Risk-based screening of selected contaminants in the Great Lakes Basin

A risk-based screening exercise was carried out to evaluate the significance of chemicals of emerging concern measured in water and sediment of the Great Lakes Basin. Chemical classes included pesticides, pharmaceuticals, organic wastewater constituents, nonylphenol ethoxylates, perfluorinated surfactants, chlorinated paraffins, synthetic musks and flame retardants. Maximum measured concentrations were compared to benchmarks selected or developed to reflect a conservative no-effect level and/or the lowest-effect level. These benchmarks reflected traditional effect information such as survival, growth and reproduction. From this analysis, several pesticides, pharmaceuticals, polycyclic aromatic hydrocarbons and nonylphenol ethoxylates were identified as potential concerns and needs for further work were identified. Five of these chemicals (all pesticides) were identified in waters of both the US and Canada (azinphos-methyl, chlorpyrifos, diazinon, malathion and metolachlor). Chlopyrifos, malathion and metolachlor are still registered for use in both jurisdictions; diazinon is registered for use only in the US and azinphos-methyl is not registered for use in either jurisdiction, reflecting the persistence of these chemicals. The results of this screening exercise also were compared to those of several other studies, revealing some common chemicals. Although there are several uncertainties and data gaps in the benchmarks and monitoring data used in the current screening exercise, the results of this risk-based screening can be used by agencies for priority setting, program development, and to support ongoing collaborative research and monitoring programs.