Asbestos lung residue and asbestosis risk

Our plain-English summary of Asbestos lung residue and asbestosis risk, by R. Howie (The Annals of Occupational Hygiene, 2005).

The study

• Author: R. Howie
• Journal: The Annals of Occupational Hygiene
• Published: 2005;49(1):95-7
• Type of article: Letter
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

In plain English

This letter to the editor came from an author involved in a civil compensation claim for a deceased retired boilerman/plant operator who had been diagnosed with asbestosis and pleural plaques. A laboratory engaged by one of the defenders analysed a single lung section by electron microscopy. It found, in million fibres per gram of dry tissue, amosite 0.61, crocidolite 0.40, chrysotile 0.61 and tremolite 0.20. Its report said these results were against a diagnosis of asbestosis. The author then estimated how much inhaled amosite and crocidolite would still be in the lung by 2000 under four possible exposure periods. The estimates used published lung clearance half-times and the author's own assumptions, including that 40 fibres/ml year was needed for a statistical risk of asbestosis. The calculated share remaining ranged from 1 in 10 million to 1 in 10 000 for amosite, and from 1 in 400 000 to 1 in 2000 for crocidolite. Working backwards, the author judged that ongoing low-level exposure between 1979 and 1990 better explained the lung results. The author concluded that, without detailed knowledge of the exposure pattern, lung residue data cannot be used to reject a diagnosis of asbestosis.

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 presenting the author's own calculations (simple spreadsheet models), built on one person's case from a civil compensation action
• Who was studied: One deceased retired boilerman/plant operator in the UK, diagnosed with asbestosis and pleural plaques. A single lung section was analysed for fibre content.
• Exposure: Alleged exposure to asbestos released from insulation, possibly between 1943 and about 1990. Lung fibres measured were amosite, crocidolite, chrysotile and tremolite. Four exposure periods were assessed: 1943–1990, 1943–1979, 1957–1990 and 1957–1979. The author assumed constant airborne concentrations within each period and an exposure of 40 fibres/ml year as the level giving a statistical risk of asbestosis.
• Main results:
  • The laboratory's electron microscopy results for the deceased's lung section, in million fibres per gram of dry tissue, were: amosite 0.61, crocidolite 0.40, chrysotile 0.61, tremolite 0.20.
  • The laboratory's report stated that the combined amphibole level of 1.21 million fibres per gram of dry lung was well below levels generally associated with asbestosis. It said the results pointed to cryptogenic fibrosing alveolitis and were against a diagnosis of asbestosis.
  • The author did not model chrysotile. The last known occupational exposure was about 10 years before death, about 220 half-times for chrysotile, and the author considered the chrysotile found in the lung probably due to recent inhalation from the general environment.
  • In the author's calculations, the share of all inhaled fibres still in the lungs at death ranged from 1 in 10 million to 1 in 10 000 for amosite, and from 1 in 400 000 to 1 in 2000 for crocidolite, depending on the exposure period.
  • The author worked backwards from the measured lung fibres to the exposure that would have produced them. Exposures ending in 1979 required very high amounts (for amosite, 2000 fibres/ml year for 1943–1979). Exposures ending in 1990 required much lower amounts (for amosite, 3 fibres/ml year for 1943–1990). The author read this as suggesting ongoing low-level exposure between 1979 and 1990.
  • In the author's model, the measured amosite and crocidolite lung levels would have resulted if 2% of the total inhaled amosite and crocidolite had been breathed in uniformly between 1979 and 1990.
• The authors' conclusion: The author concluded that sound interpretation of lung residue results depends critically on detailed knowledge of the deceased's likely exposure pattern, especially if less than 20 years passed between last exposure and death. Without that knowledge, lung residue data cannot be used to reject a diagnosis of asbestosis. In this case, the author considered that the deceased could have been exposed in any of the four periods to enough amosite, crocidolite and chrysotile for each to have caused a calculable risk of asbestosis.
• Limitations the authors state:
  • The author assumed that all inhaled fibres were deposited in the lungs, while noting that in practice some would be exhaled.
  • No clearance half-time data were given for tremolite, so the author assumed it was the same as for crocidolite (536 days).

Topics

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

Related studies

• Asbestos lung residue and asbestosis risk — A. Rogers (2005)
• The effect of asbestosis on lung cancer risk beyond the dose related effect of asbestos alone — A. Reid, N. de Klerk, et al. (2005)
• Pi*S and Pi*Z alpha 1 antitrypsin polymorphism and the risk for asbestosis in occupational exposure to asbestos — M.J. Lafuente, X. Casterad, et al. (2002)
• The natural course of lung function decline in asbestos exposed subjects with pleural plaques and asbestosis — M. Barnikel, P.M. Million, et al. (2019)
• Regarding "absence of radiographic asbestosis and the risk of lung cancer among asbestos-cement workers: extended follow-up of a cohort", by Murray Finkelstein, American Journal of Industrial Medicine 2010 — R.M. Ross (2011)
• Pleural mesothelioma and lung cancer risks in relation to occupational history and asbestos lung burden — C. Gilham, C. Rake, et al. (2016)

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