disease risks directly or modify a person’s susceptibility to the effects of other agents (Shankardass et al. 2009). The direct effects of psychosocial risk factors on health outcomes are beyond the scope of this report, but their role as modifiers of exposures is within the committee’s charge. Figure 3-1 provides a general schema for thinking about the components of exposure assessment in environmental epidemiology. Each of the components shown in solid boxes represent areas where exposure science can contribute, providing data on determinants of people’s exposures (the intensity of the spatio-temporal exposure fields they are moving through and their personal time/activity patterns in that field) and direct measurements of individuals’ external exposures or internal doses, along with relevant modifying factors. The hypothesized (but not directly observable) history of doses to the relevant target organs are then used by epidemiologists to relate to the health outcomes.
FIGURE 3-1 General schema of exposure assessment in environmental epidemiology. Items in gray, related to health outcomes and their determinants other than environmental exposures, are included to place exposure assessment in context but are outside the charge of this committee. Boxes represent measurable quantities, and ovals denote hypothetical intermediate variables that can be assessed only indirectly. Solid arrows denote direct effects, and dashed arrows indicate modifying effects. For example, the oval marked “personal exposure” represents the entire history of an individual’s true biologically-relevant exposure, which is not directly observable. The boxes labeled “personal external exposure monitoring” and “biomarkers of exposure” represent the data that are potentially observable.