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

Ann Occup Hyg. 2008 Aug;52(6):455-61. doi: 10.1093/annhyg/men036. Epub 2008 Jun 23.


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.

MeSH terms

  • Asbestos / analysis*
  • Data Interpretation, Statistical
  • Dust / analysis
  • Humans
  • Lung / chemistry*
  • Lung Neoplasms / chemistry
  • Lung Neoplasms / etiology
  • Male
  • Mesothelioma / chemistry
  • Mesothelioma / etiology
  • Mineral Fibers / analysis
  • Occupational Diseases / etiology
  • Occupational Diseases / metabolism
  • Occupational Exposure / analysis*


  • Dust
  • Mineral Fibers
  • Asbestos