A Systematic Investigation on Contamination of Pesticides and Relevant Metabolites in Pre- and Post-Treatment Drinking Water from the Yangtze River Delta, China

This study aimed to investigate the distribution of commonly used pesticides and their metabolites in drinking water before and after treatment at drinking water treatment plants (DWTPs) in the Yangtze River Delta and to assess the health risks from the perspective of non-carcinogenicity and carcinogenicity. A total of 85 pesticides and their metabolites were analyzed in source, finished, and tap water using online solid-phase extraction coupled with liquid chromatography–tandem mass spectrometry. Across 91 water samples, 31 parent compounds and 9 metabolites were detected, with the median total concentrations of 62.2 (range: 6.20 to 392) ng/L. Atrazine, 2-hydroxyatrazine, and S-metolachlor were detected in all samples. Advanced treatment processes at DWTPs effectively reduced the residues of pesticides and their metabolites (removal rates 51.5~95.2%), with removal rates for metabolites significantly lower than those for parent compounds (p = 0.03). Regarding health risks, the estimated carcinogenic risk for pesticides and metabolites detected in tap water was within acceptable limits and the non-carcinogenic risk was insignificant. However, it is important to note that both of the two compounds with the relatively highest non-carcinogenic risks are pesticide metabolites. Overall, this study showed that despite dozens of pesticides and metabolites being detected in water from the Yangtze River Delta, their health risks were assessed to be insignificant. The lower effectiveness of current advanced treatments in removing pesticide metabolites indicates the necessity of technique improvement in DWTPs.