Multimedia transport and retention of medium-to-high risk neonicotinoids in the impounded lake: driven by hydrological conditions and intrinsic properties

Neonicotinoids (NEOs) are among the most widely used pesticides globally, yet there is limited information on multimedia transport and retention processes in impounded lakes. This study investigated the spatiotemporal distribution of ten commonly used NEOs in the largest impounded lake along the South-to-North Water Diversion Eastern Route. NEO sources were apportioned using Positive Matrix Factorization (PMF), ecological risks assessed via the Risk Quotient (RQ) method, and transport and retention of medium-to-high risk NEOs analyzed using a Level III multimedia fugacity model. Results showed that concentrations of all ten NEOs were higher during the late diversion period (LDP) than during the early diversion period (EDP) across three media: water (362.8 ng/L compared with 109.7 ng/L), suspended particulate matter (689.9 ng/g dw compared with 495.5 ng/g dw), and sediment (31.3 ng/g dw compared with 22.9 ng/g dw). Six NEOs (acetamiprid, imidacloprid, thiamethoxam, nitenpyram, clothianidin, and thiacloprid) posed medium-to-high risks. Agricultural application contributed 63% of total NEO inputs, followed by urban wastewater (24%) and internal release (13%). The multimedia transport and retention of NEOs were driven by their solubility and organic carbon partition coefficients ( K oc ): sediment served as the main sink for acetamiprid, imidacloprid, clothianidin, and thiacloprid (>53.7%), whereas thiamethoxam and nitenpyram remained predominantly in water (>70.0%). These findings provide a theoretical foundation for formulating control strategies for NEOs and optimizing ecological water diversion schemes.