Fiber size and number in amphibole asbestos-induced mesothelioma

Our plain-English summary of Fiber size and number in amphibole asbestos-induced mesothelioma, by A. Churg, B. Wiggs (The American Journal of Pathology, 1984).

The study

• Authors: A. Churg, B. Wiggs
• Journal: The American Journal of Pathology
• Published: 1984;115(3):437-42
• Cited by: 33 articles, as counted by NIH iCite
• Read it: PubMed · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 001645).

Abstract

Numbers and sizes of fibers from the lungs of 10 patients who had an amphibole asbestos-induced malignant pleural mesothelioma were analyzed. Amosite was found in 10 lungs and crocidolite in 9; the average ratio of amosite to crocidolite was approximately 14:1. In the 8 patients who were not long-time asbestos insulators , the mean number of amosite fibers was 2.3 X 10(6) fibers/g dry lung, and of crocidolite fibers, 0.2 X 10(6)/g; these values represent an approximately 250-fold increase over those found in the general population. Crocidolite fibers were significantly narrower than amosite fibers (mean width, 0.13 versus 0.23 mu), were significantly shorter (mean length, 4.0 versus 5.8 mu), and had a significantly higher mean aspect (length to width) ratio (48 versus 34). Aspect ratios in general increased with increasing fiber length and decreasing fiber width, but the highest values were found for thin amosite fibers at about 13 mu in length, and thin crocidolite fibers at 8 or 15-17 mu in length. Comparison with data from other asbestos-exposed populations indicates that mesothelioma can be induced by relatively small numbers of amphibole fibers and also indicates that amosite is an effective mesothelial carcinogen in humans. Comparison of these data with epidemiologic and experimental predictions of carcinogenic size ranges for mesothelioma induction implies that either the carcinogenic size range is much broader than has been claimed (in particular, fibers considerably shorter than 8 mu and broader than 0.05 mu can produce mesothelioma), or, alternately, that extraordinarily small absolute numbers of fibers in certain size ranges can induce tumors in humans.

In plain English

The authors analyzed lung tissue from 10 patients with malignant pleural mesothelioma who had worked in the Pacific Northwest. All their lungs showed increased amounts of the amphibole asbestos fibers amosite and/or crocidolite. Cases with increased chrysotile were excluded. Listed jobs included shipyard work, asbestos insulation and sheet metal work. Using electron microscopy, the authors counted and measured fibers. Amosite was found in all 10 lungs and crocidolite in 9, with an average amosite-to-crocidolite ratio of about 14 to 1. In the 8 patients who were not long-term insulators, the means were 2.3 million amosite and 0.2 million crocidolite fibers per gram of dry lung, together about 250 times the general-population level. Crocidolite fibers were on average shorter (4.0 versus 5.8 micrometres) and narrower (0.13 versus 0.23 micrometres) than amosite fibers. Only small proportions of fibers fell within previously proposed cancer-causing size ranges. The authors concluded that relatively small numbers of amphibole fibers can induce mesothelioma and that amosite is an effective mesothelial carcinogen. They also concluded that either the cancer-causing size range is broader than claimed or extraordinarily small numbers of fibers can cause tumors.

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: Case series: lung tissue fiber analysis (fiber counting, sizing and identification by electron microscopy) in mesothelioma cases selected from the authors' files
• Who was studied: 10 patients (9 men, 1 woman, aged 48 to 80) with pleural mesothelioma confirmed on histologic review, all of whom had worked in the Pacific Northwest (Oregon, Washington, British Columbia)
• Exposure: Amosite and crocidolite fibers in lung. Cases with increased chrysotile (or the tremolite, actinolite or anthophyllite that accompany chrysotile) were excluded. Listed occupations included shipyard work, asbestos insulation (2 patients), asbestos siding installation, sheet metal work in shipyards, and office work at a shipyard.
• Main results:
  • Amosite was found in all 10 cases (0.1 to 75.7 x 10^6 fibers/g dry lung) and crocidolite in 9 of 10 cases (0.1 to 17.2 x 10^6 fibers/g dry lung). Means for all 10 were 9.9 (amosite) and 2.9 (crocidolite) x 10^6 fibers/g. Except in 1 case, amosite exceeded crocidolite, with an average amosite to crocidolite ratio of 14:1.
  • In the 8 patients who were not long-term insulators, mean amosite was 2.3 x 10^6 and mean crocidolite 0.2 x 10^6 fibers/g dry lung. The combined total of 2.5 x 10^6 fibers/g was about 250-fold the values in a nonexposed background population.
  • 766 amosite and 133 crocidolite fibers were measured. Mean length was 5.8 micrometres for amosite versus 4.0 for crocidolite. Mean width was 0.23 versus 0.13 micrometres. Mean aspect ratio was 34 versus 48. All three differences had P less than 0.001.
  • 55% of crocidolite fibers were shorter than 3 micrometres, compared with 38% of amosite fibers. 55% of crocidolite fibers were narrower than 0.1 micrometre, compared with 21% of amosite fibers.
  • Aspect ratio peaked at about 13 micrometres length for amosite, and at about 8 and about 15 to 17 micrometres for crocidolite.
  • Only 3.3% of amosite and 14% of crocidolite fibers were narrower than 0.05 micrometres. About 11% of amosite and 7.5% of crocidolite fibers were longer than 8 and narrower than 0.25 micrometres (the size range suggested by Stanton et al).
• The authors' conclusion: The authors concluded that mesothelioma can be induced by relatively small numbers of amphibole fibers and that amosite is an effective mesothelial carcinogen in humans. They also concluded that either the carcinogenic size range is broader than claimed (including fibers shorter than 8 and broader than 0.05 micrometres) or extraordinarily small numbers of fibers in certain size ranges can induce tumors.
• Limitations the authors state:
  • The authors stated that their view that shorter and broader fibers are important is not strictly provable from their data.
  • Because few crocidolite fibers were found, results from central and subpleural lung samples were averaged rather than reported separately.
  • Comparison with mesothelioma studies from other laboratories is sometimes difficult because of differences in methods.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Amosite, Crocidolite, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Amphibole Asbestos, Mesothelioma, Pleural Mesothelioma, Amosite, Crocidolite, Insulator, Aspect Ratio (Length-to-diameter ratio), Fiber Length.

Related studies

• Fiber size and number in workers exposed to processed chrysotile asbestos, chrysotile miners, and the general population — A. Churg, B. Wiggs (1986)
• Tumor incidence was not related to the thickness of visceral pleural in female Syrian hamsters intratracheally administered amphibole asbestos or manmade fibers — S. Adachi, K. Kawamura, et al. (1992)
• Types, numbers, sizes, and distribution of mineral particles in the lungs of urban male cigarette smokers — A. Churg, B. Wiggs (1987)
• Amphibole fibers in a taconite mine and in the lungs of the miners — B. Gylseth, T. Norseth, et al. (1981)
• Effect of size fractionation on the toxicity of amosite and Libby amphibole asbestos — K.E. Duncan, A.J. Ghio, et al. (2010)
• Mass, number and size of lung fibres in the pathogenesis of asbestosis in sheep — P. Sébastien, R. Bégin, et al. (1990)

Browse more research in The American Journal of Pathology, or return to medical research.