The health hazards of organophosphate use in South Africa

The use of organophosphate compounds (OPs) for pest control in South Africa has increased substantially over the past decades, particularly in the fruit and vegetable-producing sectors. Expenditure on agrochemicals as a whole nearly doubled from US$93 million in 1985 to US$177 million in 1990(1). Leslie London of Cape Town University investigates.

At present, over 25 different types of OPs (in 55 different formulations) are registered by the Department of Agriculture for use in different crop sectors(2), including parathion, one of the Pesticide Action Network's 'Dirty Dozen'.
    However, data on actual quantities of OPs used in South Africa (as opposed to prices paid for OP use) are not routinely available, as no effective monitoring or surveillance mechanism currently exists for this purpose. In 1976, the Department of Agriculture discontinued its practice of requiring agrochemical companies to submit returns on agrochemical production(3). However, no alternative system of monitoring potential exposures was put in its place. As a result the last published figures for quantities of agrochemical usage were for 1978-79 when 24,598 metric tons of OPs were reported as used in South Africa for pest control(4). At that time, this figure represented 39% of all insecticide use in the country.
    In the absence of statutory reporting requirements, a practice used widely in developed countries, market research data from industry may give some idea of OP usage in agriculture. Analysis of these data suggests that 144,000 kg of active ingredient of OPs were used in farming activities in the Southern Region of South Africa in 1989, and that 65% of all insecticide usage in fruit farming in the region involved OPs(5).
    The relationship between usage and actual human exposure depends on many other factors such a workplace hygiene, safety behaviour and use of protective equipment. Farm workers in South Africa are a particularly marginalised group with extremely low levels of education, little access to information, and often suffer harsh working and living conditions(6,7,8). For example, mean educational levels are of the order of five years of schooling(9). A recent study showed that 20% of farm workers involved in chemical application were illiterate(10). Alcoholism is widespread among farm workers, particularly in areas where the 'dop' system (payment of wine in lieu of wages) is still in operation(11,12,13). In these conditions, measures to limit workers' exposure to pesticides are frequently non-existent. Availability and usage of protective equipment for workers handling agrochemicals are often low, with estimates ranging from 0%(15) to between 20 and 70 %(15) . Training of workers in safe handling of pesticides is rare. One survey in the Western Cape found that less than 12% of workers responsible for pesticide application had received any training in safe handling, other than in-service orientation from the farmer(16).
    An additional route of OP exposure for farm workers is environmental as most of their dwellings are commonly adjacent to, or surrounded by fields or orchards subject to spray. Spray drift may contaminate workers homes, although there has been no research into the extent of this hazard. Similarly, groundwater contamination with OPs and other agrochemicals has not been systematically investigated in South Africa's rural areas. Given growing concerns for long-term health effects arising from chronic low-dose environmental chemical exposures(17), and the fact that most farm workers receive their drinking water from borehole or surface water(18), such routes may contribute substantially to lifetime burdens of OP exposure.

Health effects of OP exposure
Poisoning due to pesticides is a notifiable condition in South Africa, and between 100 and 150 cases are reported per year, with a case fatality rate of the order of 10%(19). However, these figures are a substantial underestimate of the true rates. Reviews of hospital admissions suggest that only one-fifth of hospital cases are reported(20,21). The majority of reported cases involve OPs, (approximately 68% in the Western Cape in 1987-91) they most frequently occurred in the setting of workplace poisoning (18%), domestic accidents (48%) and suicide (34%) on farms in the region(22). Farm workers attempting suicide appear to have a four-fold higher risk of killing themselves than town or urban residents, possibly due to greater OP access.
    Many farm workers attempt suicide with OPs. It is disturbing that storage and disposal practices on many farms in South Africa are inadequate. For example, an audit of 39 randomly selected farms in the Western Cape found that more than half of the farms had pesticide stores unlocked at the time of audit, and that 49% kept materials other than pesticides in their farm stores(23). Similarly, legal disposal of containers requires puncturing, crushing and burying (or burning) the empty container, but anecdotal evidence suggests that these steps are not followed. Re-use of containers for domestic use by farm workers is also a key source of OP poisoning.

Biological monitoring
Until recently, farm workers were excluded from the provisions of health and safety legislation(24). As a result, little surveillance of workers exposed to pesticides takes place in South Africa, despite the role that biological monitoring may play in reducing OP related morbidity and mortality. A study among workers on a deciduous fruit farm in the Western Cape found that 15% of workers involved in routine spraying had biochemical evidence of OP exposure resulting in reduction of plasma cholinesterase activity(25). This study suggested that adverse effects due to OP exposure may be widespread, although these findings have not been consistently demonstrated in other investigations locally.
    Apart from acute morbidity, chronic effects of low-dose long-term exposures to OPs are attracting increasing concern(26). This is particularly important in South Africa for a number of reasons. Potential exposures are widespread, and may be environmental in origin. Current agrochemical registration procedures rely almost exclusively on data on acute toxicity and grading of toxicity is based on LD50s, measures which do not take account of long-term toxicity. Farm workers are particularly vulnerable to long term health hazards, given their poor living and working conditions. A pilot study investigating the effect of long-term OP exposure on workers peripheral vibration sense found that pesticide application had significantly reduced peripheral vibration sense compared to a control group of packstore workers(27). Further studies into the possible chronic effects of low dose exposures are urgently needed(28).
    In conclusion there is little doubt that OPs remain a key potential health hazard in South Africa in common with the rest of the developing world.

References:
1. London L, An Overview of Agrichemical Hazards in the South African farming sector, South African Medical Journal, 1992, 81:560-564.
2. Vermeulen JB, Sweet S, Krause M, et. al., A Guide to the Use of Pesticides and Fungicides in the Republic of South Africa, Plant Protection Inst., Department of Agriculture, Pretoria, 1990.
3. Barlin-Brinck M, Pesticides in South Africa, The Wildlife Society of South Africa, Durban, 1991.
4. Fourie HO, Toxicological consequences of pesticidal use in the Republic of South Africa, PhD Thesis, University of Cape Town, 1986.
5. London L, Myers JE, Critical issues in agrichemical safety in South Africa, American Journal of Industrial Medicine, 1995, 27(1):1-14.
6. Emanuel K, Poisoned pay: Farmworkers and the South African Pesticide Industry, Group for Environmental Monitoring and The Pesticides Trust [now PAN UK], Johannesburg, 1992.
7. Davies W, We cry for our land: farm workers in South Africa, Oxfam, Oxford, UK, 1990.
8. Keenan J, Sarakinsky M, Reaping the Benefits: Working conditions in agriculture and the bantustans, In: "South African Review 4," Ed. Moss G, Obery I, Raven Press, Johannesburg, 1987.
9. De Graaff JF, Louw W, Van der Merwe M, Farm schools in the Western Cape: A sociological analysis, Department of Sociology Occasional Paper 14, University of Stellenbosch, 1990.
10. London L, Myers JE, Nell VN, Thomson ML, Mbuli S, Neurotoxic effects of long-term agrichemical exposures amongst farm workers in South Africa, Paper: 5th Int. Symposium of Neurobehavioural Methods and Effects in Occupational and Environmental Health, Cairo, 1994.
11. op. cit. 7.
12. op.cit. 8.
13. op. cit. 10.
14. op. cit. 6.
15. London L, Agrichemical safety practices on farms in the Western Cape, South African Medical Journal, 1994, 84:273-278.
16. Ibid.
17. Landrigan PJ, Graham DG, Thomas RD, Strategies for the Prevention of Environmental Neurotoxic Illness, Env. Res., 1993, 61:157-163.
18. op. cit. 15.
19. op. cit. 5.
20. op. cit. 6.
21. London L, Ehrlich R, Rafudien S, Krige F, Vurgarellis P, Notification of pesticide poisoning in the Western Cape 1987 - 1991, South African Medical Journal, 1994, 84:269-272.
22. Ibid.
23. op. cit. 15.
24. Dept. of Manpower, Occupational Safety and Health Act 85/93, Govt. Printers, Pretoria, 1993.
25. Innes DF, Fuller BH, Berger GMB, Low serum cholinesterase levels in rural workers exposed to organophosphate pesticide levels, South African Medical Journal, 1990, 78:581-583.
26. Davies JE, Neurotoxic Concerns of Human Pesticide Exposure, American Journal of Industrial Medicine, 1990, 18:327-331.
27. Manjra S, London L, Myers JE, Vibration sense loss among fruit farm workers, in prep., Dept. of Community Health, University of Cape Town, 1995.
28. op. cit. 10.
29. op. cit. 5.

Leslie London works for the Department of Community Health at the medical School, University of Cape Town, Observatory 7925, South Africa.

[This article first appeared in Pesticides News No. 27, March 1995, pages 6-7]