Source-Specific Dynamics of Emerging Contaminants in a Megacity River Basin Revealed by Targeted and Nontargeted Analysis

Urban rivers in megacities serve as major sinks for diverse emerging contaminants (ECs). However, a comprehensive understanding of their sources and dynamics remains limited. This study employs an integrated targeted and nontargeted analysis to investigate ECs in the Wenyu River basin of Beijing and its associated sewage treatment plant (STP) effluents. We identified/tentatively identified and quantified 480 ECs, with household chemicals dominating the contaminant profile. Hierarchical cluster analysis delineated five distinct anthropogenic source types: influenza prevention compounds, daily lifestyle chemicals, sunscreen/insecticide residues, rural diffuse inputs, and traffic/waterfront landscape emissions. Results indicate that STP effluents constitute the primary intermediary for the first three categories, exerting a dominant influence on riverine EC levels, demonstrated by path coefficients of 0.736 in spring and 0.585 in summer. Seasonal variations revealed clear patterns: influenza- and sunscreen-related sources showed pronounced fluctuations corresponding to flu season and sunlight exposure periods, whereas traffic-landscape sources peaked during summer rainfall events. Ecological risk assessment indicated that 91.4% of the total environmental risk originated from STP-derived ECs, with telmisartan and fipronil identified as the compounds posing the highest ecological risk. This study provides new insights into the source-specific dynamics and seasonal drivers of ECs in urban rivers, offering a scientific basis for targeted pollution control strategies.