Pesticide Use,Poisoning,and Knowledge and Unsafe Occupational Practices in Thailand

Introduction

Thailand is predominantly an agricultural country and a major exporter in the world rice market. Thirty-nine percent of the population is engaged in an agricultural sector, and 46.5 percent of the total land area is used for agricultural purposes.^1,2 In recent decades, the Thai government has made an effort to enhance agricultural productivity by increasing land use and enacting favorable tax policies for agrochemical imports. These actions have resulted in an agricultural system in Thailand that has shifted from traditional to commercial agriculture. The gross domestic product from agriculture is continuously increasing, while pesticide imports into Thailand are also increasing for the purpose of enhancing agricultural productivity.^2–4 Complex pesticide mixtures are excessively used in crop areas, resulting in contamination of the environment and humans. ⁵ Academia and nongovernmental organizations provide scientific data on the adverse effects of pesticides on the environment and humans. They also call for bans and restrictions on some highly toxic pesticides, such as chlorpyrifos, paraquat, and glyphosate. However, the scientific data available in Thailand are limited and inconsistent. Thus, this article reviews research studies regarding pesticide use, poisoning and symptoms, pesticide knowledge, and unsafe occupational practices in Thailand. The topics are as follows: (1) agricultural systems and pesticide use, (2) pesticide residues in the environment, (3) pesticide poisoning, (4) factors affecting health and symptoms of pesticide poisoning, (5) determination of pesticide exposure levels, (6) lack of pesticide knowledge, (7) unsafe occupational practices of pesticide use, and (8) ways to reduce pesticide use and risks in Thailand.

A literature search was conducted of articles published between 2006 and 2017. Databases such as PubMed, SCOPUS, ScienceDirect, and Google Scholar were used as sources. The search used the keyword “Thailand” or “Thai” combined with other keywords such as “pesticide,” “farmer,” “agriculture,” and “farm worker.” Literature in the Journal of Health also was searched (http://www.jhealthres.org/). The websites used are as follows: Office of Agricultural Economics, Department of Agriculture (http://www.oae.go.th); Office of Agricultural Regulation, Department of Agriculture (www.doa.go.th/ard/); Food and Fertilizer Technology Center for the Asian and Pacific Region (http://ap.fftc.agnet.org/ap_db.php); and Bureau of Epidemiology, Ministry of Public Health (http://boe.moph.go.th).

Agricultural System and Pesticides

In Thailand, as in most Southeast Asian countries, the agricultural system and land uses have been transformed from traditional cultivation to commercial crop cultivation. Thailand is ranked third of fifteen Asian countries in terms of pesticide use per unit area. On the other hand, the product yield per area unit in Thailand is very low when compared with other countries. ⁵ Rice is the most important economic crop in Thailand, which has the highest cultivated area (13,164,706 ha [hectare] of wet-season rice and 1,529,412 ha of off-season rice). Other major crops are cassava, corn, sugarcane, oil crops, para rubber, fruit tree, and others (Table 1). ⁶ Therefore, rice uses the highest total amount of pesticides because it has the highest area of cultivation. ⁷

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Table 1.

Forecasted Data of Crop Area, Production Yield, and Value of Economic Crops in 2015, Thailand.

Crops	Cultivated area (hectare, ha)	Production yield (tons)	Product yield per ha (kg)
Wet-season rice	13,164,706	22,980,000	1746.75
Off-season rice	1,529,412	4,030,000	2635
Cassava	2,049,412	31,040,000	15,130
Corn	1,703,529	4,710,000	2766.75
Para rubber	4,614,118	4,320,000	986
Sugarcane	2,096,471	110,020,000	52,487.5
Oil palm	1,063,529	11,680,000	10,994.75
Longan	252,460	941,893	3731.5
Durian	136,901	641,941	4687.75
Pineapplea	105,882	1,780,000	nd
Mangosteen	97,452	291,410	2690.25
Coffeea	59,061	26,061	437.75
Soybean	44,706	51,776	1173
Potato	11,773	136,527	nd
Orchid	5235	51,840	nd

Note. nd = no data.

^aStatistic data in 2015.

Source: Office of Agricultural Economics, Department of Agriculture 2016. ²

The change in agricultural systems in Thailand has resulted in the increasing use of pesticides. Praneetvatakul et al. ⁸ stated that the external costs of pesticide use in Thailand were approximately 27.1 USD/ha of agricultural land in 2010. Economic growth in crop production leads to overuse and misuse of pesticides based on the concept of effective pest control and saving labor and time. The study of Grovermann et al. ⁹ found that seventy-nine percent of the pesticides applied were overused according to the personal statements of farmers.

It is possible that farmers’ low level of education might affect the overuse of pesticides. Most farmers have only graduated from primary school; therefore, it is difficult for them to understand technical terms and complicated instructions on labels. Farmers usually used the types and quantities of pesticides based on the suggestions of neighbors, advertisements on television, and retailers.^10–12

Additionally, levels of agricultural commercialization affected the quantity of pesticides used. A study focused on agriculture in the uplands of northern Thailand found subsistence farms used pesticides at a rate of approximately 2.7 kg/ha, whereas commercial farms used pesticides at a rate of approximately 215 kg/ha. ¹³ Consequently, commercial farms result in adverse changes to ecosystems such as pest resistance, damage to beneficial organisms, and pesticide residues in the water, soil, food, and organisms. This type of farming has resulted in increased health risks to Thai farmers and consumers.^5,14

Thailand’s pesticide imports have steadily increased from 2012 to 2016. In 2016, herbicides were the most imported pesticide (67,445.87 tons and 296.99 million USD), followed by fungicides (7957.79 tons and 138.04 million USD) and insecticides (6840.56 tons and 119.52 million USD) (Tables 2 and 3). The three most imported herbicides were glyphosate-isopropylammonium (31,084.37 tons), paraquat dichloride (12,750.35 tons), and 2,4-D dimethyl ammonium (5869.83 tons), whereas the three most imported insecticides were chlorpyrifos (1723.02 tons), pirimiphos-methyl (750.46 tons), and cypermethrin (672.52 tons). The most imported fungicides were mancozeb (1659.28 tons), propineb (1156.23 tons), and carbendazim (1011.18 tons). ¹⁵ To control weed and plant detritus, there are three choices, cutting, burning, or herbicide use. Most farmers do not use a cutting method due to a labor shortage. Among farmers, burning is the simplest and preferred method to control weed and plant detritus after harvesting and to prepare the cultivation area for the next crop. However, Thailand, especially northern Thailand, has a problem with haze and smog from burning. The government therefore has mandated that burning must stop for all activities in the dry season in northern Thailand. Hence, herbicides are extensively applied on farms because they are a practical choice for farmers. Regarding use of insecticides and fungicides, the quantities of their use fluctuate each year, depending on outbreaks of insects and fungi.

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Table 2.

Quantity of Pesticide Imports in Thailand From 2012 to 2016.

Pesticides	Quantity of ingredients (tons)a
	2012	2013	2014	2015	2016
Herbicides	60,231.52	42,360.31	64,429.44	64,445.46	67,445.87
Fungicides	4420.97	2828.59	6682.56	7040.54	7957.79
Insecticides	4065.47	3021.77	5986.76	5385.47	6840.56
Plant growth regulators (PGR)	501.68	204.77	291.66	416.94	557.55
Fumigants	666.35	462.86	851.23	830.08	803.96
Molluscicides	201.62	24.86	21.98	25.21	21.54
Miticides	68.02	235.62	736.48	664.72	602.87
Rodenticides	0.008	–	108.48	194.88	139.12
Nematocides	0.0004	0.0000007	0.007	0.000006	0
Biopesticides	103.09	59.69	106.02	87.32	137.07

^aQuantity of pesticides was reported in active ingredients.

Source: Office of Agricultural Regulation, Department of Agriculture, 2012–2016.

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Table 3.

Costs of Pesticide Imports in Thailand From 2012 to 2016.

Pesticides	Costs (million USD)
	2012	2013	2014	2015	2016
Herbicides	346.18	250.98	411.84	337.69	296.99
Fungicides	119.04	77.45	144.31	117.68	138.04
Insecticides	112.99	68.86	123.03	112.95	119.52
Plant growth regulators (PGR)	6.80	2.88	5.01	6.68	8.59
Fumigants	4.73	3.31	7.95	7.02	51.90
Molluscicides	1.64	0.20	0.35	0.35	0.32
Miticides	1.97	1.81	5.13	7.62	11.19
Rodenticides	0.00007	0	0.92	1.67	3.85
Nematocides	0.0011	0.0006	0.0014	0.00007	0
Biopesticides	0.65	0.69	0.72	0.74	1.2

Source: Office of Agricultural Regulation, Department of Agriculture, 2012–2016.

The Thai pesticide market includes a large number of pesticide trade names. Each pesticide has several trade names, and retailers can sell the same product under the different trade names to increase their sales. Retailers can sell the same pesticide under different trade names because the law on pesticides imports did not set the duration for pesticide registration. Therefore, pesticide users are confused about the many trade names for the same product, and their use is difficult to monitor and control by government. ¹⁴

Pesticide Residues in the Environment

The heavy use of pesticides in agricultural systems causes environmental contamination of water, soil, food, and organisms. The major types of pesticide residues in the environment are organophosphates, carbamates, and herbicides. A few organochlorine insecticides are still found in the environment, although these chemicals have been banned for many years.^16,17 A study conducted in Songkhla Province of southern Thailand in 2006 found organophosphate residue levels in drinking water from an artesian well at approximately 0.085 μg/L in the dry season and 0.418 μg/L in the wet season in agricultural communities, and 0.004 μg/L in nonagricultural communities in both seasons. ¹⁸ In Khon Kaen Province of northeastern Thailand, a study conducted in 2010 found the average of the chlorpyrifos residues in ambient air samples was 0.258 ± 0.2686 mg/m³ in the summer and 0.1003 ± 0.0449 mg/m³ in the winter. The average of the pesticide residues in surface water samples was 1.3757 ± 0.5014 mg/L for dicrotophos in the summer and 0.3629 ± 0.4338 mg/L for ethion in the winter. The average of ethion in the soil samples was 42.2893 ± 39.0711 mg/kg in the summer and 90 ± 24.1644 mg/kg in the winter. ¹⁹

In these studies, the insecticides were at higher levels in the summer than in the winter. Farming in Thailand happens in both seasons. However, main crops, such as rice and corn (60.9 percent of total cultivated area), are planted in the summer and harvested in early winter. Rice starts seeding in the summer (during May and September) and is harvested between the latter part of the rainy season and early winter (between November and December). Corn also starts seeding in the summer (between May and June) and is harvested in the rainy season (between September and October). Before the rice and corn seeding process, farmers usually use herbicides and insecticides to remove weeds and pests in the farm area (between March and April). They also use pesticides throughout planting until harvesting. Therefore, more pesticides were used for these main crops in the summer. Other main crops, such as cassava, para rubber, and sugarcane (32.5 percent of total cultivated area), are cultivated all year round. However, the cultivated area of these crops is lower than those of rice and corn. Furthermore, herbicides are usually used in cassava and sugar cane farming during the summer and the rainy season (between March and September for cassava farming, and between March and July for sugarcane farming).^2,20 Another possibility for the increase in insecticide use in the summer is that the temperatures in the summer are suitable for growth of insects. In the winter, many insects usually escape cold climates and conserve their energy in a shelter. Some insects migrate to warmer weather, and some insects survive as eggs, larvae, or pupae. In the summer, insects emerge from their shelter and start reproducing and seeking food because there are suitable temperatures and humidity levels.^21,22

A study of pesticide residues in food conducted between 2013 and 2014 detected pesticides in vegetable samples from the central and northeastern regions of Thailand. Chinese kale was detected at levels of one hundred percent (local markets) and ninety-nine percent (supermarkets), pak choi at ninety-eight percent (local markets) and one hundred percent (supermarkets), and morning glory at ninety-nine percent (local markets) and ninety-seven percent (supermarkets). The detected pesticides were above the maximum residue limits that are thirty-five to forty-eight percent for Chinese kale, fifty-five to seventy-one percent for pak choi, and forty-two to forty-nine percent for morning glory. ²³ Regarding fruit samples, five pesticides that included carbofuran, chlorpyrifos, diazinon, dimethoate, and metalaxyl were detected in 90.7 percent of the watermelon samples, and three pesticides that included dichlorvos, dimethoate, and metalaxyl were detected in ninety percent of the durian samples. However, these levels of pesticides were lower than the maximum residue level values. In ninety-seven percent of the mangosteen samples, at least one of the following were above the maximum residue limit: chlorothalonil, chlorpyrifos, diazinon, dimethoate, metalaxyl, or profenofos.^24,25 In northern Thailand, the most detected organophosphate in vegetable samples was chlorpyrifos found in fifty percent of the farm samples, 33.9 percent of the local market samples, and 33.3 percent of the supermarket samples. The highest chlorpyrifos level was found in lemon balm (2.423 mg/kg) for farms, garlic (7.785 mg/kg) for local markets, and parsley (0.027 mg/kg) for supermarkets. Additionally, organophosphate residues exceeding the maximum residue limit values were found on 59.3 percent of the farms and 13.2 percent of the local markets. ²⁶ However, these results may not represent the pesticide residues found in the food throughout Thailand because the samples were taken only in some parts of Thailand.

Pesticide Poisoning

Based on the report of the Bureau of Epidemiology, Ministry of Public Health, during 2012–2015, the reported cases of pesticide poisonings per 100,000 people were 2.35, 0.85, 0.43, and 3.71, respectively. The highest reported cases of pesticide poisonings were found during May and August within a year. The incidence of pesticide poisoning was higher in males than females because males worked and did the major tasks on the farms, such as mixing and spraying pesticides.^27,28

In 2015, the highest cases of pesticide poisonings were found in the northeastern region of Thailand (5.31 cases per hundred thousand people), followed by northern, central, and southern regions of Thailand (4.57, 2.99, and 0.48 cases per hundred thousand people, respectively) (Figure 1). People between fifty-five and sixty-four years old were found to have the highest number of poisoning cases (5.11 cases per hundred thousand people), followed by people between forty-five and fifty-four years old and thirty-five and forty-four years old (4.73 and 4.62 cases per hundred thousand populations, respectively). Most poisoning cases were caused from the use of organophosphates and carbamates (666 cases), followed by herbicides and fungicides (605 cases), rodenticides (sixty-nine cases), and halogen insecticides (fifty-two cases). ²⁷ However, the reported cases were lower than the actual number of poisonings. It is possible that the symptoms of pesticide poisoning are difficult to diagnose because of the lack of capacity of healthcare units. Generally, pesticide poisoning cases are reported through surveillance systems by hospitals, which have occupational disease clinics. In fact, farmers generally go to a primary care unit near their village when they are sick. Health officers at primary care units might not have the ability to diagnose pesticide poisoning because some symptoms of pesticide poisoning are general (i.e., headache, dizziness, nausea, vomiting, cramps, and muscular weakness, etc.). Therefore, the health officers might not transfer the cases to the hospital. Another reason for the difference is that the people who had less severe cases of pesticide poisoning did not go to the hospital for treatment. Hence, the statistical data do not include the less severe cases.^10,29

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Figure 1.

Reported cases of pesticide poisoning per 100,000 population in each region of Thailand.

Determination of Pesticide Exposure Levels

Pesticide exposure levels can be detected in humans by measuring the pesticide residues in biological fluids, including blood, urine, meconium, and placenta. Pesticide levels in the blood are used as biomarkers of organophosphate and carbamate toxicity and are determined by measuring cholinesterase inhibition and beta-glucuronidase. Organophosphates can cause the cleavage of the egasyn-glucuronidase complex, which leads to the release of beta-glucuronidase into the blood. Therefore, plasma beta-glucuronidase is more sensitive than cholinesterase inhibition. ⁴¹ Pesticide metabolite levels in urine are a common and convenient biomarker for estimating and monitoring levels of pesticide exposure, including organophosphates, carbamates, pyrethroids, and herbicides. Panuwet et al. ⁴² investigated urinary pesticide levels among farmers in Chiang Mai Province of northern Thailand. The highest average urinary dialkyl phosphate (DAP) metabolite levels as a biomarker of organophosphate exposure was 49.2 μg/g creatinine. The most detected herbicide was 2,4-D with its highest average at 0.61 μg/g creatinine, whereas the most detected pyrethroid was 3-phenoxybenzoic acid with its highest average at 1.0 μg/g creatinine. Other studies on rice farmers and corn farmers in Phayao Province of northern Thailand found that the average DAP level was between 6.5 and 10.91 μg/g creatinine.^11,39 The urinary DAP level was approximately 51.1 μg/g creatinine for vegetable farmers and 122.2 μg/g creatinine for fruit farmers in Nakhon Ratchasima Province of northeastern Thailand. ⁴³ Some studies evaluated dermal exposure to organophosphates among farmers by using gauze patches. The results demonstrated that the levels of chlorpyrifos in males (526.34 ± 478.84 mg/kg) were significantly higher than the levels in females (500.75 ± 595.15 mg/kg), and the urinary DAP levels were correlated with dermal exposure.^44,45

Children living in agricultural communities also have a greater potential for exposure to pesticides from the environment and prenatal exposure. In Songkhla Province of southern Thailand, the mean level of urinary DAP metabolites in children who lived in or near vegetable farming areas ranged from 2.14 ± 2.5 μg/g creatinine dimethyl phosphate (DMP) to 8.09 ± 10.2 μg/g creatinine dimethyl thiophosphate (DMTP) for the dry season and 0.71 ± 2.0 μg/g creatinine DMP to 3.26 ± 2.2 μg/g creatinine diethyl phosphate (DEP) for the wet season. The remarkable findings were that the children who lived in or near farming areas had higher urinary DAP levels than the children who lived outside the farming area. The author found that pesticide spraying during the dry season caused exposure to pesticides in farm children. ⁴⁶ In Pathum Thani Province of central Thailand, the geometric mean of urinary DAP and 3,5,6-trichloro-2-pyridinol levels were significantly higher in children who lived in the rice farming community (270 μg/g creatinine for DAP and 6 μg/g creatinine for 3,5,6-trichloro-2-pyridinol) than those who lived in an aquaculture farming community (101 μg/g creatinine for DAP and 2.6 μg/g creatinine for 3,5,6-trichloro-2-pyridinol). The factors affecting urinary DAP and 3,5,6-trichloro-2-pyridinol levels in children were the frequency of organophosphate use, proximity to rice farms, being with parents on rice farms, playing on rice farms, and dirt on the body. However, the urinary pyrethroid metabolite level was not different between children who lived in rice farming areas and those who lived outside farming areas.^47,48 In regions outside of Bangkok, a study in children from a rice farming community and an aquaculture community found that children from a rice farm had higher DAPs and chlorpyrifos levels than those from an aquaculture community. ⁴⁹ In Chiang Mai Province of northern Thailand, children of farmers had significantly higher levels of urinary pyrethroid metabolites than children of merchants, government officers, and company employees. In addition, the study stated that dietary sources were the major factors of pesticide metabolites in urine. ⁵⁰ Naksen et al. ⁵¹ also reported that prenatal exposure to organophosphate pesticides was associated with decreasing birth weight and head circumference in newborns in the Fang District of northern Thailand.

Lack of Pesticide Knowledge

Several studies have shown that farmers may not be aware of the hazards and health effects of pesticides, or environmental impacts either. Further, they may not have been trained or received adequate health and safety training regarding work with pesticides. The study of Hongsibsong et al. ¹¹ found a positive association between knowledge and practice in northern Thai farmers in many categories. However, no association was found for checking spray equipment and mixing pesticides outdoors. The authors suggested that this likely was due to unsafe work practices either because the work environment presented challenges to these practices and/or because of a lack of safety awareness for these activities.

In northeastern Thailand, a low level of knowledge was found in chili-growing farmers, and a low positive association was found between knowledge, attitude, and practice. ⁵² In western Thailand, poor knowledge related to reading safety symbols, labels, and first-aid protocols was found. ¹² Concerning information on pesticide use, farmers usually obtained information on pesticides from neighbors, advertisements on television, and retailers. Few farmers received the information from government officers.^10,11 Obtaining information from neighbors, television, and retailers may result in farmers receiving erroneous information and in misusing and overusing pesticides.

Education on pesticide knowledge and safety behavior is an important solution for reducing exposure to pesticides among farmers. ⁵³ Another solution is a participatory action program. Tandhanskul et al. ⁵⁴ adopted a self-help action program which emphasized participation, a positive approach, and locally made solutions to improve occupational health, safety, and ergonomics in small-scale enterprises in Thailand. The program motivated enterprises to act, organize group discussions, assess actions, and initiate improvements. The results showed that this program was successful and resulted in positive attitudes and focusing on locally available solutions. Buranatrevedh and Sweatsriskul ³¹ developed a model to promote occupational health among rice farmers. The model motivated farmers to analyze situations of occupational health and safety, prioritize the problems, develop a model to address the problem, and implement the model. The results found that farmers decided to address pesticide problems and a farmer network was established in the community.

Unsafe Occupational Practices of Pesticide Use

Ways to Reduce Pesticide Use and Risk

There are several solutions to the pesticide problem, such as rigorous legislation and regulations, launching campaigns on reducing pesticide use, and education and training. ⁵⁵

Legislation for banning highly toxic pesticides is an urgent need. The Thai government has a plan to end the use of paraquat and chlorpyrifos in 2019 and restrict the use of glyphosate. Other highly toxic pesticides should be banned and restricted as well. Legislation with expensive fines and legal punishments for using illegal pesticides is also needed. Furthermore, law enforcement and punitive actions should be strictly and continuously performed. The Thai government and other organizations have launched many campaigns and programs to reduce pesticide use such as Integrated Pest Management, good agricultural practice, organic farming adoption, and biopesticide promotion. ¹⁴ However, these campaigns were adopted in only some areas of Thailand. Expansion of these campaigns to other areas is necessary to reduce pesticide use and production costs and lead to sustainable agriculture. In addition, an evaluation of the implementation of all campaigns is needed. Successful and adaptable implementation can be applied as a model for other areas.

Some farmers still believe that pesticides are necessary to protect crops from pests. ⁶⁵ Therefore, it is necessary to educate and change the attitude of farmers about pesticides and at the same time apply other campaigns continuously.^28,66 The essential issues on which to educate farmers are the types, toxicity and health effects of pesticides, safe use of pesticides, and alternatives to pest control. Training programs are also an effective method for reducing exposure to pesticides among farmers. ⁵³ The participatory action program may be a suitable way to address pesticide problems.^31,54

Conclusion

In recent decades, Thailand has seen a shift from traditional to commercial agricultural systems. The share of gross domestic product from agriculture has continuously increased, while pesticide imports into Thailand have also increased agricultural productivity. The economic growth of crop production has led to the overuse and misuse of pesticides, resulting in pesticide contamination in the environment and humans. Thus, Thai farmers and consumers are at an increased risk for adverse health outcomes due to occupational and environmental exposure to pesticides. There are several solutions to address pesticide use, and the Thai government has an important role in making policy and regulations and encouraging sustainable agriculture. First, the government needs to enact laws to ban highly toxic pesticides and to implement expensive fines and legal punishment for using illegal pesticides. In addition, the government should strictly enforce pesticide laws and punitive actions. Second, the government and other organizations need to expand Integrated Pest Management and good agricultural practice campaigns, organic farming adoption, and biopesticide promotion to other areas. Finally, the government and other organizations need to educate and shift the paradigm of farmers. Implementing these solutions simultaneously is the best way to move toward sustainable agriculture in Thailand.