Canadian chrysotile report released--at last

Our plain-English summary of Canadian chrysotile report released--at last, by T.L. Ogden (The Annals of Occupational Hygiene, 2009).

The study

• Author: T.L. Ogden
• Journal: The Annals of Occupational Hygiene
• Published: 2009;53(4):307-9
• Type of article: Editorial
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Summary of the article

This editorial, by the chair of an expert panel convened by Health Canada, described the delayed release of the panel's reports on the risks of chrysotile asbestos. In November 2007 Health Canada brought together experts who had previously expressed very different views on chrysotile, to see what degree of consensus existed. The reports were delivered in March 2008. They were released only on 9 April 2009, after several applications under the Canadian Access to Information Act. The author speculated that the delay was due to a perceived threat to Canadian chrysotile production. The panel's main discussion compared two meta-analyses of exposure–response relationships, by Hodgson and Darnton (2000) and by Berman and Crump (2003 draft). The author outlined differences between them, including how they handled tremolite contamination, linear versus non-linear models, and inclusion of the Charleston textile cohort. Despite these differences, the two analyses agreed to within an order of magnitude. A worker with a cumulative chrysotile exposure of 1 f-year/ml had an estimated probability of the order of 1 in 10 000 of dying of cancer due to the exposure. Both analyses concluded that amphiboles were many times more likely than chrysotile to cause mesothelioma. The panel supported both approaches but did not specifically endorse their figures, and two members recorded reservations. The author concluded that chrysotile risk was still a political issue, but that wide agreement existed on the science.

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 was an editorial, not a new study. In November 2007 Health Canada convened experts with very different views on chrysotile asbestos; the author chaired the panel, whose report was released on 9 April 2009. The report presented no new analysis but compared two meta-analyses, by Hodgson and Darnton (2000) and Berman and Crump (2003 draft). The editorial reported that the two gave broadly similar results despite differing methods. A worker exposed to chrysotile at work for 10 years at an average of 0.1 fibres per millilitre had an estimated chance of the order of 1 in 10 000 of dying of cancer due to the exposure. The figures were for a mixed population of smokers and non-smokers. Both meta-analyses concluded that amphiboles are many times more likely than chrysotile to cause mesothelioma, with much uncertainty about the exact ratio. Berman and Crump could not reject the hypothesis that tremolite-free chrysotile did not cause mesothelioma. The panel did not specifically endorse the figures. The author concluded that chrysotile risk remained a political issue but that wide agreement existed on the science.

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: Editorial describing an expert panel report; no new data or analysis
• Who was studied: No people were studied directly. The editorial concerned an expert panel convened by Health Canada in November 2007, which compared two meta-analyses of asbestos epidemiological studies: Hodgson and Darnton (2000) and Berman and Crump (2003 draft).
• Exposure: Chrysotile asbestos (in some cohorts with tremolite contamination), compared with amphiboles. Exposure was cumulative workplace exposure in fibre-years per millilitre, measured by phase contrast optical microscopy. The diseases were lung cancer and mesothelioma.
• Main results:
  • The two meta-analyses gave broadly similar risk estimates for chrysotile despite methodological differences.
  • Consider a worker exposed to chrysotile at work for 10 years at an average of 0.1 fibres per millilitre, a cumulative exposure of 1 fibre-year per millilitre. That worker's estimated probability of dying of cancer due to the exposure was of the order of 1 in 10 000.
  • Lung cancer deaths per 100 000 exposed at 1 fibre-year per millilitre: Berman and Crump 2.8, 8.3, 21; Hodgson and Darnton possibly 0, 2, 30. The middle figure is each analysis's best estimate. The outer figures are confidence limits (Berman and Crump) or cautious or arguable figures (Hodgson and Darnton).
  • Mesothelioma deaths per 100 000 exposed at 1 fibre-year per millilitre: Berman and Crump 0, 1, 8.2; Hodgson and Darnton 1, 5, 20.
  • In the Charleston textile plant cohort, the exposure-specific lung cancer risk lay above the confidence limits of all other chrysotile cohorts.
  • The report quoted Berman and Crump's 2003 conclusion on lung cancer. Amphiboles seemed to cause about twice as much disease as tremolite-free chrysotile at the same exposure, but the hypothesis that the two are equally potent could not be rejected.
  • For mesothelioma, both meta-analyses concluded that amphiboles are many times more likely to cause disease than chrysotile, with a lot of uncertainty about the actual potency ratio.
  • Berman and Crump could not reject the hypothesis that tremolite-free chrysotile did not cause mesothelioma.
  • All panel members agreed with the Consensus Report, but two recorded reservations.
• The authors' conclusion: The author concluded that the unexplained long delay in publishing the report showed that chrysotile risk was still a political issue, but that the report showed wide agreement now exists on the science.
• Limitations the authors state:
  • The panel supported the approaches of the two meta-analyses but did not specifically endorse their figures.
  • Because the two meta-analyses used different approaches, their estimates are not fully equivalent.
  • The figures apply to a mixed population of smokers and non-smokers. Lung cancer risk is probably higher for smokers and lower for non-smokers than shown.
  • At low exposures there are few epidemiological data to distinguish between the linear and non-linear models.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Chrysotile, Tremolite Contamination, Amphibole Group, Mesothelioma.

Related studies

• Canada, chrysotile, and the search for truth — T. Ogden (2008)
• Exposing the "myth" of ABC, "anything but chrysotile": a critique of the Canadian asbestos mining industry and McGill University chrysotile studies — D. Egilman, C. Fehnel, et al. (2003)
• Canadian hypocrisy regarding chrysotile — J. Bridle, J. Hoskins (2011)
• The biopersistence of Canadian chrysotile asbestos following inhalation: final results through 1 year after cessation of exposure — D. Bernstein, R. Rogers, et al. (2005)
• The biopersistence of Canadian chrysotile asbestos following inhalation — D.M. Bernstein, R. Rogers, et al. (2003)
• Statement in response to asbestos industry efforts to prevent a ban on asbestos in Pakistan: chrysotile asbestos use is not safe and must be banned — G. Aguilar Madrid, M. Beaudry, et al. (2013)

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