Pesticides in three rural rivers in Guangzhou, China: spatiotemporal distribution and ecological risk.

Frequent and widespread pesticide use is a major concern for both human and environmental health. The aim of this study was to screen for 19 pesticides in rural rivers in Guangzhou, China, evaluating the potential impact of detected pesticides on the local ecosystem. Sampling was performed in rural rivers in three environment types: agricultural, industrial, and unpolluted, with sampling of water and sediments in both wet and dry seasons. A total of 11 pesticides were detected overall and their spatiotemporal distribution in water and ecological risk were assessed. Five pesticides were detected at concentrations above 100 ng L-1, with the highest concentration pesticides being dimethoate (1318 ng L-1) in surface water and quinalphos (328 ng g-1 dry weight (dw)) in sediments. The most commonly detected pesticides were chlorpyrifos, acetochlor, and butachlor with detection frequencies of 50-57% and 29-43%, in water and sediments, respectively. Samples from the agricultural rural river contained the most pesticides and at higher concentrations, as compared to industrial and unpolluted areas, especially during the wet season. Ecotoxicological risk assessment through Risk Quotients (RQs) showed that chlorpyrifos and fenvalerate pose high ecological risks in water and therefore, reduction of the source input of these pesticides is essential.