Agriculture in Thailand, which employs over 30 percent of the workforce and contributes significantly to the country’s gross domestic product, is a key sector of its economy. Import and use of pesticides has increased over the past decade due to Thailand's major role as a leading exporter of food and agricultural products. The widespread and poorly regulated use of pesticides presents a potential risk to the health of farmers, farm families, the general population including children and the environment. This article is a result of the Southeast Asia GEOHealth Network Meeting of February 2019. It summarizes the current situation on pesticide use and regulation in Thailand and reports research findings on the potential health and environmental impacts of pesticide use, as well as highlighting gaps in research that could play an important and influential role in future policy initiatives on pesticides. Although Thailand has made remarkable progress in improving agricultural health and safety and similarly strong research and policy programs are being developed in other countries in the region, there are still significant gaps in research and policy that need to be filled.

A birth cohort was begun to investigate the levels and sources of pesticide exposure in pregnant women living in Thailand, and to examine the effects of pesticide exposure on infant neurodevelopment at five months of age. Subjects were interviewed using questionnaires regarding their demographic characteristics, educational background, and work and home activities related to pesticide exposures. Spot urine samples were collected at 28 weeks gestation and analyzed by gas chromatography-mass spectrometry to determine maternal metabolite levels of organophosphate pesticides including dimethyl phosphate (DMP); total DEP (diethyl phosphate (DEP), diethyl thiophosphate (DETP), and diethyl dithiophosphate (DEDTP), and total DAP (the sum of all metabolite levels). At five months of age, infant development was evaluated using the Bayley Scales of Infant and Toddler Development-III (Bayley-III). Higher total DEP and total DAP metabolite levels from the mother at 28 weeks’ gestation were significantly associated with reduced motor composite scores on the Bayley-III at five months of age. The total DEP levels were also significantly associated with reduced cognitive composite scores. Prenatal concentrations of maternal urinary metabolites were associated with infant cognitive and motor development. The results of several studies now suggest the need for public health intervention to reduce prenatal pesticide exposures from both agricultural and domestic use.

Pesticides can act as endocrine disruptors by different mechanisms including inhibition of iodine absorption, increases in thyroid hormone clearance, decreased cellular uptake of thyroid hormones, or changes in expression of thyroid hormone regulated genes. This study examined how exposure to pesticides impacts thyroid hormone levels, thyroid stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4), free T3 (FT3), and free T4 (FT4) by comparing conventional (n = 195) and organic farmers (n = 222), and by evaluating which types of pesticides might be associated with changes in thyroid hormone levels. Questionnaires were used to collect information about farmer characteristics, self-reported stress, agricultural activities, and history of pesticide use. Conventional farmers were asked to report the type and quantity of pesticides used each day. The TSH, FT3, T3, and T4 levels of conventional farmers were 1.6, 1.2, 1.3, and 1.1 times higher than those of organic farmers, respectively, after adjusting for covariates. Several specific herbicides had a significant relationship between the amount applied and an increase in thyroid hormone levels, after covariate adjustment. They included: paraquat (TSH, FT3 and T3); acetochlor (FT4); atrazine (TSH, FT3 and T3); glyphosate (T4); diuron (TSH) and the “other” herbicides including alachlor, propanil, and butachlor (FT4 and T3). The most commonly used herbicide among conventional farmers was glyphosate, followed by paraquat, 2,4-dichlorophenoxyacetic acid (2,4-D). These findings suggest that exposure to pesticides could impact the development of metabolic diseases and other health outcomes by altering the endocrine system (the thyroid hormone levels) through the hypothalamic–pituitary–thyroid (HPT) axis. This work is a part of a longitudinal study which will evaluate the sub-chronic effects of repeated exposure to different types of pesticides on thyroid hormone levels.

Pesticide exposure has been implicated as a risk factor for developing a wide range of adverse health issues. Some examples are metabolic syndromes, including diabetes. This study investigated the relationship between current occupational use of pesticides and metabolic and cardiovascular biomarker levels among organic and conventional farmers in Thailand. In total, 436 recruited farmers were divided into two groups: conventional farmers (n = 214) and organic farmers (n = 222). Participants, free of diabetes, were interviewed and submitted to a physical examination. Serum samples were collected for clinical laboratory analyses, i.e., serum glucose and lipid profiles (triglycerides, total cholesterol, high-density lipoproteins, and low-density lipoproteins). Potential risk factors such as smoking, alcohol consumption, and heavy exercise were significantly different between the two groups. There were significant differences in terms of the years of pesticide use, pesticide use at home, sources of drinking water, and distance between the farmers’ homes and farms between the groups. After adjusting for confounders, current conventional farmers had significantly higher abnormal body mass index (BMI), waist circumference, body fat percentage (% body fat), triglyceride, total cholesterol, and low-density lipoprotein values as compared to organic farmers. Conventional farmers had higher risk of many metabolic and cardiovascular risk factors as compared to organic farmers, putting them at higher risk of metabolic diseases in the future.

This study aimed to assess paraquat concentrations in the urine of women at 28 weeks of pregnancy, delivery and 2 months postpartum and in the meconium of neonates. In all, 79 pregnant women were recruited from three hospitals located in agricultural areas in Thailand. The subjects were interviewed about personal characteristics, agricultural activities and pesticide use patterns. Paraquat was analyzed in urine and meconium using high performance liquid chromatography equipped with a fluorescence detector. The geometric mean (GSD) of urinary paraquat concentrations at 28 weeks of pregnancy, delivery and 2 months postpartum were 2.04 (4.22), 2.06 (5.04) and 2.42 (5.33) ng/mL, respectively. The urinary paraquat concentrations at 28 weeks of pregnancy, delivery and 2 months postpartum between agriculturist and non-agriculturist were not significantly different (p = 0.632, p = 0.915, p = 0.57 respectively). The geometric mean (GSD) of paraquat concentration in the meconium was 33.31 (4.59) ng/g. The factors predicting paraquat exposures among pregnant women and neonates included working outside, living near farmland, having family members who work on a farm, drinking well water and using herbicides or paraquat.

Organic farming has been promoted in Thailand by King Rama the ninth. In addition to being healthier for consumers, organic farming is healthier for agricultural workers. The cross-sectional study was conducted to investigate the frequency of chronic disease conditions, accidents, health symptoms, and ergonomic problems among 243 conventional (pesticide using) farmers and 235 organic farmers. Data were collected using questionnaires in face-to-face interviews. The results indicated symptoms that could be related to pesticide exposure (skin rashes, water blisters, headache, dizziness, and loss of appetite) were significantly higher among conventional farmers than organic farmers. The organic farmers reported significantly more health symptoms such as hives, chest pain, mild fever, flatulence, and frequent urination than the conventional farmers. The organic farmers reported significantly more pain, numbness, or weakness in the wrists/hands, fingers, upper back, hips, and ankles/feet than conventional farmers.