This study presents a comprehensive investigation into the occurrence, seasonal variations, and ecological risks of 484 contaminants of emerging concern (CECs) in the surface waters of the Yangtze River Delta. In winter, 209 CECs were detected, with industrial chemicals representing the most dominant category in terms of both concentration and proportion, underscoring industrial discharge as the primary source of pollution in the region. Significant seasonal shifts in contaminant composition were observed: industrial intermediates, surfactants, and antibiotics dominated in winter, whereas industrial intermediates, plasticizers, and herbicides prevailed in summer, reflecting the combined influence of climatic conditions and anthropogenic activities. Spatially, pollution hotspots varied dynamically with the seasons, concentrating in the highly industrialized Yangtze River basin during winter and shifting to the agriculturally intensive Taihu Lake basin in summer. Ecological risk assessment identified 18 high-risk substances, predominantly PPCPs and pesticides, among which the antifungal agent clotrimazole exhibited an extreme hazard quotient (HQ) exceeding 500. A core list of six compounds consistently posed high risks across both seasons. The risk evaluation further revealed pronounced species-specific sensitivity, with Daphnia magna being the most vulnerable, as well as notable seasonal variability, indicating that single-season assessments may underestimate the annual ecological risk. These findings provide a scientific basis for developing targeted region-, risk-, and season-specific management strategies for CECs in the Yangtze River Delta.
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