Abstract:The rising detection of contaminants of emerging concern (CECs) in aquatic environments necessitates robust prioritization strategies to guide further testing and potential inclusion in monitoring programs. Existing CEC prioritization methods typically compare environmental concentrations with toxicity data (e.g., whole-organism or high-throughput assays) to identify “high priority” chemicals, but integrating mechanistic insights into adverse effects remains limited. Here, a CEC prioritization framework that combined exposure−activity ratios with adverse outcome pathways was developed and applied in the Yangtze River Basin in China. A total of 162 CECs across nine categories in surface water samples from the Yangtze River Basin were evaluated, and the most sensitive assay endpoints of these CECs were identified. Results showed that among all target CECs (nondetectable to 12,300 ng/L), 11 chemicals exhibited a 100% detection rate, with moclobemide (12,510 ng/L) and venlafaxine (12,300 ng/L) having the highest concentrations. Based on exposure−activity ratio and detection status, tri-iso-butyl phosphate, aldicarb, methomyl, acetamiprid, perfluorodecanoic acid, nalidixic acid, and moclobemide were identified as Level 1 priority chemicals. By linking high exposure–activity ratio molecular targets to validated adverse outcome pathways, we connected analytical chemistry data with predictions of specific adverse outcomes, including endocrine disruption–associated reproductive failure, porphyria-like metabolic disorders, and impairments in cognitive function and growth, which not only provide a mechanistic basis for analyzing the diverse biological effects induced by high-risk chemicals but also facilitate the screening-level prediction of potential associated ecological and human health risks.