Asbestos fiber length as related to potential pathogenicity: a critical review

Our plain-English summary of Asbestos fiber length as related to potential pathogenicity: a critical review, by R.F. Dodson, M.A. Atkinson, J.L. Levin (American Journal of Industrial Medicine, 2003).

The study

• Authors: R.F. Dodson, M.A. Atkinson, J.L. Levin
• Journal: American Journal of Industrial Medicine
• Published: 2003;44(3):291-7
• Type of article: Review
• Cited by: 103 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Asbestos inhalation is recognized as an exposure that increases the risk for the development of lung disease. It is unique among dusts in that it is both a carcinogen and capable of inducing extrapulmonary responses such as pleural thickening and fibrosis as well as malignancy. One feature of asbestos suggested as crucial in its pathological activity is its fibrous morphology. Long fibers that have been inhaled are cleared less readily and are thus more persistent in the body. Furthermore certain experimental models link fiber length to levels of risks for development of certain diseases. The present review will survey the data on this subject.

Methods: The review considers experimental models that have been used to assess the response to various lengths of fibers in animal models in addition to data obtained from studies of human materials. The review also emphasizes the importance in defining the method by which a sample is categorized.

Results: Data are offered which support the potential for longer fibers as well as shorter fibers to contribute to pathological responses.

Conclusions: The data presented argue that asbestos fibers of all lengths induce pathological responses and that caution should be exerted when attempting to exclude any population of inhaled fibers, based on their length, from being contributors to the potential for development of asbestos-related diseases.

Copyright 2003 Wiley-Liss, Inc.

In plain English

This article was a review, not a new study. The authors surveyed published animal experiments and studies of human tissue on whether the length of asbestos fibers affects their ability to cause disease. They noted that experiments by Stanton linked tumors in rats mainly to long, thin fibers. Experiments by Pott and colleagues, however, found tumors in 30% of rats injected with milled chrysotile in which 99.8% of fibers were short. Davis and colleagues reported that a tremolite sample with relatively few asbestiform fibers produced tumors in 70% of rats. Among human tissue studies, the authors cited a report that short, medium and long amphibole fibres were all associated with mesothelioma risk. Their own laboratory found that most asbestos fibers in lung, lymph nodes and pleural plaques were short. Their laboratory's work also showed that light microscopy would miss many fibers, especially chrysotile. The authors concluded that it is difficult to exclude fibers of any particular length from a role in causing disease. They noted that the animal experiments tested only narrow ranges of fiber lengths.

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: Narrative critical review of published experimental and human tissue studies
• Who was studied: No new subjects. The review covered published animal experiments (mainly rats given fibers by injection into the chest or abdominal cavity) and published studies of human lung and other tissues.
• Exposure: Asbestos fibers of different lengths, including chrysotile, amosite, crocidolite and tremolite. The experiments reviewed also included non-asbestos fibers such as fiberglass, basalt and ceramic fibers.
• Main results:
  • Reviewed study (Stanton et al. 1981, pleural implants in rats): pleural sarcoma correlated best with fibers 0.25 or less in diameter and more than 8 in length. Relatively high correlations were also seen for fibers in other size categories. Units are printed as 'mm' in this copy.
  • Reviewed study (Pott et al., rats injected in the abdominal cavity): 30% of animals given milled chrysotile developed tumors. In that material, 99.8% of fibers were shorter than 5 (units printed as 'mm').
  • Reviewed study (Davis et al. 1991, tremolite injected into the abdominal cavity of rats): all tremolite samples, whatever their form or length, had some potential to produce mesothelioma. This included samples consistent with cleavage fragments.
  • Same reviewed study (Davis et al. 1991): one tremolite sample with relatively few asbestiform fibers produced tumors in 70% of rats.
  • Reviewed study (McDonald et al. 2001, people with mesothelioma aged 50 or younger at diagnosis): short, medium and long amphibole fibres were all associated with mesothelioma risk. Fibres longer than 10 (units printed as 'mm') had the greatest increase in risk per fibre.
  • Reviewed study (Churg and Vedal 1994, workers heavily exposed to amosite and chrysotile): those authors concluded that mesotheliomas were not associated with long fibers.
  • The authors' earlier laboratory study (Dodson et al. 1997, lung tissue from 55 mesothelioma cases, transmission electron microscopy): 48% of amosite fibers met Stanton's size criteria. Only 33% would have met them if counted by light microscopy.
  • Same study (Dodson et al. 1997): 39% of chrysotile fibers met Stanton's criteria, but only 1.4% would have been detected by light microscopy.
  • The authors' earlier laboratory study (Dodson et al. 1990, occupationally exposed individuals): most asbestos fibers in lung, lymph nodes and pleural plaques were short. Only 4% of chrysotile fibers in the lung were longer than 10 (units printed as 'mm'), and none that long were found in the plaques or lymph nodes. Of amphibole fibers, 20% in the lung, 8% in pleural plaques and 2.5% in lymph nodes were that long.
  • Reviewed studies (Suzuki and Yuen 2001, 2002, people with mesothelioma): only 4% of fibers in lung and mesothelial tissues fitted Stanton's dimensions.
  • Reviewed study (Sebastien et al. 1980, 29 cases): 16 of 29 pleura samples and 27 lungs were positive for asbestos. Fibers in the pleura were almost all chrysotile, with a mean length of 2.3 compared with 4.9 in the lung (units printed as 'mm').
• The authors' conclusion: The authors concluded that it is difficult to exclude fibers of any particular size from a role in causing disease in the lung or outside it, because both exposures and tissue burdens contain fibers of varying lengths and widths. They also stated that in most tissues the great majority of asbestos fibers are short.
• Limitations the authors state:
  • The authors stated that the experimental animal models tested fibers of very limited length distributions.
  • The authors stated that the studies they cited address only a few of the non-size factors that may affect toxicity, and only for a few fiber types.

Topics

Medical terms in this study, explained in our Lexicon: Fiber Length, Pleural Thickening, Fibrosis.

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