Mineralogic correlates of fibrosis in chrysotile miners and millers

Our plain-English summary of Mineralogic correlates of fibrosis in chrysotile miners and millers, by A. Churg, J.L. Wright, L. DePaoli, et al (The American Review of Respiratory Disease, 1989).

The study

• Authors: A. Churg, J.L. Wright, L. DePaoli, B. Wiggs
• Journal: The American Review of Respiratory Disease
• Published: 1989;139(4):891-6
• Cited by: 39 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000059).

Abstract

To determine which mineral parameters relate to the degree of interstitial fibrosis (asbestosis) in the lungs of chrysotile miners and millers, we graded fibrosis histologically and correlated fibrosis grades with fiber concentration and mean size, surface area, and mass, and with total sample fiber length, surface area, and mass in 21 cases. A positive correlation of fibrosis grade with tremolite concentration and a lesser correlation with chrysotile concentration was found for whole lungs, specific sites within lungs, and, for tremolite, single microscopic fields. No correlations were found for measures of chrysotile fiber size, surface area, or mass, but tremolite mean fiber length, aspect ratio, and surface area were, surprisingly, negatively correlated with fibrosis grade. Measures based on total rather than on mean case or site parameters failed to show correlations with fibrosis. We conclude that: (1) degree of pulmonary fibrosis reflects fiber concentration at both a bulk and a microscopic level; (2) mean fiber length and parameters related to mean fiber length also correlate with fibrosis grade, but, contrary to predictions from animal studies, this correlation is negative, suggesting that short fibers may be more important in the genesis of pulmonary fibrosis than is commonly believed; (3) there is no evidence that parameters such as total fiber length, surface area, or mass provide predictors of degree of fibrosis.

In plain English

This study examined autopsy lungs from 21 long-term chrysotile miners and millers, supplied by a hospital in Thetford Mines, Quebec. The authors graded lung scarring (interstitial fibrosis, or asbestosis) under the microscope on a scale from zero to 4. They used electron microscopy to identify chrysotile and tremolite fibers in several tissue samples from each lung and in small microscopic fields. Fibrosis grade was positively correlated with tremolite concentration and, less strongly, with chrysotile concentration. This held for whole lungs and for specific sites within the lungs. In single microscopic fields, higher tremolite concentrations went with higher grades (p less than 0.01). Unexpectedly, mean tremolite fiber length, aspect ratio and surface area were negatively correlated with fibrosis grade. No chrysotile size measure correlated with fibrosis, and neither did any total fiber length, surface area or mass. The authors concluded that fibrosis reflects fiber concentration. They suggested that short fibers may matter more in fibrosis than commonly believed, while stating that they could not prove this. They noted that only a small residual fraction of the inhaled chrysotile remained in the lungs.

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 correlating microscopic fibrosis grades with electron microscopic fiber concentration and size measurements
• Who was studied: Autopsy lungs of 21 long-term chrysotile miners and millers, obtained from the Hopital General de la Region de l'Amiante at Thetford Mines, Quebec; 84 tissue sites in total (four per case)
• Exposure: Chrysotile mining and milling. Chrysotile and tremolite fibers were identified and measured in lung tissue by electron microscopy and X-ray spectroscopy.
• Main results:
  • Fibrosis grade was positively correlated with tremolite concentration and less strongly with chrysotile concentration. This held for whole lungs and specific sites, and for tremolite also in single microscopic fields.
  • In individual microscopic fields (tremolite only, as very few chrysotile fibers were found), higher fiber concentration tended to go with higher fibrosis grades; the chi-square test was significant at p less than 0.01.
  • Mean tremolite fiber length, aspect ratio and surface area were negatively correlated with fibrosis grade.
  • Site data (84 sites) showed correlations with the same parameters as the whole-case data, but with smaller correlation coefficients.
  • No chrysotile size-related measure correlated with fibrosis grade.
  • No measure of total fiber length, surface area or mass correlated significantly with fibrosis grade, for any type of sample or fiber.
• The authors' conclusion: The authors concluded that the degree of fibrosis reflects fiber concentration at both a bulk and a microscopic level. They also concluded that the negative correlation with mean fiber length suggests short fibers may be more important in causing pulmonary fibrosis than commonly believed.
• Limitations the authors state:
  • Only a small residual fraction of the inhaled chrysotile remained in the lungs, which may explain the weaker chrysotile correlations.
  • Chrysotile fibers are hard to detect in thin electron microscope sections.
  • In the microscopic field sections, fiber sizes could not be determined; only fiber number was assessed.
  • The authors could not rule out that fibrotic lung areas retain more (short) fibers, which could produce the negative length correlation.
  • The authors stated that they could not prove the hypothesis that short fibers are more fibrogenic.

Topics

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

Medical terms in this study, explained in our Lexicon: Fibrosis, Chrysotile, Interstitial Fibrosis, Fiber Length, Tremolite, Aspect Ratio (Length-to-diameter ratio), Pulmonary Fibrosis.

Related studies

• Fiber burden and patterns of asbestos-related disease in chrysotile miners and millers — A. Churg, J.L. Wright, et al. (1993)
• Fiber size and number in workers exposed to processed chrysotile asbestos, chrysotile miners, and the general population — A. Churg, B. Wiggs (1986)
• The morbidity and mortality of vermiculite miners and millers exposed to tremolite-actinolite: Part III. Radiographic findings — H.E. Amandus, R. Althouse, et al. (1987)
• Inferences on the kinetics of asbestos deposition and clearance among chrysotile miners and millers — M.M. Finkelstein, A. Dufresne (1999)
• Respiratory cancer in chrysotile textile and mining industries: exposure inferences from lung analysis — P. Sebastien, J.C. McDonald, et al. (1989)
• Lung asbestos content in long-term residents of a chrysotile mining town — A. Churg (1986)

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