The health effects of chrysotile: current perspective based upon recent data

Our plain-English summary of The health effects of chrysotile: current perspective based upon recent data, by D.M. Bernstein, J.A. Hoskins (Regulatory Toxicology and Pharmacology, 2006).

The study

• Authors: D.M. Bernstein, J.A. Hoskins
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2006;45(3):252-64
• Type of article: Review
• Cited by: 61 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This review substantiates kinetically and pathologically the differences between chrysotile and amphiboles. The serpentine chrysotile is a thin walled sheet silicate while the amphiboles are double-chain silicates. These different chemistries result in chrysotile clearing very rapidly from the lung (T(1/2)=0.3 to 11 days) while amphiboles are among the slowest clearing fibers known (T(1/2)=500 days to infinity). Across the range of mineral fiber solubilities chrysotile lies towards the soluble end of the scale. Chronic inhalation toxicity studies with chrysotile in animals have unfortunately been performed at very high exposure concentrations resulting in lung overload. Consequently their relevance to human exposures is extremely limited. Chrysotile following subchronic inhalation at a mean exposure of 76 fibers L>20 microm/cm(3) (3413 total fibers/cm(3)) resulted in no fibrosis (Wagner score 1.8-2.6), at any time point and no difference with controls in BrdU response or biochemical and cellular parameters. The long chrysotile fibers were observed to break apart into small particles and smaller fibers. Toxicologically, chrysotile which rapidly falls apart in the lung behaves more like non-fibrous mineral dusts while response to amphibole asbestos reflects its insoluble fibrous structure. Recent 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 have also differentiated between these two minerals. The most recent analyses also concluded that it is the longer, thinner fibers that have the greatest potency as has been reported in animal inhalation toxicology studies. However, one of the major difficulties in interpreting these studies is that the original exposure estimates rarely differentiated between chrysotile and amphiboles. Not unlike some other respirable particulates, to which humans are, or have been heavily occupationally exposed, there is evidence that heavy and prolonged exposure to chrysotile can produce lung cancer. The value of the present and other similar studies is that they show that low exposures to pure 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 if even any high exposures experienced were of short duration.

In plain English

This article is a review of mineralogical, animal and human (epidemiological) studies that distinguish chrysotile (white asbestos) from amphibole asbestos such as amosite, crocidolite and tremolite. The authors described chrysotile as a thin rolled sheet that breaks apart in the lung, while amphibole fibres resist dissolving. In animal studies they tabulated, chrysotile fibres longer than 20 micrometres cleared from rat lungs with half-times of 0.3 to 11.4 days, compared with 418 days for amosite and 536 days for crocidolite. The authors argued that earlier long-term animal studies of chrysotile used doses so high that the lung's clearance was overwhelmed. They summarised a separate 90-day rat study (Bernstein et al., 2006). In that study the lower dose caused no fibrosis, and the higher dose caused slight fibrosis. They also discussed reviews of studies in people, noting that past exposure estimates rarely separated chrysotile from amphiboles. The authors concluded that heavy and prolonged chrysotile exposure can produce lung cancer, but that low exposures to pure chrysotile do not present a detectable risk to health.

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 mineralogical, toxicological (animal and in-vitro) and epidemiological studies
• Who was studied: Published studies that differentiate the serpentine mineral chrysotile from amphiboles: animal inhalation studies (mainly in rats) and epidemiological reviews of exposed workers and residents
• Exposure: Chrysotile (a serpentine) compared with the amphiboles amosite, crocidolite, anthophyllite, tremolite and actinolite. In the animal studies, commercial chrysotiles (Calidria, Brazilian, Canadian textile grade) were compared with amphiboles and synthetic vitreous fibres.
• Main results:
  • In the clearance table the authors compiled from rat inhalation studies, half-times for fibres longer than 20 micrometres were 0.3 days for Calidria chrysotile, 1.3 days for Brazilian chrysotile and 11.4 days for Canadian textile-grade chrysotile. The same table gave 418 days for amosite and 536 days for crocidolite.
  • The authors argued that the chronic (long-term) rat inhalation studies of chrysotile were performed at very high exposure concentrations, under conditions of lung overload.
  • In a separate 90-day rat inhalation study they summarised (Bernstein et al., 2006, in Wistar male rats), chrysotile at a mean of 76 fibres longer than 20 micrometres per cubic centimetre (3413 total fibres per cubic centimetre) produced no fibrosis (Wagner score 1.8 to 2.6) at any time point. At this dose there was no difference from controls in BrdU response or in biochemical and cellular parameters.
  • In the same 90-day study, the higher exposure of 207 fibres longer than 20 micrometres per cubic centimetre (8941 total fibres per cubic centimetre) produced slight fibrosis.
  • In contrast, tremolite (an amphibole) produced granuloma, interstitial fibrosis, numerous macrophage aggregates and multinucleated giant cells after only 5 days of inhalation exposure in an earlier biopersistence study (Bernstein et al., 2005a).
  • Among the epidemiological analyses they reviewed, the authors reported that Hodgson et al. (2005) gave chrysotile zero weight in models of male mesothelioma deaths in Great Britain from 1968 to 2001. In those models, mesothelioma was explained by amosite and crocidolite.
• The authors' conclusion: The authors concluded that there is evidence that heavy and prolonged exposure to chrysotile can produce lung cancer. They also concluded that low exposures to pure chrysotile do not present a detectable risk to health, and that risk may be low if any high exposures were of short duration.
• Limitations the authors state:
  • The original exposure estimates in the epidemiological studies rarely differentiated between chrysotile and amphiboles.
  • The authors' lung-overload comparison cannot exclude the possibility that the small percentage of longer fibres caused the tumours seen in the chronic chrysotile studies.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Amphibole Group, Serpentine Group, Silicate, Double-Chain Silicate, Mineral Fiber, Fibrosis, Amphibole Asbestos.

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• Kerosene soot genotoxicity: enhanced effect upon co-exposure with chrysotile asbestos in Syrian hamster embryo fibroblasts — M. Lohani, E. Dopp, et al. (2000)
• Comparison of Calidria chrysotile asbestos to pure tremolite: inhalation biopersistence and histopathology following short-term exposure — D.M. Bernstein, J. Chevalier, et al. (2003)
• The toxicological response of Brazilian chrysotile asbestos: a multidose subchronic 90-day inhalation toxicology study with 92-day recovery to assess cellular and pathological response — D.M. Bernstein, R. Rogers, et al. (2006)
• Health risk of chrysotile revisited — D. Bernstein, J. Dunnigan, et al. (2013)
• Recent Scientific Evidence Regarding Asbestos Use and Health Consequences of Asbestos Exposure — M. Valenzuela, M. Giraldo, et al. (2016)

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