Lung mineral fibers of former miners and millers from Thetford-Mines and asbestos regions: a comparative study of fiber concentration and dimension

Our plain-English summary of Lung mineral fibers of former miners and millers from Thetford-Mines and asbestos regions: a comparative study of fiber concentration and dimension, by A. Nayebzadeh, A. Dufresne, B. Case, et al (Archives of Environmental Health, 2001).

The study

• Authors: A. Nayebzadeh, A. Dufresne, B. Case, H. Vali, A.E. Williams-Jones, R. Martin, C. Normand, J. Clark
• Journal: Archives of Environmental Health
• Published: 2001;56(1):65-76
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Fiber dimension and concentration may vary substantially between two necropsy populations of former chrysotile miners and millers of Thetford-Mines and Asbestos regions. This possibility could explain, at least in part, the higher incidence of respiratory diseases among workers from Thetford-Mines than among workers from the Asbestos region. The authors used a transmission electron microscope, equipped with an x-ray energy-dispersive spectrometer, to analyze lung mineral fibers of 86 subjects from the two mining regions and to classify fiber sizes into three categories. The most consistent difference was the higher concentration of tremolite in lung tissues of workers from Thetford-Mines, compared with workers from the Asbestos region. Amosite and crocidolite were also detected in lung tissues of several workers from the Asbestos region. No consistent and biologically important difference was found for fiber dimension; therefore, fiber dimension does not seem to be a factor that accounts for the difference in incidence of respiratory diseases between the two groups. The greater incidence of respiratory diseases among workers of Thetford-Mines can be explained by the fact that they had greater exposure to fibers than did workers at the Asbestos region. Among the mineral fibers studied, retention of tremolite fibers was most apparent.

In plain English

This study compared mineral fibers in autopsy lung tissue from 86 former chrysotile miners and millers in Quebec: 45 from the Thetford-Mines region and 41 from the Asbestos region. The authors used electron microscopy to identify fibers and sort them into three length groups: under 5, 5 to 10, and over 10 micrometers. Tremolite was found in every subject's lungs. Asbestos region workers had one-fourth the concentration of short tremolite fibers found in Thetford-Mines workers. Thetford-Mines workers had twice the concentration of longer tremolite fibers. Chrysotile concentrations were higher in Asbestos region workers, but the authors said their counting method may partly explain this. Amosite and crocidolite were found in many Asbestos region workers and only rarely, at low levels, in Thetford-Mines workers. Total fiber concentrations were comparable, and fiber dimensions did not differ consistently. The authors concluded that the higher rate of respiratory disease in Thetford-Mines is related to higher exposure to fibers, particularly tremolite, and that differences in fiber size were of dubious biological significance. They noted likely autopsy selection bias and missing cumulative exposure data.

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: Comparative lung fiber burden study of autopsy lung tissue, analyzed by transmission electron microscopy with x-ray spectrometry
• Who was studied: 86 autopsied former miners and millers in Quebec, Canada. The Thetford-Mines group had 45 subjects, from autopsies in 1989 to 1991. The Asbestos region (Jeffrey Mine) group had 41 subjects, from autopsies in 1983 to 1991 at the University Regional Hospital at Sherbrooke. In the Asbestos region group, 15 had lung cancer and 5 had mesothelioma. In the Thetford-Mines group, 22 had lung cancer and 2 had mesothelioma. All 86 had some degree of interstitial fibrosis.
• Exposure: Work in chrysotile mining and milling. The average duration of exposure was 36.8 years for Asbestos region workers and 37 years for Thetford-Mines workers. Fibers measured in lung tissue were tremolite, chrysotile, amosite, crocidolite, talc/anthophyllite and other silicates. Cumulative exposure indices were not available.
• Main results:
  • Tremolite fibers were found in the lung tissue of every subject from both regions.
  • The concentration of short (under 5 micrometer) tremolite fibers in Asbestos region subjects was one-fourth that in Thetford-Mines subjects (p less than .01).
  • Concentrations of 5 to 10 micrometer and over 10 micrometer tremolite fibers in Thetford-Mines workers were twice those in Asbestos region workers (p less than .05 for both size groups).
  • Chrysotile was detected in 36 of 41 (88%) Asbestos region cases and in 31 of 46 (67%) Thetford-Mines cases, as printed.
  • Geometric mean chrysotile concentrations, in all three size groups, were higher in Asbestos region workers than in Thetford-Mines workers.
  • In the Asbestos region group, the article reports 20 of 41 subjects (printed as 52%) with detectable amosite and 29 of 41 (71%) with crocidolite.
  • In the Thetford-Mines group, rare amosite fibers were found in 5 of 45 subjects (11%) and crocidolite in 6 of 45 (13%), at concentrations just above the detection limit.
  • Geometric mean concentrations of total fibers were comparable between the two groups, with no statistically significant difference in any size group.
  • The geometric mean concentration of asbestos bodies was higher in Thetford-Mines subjects; the difference was of borderline significance (p less than .1).
  • Fiber dimension measures were not consistently different between the two groups. Chrysotile fiber length showed no statistically significant difference in any size group.
• The authors' conclusion: The authors concluded that the higher rate of respiratory diseases among Thetford-Mines miners and millers is related to their higher exposure to fibrous particles, particularly tremolite. They judged the differences in fiber dimensions between the two areas minor, inconsistent and of dubious biological significance.
• Limitations the authors state:
  • Selection bias in which workers came to autopsy remains very likely.
  • Cumulative exposure indices were not available, so they could not be used in the analysis.
  • The higher chrysotile concentration in Asbestos region subjects may partly reflect a limitation of the counting method: the many tremolite fibers in Thetford-Mines lungs may have reduced the chance of detecting chrysotile.
  • Chrysotile clears from the lung relatively quickly, so the lung analysis may not show the separate roles of chrysotile and tremolite in causing disease.
  • Few fibers were longer than 15 or 20 micrometers, which limited the study's ability to address effects of very long fibers.
  • The analytical method could not distinguish talc from anthophyllite fibers.
  • Marked variation in fiber and body counts between laboratories complicates comparison with other studies.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Jeffrey mine, Asbestos, Quebec

All asbestos mines

Topics

The National Library of Medicine indexes this study under subjects our site covers: Amosite, Asbestosis, Crocidolite, Tremolite.

Medical terms in this study, explained in our Lexicon: Mineral Fiber, Fiber Dimensions, Autopsy, Chrysotile, Tremolite, Amosite, Crocidolite.

Related studies

• Long-term mortality experience of chrysotile miners and millers in Thetford Mines, Quebec — W.J. Nicholson, I.J. Selikoff, et al. (1979)
• Mineralogical and exposure determinants of pulmonary fibrosis among Québec chrysotile miners and millers — A. Nayebzadeh, B.W. Case, et al. (2006)
• Fiber burden and patterns of asbestos-related disease in chrysotile miners and millers — A. Churg, J.L. Wright, et al. (1993)
• Pulmonary mineral fibers after occupational and environmental exposure to asbestos in the Russian chrysotile industry — A. Tossavainen, E. Kovalevsky, et al. (2000)
• Fibers in lung tissues of mesothelioma cases among miners and millers of the township of Asbestos, Quebec — A. Dufresne, M. Harrigan, et al. (1995)
• Malignant pleural and peritoneal mesotheliomas in former miners and millers of crocidolite at Wittenoom, Western Australia — G. Berry, N.H. de Klerk, et al. (2004)

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