Analysis of lung asbestos content

Our plain-English summary of Analysis of lung asbestos content, by A. Churg (British Journal of Industrial Medicine, 1991).

The study

• Author: A. Churg
• Journal: British Journal of Industrial Medicine
• Published: 1991;48(10):649-52
• Type of article: Editorial
• Cited by: 25 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 004408).

Summary of the article

The author reviewed what analysis of lung asbestos content by analytical electron microscopy could and could not show. He noted that absolute fibre concentrations varied widely between laboratories, even for the same sample, so a single value from one laboratory was meaningless and each laboratory needed its own background ranges. However, in a seven-laboratory trial all laboratories identified high and low samples correctly, and fibre burdens correlated well with exposures estimated from air sampling. Chrysotile was retained poorly in lung compared with amphiboles, so chrysotile exposure could be missed. Tremolite content and fibre length could help: in the author's work, chrysotile or tremolite fibres longer than 8 µm were highly specific for occupational exposure. In the author's laboratory the upper 95th percentile for the Vancouver general population was around 1 000 000 fibres each of chrysotile and tremolite and 10 000 fibres of amosite plus crocidolite per g of lung tissue. Residents of Quebec chrysotile mining townships who were never employed in the industry carried five- to tenfold more chrysotile than urban dwellers, without evidence of asbestos-related disease. The author concluded that some fibre burden can be tolerated without disease. He also concluded that chrysotile with its tremolite contaminant can cause mesothelioma, but only at very high fibre loads. In his laboratory, disease appeared at about one order of magnitude lower amphibole than chrysotile burden, and he concluded that chrysotile is less pathogenic than amphiboles. The effects of fibre size and distribution remained unclear.

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 article is an editorial, not a new study. The author, from the Department of Pathology at the University of British Columbia, reviewed what analysis of asbestos fibres in human lung tissue with the analytical electron microscope can and cannot show, drawing on published work that includes the author's own laboratory's earlier studies. The author noted that laboratories report widely different fibre counts even for the same sample, so a single value from one laboratory is meaningless on its own. Chrysotile is retained in the lung poorly compared with amphiboles, so chrysotile exposure can be missed. In the author's laboratory, the upper 95th percentile for the general population of Vancouver was around 1 000 000 chrysotile, 1 000 000 tremolite and 10 000 amosite plus crocidolite fibres per gram of lung tissue. The author wrote that chrysotile plus its tremolite contaminant can cause mesothelioma, but only at very high fibre loads. Disease appeared at considerably lower amphibole (amosite or crocidolite) burdens than chrysotile burdens. The author concluded that some fibre burden can be tolerated without disease. The author described a dominant role for commercial amphibole in producing disease as a conclusion only starting to emerge from fibre burden studies.

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: Editorial (narrative review and opinion on lung fibre burden analysis; no new data reported)
• Who was studied: No study population of its own. The editorial discusses published lung fibre analyses of the general population (including Vancouver), long-term residents of the chrysotile mining townships of eastern Quebec, and occupationally exposed workers such as chrysotile miners, millers and textile workers.
• Exposure: Asbestos fibres measured in lung tissue: chrysotile, tremolite (a contaminant of most chrysotile ores), and the commercial amphiboles amosite and crocidolite
• Main results:
  • Because fibre counts differ widely between laboratories, the author stated that a single value from one laboratory is meaningless by itself and that each laboratory needs its own background standards.
  • Compared with amphiboles, chrysotile is retained poorly in lung tissue.
  • In the author's earlier work, chrysotile or tremolite fibres longer than 8 micrometres were highly specific for occupational chrysotile exposure.
  • In the author's laboratory, the upper 95th percentile for the general population of Vancouver was around 1 000 000 chrysotile fibres, 1 000 000 tremolite fibres, and 10 000 amosite plus crocidolite fibres per g lung tissue.
  • Residents of the Quebec chrysotile mining townships who never worked in mining or milling carried a five to 10-fold greater chrysotile burden (and tremolite in some areas) than typical North American urban dwellers.
  • Lung analyses of Quebec miners and millers with mesothelioma were described as showing that chrysotile plus its tremolite contaminant can cause mesothelioma, but that very high fibre loads are required. Whether tremolite rather than chrysotile is the actual cause was described as unresolved.
  • For any given condition, disease appeared at a considerably lower amphibole burden than chrysotile burden. In the author's laboratory the difference was about one order of magnitude in mean or median fibre burden.
• The authors' conclusion: The author concluded that fibre analysis has methodological limitations but gives consistent correlations when worker groups are selected carefully. The author also concluded that there is a burden of asbestos fibres that can be tolerated without disease, which for chrysotile and tremolite is considerably higher than most North American city dwellers carry. The author described the dominant role of commercial amphibole in producing disease as a conclusion only starting to emerge from fibre burden studies, and said the observations lend support to the idea that chrysotile is less pathogenic than the amphiboles.
• Limitations the authors state:
  • Absolute fibre concentrations differ widely between laboratories, even when the same sample is analysed.
  • Substantial chrysotile exposure may be missed if fibre analysis is the only way exposure is determined.
  • In end users of chrysotile products other than miners and textile workers, tremolite content varies and may not indicate past exposure.
  • Little information is available on the effects of fibre size or distribution in human subjects.

Topics

Medical terms in this study, explained in our Lexicon: Air Sampling, Chrysotile, Amphibole Group, Tremolite, Occupational Exposure, Amosite, Crocidolite, Quebec Chrysotile.

Related studies

• Pulmonary asbestos and dust content in East Anglia — P.G. Stovin, P. Partridge (1982)
• Discrepancies of asbestos body and fiber content between formalin-fixed and corresponding paraffin embedded lung tissue — B.K. Kuhn, F. Barresi, et al. (2021)
• Correlation between fibre content of lung and disease in east London asbestos factory workers — R.M. Rudd (1989)
• Lung asbestos content in chrysotile workers with mesothelioma — A. Churg, B. Wiggs, et al. (1984)
• Asbestos fiber content of the lungs in patients with and without asbestos airways disease — A. Churg (1983)
• Mineral fiber content of lungs in patients with mesothelioma seeking compensation in Québec — A. Dufresne, R. Bégin, et al. (1996)

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