Legacy and Current-Use Insecticides in Agricultural Sediments from South China: Impact of Application Pattern on Occurrence and Risk.

Legacy and current-use insecticides were analyzed in sediments collected from a typical rice-planting region in South China. Total concentrations of insecticides varied from 1.63 to 775 ng g-1 with mean and median values of 67.0 and 11.5 ng g-1, respectively. Pyrethroids predominated pesticide composition (31.7%), followed by organophosphates (23.0%) and fiproles (20.8%). Sediment risk analysis showed that pyrethroids, fiproles, and abamectin posed significant risk to benthic invertebrates in one-third of sediments. Different distributions of pyrethroids and organophosphates in urban and agricultural areas were consistent with their application patterns, whereas legacy organochlorine pesticides showed no region-specific distribution because of rapid transition of land use pattern from agricultural to urban areas. Likely illegal use of pyrethroids and fipronil caused serious ecological risks in agricultural waterways. Pyrethroids and fipronil were restricted to use in paddy fields, but their occurrence and risk in agricultural waterways were high, calling for better measures to regulate the illegal use of insecticides.