Pilot survey of pesticide-specific urinary metabolites among farmers in Chiang Mai highland agricultural area

This study surveyed the exposure to pesticides among farmers in Chiang Mai highland agricultural area. Ethnic Hmong farmers, living in Baan Buak Jan, Mae Rim District, Chiang Mai Province were selected as the study population. Pesticide-specific urinary metabolites were used as biomarkers of exposure to a variety of pesticides, including organophosphorus pesticides, synthetic pyrethroids and selected herbicides. Our method employed a simple solid-phase extraction, followed by a gold standard analytical method, using isotope dilution high performance liquid chromatography-tandem mass spectrometry (LC/MS/MS). A total of 40 urine samples from Hmong farmers were analyzed for 19 specific pesticide metabolites. We found that para-nitrophenol (PNP, a specific metabolite of methyl parathion and parathion) was the dominant analyte, having the highest amounts in all urine samples tested. We also found the metabolites of chlorpyrifos, common pyrethroids and ermethrin/cypermethrin, namely 3,5,6-trichloro-2-pyridinol (TPCY), 3-phenoxybenzoic acid (3-PBA) and cis- and trans-3-(2,2-dichlorovinyl)-2, 2-dimethylcyclopropane-1-carboxylic acids (c- and t-DCCA) respectively. The Hmong farmers were classified into groups according to their type of plantation or crop, resulting in the following breakdown: flower plantations (n=20), vegetable plantations (n=11) and flower and vegetable plantations (n=9). Thai farmers who had pesticide-free vegetable plantations (n=8) were used as a comparison group. The results showed that there was no significant difference among all analytes detected in farmers with different crop types (Mann-Whitney-U test p GT 0.05). However, a significant difference in PNP concentrations was found between farmers on plantations using pesticides and those on pesticide-free plantations (Mann-Whitney-U test p LT 0.05). No correlation was observed among individual analytes except for 3-PBA and t-DCCA (Pearson p=0.00), suggesting a common source for these two analytes, likely permethrin or cypermethrin insecticides. This study demonstrated pesticide exposure among farmers who use pesticides on their plantations in Thailand. Further studies are required to determine if any pesticide-related health outcomes are associated with these exposures.