Numbers and types of asbestos fibers in subjects with pleural plaques

Our plain-English summary of Numbers and types of asbestos fibers in subjects with pleural plaques, by M.L. Warnock, B.T. Prescott, T.J. Kuwahara (The American Journal of Pathology, 1982).

The study

• Authors: M.L. Warnock, B.T. Prescott, T.J. Kuwahara
• Journal: The American Journal of Pathology
• Published: 1982;109(1):37-46
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Free full text

Abstract

The authors analyzed asbestos fibers in lung samples from 20 subjects with pleural plaques discovered on autopsy and compared the findings to their previous analyses of lungs from subjects with little or no asbestos exposure and no plaques. Sixteen of the subjects with plaques had a history of exposure to asbestos. The authors used electron-optical methods and energy-dispersive x-ray spectroscopy to investigate the structure, diffraction patterns, and chemical composition of the asbestos fibers. The subjects with plaques had significantly higher median concentrations than the control subjects for amosite and crocidolite fibers (P less than 0.01) but not for the other fiber types. Minimal microscopic asbestosis was present in the 3 subjects who had the highest amosite concentrations. In the subjects with typical plaques, a history of asbestos exposure, and more fibers than in the control population, the relation of the plaques to asbestos was confirmed; for others, it was uncertain.

In plain English

This study measured asbestos fibers in the lungs of 20 people (19 men, 1 woman) found at autopsy in 1980 and 1981 to have pleural plaques. Sixteen had a history of asbestos exposure, mostly on ships, in shipyards or on docks. Using electron microscopy with chemical and diffraction analysis, the authors compared them with 11 previously studied men without plaques who had a light asbestos burden. The median amosite and crocidolite concentration was 25.9 thousand fibers per gram of wet lung in the plaque group and 1.8 thousand in the comparison group (P less than 0.001). Chrysotile was significantly lower in the plaque group. Tremolite, anthophyllite and actinolite did not differ significantly between the groups. Three subjects without a clear exposure history had no fiber type above the highest comparison value. Fibers were found in 5 of the 12 plaques examined. The three subjects with the highest amosite concentrations had minimal microscopic asbestosis; no lung showed fibrosis by eye or touch. The authors concluded that, if epidemiologic evidence of a causal link is accepted, their study implicates amosite and crocidolite in most cases. They noted that fiber concentrations overlapped with those of the comparison group.

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 fiber-burden study of subjects with pleural plaques, selected prospectively and compared with a previously analyzed control group
• Who was studied: 20 subjects (19 men, 1 woman), aged 36 to 84, with fibrous pleural plaques at autopsy at the University of California, San Francisco, and the Solano County coroner's office, September 1980 to August 1981. Subjects with mesothelioma or macroscopic fibrosis were excluded. The control group was 11 previously described men with fewer than 100 asbestos bodies per gram of wet lung.
• Exposure: Occupational histories were taken from relatives. Sixteen subjects had a history of asbestos exposure: 14 possibly on ships, in shipyards or on docks, and 2 in foundries or construction. Fibers measured were chrysotile, amosite and crocidolite (combined), and tremolite, anthophyllite and actinolite (combined).
• Main results:
  • Median amosite and crocidolite concentration was 25.9 x 10^3 fibers per gram of wet lung in the plaque group versus 1.8 x 10^3 in the controls, about an order of magnitude higher (P less than 0.001)
  • Median chrysotile concentration was significantly lower in the plaque group (16.2 x 10^3 per gram) than in the controls (60.8 x 10^3 per gram)
  • Median concentration of tremolite, anthophyllite and actinolite fibers (12.2 x 10^3 per gram in the plaque group, 7.9 x 10^3 in the controls) did not differ significantly
  • Fifteen of the 20 plaque subjects had more amosite and crocidolite fibers than the peak control value. Three subjects (Cases 2, 3 and 6) had no fiber concentration above the peak control value.
  • Asbestos fibers were found in 5 of the 12 pleural plaques that could be examined
  • Minimal microscopic asbestosis was present in the 3 subjects (Cases 18, 19 and 20) with the highest amosite concentrations. The lesions were widely scattered and usually less than 1 mm in diameter.
  • Lung slices from all 20 subjects showed no fibrosis by eye or palpation
  • Amosite and crocidolite fibers were significantly more concentrated in the central upper lobe than in the central lower lobe (P less than 0.01). Chrysotile showed no preferential location.
• The authors' conclusion: The authors concluded that, if epidemiologic studies indicating a causal relation between asbestos and plaques are accepted, their study implicates amosite and crocidolite rather than other asbestos types in most instances. They stated that the range of concentrations overlapped with the control group, and that plaques in the 3 subjects with few fibers and no exposure history may not have been related to asbestos.
• Limitations the authors state:
  • The comparison group was not chosen to demonstrate a causal relationship between total fiber burden and plaques
  • Fibers may be cleared from the lungs over time, so current fiber concentrations may poorly reflect past burden
  • Exposure information given by relatives is often unreliable
  • Plaque tissue could be analyzed in only 12 cases, because formalin-fixed plaques could not be fully digested
  • Fibers shorter than 1 micron were mostly excluded from analysis because debris obscured them
  • The authors could not be certain that their subjects had inhaled chrysotile
  • In this heterogeneous group, no comment could be made about the effect of smoking

Topics

Medical terms in this study, explained in our Lexicon: Pleural Plaques, Autopsy, Asbestos Exposure, Amosite, Crocidolite.

Related studies

• Serum biomarkers in patients with mesothelioma and pleural plaques and healthy subjects exposed to naturally occurring asbestos — M. Bayram, I. Dongel, et al. (2014)
• Focused X-Ray Histological Analyses to Reveal Asbestos Fibers and Bodies in Lungs and Pleura of Asbestos-Exposed Subjects — L. Pascolo, A. Gianoncelli, et al. (2016)
• Analysis of asbestos fibers in lung parenchyma, pleural plaques, and mesothelioma tissues of North American insulation workers — N. Kohyama, Y. Suzuki (1991)
• Asbestos fibers and pleural plaques in a general autopsy population — A. Churg (1982)
• Refractory ceramic fiber exposure and pleural plaques — J. Lockey, G. Lemasters, et al. (1996)
• Changes in numbers and dimensions of chrysotile asbestos fibers in lungs of rats following short-term exposure — V.L. Roggli, A.R. Brody (1984)

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