Spatiotemporal distribution and fates of neonicotinoid insecticides during the urban water cycle in the lower reaches of the Yangtze River, China.

Neonicotinoid insecticides (NNIs) are the most popular insecticides worldwide, yet their spatiotemporal distribution and fates during the urban water cycle remain limited on a large watershed scale. Thus, we investigated ten kinds of NNIs in surface water from the lower reaches of the Yangtze River and hubs of the urban water cycle in all seasons. In brief, eight out of ten NNIs were detected, and thiamethoxam (THM), imidacloprid (IMI), and dinotefuran (DNT) were the most abundant NNIs in surface water, with concentrations of 0.29-48.15 ng/L, 1.69-20.57 ng/L, and 0.98-25.32 ng/L, respectively. The average concentrations of total NNIs in summer were 1.96-4.41 folds higher than those in other seasons. NNIs in the effluents of municipal wastewater treatment plants (WWTPs) were lower than those in surface water, while the average concentrations of total NNIs in the effluents of industrial WWTPs were 1.56-6.86 folds higher than those in surface water, indicating that insecticide production is an important source for NNIs in surface water. DNT was the most recalcitrant NNI in WWTPs, with an average removal efficiency of 49.89%, while in drinking water treatment plants (DWTPs), the removal efficiencies of most NNIs were limited, except for clothianidin (CLO) (90%). Risk assessment showed that NNIs posed medium or high risks to aquatic life, and DNT contributed 26.86-51.48% to the cumulative risks of detected NNIs. This study investigates the spatiotemporal distribution and risks of NNIs and provides information for the supervision of NNIs in the Yangtze River basin, China.