From: National Academies of Sciences, Engineering, and Medicine
Published March 28, 2017 02:21 PM

New Report Finds EPA's Controlled Human Exposure Studies of Air Pollution Are Warranted

The U.S. Environmental Protection Agency (EPA) carries out experiments in which volunteer participants agree to be intentionally exposed by inhalation to specific pollutants at restricted concentrations over short periods to obtain important information about the effects of outdoor air pollution on human health.  A new report by the National Academies of Sciences, Engineering, and Medicine finds these studies are warranted and recommends that they continue under ­­two conditions: when they provide additional knowledge that informs policy decisions and regulation of pollutants that cannot be obtained by other means, and when it is reasonably predictable that the risks for study participants will not exceed biomarker or physiologic responses that are of short duration and reversible.

 In controlled human inhalation exposure (CHIE) studies, participants are exposed to one or several common air pollutants usually for a few hours at concentrations that are not expected to produce adverse responses. The goal is to observe temporary and reversible responses without causing clinical effects.  The studies are designed to minimize the effects of extraneous factors and focus on the relationship between the experimental exposure conditions and the biologic response being measured, for example, a temporary change in lung function.  These experiments are done in order to understand pathways of toxicity by which air-pollutant exposures might lead to illness or premature death to sensitive individuals in the general population. 

 Results from CHIE studies are used to inform the periodic review of National Ambient Air Quality Standards (NAAQS) for common pollutants, such as ozone and particulate matter (PM), and advise other policy decisions. The NAAQS process has broad health importance because it regulates the outdoor air concentrations of those pollutants. The committee that conducted the study and wrote the report examined the contributions of CHIE experiments to the scientific information used for the reviews of NAAQS for ozone and PM. Ozone and PM CHIE studies have enabled investigators to separate the effects of exposure to such individual pollutants from effects associated with exposures to ambient complex mixtures.  They have provided unique information on short-term exposure-response relationships that cannot be obtained from animal inhalation studies or epidemiologic studies of people engaged in their normal daily activities.

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