BIOPERSISTENCES OF MAN-MADE VITREOUS FIBERS AND CROCIDOLITE FIBERS IN RAT LUNGS FOLLOWING SHORT-TERM EXPOSURES

Biopersistence of commercial man-made vitreous fibers (MMVF) and crocidolite were studied in Fischer 344 rats. MMVF used were size-selected to be rat-respirable, and rats were exposed nose-only 6 h/day for 5 days to gravimetric concentrations (30 mg/m3) of two fiber glass compositions-a rockwool, and a slagwool-or to 10 mg/m3 of long-fibered crocidolite, or to filtered air. Animals were sacrificed at 1 hr, 1, 5, 31, 90, 180, 270, 365, and 545 days after exposure stopped. Fibers were recovered from digested lung tissue to determine changes in concentrations (fibers/mg dry lung) and fiber retentions (expressed as percent of day 1 retention (PRI) for selected dimension categories. One-day average concentrations of lung-retained MMVF and crocidolite fibers, of diameter greater than or equal to 0.5 mu m or >20 mu m in length, were nearly equal, permitting direct comparisons between MMVF and crocidolite. At 270 days average PR for MMVF greater than or equal to 0.5 mu m in diameter were from 3 to 6 +/- 2% and 27 +/-:9% for crocidolite. For fibers >20 mu m, PR were 1 to 4 +/- 4% for MMVF and 37 +/- 20% for crocidolite. At 545 days, MMVF >20 mu m in length were at background level while concentration of crocidolite fibers >20 mu m in length remained at 2000 +/- 400 f/mg DL (dry lungi, or 38 +/- 9% of day-1 retention. These results suggest strongly that MMVF dissolved or fractured in vivo whereas crocidolite fibers did not change.