Occurrence, potential sources and ecological risk of current-use pesticides in mangrove sediments from South China

Mangrove forests act as sinks for contaminants carried by inland runoff, while the occurrence and potential ecological risk of current-use pesticides (CUPs) in mangrove sediments are limitedly known. In this study, 75 of pesticides (including 57 insecticides, 13 herbicides and 5 fungicides) were analyzed in 38 mangrove sediments from urban, agricultural, and aquicultural areas in Zhanjiang, China. The total pesticide concentrations in sediments ranged from 4.55 to 364 ng/g dry weight (dw) (mean ± standard deviation: 68.1 ± 67.3 ng/g dw), with insecticides dominating at 96%. Among the regions, mangrove sediments from urban areas exhibited the highest pesticide concentrations. Legacy organochlorines were identified as the predominant insecticides, accounting for 65% of the total insecticide concentrations. Pyrethroids were the most abundant CUPs, accounting for 79% of the total concentrations of current-use insecticides on average. The spatial distribution of pesticide categories varied across functional regions, reflecting different sources and land-use influences. Tetramethrin, a pyrethroid, posed a high risk to benthic organisms in mangrove sediments, with risk quotients exceeding 10. Some neonicotinoids, organophosphates, and herbicides presented medium ecological risks, although the majority of pesticides (69%) showed low risk. Despite lower concentrations of CUPs compared to legacy organochlorines, the ecological risks posed by CUPs in mangrove sediments cannot be ignored, underscoring the need for further risk assessment focused on benthic organisms.