Chronic Inhalation and Biopersistence of Refractory Ceramic Fiber in Rats and Hamsters R.W. Mast/ TW. Hesterberg/ L R. Glass; E. E. McConneU?

mg/m3 produced no excess lung tumors; no fibrosis was seen at 3 mg/m3. A significant increase in lung tumors and interstitial fibrosis was observed at 30 mg/m3. A single mesothelioma was observed in rats exposed to 9 mg/m3, while two occurred at 30 mg/m3. Hamsters were similarly exposed to 30 mg/m3 Kaolin RCF for 18 months; no lung tumors were induced, but pulmonary and pleural fibrosis were observed and there was a 42% incidence of mesothelioma. Multiple interim sacrifices together with recovery animals allowed detailed assessment of the lung burden of RCF, which was found to be dose related and, at the high doses, exceeded 105 fibers/mg of dry lung. During the various recovery periods there was a clear reduction in fiber burden. Mathematical modeling of these data for deposition, clearance, and retention and for species is currently underway.? Environ Health Perspect 102(Suppl 5):207-209(1994)