Biopersistences of man-made vitreous fibers and crocidolite fibers in rat lungs following short-term exposures.

Abstract

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 [PR]) for selected dimension categories. One-day average concentrations of lung-retained MMVF and crocidolite fibers, of diameter > or = 0.5 micron or > 20 microns in length, were nearly equal, permitting direct comparisons between MMVF and crocidolite. At 270 days average PR for MMVF > or = 0.5 micron in diameter were from 3 to 6 +/- 2% and 27 +/- 9% for crocidolite. For fibers > 20 microns, PR were 1 to 4 +/- 4% for MMVF and 37 +/- 20% for crocidolite. At 545 days, MMVF > 20 microns in length were at background level while concentration of crocidolite fibers > 20 microns in length remained at 2000 +/- 400 f/mg DL (dry lung), or 38 +/- 9% of day-1 retention. These results suggest strongly that MMVF dissolved or fractured in vivo whereas crocidolite fibers did not change.

Prediction of mesothelioma and lung cancer in a cohort of asbestos exposed workers

“…A measurement study in former Wittenoom workers [29], showing an elimination rate of about 9%, seems to confirm this assumption. Experiments in rats showed higher rates of elimination of crocidolite from the lungs [30,31], but it has been claimed that extrapolation of these results for humans is not straightforward [32].…”

Respiratory cancer and exposure to man‐made vitreous fibers: A systematic review

“…These reviews suggest that exposures to rock and slag wool are associated with increased risk of cancer, but they emphasize that the evidence for a causal association between exposure and risk is mixed. Diverse MMVF's produce various kinds of cancers in animals [IARC, 1988;Hesterberg et al, 1994;Musselman et al, 1994;Lockey, 1996;OSHA, 1999]. In 1988, the International Agency for Research on Cancer (IARC) classified glass, rock, and slag wool as agents that are possibly carcinogenic to humans, IARC CLASS 2B [IARC, 1988].…”

Behavior of rock wool in lungs after exposure by nasal inhalation in rats

“…In preceding studies, manmade vitreous fibers of all sizes decreased by 30-50% during 30 days after exposure [18,19]. Fibers that are inhaled and precipitated in the lungs show different mechanisms for clearance depending on the site of precipitation.…”