Mesothelioma risk from chrysotile

Our plain-English summary of Mesothelioma risk from chrysotile, by J.T. Hodgson, A. Darnton (Occupational and Environmental Medicine, 2010).

The study

• Authors: J.T. Hodgson, A. Darnton
• Journal: Occupational and Environmental Medicine
• Published: 2010;67(6):432
• Type of article: Comment, Letter
• Cited by: 36 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Summary of the article

This letter responded to a 2009 analysis by Loomis et al of asbestos-related mortality in North Carolina textile plants exposed to chrysotile. The authors compared those results with their own earlier meta-analysis. The new lung cancer risk, a relative risk of 1.102 per 100 f/ml.yr, translated almost exactly to an excess of 0.1% per f/ml.yr, identical to their earlier best estimate. The new mesothelioma risk was 10 times higher than in the meta-analysis. In a chart of chrysotile cohorts, the Canadian mines gave a low, reasonably precise estimate of about 0.001. With the mines excluded, the remaining cohorts were statistically consistent (p=0.075), mainly because the estimates were imprecise. Their mean risk was 0.0070 (confidence limits 0.0038 to 0.013). The two mining cohorts combined gave 0.00096 (95% CI 0.00069 to 0.0013). The new estimate rested on eight cases, and up to three may have been due to amosite exposure in one plant. An estimate of 0.007% per f/ml.yr was still at least an order of magnitude below the amphibole estimates (0.5 for crocidolite, 0.1 for amosite). Mixed-fibre cohorts suggested a chrysotile risk well below 0.01 in friction products. The authors concluded that the new results strengthened the case that the per-fibre mesothelioma risk from chrysotile is greater in textile plants than in mines. They said it was unclear whether this difference applies in other settings.

PubMed has no abstract for this study, and the article doesn't print one. We wrote this summary from the full article with the help of AI. It is not the authors' wording.

In plain English

This is a letter to the editor, not a new study. The authors compared a 2009 analysis by Loomis et al of workers at four North Carolina textile plants with their own earlier meta-analysis of chrysotile cohorts. They noted that the Loomis lung cancer estimate matched their earlier best estimate, an excess of about 0.1% per f/ml.yr. The Loomis mesothelioma estimate, however, was about 10 times higher than their meta-analysis had found. On the authors' mesothelioma mortality index, expressed in % per f/ml.yr, the Canadian mines gave a low estimate of about 0.001, and the two mining cohorts combined gave 0.00096 (95% CI 0.00069 to 0.0013). The non-mining cohorts averaged 0.0070% per f/ml.yr (confidence limit 0.0038 to 0.013). The North Carolina estimate rested on eight cases, up to three of which may have been due to amosite. The authors said small numbers made all the estimates statistically uncertain. They concluded that the new results strengthen the case that the per-fibre mesothelioma risk from chrysotile is greater in textile plants than in mines. They added that it remained at least ten times lower than their estimates for crocidolite and amosite.

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: Letter to the editor commenting on another group's study (Loomis et al 2009) and comparing its results with the authors' own earlier meta-analysis; not an original study
• Who was studied: Chrysotile-exposed worker cohorts: new data from four North Carolina textile plants (Loomis et al), set alongside the chrysotile cohorts from the authors' earlier meta-analysis. Those cohorts were South Carolina (men and women), New Orleans (plant 2), Connecticut, the Italian Balangero mines and the Canadian (Quebec) mines.
• Exposure: Chrysotile exposure in textile plants, other processing plants and mines, expressed as cumulative exposure in f/ml.yr. Mesothelioma risk is given as an exposure-specific mesothelioma mortality index (Rm) in % per f/ml.yr. The authors also make comparisons with amphibole fibres (crocidolite, amosite).
• Main results:
  • The lung cancer risk from the Loomis data (relative risk 1.102 per 100 f/ml.yr) translates almost exactly to an excess over expected of 0.1% per f/ml.yr. The authors say this is identical to the best estimate from their earlier meta-analysis.
  • The mesothelioma risk derived from the new North Carolina data was higher by a factor of 10 than the authors' meta-analysis estimate.
  • The Canadian mines, the largest single set of observations, gave a low and reasonably precise mesothelioma estimate of about 0.001 (% per f/ml.yr).
  • The remaining cohorts, excluding the Canadian mines and the Italian Balangero mines, had a mean mesothelioma risk of 0.0070% per f/ml.yr, with a confidence limit from 0.0038 to 0.013. The authors said these cohorts were statistically consistent mainly because their estimates were imprecise, not because the estimates were similar.
  • Combining the two mining cohorts gave a joint mesothelioma estimate of 0.00096% per f/ml.yr (95% CI 0.00069 to 0.0013).
  • The North Carolina estimate was based on eight mesothelioma cases. Assuming Poisson variability, the underlying risk could correspond to between four and 16 cases.
  • An estimate of 0.007% per f/ml.yr for chrysotile is still at least an order of magnitude lower than the authors' estimates for amphiboles: 0.5 for crocidolite and 0.1 for amosite.
  • In the Ferodo mixed-fibre (friction products) cohort, which had an overall risk of 0.014, there was a strong indication that 11 of the 13 mesothelioma deaths were due to crocidolite. The authors infer that the implied chrysotile risk in that setting would be well below 0.01.
• The authors' conclusion: The authors concluded that the new results strengthen the case that the per-fibre mesothelioma risk from chrysotile in textile plants is greater than in the mines. They said it is not clear whether this difference applies in other settings.
• Limitations the authors state:
  • Small numbers mean all the estimates are subject to substantial statistical error.
  • Up to three of the eight North Carolina cases may be due to amosite exposure in plant 3. Some mesothelioma cases may also have been missed before ICD-10 was introduced.
  • The absence of mesothelioma deaths in the New Orleans and Connecticut cohorts is statistically consistent with a risk of 0.01, though more consistent with the mines estimate of 0.001.

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Chrysotile, Meta-Analysis, Lung Cancer, Relative Risk, Amosite, Amphibole Group, Crocidolite.

Related studies

• An epidemiological study of the role of chrysotile asbestos fibre dimensions in determining respiratory disease risk in exposed workers — L. Stayner, E. Kuempel, et al. (2008)
• Asbestos standards: Impact of currently uncounted chrysotile asbestos fibers on lifetime lung cancer risk — D.B. Richardson, A.P. Keil, et al. (2018)
• Occupational exposure to rock wool and glass wool and risk of cancers of the lung and the head and neck: a systematic review and meta-analysis — L. Lipworth, C. La Vecchia, et al. (2009)
• Hand-spinning chrysotile exposure and risk of malignant mesothelioma: A case-control study in Southeastern China — Z. Jiang, T. Chen, et al. (2018)
• Exposure-specific lung cancer risks in Chinese chrysotile textile workers and mining workers — X. Wang, S. Lin, et al. (2014)
• Human evidence: lung cancer mortality risk from chrysotile exposure — J.M. Hughes (1994)

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