Assessments of priority substances under the Canadian Environmental Protection Act Variations in exposure and response.

Under the Canadian Environmental Protection Act (CEPA), assessments have been completed for 44 environmental contaminants on the first Priority Substances List. The principles developed for the assessment of risk to human health for Priority Substances under CEPA are outlined, with specific emphasis on variations in exposure and response. These include the 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 non-neoplastic effects.