Defining pesticide water quality standards for multi-use water resources to protect human health

Regulatory agencies worldwide established water quality standards (WQS) for pesticides primarily based on human exposure via drinking water ingestion. However, pesticide exposure varies by water use. This study defined six water usage types (drinking water, recreational waters, fisheries and aquaculture, natural reservations and conservation areas, rural water uses, and urban water uses) and derived corresponding WQSs based on pathway-specific and aggregated human exposure and associated health risks. Exposure analysis revealed that pesticide properties could cause over 10⁷-fold variation in external exposure dose factors across water types. WQSs for hydrophilic pesticides ranged from 0.33 to 2.24 × 10⁵ mg L^-1, ranked: natural reservations and conservation areas > fisheries and aquaculture > recreational waters > drinking water resources > rural water uses > urban water uses. Lipophilic pesticides WQSs ranged from 1.10 × 10^-3 to 51.7 mg L^-1, ranked: natural reservations and conservation areas > recreational waters > drinking water resources > rural water use > urban water use > fisheries and aquaculture. Therefore, priority should be given to controlling pesticide levels in urban water use and fisheries and aquaculture waters to mitigate risks. This study also compared WQSs for eight pesticides (aldrin, atrazine, bromoxynil, chlorothalonil, dichlorodiphenyltrichloroethane, hexachlorobenzene, heptachlor, and oryzalin) with corresponding regulatory standards (RSs) in Brazil, China, and the United States. Results indicated that most RSs remain inadequate in preventing carcinogenic risks. Our findings provide insights for developing more comprehensive and protective WQSs. Future studies can improve framework by refining exposure parameters, incorporating more pesticides as toxicity data becomes available, and integrating ecological risks.