Use of Toxicological and Nutritional Data for the Risk Assessment of Essential Trace Elements (ETEs). C. O. Abernathy and J. M. Donohue, U.S. EPA (4304), 401 M Street, SW, Washington, DC 20460
The EPA is required to set regulatory limits for a variety of chemicals. In order to set adequate guidelines, the Agency must review the complete health effects data base prior to conducting a risk assessment of a chemical chosen for regulation. Since some ETEs, e.g., zinc and selenium, have been found in public drinking water systems, the EPA has had to conduct risk assessments on several of these chemicals. For the noncarcinogenic effects of chemicals, the Reference Dose (RfD) methodology is used. This method considers the adverse effects of exposures to toxic doses and seeks to set an RfD at a point where adverse effects will probably not occur. Unlike the risk assessment of most chemicals, it is necessary to consider the potential for adverse effects of the lack of exposure to an ETE as certain level of ETEs are required to maintain normal physiological states. Accordingly, the Agency must not only focus on the adverse health effects of higher doses, it must also factor in the potential effects of the deficiency state. For example, the EPA used the Recommended Dietary Allowance (RDA) for selenium of 70 µg/day as a baseline when deriving the RfD for this chemical, while selecting alteration in prothrombin time as an adverse effect from higher doses.