CHRONIC INHALATION STUDY OF FIBER GLASS AND AMOSITE ASBESTOS IN HAMSTERS - 12-MONTH PRELIMINARY-RESULTS

The effects of chronic inhalation of glass fibers and amosite asbestos are currently under study in hamsters. The study includes 18 months o f inhalation exposure followed by lifetime recovery. Syrian golden ham sters are exposed, nose only, for 6 hr/day, 5 days/week to size-select ed test fibers. MMVF10a (Schuller 901 insulation glass); MMVF33 (Schul ler 475 durable glass), amosite asbestos (three doses); or to filtered air (controls). Here we report interim results on airborne fiber char acterization, lung fiber burden, and pathology (preliminary) through 1 2 months. Aerosolized test fibers averaged 15 to 20 mu m in length and 0.5 to 1 mu m in diameter. Target aerosol concentrations of World Hea lth Organization (WHO) fibers (longer than 5 mu m) were 250 fibers/cc for MMVF10a and MMVF33, and 25, 125, or 250 fibers/cc for amosite, WHO fiber lung burdens showed time-dependent and (for amosite) dose-depen dent increases. After a 12-month exposure, lung burdens of fibers long er than 20 um were greatest with amosite high and mid doses, similar f or low-dose amosite and MMVF33, and smaller for MMVF10a. Biological re sponses of animals exposed for 12 months to MMVF10a were limited to no nspecific pulmonary inflammation. However, exposures to MMVF33 and eac h of three doses of amosite were associated with lung fibrosis and pos sible mesotheliomas (1 with MMVF33 and 2, 3, and 1 with amosite low, m id, and high doses, respectively). Pulmonary and pleural charges assoc iated with amosite were qualitatively and quantitatively more severe t han those associated with MMVF33. As of the 12-month time point, this study demonstrates that two different fiber glass compositions with si milar fiber dimensions but different durabilities can have distinctly different effects on the hamster lung and pleura after inhalation expo sure. (Preliminary tumor data through 18 months of exposure and 6 week s of postexposure recovery became available as this manuscript went to press: No turners were observed in the control or MMVF10a groups, and no additional tumors were observed in the MMVF33 group; however, a nu mber of additional mesotheliomas were observed in the amosite groups.) .