Spatiotemporal trends and ecological risks of neonicotinoid insecticides in Korean surface waters

Neonicotinoid insecticides (NNIs) are among the most widely used pesticides globally, yet large-scale monitoring data on their occurrence in Korean rivers remain limited. This study conducted a nationwide assessment of nine NNIs and six transformation products (TPs) in four major river basins of Korea. Over a two-year period, water samples were collected from 130 sites to analyze their spatiotemporal distribution and associated ecological risks. The most frequently detected NNIs were dinotefuran (88.9 %), clothianidin (63.7 %), and imidacloprid (56.5 %), with mean concentrations of 121.2 ng/L, 39.0 ng/L, and 38.6 ng/L, respectively. Higher NNI concentrations were observed in southern agricultural regions, with significant seasonal variations peaking during major crop cultivation periods. To evaluate ecological risks, a Species Sensitivity Distribution-based risk assessment was applied. Risk assessment results indicated that clothianidin, imidacloprid, and dinotefuran frequently exceeded chronic toxicity thresholds, highlighting potential threats to aquatic ecosystems. Mixture toxicity analysis revealed that chronic exposure risks were largely driven by individual NNIs rather than synergistic effects. This study provides the first nationwide dataset on NNIs and their TPs in Korean rivers, demonstrating their widespread presence and ecological risks. The findings emphasize the need for enhanced pesticide regulation and long-term monitoring strategies to mitigate potential impacts on aquatic ecosystems.