Pesticide pollution in the Yangtze River mainstem under extreme drought climate: Occurrences, risks and linkages to land use

Extreme climate events may alter pesticide input and risks in agricultural river basins, yet the impact at large river basin scales like the Yangtze remains unclear, particularly under extreme drought. Here we conducted a comprehensive field investigation along the mainstem of the Yangtze River during the extreme drought year of 2022, collecting 57 surface water samples from Chongqing to Shanghai (about 2400 Km). A total of 46 pesticides were detected out of 71 targets, with average total concentrations: 21 organophosphorus pesticides > 3 herbicides > 7 pyrethroids > 8 neonicotinoids > 7 organochlorines. Ecological risks were evaluated by applying a tiered method incorporating the risk quotient (RQ), semi-probabilistic assessment, and a prioritization index. Parathion, fensulfothion, endrin, and fenvalerate I were identified as high-risk pesticides and recommended as priority control pollutants. Carcinogenic risk from dermal exposure remains a concern. Spatial variation in pesticide pollution was positively correlated with agricultural land and surface water area. Rainfall promotes pesticide runoff, though concentrations were generally lower during extreme drought. Although drought may reduce pesticide input, ecological and health risks persist. This study reveals the patterns and risks of pesticide contamination in the Yangtze River mainstem under hydroclimatic drought, providing critical support for understanding the potential relationship between extreme climate change and pesticide pollution in large agricultural river basins. • Pesticides were detected in the Yangtze River mainstem water during extreme drought. • Dominant pesticides OPPs and HERs were linked to agricultural land use. • Parathion and fensulfothion were predicted as priority pollutants to aquatic ecosystem. • Dermal OCPs exposure posed considerable carcinogenic risks at specific sites. • Extreme drought may reduce pesticide levels in the water from the Yangtze River.