Health risk of chrysotile revisited

Our plain-English summary of Health risk of chrysotile revisited, by D. Bernstein, J. Dunnigan, T. Hesterberg, et al (Critical Reviews in Toxicology, 2013).

The study

• Authors: D. Bernstein, J. Dunnigan, T. Hesterberg, R. Brown, J.A. Velasco, R. Barrera, J. Hoskins, A. Gibbs
• Journal: Critical Reviews in Toxicology
• Published: 2013;43(2):154-83
• Type of article: Review
• Cited by: 102 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

This review provides a basis for substantiating both kinetically and pathologically the differences between chrysotile and amphibole asbestos. Chrysotile, which is rapidly attacked by the acid environment of the macrophage, falls apart in the lung into short fibers and particles, while the amphibole asbestos persist creating a response to the fibrous structure of this mineral. Inhalation toxicity studies of chrysotile at non-lung overload conditions demonstrate that the long (>20 µm) fibers are rapidly cleared from the lung, are not translocated to the pleural cavity and do not initiate fibrogenic response. In contrast, long amphibole asbestos fibers persist, are quickly (within 7 d) translocated to the pleural cavity and result in interstitial fibrosis and pleural inflammation. Quantitative reviews of epidemiological studies of mineral fibers have determined the potency of chrysotile and amphibole asbestos for causing lung cancer and mesothelioma in relation to fiber type and have also differentiated between these two minerals. These studies have been reviewed in light of the frequent use of amphibole asbestos. As with other respirable particulates, there is evidence that heavy and prolonged exposure to chrysotile can produce lung cancer. The importance of the present and other similar reviews is that the studies they report show that low exposures to chrysotile do not present a detectable risk to health. Since total dose over time decides the likelihood of disease occurrence and progression, they also suggest that the risk of an adverse outcome may be low with even high exposures experienced over a short duration.

In plain English

This article reviewed laboratory, animal and worker studies comparing chrysotile with amphibole asbestos (amosite, crocidolite, tremolite). It was prepared with a grant from the International Chrysotile Association and reported no new data. In one reviewed laboratory study, chrysotile kept 30% of its weight after 24 weeks in fluid mimicking the inside of immune cells, versus 75% for amosite. In a reviewed 90-day rat inhalation study, the lower chrysotile dose caused no lung fibrosis and the higher dose caused slight fibrosis. In a 5-day rat inhalation study, amosite caused Wagner grade 4 interstitial fibrosis within 28 days after exposure and reached the pleural cavity within 7 days after exposure; chrysotile mixed with sanded joint compound caused no pathological response. The authors argued that South Carolina textile and Chinese plant cohorts, both reporting excess lung cancer, involved amphibole or other exposures. A reviewed Greek cement-factory study found a lung cancer SMR of 1.71 (95% CI 0.98–2.78), which was not statistically significant. The authors concluded that heavy, prolonged chrysotile exposure can produce lung cancer but low exposures do not present a detectable risk.

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 review of in-vitro, animal toxicology and epidemiology studies of chrysotile-only or predominantly chrysotile exposure, prepared with grant support from the International Chrysotile Association
• Who was studied: Published studies: in-vitro dissolution studies, rat and hamster inhalation studies, and worker cohorts and case-control studies (for example South Carolina textile workers, Quebec miners and millers, Balangero mine workers, asbestos-cement workers in the US, UK, Sweden and Greece, and a Chinese asbestos plant)
• Exposure: Chrysotile (serpentine) asbestos compared with amphibole asbestos (amosite, crocidolite, tremolite), including chrysotile in high-density cement products and in a joint compound
• Main results:
  • Reviewed in-vitro study (Osmond-McLeod et al. 2011): after 24 weeks in a fluid adjusted to mimic macrophage conditions, chrysotile was recovered at 30% of its original weight and amosite at 75%
  • Reviewed 90-day rat inhalation study of Brazilian chrysotile (Bernstein et al. 2006): the lower exposure (76 fibers longer than 20 µm per cm3; 3413 total fibers per cm3) produced no fibrosis at any time point after 92 days of recovery, and the higher exposure (207 fibers longer than 20 µm per cm3) produced slight fibrosis
  • Reviewed 5-day rat inhalation study (Bernstein et al. 2010, 2011): chrysotile with sanded joint compound particles produced no pathological response, and long chrysotile fibers cleared with a half-time of 4.5 days and were not seen in the pleural cavity. Amosite produced Wagner grade 4 interstitial fibrosis within 28 days after exposure, and long amosite fibers were seen in the pleural cavity within 7 days after exposure
  • Reviewed lung-burden study of the South Carolina textile plant (Green et al. 1997): 28% of textile workers and 13% of controls had crocidolite or amosite above 1 million fibers per g dry lung. The authors concluded the cohort was not a pure chrysotile cohort
  • Reviewed Chinese plant study (Yano et al. 2001) reported an adjusted relative risk of lung cancer of 8.1 (95% CI 1.8 to 36.1) for workers exposed to high versus low asbestos levels. The review authors argued that most of the measured dust was not chrysotile and that this was not a pure chrysotile exposure
  • Reviewed Greek asbestos-cement factory study (Sichletidis et al. 2009, 317 workers): overall mortality SMR was 0.71 (95% CI 0.53–0.93). Lung cancer SMR was 1.71 (95% CI 0.98–2.78), which was not statistically significant. No mesothelioma was reported
  • Reviewed European case-control study (Carel et al. 2007): the lung cancer odds ratio for asbestos exposure was 0.92 (95% CI 0.73–1.15) in Central and Eastern Europe and 1.85 (95% CI 1.07–3.21) in the UK. The review authors attributed the difference to amphibole use in the UK
• The authors' conclusion: The authors concluded that heavy and prolonged exposure to chrysotile can produce lung cancer, but that the studies reviewed show low exposures to chrysotile do not present a detectable risk to health
• Limitations the authors state:
  • The authors stated that the early epidemiology studies they reviewed were limited by use of the generic term asbestos and by incomplete occupational histories, so fiber-specific exposure was poorly characterized
  • The authors stated that in the predominantly chrysotile cohorts, fiber type and fiber length distributions were not measured from workplace air samples at the time of exposure

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Amphibole Asbestos, Macrophage, Pleural Cavity, Fibrogenic, Interstitial Fibrosis, Inflammation, Mineral Fiber.

Related studies

• Response to Murray M. Finkelstein, letter to the editor re Bernstein et al: Health risk of chrysotile revisited. Crit Rev Toxicol, 2013; 43(2): 154-183 — D. Bernstein, J. Dunnigan, et al. (2013)
• Letter to the Editor re Bernstein et al: Health risk of chrysotile revisited. Crit Rev Toxicol, 2013; 43(2): 154-183 — M.M. Finkelstein (2013)
• Sumas Mountain chrysotile induces greater lung fibrosis in Fischer344 rats than Libby amphibole, El Dorado tremolite, and Ontario ferroactinolite — J.M. Cyphert, A. Nyska, et al. (2012)
• 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)
• Electricians' chrysotile asbestos exposure from electrical products and risks of mesothelioma and lung cancer — J.E. Goodman, M.K. Peterson, et al. (2014)
• Minimising health hazards associated with derogated products and in-situ materials containing chrysotile contaminated with amphibole asbestos fibres — R.M. Howie (1999)

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