Asbestos fiber concentrations in the lungs of brake repair workers: commercial amphiboles levels are predictive of chrysotile levels

Our plain-English summary of Asbestos fiber concentrations in the lungs of brake repair workers: commercial amphiboles levels are predictive of chrysotile levels, by G.M. Marsh, A.O. Youk, V.L. Roggli (Inhalation Toxicology, 2011).

The study

• Authors: G.M. Marsh, A.O. Youk, V.L. Roggli
• Journal: Inhalation Toxicology
• Published: 2011;23(12):681-8
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: To investigate the impact of extreme data points in Finkelstein's 2009 findings of no association between lung levels of commercial and non-commercial amphiboles (principally tremolite as a marker for chrysotile asbestos) in brake repair workers with mesothelioma.

Methods: We first identified potential outliers, high leverage points, and influential points among lung levels of commercial amphiboles and tremolite among 15 persons whose only known exposure to asbestos was through brake repair work. We used sensitivity analysis and quantile regression to account for extreme data points and model commercial amphibole levels as a predictor of tremolite levels. We also used quantile regression to evaluate whether case-reported duration of employment as a brake repair worker predicted lung levels of commercial amphiboles or tremolite.

Results: We found lung levels of commercial amphiboles are a statistically significant predictor of tremolite levels via sensitivity analysis (r = 0.82, slope estimate P-value = 0.001, R² = 0.68) and quantile regression (slope estimate P-value <0.0001). Our data provide no evidence that duration of employment as a brake repair worker was a predictor of lung levels of tremolite or commercial amphiboles.

Conclusions: Our findings suggest that elevated lung levels of tremolite in the lungs of brake repair workers with elevated levels of amphiboles arose from concurrent exposures to commercial amphibole and chrysotile asbestos in occupational settings other than brake repair work. These findings are supported by five new cases. The weight of the scientific evidence does not support a role for occupational exposure to brake dust and other friction products in the development of mesothelioma.

In plain English

This study reanalyzed lung fiber data from 15 people with mesothelioma whose only known asbestos exposure was brake repair work. Ten came from Butnor et al. (2003), with three data errors corrected; five were new cases. The authors tested whether lung levels of commercial amphiboles predicted levels of tremolite, used as a marker of chrysotile. A 2009 analysis by Finkelstein had found no such link. In the 10 original cases, the link was not statistically significant (r = 0.43, P = 0.21). With all 15 cases it was significant (r = 0.53, P = 0.04) but fit poorly (R-squared 0.28). With three extreme cases removed it was stronger (r = 0.82, P = 0.001, R-squared 0.68). Quantile regression, which limits the influence of extreme cases, gave P less than 0.0001. Reported years of brake work did not predict either fiber level (P = 0.90). The authors concluded that their findings suggested the elevated tremolite in workers with elevated amphiboles arose from concurrent exposures to commercial amphibole and chrysotile asbestos in jobs other than brake repair. They also stated that the evidence does not support a role for brake dust in mesothelioma. They noted the small medico-legal sample, many results below detection limits, and possible recall bias.

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 (regression diagnostics, sensitivity analysis, quantile regression) of a published case series, extended with five new cases
• Who was studied: 15 mesothelioma cases whose only known asbestos exposure was occupational contact as a brake repair worker. Ten came from Butnor et al. (2003) and five were new cases from the Roggli et al. case series. The five new cases were all males aged 40 to 70 (median 58); four had pleural and one had peritoneal mesothelioma.
• Exposure: Occupational brake repair work. The study measured lung levels of commercial amphiboles and of tremolite (non-commercial amphibole, used as a marker for chrysotile) in fibers per gram of wet lung for fibers 5 μm or longer. It also used case-reported duration of employment as a brake repair worker.
• Main results:
  • The authors identified and corrected three errors in the Butnor et al. (2003) lung fiber data for two of the 10 original cases.
  • Using the 10 original cases with corrected data (Model 1), commercial amphibole level was not a statistically significant predictor of tremolite level (r = 0.43, slope P = 0.21; R-squared 0.19).
  • Using all 15 cases (Model 2), commercial amphibole level was a statistically significant predictor of tremolite level (r = 0.53, slope P = 0.04), but the fit was poor (R-squared 0.28).
  • Regression diagnostics identified Cases 2, 3 and 9 as extreme points, and these were removed in the sensitivity analysis.
  • With the three extreme cases removed (Model 3, 12 cases), commercial amphibole level was a statistically significant predictor of tremolite level (r = 0.82, slope P = 0.001, R-squared 0.68).
  • In quantile regression using all 15 cases (Model 4), commercial amphibole level was a statistically significant predictor of tremolite level (slope P less than 0.0001).
  • Case-reported duration of employment as a brake repair worker did not predict lung levels of tremolite or of commercial amphiboles (slope P = 0.90 for both models).
• The authors' conclusion: The authors concluded that their findings suggested the elevated tremolite (as a marker of chrysotile) in the lungs of some brake repair workers with elevated amphiboles arose from concurrent exposures to commercial amphibole and chrysotile asbestos in jobs other than brake repair. They stated that Finkelstein's 2009 finding was invalid. They also stated that the weight of the scientific evidence does not support a role for occupational exposure to brake dust and other friction products in mesothelioma.
• Limitations the authors state:
  • Fifteen cases is a relatively small sample.
  • Many amphibole and tremolite measurements were below the detection limit; half the detection limit was substituted for these.
  • The cases were medico-legal cases and may not represent all workers occupationally exposed to friction products.
  • Work histories obtained by patient interview are subject to recall bias. The authors said this may explain why no exposures to commercial amphiboles were reported.

Topics

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

Medical terms in this study, explained in our Lexicon: Amphibole Group, Chrysotile, Tremolite, Mesothelioma, P-Value, Occupational Exposure, Friction Products.

Related studies

• 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)
• 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 fibre concentrations in the lungs of brake workers: another look — M.M. Finkelstein (2008)
• Report of a recent "brake" through in the fiber burden-mesothelioma dialogue — D. Egilman (2012)
• Evaluation of asbestos exposure during brake repair and replacement — H. Kakooei, M. Hormozy, et al. (2011)
• Exposure to brake dust and malignant mesothelioma: a study of 10 cases with mineral fiber analyses — K.J. Butnor, T.A. Sporn, et al. (2003)

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