domestic animalsCompanion animals usually present with signs of haemorrhage or anaemia, or with a history of recent ingestion of anticoagulant bait but no clinical effects. In the latter cases, either the dose ingested is insufficient to cause significant inhibition of vitamin K-dependent clotting factor production, or insufficient time has elapsed to deplete pre-exposure plasma clotting factor concentrations to the point of deficiency. Because treatment of anticoagulant toxicosis can be expensive (especially with large dogs exposed to second-generation products requiring prolonged therapy), animals presenting with a history of exposure but no clinical signs should be assessed carefully before treatment is initiated.

Therapeutic goals for veterinarians in the treatment of anticoagulant poisoning are (1) to decrease toxicant absorption; (2) to correct low haematocrit and/or hypovolemia; and (3) to correct clotting factor deficiencies. Recommendations for the treatment of anticoagulant toxicosis in companion animals are as follows (Mount & Feldman 1983; Murphy & Gerken 1989; Osweiler1996b; Beasley et al. 1997d):

Animal is presented asymptomatic, within several hours of suspected/confirmed oral exposure: Induce emesis with household salt solution or washing soda crystals (if

<3 hours) or perform gastric lavage. Administer activated charcoal (1–2 g/kg) with a saline cathartic (magnesium

sulphate at 250 mg/kg in 5–10 times as much water).

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Decision to initiate vitamin K therapy depends on potential exposure dose and effectiveness of emesis. If suspected dose ingested is low (< 10% of LD50), may elect to decontaminate and release with instructions to monitor for signs of haemorrhage. If potential exposure is more significant, measure PT at 24, 48 and 72 hours after ingestion. If results are normal, defer treatment but monitor for 10–30 days (depending on the compound involved).

Animal is presented with signs of haemorrhage and/or anaemia: Animals with a packed cell volume of <15% with severe bleeding, or with

associated complications of anaemia, require clotting factor replacement immediately (Murphy 1999). Correct low haematocrit and/or hypovolemia, and provide clotting factors with IV transfusion of fresh whole blood or plasma at 10–20 mL/kg. The initial 25% of the volume is given relatively rapidly, and the remainder by slow drip.

Handle affected animals with care. Sedate as needed (avoid protein-binding drugs like promazine that may displace toxicant residues and exacerbate signs). Maintain core body temperature. Oxygen may be beneficial with severe dyspnoea. Give replacement IV fluids only after clotting factors are on board.

Initiate antidotal therapy using vitamin K1 (phytonadione, phylloquinone), which is the most effective form available. Vitamin K3 is not recommended. Hepatic bioavailability of oral vitamin K1 is greater than the parenteral form, so this route should be used unless contraindicated (e.g. in cases of vomiting, gastrointestinal haemorrhage, or concurrent administration of activated charcoal). If parenteral administration is required on initial presentation, approved vitamin K1 formulations can be given IV (slowly, over 15–20 minutes, with a small-bore needle), although this route is associated with frequent anaphylactoid reactions. The subcutaneous route is safer, but absorption is slow in dehydrated animals.

Recommended doses of vitamin K1 for companion animals range from 1 mg/kg (once a day) for first-generation products such as warfarin and pindone, to 2.5 mg/kg for bromadiolone, and 2.5–5.0 mg/kg for potent, second-generation anticoagulants such as brodifacoum and diphacinone. Specific doses are not available for flocoumafen and coumatetralyl, but a starting dose of 2.5 mg/kg is reasonable (Felice & Murphy 1995). Oral bioavailability is enhanced by concurrent feeding of a small fatty meal.

Oral vitamin K1 therapy must be maintained for as long as the toxicant is active in inhibiting vitamin K epoxide recycling. Recommendations for duration of treatment in companion animals range from 7–14 days for warfarin and pindone, to 21 days for bromadiolone, and 30 days for brodifacoum and diphacinone (Felice & Murphy 1995; Beasley et al. 1997d). In all cases, premature termination of treatment should be avoided, and prothrombin time should be measured 5–7 days after the end of the treatment period.

Avoid protein-bound drugs, elective surgery, strenuous exercise, and large volumes of fatty food during the convalescent period. Previously exposed animals may be more sensitive to subsequent anticoagulant exposure for weeks to months after recovery, due to biologically active residues in the liver.

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2.1.6 Non-target effectsBrodifacoum has the potential to cause both primary and secondary poisoning of non-target species. However, as with the other vertebrate pesticides, the adverse effects of brodifacoum on wildlife are dependent more on how baits are used and the behaviour of non-target species than susceptibility of individual species to the toxin. Baits in bait stations are less accessible to non-target species than baits on the ground. Secondary poisoning of birds is likely where target species (e.g. rabbits and rats) are a major constituent of the diet (e.g. brown skua and harriers).

Despite these distinctions, a wide range of small and large birds have been found dead from primary or secondary poisoning after field use of brodifacoum in New Zealand: saddlebacks, blackbirds, chaffinches, house sparrows, hedge sparrows, silvereyes, song thrushes, paradise shelducks, Australian magpies, robins, western weka, Stewart Island weka and brown skuas (Towns et al. 1993; Williams et al. 1986a,b; Taylor & Thomas 1993; Taylor 1984; D. Brown, pers. comm.; L. Chadderton, pers. comm.).

These findings suggest that the reported differences in sensitivity (from published LD50 values; see Table 13) may be either inaccurate or irrelevant predictors of susceptibility to brodifacoum, since species such as house sparrows, silvereyes, and paradise shelducks are reported to be moderately resistant.

The impacts of brodifacoum-poisoning operations on populations of non-target species that might have eaten baits have been monitored in several studies. Numbers of three indigenous bird species (western weka, Stewart Island weka, and pukeko) have been severely reduced in poison areas. For example, the entire western weka population on Tawhitinui Island was exterminated by direct consumption of Talon® 50WB intended for ship rats, which they obtained by reaching into bait stations, by eating baits dropped by rats, and by eating dead or dying rats (Taylor 1984). About 80–90% of the Stewart Island weka on Ulva Island were similarly killed by Talon® 50WB intended for Norway rats (L. Chadderton, pers. comm.), and 98% of the western weka on Inner Chetwode Island were killed after the aerial distribution of Talon® 7-20 (Wanganui No.7 cereal baits with 20 ppm brodifacoum) intended for kiore (D. Brown pers. comm.). More than 90% of pukeko on Tiritiri Matangi Island were killed after aerial distribution of Talon® 20P for eradication of kiore (C.R. Veitch pers. comm.). Some introduced ground-feeding bird species such as brown quail, blackbirds, house sparrows, and common mynahs on Tiritiri Matangi Island were also decimated (C.R. Veitch pers. comm.). However, despite deaths of some individuals, populations of other bird species have been less affected. For example, on Stanley Island 41 of 43 banded North Island saddlebacks were still alive more than 1 month after aerial distribution of Talon® 20P (Towns et al. 1993). On Red Mercury Island, all nine little spotted kiwi with radio transmitters were still alive 1 month after aerial distribution of Talon® 20P (Robertson et al. 1993). On Tiritiri Matangi Island, little spotted kiwi, North Island saddlebacks, and North Island robin populations were not detrimentally affected by aerial distribution of Talon® 20P (C.R. Veitch pers. comm.). The South Island robin population on Breaksea Island was not detrimentally affected by the use of Talon® 50WB in bait stations (Taylor & Thomas 1993), and all banded South Island robins on Inner Chetwode Island are thought to have survived aerial distribution of Talon® 20P (D. Brown pers. comm.). Brodifacoum residues have been detected in dead birds after aerial application of baits for rodent eradication

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(Morgan et al. 1996a), but the extent of wildlife contamination and impact after continued use has not been comprehensively studied.

Sub-lethal doses of brodifacoum have caused abortions and reduced lambing rates in sheep (Godfrey 1985), and concerns have been expressed about the adverse effects of small doses of anticoagulants on tawny owls (Townsend et al. 1981). However, there are no publications that elucidate any potential long-term effects of low-level brodifacoum exposure in birds.

There are no published LD50 data on the direct acute toxicity of brodifacoum to New Zealand bats. However, data from other anticoagulants suggest they may be susceptible if they were to consume the toxin.

There are no published LD50 data on the acute toxicity of brodifacoum to reptiles or amphibians. However, reptiles, at least, are known to be susceptible to brodifacoum. Telfair’s skinks (Leiolopisma telfairii) were found dead after eating rain-softened Talon® 20P used for rabbit eradication on Round Island, Mauritius, and post-mortem analyses revealed brodifacoum concentrations of 0.6 mg/kg in samples of liver (Merton 1987). Skink numbers have increased markedly since the removal of rabbits (North et al. 1994). In New Zealand, lizard numbers increased after use of Talon® 20P to eradicate rabbits and rats on Stanley Island (Towns et al. 1993) and rats on Tiritiri Matangi Island (C.R. Veitch pers. comm.).

Invertebrates have been seen eating baits containing brodifacoum, and residues of brodifacoum have been found in beetles (Coleoptera) collected from bait stations containing Talon® 50WB intended for rats on Stewart Island (G.R.G. Wright unpubl. data). It is considered that invertebrates are unlikely to be directly killed by brodifacoum (Shirer 1992; Morgan et al. 1996a). However, a number of unpublished observations suggest that brodifacoum may be toxic to molluscs (D. Merton pers. comm.). Contaminated invertebrates may pose a risk of secondary poisoning to insectivorous vertebrates. However, recent studies have shown that brodifacoum does not persist in weta. If there is a similar lack of persistence in other invertebrates, then the risk of secondary poisoning via invertebrates would be short-lived. However, at this time the persistence of brodifacoum in molluscs has not been elucidated. Molluscs have a hepato-pancreas; in mammals anticoagulant rodenticides binds to vitamin K epoxide reductase in both the pancreas and the liver. It is therefore conceivable that the hepato-pancreas is a target organ in molluscs.

Secondary poisoningThe risk of secondary poisoning to non-target species is far greater from second-generation anticoagulants such as brodifacoum than from first-generation anticoagulants such as warfarin, because second-generation compounds are not substantially metabolised and excreted before death. For example, five out of six owls died after feeding on rats killed by brodifacoum for 8–11 days (Mendenhall & Pank 1980).

The only confirmed report of secondary poisoning of insectivorous birds with brodifacoum was in a zoo, where avocets, rufous-throated ant pittas, golden plovers, honey creepers, finches, thrushes, warblers, and crakes died in an aviary after feeding on pavement ants and cockroaches that had eaten brodifacoum baits (Godfrey 1985).

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However, the potential for invertebrates to ‘carry’ poison to birds has been suggested (Stephenson et al. 1999).

In New Zealand, predator and scavenger populations have been monitored during five brodifacoum-poisoning operations. Comparable numbers of brown skuas and New Zealand falcons, the main avian predators at risk, were seen before and after use of Talon® 50WB in bait stations for eradication of Norway rats on Hawea Island (Taylor & Thomas 1989). There was no evidence of New Zealand falcons or moreporks being killed by use of Talon® 50WB in bait stations for eradication of Norway rats on Breaksea Island (Taylor & Thomas 1993). There was no evidence of a detrimental effect on populations of moreporks on Stanley Island (Towns et al. 1993) or Red Mercury Island (Robertson et al. 1993) after aerial distribution of Talon® 20P for eradication of kiore. Moreporks and Australasian harriers on Tiritiri Matangi Island decreased after aerial distribution of Talon® 20P, but it is not known whether this was induced by poisoning (C.R. Veitch pers. comm.) or the removal of their major food item, rats.

The perceived hazards of secondary poisoning to non-target wildlife have restricted second-generation anticoagulants such as brodifacoum from being registered for field use in the USA (Colvin et al. 1991). The detection of brodifacoum residues in a range of wildlife including native birds such as kiwi (Apteryx spp.) (Robertson et al. 1993), raises serious concerns about the long-term effects of broad-scale field use of brodifacoum in New Zealand. This is compounded by the recent detection of residues in a wide range of species: weka, morepork, Australian harrier, pukeko, grey duck, mallard, black-backed gull, robin, saddleback, chaffinch, mynah, magpie, and blackbird (Murphy et al. 1998; Dowding et al. 1999; G.R.G. Wright, pers. comm.). Of far less concern was the detection of brodifacoum in cats and stoats, introduced species regarded as pests and largely responsible for the decline of native birds, such as kiwi. Nevertheless, because of the potential for uncontrolled contamination of wildlife (demonstrated by field survey data) broad-scale field use of brodifacoum in New Zealand (Eason et al. 1999c, 2000) is currently being restricted by the Department of Conservation.

Recent surveys of wildlife have indicated that extensive contamination has occurred where there has been sustained use of brodifacoum. Samples of liver were collected from feral pigs, feral red deer, feral cats, stoats, and weka that were shot, or trapped, except for one feral pig and six weka found dead (Eason & Murphy 2000). All the animals were killed in areas where brodifacoum was currently in use for possum and rat control. In all cases the method of application of baits followed label instruction and bait stations were used. Fourteen out of 35 pigs (40%) contained no residues. The remaining 21 pigs, including one which was found dead, contained residues of brodifacoum at concentrations ranging from 0.007 to 1.78 mg/kg. The pig found dead contained the highest liver residue. Eleven of 33 feral deer (33%) were contaminated but the concentration did not exceed 0.03 mg/kg. Clearly, in the case of deer, the most likely route of ingestion of brodifacoum is by feeding on baits that were not adequately contained in bait stations. (Possums are known to spill significant amounts of baits when feeding). This being the case, it seems probable that at least some of the pigs may have ingested bait in the same way as deer, compounded by some ingestion of brodifacoum-poisoned target species. Fifty-seven out of 71 cats (80%), and 98 out of 115 stoats (85%) contained residues. Concentrations in cats ranged from 0.078 to

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1.84 mg/kg and in stoats from 0.008 to 1.32 mg/kg. Six weka were found dead and contained residues of between 0.11 and 2.3 mg/kg. The other 12 weka were trapped; four contained no residues, and eight (67%) contained between 0.01 and 0.95 mg/kg.

These recently acquired residue results reinforce earlier recommendations that pigs and possums should not be hunted for human consumption, from areas where baits containing brodifacoum have been used for possum control, for at least 9 months after the application of the baits (Eason et al. 1996d).

In summary, indigenous New Zealand birds most at risk from feeding directly on cereal-based baits containing brodifacoum are those species that are naturally inquisitive and have an omnivorous diet (e.g. weka, pukeko, brown skua, and kea). The risk of secondary poisoning is probably greatest for predatory and scavenging birds (especially the weka, brown skua, Australasian harrier, morepork, and southern black-backed gull) that feed on target species (e.g. live or dead rats, rabbits, and possums). Recently published surveys by Department of Conservation and Landcare Research staff clearly demonstrate widespread wildlife contamination that extends to native birds as well as game species (Murphy et al. 1999; Gillies & Pierce 1999; Dowding et al. 1999; Meenken et al. 1999; Eason et al. 1999c; Robertson et al. 1999a; Stephenson et al. 1999). This pattern is mirrored overseas where there is field use of second-generation anticoagulants (Young & de Lai 1997; Shore et al. 1999; Stone et al. 1999).

The risks of non-target mortality and contamination after pest control must be carefully balanced against the benefits. The eradication of rabbits using brodifacoum on Round Island, Mauritius, in 1986 illustrates this most clearly. Telfair’s skinks and other lizards on the island were considered at risk from poisoning by eating poisoned insects and/or bait and some were killed (Merton 1987). Three years after eradication of the rabbits there has been a dramatic regeneration of vegetation and marked increases in the numbers of lizards, including Telfair’s skink (North et al. 1994). In New Zealand, the benefits of using brodifacoum (or related compounds) to eradicate rats and/or rabbits from offshore islands are also becoming apparent. For example, eradication of rats from Korapuki Island (using bromadiolone, a second-generation anticoagulant related to brodifacoum) in 1986 resulted in a 10-fold increase in lizard numbers in 3 years (Towns 1991) and a 30-fold increase in 6 years (Towns 1994). Similarly, in 1996, the successful removal of rats from Kapiti Island has resulted in a significantly improved survival rate for stitchbirds and saddlebacks, and benefits to other taxa are expected (Empson & Miskelly 1999). However, on mainland sites where the persistence of brodifacoum raises concerns about the possible transfer of this compound through the food chain to humans, dogs, or wildlife, a precautionary approach is recommended. Because of this, the use of this poison has been under review. Nevertheless, its total removal from mainland use leaves a significant gap in the armoury of the conservationist, pest controller involved in endangered species protection (Stephenson 2000).

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2.1.7 Summary

Advantages Disadvantages

Generally available and no licence required. High risk of secondary poisoning of non-target species

Effective against possums that have developed poison/bait shyness and

Effective for rodent control

Persistent (>9 months) in liver of vertebrates (can enter food chain and put meat for human consumption at risk)

Antidote available Although an antidote (vitamin K) is available, long-term treatment is needed

Expensive compared to 1080 or cyanide

Possums can eat excessive amounts of bait (increase costs)

Possums take 2–4 weeks to die

Brodifacoum is a synthetic pesticide that was developed approximately 20 years ago.

Brodifacoum is not readily soluble. It binds strongly to soil and is slowly degraded. It is most unlikely to significantly contaminate waterways unless large amounts of baits enter streams.

It is a potent anticoagulant, which acts by interfering with the synthesis of vitamin K-dependent clotting factors. Brodifacoum is toxic to mammals, birds, and reptiles.

Brodifacoum is extremely persistent in the livers of lethally poisoned, and to a lesser extent the meat of sub-lethally poisoned, animals, which heightens the risk of secondary poisoning of non-target species.

Livestock must not be allowed access to brodifacoum baits as residues may persist in survivors of a sub-lethal dose for >9 months.

Non-target effects on individual birds of a number of species have occurred after brodifacoum use for rodent control.

Adverse effects on individual populations of a number of species of birds have been observed after brodifacoum use for rodent control. However, short-term losses are likely to be superseded by long-term gains once predators have been removed.

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2.2 Flocoumafen (Storm®)

Chemical Name: 4-hydroxy-3-[1,2,3,4-tetrahydro-3-[4-

(4-trifluoromethylbenzyloxy) phenyl]-1-naphthyl) coumarin

Synonyms: Flocoumafen is the approved name, Storm® is the trade name.

Flocoumafen and brodifacoum are extremely similar in terms of their chemistry, biological activity, potency, persistence, and risk of secondary poisoning. For further details on the toxicology, mode of action, etc. of flocoumafen see the previous section on brodifacoum.

2.2.1 Physical and chemical propertiesFlocoumafen is an off-white solid with a melting point cis-isomer of 181–191C and a vaporisation point at 133 pPa (25ºC). Flocoumafen’s solubility is 1.1 mg/L in water and >10 g/L in acetone, alcohols, chloroform, and dichloromethane. It is stable to hydrolysis and does not undergo any detectable degradation when stored at pH7–9 for 28 days at 50ºC.

2.2.2 Historical development and useFlocoumafen is a second-generation anticoagulant that was developed by Shell Research in the early 1980s. Flocoumafen has been used against a wide range of rodent pests including the principal commensal species. It is also effective against rodents that have become resistant to other anticoagulant rodenticides. It is currently registered for use in New Zealand as a rodenticide under the trade name ‘Storm’. Flocoumafen is not extensively used in the field in New Zealand.

2.2.3 Fate in the environmentFlocoumafen is not readily soluble in water. In physico-chemical terms flocoumafen is extremely similar to brodifacoum. Hence if flocoumafen-containing baits were to be used in the field, when these baits disintegrate flocoumafen is likely to remain in the soil where it will be slowly degraded by soil micro-organisms. Microbial degradation will be dependent on climatic factors such as temperature, and the presence of species able to degrade flocoumafen.

2.2.4 Toxicology and pathologyOnset of symptomsFlocoumafen is a potent second-generation anticoagulent similar to brodifacoum. Its symptoms, time to onset of poisoning, mode of action, and toxicity to birds and mammals are like those of brodifacoum (Table 14). For practical considerations, species such as dogs, cats, and pigs, the risk of poisoning from baits or secondary poisoning from eating contaminated rodents will be similar to that for brodifacoum.

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Table 14. Acute oral toxicity (LD50mg/kg) of flocoumafen (Hone & Mulligan 1982)

Species LD50 (mg/kg)

Dog 0.075–0.25

Gerbil 0.18

Rat 0.25

Rabbit 0.70

Sheep >5.0

Cat >10.0

Goat >10.0

Pig 60.0

Mode of actionLike other anticoagulant toxins, flocoumafen acts by interfering with the normal synthesis of vitamin K-dependent clotting factors in the liver of vertebrates (Hadler & Shadbolt 1975). In the liver cells the biologically inactive vitamin K1-2,3 epoxide is reduced by a microsomal enzyme into biologically active vitamin K, which is essential for the synthesis of prothrombin and other clotting factors. Flocoumafen antagonism of the enzyme vitamin K1-epoxide reductase in the liver causes a gradual depletion of the vitamin and consequently of vitamin K-dependent factors, which results in an increase in blood-clotting time until the point where no clotting occurs.

Pathology and regulatory toxicologyPathological lesions in animals poisoned with flocoumafen are similar to those for brodifacoum and other anticoagulants. In regulatory studies flocoumafen has been shown to lack genetoxicity in a range of in vitro and in vivo regulatory toxicology studies evaluating the potential of this toxicant to induce chromosomal damage or genetic mutation.

In a teratogenicity study in rats some deaths or signs of haemorrhaging were reported at 0.4 mg/kg/day in females, but there were no reports of teratogenicity in foetuses. Hence regulatory studies indicate that flocoumafen lacks mutagenic or teratogenic effects at the doses tested (WHO 1995).

Fate in animals (see section 2.1.4)

Absorption, metabolism, and excretionThe persistence of flocoumafen in sub-lethally exposed animals is as great, if not greater, than that of brodifacoum (see Table 11). In rats, absorption of flocoumafen is also rapid reaching a maximum concentration in blood after 4 hours (Huckle et al.

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1989) (see Table 15). Similar rapid absorption occurs for other anticoagulants (Kamil 1987) (Table 15).

Table 15. Occurrence of peak plasma concentrations in animals after oral ingestion of anticoagulants

Anticoagulant and dose Species Tmax hours Reference

Warfarin 50 mg/kg

Bromadiolone 0.8 mg/kg

Flocoumafen 0.14 mg/kg

Possum

Rat

Rat

6

6–9

4

Eason et al. 1999a

Kamil 1987

Huckle et al. 1989

Following administration of flocoumafen, liver residues in rats consisted mainly of unchanged flocoumafen, although in a repeat-dose study a polar metabolite was also detected, indicating some low level of metabolism is occurring (Warburton & Hutson 1985; Huckle & Warburton 1986).

In rats, eight urinary metabolites have been detected after percutaneous exposure to 14C-flocoumafen (Huckle & Warburton 1986). However, they represented only a small proportion of the total dose, with most excretion occurring in the faeces as unchanged flocoumafen. Unchanged flocoumafen comprised the major proportion of the hepatic radioactivity in rats and was eliminated with a hepatic half-life of 220 days (Huckle et al. 1989). Veenstra et al. (1991) found retention of about 8% of an administered flocoumafen dose of 0.4 mg/kg in the liver of beagle dogs 300 days after dosing.

There are insufficient comparative data in different species to clarify whether or not there is a pattern of species variation in the metabolism of flocoumafen. However, it appears that quail are able to metabolise floucoumafen more effectively than rats (Huckle & Warburton 1989).

The metabolism of flocoumafen by Japanese quail may be partly responsible for the shorter liver retentions of this toxicant in quail (hepatic half-life 155 days; Huckle & Warburton 1989) versus rats (hepatic half-life 220 days; Huckle et al. 1988). Up to 12 radioactive components were detected in the excreta of quail (Huckle & Warburton 1989). Faecal excretion of radio-labelled flocoumafen following an oral dose of 0.14 mg/kg body weight accounted for 23–26% of the dose over the 7-day period; approximately half of this was recovered within the first 24 hours. Less than 0.5% of the dose appeared in the urine within 7 days (Huckle et al. 1989).

When oral14C-flocoumafen doses of 0.02 mg/kg body weight or 0.1 mg/kg body weight were given to rats, once weekly for up to 14 weeks, approximately one-third of each weekly low dose was eliminated through the faeces within 3 days, mostly within the first 24 hours. At the higher dose the faecal excretion ranged from 18% after the first dose to 59% after the 10th dose (Huckle et al. 1988).

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Species variation in response to flocoumafenFor a number of species the LD50 is less than 1 mg/kg and this is similar to brodifacoum (see Tables 12 and 14). However, there are several species with surprisingly high LD50 values, e.g. pigs. No aquatic toxicity data was found.

2.2.5 Diagnosis and treatment of poisoningAs for brodificoum, see Section 2.1.5 (pp. 57–60).

2.2.6 Non-target effectsFlocoumafen has the potential to cause both primary and secondary poisoning of non-target species. However, the adverse effects of flocoumafen on wildlife are dependent more on how baits are used and the behaviour of non-target species than the susceptibility of individual species to the toxin. Baits in bait stations are less accessible to non-target species than baits on the ground. Secondary poisoning of birds (e.g. brown skua and harriers) is likely where target species (e.g. rabbits and rats) are a major constituent of the diet. Flocoumafen is extremely persistent in the livers of lethally and sub-lethally poisoned animals, which heightens the potential risk of secondary poisoning in non-target species. As the use of flocoumafen is largely restricted to commensal rodents, the risks of exposure of wildlife are lower, except when it is used around farm buildings.

Livestock must not be allowed access to flocoumafen baits as residues are likely to persist in their livers for up to 9 months or more. There is very little detailed information available on the non-target impacts of this toxin. However, as the properties of this toxin are very similar to those found in brodifacoum, the potential for non-target impacts are likely to be very similar.

2.2.7 Summary

Advantages Disadvantages

Generally available and no licence required High risk of secondary poisoning of non-target species if used widely in the field

Effective for rodents Persistent (>9 months) in liver of vertebrates (can enter food chain and put meat for human consumption at risk) if used in the field

Antidote available Although an antidote (vitamin K) is available, long-term treatment is needed.

Expensive compared to 1080 or cyanide

Flocoumafen has chemical and biological effects that are almost indistinguishable from brodifacoum.

Flocoumafen is a synthetic pesticide that was first registered for use approximately 20 years ago.

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Flocoumafen is not readily soluble, it binds strongly to the soil, and is slowly degraded. It is most unlikely to contaminate waterways as it is used principally for controlling commensal rodents or in bait stations.

It is a potent second-generation anticoagulant, which acts by interfering with the synthesis of vitamin K-dependent clotting factors. Flocoumafen is toxic to mammals, birds, and reptiles.

When used near farms, livestock must not be allowed access to flocoumafen baits, as residues may persist in the survivors for >9 months.

2.3 Bromadiolone (Rid Rat®, Contrac®, Supersqueak®)

Chemical Name: 3-[3-(4'- bromobiphenyl-4-yl)-3-hydroxy-1-phenylpropyl]-4-hydroxycoumarin.

Synonyms: Bromadiolone is the approved name

Baits containing bromadiolone include Rid Rat®, Contrac®, Supersqueak®, and are targeted at rodents. Bromadiolone has chemical and biological effects that are similar to brodifacoum. However, it is slightly less potent than both brodifacoum and flocoumafen.

2.3.1 Physical and chemical propertiesThe empirical formula for bromadiolone is C30 H23 BrO4 and the molecular weight is 527.4. Technical grade bromadiolone (97% pure) is a yellowish powder with a melting point of 200–210ºC. Its solubility at 20ºC is 19 mg/L in water, 730 g/L in dimethylformamide, 8.2 g/L in ethanol, and 25 g/L in ethyl acetate. Bromadiolone is stable at temperatures <200ºC.

2.3.2 Historical development and useBromadiolone was synthesised and marketed by a French company in the mid-1970s, and has since been widely used to control commensal and field rodents in many countries. The toxicant was introduced into New Zealand for sale about 1980 and is registered as a rodenticide, and has on occasion been used in New Zealand for rabbit or rat control on islands. It is not widely used in the field in New Zealand. It is not registered in New Zealand for possum control, and is marketed principally for commensal rodent control.

In spite of bromadiolone belonging to a group of more potent second-generation anticoagulants, resistance problems have been encountered in rodents after repeated use overseas. It can, however, be effective, in cases where it has not been used before, against rodents that have become resistant to other anticoagulant rodenticides. In some countries, particularly in Europe, bromadiolone has increasingly been used for field control of rodents, which is leading to secondary contamination of non-target species, including mustelids and birds (Shore et al. 1999). This situation parallels the

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phenomena we have observed in New Zealand with brodifacoum. Advocates for the use of bromadiolone in the field suggest that there is a lower risk of secondary poisoning compared to brodifacoum because it is less potent.

2.3.3 Fate in the environmentBromadiolone is a second-generation anticoagulant, and as such has many of the properties that are common to the other anticoagulants. It is only slightly insoluble in water, and binds strongly to the soil, and is slowly degraded. In a study carried out in four types of soil, bromadiolone scarcely moved in soil rich in organic matter, but could be shifted through soil with low clay or organic compounds (WHO 1995).

2.3.4 Toxicology and pathology

Onset of signsAs for other anticoagulants.

Mode of actionBromadiolone, as a second-generation anticoagulant, interferes with the Vitamin K1-dependent clotting factors when a lethal or sub-lethal dose is ingested. In the liver cells the biologically inactive vitamin K1-2,3 epoxide is reduced by a microsomal enzyme into biologically active vitamin K, which is essential for the synthesis of prothrombin and other clotting factors. Bromadiolone antagonism of the enzyme vitamin K1-epoxide reductose in the liver causes a gradual depletion of the vitamin and consequently of vitamin K-dependent clotting factors, which results in an increase in blood-clotting time until the point where no clotting occurs. It is cumulative and will remain in the system in sub-lethal quantities for extended periods.

Pathology and regulatory toxicologyGeneralised haemorrhage is frequently evident at post-mortem. As for other anticoagulants, areas commonly affected are the thoracic cavity, subcutaneous tissue, stomach, and intestine. The heart is sometimes rounded and flaccid with subepicardial and subendocardial haemorrhages. Histomorphological analysis of the liver may reveal centrilobular necrosis as a result of anaemia and hypoxia.

In regulatory toxicology studies, bromadiolone has been shown to lack mutagenicity in in vitro (the Chinese hamster ovary cells) and in vivo (mouse micronucleus) test symptoms, and teratogenic effects (WHO 1995).

Fate in animals(See section 2.1.4). The persistence of bromadiolone is similar to that of brodifacoum (see Table 11). The half-life in the liver of rats is 170 days (Parmar et al. 1987) and residues have been detected in sheep liver after 256 days (Nelson & Hickling 1994).

Species variation in response to bromadioloneThe acute oral LD50 for various species is detailed in Table 16. No information was found for aquatic toxicology.

Table 16. Acute oral toxicity (LD50mg/kg) of bromadiolone (Hone & Mulligan 1982)

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Species LD50(mg/kg)

Dog c.10.0

Rat 0.65 (acute)

Mouse 0.99

Rabbit c.1.0

Guinea pig 2.8

Pig c.3.0

Chicken c.5.0

Rat 0.06 to 0.14 5 (chronic)

2.3.5 Diagnosis and treatment of poisoning

As for brodificoum, see Section 2.1.5 (pp. 57–60).

2.3.6 Non-target effectsBromadiolone is persistent in the livers of sub-lethally poisoned animals, which heightens the potential risk of accumulated secondary poisoning to non-target species.

Livestock must not be allowed access to bromadiolone baits as residues may persist in the liver for up to 9 months or more (WHO 1995).

There are no published LD50 data on the acute toxicity of bromadiolone to bats, reptiles, or amphibians. However, reptiles are known to be susceptible to brodifacoum, a similar anticoagulant toxicant.

In a laboratory study, only one out of six owls died following 10 days treatment with bromadiolone-poisoned rats, compared with five and six deaths in owls eating brodifacoum-poisoned rats (Mendenhall & Pank 1980). Nevertheless, there are increasing concerns overseas regarding non-target mortality and contamination of raptors where there is broad-scale field use of bromadiolone (Shore et al. 1999). The reduced risk of secondary poisoning from bromadiolone compared with brodifacoum that is suggested by Mendenhall & Pank (1980) may not imply limited risk if there is sufficient exposure to allow bromadiolone to accumulate to toxic levels.

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2.3.7 Summary

Advantages Disadvantages

No licence requirement Very limited field data in New Zealand, marketed principally for commensal rodents

Antidote available Persistent and likely to lead to secondary poisoning or contamination of non-target species, if widely used in the field

Effective for rodents

Bromadiolone is a synthetic pesticide that was first registered for use approximately 20–30 years ago.

Bromadiolone is not readily soluble, it binds strongly to soils, where it is slowly degraded. It is most unlikely to contaminate waterways as it is used principally for controlling commensal rodents or in bait stations.

It is a potent anticoagulant, which acts by interfering with the synthesis of vitamin K-dependent clotting factors.

Bromadiolone is toxic to mammals, birds, and reptiles.

Livestock must not be allowed access to baits containing bromadiolone as residues may persist in the survivors for >9 months.

Bromadiolone is effective against rodents that have become resistant to other first-generation anticoagulant rodenticides.

2.4 Coumatetralyl (Racumin®, No rats & mice®)

Chemical Name: 4-hydroxy-3-(1,2,3,4-tetrahydro-1-naphthyl) coumarin

Synonyms: Coumatetralyl is the approved common name

Coumatetralyl is classified as a first-generation anticoagulant. It is less potent than brodifacoum, flocoumafen, or bromadiolone, but more potent than warfarin and pindone. Internationally it is sold under the trade name Racumin®, No rats & mice®.

2.4.1 Physical and chemical propertiesThe empirical formula for coumatetralyl is C19H16O3 and the molecular weight is 292.6. It is practically insoluble in water, slightly soluble in ether and benzene, soluble in alcohol and acetone, and readily soluble in dimethyl formamide.

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2.4.2 Historical development and useThis rodenticide was developed in 1957 by scientists at Bayer, and is marketed worldwide. It is used as a tracking powder or as a cereal bait, wax block, and paste for rodent control.

2.4.3 Fate in the environmentNo published information is available on the fate of this rodenticide in soil. It would be likely to be broken down slowly in soil by micro-organisms.

2.4.4 Toxicology and pathologyOnset of signsCoumatetralyl baits containing 1 mg/kg will kill rats in 5–8 days. In general, the symptoms of poisoning do not appear suddenly.

Mode of actionAs for other anticoagulant rodenticides (see brodifacoum), post-mortem examinations reveal extensive multiple haemorrhages throughout the body with considerable quantities of unclotted blood in the chest and abdominal cavities. Rats can withstand single doses of 50 mg/kg of this toxicant, but are unable to survive doses of 1 mg/kg when that dose is ingested over 5 successive days.

Pathology and regulatory toxicologyWe could not find any regulatory toxicology studies in the published literature.

Fate in animalsCoumatetralyl is markedly less persistent (in sub-lethally poisoned animals) than brodifacoum (see Table 11). The hepatic half-life of sub-lethally exposed rats is 55 days (Parmar et al. 1987).

Species variation in response to coumatetralyl:There are comparatively few acute toxicity data for coumatetralyl (Table 17).

Table 17. Acute oral toxicity (LD50 mg/kg) of coumatetralyl (Hone & Mulligan 1982; Worthing & Hance 1991)

Species LD50 mg/kg

Rat 16.5 (single dose)

0.3 (5 days)

Pig 1.0–2.0 (1–7 days)

Hen 50.0 (8 days)

Fish 1000.0 (96 hours)

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2.4.5 Diagnosis and treatment of poisoningAs for brodificoum, see Section 2.1.5 (pp. 57–60).

2.4.6 Non-target effectsOther than pets gaining access to bait, there are few references to non-target deaths in other species. In recent studies coumatetralyl-poisoned rat carcasses were fed to weka and ferrets. One out of 10 ferrets died, but no weka were killed (O’Connor & Eason 1999).

2.4.7 Summary

Advantages Disadvantages

No licence required Not as potent as brodifacoum or other second-generation anticoagulants

Effective for rodent control

Antidote

Less persistent than brodifacoum, flocoumafen, and bromadiolone

This compound was first introduced in 1957 and is sold as Racumin®, and is used as a tracking powder or as a cereal bait for rodent control.

This bait needs to be ingested over several consecutive days to be most effective.

As for other anticoagulants, rodents die within 5–7 days after ingesting a lethal dose of the toxin.

As for other anticoagulants, coumatetralyl interferes with the synthesis of vitamin K-dependent clotting factors. If ingested in large enough quantities, it is toxic to mammals, birds, and reptiles.

2.5 Diphacinone (Ditrac®, Liquatox®, PESTOFF® (for ferrets))

Chemical Name: 2-(diphenylacetyl-1,3-indandione

Synonyms: Diphacinone is the approved common name

Like coumatetralyl, diphacinone is classified as a first-generation anticoagulant.

2.5.1 Physical and chemical propertiesThe empirical formula for diphacinone sodium salt is C23H15O3 Na and the molecular weight is 362.4. It is soluble in water; more soluble in ethyl alcohol, acetone and hot water; insoluble in benzene and toluene.

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2.5.2 Historical development and useDiphacinone is a first-generation anticoagulant, of the indandione class, produced and primarily used in the USA where it is used to control mice, rats, prairie dogs (Cynomys spp.), ground squirrels, voles and other rodents (Hayes & Laws 1991); and in South America where cattle are treated with diphacinone to provide live baits for vampire bats (Mitchell 1986).

Diphacinone is more toxic than warfarin or pindone to most rodents. In New Zealand it is registered primarily for rodent control, and more recently it has been incorporated into a fish-based bait for ferret control (Ogilvie et al. 1995).

This anticoagulant was first introduced for use in New Zealand in the 1950s as a rodenticide. It is available in both a liquid concentrate (Liquatox®) on a limited-sale basis in 50-ml plastic envelopes that are mixed with a litre of water for use as a liquid rodent bait, and a Ditrac® All Weather Block.

2.5.3 Fate in the environmentComparative soil absorption and mobility studies have shown diphacinone to be relatively immobile. When tested in the laboratory, the half-life of diphacinone in soil under aerobic conditions is about 30 days and under anaerobic conditions is about 60 days (WHO 1995).

2.5.4 Toxicology and pathologyOnset of signsDiphacinone baits at 3 mg/kg will kill rodents in 5–8 days. Rats can withstand relatively high single doses of this toxicant, but are unable to survive doses of <1 mg/kg when that dose is ingested over 5 successive days.

Mode of actionDiphacinone, like other anticoagulants, inhibits the formation of vitamin K-dependent clotting factors. This inhibition is prolonged when compared with the relatively short effect of warfarin. This is consistent with its prolonged persistence (90 days) in the liver (Bullard et al. 1976).

Pathology and regulatory toxicologyClinical and post-mortem signs of toxicosis are as for other anticoagulants. Post-mortem examinations have revealed extensive multiple haemorrhages throughout the body with considerable quantities of unclotted blood in the chest and abdominal cavities.

Multidose studies with diphacinone in rats have demonstrated the difficulty in establishing a clear NOEL with persistent bioaccumulative compounds (like most anticoagulant rodenticides). No clear NOELs were obtained in a 90-day study spanning doses of 1.7–27.0 µg/kg/day (Elias & Johns 1981).

Fate in animalsSee brodifacoum (section 2.1.4) and Table 11.

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Absorption, metabolism, and persistence:When diphacinone was administered (orally) to rodents, as with other anticoagulants concentrations reached their highest levels in the liver. Eight days after the administration of the compound in rats and 4 days in mice, the liver had the highest level of residues, but kidneys and lungs also contained significant concentrations of diphacinone; brain, fat, and muscles had the lowest levels (Yu et al. 1982). This is the typical pattern observed in tissue distribution studies with all anticoagulant poisons (see Table 18).

Table 18. Radioactivity in the tissue of female rats 8 days after oral administration of a single dose of 14C-diphacinone (0.4 mg/kg). Results are ppm equivalent expressed as a mean SE (Adapted from Yu et al. 1982)

Tissue Concentration

Liver

Kidney

Lung

Gonad

Spleen

Blood

Heart

Fat

Muscle

1.394 0.072

0.239 0.050

0.110 0.011

0.081 0.018

0.075 0.002

0.051 0.007

0.031 0.005

0.026 0.009

0.017 0.004

Few data exist on the changing patterns of tissue distribution over time. However, by comparing two different publications on diphacinone distribution (in rats after 8 days: Yu et al. 1982 and cows after 90 days Bullard et al. 1976), it would appear that residue can readily be detected in a range of tissues within a week of ingestion (Table 18), but after 3 months the liver and kidney are the only organs containing significant concentrations (Table 19).

Table 19. Detectable diphacinone residues (mean S.d.) in tissue of cattle given a single injection of 1 mg/kg (Adapted from Bullard et al. 1976)

Days after treatment Residues found (ppm S.D.)

Liver Kidney

30

60

90

0.15 0.01

0.14 0.1

0.15 0.00

0.08 0.01

0.10 0.02

0.08 0.00

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Metabolism of this compound in rats involves mainly hydroxylation and conjugation reactions (Hayes & Laws 1991). The persistence of diphacinone in the liver is more prolonged than of warfarin or pindone (see ection 2.1.4).

Species variation in response to diphacinoneThere is a marked species variation in the susceptibility of animals to the toxic effects of diphacinone (Table 20).

Table 20. Acute oral toxicity (LD50mg/kg) of diphacinone

Species Acute oral LD50

(mg/kg)

Rat (unspecified) 0.3–2.3

Dog 3.0–7.5

Cat 14.7

Rabbit 35.0

Pig 150.0

Mouse 340.0

Mallard duck 3158.0

2.5.5 Diagnosis and treatment of poisoningAs for brodificoum, see Section 2.1.5 (pp. 57–60).

2.5.6 Non-target effectsOther than pets gaining access to bait, there are no references to non-target deaths in other species in New Zealand. Birds have been shown to have been poisoned by eating carcasses. Both great-horned owls and saw-wet owls eating poisoned carcasses were affected, but not barn owls. In the USA golden eagles showed signs of haemorrhages after eating meat from animals poisoned with diphacinone (Savarie et al. 1979).

Bats have been shown to be susceptible to diphacinone. In Latin America, where paralytic bovine rabies is transmitted by the common vampire bat (Desmodus rotundus), cattle are given sub-lethal intramuscular doses of diphacinone. These cattle effectively act as live baits, and bats that suck blood from treated cattle are killed (Thompson et al. 1972; Mitchell 1986; Said Fernandez & Flores-Crespo 1991). Although information derived in vampire bats cannot be extrapolated to the susceptibility of New Zealand’s short and long-tailed bats, it does suggest that they may be susceptible to anticoagulants via primary or secondary poisoning. Diphacinone is likely to have a slightly lower tendency to cause secondary poisoning when compared with bromadiolone, brodifacoum, or flocoumafen, because it is less potent.

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2.5.7 Summary

Advantages Disadvantages

No licence required More persistent than coumatetralyl

Effective for rodent control Less potent than brodifacoum

Antidote

Less persistent than brodifacoum

Diphacinone is a first-generation anticoagulant.

Diphacinone in bait formulations needs to be ingested over several days before a lethal dose is taken. Rodents will die within 5–8 days of ingesting a lethal dose.

Like other anticoagulants diphacinone interferes with the synthesis of vitamin K-dependent clotting factors. If ingested in large enough quantities, it is toxic to mammals, birds, and reptiles.

Diphacinone is not readily soluble, it binds strongly to the soil and is slowly degraded.

2.6 Pindone

Chemical Name: 2-pivaloyl-1,3-indandione.

Synonyms: Pindone is the approved common name.

Pindone is one of the earliest first-generation anticoagulant rodenticides developed in the 1940s.

2.6.1 Physical and chemical propertiesThe empirical formula for pindone is C14H14O3 and the molecular weight is 230.3. It is a yellow crystalline powder with a melting point of 108.5–110.5ºC and low solubility in water (18 mg/L) at 25ºC. A sodium salt (‘Pival’ or pindone-sodium) C14H13NaO3

with a molecular weight 252.3 is readily water soluble.

2.6.2 Historical development and usePindone, like diphacinone, belongs to the indandione class of anticoagulants, which differ chemically from coumarin anticoagulants such as brodifacoum or warfarin.

Pindone was synthesised in 1937 (Beauregard et al. 1955) and developed as a pesticide in the early 1940s. It was originally evaluated as an alternative to pyrethrin because of its insecticidal properties (Kilgare et al. 1942). Subsequently it was selected for extended study as it possessed the strongest insecticidal and anticoagulant

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characteristics of a series of 1,3 indandiones (Crabtree & Robinson 1953). In 1948 pindone was shown to be an effective alternative to DDT for the treatment of body lice (Eddy & Bushland 1948), but it has not been widely used as an insecticide.

Pindone has been used worldwide to control rodents, though its use for the control of rats and mice has decreased following the introduction of more potent anticoagulants such as brodifacoum. There are two other indandiones, diphacinone and chlorophacinone, which were synthesised in the 1950s and 1960s, and these two newer, more potent compounds have also contributed to a reduction in pindone use for rodent control.

In New Zealand pindone has been used to control wallabies and possums, but in both Australia and New Zealand it has proved most effective for rabbit control (Eason & Jolly 1993). Pindone is currently registered in New Zealand for the control of rabbits and possums. It is most effective for rabbit control.

2.6.3 Fate in the environmentThere are no published data on the fate of pindone or its metabolites in soil and water. However, there are unpublished data that indicate that pindone is slowly degraded in soil and water (G. Wright, pers. comm.).

In comparative studies, pindone is more slowly leached from oat grain bait for rabbits when compared with 1080. The authors attribute this to the lower solubility of pindone in water (Wheeler & Oliver 1978). This has recently been confirmed by New Zealand researchers (Booth et al. 1999a), which may in part explain the higher than expected non-target mortality observed after broad-scale use of pindone.

A small survey of water samples in a catchment area where pindone baits had been aerially sown for rabbit control was completed in 1994 (G.R.G. Wright pers. comm.). No pindone residues were detected.

2.6.4 Toxicology and pathologyOnset of signsAs for other anticoagulants.

Mode of actionPindone acts like the other anticoagulant toxicants by interfering with the normal synthesis of vitamin K-dependent clotting factors in the liver. The weaker potency of first-generation anticoagulants such as pindone is related to a generally lower binding affinity when compared to second-generation compounds (Parmar et al. 1987; Huckle et al. 1988). The mechanism by which pindone exerts insecticidal and fungicidal activity has not been described in the literature.

Pathology and regulatory toxicologyAs with all other anticoagulant compounds, clinical signs of toxicosis in animals will usually reflect some manifestation of haemorrhage. Onset of signs may occur suddenly; this is especially true when haemorrhage of the cerebral vasculature or pericardial sac occurs. Clinical signs commonly include anaemia and weakness. Haemorrhaging may be visible around the nose, mouth, eyes, and anus and animals

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may pass bloody faeces. When pulmonary haemorrhage has occurred, blood-tinged froth may be visible around the nose and mouth. Swollen, tender joints are common and, if haemorrhage involves the brain or central nervous system, ataxia or convulsions can occur. Poisoned animals will die usually of multiple causes associated with anaemia or hypovolemic shock. Some possums receiving high doses of pindone have died without any signs of haemorrhaging, and necropsy has revealed liver damage (Jolly et al. 1994). The authors were unable to locate any regulatory toxicology data relating to pindone.

Fate in animals

Absorption, metabolism, and excretion:Pindone is absorbed through the gastrointestinal tract. Tissue distribution of pindone seems to be somewhat different from other anticoagulants. Plasma concentrations remain higher than tissue concentrations for 8 days and concentrations in the liver and kidney are comparable (Fitzek 1978). Pindone is far less persistent than second-generation anticoagulants such as brodifacoum, and is less persistent than diphacinone, which is consistent with our understanding of the mode of action and relative potencies of these compounds.

In dogs this compound is fairly well absorbed (67%) and the plasma elimination half-life is approximately 100 hours after administration of 3 mg/kg (Fitzek 1978). In sheep, residues were detected in the liver and fat of animals dosed with 20 mg/kg for 8 days, but at 2 weeks none was detected (Nelson & Hickling 1994).

Species variation in response to pindone:There are limited acute toxicity data available on pindone, but even these data show marked species variation. For first-generation anticoagulants such as pindone, either very large single doses or repeated smaller doses are generally needed to induce death. A single dose of approximately 18 mg/kg is, however, sufficient to kill rabbits (Table 21).

In rabbits the repeat dose (7 days) LD50 is 0.52 mg/kg/day, while all rabbits receiving 1 mg/kg for 7 days died. By contrast, pindone doses of up to 12 mg/kg/day do not cause clinical or post-mortem haemorrhage in sheep (Oliver & Wheeler 1978). Possums appear to be even more resistant to pindone than sheep. None of 12 possums dosed at 8 and 16 mg/kg/day for 5 days died. One of 12 possums died when dosed with 32 mg/kg/day for 5 days, and 9 of 14 possums died when dosed with 64 mg/kg/day for 5 days. From these data an LD50 of 51 mg/kg/day for 5 days was calculated (Jolly et al. 1994).

Non-target research conducted in Australia provides information on the susceptibility of horses, cattle, goats, chickens, dogs, and cats. All these species were less susceptible than rabbits. Daily doses of pindone, ranging from 0.3 to 2.5 mg/kg, were administered for 5 days. No mortalities occurred and susceptibility was assessed by using extension of prothrombin time as a biomarker of poisoning. In this study, cattle and cats appeared most susceptible out of the six species tested, and horses least susceptible to pindone toxicity (Martin et al. 1991). Nevertheless, the rabbit remains outstanding as the most susceptible mammalian species evaluated to date.

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Table 21. Acute oral toxicity (LD50mg/kg) of pindone (Beauregard et al. 1955; Oliver & Wheeler 1978; Hone & Mulligan 1982; Eason & Jolly 1993).

Species LD50 ((mg/kg)

Rabbit 6–18

Dog 50

Norway rat 75–100

Sheep approx. 100

Possum >100

Aquatic toxicology:There are no published aquatic toxicity data for pindone.

2.6.5 Diagnosis and treatment of poisoningAs for brodificoum, see Section 2.1.5 (pp. 57–60).

2.6.6 Non-target effectsNo systematic studies have been conducted to monitor the non-target impact of baits. During 1992–94 the aerial application of pindone baits to control rabbits increased. There have been numerous anecdotal reports (E.B. Spurr, pers. comm.) of extensive bird kills from both primary and secondary poisoning following broad-scale rabbit control in New Zealand, but no monitoring to determine whether or not populations are being affected. Birds found killed included plovers, quails, rails, wrybills, silvereyes, grey warblers, black-back gulls, and Australian harriers (Sullivan 1994). Even less is known about the effects of pindone on invertebrates and reptiles.

In Australia similar rabbit poisoning operations have caused concern with wedge-tailed eagles, noted to be a species at risk. Doses as low as 1–4 mg/kg/day for 5–7 days have caused deaths in this species (D. King pers. comm.).

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2.6.7 Summary

Advantages Disadvantages

No licence required Not as potent as second-generation anticoagulants or non-anticoagulant poisons such as 1080, cholecalciferol, or cyanide

Effective for rodent control Not potent for possum control

Highly effective for rabbit control

Antidote

Less persistent than brodifacoum

Pindone is a synthetic pesticide that was first synthesised in 1937. Its insecticidal and rodenticidal properties were demonstrated in the 1940s.

Pindone is not readily water soluble, but the sodium salt of pindone (pival) is readily water soluble and is sometimes used in New Zealand instead of pindone.

Pindone is a first-generation anticoagulant with low potency compared to compounds like brodifacoum, a second-generation anticoagulant.

Pindone is moderately toxic to a range of species. Rabbits are extremely susceptible; by contrast sheep, possums, and horses are comparatively resistant. There are anecdotal reports that raptors are particularly susceptible to secondary poisoning.

Pindone is far more effective for rabbit control than it is for possums.

Pindone is moderately persistent; far more persistent in animals than 1080, but considerably less persistent than brodifacoum.

The toxicity and non-target impacts of pindone are poorly documented.

2.7 Warfarin

Chemical Name: 3-(-acetonylbenzyl)-4-hydroxycoumarin.

Synonyms: Warfarin.

Warfarin, like pindone, is one of the earliest first-generation anticoagulant rodenticides

2.7.1 Physical and chemical propertiesThe empirical formula for warfarin is C19H16O4 and the molecular weight is 308.3. It is a colourless, odourless, and tasteless crystalline powder with a melting point of 161ºC. It is insoluble in water and benzene, freely soluble in alkaline solution, readily soluble in acetone, and only moderately soluble in alcohols.

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2.7.2 Historical development and useWarfarin baits are registered in New Zealand for rodent control, but bromadiolone, brodifacoum, and flocoumafen are often preferred by pest managers because of their greater potency. Warfarin is a first-generation anticoagulant that has been used in a range of rodent baits since it was first introduced in 1947.

Cereal pig-baits containing warfarin are available from the Animal Control Products factory in Wanganui.

As warfarin is a first-generation anticoagulant, for most animals the baits will need to be ingested regularly over several days before any of the symptoms of poisoning will occur.

2.7.3 Fate in the environmentThere are no published data on warfarin degradation. However, significant contamination of soil and water following the use of bait stations is extremely unlikely. Minor contamination is likely around the bait station, which should not be a major risk to non-target species. Degradation by soil micro-organisms and slow dispersal of warfarin in the soil is probable: this is based upon data on the degradation of similar anticoagulant toxicants.

2.7.4 Toxicology and pathologyOnset of signs and pathologyAs for all anticoagulants, the onset of symptoms will depend on the dose, nature, and amount of bait consumed.

RatsWarfarin baits administering 1 mg/kg will kill rats in 5–8 days. Rats can withstand single doses of 50 mg/kg, but are unable to survive doses of 1 mg/kg bodyweight when that dose is ingested for 5 successive days. In general the symptoms of poisoning do not appear suddenly, and will culminate in death within 5–7 days of the initial ingestion of a lethal dose.

PigsApproximately 3 days after poisoning, some pigs will become lame, depressed, and lethargic. Food consumption decreases and blood is commonly observed in faeces. There is a great deal of individual variation in the time it takes for pigs to die from warfarin poisoning, with some pigs dying before or soon after they have shown the initial symptoms of poisoning and others living up to 31 days, progressively weakening over time.

Mode of actionWarfarin, like the other anticoagulants, inhibits the synthesis of vitamin K-dependent clotting factors. In addition, warfarin is reported to induce capillary damage. Two different metabolites are thought to be responsible for these effects: 4-hydroxycoumarin inhibits the formulation of prothrombin and reduces the clotting power of the blood, whereas there is some evidence that, at sufficient dosage, benzalacetone produces capillary damage that exacerbates bleeding.

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Pathology and regulatory toxicologyAnimals may be subjected to a hypovolemic crisis secondary to massive haemorrhage into body cavities, subcutaneous tissues, and the alimentary, respiratory, and urinary tracts in cases where large doses of the toxin have been ingested. Animals that receive a lower dose of the toxin may show signs of lethargy, anaemia, anorexia, bloody faeces, and abdominal pain. In pigs, extensive haemorrhages into the stomach and the small and large intestine are the most common signs of anticoagulant pathology, with skeletal muscle, peritoneum, and weight-bearing joints common sites of haemorrhage.

There are limited regulatory toxicology studies on warfarin and no data relating to potential mutagenic effects. While all anticoagulant rodenticides are likely to be embryotoxic if ingestion occurs at a sufficiently high dose, warfarin is unique in this class of compounds and was found to be both embryotoxic and teratogenic when administered to rats (WHO 1995), causing internal hydrocephalus and anomalies of skeletal ossification. In humans undergoing continuous drug treatment with warfarin, defects have in the past been classified as warfarin embryopathy and include both skeletal and non-skeletal abnormalities. No cases of embryopathy from anticoagulants in their use as rodenticides have been reported.

Fate in animals

Absorption, metabolism, and excretionWarfarin is readily hydroxylated by rat microsomal enzymes to at least eight metabolites, including 6-,8- and especially 7-hydroxywarfarin (Sutcliffe et al. 1987). It is not persistent, and is readily excreted with an elimination half-life of about 18 hours in male rats and 28 hours in female rats (Pyrola 1968). The half-life in rat liver is reported to be 7–10 days for warfarin, which contrasts with half-lives exceeding 100 days for second-generation anticoagulants (Thijssen 1995) (see Tables 10 and 11).

Species variation in response to warfarinThe toxicity of warfarin varies according to species and whether exposure was a single or multiple dose (Table 22). For example, the single dose LD50 is 50–100 mg/kg in rats (species unspecified) versus 1 mg/kg for 5 days (Osweiler et al. 1985).

Table 22: Acute oral toxicity (LD50mg/kg) of warfarin (Osweiler et al. 1985)

Species Single dose (mg/kg) Repeated dose (mg/kg)

Pig 3 0.5

Dog 50 5

Rat (unspecified) 50–100 1

Cat 50–100 1

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Values for the acute oral LD50 of warfarin for Norway rats vary between 1.5 and 3.75 mg/kg (Hone & Mulligan 1982). The strain and sex of the test animals and the carrier used in the administration probably affected the results obtained.

Aquatic toxicologyThere are no published data available for warfarin.

2.7.5 Diagnosis and treatment of poisoningAs for brodificoum, see Section 2.1.5 (pp. 57–60).

2.7.6 Non-target effectsAlthough less potent than 1080 or brodifacoum, warfarin still has the potential to cause primary poisoning of non-target species. Secondary poisoning is relatively uncommon (Osweiler et al. 1985; Prakash 1988).

If warfarin baits are used for control of pest species, it is important that the baits are not positioned where livestock may eat them.

2.7.7 Summary

Advantages Disadvantages

No licence required Not as potent as second-generation anticoagulants or non-anticoagulant poisons such as cholecalciferol and 1080

Effective for rodent control

Antidote

Less persistent than brodifacoum

Warfarin is a first-generation anticoagulant.

In order for a lethal dose to be ingested, the target species needs to consume either one large single dose or a small dose for several days in a row.

Because warfarin has a slow mode of action, bait shyness is not readily induced.

It is not persistent when compared to brodifacoum, but is considerably less potent than second-generation anticoagulants.

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SECTION 3 : TOXINS NO LONGER USED BY THE DEPARTMENT OF CONSERVATION

3.1 Phosphorus

Chemical Name: P4.

Synonym: Phosphorus.

Phosphorus is used as a paste and is generally applied to turf spits on the ground. It is only available to licensed operators.

3.1.1 Physical and chemical propertiesPhosphorus is a yellow solid with a waxy lustre that has a melting point of 44.1ºC. Phosphorus is mixed with water, bentonite, and magnesium oxide to produce an emulsion that is incorporated into a fruit paste for the control of rabbits and possums.

Raw phosphorus is a corrosive dangerous product. Pastes have somewhat different properties.

3.1.2 Historical development and usePhosphorus was first used in rabbit control in New Zealand and Australia in the early 1920s. The initial use of this toxicant was in pollard pellets by dissolving the phosphorus sticks in carbon bi-sulphide or mixing phosphorus in boiled water and then adding pollard to make the pellets. It was also used on oats and wheat.

In the 1950s phosphorus was incorporated into paste for rabbit control. In the 1960s phosphorus pellets were withdrawn from the market because the phosphorus broke down (oxidised) quickly in the bait, and was ineffective.

Phosphorus paste is still used by regional councils and is publicly available. Under the Pesticides (Vertebrate Pest Control) Regulations 1977, the operator must either hold a licensed operators certificate or be working under the supervision of a certificate holder to use phosphorus for pest control.

3.1.3 Fate in the environmentPhosphorus is unlikely to be persistent in the environment. Phosphorus is usually added to paste bait for possum control. On exposure to air the phosphorus oxidises to phosphates, which are not poisonous. Accordingly, phosphorus is more stable in paste, which tends to ‘cake’ and protect the phosphorus from oxidation.

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3.1.4 Toxicology and pathologyOnset of signsIn the veterinary literature, phosphorus poisoning is usually categorised in three phases: (1) An acute initial phase occurring within hours of ingestion characterised by gastrointestinal, abdominal, and circulatory signs. Initial signs generally involve vomiting and diarrhoea. If the dosage is sufficiently large, shock, cyanosis, incoordination and coma may develop, with death occurring before the second and third phases appear; (2) An interim or latent phase with apparent recovery occurs at lower doses approximately 48 hours to several days after initial clinical signs; (3) The third stage is characterised by recurrence of marked clinical signs involving the gastrointestinal tract. Liver failure then occurs. These literature reports suggest that death may occur in 1–2 days, or there may be improvement for 1–2 days before vomiting, diarrhoea, and other signs return. Death is usually due to liver necrosis and heart failure. There may be a delay of up to 3 weeks after ingestion before convulsions, coma, and death. Recent trials at Landcare Research have shown that possums eating phosphorus-paste baits die within 18 hours and do not experience the prolonged toxicosis commonly attributed to phosphorus in the scientific and veterinary literature (Eason et al. 1997, 1998b; O’Connor et al. 1998).

There is no antidote to phosphorus, but with early diagnosis the poison may be removed by vomiting or gastric lavage, then treated with 0.1% potassium permanganate or 2% hydrogen peroxide (to oxidise the toxicant to harmless phosphates) and mineral oil (which prevents absorption). However, if there is bleeding or ulceration treatment is more difficult.

Mode of actionThe mode of action is unknown. It has not been possible to associate the main clinical or pathological features of intoxication with inhibition of any particular enzyme or class of enzymes. Phosphorus is sometimes referred to as a protoplasmic poison, but it is difficult to distinguish its possible direct effects on the liver, kidney, brain, and heart from the effects of anoxia on those organs. The peripheral vascular dilatation, which is the first and most pervasive systemic effect of phosphorus, contributes to all the disorders that may be seen in various organs. However, the mechanism of this dilatation is not clear.

Phosphorus not only leads to structural damage of vital organs, but also produces serious disruption of their metabolic function, as evidenced by hypoglycemia, azotemia, inhibition of glycogen formation in the liver, and many other disorders.

Pathology and regulatory toxicologyPathological changes include gross evidence of fatty degeneration and swollen livers, as well as gastrointestinal irritation, necrosis, and haemorrhage. If death is sufficiently prompt, there is no pathology except irritation of the oesophagus and stomach. Perforation may occur. Following survival for several days, fatty degeneration is striking in the liver, heart, and kidney but may be found in all organs, including the brain. We were unable to locate any material relating to genotoxicity or teratogenicity, or data from other regulatory toxicology studies on phosphorus.

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Fate in animalsPhosphorus is readily absorbed but its persistence in lethally and sub-lethally poisoned possums has not been elucidated.

Species variation in response to phosphorusThere is little species variation in response to phosphorus and most species are at risk if they eat bait (Table 23).

Table 23. Acute oral toxicity (LD50mg/kg) of phosphorus (Hone & Mulligan 1982)

Species LD50 (mg/kg)

Sheep 1

Pig 1–6

Rabbit 4

Dog 3–6

Cat 3–6

Possum 6–10

Poultry (unspecified) 10

Aquatic toxicologyUnknown. It is unlikely that significant amounts of phosphorus baits used for possum control will enter watercourses.

3.1.5 Current useThis poison has been in use since the 1920s and is one of the few poisons that is still available to the public as an acute poison for rabbit and possum control. It is also still used in some instances to poison pigs. It is not currently used by the Department of Conservation, but is used around houses and public areas by regional councils where there is a risk to dogs from 1080. However, use of phosphorus is also associated with secondary poisoning of dogs.

Advantages Disadvantages

Effective (kills of >90% achieved)

Less public opposition than with 1080†

Has some animal welfare concerns‡)

Secondary poisoning risk to dogs and birds

Risk of fire

Antidotes of limited value

† When farmers or the community oppose the use of 1080 they will often accept phosphorus as a replacement.

‡ Studies show that the symptoms of phosphorus poisoning in possums differ from those reported in the veterinary literature for other animals

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3.2 Arsenic

Chemical Name: Arsenic trioxide (As2 O3).

Synonyms: White arsenic, arsenous oxide.

3.2.1 Physical and chemical propertiesArsenic is a naturally occurring toxin found in combination with other metals, particularly iron as arsenic pyrite (FeAs), and iron-arsenic sulphide. Two other forms of arsenic sulphide, orpiment and regular white arsenic (arsenic trioxide), are less common.

3.2.2 Historical development and useThe first recorded use of arsenic in New Zealand and Australia was in the 1880s where it was used in a variety of baits including oats, wheat, root crops, apples, and pollard pellets.

In the early 1970s arsenic was discontinued from use in rabbit control due to its inability to decompose. In addition to this, a number of people were reported to have been affected by arsenic’s cumulative properties.

When still in use in the 1970s, arsenic was available to the public. Under the Pesticides (Vertebrate Pest Control) Regulations 1977, the operator had to either hold a licensed operator’s certificate or be working under the supervision of a certificate holder. All of these certificates were withdrawn by the Pesticides Board on the advice of the then Agricultural Pest Destruction Council when arsenic was withdrawn from use in New Zealand.

3.2.3 Fate in the environmentArsenic from baits is converted into various inorganic and organic arsenic compounds, most or all of which will be toxic to a varying extent. Arsenic baits were not considered safe to livestock until they had decomposed or had been completely disintegrated by rain.

3.2.4 Toxicology and pathologyOnset of signsDeath from a single dose appears to be a painful process occurring over several hours or days.

Mode of actionArsenic causes severe gastroenteritis, vomiting, copious watery or bloody diarrhoea, with convulsions and coma preceding death. The corrosion of the gastrointesinal tract is thought to lead to shock as well as haemorrhage.

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Fate in animalsSubstantial elimination of a sub-lethal dose will occur in 1–6 weeks in most animals. Arsenic is well distributed throughout all tissues and remains for long periods in bone, skin, and hair.

Species variation in response to arsenic:One of the main disadvantages of arsenic, in addition to its extremely inhumane mode of action, is its low toxicity to rats and possums as compared to its toxicity to humans (Table 24).

Table 24. Acute oral toxicity (LD50mg/kg) of arsenic (Hone & Mulligan 1982)

Species LD50

mg/kg

Human 1.43

Possum 8.22

Mouse 45.00

Rat 138.00

3.2.5 Current useArsenic is no longer available for use in New Zealand.

3.3 Strychnine

Chemical Name: Strychnine alkaloid.

Synonyms: Strychnine.

3.3.1 Physical and chemical propertiesThe empirical formula for strychnine is C21H22N2O2 and its molecular weight is 334.4. Strychnine is an odourless bitter white powder. Its melting point is 270º–290ºC. Strychnine has a solubility in water at room temperature of 143 mg/L. Its salts are more soluble in water; for example, the sulphate is soluble in water at 30 g/L at 15ºC. Strychnine is soluble in chloroform, slightly soluble in benzene, and less soluble in diethyl ether and petroleum ether.

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3.3.2 Historical development and useStrychnine is found in the seeds of the Indian tree Strychnos nux-vomica where it is one of a number of different alkaloids. It has a long history as a rodenticide (Schwartze 1922), being used first in Germany in the 16th Century. It affects the central nervous system, leading to paralysis a few minutes after intake and to death within half an hour in rodents (Prakash 1988).

The first recorded use of strychnine in New Zealand and Australia was in the 1880s where it was used in conjunction with a variety of baits including oats, wheat, root crops, thistle roots, apples, and pollard pellets. It was also used in grain to control problem birds.

In the early 1980s strychnine was withdrawn from use in New Zealand on the grounds that the type of death that it caused was inhumane.

When strychnine was used in the early 1970s, an operator was required, under the Pesticides (Vertebrate Pest Control) Regulations 1977, to hold a licensed operators certificate or to be working under the supervision of a certificate holder. All licences were then cancelled by the Pesticides Board on the advice of the then Agricultural Pest Destruction Council on the grounds that the toxin was inhumane and dangerous to staff.

3.3.3 Fate in the environmentStrychnine is a stable alkaloid that retains its toxicity indefinitely in the bait and in the carcass of the poisoned animals. Strychnine bait must be completely decomposed or washed out before a poisoned area could be determined as toxin-free.

3.3.4 Toxicology and pathologyOnset of signsPoisoned animals often die in less than an hour as a result of respiratory failure (asphyxia), but death may take 24 hours or longer if the dose is low. The typical signs of strychnine poisoning are restlessness and muscular twitching that progresses to convulsive seizures continuing for 45 minutes or more before death. Violent muscular spasms extend the limbs and curve the neck upwards and backwards; the jaws fix and the eyes protrude (Osweiler et al. 1985).

Poisoned animals are generally found close to the bait because of the poison’s rapid action. Strychnine and its salts (especially strychnine sulphate) are highly toxic to all mammals, less so to birds. The LD50 to the Norway rat is 5–6 mg/kg (Prakash 1988). The oral LD90 for strychnine in mice is approximately 5 mg/kg (Mutze 1989). Strychnine induces poison shyness in rats and similar shyness is thought to occur in other vertebrate pests (Prakash 1988). The bitter taste is usually masked by a sweetening agent (icing sugar) in baits.

Mode of actionStrychnine is a fast-acting poison that is readily absorbed into the circulatory system from the intestinal tract. Highest concentrations of strychnine are found in blood,

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liver, and kidney. Even though it is a neurotoxin, strychnine does not appear to concentrate preferentially in nervous tissues (Hayes 1994).

Fate in animalsStrychnine is highly persistent in baits and poisoned carcasses.

Species variation in response to strychnine:Strychnine is highly toxic to most domestic animals and wildlife (Table 25). Studies in the USA have shown a 50% reduction in horned lark populations after using strychnine (Apa et al. 1991). Some individual non-target bird species have been reported killed in mouse control operations in Australia (Anthony et al. 1984; Mutze 1989).

Table 25. Acute oral toxicity (LD50mg/kg) of strychnine (Hone & Mulligan 1982; Osweiler et al. 1985)

Species LD50mg/kg

Cow 0.5

Horse 0.5

Cat 0.75

Norway rat 6.8

Duck 2.9

Chicken 5.0

Pigeon 2.1

House sparrow 4.0

3.3.5 Current useThis toxin had been in use since the late 1800s for pest control but has now been banned from use in New Zealand.

It is still used in Australia for mouse plagues and in the USA to control several pests, including skunks, targeted for control in rabies-infected areas, using strychnine-injected eggs. It is also used in Fiji and other islands in the Pacific.

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SECTION 4: COMPARATIVE RISK ASSESSMENT FOR COMMONLY USED VERTEBRATE PESTICIDES

Here we review some of the information provided in the previous sections on individual poisons used for possum control, for comparative risk-assessment purposes.

4.1 What and where are the exposure and non-target risks?

Risks = Hazard Exposure

Risks to human health and non-target wildlife or livestock are dependent on the inherent toxicity of the pesticide (i.e. hazard) and the potential for exposure to either residues or toxic baits (Eason et al. 1997). Clearly all poisons used for vertebrate pest control are hazardous. Risks can be minimised by preventing exposusre of non-target species to these compounds. Some risks will be common for all types of toxic bait, e.g. the risk of a child eating toxic material if it is not stored in a secure location. Other risks, such as the risk of secondary poisoning, will vary dependent on the properties of the pesticide and how it is used Refer to the DOC ‘Information on the Animal Pest QCM Module, The Safe Handling of Pesticides’, published April 2000.

4.1.1 Persistence in water, soil, and plants 1080: Extensive research has demonstrated that 1080 may be degraded in

most moist soils over 2 or more weeks by naturally occurring micro-organisms (e.g. Pseudomonas, Fusarium), although in climatic extremes (e.g. drought and extreme cold) the breakdown may take several months (Walker & Bong 1981; Wong et al. 1992; King et al. 1994; Parfitt et al. 1994; Walker 1994).

After 1080 is leached from baits into soils, theoretically there may then be an uptake of the toxin into terrestrial plants. In a laboratory study a single bait containing 0.15% 1080 was placed on the soil in 130-mm pots containing perennial ryegrass and broadleaf. Mean 1080 concentrations peaked at 0.08 ppm in ryegrass after 3 days then declined below detection limits after 7 days; and broadleaf concentrations peaked at 0.06 ppm after 10 days and persisted at measurable concentrations (>3 ppb) for a further 28 days (Eason et al. 1998a). Although uptake of 1080 by plants in the field is likely to be much lower, there are currently no data available on 1080 in plants after baits have been aerially broadcast. Extremely low 1080 concentrations in plants for only short periods of time are thought to present an extremely low risk to animal health.

Although it may be leached through some soils, to date no detectable amounts of 1080 have been measured in groundwater following control operations (Parfitt et al. 1994; C. Eason unpubl. data).

Legislation requires that baits not be aerially broadcast within 100 m of streams, yet there have been incidents where measurable amounts of 1080 have been detected in stream water. The amounts recorded to date have usually been less than 9 ppb and were only detected over short periods after aerial application of 1080. Although 1080

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is not degraded in distilled water, the concentration of 1080 will decline in stream water (Booth et al. 1999b), and these rates of degradation are about 60% higher when temperatures are increased from 11C to 21C (Ogilvie et al. 1996). Immediately following aerial control the Ministry of Health normally requires managers to collect and then send samples of stream water for laboratory analysis of 1080 concentration.

Proper use of bait-station limits contamination of waterways.

Cyanide: Cyanide paste is rapidly degraded by moisture and is therefore likely to remain in the environment for a short period only. Feratox® (pellets) may, however, persist for 2–3 months even when exposed to the weather (Warburton et al. 1996). Cyanide used in bait stations or as a paste is unlikely to contaminate waterways.

Cholecalciferol: Cholecalciferol is used in bait stations and is therefore also unlikely to be found in waterways. It is degraded by sunlight and is also slowly oxidised when exposed to air. There is no published information on the fate of cholecalciferol in soils. However, its physico-chemical characteristics imply minimal leaching is probable.

Brodifacoum: Environmental contamination by brodifacoum can be minimised by using it in well-constructed bait stations. Brodifacoum used in bait stations is unlikely to be detected in waterways, and is persistent in soils.

Pindone: There is little published on the fate of pindone in soils. It is only slowly leached from baits, and no pindone was recovered from the soil under baits that were subjected to 200 mm of rain (Booth et al. 1999a). Rates of microbial degradation may be slow because of the insecticidal and fungicidal properties of pindone (Oliver & Wheeler 1978). Under standard conditions of use there was no pindone found in water samples following an aerial operation to control rabbits (Nelson & Hickling 1994).

Phosphorus: This compound is readily oxidised. Baits that quickly dehydrate in hot, dry weather can ignite by spontaneous combustion and cause fires.

Persistence of residues in animal tissues1080: Residues of 1080 may persist in sub-lethally poisoned vertebrates for

up to about 4 days (Eason et al. 1994c). However, residues of 1080 can persist in the carcasses of dead animals for at least 80 days (Meenken & Booth 1997), and these may be lethal to cats, dogs, rats, stoats, and ferrets (Hegdal et al. 1986; McIlroy & Gifford 1992), mustelids (Alterio 1996, 2000; Heyward & Norbury 1999; Murphy et al. 1999), and possibly some omnivores (e.g. hedgehogs). Furthermore, some insectivorous birds that feed on insects and larvae on carcasses (Hegdal et al. 1986) may be exposed to residues.

Cyanide: Cyanide is comparatively rapidly metabolised and excreted over several days. The risks to non-target species associated with cyanide control of possums are therefore mainly through primary poisoning. However, animals recently poisoned with cyanide should be regarded as hazardous. (Mouth-to-mouth resuscitation of humans who have ingested cyanide is also dangerous.)

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Cholecalciferol: Cholecalciferol is metabolised in possums to 25-hydroxycholecalciferol which is toxic and will be present in the carcasses of poisoned possums. The risk to dogs and cats by secondary poisoning is low when compared with 1080. Dogs that ate one or two carcasses of possums poisoned with cholecalciferol (Campaign®) exhibited no ill effects, while dogs eating five carcasses over a period of 5 days showed moderate clinical signs of poisoning (Eason & Wickstrom 2000). Cats fed the carcasses of possums that had been killed by cholecalciferol had slightly higher serum calcium levels after eating possum meat for 5 days, but these returned to normal within a few weeks. Human consumption of game meat in areas where cholecalciferol baits have been used is not recommended since carcasses could contain significant amounts of 25-hydroxycholecalciferol for several weeks.

Brodifacoum: Field use of brodifacoum will kill possums, rats, and mice (Gillies & Pierce 1999; Thomas 1998). Both rodent and possum carcasses will be predated by birds and mammals that eat carrion (Eason et al. 1999c) after eating brodifacoum baits as some die in the open (Cox & Smith 1992; Meenken et al. 1999). This has resulted in secondary poisoning of owls in New Zealand and overseas (Mendenhall & Pank 1980; Hegdal & Blaskiewicz 1984; Hegdal & Colvin 1988; Newton et al. 1990; Ogilvie et al. 1997; Stephenson et al. 1999), and raptors (Radvanyi et al. 1988), domestic cats and dogs (Dodds & Frantz 1984; Marsh 1985; Du Vall et al. 1989; Hoogenboom 1994; Young & De Lai 1997; Stone et al. 1999), and mustelids (Alterio 1996; Shore et al. 1999). In addition to the 33 species of indigenous birds at risk from primary poisoning, and eight species of indigenous birds at risk from secondary poisoning with brodifacoum (Eason & Spurr 1995), residues have recently been identified in dead whiteheads, parakeets, and kokako (Eason & Murphy 2000). Brodifacoum residues have also been identified in wild venison and pork from meat samples taken at processing factories. As brodifacoum will persist in the meat and livers of sub-lethally poisoned sheep and possums for at least 9 months (Laas et al. 1985; Eason et al. 1996a), there is a theoretical potential for humans to be exposed to brodifacoum residues (Eason et al. 1996a). Brodifacoum use should therefore be limited to bait-station control of rodents and low-density possum populations so that non-target predators or scavengers are placed at less risk of eating animals containing residues. The Department of Conservation has in January 2000 taken steps to reduce the mainland field use of brodifacoum.

Pindone: Pindone, like other first-generation anticoagulants, is less persistent in animal tissues than second-generation anticoagulants such as brodifacoum (Parmar et al. 1987; Huckle et al. 1988). For example, in sheep, residues were detected in the liver and fat of animals dosed with 10 mg/kg for 8 days, but at 2 weeks none was detected (Nelson & Hickling 1994).

Phosphorus: Phosphorus residues may persist for some time in the stomach or tissues of carcasses that have been poisoned with phosphorus, and this causes secondary poisoning of birds (Sparling & Federoff 1997) and dogs (Gumbrell & Bentley 1995).

4.1.2 Susceptibility and risk reduction for pets and livestock1080: Dogs are highly susceptible to 1080 (Eisler 1995). Residues in possum

carcasses may be lethal to dogs for more than 80 days following 1080 poisoning

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(Meenken & Booth 1997). Dogs should therefore be excluded from control areas where 1080 has been applied for possum control for at least 3 months from the date of application or longer if dry. In areas frequently used by the public it may be necessary for managers to either caution dog owners about the need to fit muzzles to their dogs, or to use an alternative poison that does not present the same residue problems (e.g. cholecalciferol or cyanide). There have also been instances of livestock (e.g. sheep, deer, cattle) being poisoned by baits or by scavenging (e.g. cats, mustelids, and pigs) carcasses of animals that have been killed by 1080 (Annison et al. 1960; Gillies & Pierce 1999; Murphy et al. 1999; Alterio 2000). Most reported livestock deaths are as a result of baits being unintentionally applied in the wrong place, or of inadequate withholding periods before stock are reintroduced into control areas.

Pregnant ewes are more susceptible than non-pregnant sheep; nevertheless, a single sub-lethal dose of 1080 had no long-term effects on the health or productivity of sheep (Wickstrom et al. 1997b; O'Connor et al. 1999).

Cyanide: Cyanide is not a persistent toxin, but there have been several reports of sheep, cattle, and dogs (Hughes 1994) ingesting lethal amounts of recently laid baits. To minimise the exposure of non-target species to cyanide, paste baits should be placed sensibly and destroyed after they have been in the field for 2 nights. Uneaten Feratox® capsules should be retrieved.

Cholecalciferol: There is a danger that baits containing cholecalciferol may be used less carefully than other bait types because cholecalciferol is known to be vitamin D3, and perceived to be ‘safe’. It is most important, therefore, to re-emphasize that cholecalciferol at the concentrations used in possum or rodent baits is potentially highly toxic to most animals. Cholecalciferol bait may be toxic to pets and domestic stock if they feed on sufficient amounts, and for this reason delivery in bait stations is recommended. The risks of secondary poisoning are low compared to 1080. Nevertheless, pets should be discouraged from eating carcasses as repeated exposure will induce toxicosis.

Brodifacoum: Where bait stations are located along fence lines or in trees within the reach of animals, some livestock (especially cattle) are inclined to rub against bait stations and dislodge bait, which they then eat. Particular care is needed to exclude brodifacoum baits from livestock access. Other domestic animals feeding on carcasses containing brodifacoum residues may ingest lethal amounts of brodifacoum through secondary poisoning (e.g. dogs and cats). Antidotes are available (Vitamin K) for brodifacoum and pindone, but treatment of brodifacoum poisoning is prolonged.

Pindone: Pindone is highly toxic to rabbits (LD50 = 6–18 mg/kg), but less toxic to dogs (LD50 = 75-100 mg/kg) and sheep (LD50 100 mg/kg) (Eason 1996). Evaluation of prothrombin times demonstrated that cats were the most susceptible domestic animal to pindone, that cattle may be affected by moderate doses, and horses are the least susceptible (Martin et al. 1991). Sheep administered sub-lethal amounts of pindone eliminated all of the toxicant within 2 weeks of dosing (Nelson & Hickling 1994).

Phosphorus: Phosphorus is lethal to all domestic livestock that feed on paste baits. Cats, dogs, and pigs are also at risk from secondary poisoning. Although only 2–4 tonnes of phosphorus paste were used annually for possum control in New

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Zealand, between 1960 and 1976 there were 117 confirmed dog deaths by phosphorus compared to 254 deaths with 1080 (Rammell & Fleming 1978).

4.1.3 Risk of exposure and toxicity to non-target vertebrates (wildlife)Non-target animals are principally at risk from eating baits or poisoned carcasses.

1080: The risk to non-target species during aerial control has been extensively studied (Spurr 1993a; Spurr 1994a; Fraser et al. 1995; Spurr & Powlesland 1997; Powlesland et al. 1999; Sherley et al. 1999; Fraser & Sweetapple 2000). Ongoing research is further evaluating species that may be at risk, and options that may further improve the safety of all possum control could include the use of more-potent bird repellents. Although most dead birds found following possum control have been exotic species (e.g. blackbird, chaffinch), native birds (e.g. whitehead, robin, tomtit, morepork) have also been killed (Spurr 1994a). The numbers of birds killed following aerial application of bait has declined since operators started routinely screening carrot bait to remove highly toxic fragments (Spurr 1994a); adding green dye (Caithness & Williams 1970) and cinnamon (Udy & Pracy 1981) as bird deterrents; and reducing sowing rates (Morgan et al. 1997).

To date aerial control has had no long-term effects on populations of bats (Lloyd & McQueen 1998). The impact of aerial operations on lizard and skink populations has not been well assessed, but it would seem there is some mortality of these vertebrates when exposed to 1080 baits or to insects that have fed on baits (Whitaker & Loh 1991). The impact of aerial control on native frogs has not been assessed, but research conducted in Australia suggests that frogs are not very susceptible to 1080 (McIlroy 1986).

The extent of non-target interference with baits in bait stations has not been well researched. Kaka may eat both plain cereal baits (Spurr 1993b) and baits dyed green and containing 0.1% cinnamon (Hickling 1997) when first exposed to them. However, cinnamon-lured baits are eaten less frequently and in significantly smaller amounts by kaka after they have been exposed to them two or more times (Hickling 1997). Although kiwi may eat cereal baits (Pierce & Montgomery 1992) but not carrot (MacLennan et al. 1992), there have been no kiwi deaths reported following 1080 operations (Spurr 1994a; Robertson et al. 1999b).

Although rats and mice use bait stations (Thomas 1998) it is not known how many other species are at risk by primary poisoning. Possums, mice, rabbits and rats poisoned with 1080 are in themselves a hazard to other animals that eat them. Secondary poisoning of predators is commonly reported (Murphy et al. 1999; Heyward & Norbury 1999) and mortality in deer, usually 30–40% after aerial operations (Fraser et al. 1995) has been higher, i.e. >90% (Fraser & Sweetapple 2000).

Cyanide: There are fewer reports of birds being killed by cyanide than by 1080 or traps (Spurr 1991). However, some ground-dwelling species are at risk, and unfortunately in some regions there have been reports of weka and kiwi being killed where cyanide paste was used. For example, in 1984 some 66 hunters reported 37 kiwi poisoned by cyanide paste, about a quarter of the number caught in traps (Spurr 1991). In comparison no kiwi have been reported poisoned after 1080 operations. The

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risks that discarded cyanide capsules (i.e. Feratox®) present to non-target species has not been formally assessed. There are anecdotal reports of Feratox® killing hedgehogs, stoats, and cats, but not birds (J. Kerr, pers. comm.).

Cholecalciferol: Cholecalciferol is less toxic to birds than 1080 (Wickstrom et al. 1997a; Eason & Wickstrom 2000), and is therefore likely to kill very few birds by either primary or secondary poisoning. Captive mallard ducks survived very high doses (2000 mg/kg) of cholecalciferol (Marshall 1984; Eason & Wickstrom 2000), but some canaries and chickens receiving the same dose subsequently died. Risk of exposure of non-target mammals or birds in the field has not yet been quantified.

Brodifacoum: Brodifacoum is a potent second-generation anticoagulant that is toxic to many non-target species by both primary and secondary poisoning (Godfrey 1985; Eason & Spurr 1995). For example, most blackbirds on Red Mercury Island not killed by aerial application of brodifacoum baits were subsequently found to contain brodifacoum residues (Morgan & Wright 1996), and there are now extensive reports of other species of birds and mammals, including feral pigs, showing residues (Ogilvie et al. 1997; Empson & Miskelly 1999; Dowding et al. 1999; Stephenson & Minot 1999; Robertson et al. 1999a; Eason et al. 2000). A wide range of bird species (e.g. saddleback, silvereyes, paradise shelduck, morepork, skua, robin, and weka) have been found dead from poisoning after field use of brodifacoum in New Zealand (e.g. Taylor 1984; Taylor & Thomas 1993; Towns et al. 1993; Williams et al. 1986a,b; Stephenson et al. 1999). The manufacturer of brodifacoum concentrate (Zeneca) recommends that the pesticide should not be aerially broadcast for the control of pests, and that systems for controlled delivery of baits should be used.

Further research in brodifacoum control areas is required to assess the risks to insectivorous birds feeding on invertebrates; the risks to predatory (e.g. New Zealand falcon, morepork) and omnivorous birds; the risk to folivores and seed-eating birds that may eat baits (e.g. Ogilvie et al. 1997); and the impacts of an exposure to brodifacoum on the breeding success of selected bird species. Detrimental effects on some individuals may, however, be counter-balanced by improved survival and breeding success in the absence of possums and rodents. In the short term a research priority is to establish whether or not the extent of brodifacoum transfer through the food web can be contained, for example, by using brodifacoum for rodents alone, or only using brodifacoum in pulses after 1080, cyanide, or cholecalciferol for initial control.

Pindone: Research has demonstrated that pindone presents a risk of primary and secondary poisoning of birds (Martin et al. 1994). Scavengers such as the harrier hawk are likely to be most at risk from secondary poisoning (Calvin & Jackson 1991), and raptors tended to be more susceptible (0.25 mg/kg) than magpies, pigeons, parrots, and ducks (4–5 mg/kg) in dose-ranging experiments (Martin et al. 1994). However, the risks of inducing secondary poisoning are likely to be less pronounced than with brodifacoum, dependent of course on how the toxic baits are applied. In New Zealand there have been anecdotal reports (E.B. Spurr pers. comm.) of extensive bird kills from both primary and secondary poisoning after the use of pindone for rabbit control, but there has been no monitoring to determine whether or not pindone has any long-term effects on the local abundance of bird populations.

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Phosphorus: Phosphorus is known to kill birds that feed on carrion. Although the non-target effects on indigenous birds in New Zealand have not been assessed, it is expected that morepork, New Zealand falcon, black-backed gull, skua, weka, and harriers will be at some risk from secondary poisoning.

4.1.4 Risk of exposure and toxicity to invertebratesInvertebrates are at risk from contact with baits, eating baits or poisoned carcasses, or from exposure to residues in soil or other environmental media.

1080: There have been no significant changes in the relative abundance of different invertebrate taxa monitored before and after aerial poisoning that can be attributed to insect populations having been exposed to 1080 poison (Spurr 1994b; Spurr & Drew 1999). However, residues of 1080 have been measured in some insects (e.g. weta and cockroach) for up to 3 weeks following aerial application of 1080 baits (Eason et al. 1998a). Invertebrates with 1080 residues may present a risk to insectivorous birds (Hegdal et al. 1986). It has been shown that the addition of cinnamon to baits is a deterrent to some invertebrates (Spurr & Drew 1999). Recent research has confirmed that 1080 is not persistent in invertebrate species (e.g. Booth & Wickstrom 1999). Sherley et al. (1999) have raised concerns over the number of invertebrate species food in contact with 1080 baits, and research is now focusing on the incorporation of an invertebrate repellent into baits to enhance target specificity, and decrease the risk of secondary poisoning via species such as weta, which are known to eat 1080 baits.

Cyanide: Although the effect of cyanide on invertebrates in New Zealand has not been researched, it is lethal to aquatic invertebrates at relatively low concentrations (i.e. <200 ppb, Hone & Mulligan 1982). Although this indicates that the hazards of cyanide to invertebrates may be high, the exposure of invertebrates to cyanide will be low, particularly if Feratox® pellets are used.

Cholecalciferol: Few studies have assessed the risk to invertebrates from cholecalciferol baits. One trial on 18 captive weta indicated that weta would eat cholecalciferol baits, but that the baits were not toxic to them (Ogilvie & Eason 1996). When cholecalciferol stock solution was orally administered to weta they survived the highest dose volume (250 µg/g), indicating cholecalciferol lacks insecticidal properties, at least in this species (Eason & Wickstrom 2000).

Brodifacoum: Field studies have demonstrated that only some invertebrates (e.g. slugs, weta) contained brodifacoum residues after Talon® 20P bait was aerially broadcast for rodent control (Morgan & Wright 1996; Ogilvie et al. 1997), and that there is no measurable change in abundance of invertebrates during such control (Spurr & Powlesland 1997). Brodifacoum had no significant effect on weta when they were orally dosed (Morgan et al. 1996b). No data are available for other invertebrate species. The survival of weta exposed to brodifacoum may in part be due to the fact that they can metabolise and excrete it because they do not have the same blood-clotting systems as vertebrates (Shirer 1992). The role of invertebrates as a vector in transferring brodifacoum from baits or carcasses to insectivorous birds is, however, unknown.

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Pindone: Pindone was initially evaluated as an insecticide (Kilgare et al. 1942), and was demonstrated to be effective at controlling body lice (Eddy & Bushland 1948). It may, therefore, be lethal to invertebrates feeding on baits or pindone residues in carcasses. The effects on invertebrate populations in New Zealand have not been assessed. Prior to assessing populations, the insecticidal properties reported in the 1940s should be verified if there are concerns that pindone may be having an effect on invertebrates.

Phosphorus: The effects on invertebrates are not known. However, there are anecdotal reports of bees being found dead on paste baits.

When new bait formulations are produced, part of the research and development process should include an assessment of their attractiveness to invertebrates. Contamination of honey bees presents a human health risk, and all baits must be proven to be unattractive to bees.

4.1.5 Risk of exposure to humansHuman exposure might arise from drinking contaminated water, ingestion of toxic baits, consumption of food contaminated by contact with bait, or by inhalation of bait dust or contact with the active ingredient or stock solutions by pest control operators and bait manufacturers. Potentially the most significant source of general public exposure was considered to be contamination of surface water in public-water-supply catchments by aerially sown 1080 baits.

1080 – Risk of exposure: Ministry of Health Model Permit Conditions place strict controls on the broadcasting of 1080 baits, which is not permitted within 20 m of any camping ground, formed public road currently in use, picnic areas, lake, pond, water supply intake or stream/river specified by the Medical Officer of Health. Bait applied within 60 m of these areas must be applied by helicopter, either with a competent observer in the aircraft, or by an aircraft fitted with and using a recording GPS. The bait must be laid by hand if it is to be applied closer than 20 m to any such areas.

After 1153 samples of stream water collected during 1990–2000 shortly after the aerial application of 1080 were analysed, residues of 1080 above 2 ppm were rarely found (Eason et al. 1999b; G.R.G. Wright, pers. comm.). Monitoring of water has shown the detection of 1080 in stream water to be of a short duration. (Parfitt et al. 1994; Ogilvie et al. 1996). (See section 4.1.2 for further details).

The toxin 1080 is metabolised and largely excreted within 4 days of a single exposure (Rammell 1993; Eason et al. 1994b). This limits the risk of meat being consumed that contains 1080 residues. Withholding milk for a minimum of 1 week would be appropriate should inadvertent poisoning of cows be suspected. Witholding periods of 5–10 days are recommended when incidents of livestock poisoning have occurred. It would be unwise to take game from areas that have been poisoned, until all poisoned carcasses have degraded. Pesticide regulations require that hunting permits must warn hunters of areas where 1080 poisoning is planned, and toxic baits not in use must be secured in safe storage. Game meat can now only be sold to packhouses by approved suppliers, and this meat must contain no 1080 residues. The Ministry of Agriculture

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and Forestry regulations regarding the procurement of game meat have recently been reviewed.

To prevent both bee mortality and 1080 contamination of honey, the original paste that contained sugar was withdrawn from the market (Morgan & Goodwin 1995) and legislation precludes control with pastes within 4 km of beehives (Ministry of Health 1995). Formulations that are unattractive to bees have since been introduced for possum control (Morgan & Goodwin 1995).

To date only one person has been reportedly killed (a suicide) in New Zealand from 1080 poisoning (Hughes 1994).

Cyanide – Risk of exposure: Cyanide is degraded in the environment, is unlikely to contaminate waterways, and does not persist in animals. Cyanide pastes and pellets are potentially extremely hazardous to pest control operators and the public. However, if used properly and stored securely, pastes or Feratox® pellets are unlikely to pose a significant health risk.

Cholecalciferol – Risk of exposure: Cholecalciferol is unlikely to contaminate surface water because it is used in bait placed in bait stations, and is unlikely to be mobile in soil. The risks that residues will occur in meat are low compared with brodifacoum because cholecalciferol is rapidly absorbed and converted to toxic metabolites (e.g. 25-hydroxycholecalciferol; 1,25 dihydroxycholecalciferol), which are in themselves subsequently metabolised and excreted over a period of days or weeks, depending on the dose ingested (Bahri 1990; Eason & Wickstrom 2000). These hydroxylated metabolites are retained mainly in the plasma, liver, heart, and adipose tissue of poisoned animals (Eason et al. 1996c; Wickstrom et al. 1997a; Eason & Wickstrom 2000). These toxic metabolites are present in poisoned possums at high enough concentrations to cause toxicosis (e.g. hypercalcaemia, kidney damage, and loss of appetite) in dogs that were repeatedly fed poisoned possum carcasses (Eason & Wickstrom 2000). Whilst these dogs recovered, a precautionary approach would be to limit the procurement of game meat from areas where cholecalciferol had been used. The greatest hazard to humans would be from game species that had recently gained direct access to bait.

Brodifacoum – Risk of exposure: Brodifacoum is unlikely to contaminate surface water since it is principally used in baits enclosed in bait stations, and it does not migrate through soil because it is not readily soluble in water (Jackson et al. 1991).

Exposure to brodifacoum residues by eating the meat (especially livers or kidneys) of animals that have ingested the poison is theoretically possible. Animals may become contaminated with brodifacoum residues by eating baits, or by eating the carcasses of other animals poisoned with brodifacoum (e.g. wild pigs that have fed on possum carcasses and baits: Eason et al. 1999c, 2000). Brodifacoum therefore represents a potential health risk to hunters who repeatedly eat the livers of wild pigs and/or wild pork from pigs shot in areas where brodifacoum has been extensively used for pest control (Eason et al. 1999c, 2000).

Pindone – Risk of exposure: Pindone is unlikely to occur in surface water. Livestock (e.g. sheep) contaminated with pindone are likely to metabolise and excrete

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it within approximately 2 weeks (Nelson & Hickling 1994), and it is therefore unlikely to be present in meat for human consumption unless there has been fairly recent exposure to baits. An adequate withholding period of at least 1 month would be sensible if exposure to pindone was suspected.

Phosphorus – Risk of exposure: Phosphorus is unlikely to occur in surface water. Dogs may be at risk of secondary poisoning if they consume carcasses of possums poisoned with phosphorus (Gumbrell & Bentley 1995). This suggests that wild pigs eating baits or the carcasses of possums poisoned with phosphorus may also contain phosphorus residues. The duration of phosphorus residues in game or other wildlife after sub-lethal exposure is unknown.

Risks to pest controllersPersonnel regularly handling toxic baits or who are exposed to toxic concentrates must comply with label instructions and information supplied in material safety data sheets (MSDS). Those persons most at risk from exposure are those frequently handling materials that are very hazardous. Poisons may be ingested accidentally, resulting in a single sub-lethal exposure, or by careless use, which may result in repeated sub-lethal exposures. The known effects of substantial but sub-lethal exposures on animals and humans are summarised below (Section 4.1.6). The effects or lack of sub-lethal effects from single or multiple exposures will be dose-dependent. Not surprisingly animals or humans surviving substantial doses of a poison may be permanently affected through brain damage or effects on some other target organs. It has, in the past, been mistakenly assumed (in the New Zealand pest control industry) that rapidly eliminated poisons only have short-term effects. This is a misunderstanding of the basic principles of toxicology, confusing rates of metabolism or excretion with the lack or presence of toxic effects.

Monitoring of blood and urine of workers in the pest control industry is important to ensure safety procedures minimise exposure.

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4.1.6 Toxic effects and humaneness in non-target species Figure 1 illustrates the range of levels at which ecotoxicological and toxicological evaluations, including effects studies on non-target species, can be undertaken. Toxicological risk assessment integrates information from different levels of organisation.

Figure 1. Relationships of aspects of the science of ecotoxicology and toxicology and the different levels of biological organisation.

1080: 1080 is a broad-spectrum poison capable of readily inducing death in most species ingesting sufficient bait. A single sub-lethal exposure may cause a variety of effects, including 1080-induced myocardial lesions (Buffa et al. 1977), as observed in the cardiac muscle of sheep (Annison et al. 1960; Schultz et al. 1982; Wickstrom et al. 1997b; O’Connor et al. 1999). Large single doses (100 and 200 mg/kg) caused a reduction in plasma testosterone concentrations and degeneration of seminiferous tubules in skinks (Twigg et al. 1988). Single doses of 15 and 60 mg/kg resulted in damage to the kidneys of rats (Savarie 1984). Humans sub-lethally poisoned have on occasions suffered chronic cardiac dysfunctions or renal problems (Chung 1984; Chi et al. 1996), and neurophysiological effects (Trabes et al. 1983). A very large sub-lethal exposure caused permanent brain damage to a child (McTaggart 1970). Neurophysiological effects are likely to be linked to glial cell dysfunction. Glial cells in the brain are implicated in brain extracellular fluid ion and acid base homeostasis. Glial cells are very sensitive to fluorocitrate which is described as a glial toxin (Erlichman et al. 1998).

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Molecular level

Cells

Organs

Individualorganisms

Populations

Community

Ecosystems

Increasingimportance of

data

Increasing ease of

obtaining data

Increasing level of

uncertainty

Increasing time to

complete research

Presentstatus of

knowledge

Repeated sub-lethal exposure to 1080 has resulted in lower levels of spermatogenesis in rats (Sullivan et al. 1979; Miller & Philips 1955) and mink (Hornshaw et al. 1986), and foetal abnormalities in rats (Eason et al. 1999b). In a 90-day rodent exposure study no effect levels have been established for effects on spermatogenesis. The testes are the most sensitive target organ in rats. Partial recovery to normal sperm production has been shown following the cessation of treatment. Sheep receiving repeated sub-lethal doses of 1080 had myocardial degeneration as well as necrosis of individual or small groups of myocardial fibres (Schultz et al. 1982).

Cyanide: Cyanide is an extremely hazardous substance due to the release of HCN gas when it is exposed to air. Ingestion of cyanide pellets or paste or inhalation of the gas produces adverse reactions within seconds. Signs of sub-lethal poisoning in humans include hyperventilation, headache, nausea, vomiting, and generalised weakness. Both manufacturers and pest controllers must therefore avoid inhaling cyanide fumes by ensuring they operate in a well-ventilated area and/or wear breathing apparatus (especially during bait manufacture). The scientific literature suggests that repeated exposure to substantial sub-lethal amounts of cyanide could potentially cause lasting neurological effects (Kanthasamy et al. 1994).

Cholecalciferol: No known accidental poisoning with cholecalciferol rodenticides have been lethal (Pelfrene 1991). However, it should be noted that cholecalciferol has been used worldwide as a rodenticide at 0.075%. In possum baits the concentration is 0.8% and these baits therefore present a greater risk. A single sub-lethal poisoning may result in soft tissue calcification (Toda et al. 1985; Pelfrene 1991).

Long-term exposure to sub-lethal doses of cholecalciferol can also result in hypervitaminosis D whereby calcium mobilised from the skeleton may be deposited in many soft tissues (renal arteries and tubules, heart and coronary arteries, lungs, bronchi, and stomach). Clinical signs include fatigue and weight loss. High repeat doses of cholecalciferol may also cause foetal abnormalities and embryo toxicity (Pelfrene 1991).

Brodifacoum: Brodifacoum is potent (as well as persistent), hence a single exposure of sufficient magnitude could alter clotting factors, resulting in haemorrhage. The effects or lack of effects range from no effect on blood clotting, to death and, as with other anticoagulants, will be dose-dependent.

Brodifacoum is highly toxic if it is orally ingested or inhaled (Pelfrene 1991), and it may be absorbed through the skin. Brodifacoum persists in the liver and muscle of sub-lethally poisoned animals and may be equally persistent in pest controllers exposed to it. If sufficient brodifacoum was ingested by humans, toxicosis can readily be detected by alteration in blood-clotting parameters. The effects of long-term exposure to low doses of brodifacoum are largely unknown. However, there are reports of an adverse effect on bone metabolism and the development of osteoporosis (Szulc et al. 1993). Repeated exposure to another anticoagulant warfarin (as a therapeutic agent) has also been linked with developmental malformations in pregnant women (Tasheva 1995). In laboratory studies there was no evidence that brodifacoum is either a teratogen or mutagen, but care should be taken to ensure that operators are not unnecessarily exposed to the poison.

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Pindone: Pindone is not as potent as brodifacoum, and therefore larger doses would be needed to result in alterations in blood clotting parameters, bruising, or haemorrhaging. Clinical signs may include anaemia and weakness.

Phosphorus: In humans the initial signs of phosphorus poisoning are severe epigastric pain, nausea, vomiting, dizziness, headache, and a garlic odour on the breath. A large sub-lethal dose may cause liver damage (e.g. cirrhosis: Moeschlin 1965), kidney failure (Cushman & Alexander 1966), myocardial damage, hypoglycaemia (Clarkson 1991), hypocalcaemia (Cushman & Alexander 1966), and abortions (Piribauer & Wallenko 1961).

Chronic poisoning in humans leads to toothache followed by swelling of the jaw and then necrosis of the mandible (colloquially known as ‘phossy jaw’). This condition may be the only clinical sign from mild exposures to phosphorus, although higher repeat doses also cause liver and kidney damage (Clarkson 1991). Signs of chronic high exposures to phosphorus are weakness, weight loss, anaemia, loss of appetite, and spontaneous fractures.

4.1.7 Humaneness in target speciesThe RSPCA New Zealand is opposed to the use of any toxicant that causes any animal to suffer and is particularly opposed to the use of arsenic and strychnine (Loague 1994). The humaneness of poisons is dependent on the duration and severity of distress or pain that animals experience during three stages of toxicosis described as: an initial lag phase until the onset of clinical signs; a period of sickness behaviour when animals are most likely to experience pain; and, a final phase preceding death when animals may be unconscious (Eason et al. 1998b). These stages have been described in possums for cyanide (Gregory et al. 1998; O’Connor et al. 1998), 1080 (Eason et al. 1998b) phosphorus (O’Connor et al. 1998), and brodifacoum (Littin et al. 1999). Ongoing research is evaluating the behavioural, physiological, and pathological effects of brodifacoum and cholecalciferol on the welfare of possums (pers. comm. C. O’Connor). The amount of distress and times to death are dose-dependent (O’Connor et al. 1998), and for some poisons the individual responses during toxicosis are extremely variable (e.g. cholecalciferol, brodifacoum); a general overview of welfare for the five commonly used possum toxicants is summarised in Table 26.

Cyanide is the fastest acting vertebrate pesticide used in New Zealand and causes least distress. Cyanide is therefore regarded as the most humane of the toxicants evaluated. In comparison brodifacoum is slow-acting, and possum sometimes take a long time to die, an average of 21 days after eating baits. Phosphorus causes behavioural responses associated with inflammation of the stomach lining and duodenum (e.g. a crouched/hunched posture), but the clinical signs of phosphorus poisoning in possum given paste are less severe and less prolonged than has been previously reported for other species. The times to death after possums eat 1080 baits (or other poisons) are dose-dependent, but are on average considerably less than that recorded for phosphorus, and possums dosed with 1080 exhibit few overt signs of pain. Cholecalciferol causes anorexia, with possums on average losing 20% of their body weight before death. There have been no studies on the humaneness of pindone.

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Table 26 Summary of mean times to onset of clinical signs of toxicosis, duration of key symptoms during sickness behaviour, and times to death in possums following ingestion of poison baits (Eason et al. 1998b; O’Connor & Littin, unpubl. data).

Toxin Mean time until onset of sickness

Sickness behaviour Mean duration Mean time

until death

Cyanide 2 min Ataxia, impaired co-ordination, breathlessness, muscular spasms.

12 min 14 min

1080 3 hours Anorexia, ataxia, occasional retching, spasms, breathlessness, laboured

breathing

8.5 hours 11.5 hours

Phosphorus paste 5 hours Retching, vomiting, hunched posture, intermittent repositioning, ataxia

13 hours 18 hours

Cholecalciferol 5 days Loss of appetite, lethargic, breathlessness

3.5 days 8.5 days

Brodifacoum 16 days Anaemia, haemorrhage, loss of appetite, hunched posture, anorexia.

3 days 19 days

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4.1.8 Summary of characteristics of poisons used for possum control in New Zealand

Key advantages, disadvantages, and risk factors

1080 moderately rapid and humane• essential for aerial control very effective low environmental persistence secondary poison risks no antidote

Cyanide rapid action, most humane cyanide aversion influences effectiveness low environmental persistence low secondary poison risk effective antidotes lacking

Cholecalciferol effective lower toxicity to birds than 1080 low risk of secondary poisoning expensive compared with 1080 or cyanide

Brodifacoum• possums take 2–4 weeks to die effective against low-density, poison/bait-shy possums very persistent high secondary poisoning risk widespread contamination of wildlife and game possible antidote available expensive compared with 1080 or cyanide

Pindone• possums take 2–3 weeks to die low effectiveness moderate persistence low secondary poison risk antidote available

Phosphorus causes longer periods of pain and sickness than cyanide and 1080 effective causes secondary poisoning effective antidotes lacking

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AcknowledgementsStaff from the Department of Conservation provided useful comments on earlier draft versions of the manual. The first edition was produced in 1997 with editorial assistance from DOC staff, in particular Nicola Haydock. Many staff members of the Department of Conservation and regional councils responded with useful comments and the provision of both unpublished and published material. Information on the treatment and diagnosis of toxic poisoning was peer reviewed by toxicologists of the National Toxicology Group. Kate Littin reviewed the draft manuscript, and various anonymous referees suggested further improvements.

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Address listfor suppliers of pest control products

Animal Control Products LtdGeneral Manager Private Bag 3018101 Heads RoadWanganuiPh: 06 344 5302Fax: 06 344 2260

Feral ControlPO Box 58 613GreenmountAucklandPh: 09 273 4333Fax: 09 273 4334

Cropcare Holdings Ltd25 McPherson StPO Box 3344RichmondNelsonPh: 03 544 6096Fax: 03 543 9998

Southern Fencing Supplies189 Main South RoadSockburnPO Box 11269Christchurch Ph: 03 3480629Fax: 03 348 0628

Key Industries LtdPO Box 34373 BirkenheadAucklandPh: 09 483 5526Fax 09 483 9760

Kiwicare Corporation Ltd171 Pages RoadAranuiPO Box 15050ChristchurchPh: 03 3890 778Fax: 03 3890 669

Landcare ResearchCanterbury Agriculture and Science CentreGerald StreetPO Box 69Lincoln 8152Ph: 03 325 6700Fax: 03 325 2418

Pest Management Services Ltd11 Sunset TerracePO Box 121WaikanaePh: 04 293 1392Fax: 04 293 1456

Rentokil Initial Ltd Rentokil Pest Control297 Neilson Street 7C Bassant AvenuePO Box 13 445 PenroseOnehunga AucklandAucklandPh: 09 634 0079 Ph. 09 525 3400Fax: 09 666977

Trappers Cyanide CompanyGeneral Manager 251 Styx Mill RoadChristchurch Ph: 03 359 4150Fax: 03 359 4150

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APPENDICES

Appendix 1: Glossary of terms

abomasum 4th stomach of a ruminant

ACT activated coagulation time

albuminuria kidney disease — raised albumin in urine

anaemia low iron levels

anoxia severe hypoxia — lack of oxygen to tissues

apnea respiratory arrest

APTT activated partial thromboplastin time

asystole cardiac arrest

ataxia loss of control of body movements

azotemia increased blood urea nitrogen and creatinine

b.i.d. twice a day

biodegradation breakdown of chemical structure by biological process

biomagnification accumulation of compound through increasing trophic levels

bradycardia decreased heart rate

BUN blood urea nitrogen

coagulopathy blood clotting disorders

centrilobular necrosis death of liver cells at the centre of the liver lobes

cyanosis/cyanotic blueness of the skin and mucous membrane due to insufficent oxygen in the blood. May be peripheral due to poor circulation or central due to failure of oxygenation

cystine amino acid found in plants, egg albumin, and keratin

cytotoxic cell-poisoning

daphnia water flea

defluorinate to remove fluorine

dermal skin

diaphoresis perspiration

dyspnoea difficulty breathing

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dystonia disordered muscle tone

ecchymoses discolouration due to bleeding under the skin

ECG electrocardiogram

EDTA ethylenediaminetetraacetic acid

emetic medicine that causes vomiting

EPA Environmental Protection Agency

epistaxis nose bleed

erythrocytes red blood cells

fasciculation muscle twitching involving contiguous groups of muscle fibres

glucosuria raised glucose levels

glycolytic enzyme an enzyme that breaks up the glycotic compound

haematemesis vomiting blood

haematocrit packed cell volume

haemoptysis bleeding from the lungs

HCN hydrogen cyanide

homeostasis state equilibrium

hypercalcaemia excess of calcium in the blood

hyperparathyroidism disturbance of calcium metabolism

hypomagnesemia deficiency of magnesium in the blood

hypervitaminosis excessive intake of a vitamin

hypocalcaemia deficiency of calcium in the blood

hyposthenuria decreased urine specific gravity

hypovolemic decrease in volume of circulatory blood

hypoxia deficiency of oxygen in tissues

icteric jaundiced

IM intramuscular

intima innermost lining of blood vessel

intraperitoneal introduced into the peritoneal cavity

ipecac syrup an emetic

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INR international normalised ratio

IU international units

IV intravenous(ly)

lacrimation flow of tears [alternative spelling lachrymation]

lactate ester of lactic acid

LD80 lethal dose that kills 80% of the test organisms

LD50 lethal dose that kills 50% of the test organisms

malaena ‘tarry’ faeces

mediastinum membranous middle septum between the lungs

metabolites the breakdown of compounds resulting from the metabolism of a parent compound

methaemoglobinemia inactive form of haemoglobin present in blood

mucosa a tissue layer found lining various tubular cavities of the body.

mydriasis pupillary dilatation

nephrocalcinosis deposits of calcium salts on the kidneys

NOEL No observable effect level. A dosage of a toxicant that fails to produce any discernable signs of toxicosis, which may include a lack of morphological, biochemical, or physiological change

opisthotonus spasm in which head and hind legs are bowed backwards

osteoclast bone cell that has a function in dissolution of unwanted bone

paraesthesias abnormal sensation caused by damage to peripheral nerves

parenteral administered or occurring elsewhere in the body than in the alimentary canal

pathognomonic specific, definitive pathological changes

peracute very acute and violent

petechial a small red spot cause by a minute haemorrhage into the skin

phosphocreatine compound in muscles that release energy for muscle contraction

polar water soluble

pollard product milled from grain

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polydipsia increased water consumption

polyuria increased urination

ppb parts per billion (1 mg/kg)

proteinuria protein in urine

prothrombin blood clotting agent

PT prothrombin time

recumbency lying down

rhodamine red dye

rodenticide rodent poison

subendocardial under the heart

subepicardial under the serious membrane which covers the heart

tachycardia rapid heart rate

tachyponea rapid respiratory rate

thrombocytopenia persistent decrease in number of blood platelets usually associated with haemorrhagic conditions

t.i.d. three times a day

toxicosis poisoning

toxin a natural occurring poison, e.g. 1080, cyanide

toxicant a synthetic man-made poison, e.g. brodifacoum

trans-dermal through the skin

viscera body organs

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Appendix 2 : Quality specifications for 1080 pellet baits for possum control in New Zealand

Cinnamon-masked 1080 pellet baits

Efficacy: When 40 individually caged possums are presented paired trays containing 100 g of bait containing 0.15% 1080 and 100 g of non-toxic RS5 bait at least 90% of possums shall eat a lethal amount of toxic bait. To ensure most animals are killed quickly and humanely, it is recommended that a minimum of 35 of 40 caged possums eat at least 8 g of bait (i.e., the amount of bait that administers 4 mg/kg of 1080 to a 3-kg possum).

Baits

General: Baits shall be grain-based, regular in shape, poisoned with monofluoroacetate (1080), masked with cinnamon, and coloured green. The cereal grain for bait manufacture should contain no more than 13% moisture, and have less than 5% screenings. Before pelleting the grain shall be milled with a screen not exceeding 3 mm, so most particle sizes fall in a range from 0.25–0.50 mm. An approved biscuit grade of wheat is recommended for optimal binding of pellet ingredients. To prevent “sweating” of recently manufactured cereal baits, they must be cooled to a temperature of no more than 8C above ambient room temperature before they are packaged.

Palatability: The palatability of toxic bait should exceed 40% compared to recently manufactured non-toxic RS5 bait (of similar size).

Fracture/breakage/ dust and bait hardness: Dust and fragments (i.e. pieces less than 1 g) shall comprise no more than 5% by weight.

Size: Baits used during aerial control operations shall have a mean weight not less than 6 g. The standard deviation of 50 individually weighed baits should not exceed 1 g (one gram), with 95% of baits by weight weighing more than 4 g.

Hardness: A pointed 2-mm diameter probe shall penetrate baits when the mean pressure applied to the side-walls of 40 large (6 g) baits is 5–12 kg; or when 2–7 kg is applied with a pointed probe to the side-walls of 40 small (1.5 g) RS5 baits. The standard deviation of 40 baits shall not exceed ±5 kg pressure, with 95% of baits penetrated with 2–15kg of pressure on the probe.

Toxin: The toxin, 1080, used in baits shall be at least 93% pure sodium monofluoroacetate and contain less than 0.25% inorganic fluoride. The pH of a 0.1% aqueous solution of the 1080 powder shall be 6.5 or less.

1080 concentration: The concentration of 1080 in samples of 10 baits shall be 1.5 ± 0.22 mg/g (i.e. all samples should have a concentration within 15% of the nominal concentration). The means of 10 or more such samples shall lie within ±5%

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of the nominal concentration. The concentration in 90% of 10 individual baits shall be within ±25% of the nominal concentration.

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Colour: A green colour shall be incorporated into the bait to ensure it has a colour range of 221–267 by the New Zealand Standard Specification 7702 (section 23, Standards Act 1965). Surface colour shall be 98% or more of the surface area when tested by intercepts on a dot grid 1 cm × 1 cm over a random sample of not less than 100 baits.

Masks: Food grade cinnamon flavour (Bush, Boake and Allen, Auckland; Product No:02-7780) in monopropylene glycol with a specific gravity of 1.05 shall be mixed into baits at 0.2% wt/wt to mask the taste and odour of 0.15% 1080. Cinnamon concentrations should never be less than 0.1% or more than 0.5% wt/wt.

Stability: Baits shall be stored for no longer than 6 months with a moisture content of 12 %, 3 months with a moisture content of 14%, and less than a month with a moisture content of 16%. Baits shall have a mould count less than 400 cfu/g . Bait should be stored in a cool, dry storeroom containing few micro- and macro-organisms.

Leaching: Baits shall retain 80% or more of their toxic loading after 5 mm of rainfall over 24 hours.

Storage and stacking of 1080 pelletsBait shall be stored in a clean, dry, locked enclosure until it is used. Pallets of bait shall be stacked no more than two high during transport and storage.

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Appendix 3: Quality specifications for 1080 carrot baits for possum control in New Zealand

Recommended specifications for carrot bait

Cinnamon-masked 1080 baits

Efficacy: When 40 individually caged possums are presented paired trays containing 100 g of bait containing 0.15% 1080 and 100 g of non-toxic RS5 bait, at least 90% of possums shall eat a lethal amount of toxic bait. To ensure most animals are killed quickly and humanely, it is recommended that a minimum of 35 of 40 caged possums eat at least 8 g of bait (i.e., the amount of bait that administers 4 mg/kg of 1080 to a 3-kg possum).

Baits

Specifications for carrot growers: Carrots supplied will be: Royal Chantenay; harvested at a time when 90% of carrots weigh 100–200 g; clean-pulled within 4 days prior to requested date of delivery of the

consignment; topped; free of carrot worm, stem rot, woody pith, mould, bruising, weed and weed

seed, stones and other foreign objects; washed so that the consignment contains 99% carrot by weight.

On arrival at the airstrip carrots should be: covered by tarpaulins if there is a risk of overnight frosts; stored for no longer than is absolutely necessary. If delays occur because of

weather then the period of storage will depend on temperature and humidity, but should not exceed 1 month in ideal weather conditions (i.e., low humidity, cool temperatures);

free from signs of decay (heat, smell, or softness).

Palatability: The palatability of toxic bait should exceed 40% compared to recently manufactured non-toxic RS5 bait (6 g).

Bait size and chaff: Carrot baits shall have a mean weight of 6 g and 95% of baits by weight

shall weigh between 3 and 10 g. Chaff (pieces of carrot less than 0.5 g) shall make up less than 1.5% by

weight of useable bait. Chaff as a byproduct will make up less than 40% by weight of the pre-

processed carrot.

Toxin: The 1080 used in baits shall be at least 93% pure sodium monofluoroacetate and contain less than 0.25% inorganic fluoride. The pH of a 0.1%

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aqueous solution of the 1080 powder shall be 6.5 or less. The 1080 stock solution will be 20% (± 0.5%) sodium monofluoroacetate.

1080 concentration: Sodium monofluoroacetate will be surface-applied to carrot baits such that the concentration of 1080 in samples of 10 baits should be 1.5 ± 0.22 mg/g (i.e. all samples should have a concentration within 15% of the nominal concentration). The means of 10 or more such samples shall lie within ±5% of the nominal concentration. The concentration in 90% of 10 individual baits shall be within ±25% of the nominal concentration.

Colour: A green colour shall be incorporated into the bait to ensure it has a colour range of 221–267 by the New Zealand Standard Specification 7702 (section 23, Standards Act 1965). Surface colour shall be 98% or more of the surface area when tested by intercepts on a dot grid of 1 cm × 1 cm over a random sample of not less than 100 baits.

Masks: Food-grade cinnamon flavour (Bush, Boake and Allen, Auckland; Product No:02-7780) shall be used to mask 1080 by mixing it into baits at 0.3% wt/wt. The lure mixture shall be made by adding 3 litres of flavour concentrate to approximately 16 litres of soya bean or peanut oil, and applying 2 litres of this mix per tonne of cut bait. Alternatively, 300 mls of cinnamon lure should be mixed in 700 mls of monopropylene glycol, and added to the spray tank containing 1080 solution at the rate of one litre per tonne of carrot. Cinnamon concentrations following bait preparation should never be less than 0.1% or more than 0.4% wt/wt.

Stability: If, because of storage, uncut carrots start to become soft or ferment, the carrots should not be used for manufacture of baits. Carrot baits may remain palatable for a week after manufacture (i.e. palatability to 20 individually caged possums will be 40%). The 1080 concentration in a sample of stored carrot bait should be within ±15% of the nominal concentration.

Leaching: Detoxification of carrot is reliant on biodegradation of 1080 by micro-organisms as baits rot, therefore intact baits must be analysed for traces of 1080 before livestock are introduced back into control areas.

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APPROVED ESSENTIAL OILS AND ESSENCES FOR USE AS MASKS WITH 1080 CARROT BAIT. Supplier: Bush, Boake and Allen (Auckland) except for one (H.E. Terry Auckland)

Mask Concentration (v/w) Description and Code No.

Cinnamon 0.1% Cinnamon flavouroil 02.7780

Orange 0.125% Firmenich product52.596/T

Orange 0.5% WJB orange oil 78.0675

Aniseed 0.1% Aniseed China Staroil 72.2358

Plum 0.2% Plum flavour 11.2114

Cherry 0.2% Cherry flavour 2.1660

Lemon 0.5% WJB lemonoil 75.9794

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Appendix 4: Possum baits per lethal dose (LD) [1999 prices and details]

Product & bait size Pack size Cost No. of Baits Baits per LD

ACP No.7 1080 pellet bait 12 g 25 kg $ 52.76 2080 1

ACP RS5 1080 pellet bait 6 g 25 kg $ 44.23 4165 2

ACP Pestoff Pro 1080 paste 8 g 20 kg $117.23 2500 1

ACP Phosphorus D/S paste 8 g 20 kg $129.95 2500 1

ACP Cyanide paste 55% 1 g 500 g $ 24.50 500 1

ACP Pestoff brodifacoum bait 2 g 10 kg $ 35.00 5000 50

Feratox® encapsulated cyanide 1000 $450.00 1000 1

FeraCol® paste 20 g 4.5 kg $180.00 225 1

Campaign® pellets 2 g 10 kg $400.00 5000 8

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