CHRONIC INHALATION STUDY OF SIZE-SEPARATED ROCK AND SLAG WOOL INSULATION FIBERS IN FISCHER 344 N RATS/

This study was designed to investigate the potential pathogenic effect s in Fischer 344/N rats oi two different types of man-made vitreous fi bers (MMVF). Eight-week-old male rats were exposed in nose-only inhala tion chambers, 6 h/day, 5 days/wk, for 24 mo to 3 concentrations (3, 1 6, and 30 mg/m(3)) each of the two MMVFs: a basalt-based rock wool (st one wool), and a slag wool (blast furnace). Crocidolite asbestos (10 m g/m(3)) was used as a positive control. The experimental groups were c ompared to unexposed (chamber) controls. The MMVFs used in this study were size selected to be largely respirable in rats. Interim sacrifice s took place at 3- and 6-mo intervals to monitor the progression of pu lmonary changes. Fibers were recovered from digested lung tissue for d etermination of changes in fiber number and morphology. Exposure to cr ocidolite asbestos was terminated after 10 mo because oi increased mor bidity/mortality. Exposure to rock and slag wool, while producing a do se-related nonspecific inflammatory response (rock and slag) and minim al focal pulmonary fibrosis (rock only), showed no evidence of carcino genic activity in either the lung or pleura, in contrast to crocidolit e asbestos, which induced neoplasms in both tissues. Since workplace a irborne levels are several orders of magnitude lower than even the low est exposure level to which the animals were exposed, these results su ggest that these MMVFs do not pose a significant health risk to humans at airborne levels found in the workplace, during installation or for the in-place product.