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

Our plain-English summary of Biopersistences of man-made vitreous fibers and crocidolite fibers in rat lungs following short-term exposures, by R.P. Musselman, W.C. Miiller, W. Eastes, et al (Environmental Health Perspectives, 1994).

The study

• Authors: R.P. Musselman, W.C. Miiller, W. Eastes, J.G. Hadley, O. Kamstrup, P. Thevenaz, T.W. Hesterberg
• Journal: Environmental Health Perspectives
• Published: 1994;102 Suppl 5(Suppl 5):139-43
• Cited by: 35 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

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.

In plain English

This was an animal experiment in Fischer 344 rats. Rats breathed through the nose only, 6 hours a day for 5 days. Each group got one of four size-selected man-made vitreous fibers (two glasswools, a rockwool and a slagwool) at 30 mg/m3, crocidolite asbestos at 10 mg/m3, or filtered air. Groups were killed from 1 hour to 545 days after exposure, and fibers recovered from five lungs per group were counted and measured. One day after exposure, the levels of long fibers (over 20 micrometers) per milligram of dry lung were nearly equal for the man-made fibers and crocidolite. At 270 days, 1 to 4 (plus or minus 4)% of the day-1 level of long man-made fibers remained, compared with 37 (plus or minus 20)% for long crocidolite fibers. At 545 days, long man-made fibers were at background level. Long crocidolite fibers remained at 2000 plus or minus 400 fibers per milligram of dry lung, or 38 plus or minus 9% of the day-1 level. The authors concluded that the results strongly suggest the man-made fibers dissolved or broke apart in the lung, while crocidolite fibers did not change.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Animal experiment: short-term (5-day) nose-only inhalation study in rats, with serial sacrifices to measure how long fibers persisted in the lung
• Who was studied: Fischer 344 rats. Subgroups of nine rats per fiber type and nine air controls were killed at 1 hour and 1, 5, 31, 90, 180, 270, 365 and 545 days after exposure. Lung lobes from five rats per group were analyzed at each time point. The article does not state where or when the rats were studied, beyond the paper being presented at a September 1992 workshop.
• Exposure: Four size-selected commercial man-made vitreous fibers at 30 mg/m3 each: Fiber 10, a glasswool (Manville Corp.); Fiber 11, a glasswool (Certainteed Corp.); Fiber 21, a rockwool (Roxul International); and Fiber 22, a slagwool (USG Interiors). One group received size-selected crocidolite at 10 mg/m3, and one group breathed filtered air. Exposure was nose-only, 6 hours a day for 5 days.
• Main results:
  • One day after exposure, the average lung concentrations of man-made fibers and crocidolite fibers that were 0.5 micrometers or more in diameter, or longer than 20 micrometers, were nearly equal.
  • At 270 days, the average percent of day-1 retention for fibers 0.5 micrometers or more in diameter was 3 to 6 (plus or minus 2)% for the man-made fibers and 27 (plus or minus 9)% for crocidolite.
  • At 270 days, for fibers longer than 20 micrometers, the percent of day-1 retention was 1 to 4 (plus or minus 4)% for the man-made fibers and 37 (plus or minus 20)% for crocidolite.
  • At 545 days, man-made fibers longer than 20 micrometers were at background level. Crocidolite fibers longer than 20 micrometers remained at 2000 plus or minus 400 fibers per mg of dry lung, or 38 plus or minus 9% of day-1 retention.
  • After 180 days, 90 to 100% of the long man-made fibers had been cleared from the lungs.
  • Crocidolite fibers longer than 5 micrometers fell from an average of 168,000 plus or minus 47,000 fibers per mg of dry lung at day 1 to 56,000 plus or minus 6000 at day 545.
  • The rockwool (Fiber 21) was retained at higher percentages than the other man-made fibers at 31 and 90 days, but by day 180 it was close to the others.
  • For the man-made fibers, thinner fibers (under 0.5 micrometers in diameter) were consistently retained at higher percentages than thicker fibers at each sacrifice time.
• The authors' conclusion: The authors concluded that the results strongly suggest the man-made vitreous fibers dissolved or fractured in the lung, whereas crocidolite fibers did not change. They also stated that about 40% of the long crocidolite fibers present at day 1 remained through 545 days.
• Limitations the authors state:
  • Reporting fibers per mg of dry lung does not account for the lung growing heavier with age; rat lung mass nearly doubles from 6 to 78 weeks of age. The authors note that per-lung reporting would give higher retention values, especially for crocidolite.
  • Comparing clearance among the man-made fibers is difficult because the size distribution of fibers deposited at day 1 differed by fiber type.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Crocidolite.

Medical terms in this study, explained in our Lexicon: biopersistence, Vitreous, Crocidolite, Short-Term Exposure.

Related studies

• Relationship between lung biopersistence and biological effects of man-made vitreous fibers after chronic inhalation in rats — T.W. Hesterberg, W.C. Miiller, et al. (1994)
• Investigation on the durability of man-made vitreous fibers in rat lungs — B. Bellmann, H. Muhle, et al. (1994)
• Clearance and dimensional changes of crocidolite asbestos fibers isolated from lungs of rats following short-term exposure — V.L. Roggli, M.H. George, et al. (1987)
• Evaluation of the fate and pathological response in the lung and pleura of brake dust alone and in combination with added chrysotile compared to crocidolite asbestos following short-term inhalation exposure — D.M. Bernstein, R.A. Rogers, et al. (2015)
• Short-term crocidolite inhalation studies in mice: validation of an inhalation chamber — B. Rihn, E. Kauffer, et al. (1996)
• Long-term health effects in hamsters and rats exposed chronically to man-made vitreous fibres — D.M. Smith, L.W. Ortiz, et al. (1987)

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