The Science of the Total Environment, 122 (1992) 315-319 Elsevier Science Publishers B.V., Amsterdam
315
Pesticide exposure and cholinesterase levels among farm workers in the Republic of South Africa D.B.K Rama and K. Jaga National Centre for Occupational Health, P.O. Box 4788, Johannesburg 2000, Republic of South Africa (Received August 27th, 1991; accepted October 10th, 1991)
ABSTRACT A preliminary survey was undertaken to establish the extent of pesticide exposure in a farming community. The area under investigation included a coffee plantation in the northern region of South Africa. Cholinesterase levels in red blood cells and plasma were used as markers to monitor the extent of organophosphate and carbamate exposure. Sixty-nine farm workers with specific pesticide exposure were selected for the study, and the frequency of the different symptoms which may be related to pesticide exposure was determined by interview and questionnaire. Of the workers, 77% had their red blood cell cholinesterase levels below the normal reference range, while 27% of the workers had depressed plasma cholinesterase levels.
Key words: pesticide exposure; biological monitoring; cholinesterase
INTRODUCTION
In South Africa there are approximately 1.2 million farmworkers (D. du Toit, pers. commun.). If one were to include their families, this could be extrapolated to - 7 million people dependent on agricultural activity (D. du Toit, pers. commun.). Pesticides are produced in large quantities and include a range of types, such as organophosphates, carbamates, organochlorines, pyrethrins and bipyridals. Globally, about 2 million tons are used annually [1]. The labour force and their families usually live on the farms or in close proximity thereto. Hence, a large segment of the South African population is exposed occupationally and/or environmentally to one or other type of pesticide. In this preliminary study, workers in a coffee plantation were surveyed for organophosphate exposure. The enzyme cholinesterase (ChE) is a useful marker [2-6] of occupational and environmental exposure, hydrolysing esters of choline, such as acetylcholine. Acetylcholine is very im-
316
D.B.K. RAMA AND K. JAGA
portant physiologically [3]. It is synthesised at nerve endings and acts to transmit impulses from nerve to muscle fibre. There are two types of this enzyme, the 'true' and the pseudocholinesterase [8], ChE destroys the acetylcholine after the impulse transmission has occurred, so that subsequent impulses may be transmitted if necessary. Without hydrolysis of acetylcholine, the nerve would remain electrically charged and further conduction would be inhibited. The organophosphate and carbamate pesticides inhibit this enzyme [9,10], and its activity is used as an index of exposure to these pesticides. MATERIALS AND METHODS A total of 69 workers exposed to organophosphorous and carbamate pesticides were evaluated by questionnaire with the assistance of one of the management staff and the local health inspector. Since it was difficult to obtain control subjects from the rural environment under investigation, no interviews were conducted for controls. The types of pesticides used, the mode of exposure, and the number of hours of pesticide application per day or week was noted. Workers age, sex, height, weight and symptoms experienced were recorded. Red blood cell (RBC) and plasma cholinesterase levels were assessed spectrophotometrically as described by Lewis et al., with some modifications [11]. Since baseline levels of ChE for each individual are not known, the normal levels reported in literature are used as a reference. A period of at least 30 days must separate the baseline determination from the worker's last exposure to a cholinesterase-inhibiting compound [2]. This was difficult to achieve due to the worker's commitment to their duties. Ethical consideration Informed consent was obtained from each subject after the purpose of the study was explained to them in their own language. RESULTS The workers worked an 8-h shift, 6 days per week. Most of the farmworkers were females, and the subject's sex, mean age, mean height, and mean weight is summarised in Table 1. A wide range of pesticides are generally applied by the farmworkers monitored (Table 2). Approximately 3 months prior to the survey, the farmworkers were only applying organophosphates. Pesticides were sprayed by hand applicators and tractor drivers. The workers were provided with protective clothing such as masks, gloves, overalls and boots. However, there
PESTICIDE EXPOSURE AND CHOLINESTERASE LEVELS AMONG FARM WORKERS IN SOUTH AFRICA
317
TABLE 1 Profile of the subjects monitored Sex
n
Mean agea
Mean height (range)
Mean weight (range)
Males Females
8 61
---
1.68 m (1.63-1.74) 1.55 m (1.47-1.69)
52.6 kg (46-56 kg) 52.54 kg (38-71 kg)
aMany subjects did not know their age.
was no formal occupational hygiene programme to ensure good hygiene practices regarding the use of clean and well maintained protective equipment. Table 3 summarises the percentage of workers that reported the different symptoms that could be associated with organophosphate exposure. Biological monitoring indicated depressed ChE levels in red blood cells and plasma in many workers (Table 4). DISCUSSION There is a need for farmers and their workers handling pesticides to be made aware of the health effects o f pesticides. Workers engaged in handling pesticides should be supervised by one who has knowledge and experience in the application o f pesticides. Furthermore, good occupational hygiene
TABLE 2 Types of pesticides used Organophosphates Parathion Monocrotophos Dicrotphos Trichlorfon Disulfoton Carbamates Benomyl Thiocarbamates Mancoseb: Maneb Zineb
Herbicides Bipyridals Paraquat Fluazfop-p-butyl Glyphysate Fungicides Copper oxychloride Minam Organochlorines Chlordane
318
D.B.K. RAMA AND K. JAGA
TABLE 3 Clinical findings Symptoms
Frequency (%)
Nausea/vomiting Abdominal cramp Diarrhoea Chest tightness Weakness Headaches Visual problems Dermatological Other: goitre No symptoms
7.3 36.2 50.7 43.5 53.6 68.1 31.9 7.3 1.5 1.5
standards should be adhered to. In the case of those workers spraying by hand, little knowledge of the importance of wind direction was known to ensure that they sprayed downwind and walked through untreated crops to ensure minimum exposure. Eating and smoking also took place at the spraying sites without washing up. After working in the field, no special precautions were taken such as cleaning, maintaining, and storage of protective clothing and equipment ready for use next time. Finally, no wash-up facilities are provided and the workers go home without changing the contaminated clothes. Although blood from 69 workers was collected, only 31 red blood cell and 41 plasma specimens were analysed due to problems encountered during transit of the specimens to the laboratory. The normal reference range adopted in this study is one used by many of the pathological laboratories in the Republic of South Africa (A.J. Areias, pers. commun.). A recent study in South Africa that established a reference range for serum ChE indicates a fairly similar reference range as adopted in this study [12]. It was difficult to obtain control subjects from the rural environment under investigation. TABLE 4 Cholinesterase activity
RBC Plasma
Mean
Range
n
% falling below normal range a
2469 3116
1722-3198 90-4950
30 41
77 27
aNormal reference range: RBC, 2800-5200 units/1 whole blood. Plasma, 3500-8500 units/1.
PESTICIDE EXPOSURE AND CHOLINESTERASE LEVELS AMONG FARM WORKERS IN SOUTH AFRICA
319
Control subjects selected from our laboratory personnel were within the range adopted. However, ideally it is best to compare the workers postexposure ChE level with their own baseline value. This was not possible in this study. This preliminary study indicates definite organophosphate exposure and lack of occupational hygiene standards. A detailed study is presently being planned to evaluate the ChE levels in a larger sample o f farmworkers and arrangements are being made to establish a local ChE reference range by selecting control subjects from the region under investigation. ACKNOWLEDGEMENTS The authors would like to thank National Chemical Product, Chloorkop and A.J. Areias of the South African Institute for Medical Research for analysing the blood specimens. The workers and management o f the coffee plantation are also thanked for their cooperation. REFERENCES 1 M. Marone, Forward, Workshop on the use of human exposure and health data for im"provingthe toxicologicalrisk assessment of pesticides and their regulatory control, Med. Lay., 81 (1990) 450-452. M.J. Coye, J.A. Lowe and K.T. Maddy, Biological monitoring of agricultural workers exposed to pesticides: I Cholinesterase activity determinations, J. Occ. Med., 28 (1986) 619-627. D.F. Innes, B.H. Fuller and G.M.B. Berger, Low serum cholinesteraselevels in workers exposed to organophosphate pesticide sprays, S. Afr. Med. J., 78 (1990) 581-583. R.G. Ames, S.K. Brown, D.C. Mengle, et al., Protecting agricultrual applicators from overexposure to cholinesterase-inhibitingpesticides: Perspectives from California Programme, J. Soc. Occup. Med., 39 (1989) 85-92. WHO, Early detection of Occupational Diseases. WHO, Geneva, 1986, p. 59. M. Coye, P.G. Barnett, J.E. Midttling, et al., Clinical confirmation of organophosphate poisoning of agricultural workers, Am. J. Ind. Med., 10 (1986) 399-409. 7 D.F. Heath, Organophosphorous Poisons. Anticholinesterasesand Related Compounds, Pergamon Press, New York, 1961, pp. 103-258. 8 N.W. Tietz (Ed.), Fundamentals of Clinical Chemistry, W.B. Saunders, Philidelphia, 1976, pp. 643-646. 9 L. Rosenstock and M.R. Culler, Clinical Occupatinal Medicine, Saunders, Philidelphia, 1986, p. 262. 10 R.G. Ames, S.K. Brown and D.C. Mengle et al., Cholinesterase activity depression among California agricultural pesticide applicators, Am. J. Ind. Med., 15 (1989) 143-150. 11 P.J. Lewis, R.K. Lowing and D. Gompertz, Automated discrete kinetic method for erythrocyte acetylcholinesterase and plasma cholinesterase, Clin. Chem., 27 (1981) 926-929. 12 B.H. Fuller and G.M.B. Berger, Automation of serum cholinesterase assay-paediatric and adult reference ranges, S. Afr. Med. J., 70 (1990) 577-580.
315
Pesticide exposure and cholinesterase levels among farm workers in the Republic of South Africa D.B.K Rama and K. Jaga National Centre for Occupational Health, P.O. Box 4788, Johannesburg 2000, Republic of South Africa (Received August 27th, 1991; accepted October 10th, 1991)
ABSTRACT A preliminary survey was undertaken to establish the extent of pesticide exposure in a farming community. The area under investigation included a coffee plantation in the northern region of South Africa. Cholinesterase levels in red blood cells and plasma were used as markers to monitor the extent of organophosphate and carbamate exposure. Sixty-nine farm workers with specific pesticide exposure were selected for the study, and the frequency of the different symptoms which may be related to pesticide exposure was determined by interview and questionnaire. Of the workers, 77% had their red blood cell cholinesterase levels below the normal reference range, while 27% of the workers had depressed plasma cholinesterase levels.
Key words: pesticide exposure; biological monitoring; cholinesterase
INTRODUCTION
In South Africa there are approximately 1.2 million farmworkers (D. du Toit, pers. commun.). If one were to include their families, this could be extrapolated to - 7 million people dependent on agricultural activity (D. du Toit, pers. commun.). Pesticides are produced in large quantities and include a range of types, such as organophosphates, carbamates, organochlorines, pyrethrins and bipyridals. Globally, about 2 million tons are used annually [1]. The labour force and their families usually live on the farms or in close proximity thereto. Hence, a large segment of the South African population is exposed occupationally and/or environmentally to one or other type of pesticide. In this preliminary study, workers in a coffee plantation were surveyed for organophosphate exposure. The enzyme cholinesterase (ChE) is a useful marker [2-6] of occupational and environmental exposure, hydrolysing esters of choline, such as acetylcholine. Acetylcholine is very im-
316
D.B.K. RAMA AND K. JAGA
portant physiologically [3]. It is synthesised at nerve endings and acts to transmit impulses from nerve to muscle fibre. There are two types of this enzyme, the 'true' and the pseudocholinesterase [8], ChE destroys the acetylcholine after the impulse transmission has occurred, so that subsequent impulses may be transmitted if necessary. Without hydrolysis of acetylcholine, the nerve would remain electrically charged and further conduction would be inhibited. The organophosphate and carbamate pesticides inhibit this enzyme [9,10], and its activity is used as an index of exposure to these pesticides. MATERIALS AND METHODS A total of 69 workers exposed to organophosphorous and carbamate pesticides were evaluated by questionnaire with the assistance of one of the management staff and the local health inspector. Since it was difficult to obtain control subjects from the rural environment under investigation, no interviews were conducted for controls. The types of pesticides used, the mode of exposure, and the number of hours of pesticide application per day or week was noted. Workers age, sex, height, weight and symptoms experienced were recorded. Red blood cell (RBC) and plasma cholinesterase levels were assessed spectrophotometrically as described by Lewis et al., with some modifications [11]. Since baseline levels of ChE for each individual are not known, the normal levels reported in literature are used as a reference. A period of at least 30 days must separate the baseline determination from the worker's last exposure to a cholinesterase-inhibiting compound [2]. This was difficult to achieve due to the worker's commitment to their duties. Ethical consideration Informed consent was obtained from each subject after the purpose of the study was explained to them in their own language. RESULTS The workers worked an 8-h shift, 6 days per week. Most of the farmworkers were females, and the subject's sex, mean age, mean height, and mean weight is summarised in Table 1. A wide range of pesticides are generally applied by the farmworkers monitored (Table 2). Approximately 3 months prior to the survey, the farmworkers were only applying organophosphates. Pesticides were sprayed by hand applicators and tractor drivers. The workers were provided with protective clothing such as masks, gloves, overalls and boots. However, there
PESTICIDE EXPOSURE AND CHOLINESTERASE LEVELS AMONG FARM WORKERS IN SOUTH AFRICA
317
TABLE 1 Profile of the subjects monitored Sex
n
Mean agea
Mean height (range)
Mean weight (range)
Males Females
8 61
---
1.68 m (1.63-1.74) 1.55 m (1.47-1.69)
52.6 kg (46-56 kg) 52.54 kg (38-71 kg)
aMany subjects did not know their age.
was no formal occupational hygiene programme to ensure good hygiene practices regarding the use of clean and well maintained protective equipment. Table 3 summarises the percentage of workers that reported the different symptoms that could be associated with organophosphate exposure. Biological monitoring indicated depressed ChE levels in red blood cells and plasma in many workers (Table 4). DISCUSSION There is a need for farmers and their workers handling pesticides to be made aware of the health effects o f pesticides. Workers engaged in handling pesticides should be supervised by one who has knowledge and experience in the application o f pesticides. Furthermore, good occupational hygiene
TABLE 2 Types of pesticides used Organophosphates Parathion Monocrotophos Dicrotphos Trichlorfon Disulfoton Carbamates Benomyl Thiocarbamates Mancoseb: Maneb Zineb
Herbicides Bipyridals Paraquat Fluazfop-p-butyl Glyphysate Fungicides Copper oxychloride Minam Organochlorines Chlordane
318
D.B.K. RAMA AND K. JAGA
TABLE 3 Clinical findings Symptoms
Frequency (%)
Nausea/vomiting Abdominal cramp Diarrhoea Chest tightness Weakness Headaches Visual problems Dermatological Other: goitre No symptoms
7.3 36.2 50.7 43.5 53.6 68.1 31.9 7.3 1.5 1.5
standards should be adhered to. In the case of those workers spraying by hand, little knowledge of the importance of wind direction was known to ensure that they sprayed downwind and walked through untreated crops to ensure minimum exposure. Eating and smoking also took place at the spraying sites without washing up. After working in the field, no special precautions were taken such as cleaning, maintaining, and storage of protective clothing and equipment ready for use next time. Finally, no wash-up facilities are provided and the workers go home without changing the contaminated clothes. Although blood from 69 workers was collected, only 31 red blood cell and 41 plasma specimens were analysed due to problems encountered during transit of the specimens to the laboratory. The normal reference range adopted in this study is one used by many of the pathological laboratories in the Republic of South Africa (A.J. Areias, pers. commun.). A recent study in South Africa that established a reference range for serum ChE indicates a fairly similar reference range as adopted in this study [12]. It was difficult to obtain control subjects from the rural environment under investigation. TABLE 4 Cholinesterase activity
RBC Plasma
Mean
Range
n
% falling below normal range a
2469 3116
1722-3198 90-4950
30 41
77 27
aNormal reference range: RBC, 2800-5200 units/1 whole blood. Plasma, 3500-8500 units/1.
PESTICIDE EXPOSURE AND CHOLINESTERASE LEVELS AMONG FARM WORKERS IN SOUTH AFRICA
319
Control subjects selected from our laboratory personnel were within the range adopted. However, ideally it is best to compare the workers postexposure ChE level with their own baseline value. This was not possible in this study. This preliminary study indicates definite organophosphate exposure and lack of occupational hygiene standards. A detailed study is presently being planned to evaluate the ChE levels in a larger sample o f farmworkers and arrangements are being made to establish a local ChE reference range by selecting control subjects from the region under investigation. ACKNOWLEDGEMENTS The authors would like to thank National Chemical Product, Chloorkop and A.J. Areias of the South African Institute for Medical Research for analysing the blood specimens. The workers and management o f the coffee plantation are also thanked for their cooperation. REFERENCES 1 M. Marone, Forward, Workshop on the use of human exposure and health data for im"provingthe toxicologicalrisk assessment of pesticides and their regulatory control, Med. Lay., 81 (1990) 450-452. M.J. Coye, J.A. Lowe and K.T. Maddy, Biological monitoring of agricultural workers exposed to pesticides: I Cholinesterase activity determinations, J. Occ. Med., 28 (1986) 619-627. D.F. Innes, B.H. Fuller and G.M.B. Berger, Low serum cholinesteraselevels in workers exposed to organophosphate pesticide sprays, S. Afr. Med. J., 78 (1990) 581-583. R.G. Ames, S.K. Brown, D.C. Mengle, et al., Protecting agricultrual applicators from overexposure to cholinesterase-inhibitingpesticides: Perspectives from California Programme, J. Soc. Occup. Med., 39 (1989) 85-92. WHO, Early detection of Occupational Diseases. WHO, Geneva, 1986, p. 59. M. Coye, P.G. Barnett, J.E. Midttling, et al., Clinical confirmation of organophosphate poisoning of agricultural workers, Am. J. Ind. Med., 10 (1986) 399-409. 7 D.F. Heath, Organophosphorous Poisons. Anticholinesterasesand Related Compounds, Pergamon Press, New York, 1961, pp. 103-258. 8 N.W. Tietz (Ed.), Fundamentals of Clinical Chemistry, W.B. Saunders, Philidelphia, 1976, pp. 643-646. 9 L. Rosenstock and M.R. Culler, Clinical Occupatinal Medicine, Saunders, Philidelphia, 1986, p. 262. 10 R.G. Ames, S.K. Brown and D.C. Mengle et al., Cholinesterase activity depression among California agricultural pesticide applicators, Am. J. Ind. Med., 15 (1989) 143-150. 11 P.J. Lewis, R.K. Lowing and D. Gompertz, Automated discrete kinetic method for erythrocyte acetylcholinesterase and plasma cholinesterase, Clin. Chem., 27 (1981) 926-929. 12 B.H. Fuller and G.M.B. Berger, Automation of serum cholinesterase assay-paediatric and adult reference ranges, S. Afr. Med. J., 70 (1990) 577-580.
