Ecological Risk Assessment of Organophosphorus Pesticides in Aquatic Ecosystems of Pearl River Estuary

The risk quotient method and a probabilistic risk assessment method were applied for assessing aquatic ecological risk of nine organophosphorus pesticides,including thimet,dichlorovos,disulfoton,dimethoate,dimethyl parathion,chlorpyrifos,ethoprophos, sumithion and malathion on eight aquatic organisms in the Pearl River Estuary. Results using the risk quotient method revealed that the risk level of opossum shrimp was the highest among eight aquatic organisms of the Pearl River Estuary. The risk of water flea and midge was in medium level,followed by the rest six aquatic organisms,including diatom,oyster,carp,catfish and eel,which were in the low risk by the examined organophosphorus pesticides. It was found that thimet made the largest contribution to total aquatic ecological risk among nine organophosphorus pesticides to every organism. The results from probabilistic risk assessment showed that the total ecological risk in high water period was higher than that in low water period determined by the HC5under the 95% confidence level. The largest contribution of thimet to total aquatic ecological risk subject to the HC5in 50% confidence level was regarded as the toxic reference value. The probabilistic risk of a single contaminant showed that thimet and disulfoton were harmful to exceeded 10% organisms in the estuarine. The probabilistic risk of nine pesticides mixture in high water period was also higher than that in low water period,and both risks were greater than 5% which exceeded safety threshold for 95% organisms in the Pearl River Estuary.