Priority screening of contaminants of emerging concern in drinking water sources of eastern China: Assessing risks based on exposure-activity ratios (EARs)

Increasing and widely detected contaminants of emerging concern (CECs) pose a threat to drinking water safety. Compared with traditional methods, the exposure-activity ratio (EAR) method based on the ToxCast database may have unique advantages in risk assessment of drinking water sources because it provides massive multi-target high-throughput screening toxicity effect data assessment for chemicals with missing traditional toxicity data. In this study, 112 CECs at 52 sampling sites in drinking water sources in Zhejiang Province of eastern China were investigated. Based on EARs and occurrence, priority chemicals were identified as difenoconazole (priority level 1), dimethomorph (priority level 2), acetochlor, caffeine, carbamazepine, carbendazim, paclobutrazol and pyrimethanil (priority level 3). Different from single observable biological effect in traditional methods, a variety of observable biological effects caused by high-risk targets were explored through adverse outcomes pathways (AOPs), revealing ecological risks as well as human health risks, for example, hepatocellular adenomas and carcinomas. Furthermore, the difference between the maximum EAR for a given chemical in a sample (EARmax) and the toxicity quotient (TQ) in priority screening of CECs was compared. The results show that screening priority CECs based on the EAR method is acceptable and more sensitive, suggesting the difference between in vitro and in vivo toxic effects and the necessity of incorporating the harm degree of biological effects into the EAR method to screen priority chemicals in the future.