LC-HRMS Screening, Risk Assessment, and Source Tracing of Neonicotinoid Insecticides and Their Transformation...

The widespread application of neonicotinoid insecticides (NEOs) in urban areas has led to their transport from terrestrial ecosystems into freshwater catchments, where they undergo complex transformation processes. However, the occurrence and potential risks of NEOs and their transformation products (TPs) in urban aquatic ecosystems remain poorly understood. In this study, a comprehensive screening workflow was developed by integrating target analysis, suspect screening, and nontarget analysis through diagnostic fragment searching and molecular networking, and 104 TPs were identified for 11 NEOs in 35 coastal urban river waters from Qingdao, China. In each sample, the cumulative concentrations of NEOs and their TPs ranged from 118 to 4755 ng/L. Five NEOs and seven TPs were ranked as high-priority based on the ToxPi score, which integrated detection frequency, signal intensity, persistence, mobility, and toxicity. Notably, four NEOs (i.e., clothianidin, imidacloprid, thiacloprid, and thiamethoxam) exceeded their respective Environmental Quality Standards in 17-89% of water samples. One additional NEO (i.e., dinotefuran) and seven TPs (i.e., thiacloprid amide, TP_271b, TP_340b, TP_201b, imidacloprid desnitro, TP_247a, and TP_213b) were ranked higher than clothianidin. Simultaneously, 18 TPs had a higher regulatory priority than the corresponding NEOs, highlighting that these TPs warrant equal attention. Source tracing analysis revealed that urban application and agricultural activities were the primary sources of NEOs and their TPs in urban and mixed land-use areas, respectively. Future efforts should focus on clarifying the ecological risks and major sources of neonicotinoid contamination, in terms of parent NEOs and their TPs, in coastal urban rivers to support source-control regulations for preserving freshwater and marine organisms.