Occurrence, landscape impact, and risk assessments of pesticides in a major river basin of a tropical island, South China.

In tropical river basin, the influence of different landscapes on the pesticide contamination remained unclear. In this study, levels and seasonal variations of 14 insecticides, 6 fungicides, and 1 herbicide, were investigated in a tropical island, South China, in dry and wet seasons, 2024. All the compounds were found in both seasons, with thiamethoxam (THIAM) and clothianidin (CLOTH) dominating insecticides and carbendzim (CARB) and metalaxyl (META) dominating fungicides. In wet season, the increased runoff likely resulted in increased input of CLOTH into surface water, while diluted the concentrations of THIAM and META. Additionally, the spatial variabilities of the dominating compounds were reduced in wet season. For the landscape impact, the irrigated cropland was the dominating sources of the pesticides. Deciduous shrubland was another dominating landscape, and played an important role in mitigating the pesticide contamination in surface water. Additionally, pesticide concentrations positively correlated with the covers of forests, but negatively correlated with impervious surface, highlighting the importance of increasing greenness in urban systems. Finally, ecological and health risk assessments showed that the risks of the target compounds were negligible in most sampling sites. These outcomes will deepen our understandings on the pesticide contamination in tropical regions.