Pesticide use pattems in China have changed in recent years;however,the study of the environmental fate of current-use pesticides (CUPs) and their ecotoxicological significance in aquatic ecosystems is limited.In the current study,sediments were collected from an urban stream in the Chinese city of Guangzhou.Sediment-associated legacy organochlorine pesticides and CUPs,including organophosphates,pyrethroids,fipronil and abamectin were analyzed.Additionally,the relative toxicity of the sediments was evaluated with 10-d bioassays using Chironomus dihutus.Fifteen of 16 sediments collected from the stream were acutely toxic to C.dilutus with 81% of the samples causing 100% mortality.Abamectin,fipronil and pyrethroids (mainly cypermethrin) were identified as the principal contributors to the noted toxicity in the midges,with median predicted toxic units of 1.63,1.63,and 1.03,respectively.Sediments taken from downstream sites,where residential and industrial regions were located,had elevated CUP concentrations and sediment toxicity compared to upstream sites.This is the first study of its kind to link sediment CUPs,fipronil and abamectin concentrations,with toxicity in urban streams in China with a focus on shifting pesticide usage pattems.