|Impact of Pesticide Use on Health in Developing Countries (IDRC, 1993, 346 p.)|
|Part I: Epidemiology of pesticide poisoning - practical research experience in developing countries|
R.M. Sansur, S. Kuttab, and S. Abu-AI-Haj
Center for Environmetal and Occupational Health Sciences and Chemistry Department, Birzeit University, West Bank, via Israel
The aim of this study was to determine the extent to which farm workers were exposed to organophosphate pesticides and, based on the results, to develop a program to teach farmers safe practices in the handling and use of pesticides. Low acetylcholinesterase (AChE) levels were found among participating farmers; recovery was dependent on the dose. AChE levels were higher during the spraying season than at the end of the season possibly due to enzyme induction resulting from long-term exposure. Legs were the parts of the body most exposed during spraying. A knowledge, attitudes, and practices (KAP) survey revealed lack of knowledge about the sap handling of pesticides and the dose required for spraying. An intensive long-term training program on the sap use of pesticides is urgently needed.
When used properly, pesticides have been of tremendous benefit to humans and the environment, but, when used carelessly, they have caused considerable and, in some instances, inestimable harm. In developing countries, the increasing use of pesticides in agriculture and the absence of adequate worker education and effective control measures have given rise to a growing concern about the magnitude of the health risk to farm workers exposed to these chemicals. It is suspected that many illnesses and deaths go unrecorded.
In the Jordan Valley of the West Bank (Al Ghor), spraying of crops with pesticides has increased tremendously over the last 20 years. The increased use of dangerous organophosphate insecticides as substitutes for chlorinated hydrocarbons, which degrade more slowly and have a higher environmental impact, has added a new dimension to a serious occupational health problem in this area.
Al Ghor is on the west side of the river Jordan. It is a warm, semitropical area, 100 200 m below sea level and is unique in that farm produce can be cultivated during the winter months. Intensive agriculture is thus practiced from October to May. Although now diminished in size, the Palestinian area being cultivated amounts to 40 km². The Arab population is about 30 000, two-thirds of whom are involved in agriculture. Agriculture involves all members of the farming families, including pregnant women and children. About half the farmers are landowners; the others are tenants.
Organophosphates are potent inhibitors of acetylcholinesterase (AChE), an enzyme responsible for the hydrolysis of acetylcholine, which is synthesized at nerve endings and is involved in transmission of impulses from nerve to muscle fibres. A 40% decrease in blood AChE is associated with the first symptoms of pesticide poisoning and an 80% decrease is associated with severe neuromuscular effects. Absorption of organophosphate sufficient to inactivate all red blood cell AChE may result in death. Absorption may occur through the skin, by inhalation, or by ingestion.
Farmers are exposed to organophosphates either through continuous spraying of these pesticides or from contact with their residues on treated plant surfaces. No statistical information was available concerning poisoning incidents related to crop-spraying activity among the farmers of the region. However, a preliminary survey of a small number of farming operations revealed unacceptable mixing and spraying habits. Chronic exposure, poor working conditions, and lack of education about potential hazards could have serious health and economic implications for the region.
The objective of this study was to learn the extent of exposure to organophosphate pesticides of farmers in the Jordan Valley during and after the spraying season and to determine the knowledge, attitudes, and practices (KAP) of the farm workers regarding the use of pesticides. The information will be used to design a program for farmer education and training in the safe use and handling of pesticides.
Population and sampling
All of the participants were tenant farmers from the Jiftlic region of the Jordan Valley, who leased land and shared some of the expenses and the profit with the landlord. The participants were divided into groups:
· Group I consisted of 14 farmers in three subgroups (4, 6, and 4), each spraying 1 000 L of pesticide;
· Group II consisted of 10 farmers in two subgroups (5 and 5), each spraying 2 000 L of pesticide;
· Group III consisted of 31 farmers whose blood was sampled just before the beginning of the spraying season and at the end of the summer to determine AChE levels during the off-season; and
· Group IV consisted of 24 farmers whose blood was sampled after a minimum of 3 days abstention from handling pesticides (Group IVa) or randomly, regardless of their handling of pesticides (Group IVb).
Two farmers from the same region, with junior college or vocational training, agreed to act as supervisors to ensure that participating farmers complied with the experimental protocol. Methamidophos (available under the trade names Tamaron, Prodex, and Monitor) was chosen by the farmers and was used at a concentration of 1.2 g/L. A tractor-driven 500-L tank, fitted with a pump and spray gun, was used for spraying. In each subgroup, farmers alternated every 20-30 min between carrying the hose, operating the spray gun, and driving the tractor. Thus, each farmer was exposed to about the same dose of pesticide.
The level of AChE activity in 10-µL samples of whole blood, obtained by finger-pricking, was measured spectrophotometrically using a method developed for field use (WHO 1984).
A standard protocol (WHO 1982), developed for field surveys, was used to measure the extent of exposure to the pesticide during spraying operations. Seven polyethylene-backed filter paper pads (Schleicher and Schuell, catalogue no. 295 PE), cut to 10 x 10 cm, were attached to different parts of the body with tape before spraying began. At the end of the work period, the pads were removed, a 5 x 5 cm piece was cut out and placed in a plastic envelope in a cooler for later analysis. As a control and to determine recovery, a known concentration of the organophosphorous pesticide was placed on a pad that was treated in a similar fashion.
Each 5 x 5 cm pad was cut into strips and placed in a beaker containing 5 mL ethyl acetate and extracted in an ultrasonic bath for 5-7 min. The ethyl acetate extract was concentrated and analyzed by gas chromatography using a 30-m capillary column SE 54. Column temperature was 180 C, injector temperature was 200°C, and TSD detector temperature was 300°C.
Knowledge, attitudes, and practices
The survey to determine KAP was based on a standard protocol (WHO 1982) with certain modifications to elicit information about knowledge regarding the toxicity of pesticides.
Because of the many factors that influence AChE levels, nonparametric statistical tests were used to evaluate the significance of differences in activity. These included Spearman and Wilcoxon ranked matched-pair tests. Significance tests were based on Spearmans matched-pairs rank correlation coefficient.
Results and discussion
Choice of pesticide
The choice of methamidophos, the organophosphate pesticide used in this study, was left entirely to the farmers. To achieve uniform results, we opted to work with farmers using the same pesticide throughout the study. Methamidophos was not the best choice for our purposes, as it is a relatively weak AChE inhibitor in spite of its good insecticidal activity (Quistad et al. 1970). In addition, it is highly toxic, with a Class I toxicity rating; in rats, the acute oral LD50 (lethal dose to 50% of animals tested) is 30 mg/kg in rats (WHO 1988).
The concentration of pesticide after dilution was 1.2 g/L, which is double that recommended for the type of equipment the farmers normally use. Again the choice of concentration was left to the farmers.
AChE levels in blood samples
Mean AChE levels for Group I were significantly lower (at the 95% confidence level) 2 h after completion of the spraying operation compared with levels before spraying (Fig. 1). The difference was not significant on the following 2 days, indicating a recovery in AChE level. Exposure time for this group, which sprayed 1 000 L per subgroup of 1.2 g/L methamidophos, was 1.5 2 h per subgroup. At no time did AChE levels fall below normal range.
Fig. 1. Acetylcholinesterase levels in whole blood of participating farmers at selected times after they had finished spraying pesticide.
Group II also displayed a significant decrease in AChE levels in whole blood during the first 2 h after spraying, but their AChE levels were also significantly below those measured before spraying on the following 2 days. This group sprayed 2 000 L of 1.2 g/L methamidophos per subgroup. We observed that 2 000 L (four tanks) was the minimum a farmer would use on a particular spraying day; hence this level of exposure is realistic. Total exposure time was 3-3.5 h per subgroup.
No clinical symptoms of intoxication with methamidophos were evident among the participants, except for fatigue.
AChE levels in whole blood were measured twice: during the spraying season in March and again at the end of the season in September. For the early test, farmers were asked not to handle pesticides for at least 3 days before blood samples were taken.
Mean AChE activity (measured as change in absorbance per min per mL of whole blood) was 19.13 + 0.394 (mean + standard error) at the end of the season compared with 23.34 + 0.470 during the spraying season, a significant difference of 22% for Group IVa and 15% for Group IVb. This result was opposite to what we expected, i.e., lower AChE activity during the spraying season due to the effects of organophosphate and carbamate pesticides on cholinesterase enzymes.
The seasonal differences in AChE activity may be the result of excessive contact with pesticides resulting in enzyme induction (Burgess and Roberts 1980). Roberts (1980) mentions the possibility that persistent exposure to pesticides may cause cumulative biological changes. Individual differences in AChE activity are common (Loosli 1980). The farming population in the Jordan Valley has been using pesticides for at least the past 20 years.
Dermal exposure generally accounts for 90% of total exposure to pesticides by farmers. Seven pads were placed on each subject to determine which areas of the body were most exposed (Table 1). As expected, Group II, which operated spraying equipment twice as long as Group I, experienced a higher degree of exposure. The longer duration of exposure resulted in the pesticide penetrating the clothing and becoming absorbed on the skin pads in more of the participating farmers. For both groups, the area of the body that received the highest concentration of pesticide was the leg (pads 2 and 3). A sizable reduction in dermal exposure could be achieved by covering legs and feet with boots made of rubber or other inexpensive but pesticide-proof material.
Table 1. Concentration of methamidophos (g/cm²) on pads collected from Groups I and II.
Knowledge, attitudes, and practices
The pesticide chosen by the farmers is very toxic. However, the farmers took no special precautions during mixing or spraying. Although methamidophos is classed as highly hazardous, i.e., complete protective gear must be worn during spraying operations, participants wore only their everyday clothing and some sprayed without footwear.
After an argument and some discussion, the farmers decided to prepare the pesticide at a concentration of 1.2 g/L, double the recommended level. Lack of knowledge and inability to read the package label, which was in Hebrew, contributed to the error.
The legs of farmers were most exposed and became wet from the pesticide spray. This was especially evident when it was windy. No metering of the pump, volume delivered by the spray gun, or distance walked was done to optimize the amount of pesticide used.
Except for fatigue, no gross toxic symptoms were observed. However, most of the farmers indicated that methamidophos had a bad effect on them without clarifying what they meant.
We did not observe government or other extension agents during the course of the study.
Pesticides were stored everywhere covered only by a plastic sheet: in homes, in animal or food sheds, and among plants. Children of all ages were present on the farms at all times.
Most of the participants (54%) were between the ages of 20 and 29 years, indicating that a young population is involved in farming (Table 2). In this age group, we found a number of people with vocational diplomas or college-level education. Most family members (68%) who participated in spraying and other farming activities were below the age of 20; 55% were age 16 years or younger.
Table 2. Results of the survey on knowledge, attitudes, and beliefs.
Table 2. Concluded.
Knowledge about the choice and use of pesticides was gained mostly from personal experience and, to some extent, from pesticide sales outlets. Government extension agents played a minor role; 60 serve the whole West Bank and they do not have enough vehicles or petrol to move around.
Although 8% of the farmers indicated that they had had some training in the use of pesticides, no participating farmer could substantiate that claim by giving a source for the training.
Some farmers believed that, after using pesticides for a long time, they became immune to them. Although this belief was false, our results indicated a possible adaptive mechanism involved in raising AChE levels during the spraying season.
Although 88% of the participants said that they washed or changed their clothes after spraying, our observations indicated the opposite; we saw many farmers wearing the same clothes on a number of consecutive days. In addition, 75% indicated that they did not shower or bathe after spraying.
Eating and smoking while spraying were widespread among the farmers and the responses to this question were more or less accurate.
We did not observe anyone burying empty containers in the field although 33% of those surveyed said that this was their practice. Empty containers were scattered everywhere including around homes.
This study revealed a number of areas that must be addressed in the design of a program for training farmers in the safe handling of pesticides:
· Farmers lack knowledge about the proper choice of pesticides for pest management;
· Farmers are unaware of the correct amount to be sprayed for a given concentration of pesticide;
· Spray equipment is never checked for proper dose delivery;
· Adequate information about pest and crop management is unavailable to farmers;
· Spraying is done casually without proper planning or safety precautions;
· There is no regard for reentry periods or length of time between spraying and harvest;
· There is little awareness of the long-term effects of pesticides on farmers or their families as evidenced by young children participating in spraying and the casual way in which pesticides are handled; and
· Government agencies, the media, and chemical companies advise farmers to spray prophylactically.
In conclusion, we believe that a training program for farmers and others in the safe handling of pesticides coupled with pest management is urgently needed. Such a program, if run efficiently, will benefit a wide sector of society and reduce health hazards associated with exposure to pesticides.
Acknowledgments - This study was partly funded by the International Development Research Centre, AMIDEAST, and Birzeit University. We are indebted to Khaled El Hidmi of the Union of Agriculture Work Committees, who assisted us in organizing the farmers. We thank the farmers of the Jiftlic region who helped make this study a success. Aqel-Abu-Qara, Joumana Naser El Din, and Hanan Saadeh of the Center for Environmental and Occupational Health Sciences (CEOHS) assisted us in the field and laboratory. We also thank Mrs Zreikat for typing the report. This study would not have been possible without the generous grant from the Shoman Foundation enabling CEOHS to purchase equipment. The Catholic Committee against Hunger and for Development and the Ford Foundation funded some of the pilot projects that gave impetus to this study.
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