Semi-volatile organic chemicals, such as dioxins, PCBs, and brominated flame retardants, tend to bind to the organic fraction in soil, dust, and sediment particles, and to bioaccumulate in animals and humans. Direct exposures to these chemicals can occur via many pathways, such as incidental soil ingestion, inhalation, and dermal contact. Exposures can also occur indirectly through the consumption of food, such as homegrown vegetables, maternal or dairy milk, and recreationally caught fish. Evaluating exposure to these chemicals requires careful consideration of their physicochemical and fate-and-transport properties in the environment, and their potential to be retained in the body. For example, while these chemicals generally bind strongly to organic materials, the degree to which they are bound is dependent on the number of halogen atoms (i.e., bromine or chlorine) in the specific type of molecule. Assessing dermal exposures to these chemicals in soils requires determining the fraction that may be absorbed through the skin versus the fraction that remains bound to soil particles.
Exponent scientists and engineers have estimated exposure to these chemicals under current-day conditions and have reconstructed exposures based on historical conditions (i.e., exposure or dose reconstruction) for a number of projects. Examples include estimating exposures from incinerator emissions, contact with contaminated soils and sediments, occupational contact with waste materials, and consumption of seafood and homegrown vegetables. These projects typically involve integrating multidisciplinary efforts to obtain relevant exposure information. We have developed site-specific studies to fill crucial data gaps, such as conducting an angler creel survey to assess recreational fishing patterns and fish consumption rates. To quantify exposures, we have applied or developed mathematical models that incorporate the best available scientific understanding of the behaviors of these chemicals.