The aim of this work was to study the removal of three pesticides using conventional drinking water treatment (DWT) processes. These methods are the most used in Brazil, and include coagulation–flocculation of water. The pesticides/metabolites evaluated were: endosulfan, ethylenethiourea (ETU), and 1,2,4-triazole. The laboratory tests were carried out in triplicate using the jar test. Synthetic water samples prepared with kaolin, simulating the dry and rainy periods, were contaminated with different concentrations of pesticides. Results showed that conventional DWT methods are not suitable for the removal of the pesticides/metabolites evaluated. No significant difference (p < 0.05) was observed for the dry and rainy seasons. However, the removal was observed to decrease with higher initial concentrations of the contaminants. With regard to the removal of contaminants, ETU and 1,2,4-triazole resulted in the lowest removal percentages (ETU: median ≤11% in decanted water and 1,2,4-triazole ≤18% in decanted water) compared to endosulfan (median ≤54% in decanted water). This fact can be justified by the low solubility of endosulfan in water at 20 °C and high Koc, log Kow and molar mass, in relation to the other two pesticides.

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