Approach to health risk determination for metals and their compounds under the Canadian Environmental Protection Act.

The Canadian Environmental Protection Act (CEPA) authorizes the Ministers of the Environment and of Health in Canada to investigate a wide variety of substances that may contaminate the environment and cause adverse effects on the environment and/or on human health. Under the Act, assessments have been completed for 44 environmental contaminants on the first Priority Substances List, including four metals and their compounds. The principles developed for the assessment of risk to human health for priority substances under CEPA are outlined, with specific emphasis on the metals. These include general aspects such as estimation of total exposure from all media, the development of exposure potency indices for carcinogens in lieu of low-dose risk estimates, and incorporation of toxicokinetic and toxicodynamic data, where available, to modify traditionally adopted uncertainty factors for development of tolerable intakes, or concentrations, for nonneoplastic effects. Aspects of the approach to human health risk assessment more specific to the metals considered under CEPA (i.e., arsenic, cadmium, chromium, and nickel) and implications for the subsequent strategic options process are also addressed, including the extent to which various chemical forms could be assessed (i.e., speciation) and essentiality.