Mesothelioma and asbestos

Our plain-English summary of Mesothelioma and asbestos, by G.W. Gibbs, G. Berry (Regulatory Toxicology and Pharmacology, 2008).

The study

• Authors: G.W. Gibbs, G. Berry
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2008;52(1 Suppl):S223-31
• Type of article: Review
• Cited by: 43 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The current state of knowledge concerning mesothelioma risk estimates is reviewed. Estimates of the risk of mesothelioma exist for the commercial asbestos fiber types chrysotile, amosite and crocidolite. Data also exist on which to assess risks for winchite (sodic tremolite) and anthophyllite asbestos. Uncertainty in estimates is primarily related to limitations in measurements of exposure. Differences in the dimensions of the various fiber types and of the same fiber types at different stages of processing add a further complication. Never-the-less, in practical terms, crocidolite presents the highest asbestos related mesothelioma risk. The risk associated with sodic tremolite (winchite) appears to be similar. In chrysotile miners and millers, the mesothelioma risk has been linked with exposure to asbestiform tremolite. Exposure to chrysotile in a pure form seems likely to present a very low if any risk of mesothelioma. While the majority of mesothelial tumors result from exposure to the asbestos minerals, there are other well established and suspected etiological agents. While a practical threshold seems to exist for exposure to chrysotile, it is unlikely to exist for the amphibole asbestos minerals, especially for crocidolite. To date there is no indication of an increased risk of mesothelioma resulting from non-commercial fiber exposure in the taconite industry.

In plain English

This article was a review, not a new study. The authors gathered published research on mesothelioma risk by asbestos fiber type, on other suspected causes, on whether a risk threshold exists, and on taconite miners. Citing a 2000 analysis by Hodgson and Darnton, they reported relative potencies for crocidolite, amosite and chrysotile of 500:100:1. That estimate assumed commercial chrysotile may be contaminated by tremolite. They cited work indicating that winchite (sodic tremolite) from a Montana vermiculite mine appeared to have a potency similar to crocidolite's. They also cited work linking the risk in Quebec chrysotile miners and millers to asbestiform tremolite. Re-pooling three studies of vehicle mechanics, they obtained a relative risk of 0.80 (95% confidence interval 0.44 to 1.49). They said this did not rule out a small increased risk but ruled out a large one. They reported that taconite studies to date showed no evidence of increased risk. The authors concluded that pure chrysotile probably may not cause mesothelioma in humans, and that a practical threshold seems to exist for chrysotile but is unlikely for amphiboles.

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: Review of published epidemiological and experimental research on mesothelioma and asbestos, with some re-calculations by the authors from published figures
• Who was studied: Published worker cohorts and other studies compiled by the authors. These covered crocidolite, amosite, mixed-fiber, tremolite (vermiculite), anthophyllite and chrysotile cohorts (Table 1), vehicle and brake mechanics (Table 3), women living in Quebec chrysotile mining towns, and taconite and Homestake mine workers (Table 4).
• Exposure: Commercial asbestos fiber types chrysotile, amosite and crocidolite; also winchite (sodic tremolite), anthophyllite, non-asbestos fibers such as erionite, and non-asbestiform cummingtonite-grunerite in taconite mining
• Main results:
  • Hodgson and Darnton (2000), as reported by the authors, estimated the relative potency of crocidolite, amosite and chrysotile for causing mesothelioma at 500:100:1. This estimate assumed commercial chrysotile may be contaminated by tremolite.
  • The cited work of McDonald et al. (2002, 2004) indicated that the potency for mesothelioma of the asbestiform mineral (winchite) from the Montana vermiculite mine appears to be similar to that of crocidolite.
  • In Table 2 (from Hodgson and Darnton), the total risk of mesothelioma was 0.51% of total expected mortality per fiber/ml-year for crocidolite, 0.10 for amosite and 0.0010 for chrysotile.
  • Using the Hodgson and Darnton approach but excluding all studies where crocidolite was a potential issue, the authors found the chrysotile estimate was less than 0.0009 per f/ml-year.
  • For women living in two Quebec chrysotile mining areas, the EPA model predicted 150 (range 30 to 750) mesotheliomas in the Town of Asbestos. In fact there was 1 peritoneal mesothelioma.
  • The EPA model predicted 500 mesotheliomas in Thetford Mines, and 10 pleural mesotheliomas were found. Using the Hodgson and Darnton risk, the authors calculated about 9 predicted deaths at Thetford Mines and just less than 1 at Asbestos.
  • McDonald et al. (2002) reported 12 mesotheliomas among 285 deaths in a cohort of 406 vermiculite miners. The miners were exposed to an average of 18 f/cc.
  • Wong (2001), in a meta-analysis of vehicle mechanic studies, found an overall relative risk of 0.90 (CI 0.66 to 1.23), which was not significant. Restricting the analysis to three studies, the authors obtained 0.80 (95% CI 0.44 to 1.49). They stated this does not rule out a small increased risk but rules out a large one.
  • In Quebec chrysotile miners and millers there were 38 cases of mesothelioma. None was a primary peritoneal mesothelioma, and only one invaded the peritoneum.
  • No mesothelioma occurred in Quebec asbestos mining workers employed for less than 2 years. The authors regarded this as indicative of a threshold.
  • The authors reported that, to date, taconite studies showed no evidence of increased mesothelioma risk. In Brunner et al. (2007), all but one of 17 mesothelioma cases who had ever worked as taconite miners in Minnesota (1984 to 1998) had exposure to commercial asbestos.
• The authors' conclusion: The authors concluded that there are large differences in mesothelioma risk between fiber types. They judged it probable that pure chrysotile may not cause mesothelioma in humans. They found that a practical threshold seems to exist for chrysotile but is unlikely for amphiboles. They added that taconite studies, though limited, do not so far suggest increased risk.
• Limitations the authors state:
  • Exposure estimates often had to be extrapolated into the past, and older measurements had to be converted to phase contrast microscopy equivalents.
  • The shape of the exposure-response relationship at very low doses is debated.
  • Comparisons by fiber size are not possible in practice, although some differences between industries may reflect fiber dimensions.
  • Existing taconite studies are limited for evaluating mesothelioma risk.

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Chrysotile, Amosite, Crocidolite, winchite, Tremolite, Anthophyllite, Asbestiform Tremolite.

Related studies

• An overview of the risk of lung cancer in relation to exposure to asbestos and of taconite miners — G. Berry, G.W. Gibbs (2008)
• An evaluation of the risks of lung cancer and mesothelioma from exposure to amphibole cleavage fragments — J.F. Gamble, G.W. Gibbs (2008)
• Risk assessment due to environmental exposures to fibrous particulates associated with taconite ore — R. Wilson, E.E. McConnell, et al. (2008)
• Rapporteur's Report Session 6: risk assessment of asbestos and other fibrous mineral particulates — R.P. Nolan, A.M. Langer (2008)
• Exposure of UK industrial plumbers to asbestos, Part I: Monitoring of exposure using personal passive samplers — G. Burdett, D. Bard (2007)
• A comparison of asbestos fiber potency and elongate mineral particle (EMP) potency for mesothelioma in humans — D.H. Garabrant, S.T. Pastula (2018)

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