Spatial distribution, phase partitioning, and ecological risk assessment of typical pesticides in Yangtze River Basin

Yangtze River Basin (YRB) is the largest agricultural and economic corridor in Asia, accounting for 40 % of China's rice production and 49 % of its arable land. Additionally, the Huangpu River (HR), the largest river in Shanghai, features developed agriculture and an extensive shipping industry. Overall, extensive agricultural activities coupled with frequent pesticide applications have resulted in aquatic contamination. This study investigated the spatial distribution and partitioning trends of 57 common pesticides, and assessed their ecological and human health risks in 30 river sections of YRB. We found that the total concentration of pesticides (∑₅₇ pesticides) in the dissolved phase, suspended particulate matter (SPM) phase, and surface sediment ranged 601.82 -2415.91 ng/L, 65.04 -1863.28 ng/L, and 68.54 -424.84 ng/g dry weight, respectively. Organochlorines and pyrethroids were predominant in the SPM phase, while triazines and neonicotinoids were predominant in the dissolved phase. The sources of dichlorodiphenyltrichloroethane (DDT) substances could be attributed to historical residues and vessels' antifouling systems. Most pesticides had strong migration ability and were not readily deposited in sediment. Moreover, sediment was also potential secondary pollution sources of triazines. Organochlorines, pyrethroids, and neonicotinoids posed significant ecological risks, despite its low concentration, traditional organochlorine still poses a certain ecological threat. Children were more susceptible than adults to noncarcinogenic and carcinogenic risks from unintentional oral exposure. Stringent management of pesticides is imperative with ongoing monitoring.