Speciation in health risk assessments of metals: evaluation of effects associated with forms present in the environment.

Because metals occur in various forms in the environment, speciation is an issue which must be addressed in regulatory health risk assessment programs. The manner in which speciation was addressed in a federal program in Canada is discussed in this article. Under the Canadian Environmental Protection Act, four metals, including arsenic, cadmium, chromium, and nickel, and their compounds were assessed as priority substances to determine the risk to human health associated with exposure to levels present in the general environment in Canada. The extent to which the speciation of these metals could be considered in these assessments was largely determined by the nature of available data. Very few data were identified on speciation in environmental media to which humans are exposed. Based on available data on health effects, it was possible to conduct assessments on only one form each of arsenic and cadmium (i.e., inorganic arsenic and inorganic cadmium), two forms of chromium (trivalent and hexavalent), and four forms of inorganic nickel (oxidic, sulfidic, soluble, and metallic.