This supplementary guidance document is organized according to the type of data available to the risk assessor, ranging from data rich to data poor situations. This organization reflects the approaches to chemical mixture risk assessment recommended in the 1986 Guidelines for the Health Risk Assessment of Chemical Mixtures (Appendix A). This document describes more detailed procedures for chemical mixture assessment using data on the mixture of concern, data on a toxicologically similar mixture, and data on the mixture component chemicals. The state-of-the-science varies dramatically for these three approaches. It is recommended that the risk assessor implement several of the approaches that are practical to apply and evaluate the range of health risk estimates that are produced. This document suggests that the selection of a chemical mixture risk assessment method follows the outline in the flow chart shown in Figure 2-1, which begins with an assessment of data quality and then leads the risk assessor to selection of a method through evaluation of the available data. The major concerns for the user are whether the available data are on components or whole mixtures, whether the data are composed of either similar components or similar mixtures that can be thought of as acting by similar toxicologic processes, and whether the data may be grouped by emissions source, chemical structure, or biologic activity.

"EPA 630/R-00-002." "U.S. Environmental Protection Agency." "August 2000." Includes bibliographical references.