Inhalation studies of diesel exhaust and coal dust in rats.

The preliminary 12-month data of an ongoing two-year chronic inhalation study into the effects of diesel exhaust and coat dust on rats are reported. The study design consists of four exposure regimens: coal dust, diesel exhaust, coal dust plus diesel exhaust, and filtered air (control). Total respirable particulate is being maintained at 2 mg/m3 in all exposure groups. Animals are being serially sacrificed and subjected to immunologic, biochemical, physiological, microbiological, and pathological evaluations. Extracts of diesel emissions showed marked mutagenic activities in the Ames Salmonella his reversion assay. Mutagenic compounds were not however found in the urine of the exposed animals, nor were sister chromatid exchanges detected in peripheral lymphocytes. No changes were observed in cytochrome P450 enzyme activity in lung microsomes of exposed rats. Physiological tests showed no evidence of pulmonary function impairment in any group. Light microscopic examination of the lungs showed dust deposition with the formation of macules in all exposed groups. The preliminary results revealed few pathological effects of significance and no evidence of synergism between diesel exhaust and coal dust.