Pesticide transformation products: a potential new source of interest for drinking water

Pesticide transformation products (TPs) are frequently quantified in aquatic systems, including surface and groundwater. They often present higher polarity than parent compounds, are less volatile and less biodegradable and are therefore more mobile and persistent. These properties make them compounds of main interest in water resources and drinking water. With more than 600 samples collected over two years and nearly 100,000 results available, this study was carried out to evaluate the occurrence of 157 pesticide TPs and certain active substances in raw and drinking water in France. Our study made it possible to assess the potential exposure of the population to pesticides and their metabolites through drinking water consumption and finally to put forward new TPs of interest for the monitoring of drinking water. Among TPs, chlorothalonil R471811 and metolachlor ESA were the most frequently quantified compounds, with quantification in more than 50% of raw and drinking water. TPs dimethachlor CGA369873, chlorothalonil R471811 and R417888, terbuthylazine LM2 and LM6, desphenyl chloridazon (DPC) and methyldesphenyl chloridazon (MeDPC) were monitored for the first time in drinking water in France. Concentrations exceeding the regulatory quality standard of 0.1 µg.L^-1 were observed in more than 30% of drinking water samples for chlorothalonil R471811, and a maximum concentration was measured at 9.8 µg.L^-1 for DPC in drinking water. The quantification frequencies were relatively similar in raw water and tap water, which appears to indicate poor efficiency of the majority of the currently used drinking water treatment plants. This research confirmed the benefit of focusing on TPs and parent compounds, and also to continue monitoring TPs that originate from compounds already withdrawn from the market for several years that appear to be highly persistent.