Mortality in a cohort of vermiculite miners exposed to fibrous amphibole in Libby, Montana

J. C. McDonald*, Jessica M Harris, B. Armstrong

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

98 Citations (Scopus)


BACKGROUND: Fibrous tremolite is a widespread amphibole asbestiform mineral, airborne fibres of which constitute an environmental hazard in Libby, Montana, northern California, and elsewhere.

AIMS: To determine excess risk from lung cancer, mesothelioma, and all-cause mortality in a cohort of men exposed to tremolite, but no other form of asbestos.

METHODS: Mortality by certified cause and various measures of exposure to tremolite and related amphibole fibres was assessed in a cohort of 406 vermiculite mineworkers in Libby, Montana, employed before 1963 and followed until 1999.

RESULTS: Total deaths were: lung cancer 44 (SMR 2.40), non-malignant respiratory disease (NMRD) 51 (SMR 3.09), all causes 285 (SMR 1.27); included among the total were 12 deaths ascribed to mesothelioma (4.21% of all deaths). Adjusted linear increments in relative risks (per 100 f/ml.y), estimated by Poisson regression, were: lung cancer (0.36, 95% CI 0.03 to 1.20), NMRD (0.38, 95% CI 0.12 to 0.96), and all deaths (0.14, 95% CI 0.05 to 0.26).

CONCLUSIONS: The all-cause linear model would imply a 14% increase in mortality for mine workers exposed occupationally to 100 f/ml.y or about 3.2% for a general population exposed for 50 years to an ambient concentration of 0.1 f/ml. Amphibole fibres, tremolite in particular, are likely to be disproportionately responsible for cancer mortality in persons exposed to commercial chrysotile, but to what extent cannot be readily assessed.

Original languageEnglish
Pages (from-to)363-366
Number of pages4
JournalOccupational and Environmental Medicine
Issue number4
Publication statusPublished - 1 Apr 2004


  • Aluminum Silicates
  • Asbestos, Amphibole
  • Cohort Studies
  • Humans
  • Lung Neoplasms
  • Male
  • Mesothelioma
  • Mining
  • Montana
  • Regression Analysis
  • Risk Factors


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