The NTP/HEI Collaborative Ozone Project on the health effects of chronic ozone inhalation

Publication Type:
Journal Article
Inhalation Toxicology, 1996, 8 (3), pp. 213 - 227
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Although many people are exposed to ozone, the effects of chronic exposure to this ubiquitous pollutant, especially low-level chronic exposure, are not well understood. The U.S. Environmental Protection Agency (EPA) current national ambient air quality standard for ozone is exceeded in many communities, especially during the summer. The standard is attained when the number of days per calendar year with maximum hourly average concentrations above 0.12 ppm is equal to or less than 1. The U.S. EPA estimates that 67 million people in the United States, or slightly more than a quarter of the residents, live in areas that were out of compliance with the current National Ambient Air Quality Standard (NAAQS) for ozone in 1989. Although there have been some studies of long-term exposure to ozone, many important questions remain about the health effects of chronic ozone exposure. The Health Effects Institute (HEI), in conjunction with the National Toxicology Program (NTP) carcinogenesis studies, has completed a major effort to help answer these questions. NTP included additional animals in its study for HEI investigators. Included in this effort is a set of studies examining histopathological, biochemical, morphological, and functional alterations in rats exposed to 0, 0.12, 0.5 or 1.0 ppm ozone for 20 mo. This article describes several aspects of this effort. This project can serve as a model for other large toxicological studies for which cancer may not be the only endpoint of concern. The additional animals required for the NTP/HEI Collaborative Ozone Project only represented a modest incremental cost, yet provided information on a much broader range of potential effects of ozone than the basic NTP carcinogenesis studies.
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