Connection Between Environmental Exposure and Health Outcomes

Relationships between environmental exposures and health outcomes can only be established through well-designed epidemiological, toxicological, and clinical studies. Developing evidence that environmental contaminants cause or contribute to the incidence of adverse health effects can be challenging, particularly for effects that occur in a relatively small proportion of the population or effects with multiple causes. For example:

• In cases where exposure to an environmental contaminant results in a relatively modest increase in the incidence of a disease or disorder, a large sample size for the study would be needed to detect a true relationship.
   
• There may be factors related to both the exposure and the health effect—confounding factors—that can make it difficult to detect a relationship between exposure to environmental contaminants and disease.
   
• In many cases, findings from studies in humans and/or laboratory animals may provide suggestive (rather than conclusive) evidence that exposures to environmental contaminants contribute to the incidence of a disease or disorder.

Nevertheless, extensive and collaborative data collection and research across the scientific community continue to strengthen understanding of the relationships between environmental exposures and disease.

EPA uses the results of scientific research to help identify linkages between exposure to environmental contaminants and diseases, conditions, or other health outcomes. These linkages, in turn, identify environmental contaminants and health outcomes of potential Agency interest. Research has established a relationship between exposure and disease for some environmental contaminants including:

• Radon and lung cancer.
• Arsenic and cancer in several organs.
• Lead and nervous system disorders.
• Disease-causing bacteria (such as E. coli) and gastrointestinal illness and death.
• Particulate matter and aggravation of cardiovascular and respiratory diseases.

These known linkages guided selection of the Human Exposure and Health indicators in the ROE. However, because these indicators are based on data sets representative of the national population (rather than data from targeted populations) and are not tied to specific exposures or releases, they do not directly link environmental exposure with outcome.