![[logo] US EPA](https://webarchive.library.unt.edu/eot2008/20090508235912im_/http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
Conduct Research to Protect Susceptible Subpopulations
Understanding the effects and risks of exposure to mixtures of chemicals and from exposure to chemicals from multiple routes is a major focus of the Human Health Research Program in EPA's Office of Research and Development. 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.
Research concerning the effects of pollutants on susceptible populations and on populations of people who are highly exposed to pollutants is a high priority at EPA. Susceptibility to pollutants depends on intrinsic factors, such as life stage and genetics, and on acquired factors such as pre-existing disease.
Life stage is an important factor determining susceptibility for several reasons. Children may be particularly vulnerable because of differences in exposure arising from their behavior (e.g., crawling on the floor and putting things into their mouths), absorption, or metabolism. Aging may also render individuals more susceptible to adverse effects from a pollutant because as individuals age, their bodies' ability to defend against and respond to injury may diminish.
The goal of EPA research in this area is to gain an understanding of the biological basis for the observed differences in susceptibility. Scientists are working to identify effects in susceptible populations that are different from effects in the larger population and to develop methods and animal models that can be used to predict responses in susceptible populations. Work is also underway to determine the relationship between exposures earlier in life to adverse effects later in life and to understand how exposure during critical periods of development can influence long-term health outcomes.