Fiber burden and patterns of asbestos-related disease in workers with heavy mixed amosite and chrysotile exposure

Our plain-English summary of Fiber burden and patterns of asbestos-related disease in workers with heavy mixed amosite and chrysotile exposure, by A. Churg, S. Vedal (American Journal of Respiratory and Critical Care Medicine, 1994).

The study

• Authors: A. Churg, S. Vedal
• Journal: American Journal of Respiratory and Critical Care Medicine
• Published: 1994;150(3):663-9
• Cited by: 56 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

To attempt to determine the mineralogic factors that relate to the appearance of specific types of asbestos-related disease in workers with heavy mixed exposure to amphiboles and chrysotile, we analyzed the pulmonary asbestos fiber burden in a series of 144 shipyard workers and insulators from the Pacific Northwest. Amosite was found in all lungs, and tremolite and chrysotile in most lungs, but the vast majority of fibers were amosite. Tremolite and chrysotile concentrations were significantly correlated, indicating that the tremolite originated from chrysotile products, but no correlation was found between tremolite or chrysotile concentration and amosite concentration. Time since last exposure was correlated with decreasing amosite concentration and the calculated clearance half time was about 20 yr. In a multiple regression analysis that accounted for the presence of more than one disease in many subjects, a high concentration of amosite fibers was correlated with the presence of airway fibrosis and asbestosis, whereas subjects with mesothelioma, lung cancer, pleural plaques, or no asbestos-related disease had about the same, much lower, amosite concentration. No relationship was found between the concentration of chrysotile or tremolite and any disease. Analysis of fiber size measures (length, width, aspect ratio, surface, mass) showed that pleural plaques were strongly associated with high aspect ratio amosite fibers and suggested that mesotheliomas were associated with low aspect ratio amosite fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

In plain English

The authors measured asbestos fibers in autopsy lung tissue from 144 shipyard workers, asbestos insulators and workers in related trades from Oregon, Washington and British Columbia. The lungs were referred to their laboratory from 1981 through 1991. The workers were known or presumed to have had mixed exposure to amosite and chrysotile, but no exposure measurements were available. Amosite was found in all 144 lungs, chrysotile in 102 and tremolite in 125. Amosite levels fell with time since last exposure, giving an estimated half-life in the lung of 20 years. The analysis allowed for many workers having more than one disease. In it, high amosite concentrations were associated with asbestosis and airway fibrosis. Workers with mesothelioma, lung cancer, pleural plaques or no asbestos-related disease had about the same, much lower, levels. Chrysotile and tremolite levels were not linked to any disease. Pleural plaques were associated with amosite fibers that were long relative to their width (higher aspect ratio). Only 8 workers had no asbestos-related disease, which limited statistical power. The authors concluded that only amosite concentrations correlated with specific diseases. They said this raised questions about chrysotile's role, while cautioning that lung analysis greatly underestimates chrysotile exposure.

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 fiber burden study of autopsy lungs referred to the authors' laboratory for mineral analysis. Fiber measures were compared between exposed workers with specific asbestos-related diseases and exposed workers with no asbestos-related disease, using t tests and multiple regression.
• Who was studied: 144 autopsy cases (134 men, 10 women) received from 1981 through 1991. All had at some time worked as shipyard workers, asbestos insulators, or in related trades such as pipefitters, in the Pacific Northwest (Oregon, Washington, British Columbia). About half were initially medical-legal referrals. By disease: asbestosis 23, airway fibrosis 16, mesothelioma 83, lung cancer 32, pleural plaques 103, no asbestos-related disease 8. Most had more than one disease.
• Exposure: Mixed exposure to amphibole (amosite) and chrysotile, either known or presumed from the occupation. Exposure lasted a mean of 20 years (range less than 1 to 50 years), and no exposure measurements were available. Crocidolite was found in only a very few cases and was excluded from all analyses.
• Main results:
  • Amosite fibers were found in all 144 cases, chrysotile fibers in 102 cases and tremolite fibers in 125 cases. The vast majority of fibers were amosite.
  • Tremolite and chrysotile concentrations were correlated (R = 0.37, P less than 0.001). Neither was correlated with amosite concentration.
  • Amosite concentration decreased with time since last exposure, and the estimated clearance half time for amosite was 20 years. Neither tremolite nor chrysotile concentration was associated with any measure of exposure.
  • The multiple regression accounted for more than one disease per subject. In it, high amosite concentration was associated with asbestosis (p less than 0.001) and airway fibrosis (p 0.001). Geometric mean amosite concentrations, in millions of fibers per gram dry lung, were: 10 in the 23 subjects with asbestosis; 4.3 in the 16 with airway fibrosis; 0.86 in the 83 with mesothelioma; 1.1 in the 32 with lung cancer; 1.4 in the 103 with pleural plaques; and 0.67 in the 8 with no asbestos-related disease. The authors described the association of pleural plaques with amosite concentration as marginal.
  • No correlations were found between chrysotile or tremolite concentration and the presence of any disease. The few apparently significant chrysotile values reflected higher concentrations in subjects without disease.
  • In the multiple regression, subjects with pleural plaques had significantly higher mean amosite aspect ratios than subjects without disease. The mean was 40 in the 103 subjects with plaques and 36 in the 8 subjects without disease (p 0.004).
  • Subjects with mesothelioma had near-significantly lower amosite aspect ratios. Mean aspect ratios were 30 in subjects with mesothelioma but not plaque (n = 14), 47 in subjects with plaque but not mesothelioma (n = 34), and 36 in subjects without disease (n = 8).
  • Amosite fiber length was not associated with disease. No association was found between amosite fiber width, surface area or mass and disease.
• The authors' conclusion: The authors concluded that in this population the major residual fiber is amosite, and that only amosite concentrations correlate with specific diseases, raising questions about chrysotile's role. They also concluded that mesothelioma appears at much lower amosite burdens than asbestosis, that amosite clearance from the lung takes decades, and that, except for pleural plaques, the link between fiber size and disease remains uncertain.
• Limitations the authors state:
  • No details of exposure levels were available, and exposure in years could not be correlated with measured fiber burdens.
  • The cases were selected referrals, often for compensation-related reasons. The study therefore gives no information on how common the different diseases are.
  • The no-disease reference group was small (8 subjects). The study could not statistically detect less than a tenfold increase in amosite counts in the disease groups.
  • Most subjects had more than one asbestos-related disease. Multiple regression could only partly account for this.
  • Chrysotile does not persist in lung tissue, so this type of analysis greatly underestimates chrysotile exposure. Conclusions about chrysotile's effects need considerable caution.

Topics

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

Medical terms in this study, explained in our Lexicon: Fiber Burden, Amosite, Chrysotile, Amphibole Group, Insulator, Tremolite, Fibrosis, Mesothelioma.

Related studies

• Fiber burden and patterns of asbestos-related disease in chrysotile miners and millers — A. Churg, J.L. Wright, et al. (1993)
• Quantification of the pathological response and fate in the lung and pleura of chrysotile in combination with fine particles compared to amosite-asbestos following short-term inhalation exposure — D.M. Bernstein, R.A. Rogers, et al. (2011)
• The pathological response and fate in the lung and pleura of chrysotile in combination with fine particles compared to amosite asbestos following short-term inhalation exposure: interim results — D.M. Bernstein, R.A. Rogers, et al. (2010)
• Evaluation of the exposure, dose-response and fate in the lung and pleura of chrysotile-containing brake dust compared to TiO2, chrysotile, crocidolite or amosite asbestos in a 90-day quantitative inhalation toxicology study - Interim results Part 1: Experimental design, aerosol exposure, lung burdens and BAL — D.M. Bernstein, B. Toth, et al. (2020)
• Fiber levels and disease in workers from a factory predominantly using amosite — A.R. Gibbs, M.J. Gardner, et al. (1994)
• Pulmonary mineral fibers after occupational and environmental exposure to asbestos in the Russian chrysotile industry — A. Tossavainen, E. Kovalevsky, et al. (2000)

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