BIOPERSISTENCE OF SYNTHETIC VITREOUS FIBERS AND AMOSITE ASBESTOS IN THE RAT LUNG FOLLOWING INHALATION

Fiber biopersistence as a major mechanism of fiber-induced pathogenici ty was investigated. The lung biopersistence of 5 synthetic vitreous f ibers (SVFs) and amosite asbestos was evaluated using the rat inhalati on model. In contrast to several previous studies, this study examined fibers that dissolve relatively slowly in vitro at pH 7.4. Fisher rat s were exposed for 5 days by nose-only inhalation to refractory cerami c fiber (RCF1a), rock (stone) wool (MMVF21), 2 relatively durable spec ial application fiber glasses (MMVF32 or MMVF33), HT stonewool (MMVF34 ), amosite asbestos, or filtered air. Lung burdens were analyzed durin g 1 year post-exposure. Fiber aerosols contained 150-230 fibers/cc lon ger than 20 mu m (>20 mu m). On post-exposure Day 1, long-fiber lung b urdens for the 6 test fibers were similar (12-16 x 10(5) fibers/lung > 20 mu m). After I year, the percentage of fibers >20 Ccm remaining in the lung was 0.04-10% for SVFs but 27% for amosite. Lung clearance wei ghted half-times (WT1/2) for fibers >20 mu m were 6 days for MMVF34, 5 0-80 days for the other 4 SVFs, and >400 days for amosite. This study and 3 previous studies demonstrate a broad range of biopersistences fo r 19 different SVFs and 2 asbestos types. Ten of these fibers also hav e been (or are being) tested in chronic inhalation studies; in these s tudies, the very biopersistent fibers were carcinogenic (amosite, croc idolite, RCF1, MMVF32, and MMVF33), while the more rapidly clearing fi bers were not (MMVF10, 11, 21, 22, and 34). These studies demonstrate the importance of biopersistence as an indicator of the potential path ogenicity of a wide range of fiber types. (C) 1998 Academic Press.