International Journal of Hygiene and Environmental Health
Pesticide poisoning of farm workers–implications of blood test results from Vietnam
Introduction
Indiscriminate use and improper handling of synthetic pesticides in agriculture have caused serious problems for human health in many developing countries during the past three decades. However, the true extent of the problem is hard to determine for a variety of reasons. First, farmers with mild pesticide poisoning often do not report because treatment services are costly, inaccessible, or fear that drawing attention to themselves may result in the loss of employment opportunities. Second, health-care professionals in rural areas often fail to correctly diagnose poisoning, as many of the related symptoms are quite general in nature or mimic other common health problems (e.g., headaches, dizziness, vomiting) (FAO, 2001). In Vietnam, hospital admission records attribute 11% of all poisonings to pesticide misuse: approximately 840 poisonings in 53 cities and provinces in 1999 (Poison Control Center, Vietnam Ministry of Health, 2000); however, a recent WHO report for Vietnam states that there were a total of 7170 pesticide poisoning cases in 2002 (World Health Organization (WHO), 2005). The WHO and the United Nations Environment Program (UNEP) estimate that there are 50 cases of poisoning for every case reported and registered, or between 1 and 5 million agricultural workers per year (World Resources Institute et al., 1998). At least 20,000 workers die from exposure every year, the majority in developing countries (World Health 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 has been lukewarm in developing countries. There is a widespread concern about diverting resources to alternative pest control methods when poverty, illiteracy and infant mortality are still major problems. In part, the resistance of policy makers is due to uncertainty about the severity of the problem, its sources, and suitable interventions. Their uncertainty is understandable, since systematic studies of the health effects of pesticides are scarce. Most existing studies rely on farmers’ self-reported symptoms, as appropriate pathological tests are 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 Bank collaborated with the Vietnam Association of Occupational Health (VINOH) to study pesticide poisoning among 190 Mekong Delta rice farmers during the summer–autumn–winter growing periods in 2004. The study included clinical exams by doctors from the VINOH, along with blood tests for cholinesterase inhibition (reductions in acetyl cholinesterase enzyme (AChE)) due to contamination by organophosphate and carbamate use. Epidemiological studies have linked carbamates (CM) and organophosphates (OP) with fetal death, hormonal changes, DNA damage, birth defects, and abnormal sperm, ovaries and eggs. In addition, OP, as a class of insecticides, have been linked with Non-Hodgkin's lymphoma, leukemia, and lung cancer. In children OP have been linked to aplastic anemia, the failure of the bone marrow to produce blood cells, and leukemia. Children with asthma may have severe reactions to OP in particular (Zahm et al., 1997).
Initial results from the survey reveal a high prevalence of pesticide poisoning among farmers (35%), 14% of which was acute (AChE reduction of >25%) and 21% chronic (AChE reduction of >66%). Comparing the blood test results with farmer self-reported health ailments we find a very low correlation (p=0.05–0.17). Using further information from the survey, we also estimated a probit model of the likelihood of pesticide poisoning as explained by the amount and relative toxicity of pesticides in use, determinants of exposure, and provincial environmental effects. Although the results suggest that increases in the amount of pesticides do not lead to an increase in the probability of poisoning (defined as a reduction of AChE), the use of highly toxic (WHO category Ia or Ib) pesticides increases this probability. In addition, the probability of poisoning decreases with the number of protective measures that the farmer is currently using. It may be the case that farmers are more hazard conscious when using larger amounts, however, are not fully aware of the relative toxicity of the pesticides they are using. Our results also indicated strong provincial effects with relatively higher prevalence rates in the province of Tra Vinh. This may provide general empirical support to the reports of pervasive contamination of the air, soil or water, by pesticide overuse and misuse (Huan and Thiet, 2000).
Section snippets
Pesticide use in Vietnam
Like many developing countries, Vietnam has promoted the use of pesticides to expand agricultural land and increase output per acre. The Socialist Republic of Vietnam began extensive use of pesticides in the 1950s, when agricultural production was limited to cooperatives, collective farms, and state farm enterprises. During this period, pesticides were not regulated and agronomists and farmers had little knowledge of the hazards of pesticide use. Pesticide applications were completed by
Subjects and methods
To investigate the health impacts of pesticide use, structured questionnaires designed by the World Bank team were used to collect information on farming systems, pesticide use and practices, applicator precautions, protective measures, and self-reported poisoning symptoms. All participating farmers were then examined by doctors from the Centre of Occupational and Environmental Health (COEH) of the VINOH (Hanoi, Vietnam). For the purposes of demographic and pesticide use variation, the survey
Results and discussion
Survey response on reported symptoms after mixing and spraying pesticides was quite prevalent among all 190 farmers. In Table 4, the most commonly reported symptoms were dermal (skin irritation: 66%), neurological (headache: 61%; dizziness: 49%), ocular (eye irritation: 56%), and respiratory (shortness of breath: 44%). Other studies in Vietnam report similar findings for self-reported ailments. In a study of 369 tea farmers, Xuyen et al. (1998) report similar incidence rates for headaches
Summary and conclusions
In this paper, we have assessed the incidence and determinants of pesticide poisoning among rice farmers in Vietnam's Mekong Delta. We believe that our results are of particular interest because they rely on explicit medical tests for poisoning, rather than conventional self-reporting of symptoms by farmers. Medical tests of the level of AChE in erythrocyte and plasma suggest that the overall incidence of poisoning (35%) from exposure to OP and CM is quite high in the Mekong Delta, and appears
Acknowledgments
We would like to express our appreciation to the medical research team of National Institute of Occupational and Environmental Health, Vietnam for their excellent field work and to Jostein Nygard, East Asia Environment Unit, World Bank. The findings, interpretations, and conclusions are entirely those of the authors. They do not necessarily represent the view of the World Bank, its Executive Directors, or the countries they represent.
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