Empirical evaluation of sufficient similarity in dose-response for environmental risk assessment of chemical mixtures

When toxicity data are not available for a chemical mixture of concern, U.S. Environmental Protection Agency (EPA) guidelines allow risk assessment to be based on data for a surrogate mixture considered "sufficiently similar" in terms of chemical composition and component proportions. As a supplementary approach, using statistical equivalence testing logic and mixed model theory we have developed methodology to define sufficient similarity in dose-response for mixtures of many chemicals containing the same components with different ratios. Dose-response data from a mixture of 11 xenoestrogens and the endogenous hormone, 17β-estradiol are used to illustrate the method.