Assessing Toxicity of Mixtures: The Search for Economical Study Designs

Toxicity screening and testing of chemical mixtures for interaction effects is a potentially onerous task due to the sheer volume of combinations that may be of interest. We propose an economical approach for assessing the interaction effects of chemical mixtures that is guided by risk-based considerations. We describe the statistical underpinnings of the approach and use examples from the published literature to illustrate concepts of local versus global mixture assessment. Our approach employs a sequential testing procedure to find the dose combinations that define the dose boundary for a specified acceptable risk level. The first test is conducted for a dose combination consisting of the acceptable doses of each individual chemical in the mixture. The outcome of this first test indicates the dose combination that should be tested next. Continuing in this manner, the boundary of dose combinations for the specified acceptable risk level can be approximated based on measurements for relatively few dose combinations. Dose combinations on one side of the boundary would have responses less than the response associated with the acceptable risk level, and dose combinations on the boundary would be acceptable levels of exposure for the mixture.