ARTICLE IN PRESS

Int. J. Hyg. Environ.-Health 210 (2007) 121–132

1438-4639/$ - se

doi:10.1016/j.ijh

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Pesticide poisoning of farm workers–implications of blood test results

from Vietnam

Susmita Dasguptaa,�, Craig Meisnera, David Wheelera, Khuc Xuyenb, Nhan Thi Lamc

aDevelopment Economics Research Group, Infrastructure and Environment Unit, World Bank, 1818 H Street,

Washington, DC MSN2-205, USAbNational Institute of Occupational and Environmental Health, Hanoi, VietnamcCentral Medical Laboratory, Tien Giang Preventative Medicine Centre, Hanoi, Vietnam

Received 25 May 2005; received in revised form 8 August 2006; accepted 14 August 2006

Abstract

Information on the health impacts of pesticides is quite limited in many developing countries, with many surveysrelying solely on farmer self-assessments of their health status. To test the reliability of self-reported data, an acetylcholinesterase enzyme (AChE) blood test was conducted for 190 rice farmers in the Mekong Delta, Vietnam. Resultsreveal a high prevalence of pesticide poisoning by organophosphate and carbamate exposure, where over 35% of testsubjects experienced acute pesticide poisoning (a reduction of AChE 425%), and 21% chronically poisoned (466%AChE reduction). Using the medical test results as benchmarks, we find that farmers’ self-reported symptoms havevery weak associations with actual poisoning.

To investigate the possible determinants of pesticide poisoning, a probit model was constructed with pesticideamount, toxicity, training, and the use of protective measures as explanatory variables. The results indicate thatalthough the absolute amount of pesticides used does not increase the probability of poisoning, a 1% increase in theuse of highly hazardous pesticides (WHO Ia or Ib) increases the probability of poisoning by 3.9% and an increased useof protective measures decreases the probability of poisoning by 44.3%. We also find significant provincial differencesin poisoning incidence after we control for individual factors. The provincial effects highlight the potential importanceof negative externalities, and suggest that future research on pesticide-related damage should include information onlocal water, air and soil contamination.r 2006 Elsevier GmbH. All rights reserved.

Keywords: Organophosphates and carbamates; Blood cholinesterase test; Farm workers; Vietnam

Introduction

Indiscriminate use and improper handling of syntheticpesticides in agriculture have caused serious problemsfor human health in many developing countries during

e front matter r 2006 Elsevier GmbH. All rights reserved.

eh.2006.08.006

ing author. Tel.: +1202 473 2679.

ess: sdasgupta@worldbank.org (S. Dasgupta).

the past three decades. However, the true extent of theproblem is hard to determine for a variety of reasons.First, farmers with mild pesticide poisoning often do notreport because treatment services are costly, inaccessi-ble, or fear that drawing attention to themselves mayresult in the loss of employment opportunities. Second,health-care professionals in rural areas often fail tocorrectly diagnose poisoning, as many of the related

ARTICLE IN PRESSS. Dasgupta et al. / Int. J. Hyg. Environ.-Health 210 (2007) 121–132122

symptoms are quite general in nature or mimic othercommon health problems (e.g., headaches, dizziness,vomiting) (FAO, 2001). In Vietnam, hospital admissionrecords attribute 11% of all poisonings to pesticidemisuse: approximately 840 poisonings in 53 cities andprovinces in 1999 (Poison Control Center, VietnamMinistry of Health, 2000); however, a recent WHOreport for Vietnam states that there were a total of 7170pesticide poisoning cases in 2002 (World HealthOrganization (WHO), 2005). The WHO and the UnitedNations Environment Program (UNEP) estimate thatthere are 50 cases of poisoning for every case reportedand registered, or between 1 and 5 million agriculturalworkers per year (World Resources Institute et al.,1998). At least 20,000 workers die from exposure everyyear, the majority in developing countries (WorldHealth Organization (WHO), 1990; Kishi et al., 1995;Pimental et al., 1992; Rosenstock et al., 1991).

Although the health hazards of pesticides are serious,support from policy makers for remedial measures hasbeen lukewarm in developing countries. There is awidespread concern about diverting resources to alter-native pest control methods when poverty, illiteracy andinfant mortality are still major problems. In part, theresistance of policy makers is due to uncertainty aboutthe severity of the problem, its sources, and suitableinterventions. Their uncertainty is understandable, sincesystematic studies of the health effects of pesticides arescarce. Most existing studies rely on farmers’ self-reported symptoms, as appropriate pathological testsare costly and relatively difficult for many developing-country institutions to administer.

To assess the potential health hazards of pesticides,and the reliability of self-reported data, the World Bankcollaborated with the Vietnam Association of Occupa-tional Health (VINOH) to study pesticide poisoningamong 190 Mekong Delta rice farmers during thesummer–autumn–winter growing periods in 2004. Thestudy included clinical exams by doctors from theVINOH, along with blood tests for cholinesteraseinhibition (reductions in acetyl cholinesterase enzyme(AChE)) due to contamination by organophosphate andcarbamate use. Epidemiological studies have linkedcarbamates (CM) and organophosphates (OP) withfetal death, hormonal changes, DNA damage, birthdefects, and abnormal sperm, ovaries and eggs. Inaddition, OP, as a class of insecticides, have been linkedwith Non-Hodgkin’s lymphoma, leukemia, and lungcancer. In children OP have been linked to aplasticanemia, the failure of the bone marrow to produceblood cells, and leukemia. Children with asthma mayhave severe reactions to OP in particular (Zahm et al.,1997).

Initial results from the survey reveal a high prevalence ofpesticide poisoning among farmers (35%), 14% of whichwas acute (AChE reduction of 425%) and 21% chronic

(AChE reduction of 466%). Comparing the blood testresults with farmer self-reported health ailments we find avery low correlation (p ¼ 0.05–0.17). Using furtherinformation from the survey, we also estimated a probitmodel of the likelihood of pesticide poisoning as explainedby the amount and relative toxicity of pesticides in use,determinants of exposure, and provincial environmentaleffects. Although the results suggest that increases in theamount of pesticides do not lead to an increase in theprobability of poisoning (defined as a reduction of AChE),the use of highly toxic (WHO category Ia or Ib) pesticidesincreases this probability. In addition, the probability ofpoisoning decreases with the number of protectivemeasures that the farmer is currently using. It may bethe case that farmers are more hazard conscious whenusing larger amounts, however, are not fully aware of therelative toxicity of the pesticides they are using. Our resultsalso indicated strong provincial effects with relativelyhigher prevalence rates in the province of Tra Vinh. Thismay provide general empirical support to the reports ofpervasive contamination of the air, soil or water, bypesticide overuse and misuse (Huan and Thiet, 2000).

Pesticide use in Vietnam

Like many developing countries, Vietnam has pro-moted the use of pesticides to expand agricultural landand increase output per acre. The Socialist Republic ofVietnam began extensive use of pesticides in the 1950s,when agricultural production was limited to coopera-tives, collective farms, and state farm enterprises.During this period, pesticides were not regulated andagronomists and farmers had little knowledge of thehazards of pesticide use. Pesticide applications werecompleted by specialized teams of 4–5 farmers, whoworked in conjunction with the Plant ProtectionDepartment (PPD). The PPD supplied pesticides atsubsidized prices and recommended spraying on acalendar basis, with little or no attention to fieldconditions (Pincus, 1995; Chung and Dung, 2002). Since1986, the pesticide market has been liberalized, andthere are currently nine state-owned and four privatelyowned formulation plants in Vietnam. The governmentis no longer granting licenses for new formulationplants, since it has decided that excess capacity exists.

After the land reforms of 1988, farms were recognizedas autonomous production units and householdsassumed control over all stages of production, includingpesticide use. Applications doubled during the followingdecade (Fig. 1), reaching over 30,000 tons per annum in1996 (FAO, 2004).

Expanded applications have been accompanied bywidespread use of chemicals that are hazardous forhuman health and the environment. A nation-wide

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0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

1991 1992 1993 1994 1995 1996 1997 1998 1999

Met

ric

ton

s

Fig. 1. Pesticide use in Vietnam, 1990–1999.

S. Dasgupta et al. / Int. J. Hyg. Environ.-Health 210 (2007) 121–132 123

survey conducted by the PPD in 2000 found 2500 kg ofbanned pesticides in use (methamidophos, DDT andother chemicals), along with 4753 l and 5645 kg ofillegally imported or counterfeit pesticides; many ofwhich were WHO I or II OP and CM (Plant ProtectionDepartment (PPD), 2000). Another survey in August2000, among 480 farmers in four provinces in the South,found that 97% used pesticides more intensively thanproduct labels recommended, and nearly 95% of farm-ers disposed residual pesticides into canals or ditches,reapplied it to the same crops, or sprayed crops thatwere not identified for initial use (Huan and Thiet,2000). So, the survey evidence thus far suggests thatfarmers are not only using increasing amounts of toxicpesticides, but have been careless in their use anddisposal of such products.

Cholinesterase testing

Cholinesterase is one of many important enzymesneeded for the proper functioning of the nervoussystems of humans, other vertebrates, and insects.Certain chemical classes of pesticides, such as OP andCM, kill undesirable insect pests by interfering with, or‘inhibiting’, cholinesterase. While cholinesterase-inhibit-ing pesticides are intended for insects, they can also bepoisonous to humans in some situations.

Humans have three types of cholinesterase: red bloodcell (RBC) cholinesterase, called ‘‘true cholinesterase’’;plasma cholinesterase, called ‘‘pseudocholinesterase’’;and brain cholinesterase. RBC cholinesterase is thesame enzyme that is found in the nervous system,while plasma cholinesterase is made in the liver. Whena cholinesterase blood test is taken, two types ofcholinesterase can be detected. Physicians find plasmacholinesterase readings helpful for detecting the early,acute effects of organophosphate poisoning, while RBCreadings are useful in evaluating long-term, or chronic,exposure.

Human exposure to cholinesterase-inhibiting pesti-cides can result from inhalation, ingestion, or eye or skin

contact during the manufacture, mixing, or applicationsof these chemicals. Anyone exposed to cholinesterase-inhibiting pesticides can develop lowered cholinesteraselevels. Signs and symptoms of cholinesterase inhibitionfrom exposure to CM or OP include the following:

1.

In mild cases (within 4–24 h of contact): tiredness,weakness, dizziness, nausea and blurred vision.

2.

In moderate cases (within 4–24 h of contact): head-ache, sweating, tearing, drooling, vomiting, tunnelvision, and twitching.

3.

In severe cases (after continued daily absorption):abdominal cramps, diarrhea, muscular tremors,staggering gait, pinpoint pupils, hypotension, slowheartbeat, breathing difficulty, and possibly death, ifnot promptly treated by a physician.

The cholinesterase test is a blood test used to measurethe effect of exposure to cholinesterase-inhibitinginsecticides. Both plasma (or serum) and RBC choli-nesterase are generally tested. The purpose of checkingcholinesterase levels is to alert exposed people to anychange in the level of this essential enzyme before it cancause serious illness. Following the guidelines in theTechnical Manual on Occupational and EnvironmentalHealth of Vietnam (1993), a 425% depression incholinesterase indicates that low acute poisoning hastaken place; a 433% drop signals high acute poisoning;and a 466% decline indicates severe or chronicpoisoning.

Subjects and methods

To investigate the health impacts of pesticide use,structured questionnaires designed by the World Bankteam were used to collect information on farmingsystems, pesticide use and practices, applicator precau-tions, protective measures, and self-reported poisoningsymptoms. All participating farmers were then exam-ined by doctors from the Centre of Occupational andEnvironmental Health (COEH) of the VINOH (Hanoi,Vietnam). For the purposes of demographic andpesticide use variation, the survey sample was stratifiedamong rice farmers in 10 districts of 5 provinces in theMekong Delta (An Phu and Chau Thanh (An Giangprovince), Thot Not and Vi Thanh (Can Tho province),Tan Thanh and Thu Thua (Long An province), Cai Layand Cho Gao (Tien Giang province), and Tra Cuand Tieu Can (Tra Vinh province) in the Mekong Delta.To minimize possible reporting bias, the surveyedfarmers were assured of anonymity). The primarycrop in production was rice with 44% of total pesticideuse in the form of insecticides (those normallyassociated with OP and CM). The farmers were mostly

ARTICLE IN PRESSS. Dasgupta et al. / Int. J. Hyg. Environ.-Health 210 (2007) 121–132124

male (three females were examined), ranging in age from15 to 70 years (average of 39), with an average of 8 yearsof formal education; 74% reported that they smoke and48% reported drinking alcoholic beverages at least oncea week. Over 36% of the respondents received trainingon the safe use and handling of pesticides, 53% had IPMtraining and 67% used some form of IPM technology inproduction.

Table 1. Pesticides used by sample farmers

Trade name Main active ingredient (a.i.)

PADAN Cartap

FUJI-ONE Isoprothiolane

BASSA BPMC (Fenobucarb)

SAT TRUNG

DAN

Thiosultap-sodium (Nereistoxin/Dimehypo)

TILT SUPER Difenoconazole

KUMULUS Sulfur

FUAN Isoprothiolane

SOFIT Pretilachlor

MECO Butachlor

CANTANIL Butachlor

RABCIDE Fthalide

ROVRAL Iprodione

BEAM Tricyclazole

CARBENZIM Carbendazim

MONSTER Acephate

BASUDIN Diazinon

ANVIL Hexaconazole

2,4-D 2,4-D

OK 2,4-D

KINALUX Quinalphos

FURADAN Carbofuran

VALIDACIN Validamycin (Validamycin A)

KITAZIN Iprobenfos (Iprobenphos)

ARIN Carbendazim

TRIDOZOLE Tricyclazole

ADMIRE Imidacloprid

TILT Propiconazole

NETOXIN Thiosultap-sodium (Nereistoxin/Dimehypo)

SUMITHION Fenitrothion

TILLER’S MCPA

VITASHIELD Chlorpyrifos

KASAI Fthalide

MAMBA Glyphosate

Zin Zineb

REGENT Fipronil

FLASH Tricyclazole

CATODAN Thiosultap-sodium (Nereistoxin/Dimehypo)

DITHANE M 45 Mancozeb

PERAN Permethrin

NOMINEE Bispyribac-sodium

BUTYL Buprofezin

HOPSAN BPMC (Fenobucarb)

THIODOL Endosulfan

General pesticide application by farmers averaged0.27 kg of active ingredient (a.i.) per application and anaverage of 7 applications per season. For pesticides usedby sample farmers see Table 1. In terms of thecomposition of pesticide use by farmers, Table 2classifies pesticides according to their chemical classand by the seasonality of application. OP and CM werefound to be one of the highest in terms of their

Class Pesticide

amount

(kg a.i.)

WHO

classificationa

2-dimethylaminopropane-

1,3-dithiol

63.919 II

Dithiolane 22.193 III

Carbamate 20.895 II

2-dimethylaminopropane-

1,3-dithiol

19.857

DMI: triazole 18.814 III

Multi-site: inorganic 16.768 U

Dithiolane 16.564 III

Chloroacetamide 16.235 U

Chloroacetamide 15.163 U

Chloroacetamide 7.765 U

MBI: reductase 7.681 U

Dicarboximide 7.202 U

MBI: reductase 6.996 II

Benzimidazole 6.566 U

Organophosphate 6.184 III

Organophosphate 5.787 II

DMI: triazole 5.555 U

Phenoxycarboxylic acid 5.542 II

Phenoxycarboxylic acid 5.448 II

Organophosphate 4.500 II

Carbamate 4.418 Ib

Antibiotic 4.074 U

Phosphorothiolate 3.870 III

Benzimidazole 3.558 U

MBI: reductase 2.862 II

Neonicotinoid 2.170 II

DMI: triazole 2.145 II

2-dimethylaminopropane-

1,3-dithiol

2.124

Organophosphate 2.010 II

Phenoxycarboxylic acid 1.993 III

Organophosphate 1.926 II

MBI: reductase 1.886 U

Glycine derivative 1.845 U

Multi-site: alkylenebis

(dithiocarbamate)

1.792 U

Fiprole 1.739 II

MBI: reductase 1.733 II

2-dimethylaminopropane-

1,3-dithiol

1.661

Multi-site: alkylenebis

(dithiocarbamate)

1.360 U

Pyrethroid 1.224 II

Pyrimidinyloxybenzoic 1.095 U

Unclassified 1.071 U

Carbamate 0.951 II

Cyclodiene 0.882 II

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Table 1. (continued )

Trade name Main active ingredient (a.i.) Class Pesticide

amount

(kg a.i.)

WHO

classificationa

TIGINON Thiosultap-sodium (Nereistoxin/Dimehypo) 2-dimethylaminopropane-

1,3-dithiol

0.862

CYPER ALPHA Alpha-cypermethrin Pyrethroid 0.834 II

WHIP’S Fenoxaprop-P-ethyl Aryloxyphenoxypropionate 0.793 U

FACET Quinclorac Quinolinecarboxylic acid 0.726 U

BONANZA Cyproconazole DMI: triazole 0.710 III

ANTAPHOS Alpha-cypermethrin Pyrethroid 0.660 II

FUDOMYL Benomyl Benzimidazole 0.610 U

FENKILL Fenvalerate (Sumicidin) Pyrethroid 0.600 II

FOLICUR Tebuconazole DMI: triazole 0.513 III

FASTAC Alpha-cypermethrin Pyrethroid 0.512 II

DIBUTA Butachlor Chloroacetamide 0.468 U

VINETOX Thiosultap-sodium (Nereistoxin/Dimehypo) 2-dimethylaminopropane-

1,3-dithiol

0.450

BENLATE Benomyl Benzimidazole 0.400 U

FOLPAN Folpet Multi-site: phthalimide 0.390 U

SIRIUS Pyrazosulfuron-ethyl Sulfonylurea 0.357 U

NUSTAR Flusilazole DMI: triazole 0.318 III

ACTARA Thiamethoxam Neonicotinoid 0.303 III

MIMYL Benomyl Benzimidazole 0.297 U

TUNG SONG Thiosultap-sodium (Nereistoxin/Dimehypo) 2-dimethylaminopropane-

1,3-dithiol

0.295

APPLAUD Buprofezin Unclassified 0.295 U

PHANTOM Diazinon Organophosphate 0.288 II

FENBIS Fenvalerate (Sumicidin) Pyrethroid 0.250 II

KARATE Lambda-cyhalothrin Pyrethroid 0.246 II

ALPHAN Alpha-cypermethrin Pyrethroid 0.241 II

DECIS Deltamethrin Pyrethroid 0.241 II

MOTOX Alpha-cypermethrin Pyrethroid 0.214 II

KISAIGON Iprobenfos (Iprobenphos) Phosphorothiolate 0.210 III

PERKILL Permethrin Pyrethroid 0.203 II

BINHNOMYL Benomyl Benzimidazole 0.200 U

OFATOX Fenitrothion Organophosphate 0.200 II

NURELLE Chlorpyrifos Organophosphate 0.195 II

TREBON Etofenprox Non-ester pyrethroid 0.195 U

SUNRICE Ethoxysulfuron Sulfonylurea 0.174 U

ACOVIL Carbendazim Benzimidazole 0.168 U

VIBASU Diazinon Organophosphate 0.160 II

CLINCHER Cyhalofop-butyl Aryloxyphenoxypropionate 0.151 U

VICARBEN Carbendazim Benzimidazole 0.135 U

SUMI ALPHA Esfenvalerate Pyrethroid 0.128 II

CYPERAN Cypermethrin Pyrethroid 0.121 II

TIGITHION Dimethoate Organophosphate 0.120 II

ALFATHRIN Alpha-cypermethrin Pyrethroid 0.113 II

DEROSAL Carbendazim Benzimidazole 0.112 U

SHACHONG

SHUANG

Thiosultap-sodium (Nereistoxin/Dimehypo) 2-dimethylaminopropane-

1,3-dithiol

0.099

PYANCHOR Pyribenzoxim Pyrimidinyloxybenzoic 0.088

TOPSIN—M Thiophanate-methyl Benzimidazole precursor 0.069 U

BINH-58 Dimethoate Organophosphate 0.064 II

SHERPA Cypermethrin Pyrethroid 0.060 II

TIPTOP Propiconazole DMI: triazole 0.050 II

TUNG RIN Cypermethrin Pyrethroid 0.048 II

KASUMIN Kasugamycin Hexopyranosyl antibiotic 0.031 U

ANNONGVIN Hexaconazole DMI: triazole 0.024 U

STAR Pyrazosulfuron-ethyl Sulfonylurea 0.020 U

SOUTHSHER Cypermethrin Pyrethroid 0.011 II

A total number of 1252 applications by 190 farmers.aWHO classification: Ib—highly hazardous; II—moderately hazardous; III—slightly hazardous; U—unlikely to present acute hazard in normal

use, BCPC, 2003.

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PRES

S

Table 2. Number of applications, by chemical class and season

Class No. of applications Pesticide amount (kg a.i.) Intensity (kg a.i./appl.)

Summer–autumn Autumn–winter Summer–autumn Autumn–winter Summer–autumn Autumn–winter

2-dimethylaminopropane-1,3-dithiol 106 37 78.36 10.91 0.74 0.29

Chloroacetamide 52 36 29.55 10.08 0.57 0.28

Dithiolane 49 33 31.25 7.51 0.64 0.23

DMI: triazole 208 92 22.19 5.93 0.11 0.06

Carbamate 27 10 24.63 1.63 0.91 0.16

Organophosphate 20 16 12.76 8.68 0.64 0.54

MBI: reductase 57 9 19.99 1.16 0.35 0.13

Multi-site: inorganic 3 2 3.97 12.80 1.32 6.40

Phenoxycarboxylic acid 18 16 8.77 4.22 0.49 0.26

Benzimidazole 14 10 7.23 4.82 0.52 0.48

Dicarboximide 16 11 6.56 0.64 0.41 0.06

Pyrethroid 71 51 3.50 2.21 0.05 0.04

Phosphorothiolate 6 4 3.20 0.88 0.53 0.22

Antibiotic 31 34 2.90 1.17 0.09 0.03

Multi-site: alkylenebis (dithiocarbamate) 1 4 1.36 1.79 1.36 0.45

Neonicotinoid 22 7 2.43 0.04 0.11 0.01

Glycine derivative 1 0 1.85 0.00 1.85 —

Fiprole 34 22 1.03 0.71 0.03 0.03

Unknown 8 2 1.32 0.05 0.16 0.03

Pyrimidinyloxybenzoic 35 3 1.12 0.06 0.03 0.02

Aryloxyphenoxypropionate 25 8 0.68 0.26 0.03 0.03

Cyclodiene 0 2 0.00 0.88 — 0.44

Quinolinecarboxylic acid 3 4 0.27 0.45 0.09 0.11

Sulfonylurea 15 9 0.41 0.14 0.03 0.02

Multi-site: phthalimide 0 1 0.00 0.39 — 0.39

Non-ester pyrethroid 1 2 0.05 0.15 0.05 0.07

Benzimidazole precursor 1 0 0.07 0.00 0.07 —

Hexopyranosyl antibiotic 2 1 0.01 0.02 0.01 0.02

Total 826 426 265.46 77.58

A total number of 1252 applications by 190 farmers. Chemical class was derived from the British Crop Protection Council e-Pesticide Manual, Thirteenth Edition (BCPC, 2003).

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application intensity (kg a.i./application), especiallyduring the summer–autumn season. They also appearto be more prevalent in terms of the composition ofoverall product use.

In terms of the protective measures taken to minimizethe effects of pesticide exposure, most reported the useof basic requisites including masks (61%) and hats(49%), however, the use of glasses (20%), gloves (18%)and shoes (1.4%) was strikingly lower (Table 3).

Using clinical exam results and self-reported symp-toms, the team then selected potentially poisonedfarmers for the cholinesterase inhibition test. The initialselection criteria used to screen patients included head-aches, nausea, drooling, fatigue, dizziness, tearing, pin-point pupils, shortness of breath, muscle weakness andconvulsion. The clinical exams also screened farmers forthe prevalence of skin disease, abnormal blood pressure,respiratory and cardio-vascular disease. In each case, a0.4ml blood sample drawn from the farmer’s fingertipwas used to test the level of active cholinesterase enzyme(AChE) in erythrocyte and plasma (Test-Mate-Kit,EQMR-USA). OP and CM have unique effects on

Table 3. Number of protective measures taken while applying pes

Class Trousers Shirt

DMI: triazole 291 290

2-dimethylaminopropane-1,3-dithiol 130 130

Pyrethroid 111 114

Chloroacetamide 86 86

Dithiolane 80 80

Antibiotic 58 54

MBI: reductase 66 66

Fiprole 56 55

Organophosphate 36 35

Carbamate 37 36

Pyrimidinyloxybenzoic 36 36

Phenoxycarboxylic acid 29 31

Aryloxyphenoxypropionate 31 31

Neonicotinoid 28 28

Sulfonylurea 24 24

Benzimidazole 19 19

Dicarboximide 26 25

Unknown 10 10

Phosphorothiolate 10 10

Quinolinecarboxylic acid 6 6

Multi-site: inorganic 5 5

Non-ester pyrethroid 3 3

Multi-site: alkylenebis (dithiocarbamate) 5 5

Hexopyranosyl antibiotic 2 2

Cyclodiene 2 2

Glycine derivative 1 1

Benzimidazole precursor 1 1

Multi-site: phthalimide 1 1

Total (out of 1252 applications) 1190 1186

Prevalence (%) 95.0 94.7

A total number of 1252 applications by 190 farmers.

cholinesterase enzymes. They act so as to inhibitacetylcholine hydrolysis, a necessary task for synapticresponse in the central nervous system. Stimulatingsignals are discontinued by a specific type of cholines-terase enzyme, acetylcholinesterase, which breaks downthe acetylcholine. These important chemical reactionsare continuous with acetylcholine causing stimulationand acetylcholinesterase ending the signal. If cholines-terase-affecting insecticides are present in the synapseshowever, this process is thrown out of balance. Thepresence of cholinesterase inhibiting chemicals preventsthe breakdown of acetylcholine. Acetylcholine can thenbuild up, causing a ‘‘jam’’ in the nervous system. Thus,when a person is exposed to cholinesterase inhibitingcompounds, the body is unable to break down theacetylcholine.

The duration between exposure and the blood testaveraged 24–96 h among the sample of farmers. Theblood samples were then analyzed at the central medicallaboratory of Tien Giang province, following theguidelines of the Technical Manual on Occupationaland Environmental Health of Vietnam (1993) and the

ticides, by chemical class

Mask Hat Glasses Gloves Shoes

197 153 65 60 6

86 72 25 27 0

71 55 24 20 1

64 45 16 15 0

50 36 14 11 0

30 35 14 10 1

42 32 12 17 2

32 27 8 9 3

22 18 3 7 0

20 21 7 9 0

25 18 9 8 2

20 20 8 6 0

18 20 11 4 1

18 13 6 3 0

16 13 5 9 1

15 12 4 7 0

13 10 5 2 0

7 5 3 1 0

5 2 1 1 0

3 3 4 0 0

2 2 1 1 0

1 1 1 0 0

2 0 1 0 0

1 1 0 0 0

2 2 2 0 0

0 1 0 0 0

0 0 0 0 0

1 1 0 0 0

763 618 249 227 17

60.9 49.4 19.9 18.1 1.4

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color matching methods of Fleisher and Pope (1954).Acute and chronic poisoning were defined as low acute(a reduction of AChE in red cells and in plasma425%),high acute (a reduction of AChE in red cells and inplasma 433%), and chronic poisoning (a reduction ofAChE in red cells 466%).

Results and discussion

Survey response on reported symptoms after mixingand spraying pesticides was quite prevalent among all190 farmers. In Table 4, the most commonly reportedsymptoms were dermal (skin irritation: 66%), neurolo-gical (headache: 61%; dizziness: 49%), ocular (eyeirritation: 56%), and respiratory (shortness of breath:44%). Other studies in Vietnam report similar findingsfor self-reported ailments. In a study of 369 tea farmers,Xuyen et al. (1998) report similar incidence rates forheadaches (44%), nausea (15%), skin irritation (58%)and dizziness (24%). Du and Phoung. (2003) in a studyof 2000+pesticide applicators report an incidence ofheadaches (60%) and dizziness (27%); while a survey of1,982 farmers by Hong et al. (1999) reports the incidenceof fatigue (26%), skin irritation (20%), headaches(20%), dizziness (20%) and eye irritation (4%).

Most of the surveyed farmers (88%) reported multiplesymptoms, with an average of 4 and a maximum of 9.Among farmers reporting at least one symptom, 82%attributed them to pesticide use. Subsequent clinicalexams by the VINOH doctors revealed a high pre-valence of skin disease (41%), abnormal blood pressure(18%), and a low incidence of respiratory disease (3%)and heart disease (1%).

Building upon the initial screening exam, the medicalteam administered blood tests to 190 farmers to check forcholinesterase enzyme inhibition from exposure to organo-phosphate and carbamate pesticides. The results displayedin Fig. 2 indicate that 35%, or 67 farmers, had an AChEreduction of at least 25% (acute poisoning) and of this,21% showing a reduction greater than 67% (chronicpoisoning). These prevalence rates appear to be consistentwith those found elsewhere in Vietnam as well as in otherdeveloping countries (Hruska and Corriols, 2002; Huang,2002; Kunstadter et al., 2001; Soogarun et al., 2003). Asurvey of coffee farmers in Dak Lak found declines inAChE of 430% in 7.3% of subjects; 421–30% in 17.7%and 410–20% by 23.4% of subjects (Dien and Vong,2003). Another study by Thuy et al. (2003) of rice farmers inSouthern Vietnam found that 44% of farmers had ‘normal’cholinesterase enzyme levels, 42.2% were within ‘safe’ levelsand 13.8% were at risk. In another survey of 213 workersbottling and packing pesticides, Ky and Ngoc (1998) founddecreases in overall AChE by 34.7% of the sample,decreases of AChE in red cells in 33.80% of the sampleand reductions of AChE of 430% in 8.9% of workers.

Similar findings have also been recorded in China,where the rapid development of organophosphate-basedinsecticides has led to an increasing trend of organopho-sphate poisoning. Huang (2002) cites acute organopho-sphate poisoning rates of 18% among all recordedpesticide poisonings, or in excess of 39,000 cases,between 1992 and 1995. Subsequent medical studiesconducted from 1996 to 2000 revealed AChE reductionsin the range of 5–73% among occupationally exposedworkers in China (Huang, 2002).

Using the blood test results, we first assessed therelationship between self-reported symptoms and medi-cally verified pesticide poisoning. We began by calculat-ing a correlation coefficient for each self-reportedsymptom against the blood test results. The highestcorrelation among the whole set was only p ¼ 0.17. Wethen calculated the correlation of the blood test resultagainst an index of equally weighted symptoms that arecommonly associated with blood poisoning (convul-sions, diarrhea, dizziness, eye irritation, headaches,shortness of breath and vomiting). The compositecorrelation was even weaker: p ¼ 0.05. Thus, weconclude that our evidence does not lend support tothe use of self-reported symptoms as indicators of actualpesticide poisoning. Given the relatively high incidenceof poisoning in the sample, however, our results stronglysupport regular medical testing for farmers who areexposed to highly or moderately toxic organophosphateand/or carbamate pesticides.

Determinants of cholinesterase inhibition

Using the blood cholinesterase test results, we alsoconducted a regression analysis to identify the majordeterminants of pesticide poisoning. According to themedical literature, the types and severity of cholinester-ase inhibition symptoms depend on the amount ofpesticide involved in the exposure, the toxicity of thepesticide, the route of exposure, and the duration ofexposure (Extension Toxicology Network (ECOTOX-NET), 2004). In addition, the health effects of pesticideuse can often be reduced significantly by appropriate useof protective items such as gloves, hats, jackets, eyeglasses or masks (Cropper, 1994). A priori, we wouldexpect farmers’ self-protective behavior to depend ontheir perception of risk, along with the quality of theirinformation about safe handling of pesticides. Takingthese factors into account, we specify and estimate thefollowing regression model with dummy variables tocontrol for any provincial differences:

POISONING ¼ f ðPESTAMT; PWHOIab; PWHOII,

PWHOIII; PWHOU; PTRAIN; NPROTECT;

IPMD; ProvincialDummies�Þ

ARTIC

LEIN

PRES

S

Table 4. Number of self-reported health impairments after using pesticides, by chemical class

Class Skin irritation Headache Eye irritation Dizziness Shortness of breath Vomiting Fever Diarrhea Convulsions Other problems

DMI: triazole 195 186 171 144 138 61 45 20 10 183

2-dimethylaminopropane-1,3-dithiol 95 88 85 70 62 21 24 13 3 71

Pyrethroid 80 73 73 63 51 23 18 13 4 68

Chloroacetamide 58 56 48 46 34 16 11 6 2 48

Dithiolane 54 51 36 39 32 14 11 5 2 56

Antibiotic 39 43 30 29 30 7 4 9 1 37

MBI: reductase 39 35 35 28 21 17 9 4 4 37

Fiprole 32 32 25 25 27 8 7 4 2 34

Organophosphate 29 25 21 20 16 3 7 3 4 25

Carbamate 26 28 22 17 15 8 7 1 1 22

Pyrimidinyloxybenzoic 23 22 23 20 15 8 5 4 1 23

Phenoxycarboxylic acid 19 18 19 19 17 5 7 4 0 21

Aryloxyphenoxypropionate 20 17 21 15 17 6 3 2 1 19

Neonicotinoid 22 16 17 14 15 4 6 4 1 16

Sulfonylurea 16 18 18 13 15 4 7 1 1 13

Benzimidazole 18 14 17 11 11 3 9 3 0 16

Dicarboximide 19 15 14 13 7 2 1 0 0 20

Unknown 10 7 7 6 8 4 2 0 1 8

Phosphorothiolate 6 4 7 7 9 2 3 2 1 5

Quinolinecarboxylic acid 5 4 3 5 4 0 1 1 0 5

Multi-site: inorganic 3 2 2 0 3 0 1 2 0 4

Non-ester pyrethroid 3 3 2 2 3 0 1 0 0 2

Multi-site: alkylenebis (dithiocarbamate) 3 3 0 2 2 0 0 0 0 3

Hexopyranosyl antibiotic 3 2 1 1 2 1 0 0 0 2

Cyclodiene 2 2 2 2 0 0 0 0 0 0

Glycine derivative 1 1 1 1 1 1 0 1 0 1

Benzimidazole precursor 1 0 1 1 1 0 0 0 0 1

Multi-site: phthalimide 0 0 0 0 0 0 0 0 0 1

Total (out of 1252 applications) 821 765 701 613 556 218 189 102 39 741

Prevalence (%) 65.6 61.1 56.0 49.0 44.4 17.4 15.1 8.1 3.1 59.2

A total number of 1252 applications by 190 farmers.

S.Dasgupta

etal./Int.J.

Hyg.Enviro

n.-H

ealth

210(2007)121–132

129

ARTICLE IN PRESS

Table 5. Determinants of blood cholinesterase (AChE)

inhibition

Variable Model 1 Model 2

PESTAMT �0.098** (�2.09) �0.105** (�2.24)

PWHOIab 0.039*** (2.51) 0.030** (2.08)

PWHOII 0.003 (0.46)

PWHOIII 0.008 (1.19)

PWHOU 0.006 (0.90)

PTRAIN 0.262 (1.22)

NPROTECT �0.443* (�1.86) �0.440* (�1.91)

IPMD 0.043 (0.19)

An Giang �0.118 (�0.33)

Can Tho �0.821** (�2.49) �0.628** (�2.39)

Long An �0.449 (�1.36)

Tien Giang �0.841*** (�2.58) �0.605** (�2.41)

Observations 187 187

***Significant at the 1% level.

**Significant at the 5% level.

*Significant at the 10% level.

Low acute

poisoning1

9%

High acute

posioning2

5%

Chronic

poisoning3

21%

Poisoning35%Normal

65%

1 - Reduction of numerical value of AChE in red cells and in plasma > 25%; 2 - Reduction of numerical value of AChE in red cells and in plasma >33%; 3 - Reduction of numerical value of AChE in red cells > 66%.

Fig. 2. Medical blood test results for the detection of acute and chronic pesticide poisoning.

S. Dasgupta et al. / Int. J. Hyg. Environ.-Health 210 (2007) 121–132130

where POISONING is the 1 if acute/chronic poisoningindicated by cholinesterase test, 0 otherwise; PESTAMTthe total amount of pesticides applied (kg); PWHOIabthe % of pesticides classified as highly hazardous (WHOcategory Ia or Ib); PWHOII the % of pesticidesclassified as moderately hazardous (WHO category II);PWHOIII the % of pesticides classified as slightlyhazardous (WHO category III); PWHOU the % ofpesticides with no significant hazard in normal use(WHO category U); PTRAIN the 1 if trained in safehandling of pesticides, 0 otherwise; NPROTECT theprotective items used (1 ¼ if more than 2, 0 otherwise);IPMD the 1 if integrated pest management techniquesemployed, 0 otherwise; * Dummy for Tra Vinh provincedropped to permit estimation.

We estimated a probit model that incorporatesadjustments for heteroskedasticity. The results, reportedin Table 5, provide only weak support for the standardexplanatory model of individual exposure. Three in-dividual variables are significant (pesticide amount, thepercentage of highly hazardous pesticides and use ofprotective items), however, the first has a perverse sign.Further regression analysis revealed that pesticide use isprimarily driven by the scale of the farm(elasticity ¼ 0.93), with smaller significant effects fromfarmers’ age and being located in the provinces of AnGiang, Long An and Tien Giang. Returning to theinterpretation of the results, a 1% increase in theamount of pesticides used decreases the probability ofpoisoning by 9.8%, whereas a 1% increase in thepercentage of WHO Ia and Ib pesticides used by thefarmer increases the probability of poisoning by 3.9%.Farmers who tend to use a lot of pesticides may takeextra precautions so as to limit their exposure; however,those who handle particularly hazardous pesticides maynot. For those who do use more protective measures, theprobability of poisoning falls by 44.3%. Thus there are

tremendous gains in health prevention by the use ofbasic protective requisites. Neither training in safe-handling, nor use of IPM techniques has the expectedeffect, however both are statistically insignificant. In astudy among Nicaraguan maize farmers, Hruska andCorriols (2002) found significantly lower cholinesteraselevels among farmers who did not receive IPM training.In addition, they found no significant differencesbetween those who used protective equipment and thosewho did not. Conversely, in the Mekong sample,training in pesticide safety and handling had nosignificant effect on the probability of poisoning,whereas the number of precautions decreased thelikelihood of poisoning.

ARTICLE IN PRESSS. Dasgupta et al. / Int. J. Hyg. Environ.-Health 210 (2007) 121–132 131

After controlling for these individual circumstances,we also find strong provincial effects which may beindicative of the conditions of the surrounding environ-ment. The incidence of poisoning in Can Tho and TienGiang is much lower than in Tra Vinh (excluded in theregression) and An Giang. A possible explanation couldbe that pervasive contamination from others’ pesticideuse may affect individual farmers, even if their ownpractices are prudent. Huan and Thiet (2000) cite manycases in which pesticides are often disposed of incommon-areas or local water sources. Future researchon pesticide poisoning should test this proposition byincluding measures of contamination of local surfacewater, ground water, air and soil.

Summary and conclusions

In this paper, we have assessed the incidence anddeterminants of pesticide poisoning among rice farmersin Vietnam’s Mekong Delta. We believe that our resultsare of particular interest because they rely on explicitmedical tests for poisoning, rather than conventionalself-reporting of symptoms by farmers. Medical tests ofthe level of AChE in erythrocyte and plasma suggestthat the overall incidence of poisoning (35%) fromexposure to OP and CM is quite high in the MekongDelta, and appears to be consistent with the results fromother studies in Vietnam and other developing countries(Dien and Vong, 2003; Hruska and Corriols, 2002;Huang, 2002; Kunstadter et al., 2001; Ky and Ngoc,1998; Soogarun et al., 2003; Thuy et al., 2003).

Using the medical test results as benchmarks, we findthat farmers’ self-reported symptoms have very weakassociations with actual poisoning (p ¼ 0.05–0.17). Boththe incidence of poisoning and farmers’ own apparentinability to distinguish its symptoms from other healthproblems suggest that regular checkups and blood testsshould be conducted for those who load, mix, or applyhighly or moderately toxic organophosphate andcarbamate pesticides.

A probit regression using blood cholinesterase testresults also revealed a lower incidence of poisoning forfarmers who avoid the most toxic pesticides and useprotective items. However, our results are eitherperverse or insignificant for other individual factorsthat are conventionally believed to reduce risk: totalpesticide amount, use of IPM techniques, and training insafe handling of pesticides. Farmers who use higherquantities of pesticides may take more precautions,however they may underestimate the potential hazardsof particularly toxic substances. Although the use ofIPM and training in safe handling of pesticides werefound to be insignificant, the content of local trainingprograms should be revisited, especially if agronomists

and extension agents suspect that farmers are usingWHO Ia or Ib pesticides.

We also find very large provincial differences inpoisoning incidence after we control for individualfactors. Province of Tra Vinh, Can Tho and Tien Giangappear to have far lower prevalence rates of pesticidepoisoning. This result highlights the importance ofnegative externalities, and suggests that future researchon pesticide-related damage should include informationon local water, air and soil contamination. Thesignificance of these factors suggests that collectivemeasures may provide an important complement toindividual actions in reducing farmers’ exposure topesticide hazards.

Acknowledgments

We would like to express our appreciation to themedical research team of National Institute of Occupa-tional and Environmental Health, Vietnam for theirexcellent field work and to Jostein Nygard, East AsiaEnvironment Unit, World Bank. The findings, inter-pretations, and conclusions are entirely those of theauthors. They do not necessarily represent the view ofthe World Bank, its Executive Directors, or thecountries they represent.

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