Unfolding pesticide transport from land to rivers and the resulting aquatic risks in China

Pesticides have been widely applied in China, potentially leading to negative effects on the aquatic ecosystem. However, a national risk map of pesticide active ingredients (AIs) to aquatic species is still lacking. In this study, we used a nationwide spatially explicit pesticide input dataset to estimate the riverine concentrations of 133 AIs in China and further assessed the risks to aquatic species. Our analysis shows that pesticides were intensively applied in the North China Plain and the middle and lower reaches of the Yangtze River basin, with rice and maize received the highest shares of input at 42% and 21%, respectively. Under the current pesticide input patterns, in total 631 tons of pesticides, which is approximately 0.04% of applied pesticides, were transported into rivers through runoff. Atrazine showed the highest predicted concentrations in rivers, followed by propisochlor and nicosulfuron. Aquatic risks were found in 57% of river basins, with 5% and 13% of rivers exhibiting extremely high and high risks. Extremely high and high risk were found mainly in upper reaches of the Yangtze River, middle reaches of the Yellow River, and the Pearl River. Notably, endosulfan was the major contributor to aquatic risk, with an input only accounting for 0.4% of the national input mass. Our analysis facilitates more precise pesticide supervision and the designation of risk mitigation strategies.