US EPA

The 1996 Food Quality Protection Act (FQPA) and the 1996 Safe Drinking Water Act Amendments (SDWAA) reaffirm previous Acts that mandate the EPA to evaluate risks posed by environmental chemical mixtures. The current report develops biological concepts and statistical procedures for improving applications of the Relative Potency Factor (RPF) approach in response to the need for mixtures research on current (and potential) chemicals on the Office of Water's (OW) Contaminant Candidate List (CCL) and under FQPA. The RPF approach is a general methodology for applying dose addition to mixtures of chemicals that produce toxicity by the same mode of action. This research explores the basic tenets of dose addition (i.e., the fundamental assumption that the mixture components share common toxic modes of action and a second methodologic assumption that the mixture components exhibit similarly-shaped dose-response curves) and develops mixture risk assessment methods for application when these basic tenets are not met. Three different risk characterization approaches are proposed that enrich the available library of mixture risk assessment methods beyond what is currently published in EPA guidance (1986; 2000).

U.S. EPA. Developing Relative Potency Factors For Pesticide Mixtures: Biostatistical Analyses Of Joint Dose-Response. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-32/052, 2003.