The removal of fibres of chrysotile asbestos from lung

Our plain-English summary of The removal of fibres of chrysotile asbestos from lung, by A. Morgan (The Annals of Occupational Hygiene, 1994).

The study

• Author: A. Morgan
• Journal: The Annals of Occupational Hygiene
• Published: 1994;38(4):643-6
• Type of article: Letter
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Summary of the article

In this letter, written after the Workshop on Health Risks Associated with Chrysotile Asbestos, the author addressed the uncertainty about why chrysotile fibres are removed from the lung more rapidly than amphibole asbestiform minerals, and in particular whether this is due to fibre dissolution or to clearance by macrophages. The author reviewed published evidence. Studies measuring magnesium/silicon ratios in fibres recovered from human and animal lungs gave conflicting results. Some reported magnesium depletions as high as 50%, and others found slight or no significant leaching. Radioactive tracer studies in rats had shown that about 30% of structural magnesium dissolved within 1 month of intrapleural injection, with slower leaching after that. Other rat studies showed greater leaching during the first month after intratracheal instillation, rapid removal of acid-leached fibres, and longitudinal splitting of fibres in the lung. The author discussed problems in interpreting Mg/Si ratios, including changes during fibre recovery and the limited resolution of analytical methods. Citing glass-fibre findings, the author suggested that chrysotile may dissolve faster in the lung than in the pleural or peritoneal cavities. Carcinogenicity comparisons based on intra-cavity injection might therefore not be relevant to lung cancer. The author concluded that the view that dissolution plays a very minimal role in human chrysotile clearance was difficult to sustain, that some fibres persist for years, and that further research was required.

PubMed has no abstract for this study, and the article doesn't print one. We wrote this summary from the full article with the help of AI. It is not the authors' wording.

In plain English

This letter to the editor reported no new data. Prompted by a chrysotile workshop, the author discussed published evidence on why chrysotile leaves the lung faster than amphiboles: dissolution or clearance by scavenger cells (macrophages). Cited human-lung studies conflicted: Sebastien et al. (1986) found magnesium depletions up to 50% in fibres longer than 5 micrometres and thicker than 0.1 micrometres, while Churg and DePaoli (1988) found only slight depletion in chrysotile miners' lungs many years after last exposure. In animal tracer work using relatively pure chrysotile, Morgan and colleagues (1971) found that about 30% of the magnesium dissolved within a month of pleural-cavity injection, after which leaching slowed. The author cautioned that recovery methods may alter fibres and that cavity injection may not mirror dissolution in the lung. The author concluded that chrysotile is cleared from the lung more effectively than amphiboles, which are effectively insoluble over a human lifespan, though some chrysotile persists for years. The author called for research on whether magnesium dissolves faster from fibres in the lung than after injection into body cavities.

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: Letter to the editor discussing previously published research; no original data
• Who was studied: No study population of its own. The letter discusses published studies of chrysotile fibres recovered from human lungs (including chrysotile miners) and from experimental animals (rats, guinea pigs), plus laboratory (in vitro) leaching studies.
• Exposure: Chrysotile asbestos, compared with amphibole asbestiform minerals. The studies discussed used inhalation, intratracheal instillation, and injection into the pleural or peritoneal cavity.
• Main results:
  • The letter reported that, at the Workshop on Health Risks Associated with Chrysotile Asbestos, Davis stated it was still uncertain whether chrysotile's faster removal is due to dissolution or to clearance by macrophages.
  • The cited human lung studies conflicted. Sebastien et al. (1986) found magnesium depletions as high as 50% in chrysotile fibres longer than 5 micrometres and thicker than 0.1 micrometres. Churg and DePaoli (1988) found only slight depletion in fibres from chrysotile miners many years after their last exposure.
  • In the cited radioactive tracer study in experimental animals by Morgan et al. (1971), a relatively pure sample of chrysotile was used. About 30% of its structural magnesium had dissolved within 1 month of injection into the pleural cavity, after which leaching was much slower.
  • The letter cited Bellmann et al. (1987). In rats given chrysotile by intratracheal instillation, magnesium leached faster in the first month. Chrysotile whose magnesium had been removed beforehand by oxalic acid was cleared from the lung with a half time of only a few days.
  • The letter cited a model by Hume and Rimstidt (1992). It predicted that a chrysotile fibre 1 micrometre in diameter would dissolve in lung with a half time of 9 (plus or minus 4.5) months.
  • Citing an unpublished personal communication about glass fibres, the author suggested that chrysotile may dissolve much faster in the lung than after injection into the pleural or peritoneal cavities. On that basis, the author suggested that cancer comparisons based on intra-cavity injection may not be relevant to lung cancer.
• The authors' conclusion: The author considered difficult to sustain Churg and DePaoli's view that dissolution plays a very minimal role in clearing chrysotile from human lungs. The author concluded that chrysotile fibres are removed from the lung more effectively than amphibole fibres, which are effectively insoluble over the human lifespan, but that some chrysotile persists over years. The author called for further research, in particular on whether magnesium dissolves faster from fibres in the lung than from fibres given by intra-cavity injection.
• Limitations the authors state:
  • The author noted that fibres recovered from lungs may have been changed by the ashing or digestion used to destroy lung tissue. Measured values may therefore not reflect the fibres as they were in the body.
  • The author noted that the silica left behind after magnesium dissolves may itself dissolve or disintegrate. This may set a lower limit on the measured magnesium/silicon ratio.
  • The author noted that the resolution of the analytical methods is a concern. Outer fibrils may be heavily depleted of magnesium while inner ones remain relatively intact.
  • The author noted that it is unclear whether chrysotile injected into body cavities of experimental animals dissolves at the same rate as chrysotile in the lung.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Amphibole Group, Asbestiform, Macrophage, Lung Cancer.

Related studies

• A study of the effect of chrysotile fiber surface composition on genotoxicity in vitro — M.J. Keane, J.W. Stephens, et al. (1999)
• Chrysotile and tremolite asbestos fibres in the lungs and parietal pleura of Corsican goats — P. Dumortier, F. Rey, et al. (2002)
• Acid leaching studies of chrysotile asbestos from mines in the Coalinga region of California and from Quebec and British Columbia — A. Morgan (1997)
• A comparative study of the clearance of respirable para-aramid, chrysotile and glass fibres from rat lungs — A. Searl (1997)
• Pulmonary effects in rats inhaling size-separated chrysotile asbestos fibres or p-aramid fibrils: differences in cellular proliferative responses — D.B. Warheit, M.A. Hartsky, et al. (1996)
• Deposition and clearance of chrysotile asbestos — A. Churg (1994)

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