title: Asbestos fiber concentrations in the lungs of brake repair workers: commercial amphiboles levels are predictive of chrysotile levels.
abstract: OBJECTIVE
  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.
authors.affiliation: Department of Biostatistics, Graduate School of Public Health, Center for Occupational Biostatistics and Epidemiology, University of Pittsburgh, Pittsburgh, PA, USA. gmarsh@cobe.pitt.edu
authors.forename: Gary M
authors.initials: GM
authors.lastname: Marsh
authors.forename: Ada O
authors.initials: AO
authors.lastname: Youk
authors.forename: Victor L
authors.initials: VL
authors.lastname: Roggli
mesh_terms: D017636:Asbestos, Amphibole / Q000737:chemistry* / Q000633:toxicity*; D017632:Asbestos, Serpentine / Q000737:chemistry* / Q000633:toxicity*; D001336:Automobiles; D003627:Data Interpretation, Statistical; D004391:Dust; D006801:Humans; D016015:Logistic Models; D008168:Lung / Q000737:chemistry*; D008175:Lung Neoplasms / Q000139:chemically induced; D019016:Mineral Fibers / Q000032:analysis; D009784:Occupational Diseases / Q000209:etiology; D016273:Occupational Exposure
chemical_list: D017636:Asbestos, Amphibole; D017632:Asbestos, Serpentine; D004391:Dust; D019016:Mineral Fibers