factors play a role in nearly all diseases, even ones that are not caused directly by environmental risk factors, by altering the course of disease initiated by other causes. In addition, if the total burden of disease is simply decomposed into “nature” or “nurture”, it fails to account directly for the possibly large proportion that could be due to the interplay between the two (gene—environment interactions). Improving our understanding of environmental factors and their relationships with disease is critical for preventing illness and death.

With respect to ecosystems, the 1999 National Research Council report Our Common Journey: A Transition Toward Sustainability (NRC1999) reported that the rising losses of wild nature, species number, species diversity, and ecosystem integrity were associated with exposures to environmental stressors, including those related to urban and agricultural land conversion and climate change.

Figure 1-1 illustrates the relationship of exposure to other key elements along the environmental-health continuum from the source of a stressor to an outcome. This figure has evolved from previous diagrams (for example, Smith 1988a; Lioy 1990; NRC 1998; EPA 2009a). For more than 20 years, this framework has demonstrated the central role of exposure science in environmental health science in that exposure sits midway between the sources of pollution (and other stressors) on the left—elements that typically can be controlled—and adverse health outcomes on the right, which need to be prevented. Exposure is strategically located upstream of dose and yet provides information and metrics that inform source control and health risk.

BOX 1-1 Definition and Scope of Exposure Science

Exposure science is defined by this committee as the collection and analysis of quantitative and qualitative information needed to understand the nature of contact between receptors (such as people or ecosystems) and physical, chemical, or biologic stressors. Exposure science strives to create a narrative that captures the spatial and temporal dimensions of exposure events with respect to acute and long-term effects on human populations and ecosystems.

For the purposes of this report, the committee focuses on environmental risk factors and excludes behavioral or lifestyle factors—such as diet, alcohol, and smoking—although it includes contaminants in food, water, and environmental tobacco smoke. It also excludes social risk factors (for example, crime and child abuse) but does consider them as modifying influences on exposures to stressors (Smith et al. 1999). The influence of social factors on environmental exposures is an area of active research. Natural hazards (for example, weather and arsenic contamination) are included here.

A central theme of this report is the interplay between the external and internal environments and the opportunity for exposure science to exploit novel technologies for assessing biologically active internal exposures from external sources.

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