The United States Environmental Protection Agency and Environment Canada designated 43 Areas of Concern (AOCs) under the Great Lakes Water Quality Agreement, a binational agreement drafted and adopted to ensure the long-term maintenance of the “chemical, physical, and biological integrity" of the Great Lakes ecosystem. Geographic areas that failed to meet water quality standards for beneficial uses were designated as AOCs and federal governments were required to develop Remedial Action Plans to address the degradation.
Contamination from the metals lead, nickel, copper, zinc and cadmium may harm organisms at low concentrations if the metal compounds are in a bioavailable form, but they rarely cause ecological effects through biomagnification.
Mercury is a potentially toxic metal that is widespread in the Great Lakes. It is an important toxic substance affecting human and ecosystem health in the Great Lakes. While there are natural sources of mercury, most mercury loading in the Great Lakes comes from anthropogenic discharges. Scientists estimate more than 50% of the mercury in the environment today is from non-natural sources.
Polychlorinated biphenyl (PCBs) are a class of legacy organochlorines that share a structural similarity and toxic mode of action with the insecticides Mirex and Toxaphene, and with dioxin, all known to exert multiple toxic effects throughout the food web in lakes.