Long-term inhalation studies with raw and processed shale dusts.

Abstract

Abstract Long-term inhalation studies have been conducted in which rats and monkeys were exposed 6 h per day, 5 days per week, for 2 yr to 10 and 30 mg m3 of respirable dusts of raw and spent or processed shale. A large variety of tests was employed to evaluate effects. The only significant changes were found on histopathological examination of tissues obtained from the animals at termination. Effects were confined to the lungs and peribronchial lymph nodes and were similar for both kinds of dusts and the severity of the responses was dose-related. Accumulations of pigment and particle-laden macrophages in and around end airways with inflammatory reactions in the lung were noted in both species. Pathologically these findings were not considered to be indicative of progressive fibrosis. No evidence of any carcinogenic action was seen, nor were there indications of systemic toxic effects.