Mineralogical and exposure determinants of pulmonary fibrosis among Québec chrysotile miners and millers

Our plain-English summary of Mineralogical and exposure determinants of pulmonary fibrosis among Québec chrysotile miners and millers, by A. Nayebzadeh, B.W. Case, J. Massé, et al (International Archives of Occupational and Environmental Health, 2006).

The study

• Authors: A. Nayebzadeh, B.W. Case, J. Massé, A. Dufresne
• Journal: International Archives of Occupational and Environmental Health
• Published: 2006;79(3):227-36
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: Lung fibre content was determined for 86 former chrysotile miners and millers in two Québec mining regions: Thetford mines (TM) and the Asbestos region (AR).

Methods: Fibres were assessed using transmission electron microscopy (TEM) and energy dispersive X-ray spectrometry (EDS). Asbestos body (AB) concentrations were assessed by microscopy of tissue digests. Corresponding histological lung tissue sections were quantitatively graded for the severity of interstitial fibrosis on a 12-point scale. Fibrosis score and its associations with (1) fibre concentrations and fibre dimensions within three fibre length intervals (less than 5 microm, 5-10 microm, and over 10 microm), and (2) several exposure variables were evaluated using correlation coefficients and regression techniques.

Results: Concentration of short (<5 microm) tremolite fibres was the best predictor of fibrosis grade in both mining groups (r=0.44, P<0.01 and r=0.39, P<0.01 for TM and AR, respectively). Chrysotile fibre concentration showed a lower correlation with the fibrosis grade for subjects from TM only. Long (>10 microm) amosite fibre concentration showed a linear relationship with the fibrosis score in miners and millers from AR. Exposure variables, including smoking, had no predictive value for fibrosis grade. Within fibre length categories, fibre dimension was not related to the fibrosis score.

Conclusion: Lung fibre concentration as measured by TEM/EDS, especially that of short (<5 microm) tremolite fibres, is a better predictor of fibrosis grade in these two groups of chrysotile miners than either the concentration of ABs or the duration of exposure. Due to the limitation of our counting method, almost all fibres longer than 10 microm observed in this study were shorter than 14 microm. Thus, if length plays a role in fibrogenesis, it may be related to fibres of greater length than those covered in this study.

In plain English

This study examined autopsy lungs of 86 former chrysotile miners and millers in Québec: 45 from Thetford Mines, 41 from the Asbestos region. Electron microscopy counted and identified fibres in three length groups (under 5, 5 to 10, and over 10 micrometres). A pathologist graded lung scarring (interstitial fibrosis) on a 12-point scale. Every subject had some fibrosis. Short tremolite concentration correlated with fibrosis score in both groups (r=0.44 Thetford Mines, r=0.39 Asbestos region), and tremolite correlated more strongly than chrysotile. In the Asbestos region, long amosite was associated with fibrosis, but not significantly among the 19 subjects who had such fibres. Fibre length, width and shape showed no association with fibrosis for fibres up to about 20 micrometres; the authors said very long fibres could not be adequately assessed. Smoking and exposure duration showed no significant relationship either. The authors concluded that lung fibre concentration, especially of short tremolite, predicted fibrosis better than asbestos bodies or exposure duration. They cautioned this does not necessarily mean tremolite causes more scarring than chrysotile, since short chrysotile fibres may clear from the lungs years before death.

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: Autopsy lung-tissue study: fibre analysis by transmission electron microscopy with X-ray spectrometry, plus histological grading of fibrosis, related to each other and to exposure variables by correlation and regression
• Who was studied: 86 deceased former chrysotile miners and millers who had autopsies. 45 were from Thetford Mines (male; autopsies at Centre Hospitalier de la Région de l'Amiante, deaths 1989–1991). 41 were from the Asbestos region (mine, mill and factory workers; autopsies at Centre Hospitalier de l'Université de Sherbrooke, 1983 onward).
• Exposure: Work in chrysotile mines and mills (and a small asbestos products factory in the Asbestos region). Average exposure was 36.8 years (Asbestos region) and 37 years (Thetford Mines), range 14 to 50.5 years. Lung fibres measured were tremolite, chrysotile, amosite, crocidolite, talc/anthophyllite and other silicates, plus asbestos bodies. Smoking was recorded in pack-years.
• Main results:
  • Short (under 5 micrometre) tremolite fibre concentration was the best predictor of fibrosis grade in both groups: r=0.44, P<0.01 at Thetford Mines; r=0.39, P<0.01 in the Asbestos region
  • Thetford Mines: the fibrosis score rose 0.74 units per one-unit increase in log concentration of short tremolite fibres
  • Thetford Mines: intermediate-length (5 to 10 micrometre) chrysotile (b1=0.6, P<0.01) and intermediate-length tremolite (b1=0.48, P<0.05) were also associated with fibrosis score
  • In both groups, lung tremolite concentration correlated more strongly with fibrosis score than chrysotile concentration did
  • Asbestos region: short tremolite had the second largest regression coefficient (b1=0.6, P<0.01)
  • Asbestos region: fibrosis score rose 1.67 units (0–12 scale) per one-unit increase in long (over 10 micrometre) amosite concentration (b1=1.67, P<0.01)
  • Asbestos region: the long amosite correlation was not significant when reanalysed only for the 19 subjects who had long amosite fibres (r=0.32, P=0.11)
  • Asbestos region: concentration variables including chrysotile and other silicates showed no correlation with fibrosis score (r<0.25, P>0.1 for all types/sizes)
  • Thetford Mines: lung-digest asbestos body concentration and asbestos body grade showed a positive linear relationship with fibrosis score (P<0.05). Asbestos region: asbestos bodies showed no statistical relationship with fibrosis score.
  • No fibre dimension parameter (length, diameter, aspect ratio) showed a significant relationship with fibrosis score in either group. The authors stated this lack of association applied to fibres at least up to 20 micrometres.
  • Thetford Mines: no exposure variable, including smoking, was significantly related to fibrosis score. Asbestos region: only age showed an association (r=+0.3, P between 0.05 and 0.1).
  • Multiple regression found no interaction or confounding effects between fibre concentration and exposure variables
  • Every subject had some interstitial fibrosis. Fibrosis score ranged from 1 to 11 (Thetford Mines) and 1 to 11.5 (Asbestos region). Mean score was 5.4 in the Asbestos region vs 4.3 at Thetford Mines (P=0.06).
• The authors' conclusion: The authors concluded that lung fibre concentration measured by TEM/EDS, particularly short tremolite fibre concentration, predicted pulmonary interstitial fibrosis better than asbestos body concentration or duration of exposure.
• Limitations the authors state:
  • Exposure intensities were not available, so cumulative exposure could not be calculated
  • The finding should not be taken to mean tremolite is necessarily more fibrogenic than chrysotile
  • Fibrosis may have resulted from chrysotile exposure, because short chrysotile fibres may be cleared from the lung years before death
  • The study was limited to fibres shorter than 20 micrometres, especially shorter than 10 micrometres
  • The method had limited ability to evaluate very long fibres (over 20 micrometres)
  • The concentration data do not show that short fibres are more fibrogenic than long fibres
  • Some statistics for particular fibre types and length categories may not be meaningful because they rest on few fibres
  • For Asbestos region subjects, much tissue came from unselected autopsy stock bottles, so exact site selection was not possible

Topics

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

Medical terms in this study, explained in our Lexicon: Pulmonary Fibrosis, Chrysotile, Thetford Mines, Transmission Electron Microscopy (TEM), Asbestos Body Formation, Tissue Digestion, Interstitial Fibrosis, Fibrosis.

Related studies

• Lung mineral fibers of former miners and millers from Thetford-Mines and asbestos regions: a comparative study of fiber concentration and dimension — A. Nayebzadeh, A. Dufresne, et al. (2001)
• Pulmonary fibrosis in workers exposed to non-asbestiform tremolite asbestos minerals — H.Y. Yang, R.H. Shie, et al. (2013)
• Fiber burden and patterns of asbestos-related disease in chrysotile miners and millers — A. Churg, J.L. Wright, et al. (1993)
• Mesothelioma in Quebec chrysotile miners and millers: epidemiology and aetiology — A.D. McDonald, B.W. Case, et al. (1997)
• Mineralogic correlates of fibrosis in chrysotile miners and millers — A. Churg, J.L. Wright, et al. (1989)
• Inferences on the kinetics of asbestos deposition and clearance among chrysotile miners and millers — M.M. Finkelstein, A. Dufresne (1999)

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