Chronic inhalation study of fiber glass and amosite asbestos in hamsters: twelve-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 of inhalation exposure followed by lifetime recovery. Syrian golden hamsters are exposed, nose only, for 6 hr/day, 5 day/week to size-selected test fibers: MMVF10a (Schuller 901 insulation glass); MMVF33 (Schuller 475 durable glass); amosite asbestos (three doses); or to filtered air (controls). Here we report interim results on airborne fiber characterization, lung fiber burden, and pathology (preliminary) through 12 months. Aerosolized test fibers averaged 15 to 20 microns in length and 0.5 to 1 micron in diameter. Target aerosol concentrations of World Health Organization (WHO) fibers (longer than 5 microns) 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-dependent increases. After a 12-month exposure, lung burdens of fibers longer than 20 microns were greatest with amosite high and mid doses, similar for low-dose amosite and MMVF33, and smaller for MMVF10a. Biological responses of animals exposed for 12 months to MMVF10a were limited to nonspecific pulmonary inflammation. However, exposures to MMVF33 and each of three doses of amosite were associated with lung fibrosis and possible mesotheliomas (1 with MMVF33 and 2, 3, and 1 with amosite low, mid, and high doses, respectively). Pulmonary and pleural changes associated with amosite were qualitatively and quantitatively more severe than those associated with MMVF33. As of the 12-month time point, this study demonstrates that two different fiber glass compositions with similar fiber dimensions but different durabilities can have distinctly different effects on the hamster lung and pleura after inhalation exposure. (Preliminary tumor data through 18 months of exposure and 6 weeks of postexposure recovery became available as this manuscript went to press: No tumors were observed in the control or MMVF10a groups, and no additional tumors were observed in the MMVF33 group; however, a number of additional mesotheliomas were observed in the amosite groups.