Deposition of inhaled asbestos and man-made mineral fibres in the respiratory tract

Our plain-English summary of Deposition of inhaled asbestos and man-made mineral fibres in the respiratory tract, by A. Morgan (The Annals of Occupational Hygiene, 1995).

The study

• Author: A. Morgan
• Journal: The Annals of Occupational Hygiene
• Published: 1995;39(5):747-58
• Type of article: Review
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This paper reviews publications dealing with the deposition of fibrous particles, including asbestos and man-made mineral fibres, in the respiratory tract of man and experimental animals, particularly of the rat. The effects of fibre diameter and length on total, thoracic and alveolar deposition are discussed. Total deposition in the respiratory tract of the rat increases quite steeply with aerodynamic diameter (Dae) from about 20% at a Dae of 1 micron to 100% at a Dae of 5 microns. Deposition in the alveolar region reaches a peak of about 10% at a Dae of about 2 microns, which corresponds to an actual fibre diameter of about 0.4 microns. For fibres with diameters greater than this, alveolar deposition falls rapidly. For example, long glass fibres with an actual diameter of 1.5 microns or short glass fibres with an actual diameter of 3 microns are essentially non-respirable in the rat. The fate of fibres deposited in different regions of the respiratory tract of the rat is also discussed and the factors which predispose fibres either to remain in alveolar macrophages or to be transferred to the interstitium and pulmonary lymphatics. Finally, the distributions in the lungs of fibres administered by inhalation and by intratracheal instillation are compared, and the advantages and drawbacks of each method of delivery discussed.

In plain English

This article was a review of published work on where inhaled fibres, including asbestos and man-made mineral fibres such as glass fibres, are deposited in the respiratory tract, mainly in rats. Much of the rat data came from earlier radioactive tracer studies by the author and colleagues, which used UICC reference asbestos samples and glass fibres. In those studies, deposition in the alveolar region of the rat lung peaked at an aerodynamic diameter of about 2 micrometres, with about 13% of inhaled material deposited there. It fell to a few per cent for fibres about 1 micrometre thick. Longer glass fibres were deposited more overall but less in the lower airways and alveoli. The review also covered what happens to fibres after they are deposited. It noted that putting fibres directly into the windpipe (intratracheal instillation) spreads them less evenly than inhalation does. The author noted that the alveolar figures may be slight overestimates and put the maximum nearer 10%. The author concluded that fibre diameter matters more than length, and that long-term studies should measure the size of the fibres actually deposited in the deep lung.

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: Review of published studies, presented at a workshop on assessing the toxicity of man-made mineral fibres
• Who was studied: Mainly the rat, the animal generally used in such studies. Some information on humans, hamsters and guinea pigs is also discussed.
• Exposure: Asbestos fibres, including the UICC standard reference samples (chrysotile A and B, amosite, crocidolite, anthophyllite), synthetic fluoramphibole, and man-made mineral fibres such as glass fibres. Studies of Kevlar aramid fibres, ceramic fibres and silicon carbide whiskers are also described.
• Main results:
  • In the reviewed rat studies with UICC asbestos and glass fibre, total deposition rose steeply as aerodynamic diameter increased.
  • Alveolar deposition in the rat lung peaked at an aerodynamic diameter of about 2 micrometres. At that size, about 13% of inhaled material was deposited in the alveolar region.
  • For fibres thicker than this, alveolar deposition in rats fell rapidly, to only a few per cent for fibres with an actual diameter of about 1 micrometre.
  • For sized glass fibres 1.5 micrometres in diameter and 5 to 60 micrometres long, total deposition increased with fibre length, but deposition in the lower respiratory tract and alveolar region declined.
  • Glass fibres 1.5 micrometres in diameter and 30 or 60 micrometres long were virtually non-respirable in the rat, as was the 3 micrometre diameter, 10 micrometre long material.
  • In rats exposed to anthophyllite asbestos, the length of the longest fibres that could be recovered by lung lavage declined steadily over 30 weeks. This suggested that such fibres were being lost preferentially to the lung interstitium.
  • Fibres given by intratracheal instillation were initially distributed much less uniformly than fibres given by inhalation.
• The authors' conclusion: The author concluded that both fibre length and diameter affect where man-made mineral fibres are deposited in the rat lung, with diameter the more important factor. The author also concluded that chronic toxicity studies should establish the size of the fibres actually deposited in the deep lung.
• Limitations the authors state:
  • The author stated that the alveolar deposition values may be slight overestimates. After allowing for errors in estimated breathing volumes, the maximum alveolar deposition efficiency appeared to be about 10%.
  • Calculated total deposition reached an apparent maximum of about 150%, which is impossible. The author suggested two explanations: rats swallowing fibres deposited on their noses, or the formula used overestimating the breathing volumes of restrained rats.
  • No work on the fate of man-made mineral fibres deposited in the alveolar region had been reported.

Topics

Medical terms in this study, explained in our Lexicon: Deposition, Alveolar Macrophage.

Related studies

• Studies on the deposition of inhaled fibrous material in the respiratory tract of the rat and its subsequent clearance using radioactive tracer techniques. 1. UICC crocidolite asbestos — J.C. Evans, R.J. Evans, et al. (1973)
• Studies on the deposition of inhaled fibrous material in the respiratory tract of the rat and its subsequent clearance using radioactive tracer techniques — A. Morgan, J.C. Evans, et al. (1975)
• Respiratory health effects of man-made vitreous (mineral) fibres — P. De Vuyst, P. Dumortier, et al. (1995)
• Systematic review and meta-analysis of epidemiological literature evaluating the association between exposure to man-made vitreous fibers and respiratory tract cancers — N. Suder Egnot, S.M. Benson, et al. (2020)
• Benzo[a]pyrene-enhanced mutagenesis by man-made mineral fibres in the lung of lamda-lacI transgenic rats — J. Topinka, P. Loli, et al. (2006)
• Dosimetry of inhaled elongate mineral particles in the respiratory tract: The impact of shape factor — B. Asgharian, T.P. Owen, et al. (2018)

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