Assessing human health risks using information on whole mixtures

This chapter discusses whole mixture approaches to assessing the risks of potentially hazardous chemical mixtures in the environment within the context of the risk assessment paradigm. Here, "whole mixtures" represent the combination of chemicals in the exposure being assessed. For risk assessment purposes, the environmental mixtures considered as a whole mixture can range from complex mixtures, consisting of perhaps hundreds of component chemicals, to less complex whole mixtures, such as all of the members (i.e., components) of a defined class of compounds. Whole mixture approaches are preferred to component approaches in mixture risk assessments. Because of the variability of whole mixtures encountered in the environment and the paucity of health effect studies, including dose-response studies, conducted on whole mixtures, if toxicity data are not available for an environmental mixture, the risk assessment could be based on surrogate toxicity information obtained from testing a sufficiently similar mixture. Biostatistical approaches for evaluating whether mixtures are sufficiently similar are included here as potential approaches that may, with further evaluation, prove useful in regulatory risk assessment contexts. The chapter concludes with a discussion of future directions for whole mixture risk assessment research.