Persistence of man-made mineral fibres (MMMF) and asbestos in rat lungs

Our plain-English summary of Persistence of man-made mineral fibres (MMMF) and asbestos in rat lungs, by B. Bellmann, H. Muhle, F. Pott, et al (The Annals of Occupational Hygiene, 1987).

The study

• Authors: B. Bellmann, H. Muhle, F. Pott, H. König, H. Klöppel, K. Spurny
• Journal: The Annals of Occupational Hygiene
• Published: 1987;31(4B):693-709
• Cited by: 71 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In a 2-yr study the persistence of some MMMF, crocidolite and chrysotile in the rat lung was examined after intratracheal instillation. Experiments were based on the assumption that thin, long and durable fibres are of special importance for the carcinogenic potency of these types of substance. Parameters measured included number of fibres, diameter and length distribution of fibres retained in lung ash and leaching of various elements from fibres. The results of the half-time of fibre clearance of the fibre fraction longer than 5 µm has been most important. For a special type of glass microfibre and for ceramic wool, which both had a low alkaline earth content, the half-times of lung clearance were at a level similar to that of crocidolite. For another type of glass microfibre with a high alkaline earth content and a median diameter of about 0.1 µm, a very low half-time was detected. The glass and rock wools studied, which were thicker than the other fibres, had a medium half-time. The acid pretreatment of fibrous material showed that chemical leaching of some alkaline earth and alkali cations increases the in vivo solubility.

PubMed has no abstract for this study. This is the authors' abstract, copied from the article.

In plain English

This animal experiment measured fibre persistence in rat lungs over 2 years. Female Wistar rats received 2 milligrammes of crocidolite, chrysotile, three glass microfibres, glass wool, rock wool or ceramic wool into the windpipe, some acid-treated. At 1 day and 1, 6, 12, 18 and 24 months, three rats per group were killed. Crocidolite fibres longer than 5 micrometres did not change in number over 2 years. Long chrysotile fibres increased about 15-fold, which the authors linked to fibre bundles splitting. For long fibres, half-times were about 55 days for E-glass microfibre and about 150 days for Tempstran 753. Tempstran 475 did not differ significantly from crocidolite in durability or change of size distribution, though sodium, potassium and calcium leached from it. Glass and rock wool had half-times of about 280 days and ceramic wool about 800 days; the authors noted these thicker wools were not fully comparable. Acid treatment shortened persistence of chrysotile and E-glass fibres. The authors concluded that high-calcium fibres were highly soluble in rat lungs. They called the half-times preliminary, as few animals were used.

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: fibres were instilled into the trachea (intratracheal instillation) of rats, and lung fibre content was measured at intervals over 2 years.
• Who was studied: Female Wistar rats (body weight 200-220 g). Three rats from each fibre group were killed at each sampling time: 1 day and 1, 6, 12, 18 and 24 months after instillation.
• Exposure: A single 2 mg dose of fibres in saline. The fibres were UICC crocidolite, UICC chrysotile (Zimbabwe), glass microfibres JM 104 (E-glass, Tempstran 475, Tempstran 753), glass wool, rock wool and ceramic wool. Some were pretreated with oxalic acid or hydrochloric acid.
• Main results:
  • Crocidolite: the number of fibres longer than 5 micrometres did not change for up to 2 years.
  • Crocidolite fibres shorter than 5 micrometres were cleared with a half-time of about 160 days. For all fibre types, fibres shorter than 5 micrometres disappeared faster than longer ones.
  • Chrysotile: the number of fibres longer than 5 micrometres increased continuously over 2 years to about 15-fold. The authors attributed this to fibre bundles splitting.
  • Glass microfibre 104/E-glass: half-time of 55 days for fibres longer than 5 micrometres.
  • Glass microfibre JM 104 Tempstran 475 was much more persistent. It showed no significant difference from crocidolite in durability and change of size distribution.
  • Tempstran 475 nonetheless showed leaching of sodium, potassium and calcium, with half-times of 200-400 days.
  • Glass microfibre JM 104 Tempstran 753: medium durability, with a half-time of about 150 days.
  • Mineral wools: ceramic wool had a half-time of about 800 days. Glass wool and rock wool had half-times of about 280 days. The authors noted that these thicker, longer fibres are not fully comparable with asbestos and glass microfibres.
  • Chrysotile pretreated with oxalic acid (which removed almost all its magnesium) had a lung half-time of only 2 days.
  • Hydrochloric acid treatment of 104/E-glass shortened the half-time of fibres longer than 5 micrometres from 55 to 14 days.
• The authors' conclusion: The authors concluded that fibres with a high calcium content showed high solubility in the rat lung. They judged a high alkaline earth content to be more significant for in vivo solubility than a high alkaline content, and found that acid leaching of alkaline earth cations made in vivo solubility even higher.
• Limitations the authors state:
  • The calculated half-times can only serve as preliminary guiding values.
  • The half-times have a relatively high standard error because only a small number of animals was used.
  • Results for the mineral wools are not fully comparable with those for asbestos and glass microfibres, because the wool fibres were larger in diameter and length.

Topics

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

Medical terms in this study, explained in our Lexicon: Crocidolite, Chrysotile, Carcinogenic, Cation.

Related studies

• Long-term health effects in hamsters and rats exposed chronically to man-made vitreous fibres — D.M. Smith, L.W. Ortiz, et al. (1987)
• Differences in the sensitivity of hamster and rat lung cells exposed in vitro to natural and man-made fibres — M. Aufderheide, J.W. Knebel, et al. (1996)
• Formation of 8-hydroxydeoxyguanosine by asbestos and man made mineral fibres — P. Leanderson, P. Söderkvist, et al. (1988)
• Biopersistences of man-made vitreous fibers and crocidolite fibers in rat lungs following short-term exposures — R.P. Musselman, 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)
• A comparative study of the clearance of respirable para-aramid, chrysotile and glass fibres from rat lungs — A. Searl (1997)

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