Consensus Report

Each report is produced by a committee of experts selected by the Academy to address a particular statement of task and is subject to a rigorous, independent peer review; while the reports represent views of the committee, they also are endorsed by the Academy. Learn more on our expert consensus reports.

Under the Clean Air Act, the U.S. Environmental Protection Agency (EPA) conducts a range of studies to evaluate exposure to, and effects of, air pollutants on human health. A subset of those studies involves intentionally exposing human volunteers to pollutants by inhalation under controlled experimental conditions. The exposure can produce transient and reversible physiologic responses (such as a temporary change in lung function), but it is not expected to cause clinical health effects. EPA uses the results to improve understanding the biological pathways of toxicity by which air-pollutant exposures might lead to illness or premature death in sensitive groups in the U.S. population, such as groups of people who have heart or lung disease. The agency also uses the results to inform its air-quality management decision making.

Conducted at the request of EPA, this report evaluates the scientific value of such studies, risks to participants, and whether or not they should continue. The report concludes that the studies have provided unique information that cannot be obtained from studies of animal inhalation studies or of people engaged in their normal daily activities (i.e., through epidemiologic studies). The report also concludes that the risk of a serious adverse event is unlikely to be large enough to warrant concern, although it is never possible to conclude that there is no risk. EPA should continue to undertake such studies cautiously, under two conditions: (1) only when the study is expected to provide additional knowledge that informs policy decisions and regulation of pollutants that cannot be obtained by other means and (2) when it is reasonably foreseeable that the risks for study participants will not exceed transient and reversible biomarker or physiologic responses.