F.

Mobility and Environmental Fate of Norflvtazon and

Haloxyfop-R Methyl Ester in Six Viticultural Soils ofSouth Australia

Submitted in accordance with the

requirement for the degree of

Master of Applied Science

by

Juan Chen

Department of Environmental Science and ManagementUniversity of Adelaide

July 1999

\3'Lh' o<¡

TABLE OF CONTENTS

ABSTRACT

DECLARATION

ACKNOWLEDGMENTS

LIST OF FIGURES

LIST OF TABLES

CHAPTER 1. INTRODUCTION

CHAPTER 2 LITERATURE REVIEW -

2.1 Introduction2.1.1Norflurazon2.I.2 Haloxyfop-R MethYl Ester

2.ZFactors Affecting the Environmental Fate ofNorflurazon and HaloxYfoP-R ME2.2.1 Effects of Herbicide Physicochemical Properties

on Herbicides' Environmental Fate

2.2.2 Persistence Studies of Norfl\razon2.2.3 Dissipation Studies of NorfluÍazon

2.2.4 Dissipation Studies of Haloxyfop-R ME

2.2.5 Leaching Studies of Norflurazon2.2.6 Sorption Studies of Norflutazon2.2.7 Sorption and Leaching Studies of Haloxyfop-R ME

2.2.8 Selection of Six Soils

2.3 Conclusion

CHAPTER 3 METHODOLOGY3.1 Analytical Methods

3.1.1 Introduction

111

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vii

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9

10

L1

12

L3

15

L6

T7

T9

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20

20

3.1.2 Materials3.1.3 Results and Discussion

3.1.4 Conclusion

3.2 Sample preparation

3.2.1Introduction3.2.2 Materials and Methods

3.2.3 Results and Discussion

3.2.4 Conclusion

CHAPTER 4 LEACHING BEHAVIOUR OF

NORFLURAZON AND HALOXYFOP.RMETHYL ESTER IN SOIL

4.1 Introduction4.2 Mateials and Methods

4.3 Results and Discussion

4.4 Conclusion

CHAPTER 5 DISSIPATION OF NORFLURAZONAND HALOXYFOP.R METHYL ESTER

IN SOIL5.1 Introduction5.2 Materials and Methods

5.3 Results and Discussion5.3.1 Herbicide Dissipation in Six Soils

5.3.2 Herbicide Dissipation in Six AutoclavedSoils Compared with Six Natural Soils

5.4 Conclusion

CHAPTER 6 CONCLUSION - ENVIRONMENTALFATE OF NORFLURAZON ANDHALOXYFOP.R METHYL ESTER

2L

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References 67

ABSTRACT

Norflurazon and haloxyfop-R methyl ester are two selective herbicides used widely in

Australian vineyards for inter-row weed control. The leaching behaviour and

dissipation of the herbicides in six key soils representative of the major viticultural

regions of South Australia was studied under laboratory conditions. Soil propeties

directly affected the herbicide leaching behaviour. Norflurazon concentrations in the

leachates from the terra nigro soil and the saprolite soil reached their maximum values

of 5.16 ppm and 2.79 ppm respectively after only the second simulated rainfall; while

for the terra rossa soil, norfluÍazon concentration in the leachate rose to 1.78 ppm after

the last simulated rainfall, which indicates that high soil clay content slowed

norflurazon leaching through the soils and lower soil organic matter made the herbicide

have more leaching potential. Both haloxyfop-R methyl ester and acid were detected in

very low concentrations in the leachates from the six soils, and only a small amount of

the compounds was found in the lower paft (6.5-13cm) of the soil profiles. These

results illustrate the lack of downward mobility of both haloxyfop-R methyl ester and

acid in the six soils. Residues of norflurazon and haloxyfop-R methyl ester and acid

were detected mainly in the top section (0-6.5cm) of the soil monoliths, which indicates

that both herbicides were persistent in the six soils. More norflurazon was found in the

lower part (6.5-13cm) of the soil monoliths than haloxyfop-R methyl ester and acid,

which shows that norflurazoî was more leachable and mobile in the six soil systems.

Norflurazon dissipation in the six soils was not rapid under laboratory conditions with a

half-life ranging from 150 to 300 days, while haloxyfop-R methyl ester and acid

lll

dissipation was relatively rapid under the same conditions with a half-life of 7-135

days. Dissipation of both herbicides followed first-order kinetics 1r2 > 0.89¡, and was

reduced at higher soil organic matter contents, but did not appear to be influenced by

other soil par¿rmeters. The dissipation of both herbicides was more rapid in the non-

autoclaved soils than in the autoclaved soils, probably due to the fact that only chemical

degradation occurred in the autoclaved soils, whereas in the non-autoclaved soils, both

abiotic and biotic factors could affect the herbicide degradation.

lv

DECLARATION

This work contains no material which has been accepted for the award of any other

degree or diploma in any university or other tertiary institution and, to the best of my

knowledge and belief, contains no material previously published or written by another

person, except where due reference has been made in the text.

I give consent to this copy of my thesis, when deposited in the University Library, being

available for loan and photocopying.

Juan Chen

v

Date

DECLARATION

This work contains no material which has been accepted for the award of any other

degree or diploma in any university or other lrufüary institution and, to the best of my

knowledge and belief, contains no material previously published or written by another

person, except where due reference has been made in the text'

I give consent to this copy of my thesis, when deposited in the University Llbrary,

being available for loan and photocopying'

Juan Chen

Date

/il ̂ rcl 2^"( 2-ota)

ACKNO\ryLEDGMENTS

I would like to express my great appreciation to those who have helped with

experiments, facilities, materials, and advice. My thesis would not exist without these

specific contributors:

Brian Williams (as supervisor), Hugh Possingham (as co-supervisor), Keith Cowley (as

laboratory manager) and Lyn Strachan (as laboratory technician) of the Department of

Environmental Science and Management, Joe Seton of A.C.U.E., Christine Jeffrey of

the Undergraduate Teaching Unit at Roseworthy Campus, Marie Kozulic, I-esley

Spencer and Fiona Bzowy of Roseworthy Library, Brian Glaetzer and John Willoughby

of the Faculty of Agricultural and Natural Resource Sciences, Ian Rice of the Rural

Services, Mohammad Reza Jahansooz of the Department of Agronomy and Farming

Systems, The University of Adelaide; Mike Harms of Petaluma Wines, Summertown,

S.A.; Matthew Alexzander of Southcorp Wines, Nuriootpa, S.A.; Colin Beer of Beer

Wines, Nuriootpa, S.A.; Keith Hample of Hample'Wines, Nuriootpa, S.A.; Kim Alif of

Wynns Wines, Padthaway, S.A.; Vic Patrick of Mildara Wines, Coonawarra, S.4..

Above all, I owe my greatest debt to my parents, Shoutong Chen and Huimin Zhang,

and my brother and sister - in - law, Yan Chen and Yan Li. Not just in supporting me

materially but also in encouraging me mentally during the whole of my study. I owe

them more than I can easily express.

VI

Juan Chen

LIST OF FIGURES

Figure 2.1 Chemical Structure of NorfluÍazon

Figure 2.2 Chemlcal Structure of Haloxyfop (Acid)

Figure 2.3 Chemical Structure of Haloxyfop-R ME

Figure 2.4 One of the Six Vineyards, Research Road, Nuriootpa

Figure 3.1 Calibration Curve of Norflurazon Standard(240nm) (R2 = 0.9999)

Figure 3.2Typical Chromatogram of Norflurazon Standard

Figure 3.3 Calibration^Curve of Haloxyfop-R ME Standard(240nm) (R2 = 0.9997)

Figure 3.4 Typical Chromatogram of Haloxyfop-R ME Standard

Figure 3.5 Calibration Curve of Haloxyfop-R Acid Standard(240nm) (R2 = 0.9988)

Figure 3.6 Typical Chromatogram of Haloxyfop-R Acid Standard

Figure 3.7 Solid Phase Extraction Procedure

Figure 3.8 Solid Phase Extraction Equipment

Figure 3.9 Rotavapor

Figure 4.1 Process of Collecting Soils

Figure 4.ZDiagram of the Equipment for Leaching Experiments

Figure 4.3 Equipment for Leaching Experiments

Figure 4.4 Norflurazon Concentration in Soil Leachates Collected

after Simulated Rainfall on Six Soil Profiles

Figure 4.5 Haloxyfop-R ME and Acid Concentration in Soil Leachates

Collected after Simulated Rainfall on Six Soil Profiles

Figure 4.6 Distribution of Norflurazon Residues in Extracted Profiles

of Six Soils, after Simulated Rainfall Treatment

page

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25

25

26

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29

30

31

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42

42

45

46

48

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Figure 4.7 Distribution of Haloxyfop-R ME and Haloxyfop-R Acid

Residues in Extracted Profiles of six Soils, after simulated

Rainfall Treatment

Figure 5.1 Dissipation of Norflurazon in Six Soils under Laboratory

Conditions

Figure 5.2 Dissipation of Haloxyfop-R ME and Acid in Six soils

under LaboratorY Conditions

Figure 5.3 Dissipation of Norflurazon in Six Autoclaved Soils

undeiLaboratory Conditions (compared with untreated soils)

Figure 5,4 Dissipation of Haloxyfop-R ME and Acid in Six Autoclaved

Soils under Laboratory Conditions (compared with untreated soils)

49

54

59

56

ó0

vlll

LIST OF TABLES

Table 2.I Climates of the Six Regions

Table 3.1 Norflurazon 10ppm at240nm with the ColumnNova-Pak@ C1s

Table 3.2 Norflurazon Recovery from Soil Leachates

Table 3.3 Haloxyfop-R ME Recovery from Soil Leachates

Table 3.4 Norflurazon Recovery from Six Soils

Table 3.5 Haloxyfop-R ME Recovery from Six Soils

Table 4.1 Characteristics of Six Soils

Table 5.1 Half-lives (DTso) of Herbicide Dissipationin Six Soils under Laboratory Conditions

Table 5.2 Half-lives (DT5s) of Herbicide Dissipation inSix Autoclaved Soils under Laboratory Conditions

page

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58

IX

C¡:

CFIAPTER1 INTRODUCTION

Public oonoern about the state of both the global and local environments has increased

dramatically in recent years. Problems such as habitat destruction, soil erosion, and

species extinction are today recognise.d by much of the general public as being very

important for the futr¡re of mankind. However, chemical contamination still often

arouses the most passionate consumer interest, bec¿use people realise that pollution

impacts on them directly through effects on their health, their food, and their living

environment. Therefore, more and more attention has been given to the environmental

consequences of the widespread use of chemicals particularly those used in agriculnral

production, urban and even rural roadside weed control.

The viticulture industry in Australia comprises over 5,000 independent Srape-growers

and more than 800 wineries spread across all States and Territories. These viticultural

enterprises range from the very small to the large multinational. They operate across an

extensive range of soils and climatic conditions, and use a wide range of vine, pest, and

vineyard water and soil management practices (GWRDC, 1996). Large quantities of

pesticides are used in Australian viticultr¡re due to their effectiveness in controlling

weedlinsects/fungi and thus improving production. Herbicides comprise more than

half of the amounts of pesticides applied, with insecticides and fungicides next in

importance. Norflurazon and haloryfop-R methyl ester (haloryfop-R ME) are two

herbicides licensed for use in Australian viticulilre. The resea¡ch project described in

this thesis is mainly concerned with oømining the environmental fate of these two

I

heóicides, and assessing potential environmental problems associated with trace

residues in water and soils.

The Codex Aliment¡¡ius, an intemational body established by the United Nations'

Food & Agriculûrre Organisation and World Health Organisation, sets Ma¡<imum

Residue Limits (lvß,LÐ for agrochemicals in a range of crops, including grapes. These

MRLs are used as benchmarks in Australia where MRLs a¡e set to reflect 'good

agricultral practice' (AWRI, 1996). Within Australia's viticulture industry there is a

range of management systems, particularly in relation to the use of pesticides

(insecticides, herbicides, fungicides), all uguably 'best practice' for the particular

combination of soil and climatic conditions under which a vineyard operates @ers.

comm., V. Patrick, Milda¡a Wines, Coonawa¡ra, S. A.). Even within a region growing

conditions can change markedly. For instance, it is estimated that in the Barossa there

a¡e at least twenty seven different soils used for viticulture (Northcote, 1995). The

physical and chemical heterogeneity of the natr¡ral environments found in and around

Australia's vineyards makes the accurate prediction of the fate of agrochemicals very

diffrcult. Nevertheless, the regulatory authorities and organisations such as the

Australian Wine Resea¡ch Institr¡te and the Grape and Wine Research and Development

Corporation are under pressure to guide viticulturists in selecting pesticides with

minimal residues. Since significant pesticide toxicity is often seen at sub-mg/L

concenúations, only a comparatively small amount needs to dissolve in surface water

run-offor leach through soils to cause significant environmental problems. As a result,

2

there may be significant va¡iation iq and under-estimation of,, the environmental risks

from pesticide use across the range of soils and climates experienced by the industry.

In screening and registration prognms, it is still common practice to estimate pesticide

mobility by simply determining physical and chemical properties of the pesticides e.g.,

adsorption constants, water solubilities and degradation rates, and predict their

environmental faæ based on such information. However, the environmental conditions

in these tests are quiæ different from nat¡ral soils and field conditions. Pesticides

contribute in a major way to the quality of lifg but their careless or indiscriminate use

can have harmful side effects. Efñcient and effective use of pesticides requires

knowledge of their distibution and persistence in the environment. The main újective

of this resea¡ch project was to study the environmental fate and mobility of two

herbicides registered for use in Ausûalian viticultr¡re, namely norflurazon and

haloxyfop-R methyl ester in six representative viticultural soils, by:

. developing an efficient solid phase ocEaction method for their extraction from soil

leachates and soil maüices;

o developing a precise anal¡ical method for their detection and determination in

exfiacts from soil leachates and soil matrices;

. oramining their leaching behaviour under laboratory conditions in extracted profrles

of six soils representative of the major viticultural regions of South Australia;

. oramining their residues in the extracted profiles of the six soils after simulated

3

rainfall treatnent;

o €Ðømining their dissipation in the six natural soils and the soils after autoclaving

under laboratory conditions.

Environmental contamination may pose one of the greatest threats to the health and

food security of the human race, therefore, greater understanding of the behavior¡r of

agriarlurral chemicals in the environment is necessary. This thesis introduces some of

the key chemical principles to be considered with regard to the behavio.¡r and effects of

herbicides in the Australian environmen! and describes a series of experimental

investigations into the fate and mobility of trvo in particular, namely norflurazon and

haloryfop-R methyl ester.

4

CHAPTER2 LITERATT]RE REVIEW

2.1 Intoduction

2.1.1Norflurazon

Norflurazon {IIIPAC n¡me 4-chloro-5-methylamino-2{cr,a,c-trifluoro-m-tolyl)

pyridazin-3(?.Itlone, Chemic¡t Abstracts name 4-chloro-5{methylamino)-2-[3-

(trifluoromethyl)phenyll-3(21{Þpyridazinone} is a chemical of the fluorinated

pyridazinone family, It has a molecula¡ formula of C¡2IIeCIF3N3O and a molecr¡la¡

weight of 303.7glmol. The chemical stn¡cture of norflurazon is shown in Figure 2.1

below.

CH3HN N

cloFigure 2.1 Chemical Structure of Norflurazon

Pure norflutazonis a white to greyish brown crystalline powder with a melting point of

174-180'C and vapour pressure of 0.0028mPa (20'C). Norflurazon is stable both in

aqueous solution (< S% loss after 24 days at 50'C) and under alkaline and acidic

conditions, but is degraded rapidly by sunlight. The solubility (25'C) of norflurazon is

3

N

5

2Smgll in water, l42gll in ethanol, 50g/l in acetone, 2.59A in rylene. Its partition

coefficient (octanoVwater) Ç* is 280t15 (pH6.5, 25"C) (Tomlin, 1994)

Norflurazon is placed in U.S. EPA toxicity Class IV. Mammalian toxicity: acute oral

LD56forrats)9,000 mgkg; acute percutaneous LD56 for rats ) 5,000 mglkg, rabbits >

20,000 mdkg, non-initating to skin; no obserr¡ed effectlevel (NOEL) (90 days) for dogs

12.7 mgkgdaily, (2 years) for rats 19 mg/kg daily. Other toxicity data: acute oral LD5s

for bobwhite quail and malla¡d duoks > 1,250 mglkg,; LCs for catFrsh and goldfish > 200

mgll; non-toxic to bees at 0.235 mdbee (Tomlia l9%).

Norflurazon is a selective herbicide used pre+mergence for control of annual grasses and

broadJeaved weeds, and some perennial gfasses and sedges in cotton, nuts, soya beans,

peanuts, citnrs, vines, pome fruit, stone fruit, cranberries, asparagus, a¡tichokes and

hops. The compound is absoóed by plant roots, then acts to reduce carotenoid

biosynthesis by inhibition of ph¡oene desaturase, which causes chlorophyll depletion

and hence inhibition of photosynthesis (Iomlin, 1994). Norflurazon is widely used in

Austalian vineyards for inter-row weed control. The morimum application rate

recommended is 5.0 kglha. It can be mixed with simazine when applied.

2.1.2 HaloxyfopR Methyl Ester

Haloryfop (Figure 2.2) {IIIPAC namc (RSÞ2-[4-(3-chloro-5-trifluorometþl-2-

pyridylory)phenoxyl propionic acid; Chemic¡l Abstr¡cts name (t)-2- [4- [ [3-chloro-

5-(trifluoromethyl)-2-pyridinyll oryl phenoryJ propanoic acid) is the parent acid of

6

haloxyfop methyl ester. Haloxyfop-R ME (Figt¡re 2,3) is the resolved haloryfop

methyl ester, and has a moleq¡la¡ formula of CreIIr¡ClF3NO4 and a molecular weight of

37 5.7 glmol (Tomlin, I 994).

F,CI

ocFlco2FI

Figure 2.2 Chemical Structure of Haloxyfop (Acid)

F.C o {o2cH3

cl

Haloryfop-R ME in appearance is a clear brown liquid, and has a boiling point gtreater

than 280"C, and vapour pressure of 0.328 mPa (25'C), and specific gravity of

l.372glml (20.C). It is unstable under conditions of high temperature, and unstable in

the presence of strong acids and bases and strongly oxidizing material. Haloryfop-R

ME is sparingly soluble in water (8.7amgll) at 25"C, while the solubility in acetone,

cyclohexanone, dichloromethane, ethanol, methanol, toluene, rylene is greater than I þ/l

at 20"C, The partition coeffrcient (octanol/water) Ko* of haloryfop-R ME is ll,166

(20'C) (Tomlin, 1994).

N CH3

CHs

I

I

H

Figure 2.3 Chemical Structure of Haloxyfop-R ME

7

As far as the mammalian toxicity is concernd the single dose oral toxicity is moderate

(the oral LD,o for male rats 300 mg/kg and famale rats 623 mg/kg), and a short single

exposure is not likely to cause significant skin initation, while a single prolonged

exposure is not likely to result in the material being absorbed through skin in harmful

amounts (the LD5s for skin absorption in rats > 2,000 mg/kg). However repeated skin

exposure may result in absorption of harmful amounts. Slight transient (temporary) eye

iniation may by caused the compound is slightly initating to the eyes of rabbits.

Haloryfop-R ME is acutely dangerous to fish and harmful to Daphnia species but

essentially non-toxic to birds and bees. It has a gGhour LD5s value of 0.7 mg/l for

rainbow trout, and a 48-hour LD56 value of 6.L2 mg/l for Daphnia. The toxicity to

aquatic organisms is ameliorated by hydrolysis to the parent acid which is of low

toxicity to fish. The acute oral LD5s forbobwhite quail is 1,159 mglkg, and the LDio (48

hours, both oral and contact) for bees is > 100 þglbee. Haloryfop-R ME has little or no

effect upon soil respiration and nitrifïcation processes (Tomlin, 1994).

Haloryfop-R ME is a post-emergence herbicide used for the control of annual and

perennial grasses in sugar bee! fodder beet, oilseed rape, potatoes, leaf vegetables,

onions, flarc, sunflowers, soya beans, vines, strawberries, and other broad-leaf crops.

The compound is absorbed by the foliage and roots, and hydrolysed to haloxyfop,

which is tanslocated to meristematio tissues, and inhibits their growth (Tomlin, 1994).

Haloxyfop-R ME is widely used in Australian viticulûrre, and compatible with many

8

other grass herbicides including post-emergence broadleaf herbicides. The

recoûrmended application rate is 0.8 - 0.9 kglha.

2.2Factors Affecting the Environmental Fate

ofNorflurazon atd HaloafoP-R ME

A great deal of resea¡ch has been conducted on the mobility of pesticides in the

environment, but few sh¡dies on the environmental fate of norflurazon and haloxyfop-R

ME in Australian soils have been reported. Previous resea¡ch has focused mainly on the

following aspects : persi stence, dissipation, leaching and sorption.

2.2.1 Effects of Herbicide Physicochemical Propertieson Herbicides' Environmental Fate

Many factors affect a herbicide's fate once it is applied to soil. These include the

physicochemical properties of the herbicide, va¡ious soil properties, and environmental

conditions. Herbicides vary greatly in their physicochemical properties. The unique

properties of a herbicide may determine the impact a herbicide application or a herbicide

spill may impose on the environment. First of all, the degradability of a herbicide,

though influenced by soil and other environmental conditions, is largely an intrinsic

property. Chemical degradation of some herbicides is controlled by the presence of

specifïc labile functional groups on the molecule. The recalcitrance of a herbicide to

microbial degradation is also determined largely by its stn¡cture. Sqne herbicides are

more susceptible to microbial degradation and may be readily used as a carbon, nitrogen,

or energy source, while some are considerably more resistant to biodegradation. In

addition, herbicide sorption is also inûinsically govemed by its physicochemical

9

properties. For instance, cationic agrochemicals such as paraquat and diquat, and weak

bases at low pII, are sorted by cation exchange on the soil surfaces, whereas weak acids

are not sorbed at high pH when they are predominately in anionic form. In the routine

application of most herbicides, the initial herbicide concentration in the soil solution is

usually lower than the water solubility. At spill sites, however, the opposite is often

fi¡e. When the overall herbicide concentration is such that the herbicide saturates the

solution phase, the amount of herbicide dissolved in the solution will be directly

determined by its solubility. Solubility will affect not only transport, but also

degradation since herbicide degradation is believed to occur mainly in the solution phase

(Gan and Koskinen, 1998).

2.2.2 Persistence Studies of Norflurtzon

The interactions of various factors affect the degradation and adsorption of the herbicide

and ultimately its activity in the soil (Rick et a1.,1987). Norflurazon is slightly mobile

in the soil system. Hubbs and Lavy (1990) observed limited mobility of norflurazon on

soil thin layer plates containing Herbert silt loam or Sharkey clay. Mueller et al. (1992)

found that actual herbicide concentrations were always greatest near the soil surface and

most of the applied norflurazon remained close to the soil surface 84 days after

application (DAA). Schroeder and Banks (1986a; 1986b) detected more than 60lo of the

applied norflurazon in the top 8 cm of the soil profile and < l2%o at depths below 15 cm

in five Georgia soils ll0 days after üeatnent @AT). But these investigators did not

make routine measurements of the compound in the soil profiles throughout their sûrdy.

l0

2.2.3 Dissipation Studies of Norf,urazon

Norflurazon dissipation has been shown to be biphasic in naû¡re, with a rapid initial loss

preceding a slow decline of the remaining herbicide (Willian et al., 1997), Norflurazon

half-life in soil has ranged from 45 to 180 days, depending on soil and environment¿l

factors (Tomlin, 1994). Schroeder and Banlcs (1986a; 1986b) reported that residual

carryover of norflurazon ]vas related to organic mafrer content, with reduced dissipation

at higþer organic matter contents. This is due, at least in part, to the adsorptive

cha¡acteristics of organic matter that may reduce the amount of potentially degradable

norflurazon. Norflurazon is moderately persistent, and may injure succeeding crops.

Repeated applications of l.l kghl increased norflurazon residues and rotational crop

injury in a loamy sand with less than LO% ægøruc matter (Keeling et a1.,1989). Cool

and/or dry environmental conditions can slow norflurazon dissipation. Ratrn and

Zimdahl (1973) e><tended norflurazon half- life in a sandy loam soil by lowering soil

temperafure.

Norflurazon adsorption and dissipation under field and laboratory conditions, and its

distribution within the soil profile were determined in three soils representative of

cotton-growing regions of the southeastern U.S. (William et al., 1997). Norflurazon

adsorption in the 0 - 8 cm layer of the I-exingûon silt loam (Tennessee) and the Beulatt

silt loam (Mississippi) was g[ælÊr than in the Dothan loamy sand (Georgia).

Adsorption was directly related to organic matter. Norflurazon degradation under

controlled conditions in soil from 0 to 8 crn from each State was not different a¡nong

locations, with half-lives ranging from 63 to 167 days. Degradation at 30 oC in soil from

ll

the 30- to 45- and 60- to 90-cm depths was not different among locations, and was

slower at the 60- to 90-cm depth than in surface soil. Norflurazon dissipation was more

rapid under field conditions than turder laboratory conditions, with halÊlives ranging

from 7 to 79 days in the 0- to 8-cm soil horizon. Ttris may have been caused by more

e:rte¡rsive degradatio4 leaching and possibly volatilization under field conditions. Dry

field conditions slowed norflurazon dissipation. Norflurazon vtas not detected below

l5cm in the profile in any soil, and concentrations in the 8- to 15- crn soil zone rilere

<36 ppb by weigbt (ppbw) ll2 days after treaünent. However, the authors did not

mg¿sure the norflurazon concentration in the root zone in their study to see whether

leaching was a significant contributor to norflurazon dissipation or not.

2.2.4 Dissipation Studies of Haloxyfop-R ME

Few data relating to the behaviour of haloryfop-R ME in soils are presently available.

Day and Schnelle (1993) examined the soil dissipation of haloryfop-R ME and its

meøbolites under field conditions in northern Germany. Analysis of the 0-12 cm and

12-25 cm soil horizons showed that haloryfop-R ME hydrolysed very rapidly, such

that 83Yo conversion to the acid form was observed in the soil 0 day after application.

The acid (haloxyfop) atso dissipated rapidly in these horizons, following first order

kinetics, with a calculated half-life for dissipation of 7.6 days (r- = 0.936). Hammond ef

al. (1982) reported a halflife of less than I day for the conversion of haloryfop-R ME

tothe parent acid. The half-life of the acid form va¡ied from22 to 100 days, averaging

55 days. Studies using soil thinJayer plates indicated that fluazifop (a phenory acid)

was slightly more mobile than haloryfop for Texas sandy clay loam soils@ean et al.,

t2

1983). Fluazifop and haloryfop persisted for < 28 days and no heúicide treatment

persisted for > 56 days (Cruz et al.,l99l). Martins and Fleck (1988) reported that soil

persistence, in decreasing order for a series of phenory acids was, haloxyfop > fluazifop

) fenoxaprop, and was greatest in field grown soybeans. Herbicide application rate only

affecæd the persistence of haloryfop-R ME and fluazifop. Adsorption of three

herbicides including haloxyfop-R ME on three Illinois soils was determined by Rick ef

al. (1987). They found that the adsorption of the herbicides appeared to be very low in

soils with widely varying characteristics and did not appear to be signifrcantly

influenced by organic ca¡bon content, clay conten! or pH. The studies also suggested

that little adsorption occurred and that the mobility was moderate to high. This leads to

speculation that movement of compounds of this nafi¡re in soils is more extensive than

would be predicted simply by water solubility of the parent compounds. Movement

through soils could present an e¡rvironmental concern where concentrated disposal or

spills occur. However, the previors research is basically concemed with haloxyfop-R

ME activity in the soils of other countries than Australia. There are few reports on its

behavior¡r in Australian soils. Therefore, information on the degradation and dissipation

of the herbicide in different soil types of Australia is clearly needed.

2.2.5 Leaching Studies of Norflura:zon

Herbicides have been detected in ground water, and, as a result, interest in possible

contamination of ground water by herbicides has increased dramatically during recent

years. The U.S. Environmental Protection Agency (USEPA) conducted a national

pesticide survey of wells in 1985-90, and found that 10.5% of community, and 4.2o/o of

l3

rural, water supply wells contained at least one pesticide (Kearney, 1994),

Contamination of grourd water resulting from he¡bicide leaching has become a public

ooncern in major agriculnral regions of the world Slallberg, 1988). Therefore, leaching

and sorption data are needed to develop best-management practices for non-point

pollution control and to develop and veriS models for predicting pesticide transPort.

Hubbs and Lavy (1990) reported that compared with atrazlne there was less upward

movement ('wick" effect) of norflurazon in sub-inigated columns of Hebert silt loam or

Sharkey clay from A¡kansas. After l0 days of sub-inigation in the silt loam, almost

75Yo of recrovered atrazine was at the top of the column (7.5-10 cm), while 60% of the

norflurazon was between 2.5-5.0 cm, and about 20Yo was between 5.0-7.5 cm. None of

the norflurazon had moved as far as atrazine. After I weeks of subinigation in the silt

loam about 65% of remaining norflurazon u'as at the top of the column, whereas in the

clay soil about 75Yo of the herbicide was at the 2.5-5.0 cm level. These investigators

also reported on soil TLC work with these herbicides and soils, and relative R¡ values

were consistent with the above column results. The investigations of Hubbs and Lavy

(1990) indicate that norflurazon in the field leaches to a smaller extent than atraeine but

point to the possibility that norflura:zon has the potential for measr¡rable leaching into

the soil profile. Properties directly related to leaching potential for the two herbicides

a¡e simila¡: water solubility: 33 mglL for atrazine,2S mgþ for norflurazon (Tomlin,

ß91);K*: 160 cmJgfor atrazine (Jury et a1.,1987) versus 248 ørrrJg for norflurazon

(Alva and Singtr, l99O); the hatf-life in southeastern soils was 3 weeks to 6 months for

a16az,tne (tliltbold and Buchanan, 1977; Southwick et a1.,1990) and 6 weeks to 6 months

l4

for norflurazon (Tomlin, 1994). The similarity of these properties would indicate that

the two chemicals, namely atrazine and norfluÍa:zon, have somewhat similar leaching

potentials, Water sotubilities and soil adsorption coeffrcients slightly favour leaching of

atrazine over norflurazon. Tan and SinÉ (1995) found that leaching of norflurazon in

the soil columns packed with Candler fine sand increased as the amount of applied water

increased (from 5 to 48Yo of norflurazon as the water level increased from 3.2 to

l3.0cm). Results obtained by Southwick et al. (1993) do suggest that soil leaching of

norflurazon could be an important disappearance pathway in the Mississippi river

alluvial soil.

2.2.6 Sorption Studies of Norflurazon

Sorption, as a retention process, plays an important role in determining the partitioning

of a chemical between the solid, liquid, and gaseous phases, and the subsequent potential

for a soil contaminant to leach to ground water. As sorption increases, the leaching

potential decreases. It is generally observed when studying sorption of herbicides at

low concentrations that soil organic matter and clay control the sorption process for

most herbicides in soil (Gan and Koskinen, 1998).

Bailey and White (1970) found that the sorption of herbicide depends on both physical

and chemical properties of the herbicide as well as the soil. Organic matter content of

soil is the most important factor that influences sorption of nonionic herbicides (Chiou,

1989). Other soil properties such as the type and amount of clay, soil pII, and hydrous

oxides content may have some effect on the sorption process in low organic matter soils

l5

(Hassett and Banwart, 1989). Herbicide sorption is normally much less in soils with

low organic ca¡bon and clay contents than in soils high in organic carbon and clay. The

sorption of several herbicides, including norflurazon, has been studied in Florida citn¡s

soils (Singh et a1.,1985; Alva and Singta 1990; Reddy et al., 7992; Reddy and Singh,

1993; Tan and Singfr" 1995a). From their studies, the sorption of the herbicides was

influenced by soil properties, and the sorption coeffrcient (IQ) ranged from 0.63 to 2.20

mglg for norflurazon, indicating weak to moderate binding of this herbicide to the soils.

For norflutazon, K¿ was significantly relaæd to organic carbon content, soil pH, and

cation o<change capacity. Reddy and Singþ (1993) reported on the herbicide sorption

order in various soil horizons and found that the sorption was bromacil < simazine <

norflurazon < diuror¡ with the reverse relation being true for the leaching of the

herbicides. This shows that norflurazon can remain in the top soil layers longer than

simazine and bromacil.

2.2.7 Sorption and Leaching Studies of Haloxyfop-R ME

There is limited information on the leaching behaviour of haloryfop-R ME in soils and

its sorption by soils. Hammond et al. (1982) reported a sorption constant (K*) of 75

for haloryfop-R ME and predicted a moderate potential for leaching. Rick et al. (1987)

found that haloryfop and CGA-82725 (a phenory acid) leached to similar depths in soil

column studies. The study on the leaching behaviour of haloxyfop-R ME and its

metabolites u/as conducted in northern Germany under "worst case" leaching conditions,

ie. application of haloryfop-R ME to bare sandy soil, followed by autumn rainfall in

excess of the Hamburg 30-year average @ay et al., 1993). Despite these swere

l6

conditions, neither haloryfop-RME nor its metabolite was found below 38cm and 62cm

respectively in the soil profile at çoncenfiations above the validated limit of

determination of 0.1 Fdkg which illustrates the lack of downward mobility of both

parent compotrnd and metabolites.

2.2.8 Selection of Six Soils

As soil quality has great influences on the production of Austalian vineyards, research

on optimising Australian viticuln¡ral soil resor¡rces has been undertaken (Cass, 1995). In

their resea¡ch project, Cass et al. identified a range of important soil types representing a

significant proportion (>50%) of viticultr¡ral soils in South-eastern Australia and these

were chosen for the conduct of their field experiments. In order to ma¡<imise the

usefulness of this study, these six soils, collected from the same areas, \ilere used to

determine the mobility and environmental fate of norflurazon and haloryfop-R methyl

ester in these soils. Ttris makes the obtained data more useful for the environmental

management of pollution control of the Australian vineyards

The chosen areas¡ are the six major grape-growing regions of South Australia @igure 2.4),

and have a good reputation in Australia for the quality of their wines and fortified wines.

The climates of these regions are shown in Table 2.1

t7

Soil types Regions Mean annualrainfall of the

region (mm)

Mean annual temperature

of the region (oC)

(min- mær)

Terra rossa Coonawarra 644.5 7.8-20.4

Terra nigro Padthaway 525.4 8.5-21.1

Saproliæ Summertown t079.6 l1.9-20.9

Red-brown earttr Nuriootpa 505.1 8.7-20.9

Low organic ma$ersandy loam

Nuriootpa 505. I 8.7-20.9

Low clay sand Nuriootpa 505. I 8.7-20-9

Table 2.1 Climates of the Six Regions

Figure 2.4 One of the Six Vineyards, Research Road, Nuriootpa

l8

23 Conclusion

As found in numerous str¡dies \Ã,ith herbicides at low concentration, degradation and

movement of a herbicide vary significantly in different soils, or in the same soil under

different environmenal conditions. 'When a herbicide degrades chemically, soil type,

pIL mineral or organic matter constiû¡ents, and moisture content can all affect the

degradation pathways and rates. In many instances, only herbicides in the soil solution

are subject to degradation and tansport. Active water movement will promote

degradation and transporÇ while a lack of it will inhibit herbicide transport through

convection and diffr¡sion. In addition, at sites with elevated concentrations that have

abundant macropores, preferential flow of herbicides in soil $'ater may occur, further

enhancing the potential for herbicide movement or leaching. Environmental variables

such as precipitation, temperature or solar radiation also affect herbicide degradation or

transport. Precipitation can cause water infiltration and facilitate downward movement

as well as run-offof a herbicide. Temperatr¡re affects most reaction processes. It is well

known that the rate of herbicide transformation can be doubled or even fipled when

temperature increases by lO'C. Temperature also affects the solubility of a herbicide in

water and the partitioning of a herbicide between water, soil and air (Gan and Koskinen,

1998). For these reasons, overseas studies cannot be directly related to Australian soil

and environmental conditions. No resea¡ch has been systemically undertaken on the

mobility and environmental fate of norflurazon and haloryfop-R ME in different types

of viticultural soils of South Ausfalia. It is necessary, therefore, to carry out research to

er<amine the persistence, dissipation and mobility of these herbicides in the Australian

environment.

l9

CFIAPTER3 METTIODOLOGY

3.1 Analytical Methods

3.1.1 Introduction

The method by which anal¡e levds are daermined must be established prior to any

study of herbicide residues in environmental samples. Ttris is limited to those

instn¡ments commonly used within the laboratory. For this study there was a clea¡ cut

choice - gas chromatography (GC) or high performance liquid chromatography ([PLC).

Althorgh traditionally pesticides have been determined by GC, and this is particularly

so for thermally stable and volatile analytes, there are also suggestions that GC methods

did not have enotrgh sensitivity for quantitation @isenbeiss and Sieper, 1973). HPLC

is often seen as the method of choice for polar, non-volatile and thermally labile

compounds. A large number of literat¡re reports are concerned with the use of HPLC to

determine norflurazon residues (Willian and Mueller,1994; Willian et al., 1997; Mossler

et a1.,1995; Essingtoq Tyler and Wilson, 1995). Although there are many reports on

the determination of haloryfop-R ME residues by GC (Campbell et aI., 1989; Hajslova

et al., 1988), the requirement for a single instn¡ment¿l method to determine both

chemicals, and the arguments relating to thermal lability of haloryfop-R ME essentially

ruled out GC as the routine method of choice for this study.

This section discusses some of the early investigæive work undertaken to assess the

optimum anal¡ical conditions for the target compounds, and presents simple methods

for the determination of norflurazon, haloryfop-R ME and its met¿bolite by reversed-

phase I{PLC.

20

3.L.2 Materials

(a) Herbicide standards: norflurazon (98.5yo, Chenr Service PA USA) standard

solutions prepared in mettranol; haloryfop-R ME (96.1yo, DowElanco Sd France)

st¿ndard solutions prepared in acetoniüile.

@) Chemicals: acetoniúile and methand (IPLC grade, BDH Laboratory Supplies);

haloryfop-R acid (DowElanco SA France) standard solutions prepared in acetonitrile.

(c) Solvent dçgassing: mobile phases were degassed \#ith 47mm GHP 0.45pm filters

(Gelman Sciences, MI, USA).

(d) Liquid chromatography: Waters Model 510 ttpl,C pump equipped with a U6K

manual injector and Waters Model 490 IJV detector; quantitation by peak area

integration (Waters, Mllipore Corporation, MA, USA); operating conditions: isocratic

mobile phase, temperature22t 3 oC. In all analyses the volume injec'ted was 0.025 ml.

(e) IIPLC columns: 3.9 x 150 mm i.d., stainless steel, packed with reversed-phase

dimethyloctadecylsilyl bonded amorphous silica (Nova-Palc@ Crr 60Ä 4pm, Waters,

Millipore Corporation, MA USA).

3.1.3 Results and Discussion

Essington et al. (1995) employed an HPLC system with a reversed-phase C¡s column,

an acetoniüile-water mobile phase, standards prepared in methanol and a UV detector

set at 240nm to simultaneously determine norflurazon and fluometuron concentrations

in soil extracts and leachates. Mossler et aI. (1995) analysed norflurazon and other

three chemicals by IIPLC using three isocratic mobile phases: methanol and water

(70:30), tetrahydrofuran and water (35:65), and acetonitrile and water (40:60), and

found that the acetonitrile:water mobile phase provided a higher degree of separation

2t

than the other two mobile phases. These operational parameters can provide a

warranty to some preliminary investigations on the optimum IIPLC anatytical

conditions for norflurazon determination.

The HPLC system operational parameters i.e. combinations of solvent mixü,ue, pump

speeds, wavelørgth of the IJV detector, were initially varied to ascertain the optimum

uralytical conditions for norflur¡=ott. Norflurazon standard solutions were prepared in

methanol, Ttre effect of mobile phase and florv rate on anal¡e retention time and peak

shape of a lOppm norflurazon standard solution was investigated using three solvent

systems (50:50, 80:20 and 60:40 acetonitile:water) with the IJV detector set at 240nm.

The results of these investigations are shown in Table 3.1. In gøreral, retention times

were longer when the acetonitile percentage of the mobile phase and flow rates were

decreased. The broadness of the norflurazon peak and the excessively long retention

time observed when using the 50:50 acetonitrile:water mobile phase suggested tttat this

was not an appropriate mobile phase, while the worst separation between solvent and

norflurazon peaks, observed when r¡sing the 80:20 acetonitrile:water mobile phase,

indicated that the proportions in this solvent mixu¡re were also unsuitable, although

very sharp peaks were obtained. Finally, the achievement of sharp peaks, proper

analyte retention time and greatest solvent/norflurazon peak separation was obtained

when using the 60:40 acetonitile:water mobile phase. It was concluded that it was the

most appropriate mobile phase to use for all the norflurazon analyses in this study.

Both haloryfop-R ME and its parent acid standa¡d solutions \¡/ere prepared in neat

acetonitrile. No literature reports of their determination by IIPLC were found, so that

the initial operational parameters were established with diffrculty. It was discovered

22

after investigations that the optimum HPLC analyhcal conditions for norflurazon lvere

also ideal for the two haloryfop compornds.

The calibration cune for noflurazon dete¡mination, used throughout the study, is

shown inFigure 3.1. A typical norflurazon standard chromatogram is shown in Figure

3.2. The calibration curves used for haloxyfop-R ME and haloryfop-R acid

determination are illustrated in Figure 3.3 and 3.5, and typical standard chromatograms

are in Figrre 3.4 and 3.6, respectively. All the compounds u¡ere determined by the

e¡rternal standard mettrod.

Table 3.1 Norllurazon l0ppm at 240nm with the Column Nova-PakoCre

CH¡CN:IIzO 50:50 80:20 60:40

Flow rate (mVmin) 0.9 1.6 0.9 1.6 0.9 1.6

Retention time (min) 15.38 12.57 I .0 I 0.90 2.t8 I I I

Peak height (cm) 2.7 2.6 >t8 >18 9.3 9.3

Peak area (%) 77.3 76.7 75.1 74.9 76.2 75.7

23

1601 ¡lO

1n100806040200

5 10 15

concc!ilretlon (p20

Figure 3.1 Calibration Curye of Norflurazon Standard (240nm)(R_: 0.9999)

r:tlÈllNEl ñ INJEDT Ë812619d Éer4sr56

.97

Figure 3.2 Typical Chromatogram of Norflurazon Standard

Y - 73545x

aoL3Iaoê

0

24

Y = 19.528r

0 5 10 15

cofrccilratbn þ20

Figure 3.3 Calibration Curue of HaloxyfopR ME Standard(2a0nm) (R-: 09992)

CHËII{EL fr INJEçT BGtlArE¡¿

t.7?

ooLf

4

3

3

2

21

1

!ToÈ

00

500

Figure 3.4 Typical Chromatogram of HaloxyfopR ME Standard

25

Y = 4.036x

51015

concenûation (ppm)

20

Figure 3.5 Calibration Curve of HaloxyfopR Acid Standard(2a0nm) (R-: 0.9972)

c1{Ê1.11{EL f, ¡XJEÇT €8i¿ät38 s3r?í¡r¡r1

7t

g)

EO

70

€60er50¡840

30

20

10

00

Figure 3.6 Typical Chromatogram of HaloxyfopR Acid Standard

26

3.1.4 Conclusion

The most appropriate operating conditions for the HPLC to use for the detection and

determination of norflurazon, haloxyfop-RME and its metabolite in this study were:

o standard solutions: prepared in methanol for norflutazon, and acetonitile for

haloryfop-R ME and its parent acid

o column: 3.9 x 150 mm i.d. stainless steel column packed with reversed-phase

dimethyloctadecylsilyl bonded amorphous sitica (Nova-Pak@ CrE 60Ä 4pm, Waters,

Millipore Corporation, MA USA)

o mobile phase: 60:40 acetonitrile :water

o flow rate: 0.9 mVmin (norflurazon); 0.9 mVmin (haloxyfop-R ME and its parent

acid)

o IJV detection: detector set at a wavelength of 240 nm

3.2 Sample Preparation

3.2.1 Introduction

This study examined the fate of norflurazon and haloryfop-R ME in water and soils

which could contain potential interference from any naturally ocanning organic species.

Any interferences must be separated from the active ingredients and their breakdown

products prior to analysis. Traditionally, liquidJiquid and liquid-solid phase extraction

methods have commonly been used, but increasingly solid-phase extraction (SPE)

methods are preferred, especially as the whole system can be automated. SPE is based

on the principle that the components of interest are ret¿ined on a special sorbent

contained in a disposable cartidge. By using SPE, interferences can be removed in

27

either of two ways - (i) passing through an appropriate cartridge or (ii) eluting from a

carfüdge after trapping, and then the target compounds can be isolated with selective

enrichment, The final exraction from SPE is well suited to chromatographic analysis.

SPE methods have been reported for the isolation of norflurazon from water samples

(Mossler et aI., 1995; Iohnson et al., l99l; Senseman et al., 1994), but there have been

no published reports of the use of SPE for the isolation of haloryfop-R ME residues

from environmental samples. This section presents rapid and simple SPE methods for

the isolation of norflurazon and haloryfop-R ME residues from soil leachaæs using

Sep-Pal€ Cls carüidges urd analyt€ elution with methanol.

3.2.2 Materials and Methods

(a) Herbicide standards, chenricalg solvent degassing and the liquid chromatographic

system GfpLC columr¡, mobile phase and UV detector) are as described in Section

3.t.2

(b) Sep-PalP Crs solid phase qctraction cartidges (adsorbent 500 mg hold-up volume

3cc, Waters Corporation, Md USA).

(c) Filter papers (No.2qualitative, Whatman, England); Cellulose nitrate filters (0.45

pm, Sartorius AG, Germany).

(d) Rotavapor @üchi, Swiss).

(e) Six types of soils were collected from the top-soil layer (0-13 cm) of the sites

representing major viticultural regions of South Australia (Figure 2.4 and Table 2.1).

28

Gener al metho d þr solid p h as e extr actio n ltom soil leac h ates

Figure 3.7 illustrates the gerieral method used for the solid phase extraction (SPE) of

norflurazon and halryfop-R ME from soil leachaæs. The SPE carfidges were first

conditioned by sequential washing with methanol (10 ml), then distilled water (10 ml).

The total collected leachaæ was cleaned up by passage through 0.45-¡tm filærs and then

loaded onto the cartidge at room temperature at a flow rate of ca, 5-10 mUmin. The

carfidge was then vacuum dried. Both norflurazon and haloryfop-R ME were eluted

from the carridge with two lml volumes of methanol each time by centifugation.

After making up to 2ml with methanol as required the herbicide concentrations were

determined directly ftom the 2-ml methanol solutions by HPLC. All analyses were

conducted in úiplicate.

a l0ml CH'OHb. l0 lrtl H,o Water Sarrple

+ t 0

rWash Load Elute

Figure 3.7 Solid Phase Extraction Procedure

a lml CH'OHb. lml CH'OH

t&0

29

Figure 3.8 Solid Phase Extraction Equipment

30

H erhícide ql¡actio n lrom soil

Soil samples of 59 of each soil type mixed with l0¡rg of each of the herbicide standards

were shaken overnight with 50 ml methanol or, separately, 59 of each soil types were

mixed with l00¡rg of each herbicide standard and shaken overnight with 50ml of

methanol. The soil solutions were then filtered sequentially through two qualitative

filter papers and followed by a 0.45-pm filær under vacuum. The clean exüact was

concentrated in a flask by rotary evaporation (Figw€ 3.9). The concenüate was then

removed and the flask washed with 1ù20m1 methanol. The concentrate and the

washings were combined and evaporated under a gentle nitrogen stream to lml.

Herbicide concentrations \ rere determined directly by HPLC. All analyses were

wrdertaken in triplicate.

Figure 3.9 Rotavapor

3l

3.2.3 Results and Discussion

Norflurazon and haloryfop-R ME ¡ecoveries from soil leøchates

I-eachaæ (typically 100 ml) from each soil type was collected prior to herbicide

application to the soils. Norflurazon and haloxyfop-R ME were ¿dded into the

leachates at two levels - 10 and 100 pg and ræoveries were determined in triplicate at

each lerrel. The orraction methods proved to be rapid, simple and robust. Both

norflurazon and halo:ryfop-R ME were quantitatively recovered from the leachates

(fable 3.2 and 3.3).

Norflurazon and haloryfop-R ME tecovefieslrom so¡ls

Both norflurazon and haloryfop-R ME were thoroughly mixed with a sample of each

soil type (5g) at two ler¡els - l0 and 100 ¡rg. The samples were extracted immediately

after treaünent following the method described in Section 3.2.2. Recoveries were

determined in tiplicate at each level. Both herbicides were found to be stable in the

soils over the time period of the experiments. Recoveries of both norflurazon and

haloryfop-R ME from the soils were excellent (Iable 3.4 and 3.5).

32

Table 3.2 Norflurazon Recovery from Soil Leachates

Soil leachate Lerrel (ltg) Recovery Mean recovery

(%\

Combined mean

recovery (%)0tg) (%)

I-eachate

fromTerra rossa

10.0

9.7 97.098.7

96.39.8 98.0

l0.l 101.0

100.0

92.6 92.693.895.4 95.4

93.3 93.3

I-eachatÊ

fromTerra nigro

10.2

l0.l 99.096.7

99.29.9 97.l9.6 94.t

102.0

106.0 103.9101.7101.8 99,8

103.4 101.4

I-eachate

fromSaproliæ

l0.l9.5 94.t

95.497.6

9.6 95.09.8 97.0

101.0

99.8 98.899.7100.5 99.5

101.9 100.9

Leachate

fromRed-brownearth

10.5

9.7 92.495.2

97.810.0 95.2

10.3 98. I

105.0

107.6 t02.5100.3106.4 101.3

101.9 97.0

I-eachafe

fromLow organic

matter sandy

loam

10.0

9.3 93.096.3

98.99.5 95.0

l0.l 101.0

100.0

98.4 98.4101.4103.6 103.6

t02.3 t02.3

Leachate

fromLow claysand

10.3

l0.l 98. I94.8

97.59.7 94.2

9.5 92.2

103.0

105.6 t02.5100.2t02.7 99.7

101.4 98.4

33

Tabte 3.3 Haloxyfop-R ME Recovery from Soil Leachates

Soil leachaæ Lorel Gg) Recovery Mean recovery

(%)

Combined mean

recovery (7o)(rte) (%)

I-eachat€

fromTerra rossa

I0 I9.7 96.0

95.798.2

9.5 94.1

9.8 97.0

101,0

102.4 101.4100.699.2 98.2

103.1 t02.t

I-e¿chafe

fromTerra nigro

10.6

10.4 98. I96.5

97.9l0.l 95.3

to.2 96.2

106.0

107.3 101.299.2105.5 99.5

102.7 96.9

I.eashztefromSaprolite

10.0

9.3 93.095.0

96.99.4 94.09.8 98.0

100.0

l0l.l l0l.l98.898.9 98.9

96.4 96.4

Leachate

fromRed-brownearth

10.3

9.9 96.1

101.399.5

10.6 t02.910.8 104.8

103.0

99.9 97.097.6tot.2 98.3

100.4 97.5

Leachaæ

fromLow organic

matter sandyloam

t0.29.5 93. I

96.1

96.59.8 96.1

l0.l 99.0

102.0

98.4 96.596.897.6 95.7

100.2 98.2

Leachate

fromLow claysand

I0 I9.3 92.1

96.498.5

to.2 101.0

9.7 96.0

101.0

99.0 98.0100.6103.1 t02.1

t02.6 101.6

34

Table 3.4 Norfluraizon Recovery from Six Soils

Soil type Lorel (tU) Ræovery Mean recovery

(%)

Combined mean

recovery (7o)Gg) (%)

Terra rossa

t0.28.1 79.4

76.1

78.07.7 75.5

7.5 73.5

102.0

83.6 82.079.879.0 77.5

81.4 79.8

Terra nigror0.2

8.7 85.3

87.3

87.79.1 89.2

8.9 87.3

102.0

92.6 90.888.087.5 85.8

89.3 87.5

Saproliæ

10.6

7.9 74.5

79.281.6

8.5 80.2

8.E 83.0

106.0

86.7 81.884.189.2 84.2

9t.4 86.2

Red-brownearth

10.6

7.6 7t.778.3

80.38.9 84.08.4 79.2

106.0

82.6 77.982.388.8 83.8

90.3 85.2

Low organicmatter sandy

loam

10.0

8.2 82.080.3

80.98.1 81.0

7.8 78.0

100.0

78.6 78.681.483.4 83.4

82. I 82.1

Low claysand

10.0

8.3 83.086.0

87.29.0 90.08.5 85.0

100.0

87. I 87, I88.391.0 91.0

86.8 86.8

35

Table 3.5 HaloxyfopR ME Recoyery from Six Soils

Soil type Lwel (¡tg) Recovery Mean recovery

(%)

Combinedmean

recovery (7o)(tts) (%)

Terra rossa

I 0 I7.6 75.2

76.977.3

8.0 79.27.7 76.2

101.08t.2 80.4

77.778.5 77.775.9 75.1

Terra nigroI 0 I

8.6 85. I82.8

84.08.5 84.2

8.0 79.2

101.0

82.t 8l.385.289.7 88.8

86.4 85.5

SaproliæI0 I

7.8 77.2

80.280.9

8.2 8t.28.3 82.2

101.0

85,1 84.3

81.68t.2 80.480.9 80. I

Red-brownea¡th

10.0

7.9 79.081.0

80.8

8.1 81.08.3 83.0

100.0

78.6 78.680.779.t 79.1

84.4 84.4

Low organicmatter sandyloam

10.5

8.2 78. I80.3

8l.48.5 81.08.6 81.9

105.0

90.3 86.082.487.6 83.4

81.7 77.8

Low claysand

10.0

8.3 83.0

82.3

83.77.7 77.O

8.7 87.0

100.0

86.8 86.8

85. I82.7 82.7

85.8 85.8

36

3.2.4 Conclusion

The solid-phase extraction (SPE) methods developed were able to separate the analytes

- norflurazon and haloryfop-R ME from potential anal¡ical interference prior to

analysis, The methods are rapid, robust and capable of providing extract solutions from

which sub-ppm concentrations of the analytes cot¡ld be determined with o<cellent

reproducibility. The extacts from the SPE methods were well suited to the

chromatographic analysis described in Section 3.1. Therefore, in this study SPE was

preferred to, and had considerable advanages over, more traditional approaches such as

liquid-liquid extraction methods.

37

CHAPTER 4 LEACHING BEIIAVIOT]R OFNORFLT]RAZON AND IIALOXYFOP-RMETITYL ESTER IN SOIL

4.1 Inûoduction

The physical and chemical heterogeneity ofthe naû¡ral envirmment makes the accurate

prediction of the fate of agrochemicals very diffrq¡lt. Nevertheless, ar¡thorities

worldwide are under pressure to use soil information and chemical cha¡acleristics to

guide agrochemical users in selecting pesticides with minimal residues and which a¡e less

prone to leaching into groundwater (Franklin et al., 1994). Since significant pesticide

toxicity is often seen at sub-mg/L cqrcentrations, only a comparatively small amount of

pesticides applied can cause serious contamination of grotrndwater when leaching

through the soil. In screening and registration prognms, it is still common practice to

estimate pesticide mobility by simply determining physical and chemical properties of

the pesticides e.g., adsorption constants, water solubilities and degradation rates, and

predict leachability based on such information. It is even more common to conduct

short-term leaching tests on sterile urd homogenous soils. However, the environmental

conditions in these tests are quite different from natural soils and field conditions.

Predicting pesticide transport is fi¡rther complicated by networks of interconnected

pathways within the soil which facilitate the movement of water and substances

dissolved in it. These pathways result from gedogical activity, such as sub-surface

erosion, faults and fractures, shrink-swell cracks, and biological forces such as animal

burrows, \¡rorrn holes, decaying roots, eúc.. They may transmit water and dissolved

compounds at very much higher rates than anticipated by many current theories

(Søgnitti et a1.,1995; Bergsüom and fawis, 1993; Glotfelty et a1.,1984; Frank et al.,

38

lgTg). Despite these difficulties, the fact that some pesticides can be transported lurg

distances by soil water and be detected fa¡ from the application site makes the

prediction of their environmental fate thror¡gh experimentally validated models of

utmost importance.

Undistr¡rbed soil profiles offer a better mea¡u¡ of studying preferential flow of

pesticides under field conditions than the aforenrentioned standard leaching tests,

becar¡se they presewe the natr¡ral stn¡cture of the soil (Steenhuis et al., l99l), In this

section, the leactring behavio¡r of norflurazon and haloryfopR ME under laboratory

conditions thrq¡gh undistu¡bed soil profiles exüacted from the six m{or viticultr¡ral

regions of South Australia" and the determination of their residues in the soils after the

leaching tests are discussed.

4.2 Materials and Methods

(a) Solicamo DF (norflurazon) from Sandoz Australia Pty. Ltd., NSW; VerdicP (l3ÛglL

haloxyfop present as methyl ester) from the Rrual Services, The University of

Adelaide. These were analysed to confirm their herbicide content.

(b) Herbicide st¿ndards, chemicals, solvent degassing and the liquid chromatographic

system ([DLC column, mobile phase and UV detector) are as described in Section 3.1.2

of Chapter 3.

(c) Extaction carfidges and methods are as described in Section 3.2,2 of Chapter 3.

(d) PHM6I Laboratory pH Meter - Radiometer, Copenhagen.

(e) Soil samples were extracted as soil monoliths with galvanised iron containers (15 x

15 x 15 cm, no top or bottom) from the top soil layer (0-13 cm) of the six sites

39

representative of majorviticultural regions of South Australia (Figure 4.1). The soils

were kept undisturbed until the leaching experiments were conducted.

Leaching æperíments

I-eaching behaviour of norflurazon and haloryfop-R ME in the six soils under

laboratory conditions was sh¡died after the oûacted soil monoliths were completely

wetted, and the herbicides were applied at the maximum recommended freld rates

(norflurazon: 11.25 mg/monolith; haloryfop-R ME: 1.872 mg/monolith). The first

simulated rainfall, equivalent to one fifth of the mean annud rainfall appropriate to the

regions, was then applied to the soil profiles, and leachates collected (day 0). The soils

were irrigated every day with the same volume of water for another four days, and the

leachates were collected at day l, 2,3 and 4 (Figrre 4.2 nd 4.3). The water samples

were extracted following the SPE method described in Section 3.2.2, and the 2-ml

e>rtracts obtained were stored below OoC until herbicide concentrations were deterriined

by HPLC. The experiments were conducted twice, and all analyses were undertaken in

fiplicate. Herbicide recoveries for all six soils are given in Chapter 3 Tables 3.4 and

3.5.

Examination of herbicide rcsidues in soil protiles øfier simulatedrainfall t¡eatment

The norflura:zon and haloryfop-R ME residues in each type of soil were oømined by

extnrding the soil monolith and taking two sections, each of 6.5 cm. The soils of each

section were extacted following the method described in Section 3.2.2. All the l-ml

extracts obtained were stored below OoC until examined by HPLC. The experiments

were conducted twice, and all analyses were undertaken in triplicate.

40

Tests for the dde¡mination ol soil cha¡acteristics

Soil solutions (soil : distilled water = l:5 w/w) were made for measurement of pH

values of the six soils. The soil pH was determined by PHM6I Laboratory pH Meter

(20"C) in tiplicate. Panicle size analysis was performed once using the pipette

method (Mclaren and Cameron, 1990). Total organic carbon (OC) was determined in

tiplicate using a LECO CRl2 carbon analyz.er, and values were converted to percent

organic matter by the equation: organic matter Yo: 0.35 + (1.80 xOCYI) (Alison et al.,

le6s).

Figure 4.1 Process of Collecting Soils

4l

Sim¡latdRsinfall

0

Soil

lvlesh

Metal Contairer

Funnel

Collection Conical Fla*

Figure 4.2 Diagram of the Equipment for Leaching Experiments

Figure 4.3 Equipment for Leaching Experiments

42

Tesßfor the ddermìnation of soíl charactefistics

Soil solutions (soil : distitled lvater = l:5 w/w) were made for measurement of pH

values of the six soils. The soil pH was determined by PHM6I Laboratory pH Meter

(20.C) in tiplicate. Particle size analysis was performed once using the pipette

method (Mclaren and Camerorç 1990). Total org;anic ca¡bon (OC) was determined in

tiplicaæ using a LECO CRl2 carbon analyzer, and valuæ lvere convened to percent

organic matterby the equation: organic matter Yo= 0.35 + (1.80 xOCo/ù (Alison et al.,

le6s).

43 Results and Discussion

As herbicide behaviour in soil is directly atrected by soil properties, the characteristics

of the six soils used in this study were determined, and the results are shown in Table

4.1below.

43

Table 4.1 Characteristics of Six Soils

Soil type pH Organic matter(%)

Sand Silt Clav(%)

Terra rossa 7.8 t.43 I 9 90

Terr¿ nigro 7.0 o.72 9l 8 I

Saproliæ 5.7 2.07 40 55 5

Red-brown earth 6.7 1.25 9 l0 8l

Low organicmatter sandv loam

6.5 0.81 7l l9 l0

Low clay sand 6.7 0.86 84 12 4

Norflurazon wa¡¡ detected at relatively high concentrations in all the soil leachates

collected after the simulated rainfalls. This result and the distribution of the herbicide

residue in the soil monoliths after the leaching experiments show that norfluÍazon may

be a leachable herbicide in the six viticulU¡ral soils. Southwick et al. (1993) reported

that soil leaching of norflurazon was an important dissipation pathway, which

supports the current ñnding.

Norflurazon concentrations in the leachates from the terra nigro soil and the saprolite

soil were detected at the highest values after the second simulaæd rainfall, while in the

leachaæ from the low clay sand it reached the highest value after the third simulated

rairifall, and for the low org;anic matter sandy loam and the red-brown earth the

herbicide concentations tvere highest after the fourth simulated rainfall, and for the

terra rossa soil it was highest after the last simulated rainfall @igure a,a). Moreover,

norflurazon residue in the soil monoliths after the leaching experiments was found more

in the top section (06.5cm) than in the lower part (6.5-l3cm) for the terra nigro soil,

44

the low clay sand and the low organic maffer sandy loam, while for the other three soils

the herbicide residue was detected at greater concentrations in the lower sec'tion than in

the top layer (Figure 4.6). These data suggest that soil clay and organic matter contents

may have caused the different leaching behaviour and mobility of norflurazon in the

soils. Herbicide sorption did not appear to ocq,rr in the soils with low organic ca¡bon

urd clay contents, which resulted in much herbicide leaching thtough the soils (Hassett

and Banwart, 1989). Hubbs and Lavy (1990) reported that norflurazon adsorption

increased and mobility decreased as soil organic ma$er and clay content increased. The

substantially greater quantities of norflurazon leactring throrgh the terra nigro soil and

the low clay sand than thrurgh the terra rossa soil and the red-brown earth, and the

distribution of the herbicide residue in the soil monoliths, are in agreeme,lrt with those

previous reports.

Eâ.Èt-9EEo(,Êoo

0

5

1

!

2

I

0 tm 130 2d) mm3c) 4æ 1m 5æ 5m 500 6505m llm 530lm 220 tO6 ãþ 1{O 212 æ0 660 318

R¡lilrll Vdtnt: (rml

q

¡sePrcllte ¡terre rcre ¡tcrn nlgro

Figure 4.4 Norflurazon Concentration in Soil Leachates Collectedafter Simulated Rainfall on Six Soil Profiles

¡mlifJJnl

Norflurazon

nI¡¡¡t¡¡l¡¡l¡ltaN

III

45

IIIt

-It=I

-II

ââ.ÈcIIe,3Êo(,

2g)1C)

1d)

1&1Ã1(x)

æd¡¡o

x)o

t0 20 16 2æ Æ 212 m 6æ 3t8 1æ W 121 5æ llæ 530

RrlnlellVolum (mn)

Figure 4.5 HaloxyfopR ME and Acid Concentration inSoil Leachates Collected after SimulatedRainfall on Sir Soil Profiles

No haloryfop-R ME or acid were detected in the leachates from red-brown earth and

terra rossa soil after the first simulated rainfall, or in the terra rossa soil leachate after

the second simulated rainfall. No residues \ ¡ere detected in the saprolite soil leachate

after the last simulated rainfall. Furthermore, in the other soil leachates haloryfop-R

ME and acid were detected at very low concentrations (Figure 4.5). Moreover, the

amount of the herbicide residues in the top section (0-6.5cm) of the soil monoliths

recovered after the leaching tests was much more than that in the lower part (6.5-l3cm)

of the soil monoliths (Figure a.f. Therefore, the results illustrate the lack of

downward mobility of both compounds in the soils. When studying of the leaching

behaviour of haloryfop-R ME and its meabolite in a soil of northern Germany under

"worst case" leaching conditions, Day et al. (1993) found that neither haloryfop-R ME

nor the parent acid was detected below 38cm in the soil profile, which supports this

finding. The le¿ching behaviour of haloxyfop-R ME and acid may have been influenced

erth I o.¡n l ¡lov cley

grePrcllh ¡trrre rcc:r gtern nlgro

46

by the soil properties. The data obtained in this study agree with a previous report

that the downward movement of haloryfop was greater in the coarse-texh¡red

Bloomfield sand than in the fine-texû¡red Drummer silty clay loam (Rick et al., 1987).

This report also indicates that the mobility of haloryfop did not appear to be

significantly influenced by organic ca¡bon conten! however, soil organic matter affected

halorryfop leaching behavior¡r in this shrdy. The differences could be due to the use of

different soils under different experimental conditions.

Compared with haloryfop-R ME and acid more norflurazon was found in the soil

leachates and the lower section of the soils monoliths after the leaching experiments,

which indicates that norflurazon could be a more leachable and mobile herbicide.

Meanwhile, more haloryfop-R ME and acid were detected in the top layer of the soil

monoliths than in the lower part and a small amount of each of them was found in the

soil leachates, which shows that haloryfop-R ME and acid may be more persistent in

the soil systems.

However, although the leaching potential of the two herbicides was found at measurable

levels, they may still be considered as persistent herbicides, as most of them stayed in

the top section of the soil monoliths after the leaching tests, and the amounts of their

residues in the soils were much more than in the soil leachates'

47

lrlorllunzon

0.

Figure 4.6

tcra þsst

bw dey rend

r¡d bewn ¡rüt

Soil Typerepdlc

nndy bem þw o.m)

1

torra ri¡¡loI

BEoo!5oÊ,

0

6'5 t3

llepttr(cm)

Distribution of Norllurazon Residues in ExtractedProfiles of Six Soils, after Simulated RainfallTreatment

48

llaloryfop{ llE ¡nd Acitl

1& tcrra rþro

lcru ro¡ga

bw dey rand

rrd bmw n ¡¡rür

:prdlc

SoilTypcrendy bem (br orn.)

6'5 13

Ilepth(cm)

Figure 4.7 Distribution of HaloxyfopR ME and Haloxyfop-R AcidResidues in Extracted Profiles of Six Soils, afterSimulated Rainfall Treatment

Ð

ú,gEooÉ,

49

4.4 Conclusion

The leact¡ing study suggests that soil properties have a great influence on herbicide

leachingbehavior¡r in soil. Norflurazon and haloryfop-R ME may have some leaching

potential in the six Ausfialian viticult¡ral soils, particularly in those with low organic

matter and clay contents. In this slrdy it was determined that the terra nigro soil, the

low clay sand and the low orgariic matter sandy loam are more likely to be prone to

herbicide leaching than the other three soils. Both norflurazon and haloryfopR ME arc

persistent herbicides. Norflurazon was ¡elatively mobile and leachable in the six soils as

evide,nced by its detection throughout the soil profiles and in the soil leach¿tes. As a

result, it appears possible that norflurazon would pose a moderate th¡eat to

grorndwater supplies in the areas where the six vineyards are located. Haloryfop-R

ME, on the other hand, was immobile and lacking in downward movement in the soil

systems, and as a result, it is unlikely that haloryfop-R ME would pose any significant

threat to groundwater supplies; however, due to its persistence, it is probable that the

accumulation ofthe herbicide residues in soil could cause vine injuries.

50

(.\1Íìl I r'1

CHAPTER 5 DISSIPATION OF NORFLT]RAZON AI\DIIALOXYFOP-R METITYL ESTER IN

5.1Inüoduction

Australia's grape-growing and winemaking industries comprise over 5,000 independent

grapÈgro!\rers and more than 8@ wineries spread across all States and Tenitories.

Vines are gfowrl under an errtensive range of soil and climatic conditions, with

viticult¡rists using a wide range of vine, pes! and vineyard water and soil managønøt

practices (GWRDC, 1996). Like other Austr¿lian agricultral industries, agrochemicals

are used widely by the industry, Following application, there are a number of possible

outcomes for pesticides such as norflurazon and haloryfop-R ME. They may persist

on soil sr¡rface and volatilize into the air, the herbicides may undergo chemical and/or

microbial degradation in the soil, they may reach surface water by means of run-ofl or

be transported into grapes through roots, or leach through the soil into groundwater. A

great deal of research is concerned with norflurazon and haloxyfop-R ME behavior¡r in

the environment. However, there have been no published reports on the dissipation of

these two herbicides in Australian environment, especially in Australian viticultural

soils.

By studying herbicide dissipation under laboratory conditions, some basic information

can be obtained on factors which affect herbicide dissipation without the influence of

va¡iable environmental conditions. This can be useful for undertaking a field study

since it can make the study more e,ffective and accurate. Since the primary aim of this

study is to determine the environmental fate of norflurazon and haloxyfop-R ME, this

chapter describes investigations into the dissipation of these herbicides in six key

viticultural soils of South Australia under laboratory conditions.

51

5.2 Materials and Methods

(a) The nvo herbicides a¡e as described in Section 4.2 of Chaptet 4.

(b) Herbicide standards, chemicals, solvent degassing and the liquid chromatographic

system ([DLC column, mobile phase and UV detector) are as described in Section 3.1.2

of Chapter 3.

(c) Extraction methods are as described in Section 3.2.2 of Chapter 3.

(d) Autoclave (RL Smith, Australia).

(e) Six types of soils were collected from 0-13 cm soil zones in the same locations from

which the soil monoliths were e:rtracæd for the leaching experiments.

Di s s ip atio n exp er ¡mc nts

Soil samples were presewed under moist field conditions by adding sufÏicient water as

required to maintain the original "as received" field weight. This was done by weighing

the soil each day and adding water to bring the weight back to its initial field weight.

Then I kS of each soil type u/as spread on separate trays each 32 cm x 46 cn.

Norflurazon and haloryfop-R ME were applied to the soils at the madmum

recommended field rates (norflufazon: 60 mgltray; haloryfop-R ME: 10.4 mg/tray) by

dissolving the herbicide in I liúe of water which was then poured over the soil to ensure

a uniform application. Soil samples (lg) were t¿ken from one of seven different sites

randomly selected in each tray l, 3,7,14,28,42 and 56 days after application. The

herbicide residues were ortracted from each 7-g soil mi:rture following the method

described in Section 3.2.2. All the l-ml soil extracts obtained were stored below OoC

r¡ntil determination by HPLC. The experiments were conducted twice under laboratory

conditions, and all analyses were undertaken in Íiplicate. The dissipation of both

herbicides in the six autoclaved soils was studied in the same manner as for the non-

52

autoclaved soils, after the soil samples were heated for 30 minutes at 120"C under 100

Kpa in an autoclave.

5.3 Results and Discr¡ssion

5.3.1 Herbicide Dissipation in Six Soils

Under the conditions used for this laboratory study of herbicide dissipation, processes

such as photodegradation and leaching would be minimal. The laboratory was air-

conditioned and the temperature maintained at 22oC + 3oC. The trays were covered

with aluminium foil. Therefore, degradation and volatilization \¡/ere assumed to be the

primary loss mechanism. First-order kinetics empirically fit the herbicide dissipation

data in the six soils (l > 0.9), and thus was considered to be a suitable technique for

describing norflurazon dissipation uqder laboratory conditions. The dissipation of the

herbicide was found to proceed with a relatively rapid initial loss followed by a slow

loss of remaining norflurazon in this sûrdy. This indicates that degradation, by either

volatiliz¿tion, or photodegradation may be the primary loss mechanism for norflurazon

in the time interval between its application and the first rain. This agrees with the

findings in a previous report that nofluraeon dissipated to 50% of its initial

concentration within 8 days of application to a dry soil surface (Kvien and Banks,

1985); however, it is contrary to the findings of Willian et al. (1997) that neither

chemical nor microbial degradation accor¡nts for the initial rapid norflurazon loss.

Norflurazon dissipation in the six soils was not rapid under laboratory conditions, with

a halÊlife rangng from 150 to 300 days (Table 5.1). Norflurazon concenûation had

little or no change from 14 to 56 Days after Treaünent @AT) in the saprolite soil

(Figure 5.1). Dissipation was not much different in the terra nigro soil and low clay

53

sand, with 67Yo of applied norflurazon remaining 28 DAT (Figure 5.1). Norflurazon's

half-life (DTso) in the terra rossa soil was 270 days (Table 5.1), and the dissipation rate

slowed from 14 to 56 DAT, wirh 74yo of the applied norflurazon remaining 56 DAT

(Fig,¡re 5.1). The order of norflurazon dissipation in the six soils was: saprolite < terra

rossa ( red-brown earth < low organic matter sandy loam < low clay sand < terra nigro

(Figure 5.1). These data indicate that the dissipation of the herbicide was related to soil

organic matter, but did not appear to be affecæd by other soil parameters. This result

is in agreement with a previous report that norflura;zon dissipation was reduced at

higher soil organic matter contents. This is probably due, at least in part, to the

adsorptive characteristics of organic matter which may reduce the amount of potentially

degradable or available herbicide (Schroeder and Banks, 1986).

æ

s)D o

DAT (day)o Ð o

l@

s

tæTE

720

l00

R2.0.9167

R2 = 0.9@8

R2 = 0.9æ2

R2.0.$73

R2 = 0.9077

R2 = 0.9i143

Figure 5.1 Dissipation of Norllurazon in Six Soilsunder LaboratorY Conditions

xxx

54

Haloryfop dissipation in the six soils was observed as the ester and acid form together.

Total haloxyfop residues recovered over the 56 days of observation declined in a

curvilinea¡ fashion. The decline in the terra nigro soil was simila¡ to the decline in the

low clay sand, but greater than in the other four soils @igt¡re 5.2). This greater

dissipation might be due to the lower levels of organic matter in these two soils, and the

similarity of the two soils in herbicide dissipation was probably due to the small

difference between their aganic matter contents. Haloxyfop-R ME and acid had little

clrange in concenüation from 14 to 42 DAT in the saprolite soil (Figl¡re 5.2).

Dissipation was not very different in the terra-rossa soil compared with the red-brown

earth, with 51.5% of applied herbicide remaining 56 DAT @igure 5.2). Haloryfop-R

ME and acid's time to degrade half the amount present or DT56 value in the low organic

matter sandy loam was 16 days (fable 5.1), and the dissipation slowed from 28 to 56

DAT u,ith 34.4yo of the applied herbicide remaining 56 DAT @igure 5.2). The order of

haloxyfop-R ME and acid dissipation in the six soils was: saprolite ( terra rossa ( red-

brown earth < low organic matter sandy loam < low clay sand < terra nigro (Figure 5.2).

The results indicate that dissipation of haloryfop-R ME and acid in soil is reduced at

higher soil cganic matter contents. No association l\¡as evident between the herbicide

dissipation and soil clay content.

Compared with norfluÍa:zon,the dissipation of haloryfop-R ME and acid was relatively

rapid in the six soils, following first-order kinetics (l > O.AS¡, \¡/ith calculated DT5s

values varying from 7 to 135 days (Iable 5.1). Hammond et al. (1982) reported a half-

life of less than I day for the conversion of haloryfop-R ME to the parent acid and the

halÊlife of the acid form rangng ftom 22 to 100 days, averaging 55 days. The

55

difference in DT5s values between this study and the previous research may result from

the use of different soils under different experimental conditions.

30

20

l0

0r0203040

DAT(daY)

3 red'brown earthFF =0.8S

4 sandy loam (ow o.m)F=0.H1

50 60

t(x)

90

80

Ã70Ë,

960p50BÉ, ¡f0

0

I saprclteFl2 = 0.91 16

2 tema rcssaFF =0.9152

5 low clay sandFF = 0.9012

6 tena nigmFP= 0.897

Figure 5.2 Dissipation of HaloxyfopR ME and Acid in Six Soilsunder LaboratorY Conditions

llaloxyfop{ ME and Acid

x

x

xX

6

2x

56

Table 5.1 Half-lives of Herbicide Dissipation (DTso)in Sir Soils under Laboratory Conditions

Soil type DTso (days)

norflurazon haloxvfop-R ME and acid

Saproliæ 300 135

Terra rossa 270 98

Red-brown earth 230 89

Low organic mattersandy loam

190 l6

Low clay sand 160 7

Terra nigro 150 7

5.3.2 Herbicide Dissipation in Six Autoclaved Soils Comparedwith Six Natural Soils

Figure 5.3 and 5.4 show that dissipation of both norflurazon and haloryfop-R ME

(ncluding the acid) lvas greater in the six non-ar¡toclaved soils than in the autoclaved

soils. This was probably due to only pure chemical degradation occuning in the

autoclaved soils, whereas both microbial and chemical degradation could occur in the

natural soils.

Since herbicide leaching and photodegradation could not exist in this test system, the

main pathways which could account for norflurazon dissipation in the autoclaved soils

were volatilization and chemical degradation. However, for haloryfop-R ME and acid

only chemical degradation ccx,¡ld be responsible for their dissipation in the autoclaved

soils, as volatilization of the haloryfop-acid form was not significant in the autoclaved

soils.

57

Norflurazon dissipation tva¡¡ very similar in the autoclaved and nah¡ral soils of the

saprolite and terra rossa soil types (Figure 5.3). In general, differences between

dissipation in the autoclaved and non-autoclaved soils of the same types were small for

norflurazon @igure 5.3), while these differences were relatively larger for haloxyfop-R

ME and acid (Figrre 5.a). This indicates that microbial degradation \{/as a more

important dissipation pathway for haloryfop-R ME and acid than for norflurazon,

since norflurazon dissipation did not appear to be affected to the same extent as \ilas

the dissipation of haloryfop-R ME and acid, after the soils were heated and lost their

ability to degrade the herbicide microbially.

Compared to the naû¡ral soils, both herbicide's DTso values increased in the autoclaved

soils, with a range of 155-319 days for norflurazon and 10-178 days for haloxyfop-R

ME and acid (Table 5.2). This was due to the slower herbicide dissipation in the

absence of microbial activity in the autoclaved soils.

Table 5.2 Half-tives of Herbicide Dissipation (DTs¡) in SixAutoclaved Soils under Laboratory Conditions

Soil type DTso ( )norflurazon haloxvfop-RME and acid

Terra rossa 280 t43

Terra nigro 155 l0

Saproliæ 319 178

Red-brown earth 238 153

Low organic mattersandv loam

t96 24

Low clay sand t67 ll

58

3.prcliÛl

R2 - 0.9167n

FF- 0.519aubched

1æ tæ

90

¡t

3ao=g

þ,o60

50

90

¡e

ãrotIPro

60

50

c)

I3aotI8zoÉ,

60

s¡R

gæ=Ip rc)

q)

n ¿t0

BT ldr960 o 20 40

IIT ldrÐ60

I CX) 1(x)

50

0 20 ¿10 60 20 40 60

IIT (deyf UIT(dayf

1æ 100

50

0 20 40 60 o 20 40üT (deyfBT ldeyf

Figure 5.3 Dissipation of Norflura,zon in Six Autoclaved Soilsundir Laboratory Conditions (compared with untreated soils)

50

0

90

I380J!

P70q)

$¡l

3ætIPro

q)

5060

t¡rr¡ ros¡

FP = 0.921aubclaved

nonautoclawdR2= 0.9)28

redårown earüt

R2 - O.9(Xlll

P.0.9C/8autodaved

randy loam (low o.m.)

FF= 0.9218aubclaved

nonaubchvedR2 = 0.9073

low chy sand

* -0.9137aub

RP= 0.9)Z

terra nigro

noR2= 0.943

FP= 0.9208autodaved

59

3aprol¡b*-0.955

autoclared

nor¡aubdavedR2 .0.9116

1€X)

90

80

70

60

5040

30

20

10

0

*oot!ooÉ,

1(x)

90

EO

7060

50¿f0

30

2010

0

¡a,3=EoalÉ.

1æI80

t 7c)

!æEsr&,&

æz)10

0

100

90

8070q)50

Q30

nl0o

¡aoalt!ooÉ,

100

$æ70

60

5()

4æn10

0

soo=!,oÉ,

1q)90

80

70

60

50

&30

nt00

sllotg,l¡É

0600 201ÍJBT ldryl

20ßDAT ldryf

2040DAT ldeyf

60

60 n &DAT ldayl

æ Q 60 ?o40IIT þeyfDAT ldryl

Figure 5.4 Dissipation of HaloxyfopR ME and Acid in Six AutoclavedSoils under Laboratory Conditions (compared with untreated soils)

00 60

6000

brra ræsa

R2 - 0.9152

R2= 0.${8autoclawd

F.0.8€

RP= 0.851aubdared

sandy loam (low o.m.)

nFP= 0.8981

R2 = 0.9176autoclawd

low clay sand

FP- 0.9012bved

F =0.9061aubclaned

terra nþro

R2 = 0.897

R2= 0.9)62autoclaræd

5.4 Conclusion

60

Dissipation of haloryfop-R ME and acid in the six soils was greater than for

norflurazon. The dissipation of both herbicides followed first-order kinetics 1l>O.ae¡,

with a half-life rangng from 150 to 300 days for norflurazon and 7 to 135 days for

haloryfop-R ME and acid. The order of dissipation of both herbicides in the six soils

was: Saprolite < terra rossa ( red-brown earth < low organic matter sandy loam < low

clay sand ( terra nigro, which indicates that the herbicide dissipation was reduced at

higher soil aganic matter contents, but it did not appear to be affected by other soil

parameters.

Degradation, volatilization or photodegradation are all possible loss mechanisms for

norflurazon in the time interval between application and the first rain. Hydrolysis of

haloryfop-R ME followed by microbial degradation of its metaboliæs may be a very

important pathway for the herbicide dissipation.

Dissipation of both norflurazon and haloryfop-R ME (including the acid) was more

rapid in the non-autoclaved soils than in the ar¡toclaved soils. For norflurazon, the

differences were less significant between the treated and untreated soils. Herbicide's

DT5s values increased in the autoclaved soils, with a range of 155-319 days for

norflurazon and 10-178 days for haloryfop-R ME and acid. These results suggest that

the herbicides only degraded chemically in the autoclaved soils, whereas in the natural

soils, both microbial and chemical degradation occurred.

6l

The findings from this study indicate that these chemicals could pose potential

environmental th¡eat once applied.

62

CHAPTER 6 CONCLUSION

It is very diffrcult to predict accurately the fate of chemicals used in agricultrre or other

industrial practices due to the physical and chemical heterogeneity of the natural

environment. This situation is also tn¡e for Australian vineyards and the agricultr¡rat

chemicals used in theirmanagement. The climatic conditions in Ausûalian vineyards, in

particular the longeç hotter, drier, more intense, summer daylight hours, a¡e different

from those in Europe where much of the research on such critical parameters as

application rates (in terms of efficacy and persistence) and pre-harvest with-holding

period has been undertaken. The main objective of this research project was to study

the environmental fate and mobility of two herbicides registered for use in Australian

viticulhrre, namely norflurazon and haloryfop-R methyl ester, by:

L developing an eflicient solid phase extaction method for their extraction from soil

leachates and soil matices;

2. developing a precise analytical method for their detection and determination in

extracts from soil leachates and soil matrices;

3. oramining their leaching behaviour under laboratory conditions in the extracted

profiles of six soils representative of the major viticulural regions of South

Australia;

4. o<amining their residues in the extracted profiles of the six soils after simulated

rainfatl teaünent

5. oramining their dissipation in the six autoclaved soils compared with the non-

autoclaved soils under laboratory conditions.

63

That this study was suocessful in achieving its aims and objectives is evidenced by the

fact that:

l. a rapid and robust solid phase e¡rtraction method for the ottaction of norflurazon

and haloryfop-R ME from soil leachates and soil matices was established once the

appropriate volumes and/or quantities of matrix i.e. the maximum cartridge loading

before anal¡e breakttuough uras observed, and the appropriate carüidge

conditioning, washing and elution parameters had been established;

2. development of a precise analytical method for the detection and determination of

these chemicals was relatively straighforward once the appropriate columrç mobile

phase and flow rates were determined;

3. both herbicides had some leaching potential in the six viticultural soils, particularly

in those with low øganic matter and clay contents. Norflurazon was relatively

mobile in the soils, as norflurazon was detected at high concentrations in the soil

leachates and" for th¡ee soils, more norflurazon was found in the lower section of the

soil monoliths than in the top layer. However, only a very small amount of

hatoxyfop-RME (including its parent acid) was found in the soil leachates and lower

part of the soil monoliths, which illustrates the lack of downwa¡d mobility of the

compounds in the six soils;

4. both norflurazon and haloryfop-R ME are persistent herbicides, although their

leaching poæntial is not insignificant;

5. norflurazon dissipation in the six natural soils was not rapid under laboratory

conditions with a half-life ranging from 150 to 300 days, while haloryfop-R ME and

g

acid dissipation was relatively rapid with DT56 values varying from 7 to 135 days.

First-order kinetics fit the dissipation data of both herbicides (l>O.Ae). The order

of herbicide dissipation in the six soils was: Saprolite < terra rossa ( red-brown earttr

< low organic matter sandy loam < low clay sand < terra nigro. Both herbicides

dissipated more slowly in the autoclaved soils than in the natural soils, with DT56

values of 155-319 days for norflurazon and 10-178 days for haloryfop-R ME and

acid.

These findings suggest that the leaching behaviour of both norflurazon and haloryfop-R

ME may have been g;eatly influenced by the soil's properties, and the terra nigro soil,

the low clay sand and the low org;anic matter sandy loam are more likely to be prone to

herbicideleachingthantheotherthreesoils. Norflurazon is relatively leachable so that

it would be likely pose a moderate thre¿t to groundwater supplies in the six viticultural

regions. On the other hand, it appears unlikely that haloxyfop-R ME would pose any

significant threat to groundwater supplies; however, the accumulation of the herbicide's

residue would probably cause vine injuries due to its immobile character. These results

also suggest that the dissipation of both herbicides was related to soil organic matter,

with reduced dissipation at higher cganic matter contents. Degradation, volatilization

or photodegradation cor¡ld account for the primary initial norflurazon loss between

application and the first rain. Haloryfop-R ME hydrolysis \ ¡as very rapid, and in this

c¿se the microbial degndation of its metabolites may become the main herbicide

dissipation pathway. The slower dissipation of both herbicides in the autoclaved soils

may be due to the fact that only chernical degradation occurred in the ar¡toclaved soils,

but both microbial and chemical degradation cor¡ld occr¡r in the non-autoclaved soils.

65

The findings of this study show that these two chemicals could pose some

environmental threat once applied. Therefore, caution is needed when these persistent

herbicides a¡e used in Australian vineyards.

The main recommendations for further resea¡ch arising from this study would be:

l. to examine how the physicochemical properties of norflurazon and haloryfop-R ME

afreÆt their dissipation and leaching behaviour in the key Australian viticultural soils;

2. to investigate the behaviour of herbicide adsorption in the six soils;

3. to study the photodegradation rate of norflurazon in the six soils, and identi$ its

degradation pathways and products;

4. to observe and discuss the environment¿l fate of haloryfop-RME and acid in the six

key soils individually;

5. to determine the effects of soil pH and temperature on the dissipation and leaching

behavior¡r of the herbicides in the soils.

6. Finally, the above strdies would be greatly facilitated if access was available to more

sophisticated anal¡ical equipmen! in particular LC-MS instrumentation, on a

routine basis.

Tt¡ough this study, information on the mobility of norflurazon and haloryfop-R ME in

six key Australian viticultr¡ral soils and factors determining their environmental fate was

obtained. It may be useful to the environmental management for pollution control to

meet the goal of clean green production in the Ausüalian wine industry.

66

References

Alisorl L.E., Bollen, W.B. and Moodie, C.D. (1965) Soil organic matter determination

InMethds of Soil Anaþsis (ed. Blaclq C.A.), part l, pp.l353-1364. ASÀMadison, WI.

Alvq A.K. and Singh" M. (1990) Sorption of bromacil, diuron, norflurazon, and

simazine at various horizons in two soils. Bull. Environ. Contam. Toxicol45:365-374.

AWRI (1996) Agrochemicals registered foruse in Australian viticr¡lture: a grid ofregistered agrochemicals and their MRLs in grapes for Australian wine export

destinations. pp.lO plus poster. The Australian Wine Research Institute,

Australia.

Bailey, G.W. and White, I.L. (1970) Res. Rev. 32:29

Bean, 8.W., Abernathy I.R. and Gipson I.R. (1983) Foliar and edaphic studies with

selective grass herbicides. Proc. South. Weed Sci. Soc. 36:152.

Bergstrom, L.F. and Ja¡r¡is, N.I. (1993) Leaching of dichlorprop, bentazon andrCl in wrdisü¡rbed field lysimeters of different agriculü,¡ral soils. Weed Sci

4l.,251-261.

Campbell, R.4., Kastl, P.E., Kropscot! B.E. and Bartels, M.J. (1989) Quantitative

determination of haloryfop in human urine by gas chromatography-mass

spectrometry . lnBiological Monitoringfor Pesticide Ex:posure: Measurement,

Estimation, æd Nsk Reùtction (ed. Wang, R.G.M. et al.), Chapter 20,

pp.25l-26L American Chemical Society. Washington D.C..

Carringer, R.D., Weber, J.B. and Monaco, T.J. (1975) Adsorption-desorption ofselecæd pesticides by organic matter and montnorillonite. J. Agric. Food

Chem. 23:568-572.

Cass, A. (1995) Sustainable viticultr¡ral production - optimizing soil resources.

GWRDC Project CRS 95/1. Grape and Wine Research and Development

Corporation, Australi a.

67

Chiou, C.T. (1989) lnReactions øtdMovement of Orgmic Chemicals in Soils (ed.

Sawhney, B.L. andBrown, K.), pp.l. Soil Sci. Soc. Am. Special Publication

No.22. Madison, WI.

Day, S.R., Schnelle, K., Mrbach, M.J. andZieu,E. (1993) The field leaching

behaviour and soil dissipation ofDE-535. InPraceedings of Brighton

Crop Protection Conference - Weeds, pp.803-808. Vol.2. Brighton, UK.

Essington, M.E., Tyler, D.D. and lVilson, G.V. (1995) Simultaneous fluomeh¡ron and

norflurazon analysis in soil extracts and leachates. Communications in Soil

Science and Plant Analysis. 26 (13'14):2295'23O8.

Eisenbeiss, F. and Sieper, H. (1973) The potential use of High-Performance Liquid

Chromatography in residue analysis. I. Chromatogr. 83:439446.

Fourie, J.C. (1992) Herbigation in a vineyard: persistence of four pre-emergence

herbicides in a sandy loam soil. South African fournal for Enology and

Viticultr¡re . 13 Q):6a-70.

Fourie, I.C. (1993) Herbigation in a vineyard: eflicacy and persistence of five

prÈemergence herbicides in a sandy loam soil. Sor¡th African Journal for

Enology and Viticultr¡re. 14 (l):3-10.

Fran( R. and Sirons, G.I. (1979) Afazine: Its Use in Corn Production and Its Loss to

Stream Water in Southern Ontario, 1875-1977. Sci. Total Environ. 12:223-239.

Franklin, R.E., Quisenberry, V.L., Gossett, B.J. and Murdock, E.C. (1994) Selection

of herbicide alternatives based on probable leaching to groundwater. Weed

Technol. 8:6-16.

Gan, f.Y. and Koskinen, W.C. (1993) Pesticide fate and behaviour in soil at elevated

concentrations. In Pesticide Remediation in Soils and Ílater (ed. Kearney, P.

and Roberts, T.), pp.59-84. Published John Wiley & Sons Ltd., USA.

Glofelty, D.E., Taylor, 4.W., Isens€e, 4.R., Iersey, f. and Glenn, S. (1984) Atrazine

and simazine movementtoWye River esûrary. J. Environ, Qual. l3:ll5-121.

68

GWRDC "Annual Report 1995-96" (1996), pp.l16. Grape and Wine Research and

Development Corporation, Ausüalia.

Hajslova, J., Pudil, F., Jehlickova,Z.,Yiden,I. and Davidek, J. (1988) Gas

chromatographic-mass spectrometric investigation of phenorypropanoic

acid derivatives possessing herbicidal activity. Journal of Chromatography

438:55-60.

Ilallberg G.R. (1988) Agricultural chemicals in grourdwater: extent and implications

Am. J. Alærn. Agtc. 2:3-15.

Hammond, L.E., Handly, f.V., Swann, R.L. and llanson, C.L. (1982) Soil residual

activity of Dowco 453 herbicide. Proc. Norttr Cent. Weed Conúol Conf.

37:76.

Hassett, J.J. and Banwar! W.L. (1989) lnReactions andMovement of Organic

Chemicals in Soils (ed. Sawhney, B.L. and Brown, K.), pp.3l. Soil Sci.

Soc. Am. Special PublicationNo.22. Madison, WL

Hiltbold, A.E. and Buchanan, G.A. (1977) Influence of soil pH on persistence of

afraane in the freld. rileed Sci. 25(6):515-520.

Hubbs, C.W. and Lavy, T.L. (1990) Dissipation of norflurazon and other persistent

herbicides in soil. Weed Sci. 38(l):81-88.

Johnson, W.E., Fendinger, N.J. and Plimmer,I.R. (1991) Solid-phase extaction ofpesticides from water: Possible interferences from dissolved organic material.

Arial. Chem. 63: 1510-1513.

Jury, W.4., Winer, 4.M., Spencer,}V.F. and Focht, D.D. (1987) Transport and

tansformations of organic chemicals in the soil-air-water ecosystem. Rev

Environ. Contam. Toxicol. 99: I 19-164.

Kearney, P.C. (1994) Intoduction. lnMechqtisms of Pesticide Movement into

Gromdwater (ed. Richa¡d C. Honeycutt and Daniel J. Schabacker), pp. XI-

)il/. Lewis Publishers, BocaRaton.

69

Keeling,I.W., Lloyd, R.W. and Abernathy,I.R. (1989) Rotational cfop response to

repeated applications of norflurazon. Weed Technol. 3:122'125'

Kvien, I.S. and Banls, P.A. (1985) Soil surface degradation of norflurazon.

Abstr. Weed Sci. Soc. Am. 25:95.

Mclaren, R.G. and Cameron, K.C. (1990) Physical and mechanical cha¡acteristics.

In þil Science: .,4n intúuction to the properties øtd møtagement of Nevt

7¿aland soils, Chapter 5, pp.63. Oxford University Press. Auckland, NZ.

Mossler, M.4., Shilling, D.G., Mlgram, K.E. and Querns, R. (1995) A quality control

standa¡d for fluridone analysis. I. Aquat. Plant Manage. 33:23'24.

Mueller, T.C., Jones, R.E., Bush, P.B. and Banks, P.A. (1992) Comparison of PRZM

and GLEAIvÍS computer model predictions with field data for alachlor,

metibuzin and norflurazon leaching. Environmental Toxicology and

Chemistry. llQ):a27 436.

Northcote, K.H. (1995) Soils and Australian Viticultr¡re. lnViticalnre (ed. B.G.

Coombe and P.R. Dry), pp.6l-90. Vol.l Resources. Winetitles: Adelaide,

Australia.

Rahn, P.R. and R.L. Zimdahl (1973) Soil degradation of two phenyl pyridazinone

herbicides. Weed Sci. 2l:314-317.

Reddy, K.N. and Singh, M. (1993) Effect of acrylic polymer adjuvants on leaching of

bromacil, diuron, norfh¡razon, and simazine in soil columns. Bull. Environ.

Contam. Toxicol. 50:449457.

Reddy, K.N., Singh, M. and Alvg A.K. (1992) Sorption and desorption of diuron and

norflurazon in Florida citn¡s soils. Water, Air, and Soil Pollution. 64:487494.

Rich S.K., Slife, F.W. and Banwarl W.L. (1987) Adsorption of selective grass

herbicides by soils and sediments. Weed Sci. 35:282-288.

70

Schroeder, L and Banl6, P.A. (1986a) Persistence of norfluÍa:zonin five Georgia

soils. Weed Sci. 34:595-599.

Schroeder, J. and Banks, P.A. (1986b) Persistence and activity of norflurazon and

fluridone in five Georgia soils under controlled conditions. Weed Sci.

34:599-6O6.

Senseman, S.4., Massey, J.H., Lauy, T.L. and Daniel, T.C. (1994) Preventing water

contamination at pesticide mixing-loading sites. A¡k. Farm Res. 43(5):14-15.

Singh, M., Castle, W.S. and Achhireddy, N.R. (1985) Movement of bromacil and

norflurazon in a sandy soil in Florida. Bull. Environ. Contam. Toxicol.

35:279-284.

Southwich L.M., Willis, G.H., Bengtson, R.L. and Lormand, T.J. (1990) Atrazine

and Metolachlor in Subsurface Drain Water in Louisiana. I. In, Drain Engin.

ll6(l):16-23.

Southwicþ L.M., Willis, G.H. and Bengtson, R.L. (1993) Leaching losses ofnorflurazon through Mississippi River Alluvial Soil. Bull. Environ. Contam.

Toxicol. 50:441-448.

Stagnitti, F., Parlange, J.-Y., Steenhuis, T.S., Boll, J., Pivertz, B. and 4., B.D. (1995)

Transport of moistr¡re and solutes in the unsaturated zone by preferential flow.

lnEnviroranental Hyùologt (ed. Singh, V.P.), Vol.15, pp.l93'224. Kluwer

Academic Publishers.

Steenhuis, T.S., ñjsse4 B.M., Stagniüi, F. and Parlange, J.-Y. (1991) Preferential

Solute Movement in Stn¡cn¡red Soils: Theory and Application. Instin¡te ofEngineers, Ausfialiq National Conferrence. No. 9lll 9. 3 :925-930.

Tan, S. and Singh, M. (1995a) Effects of cationic surfactants on leaching of bromacil

and norflurazon. Bulletin of Environmental Contamination and Toxicology.

55(3):359-365.

TarL S. and Singh, M. (1995b) Leaching of bromacil and norfh¡razon as affected by

herbicide mixture. J. Environ. Qual. 24:970-972.

7l

Tomli4 Clive D.S., ed. (1994) tlaloryfop. lnThe Pesticide Mamtal, incorporating

Ihe Agræhemicals Hødbook,lOth edition, pp.55l-554. The British Crop

Protection and The Royal Society of Chemistry, UK.

Tomlir\ Clive D.S., ed. (1994) Norflurazon. ln 7Tæ Pesticide Marrual, incorporating

Ihe Agrochemicals Høtdbook, lOth edition, pp.74O-741. The British Crop

Protecton and The Royal Society of Chemistry, UK.

rilillian, W.T., Mueller, T.C., llayes, R.M., Bridges, D.C. and Snipes, C.E. (1997)

Norflurazon adsorption and dissipation in three southern soils. Weed Sci.

45:301-306.

Willian, W.T. and Mueller, T.C. (1994) Liquid chromatographic determination ofnorflurazon and its initial metabolite in soil. J. Assoc. Otr Anal. Chem.

77:752-755.

72