Limited damage occurred in the lungs of rats when exposed to ozone for 20 months by UC Davis researchers participating in a study of ozone exposure. Their findings were released earlier this month as part of an ozone pollution study by the Health Effects Institute and the National Toxicology Program. The study showed that prolonged exposure to ozone had the most effects on the nose, but mild to moderate effects on other respiratory tract regions, the Massachusetts-based institute reported. The UC Davis researchers focused on potential lung damage. They found that structural and biochemical changes occurred in certain parts of the lung, particularly in a region thought to be ozone-sensitive, according to Kent Pinkerton, a professor with the UC Davis Institute of Toxicology and Environmental Health who collaborated in the study with Jerold Last, a UC Davis pulmonary medicine professor, and Charles Plopper, a UC Davis veterinary medicine professor. Because many of the observed changes -- such as thickening of normal cells, similar to a callous on a hand -- would result in the protection of airways, these changes and the lack of pulmonary function effects, indicate the animals' lungs became tolerant to the injurious effects of ozone. Yet, the study was not able to confirm tolerance because the effects were measured at only one time point, Pinkerton says.