Risk posed by pesticides to aquatic organisms in rivers of northern inland New South Wales, Australia

An ecological assessment was conducted to determine the risk posed by agricultural pesticides to inland rivers of north-west New South Wales (NSW), Australia. A preliminary screening of 30 pesticides provided a short-list of eight for further investigation (atrazine, chlorpyrifos, diuron, endosulfan, fluometuron, metolachlor, profenofos, prometryn). Selection was based on chemical characteristics, toxicity, detection frequencies and environmental concentrations. Hazard quotients were calculated for both spray and non-spray seasons. Where possible, hazard quotients were calculated for both acute and chronic exposures for crustaceans, insects, micro-organisms, molluscs, plants and vertebrates. Chlorpyrifos, endosulfan and profenofos posed a high hazard (HQ > 0.5). A probabilistic risk analysis indicated that chlorpyrifos, endosulfan and profenofos posed a risk from acute exposure during the spray season, while endosulfan also posed a risk from chronic exposure during the spray season. The fisks posed by profenofos and chlorpyrifos were characterised by a low probability of detection, but these detections affected a high percentage of species. The risks posed by acute and chronic exposures of endosulfan were characterised by a high probability of detection, but only a limited number of these detections affected a high percentage of species. Risk during the non-spray season was not assessed, as the detection of pesticides was infrequent during this period.