Assessing specific causation of mesothelioma following exposure to chrysotile asbestos-containing brake dust

Our plain-English summary of Assessing specific causation of mesothelioma following exposure to chrysotile asbestos-containing brake dust, by M.D. Freeman, S.S. Kohles (International Journal of Occupational and Environmental Health, 2012).

The study

• Authors: M.D. Freeman, S.S. Kohles
• Journal: International Journal of Occupational and Environmental Health
• Published: 2012;18(4):329-36
• Type of article: Review
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: The question of whether chrysotile asbestos-containing brake dust can plausibly serve as a cause of mesothelioma in an exposed individual has become a matter of heated debate in the medical literature despite multiple international, federal, and state governmental agencies acknowledging a causal association.

Objectives: We describe and provide an analysis of various industry and academic perspectives contributing to the debate.

Methods: A framework is presented for evaluating the general and specific causal relationship between brake dust exposure and mesothelioma utilizing the principles of forensic epidemiology, and by applying the Bradford-Hill criteria.

Results And Conclusions: We conclude that there is a "net" of evidence favoring a causal relationship between brake dust-associated chrysotile exposure and mesothelioma. The industry-sponsored position that there is insufficient evidence to support a contiguous "chain" of causation is specious from both a methodologic and evidentiary perspective. Finally, we suggest a semiquantitative approach for the evaluation of individual causation in putative cases of mesothelioma with a history of significant brake dust exposure.

In plain English

This article was a review, not a new study of patients or workers. The authors examined arguments, which they attributed largely to industry-sponsored researchers, that chrysotile asbestos in brake dust has not been shown to cause mesothelioma. They proposed a forensic epidemiology framework, using the Bradford–Hill criteria, for judging whether brake dust exposure caused an individual's mesothelioma. Using published data, they estimated approximately 5 705 900 US automotive industry workers, 182 137 (3.2%) of them full-time brake workers. They calculated that a future case–control study of automotive workers, assuming one control per case and 80% power, would need at least 845 cases to detect an odds ratio of 2.0. The 79 cases in an earlier review by Goodman et al. were 9.3% of that number. The authors noted their estimate likely understated the number needed. Under their framework, any chrysotile exposure above background rates could be considered substantial in a person with mesothelioma. The authors concluded that a "net" of evidence favored a causal relationship between brake dust-associated chrysotile exposure and mesothelioma.

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 with a proposed framework for assessing causation, including the authors' own sample-size calculation based on published estimates
• Who was studied: No new population was studied. For the sample-size estimate, the authors used published figures for US automotive industry workers, estimated at approximately 5 705 900, of whom 182 137 were full-time brake workers.
• Exposure: Chrysotile asbestos in brake dust, including occupational brake repair work and para-occupational (home) brake work
• Main results:
  • The authors estimated that a future matched case–control study of automotive workers, with full-time brake work as the exposure of interest, would need a minimum of 845 mesothelioma cases. This assumed one control per case and was for detecting an odds ratio of 2.0 with 80% power. The significance level is printed in a garbled form in the scanned text.
  • Pooling all 79 cases in the Goodman et al. review would supply only 9.3% of the cases the authors estimated were needed.
  • Under the authors' framework, any chrysotile exposure above background rates could be considered substantial in a person with mesothelioma.
• The authors' conclusion: The authors concluded that a "net" of evidence favored a causal relationship between brake dust-associated chrysotile exposure and mesothelioma. They also concluded that judging causation in an individual case is largely semiquantitative.
• Limitations the authors state:
  • Because the authors relied on industry-sponsored exposure data that miss shorter fibers, their estimate of the number of study subjects needed was likely too low.

Topics

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

Medical terms in this study, explained in our Lexicon: Specific Causation, Mesothelioma, Chrysotile, Epidemiology, Causation.

Related studies

• Evaluation of the fate and pathological response in the lung and pleura of brake dust alone and in combination with added chrysotile compared to crocidolite asbestos following short-term inhalation exposure — D.M. Bernstein, R.A. Rogers, et al. (2015)
• Evaluation of the deposition, translocation and pathological response of brake dust with and without added chrysotile in comparison to crocidolite asbestos following short-term inhalation: interim results — D.M. Bernstein, R. Rogers, et al. (2014)
• Evaluation of the dose-response and fate in the lung and pleura of chrysotile-containing brake dust compared to chrysotile or crocidolite asbestos in a 28-day quantitative inhalation toxicology study — D.M. Bernstein, B. Toth, et al. (2018)
• Assessment of the physicochemical properties of chrysotile-containing brake debris pertaining to toxicity — M.S.P. Boyles, C.A. Poland, et al. (2019)
• Asbestos dust exposure during brake repair — K. Rödelsperger, H. Jahn, et al. (1986)
• Evaluation of the exposure, dose-response and fate in the lung and pleura of chrysotile-containing brake dust compared to TiO2, chrysotile, crocidolite or amosite asbestos in a 90-day quantitative inhalation toxicology study - Interim results Part 1: Experimental design, aerosol exposure, lung burdens and BAL — D.M. Bernstein, B. Toth, et al. (2020)

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