Pesticide research for public health and safety in Malaysia, the Philippines, and Thailand
K.Y. Lum, Md. Jusoh Mamat, U.B. Cheah, C.P. Castaneda, A.C. Rola, and P. Sinhaseni
Fundamental Research Division, Malaysian Agricultural Research and Development Institute, Kuala Lumpur, Malaysia; Department of Pharmacology, College of Medicine, University of Philippines, Manila, Philippines; Center for Policy and Development Studies, University of Philippines, Los Baños, Laguna, Philippines; Science and Technology Development Board and Department of Pharmacology, Chulalongkorn University, Bangkok, Thailand.
In Malaysia, the Philippines, and Thailand, concern is growing about the impact of increased use of agropesticides on public health and safety, especially in farming communities. Based on data from public hospitals and clinics, the extent of pesticide poisoning is considered to be grossly underestimated, primarily due to underreporting. A review of public-health and safety research in these countries suggests that there is commonality in the research needs in this area. Three aspects have been identified as requiring attention: exposure assessment, application technology, and farmer education and training. Initial steps have been taken to establish a collaborative network comprising scientists from the three countries to address the problems identified. Research proposals are being drawn up to develop appropriate personal protective equipment, improved knapsack sprayers, and farmer education and training modules.
Because of their growing populations, agriculture remains an important component of the developing economies of Malaysia, the Philippines, and Thailand. In pursuit of higher agricultural productivity, the introduction of modern farming technologies in these countries has meant increased use of fertilizers and pesticides.
Growing global concern about the impact of increased use of agricultural chemicals, especially in developing countries, has raised questions about the extent and nature of the adverse effects of pesticides on farmers, consumers, and the environment. The need for more comprehensive information on the status of public-health and safety-related aspects of pesticide research has been reinforced by the recognition of the importance of regional collaboration to address pesticide problems common to the agricultural activities of these three countries.
Profile of pesticide use
In Malaysia, over 3 000 retail outlets are currently involved in the manufacture, formulation, and packaging of pesticides. In 1980, sales of pesticides amounted to 65 million USD. The continued demand for pesticides in Malaysian agriculture is evident from the increasing sales of agricultural chemicals. Sales of herbicides, insecticides, fungicides, and rodenticides increased from 95 million USD in 1984 to nearly 120 million USD in 1988 (MACA 1989). Herbicides account for nearly 80% of these sales in Malaysia; insecticides, about 15%; and rodenticides, nematicides, and others, 5% (MACA 1989).
Herbicides are used mainly on plantation crops, such as rubber, oil palm, and cocoa; the common ones are paraquat, glyphosate, 2,4-D (2,4-dichlorophenoxyacetic acid), diuron, MSMA (methylarsonic acid), picloram, and dalapon. Insecticides may also be required for disease control on rubber plantations, and fungicide and insecticide treatments are often used on cocoa plantations. Pesticides are also employed on a wide range of other agricultural crops, such as vegetables, rice, fruit, and tobacco.
Pesticide consumption in the Philippines, based on sales value of total imports, increased steadily from 1983 to 1987 (Table 1). Crops receiving the highest proportion of pesticides (based on value) in 1984 were rice (36.6%), bananas (25.5%), and vegetables (14.3%). Insecticides were used on most crops, except bananas and pineapples, where more fungicides were used.
Current pest control practices in Thailand rely primarily on chemical methods. Cotton and vegetable crops, in particular, require large amounts of pesticides. The intensification of cotton production has led to an increase in the incidence of pests and diseases (FAO 1988), resistant species, and pest resurgence problems.
Thailand imported 65.2 million USD (cost including freight) of pesticides in 1987 (Fig. 1). Typically, 50% of the imports, by value, were insecticides, 30% herbicides, and the rest fungicides and other miscellaneous pesticides. Most of the insecticides are used on rice, cotton, and vegetables. The herbicide market is focused on sugarcane, pineapple, rubber, and rice (ADB 1987). Except for paraquat, which is produced locally from imported intermediates, pesticides are either imported as finished products or as technical grade ingredients and formulated in Thailand.
Prevalence of pesticide poisoning
In general, epidemiologic description of poisoning in Malaysia is hindered by lack of coordination in data collection. The best sources of information have been in-patient data and laboratory reports from government hospitals and records from the Chemistry Department of the Ministry of Science, Technology and the Environment.
Data from this Ministry from 1979 to 1986 suggest that most poisonings are due to pesticides: mainly the widely used herbicide, paraquat (Fig.2). Ministry of Health information indicates that, in some cases, multiple agents are involved. Circumstances surrounding these poisonings show that 49.1 % were intentional and 37.8% were accidental.
Regional differences in the incidence of poisonings within a country reflect the extent of toxic substance use in these areas (Sinnaia 1989). Arcas that include large numbers of plantations and farms (where pesticides are likely to be used in large quantities) tend to record high levels of mortality due to pesticide poisoning. Also, mortality from pesticide poisoning is closely correlated with suicidal intent (72.6%), suggesting that some regulatory intervention would be useful. This is further supported by the fact that farm and plantation workers constitute 45% of the reported pesticide deaths.
More recent studies of Malaysian rice-farming communities indicate that a large percentage of farmers develop symptoms associated with pesticide poisoning. In the intensely cultivated area of the Cameron Highlands, where pesticides are widely used, 95% of all poisoning cases are attributed to pesticides. In 1980, there were 17 cases of pesticide poisoning resulting in 4 deaths; in 1981, the number of cases increased to 20 with 11 deaths; and between January 1982 and April 1983, there were 11 cases and 4 deaths (Asna et al.1989).
Malaysia recently established a National Poison Centre in the Department of Pharmacology, Universiti Kebangsaan Malaysia. The main functions of this Centre are to identify the risk of poisoning in the local population, to establish preventive measures, and to ensure proper diagnoses and provide treatment for poison victims (Tariq 1989).
Department of Health hospitals in the Philippines reported 4 031 cases of acute pesticide poisoning and 603 deaths between 1980 and 1987 (Fig. 3). Most of these were suicidal (64%); accidental and occupational poisonings accounted for 18% and 14%, respectively. Death rates from acute pesticide poisoning ranged from 13% to 21%. The distribution by gender for all acute pesticide poisoning cases from 1980 to 1987 showed a slight predominance of males (54.0%) over females (46.0%) (Castaneda and Rola 1990).
Studies of civil registry information have also been carried out in the Philippines to determine the relation between causes of mortality and pesticide use. Strong evidence has been found linking a marked increase in mortality in Central Luzon with occupational exposure to insecticides (Bantilan and Rola 1989). Municipalities with high levels of pesticide use generally have higher mortality rates than those using smaller amounts.
In response to the findings of these studies, an occupational-health and monitoring program has been initiated for workers who apply nematicide on banana plantations. It is hoped that, in the future, the industry itself will sustain the program.
In Thailand, the Division of Epidemiology in the Ministry of Public Health monitors pesticide poisoning cases and deaths from unintentional causes. Data for 1975-1987 show an increase in the number of reported pesticide intoxication cases from 518 to 4 633, accompanied by a decrease in mortality rate from 3.47 per 100 000 in 1975 to 1.00 per 100 000 in 1987. In 1981-1987, the Ministry of Public Health reported 20 outbreaks of food poisoning attributed to pesticides, involving 722 cases (Swaddiwnthipong et al.1989).
Although the incidence of pesticide poisoning in the Thai agricultural communities of Rayong province can be as high as 8 268 per 100 000, only 2.4% of this group spent time in hospital, emphasizing the possible extent of underreporting in hospital statistics (Wongphanich et al. 1985). A 3-year study by the Office of the National Environment Board (Sinhaseni 1990) determined that organophosphate insecticides such as parathion were the leading pesticides implicated in cases of poisoning. Half the cases of exposure were due to attempted suicide; 7-26% were attributable to occupational exposure. Fewer than 10% of the cases resulted from accidental exposure. In contrast, animal poisoning is usually accidental and caused by direct ingestion of highly toxic pesticides. Cattle and goats are often affected by grazing on grasses treated with sodium arsenite, a toxic herbicide formerly used on rubber estates (now withdrawn from the market).
Summary of past research
Studies of occupational exposure of spray operators have been limited in Malaysia. Swan (1969) carried out two field trials on Malaysian rubber plantations to study the exposure of operators applying paraquat with handoperated knapsack sprayers. Howard and colleagues (1981) studied the health of Malaysian plantation workers, especially those using paraquat sprayers. Chester and Woolen (1981) reported on the occupational exposure to paraquat of Malaysian plantation workers.
More recently, Lee and Chung (1985) and Lee (1987), using either Ciba-Geigy water-sensitive paper or fluorescent-tracer dye, carried out an extensive study on the potential contamination of various parts of a sprayer operator’s body, using different types of applicators and under various crops or crop-spraying situations. They concluded that the extent of chemical contamination is affected by the type of applicators used, height and position of spray nozzle, and the speed and direction of the prevailing wind at the time of spraying. A conventional knapsack sprayer caused more extensive contamination than that resulting from a control droplet applicator (CDA).
Using the method of the Operator Protection Research Group (Ministry of Agriculture, Food, and Fisheries, UK) with lissamine green tracer dye, Tan et al. (1988) carried out a study to determine quantitatively the potential dermal exposure of spray operators. Operators using knapsack sprayers were exposed to 27.84 mL/ha, on average, compared with 31.78 mL/ha for those using CDA sprayers. Potential inhalation was 0.0010-.0.0066 mL/ha for knapsack sprayers and 0.0001-0.0()47 mL/ha for CDA sprayers. The front leg of the operator was most exposed, with exposure significantly higher for those using CDA sprayers (86%) than those operating knapsack sprayers (59%).
Pesticide application techniques used for annual crops (Lim et al. 1983) and perennial crops (Sidhu et al. 1987) have been discussed in detail. For many crops, pesticides are applied by spraying the foliage although the inefficiencies and the high risk of operator exposure with this technique have long been known (Matthews 1983; Hislop 1988; Zeren and Moser 1988). In Malaysia, spraying of foliage is mainly done with conventional knapsack sprayers designed 30-40 years ago (Jusoh Mamat et al. 1987). A high percentage of sprayers owned by farmers in the “rice bowl” of Malaysia had serious faults and exhibited a volume discharge efficiency of less than 75% (Anas et al.1987). These factors contribute to the problems arising from underdosing, incorrect timing, and contamination of spray operators. Of the current application techniques, only a few, such as trunk injection, granular application to the soil, and pouring, dripping, and tea-bag techniques are relatively safe to use (Jusoh Mamat et al. 1985; Ooi 1988). However, these safer techniques are situation specific and not as versatile as conventional foliar spraying.
Protective clothing made of plastic or rubber material causes discomfort when worn for more than 3 h under the hot, humid field conditions of the tropics (Lee 1987; Jusoh Mamat and Anas 1988). Yet protective apparel is essential if minimal exposure to sprayed pesticides is to be achieved, especially when perennial crops taller than 150 cm are sprayed using ground applicators (Lee 1987). There is some interest in searching for a more suitable material for protective clothing. To date, only two lightweight disposable materials have been developed: Dupont Tyvek and Kimberley Clark Kleengard EP (Lee 1987).
The Malaysian Agricultural Research and Development Institute (MARDI), under the Ministry of Agriculture, conducts research on various pesticide-related problems in major agricultural ecosystems. In addition to studying application technology and exposure of operators, MARDI research includes investigation of environmental fate, effects, and bioefficacy. Recommendations on pesticide use for pests and diseases of specific crop systems are also made. Information and technology generated from the research are channeled to the Department of Agriculture for dissemination to farmers.
Farmers and the general public pay little attention to the proper use of pesticides, especially with regard to safety (Zain 1977; Zam 1980; Basri 1981; Heong 1982; Normiya 1982; Ooi et al.1983; Heong et al.1987; Anon.1990). As a consequence of this apathy, reports of users suffering ill effects due to improper use of pesticides are common (Dawson 1985; Umakanthan 1985; Indrani 1988).
In August 1984, in response to these findings, the Malaysian Department of Agriculture launched a nation-wide campaign to promote the safe use of pesticides. The campaign had three main objectives (Esa and Ramasamy 1988):
• To create awareness in the general public of the dangers associated with the use of pesticides;
The campaign included lectures and talks, exhibitions, distribution of pamphlets and posters, radio programs, and television screenings of documentary films on the safe use of pesticides (Esa and Ramasamy 1988). To educate farmers about the specific danger of using monocrotophos in rice and vegetables crops a “Safe Use of Pesticides” campaign in Sabak Bernam district has also been initiated (Asna 1990).
Other semigovernmental agencies, such as MARDI, the Rubber Research Institute of Malaysia, Federal Land Development Authority, Muda Agricultural Development Authority, and Federal Land Consolidation and Rehabilitation Authority, also organize short training courses for their junior technicians on the safe application of pesticides. In the private sector, since 1982, societies such as the Malaysian Plant Protection Society and the Malaysian Agricultural Chemicals Association have also held courses on pesticide application technology. These have been mainly aimed at professionals in crop protection, such as researchers, university lecturers, estate managers, and pesticide-industry personnel (Lim and Ramasamy 1983; Tech 1985).
Health and safety-related research activities in the Philippines include descriptive studies on pesticide poisoning based on reviews of hospital records, occupational exposure studies in rice- and vegetable-farming communities, development of an occupational health and monitoring program, and health economics and policy research studies.
Two retrospective studies reviewing hospital records (Castaneda and Maramba 1980; Gonzales and Chua 1984) analyzed data on pesticide poisonings by age and gender distribution, common presenting signs and symptoms, correlation between signs and symptoms and cholinesterase level in red blood cells, average dose of atropine administered, and toxicity ratings of the pesticides. Of a total of 1 074 cases of poisoning reported from 1982 to 1985, 42% involved organophosphates, 19% organochlorines, and 14% carbamates (Castaneda 1988). Peak incidence occurred among those under 40 years old and was slightly higher for males. Suicide accounted for 63% of the cases, occupational exposure 18%, and accidental exposure 16%. The highest case fatality rate was associated with organochlorine poisoning (49%) followed by organophosphates (16%).
Research efforts have also been directed toward characterizing occupational pesticide exposure among vegetable and rice farmers by examining demographic data, agricultural practices, and general health conditions. Only one study has dealt with farmers’ perceptions of the health impact of pesticide use. Generally, research on how farmers’ attitudes can affect the way in which pesticides are used is lacking.
Studies by Castaneda (this volume) determined the potential exposure of rice farmers to an organophosphate compound and concluded that workers’ hands are most exposed to dermal contamination and penetration during mixing and loading activities. Castaneda also examined the protection afforded by locally designed clothing. Such clothing was often uncomfortable and tore easily. One investigation found no difference in protection between people wearing “Gardsman” protective clothing and an unprotected group.
Several pesticides have been studied in the Philippines to determine their behaviour in model ecosystems (Tejada and Magallona 1985; Zukifli et al. 1985; Varca and Magallona 1987). These included deltamethrin, carbosulfan, chlorpyrifos (Brodan), and fenobucarb (BPMC, 2-sec-butyl-N-methyl carbamate). Carbosulfan does not have pollution potential, although its major metabolite, carbofuran, remains in soil and fish for up to 30 days at low levels. Brodan was found to be rapidly assimilated and concentrated in fish. Repeated applications of BPMC at recommended levels, on the other hand, were absorbed into the soil.
In general, research on pesticide residues in the Philippines has focused on insecticides. Both field residue trials and “market-basket” studies have generated information for a residue data base that includes insecticide residue levels in cabbages, pechay, string beans, green beans, tomatoes, bush sitao, cotton, tobacco, bananas, mangoes, fish, and the various components of the rice-paddy environment, such as soils, paddy water, rice plants, fish, and snails. Residue levels have also been measured in lactating goats and in human milk.
Other ongoing research projects in the Philippines include a project to provide training for rice and vegetables farmers in integrated pest management. Preliminary results indicate that the practices of these farmers affect the extent of their exposure to pesticides. Another study, funded by the Rockefeller Foundation, is to examine the health effects of pesticide exposure among Laguna farmers at the International Rice Research Institute (IRRI).
Research on the benefits and risks associated with pesticide use among rice and vegetable farmers has resulted in a recommendation for more government regulation and training of extension agents and farm workers (Role 1989). Mechanisms for crop insurance and further research on integrated approaches to plant protection have also been advocated.
Studies on the exposure of Thai people to pesticides revealed dangers from organochlorine insecticides and lipid-soluble herbicides; as much as 90 ppm heptachlor was found in farmers’ blood (Department of Agriculture, Division of Toxic Substances). Between 1980 and 1986, at least 10 such studies were conducted.
Surveillance of pesticide poisoning by the Ministry of Public Health’s Division of Epidemiology has generated more than 20 reports on incidents of pesticide poisoning and accidental deaths. Among the identifiable pesticides involved, organophosphate compounds caused 67.7% of the cases, carbamate 13.0%, herbicides 8.2%, pyrethroids 2.1%, rodenticides 1.3%, and chlorinated hydrocarbons 1.3% (Sinhaseni 1990).
In Thailand, research on the effects of pesticide exposure have generally concentrated on acetylcholinesterase inhibition. Efforts have been made by the Department of Medical Sciences (Sinhaseni 1990) to estimate average normal values for plasma cholinesterase levels in Thai people. Researchers have found a range of 1500-4000 milliunits (Ellman’s method), with significant differences between males (2 760 + 712 milliunits) and females (2 516 + 665 milliunits). The Shell Company (Thailand) has supported a surveillance program measuring blood cholinesterase levels in farmers in various areas and at special functions such as agricultural fairs. The Occupational Health Division, Ministry of Public Health, under the Green Esarn Project, has developed and distributed paper-strip cholinesterase test kits to village health-care personnel. About 300 tests per village in six provinces were conducted in 1990.
An integrated knowledge, attitudes, and practices (KAP) survey incorporating clinical investigations as well as cholinesterase studies is currently being conducted by a multidisciplinary team from Chulalongkorn University. The project involves 150 vegetable farmers in Bang Bua Thong, near Bangkok. In a survey of 658 agriculturists (150 families), the most common complaints were weakness (61%), dizziness (47%), headache (39%), shortness of breath (35%), poor memory (34%), and nausea or vomiting (33%) (Suwanabun et al. 1986).
Assessment of pesticide exposure has been carried out by local scientists as well as international teams (Working Group 1989; Shell Thailand 1989). Perhaps the most comprehensive field study was that conducted by Tuinman and Eadsforth (1987) on exposure and health effects after application of phosdrin formulations on vegetable farms in Thailand. No health effects were observed in any of the workers and it was recommended that attention be paid to the packaging of the concentrate to minimize the possibility of contamination of hands during preparation of formulations.
Tongsakul and Punepan (1988) conducted an exposure-assessment study using high-volume spray dye to compare exposure of the different parts of operators’ bodies when spraying crops of different heights using a knapsack mistblower. Sinhaseni and Tesprateep (1988) similarly conducted an assessment of exposure to endosulfan by gardeners who sprayed large trees.
The pesticide application research team in the Entomology and Zoology Division, Department of Agriculture, is responsible for providing information related to pesticide-application technology in Thailand. Various types of lever-operated knapsack sprayers are currently being evaluated. In addition, the Division of Plant Protection Services operates pesticide clinics; they gather farmers’ and government-owned out-of-service equipment for repair by six rotating units. These units also offer training in equipment repair.
There have been at least 16 KAP studies of Thai farmers. They have revealed that farmers usually do not use protective apparel according to guidelines (Working Group 1989). The studies have emphasized the importance of education, mass-communication tools, peer influence, and extension services to promote safe pesticide-handling practices in farming communities.
Ecological contamination has been monitored by the Division of Environmental Health of the Ministry of Health in 38 rivers in Thailand from 1978 to 1985. Organochlorine levels above World Health Organization (WHO) standards were detected in a number of instances. Pesticide levels in food have also been monitored by the Food and Drug Administration and the Department of Medical Sciences from 1982 to 1985. Multiresidue analyses revealed that 52.5% of the samples contained pesticides.
Various training activities have been carried out to promote the safe use of pesticides. With support from external agencies, such as the Agricultural Requisites Scheme for Asia and the Pacific, the Groupement international des associations rationales de fabricants de produits agrochimiques, the United Nations Environment Programme (UNEP), the Food and Agriculture Organization (FAO), and WHO, programs for training trainers and raising public awareness have been conducted.
For Malaysia, there is an obvious need to establish a mechanism for collating all statistics on the health and safety-related aspects of pesticide use. While research to improve application technology, education, and communication continues, work on exposure and ecological contamination in relation to human health must be given additional emphasis and support. There is insufficient emphasis on investigations into the acute and chronic effects of pesticides on both the farmer-user and the consumer population at large. In this context, the involvement of medical researchers is considered vital.
Technological improvements should be aimed at the small-scale farmer, with regard to application systems and safety. Education and communication must be carried out in parallel with research into improved technology. Small-farmer communities can benefit from more frequent KAP studies and education programs. Research into remediation of the contaminated environment as an approach to improving health and safety for farmers and the general population should concentrate on gathering information on the extent and status of these problems and the adaptation and adoption of available technology relevant to regional needs.
In reviewing past research in the Philippines, it is notable that health-related pesticide and residue studies have attracted the interest of only a few people. Despite this, there is sufficient baseline information for investigators to proceed to intervention studies, although data on the chronic effects of pesticide exposure and residues are still lacking. Likewise, the effects of incidental pesticide exposure, for which the general public is at risk from contaminated food and water, air pollution, and occupational exposure, also warrant investigation.
Educating farmers in the safe and proper use and handling of pesticides must be a research priority. With education, concern for the chronic effects of pesticide exposure of farmers and consumers should also be addressed. Other areas where research is needed in the Philippines include:
• KAP studies that can form the basis for education modules and approaches;
In Thailand, the emphasis has been on exposure assessment in health- and safety-related pesticide activities. Nevertheless, Thai scientists believe that much remains to be done. Research needs in Thailand can been summarized as follows.
Mitigation of risk
• Exposure assessment, especially in crops where pesticide use is high (cotton, vegetables, fruit trees, and rice);
Better identification and assessment of risk
• Integration of epidemiologic information on dose-response and appropriate control;
Increase and improve training activities
• Training the trainers to be more efficient using KAP strategy and communicative skills;
Better regulation of highly toxic pesticides
Regional collaborative pesticides research
A review of the past and current activities in Malaysia, the Philippines, and Thailand with respect to health- and safety-related aspects of pesticide use in agriculture raises several important points. Although agriculture continues to play an important role in the economies of these countries, the major crops differ. However, the health and safety problems in these countries are similar and the identified research needs are common. Three areas deserve attention: the need for comprehensive exposure assessment; the need to instill safety consciousness, especially in farming communities; and the need to upgrade pesticide-application methods, especially among small farmers.
Recognizing the commonality of research needs has been the driving force behind an initiative to develop a regional strategy for pesticides research through a network comprising scientists from Malaysia, Thailand, and the Philippines. At a meeting in July 1990 in Bangkok, Thailand, the research group reconfirmed the priorities for the region and reached consensus on the following specific research proposals:
• Exposure assessment - design and development of personal protective equipment for rice- and vegetable-farm labour, appropriate to the environmental and sociocultural conditions of the three countries;
The collaborative effort of scientists from the three countries is summarized in their mission statement:
Development of appropriate application technology and generation of exposure-assessment information, reinforced through farmers’ education and training as a strategy for the minimization of health risks in agricultural pesticide usage.
Regional collaboration is to be facilitated by a coordinated network that will improve linkage through regular meetings of the scientists, a data base of relevant research, and facilities for information exchange. More specifically, the network will aid in the development of common approaches to identified problems. It has already agreed upon common core protocols for baseline KAP surveys for all three research proposals; basic specifications for personal protective equipment and knapsack sprayers; and joint development and use of training modules and communication materials.
Collaborating scientists in each country have been charged with the task of developing projects that will be combined into a regional proposal to solicit funding from international aid agencies. The within-country and between-country linkages resulting from this effort are expected to generate information and technology that directly address the need to upgrade public health and safety in the use of agropesticides in the ASEAN (Association of South East Asian Nations) region.
Acknowledgment - This review was made possible by a grant from the International Development Research Centre, Canada.
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