Long-term inhalation studies of diesel exhaust on F344 SPF rats. Incidence of lung cancer and lymphoma.

Chronic inhalation studies of diesel exhaust (SPM 4.9 + 1.6 mg m-3) on SPF Fischer 344 rats were carried out to elucidate its effect on health. The most prominent changes observed were proliferative change of type II alveolar epithelium and respiratory bronchiolar epithelium which appeared after 6 months of exposure, and extended according to the exposure duration to whole exhaust. Neoplastic changes were found in 2-year-exposed rats, some of them being malignant. The rate of malignant tumors was higher in the rats observed for 6 months after 2 years of exposure to whole exhaust. Malignant lymphoma with a highly frequent complication of leukemia was the main cause of death in the rats exposed to filtered as well as whole exhaust, and the rate was significantly higher than that of the control group. Mammary adenoma and fibroma were seen more in the exposed groups than in the control group and multi-tumors were noted only in both exposed groups.