DIESEL EXHAUST IS NOT A PULMONARY CARCINOGEN IN CD-1 MICE EXPOSED UNDER CONDITIONS CARCINOGENIC TO F344 RATS

Differences among laboratory animal species in the pulmonary carcinoge nicity of chronic inhalation exposure to diesel exhaust have raised se veral important interpretive issues. Under similar heavy exposure cond itions, it is clear that diesel exhaust is a pulmonary carcinogen in r ats, but not in Syrian hamsters. Previous reports give conflicting vie ws of the response of mice, which is presently considered equivocal. T his report describes carcinogenicity results from a bioassay of CD-1 m ice conducted in parallel with a previously reported bioassay of F344 rats (Mauderly et al. (1987) Fundam. Appl. Toxicol. 9, 208-221). Expos ure to whole diesel exhaust 7 hr/day, 5 days/week for 24 months at soo t concentrations of 0.35, 3.5, or 7.1 mg/m(3) caused accumulations of soot in mouse lungs similar to those in lungs of rats and, like the re sults from rats, did not significantly affect survival or body weight. In contrast to the dose-related neoplastic response of rats, however, the exposures of mice did not increase the incidence of lung neoplasm s. This finding is consistent with other data showing that mice, as we ll as Syrian hamsters, differ from rats in their lung neoplastic and n onneoplastic responses to heavy, chronic inhalation exposure to diesel exhaust soot and several other particles. Although rodents serve as u seful indicators of potential human carcinogenic hazards, it is not ye t clear which, if any, rodent species have lung neoplastic responses t hat are useful for quantitative predictions of human lung cancer risk from chronic inhalation of poorly soluble, respirable particles. (C) 1 996 Society of Toxicology