Asbestos fibre concentrations in the lungs of brake workers: another look

Our plain-English summary of Asbestos fibre concentrations in the lungs of brake workers: another look, by M.M. Finkelstein (The Annals of Occupational Hygiene, 2008).

The study

• Author: M.M. Finkelstein
• Journal: The Annals of Occupational Hygiene
• Published: 2008;52(6):455-61
• Cited by: 23 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objective: To reanalyse data on the lung content of asbestos fibres among brake mechanics.

Methods: I re-analysed data published by Butnor, Roggli and colleagues on the lung content of chrysotile and tremolite asbestos fibres among brake mechanics and controls. Statistics of the distributions were estimated by maximum likelihood to accommodate observations below the detection limit. Mean concentrations were compared by the t-test, bootstrap resampling and interval-censored survival methods.

Results: The mean concentrations of fibres were higher among the brake workers than the controls. The concentration of tremolite fibres was higher than the concentration of chrysotile, a pattern similar to that observed among Quebec chrysotile miners and millers.

Conclusions: Re-analysis of published data does not support the interpretation that, in automotive brake repair workers with malignant mesothelioma, asbestos content is within the normal range. The alternative interpretation that brake mechanics have a greater than background burden of asbestos fibres, attributable to occupational exposure to dusts from friction products manufactured from Canadian chrysotile, appears more credible. This asbestos burden might be associated with an increased risk of asbestos-associated cancers.

In plain English

This paper reanalysed lung fibre counts that Butnor, Roggli and colleagues had published earlier. It compared 10 brake workers with mesothelioma with 19 controls without occupational asbestos exposure, who were a convenience sample. The counts were of chrysotile and tremolite fibres longer than 5 micrometres per gram of wet lung. The author presumed that the published non-commercial amphibole group was mostly tremolite. Because many counts fell below the detection limit, the author used maximum-likelihood estimates and three comparison methods. Mean concentrations of both fibres were higher in the brake workers. Tremolite was significantly higher in the brake workers by all three methods: the t-test p-value was 0.023, and tremolite was higher in all 30 bootstrap samples. Chrysotile was not significantly higher. In both groups tremolite exceeded chrysotile, which the author said matched the pattern in Quebec chrysotile miners and millers. The author concluded that brake mechanics had elevated lung asbestos concentrations consistent with occupational exposure to commercial chrysotile. The author cautioned that the data came from only 10 cases and 19 controls. In discussing the non-significant chrysotile result, the author noted that the t-test had only 22% power to detect a significant difference at the 5% level.

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: Statistical reanalysis of previously published lung fibre count data (brake workers with mesothelioma compared with controls)
• Who was studied: 10 brake workers with mesothelioma (data from Butnor et al., 2003) and 19 control subjects without occupational asbestos exposure, a convenience sample (data from Roggli et al., 2002), from the same laboratory's consultation files
• Exposure: Lung content of chrysotile and tremolite fibres longer than 5 micrometres per gram of wet lung. The published group of tremolite, anthophyllite and actinolite (TAA) was presumed by the author to be predominantly tremolite. The author assumed that brake friction products were made mostly from Quebec chrysotile contaminated with tremolite.
• Main results:
  • Mean concentrations of fibres were higher among the brake workers than among the controls
  • Tremolite: mean (standard deviation) of log-transformed counts was 6.9 (1.1) in the brake workers and 6.0 (1.0) in the controls
  • Chrysotile: mean (standard deviation) of log-transformed counts was 5.1 (1.9) in the brake workers and 4.3 (1.4) in the controls
  • The t-test for tremolite being higher in brake workers than in controls gave a p-value of 0.023
  • In all 30 bootstrap samples, mean tremolite concentration was higher among the brake workers than among the controls
  • All three comparison methods agreed that tremolite, but not chrysotile, was significantly higher in the brake workers than in the controls
  • Mean tremolite concentration was higher than mean chrysotile concentration in both brake workers and controls
  • The author recomputed the author's own earlier data on Quebec chrysotile miners and millers and reported the same pattern of higher tremolite than chrysotile
• The authors' conclusion: The author concluded that automotive mechanics have elevated lung asbestos fibre concentrations consistent with occupational exposure to commercial chrysotile. The author judged this interpretation more strongly supported than the original authors' interpretation that the content was within the normal range.
• Limitations the authors state:
  • Caution is needed in generalizing, because the data come from only 10 subjects with mesothelioma and 19 controls
  • The author stated this in discussing the non-significant chrysotile difference: the t-test had very low power, only 22%, to detect a significant difference in means at the 5% level
  • The analysis rests on several assumptions: Quebec chrysotile as the source, TAA as mostly tremolite, and lognormal distributions

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile, Tremolite, Quebec Chrysotile, Malignant Mesothelioma, Occupational Exposure, Friction Products.

Related studies

• Asbestos fiber concentrations in the lungs of brake repair workers: commercial amphiboles levels are predictive of chrysotile levels — G.M. Marsh, A.O. Youk, et al. (2011)
• The analysis of asbestos count data with "nondetects": the example of asbestos fiber concentrations in the lungs of brake workers — M.M. Finkelstein (2013)
• Asbestos Fiber Concentrations in the Lungs of Brake Repair Workers: An Updated Analysis Using Several Regression Methods to Handle Nondetectable Measurements — Y. Liu, G.M. Marsh, et al. (2018)
• Fibre type and concentration in the lungs of workers in an asbestos cement factory — B. Gylseth, G. Mowé, et al. (1983)
• Always Worth Another Look? Thoracic Ultrasonography before, during, and after Pleural Intervention — J.P. Corcoran, I. Psallidas, et al. (2016)
• Asbestos fibres in the lungs of an American mechanic who drilled, riveted, and ground brake linings: a case report and discussion — M.M. Finkelstein (2015)

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