Impact of land covers on pesticide contamination and the associated ecological risk in a major tributary of the Pearl River, South China.

Pesticide contamination in the river basins is closely associated with land covers. However, the impact of land covers on the pesticide contamination remains unclear. In this study, concentrations of 14 pesticides (10 insecticides, 3 fungicides, and 1 herbicide) in water were investigated along a major tributary of the Pearl River in wet and dry seasons in 2023. Thirteen pesticides were found in wet season, while all for dry season. Correlation analyses indicated that herbaceous cropland and grassland covers predominantly positively affected the overall pesticide concentrations in both seasons. Irrigated cropland cover positively affected the concentrations of 3 pesticides only in wet season, suggesting their use for the crops. Closed evergreen broadleaved forest cover negatively affected the overall pesticide concentration in only wet season, indicating the mitigation effect of forest. In dry season, positive effect of open evergreen broadleaved forest was found only for malathion, suggesting its usage in the forest. Additionally, ecological risks of the pesticides were low to moderate, with similar dominant pesticides in both seasons. Finally, the investigation of pesticide used in croplands, grasslands, and forests, and forest protection are recommended for pesticide contamination management. These outcomes will deepen our understanding of pesticide contamination control in the river basins.