Chrysotile biopersistence: the misuse of biased studies

Our plain-English summary of Chrysotile biopersistence: the misuse of biased studies, by H. Pezerat (International Journal of Occupational and Environmental Health, 2009).

The study

• Author: H. Pezerat
• Journal: International Journal of Occupational and Environmental Health
• Published: 2009;15(1):102-6
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Although it is widely accepted that exposure to any asbestos type can increase the likelihood of lung cancer, mesothelioma, and non-malignant lung and pleural disorders, manufacturers and some chrysotile miners' unions contend that chrysotile either does not cause disease or that there is insufficient evidence to reach a conclusion. At the same time, Dr. D.M. Bernstein has published several animal studies, financed by the Québec Chrysotile Institute, to determine chrysotile biopersistence in the lungs. Bernstein's study protocol induces a very short fiber half-life, from which he concludes weak chrysotile carcinogenicity. Bernstein's findings contradict results obtained by independent scientists. Bernstein's results can only be explained by an aggressive pre-treatment of fibers, inducing many faults and fragility in the fibers' structure, leading to rapid hydration and breaking of long fibers in the lungs.

In plain English

This article is a commentary by a single author, not a new experiment. The author reviewed published rat inhalation studies by D.M. Bernstein and colleagues on how long chrysotile asbestos fibers stay in the lungs, called biopersistence. Early studies were funded by Union Carbide and later ones through the Chrysotile Institute. The author compared them with work by other teams, mainly Coin et al. In Bernstein's studies, fiber half-life ranged from 16 days for Canadian chrysotile to 7 hours for Calidria chrysotile. For Canadian chrysotile, Bernstein reported a 16-day half-life for fibers over 20 micrometers. Coin et al. reported a minimum of 114 days for fibers over 16 micrometers. The author argued that lung overload did not explain this gap. Instead, the author pointed to how Bernstein prepared the fibers, including settling them in water and high-speed grinding, which likely damaged them. The author concluded that these studies lack scientific rigor and credibility. In comparing the two teams' Canadian chrysotile results, the author noted that they used different samples and that neither specified the nature of the treatment its material received before the rats were exposed.

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: Commentary and critical review of published animal inhalation studies on chrysotile biopersistence; no new data
• Who was studied: Published rat inhalation studies by Bernstein and colleagues (references 18 to 24), compared with studies by other teams, chiefly Coin et al. (1992, 1994), and also Kimizuka et al. and Roggli and colleagues
• Exposure: Inhaled chrysotile from Canadian, Calidria (United States) and Brazilian mines. Bernstein's rats were exposed 6 hours a day for 5 consecutive days; Coin's rats had a single 3-hour exposure
• Main results:
  • In Bernstein's studies, chrysotile fiber half-life ranged from 16 days (Canadian chrysotile) to 7 hours (Calidria chrysotile). The author attributed this range to differences in the geological history of the mines.
  • For Canadian chrysotile, Bernstein reported a half-life of 16 days for fibers over 20 micrometers. Coin et al. reported a minimum half-life of 114 days for fibers over 16 micrometers.
  • The two teams found opposite patterns. In Coin et al., fibers of 0.5 to 4 micrometers had a half-life of about 10 days, compared with 114 days for fibers over 16 micrometers. In Bernstein et al., fibers over 20 micrometers had a half-life of 16 days, compared with 107 days for fibers under 5 micrometers.
  • Bernstein's fiber preparation included pre-selecting long fibers by settling them in water (1994 article) and a high-speed grinding method (2003 article on Canadian chrysotile). The author argued that such treatment damages fiber structure and shortens half-life.
  • The author argued that lung overload and an excess of short fibers in Coin's study did not explain the difference. In Coin's study, the total lung load was about 30 micrograms, and 32% of deposited fibers were shorter than 4 micrometers one day after exposure. Bernstein et al. reported that 88% of deposited fibers were shorter than 5 micrometers one day after exposure ended.
  • Funding of the reviewed Bernstein studies: early studies by the Union Carbide Corporation, later studies by asbestos producers through the Chrysotile Institute.
• The authors' conclusion: The author concluded that Bernstein's chrysotile studies lack scientific rigor and credibility. In the author's view, their short half-life results are likely linked to the preliminary handling of the fiber samples, and they do not justify the claim that chrysotile behaves as a particle rather than a fiber.
• Limitations the authors state:
  • In the comparison of Canadian chrysotile results, the Bernstein and Coin teams did not study the same sample, and neither specified the nature of the treatment its material received before the rats were exposed.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, biopersistence, Lung Cancer, Mesothelioma, Chrysotile Institute.

Related studies

• Continued controversy on chrysotile biopersistence — K. Donaldson, G. Oberdörster (2011)
• Chrysotile biopersistence in the lungs of persons in the general population and exposed workers — A.M. Langer, R.P. Nolan (1994)
• Comparison of Calidria chrysotile asbestos to pure tremolite: final results of the inhalation biopersistence and histopathology examination following short-term exposure — D.M. Bernstein, J. Chevalier, et al. (2005)
• The importance of fiber biopersistence and lung dose in determining the chronic inhalation effects of X607, RCF1, and chrysotile asbestos in rats — T.W. Hesterberg, G.A. Hart, et al. (1998)
• 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 brazilian chrysotile asbestos following inhalation — D.M. Bernstein, R. Rogers, et al. (2004)

Browse more research in International Journal of Occupational and Environmental Health, or return to medical research.