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Research Programs: Human Health Risk
Cumulative Risk
Human Health Risk
Although the traditional approach has been to evaluate the risk of a single chemical from a single source (e.g., lead in drinking water), people, in fact, are exposed to mixtures of chemicals from multiple sources. Chemicals may travel from their sources to people by multiple pathways and may be taken into the body through multiple routes, including inhalation, ingestion, or uptake through the skin. A further complication is that chemicals in a mixture may interact with one another to produce effects different or more severe than they would alone. Alternatively, exposure to a mixture of chemicals or to a single chemical by multiple routes may produce an effect greater than would be predicted by simply adding the individual effects together—what could be termed a "synergistic" or "1 + 1 = 3" effect.
Understanding the effects and risks of exposure to mixtures of chemicals and from exposure to chemicals from multiple routes is a major focus of EPA's human health research. EPA scientists are working to develop efficient and accurate experimental designs and statistical models to help them understand and predict the effects of complex chemical mixtures. This research is conducted using both a top-down and a bottom-up approach (i.e., looking at whole mixtures and looking at the components of mixtures individually) and focuses on chemicals at concentrations as close as possible to those found in the environment. EPA research in this area is also designed to address questions about the influence of dose, exposure history, and exposure scenario on toxicity.
