Asbestos Fiber Type and Length in Lungs of Chrysotile Textile and Production Workers: Fibers Longer than 18 μm

Our plain-English summary of Asbestos Fiber Type and Length in Lungs of Chrysotile Textile and Production Workers: Fibers Longer than 18 μm, by B.W. Case, A. Dufresne, A.D. McDonald, et al (Inhalation Toxicology, 2000).

The study

• Authors: B.W. Case, A. Dufresne, A.D. McDonald, J.C. McDonald, P. Sébastien
• Journal: Inhalation Toxicology
• Published: 2000;12 Suppl 3:411-8
• Cited by: 18 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Excess lung cancer risk for a cohort of chrysotile textile plant workers was many times the risk observed in a cohort of chrysotile miners/millers. The latter had greater exposure to chrysotile/tremolite. A previous lung burden study confirmed this excess exposure in miners/millers and showed little difference in fiber length. Selection of too short a fiber length cut-off (5 µm or more) in the previous study could have masked differences in lung-retained fiber length. In this follow-up, we counted only those intrapulmonary fibers exceeding 18 µm in length. Lung fiber concentration and dimension were assessed by transmission electron microscopy (TEM) and energy-dispersive x-ray spectrometry (EDS) for autopsy samples from 64 textile workers and 43 chrysotile miners and millers. These long fibers were significantly more concentrated in the lungs of chrysotile miners and millers, consistent with their greater exposure. However, when only these longest fibers were compared, there was a somewhat greater mean and median intrapulmonary fiber length for chrysotile textile workers (mean fiber length, all fiber types combined, 25.2 ± 10.2 µm vs. 22.9 ± 6.6 µm in miners/millers, < .001; medians 21.6 vs. 20, p < .05). Despite their lesser apparent lung cancer risk, chrysotile, tremolite, total amphibole, and total long fiber asbestos concentrations were all highest in the lungs of miners/millers. Twenty-two of 64 textile workers had lung content of crocidolite and/or amosite (32.5% of 508). These amosite/crocidolite fibers were present in the lungs of workers who ceased employment prior to the first use of such fibers recorded in this industry. The results suggest that (I) asbestos fiber length differences cannot explain the difference in lung cancer risk excess and slope between cohorts and (2) the experience of textile workers should not be used to assess risk of lung cancer in miners, cement workers, and friction product workers, regardless of fiber type.

In plain English

This study counted long asbestos fibers in lung tissue taken at autopsy from 64 workers at a chrysotile textile plant in South Carolina and 43 male chrysotile miners and millers from Thetford Mines, Quebec. It re-examined samples from an earlier lung study, this time counting only fibers longer than 18 micrometers (µm). Earlier research had found much higher lung cancer risk in these textile workers than in the more heavily exposed miners and millers. In this study, chrysotile, tremolite and total asbestos fiber concentrations were all significantly higher in the miners' and millers' lungs. When all fiber types were combined, fibers in textile workers' lungs were somewhat longer (p less than 0.001). Twenty-two of the 64 textile workers (19 of 50 men and 3 of 14 women) had amosite and/or crocidolite in their lungs. Twelve of these 22 had stopped working between 1938 and 1947, before any documented use of these fibers at the plant. The authors concluded that fiber length alone did not explain the textile workers' higher lung cancer risk. They also concluded that these workers were not a "pure chrysotile" group, and that their experience should not be used to assess lung cancer risk in miners, cement workers or friction product workers.

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: Lung-retained fiber (lung burden) study of autopsy lung samples. It was a follow-up re-analysis of samples from an earlier study (Sebastien et al., 1989), counting only fibers longer than 18 µm by transmission electron microscopy with energy-dispersive spectrometry. It was prompted by earlier findings that the textile workers had far higher lung cancer risk than the miners and millers.
• Who was studied: Autopsy lung samples from 64 of 74 chrysotile textile workers from a plant in South Carolina (50 members of the original cohort plus 14 women meeting the same cohort definition). Also samples from a random selection of 43 of 89 male chrysotile miners/millers from Thetford Mines, Quebec. Median death year was 1978 for miners/millers and 1972 for textile workers.
• Exposure: Occupational exposure to chrysotile (with tremolite) in mining/milling versus chrysotile textile manufacture. Geometric mean cumulative exposure was 186 MPCFY (million particles per cubic foot-years) for miners/millers versus 3.63 MPCFY for textile workers. Mean years worked was 30 versus 13. Lung fibers analyzed were chrysotile, tremolite, amosite, crocidolite and nonasbestos fibers.
• Main results:
  • Concentrations of all asbestos, chrysotile and tremolite fibers longer than 18 µm were significantly higher in the miners' and millers' lungs than in the textile workers' lungs (1186 fibers counted in total).
  • With all fiber types combined, geometric mean, median and mean fiber length were greater in textile workers' lungs (p less than 0.001), even though concentrations of these long fibers were lower in that group.
  • Total amphiboles had significantly greater geometric mean fiber length in textile workers. The authors attributed this largely to the excess of shorter tremolite fibers in the miners.
  • Chrysotile fibers were significantly thinner, with significantly greater aspect ratios, in the miners' and millers' lungs.
  • Among textile workers' fibers over 30 µm (95 fibers), 42 were amosite or crocidolite and 31 chrysotile. Of the 19 fibers longer than 50 µm, 11 were amosite or crocidolite and 5 chrysotile. In miners/millers, all of the longest fibers were chrysotile or tremolite.
  • In textile workers, lung chrysotile concentration was most closely related to cumulative exposure (correlation coefficient .50, p less than 0.001). In miners/millers, exposure was most closely related to tremolite concentration (Pearson r = .39, p less than 0.01).
  • 22 of 64 textile workers (19 of 50 males and 3 of 14 females) had amosite and/or crocidolite in their lungs. The authors reported that 32% of all fibers counted in textile workers' lungs were amosite or crocidolite.
  • 12 of the 22 textile workers with commercial amphibole in their lungs stopped working between 1938 and 1947, before any documented such exposure at the plant. For 15 of the 22, amosite and crocidolite made up the majority of fibers present.
• The authors' conclusion: The authors concluded that their results do not support fiber length alone as the explanation for the textile workers' greater lung cancer risk. They also concluded that the findings do not support the textile workers being a "pure chrysotile" cohort, and that the textile workers' experience should not be used to assess lung cancer risk in miners, cement workers or friction product workers, regardless of fiber type.
• Limitations the authors state:
  • Lung-retained fiber results represent only the fraction of dose retained until death.
  • The authors could not be certain how representative the studied groups were of their cohorts. Some evidence suggests miners/millers with lung tissue available may have had higher disease incidence than the whole cohort.
  • The two groups differed in time from end of work to death, cumulative exposure, years worked and year of termination. Each of these differences could lead to underestimating the textile workers' exposure.
  • The study could not address the hypothesis that mineral oils played a role in the textile workers' excess lung cancer.

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile, Lung Cancer, Tremolite, Fiber Length, Transmission Electron Microscopy (TEM), Autopsy, Amphibole Group, Crocidolite.

Related studies

• A predictive model for determining asbestos concentrations for fibers less than five micrometers in length — M.J. Kiefer, R.M. Buchan, et al. (1987)
• Mesothelioma and asbestos fiber type. Evidence from lung tissue analyses — J.C. McDonald, B. Armstrong, et al. (1989)
• Respiratory cancer in chrysotile textile and mining industries: exposure inferences from lung analysis — P. Sebastien, J.C. McDonald, et al. (1989)
• Dust exposure and mortality in an American factory using chrysotile, amosite, and crocidolite in mainly textile manufacture — A.D. McDonald, J.S. Fry, et al. (1983)
• Follow-up study of chrysotile asbestos textile workers: cohort mortality and case-control analyses — J.M. Dement, D.P. Brown, et al. (1994)
• Cause-specific mortality in a Chinese chrysotile textile worker cohort — X. Wang, S. Lin, et al. (2013)

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