Carcinogenic implications of the lack of tremolite in UICC reference chrysotile

Our plain-English summary of Carcinogenic implications of the lack of tremolite in UICC reference chrysotile, by A.L. Frank, R.F. Dodson, M.G. Williams (American Journal of Industrial Medicine, 1998).

The study

• Authors: A.L. Frank, R.F. Dodson, M.G. Williams
• Journal: American Journal of Industrial Medicine
• Published: 1998;34(4):314-7
• Cited by: 31 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Using light and electron microscopy analysis, as well as electron diffraction, and energy-dispersive x-ray analysis, an aliquot of UICC chrysotile B was analyzed with special attention given to any tremolite contamination. Polarized light microscopy, with its limit of detection of approximately 1 micron when using dispersion staining, revealed chrysotile as the only fibrous asbestos component. Analytical electron microscopy at 333,000x of more than 20,000 consecutive fibers showed only the tubular morphology characteristic of chrysotile. These findings highlight that when this sample was used for exposure disease induced in animal models correlates with chrysotile-induced pathology, and does not support an explanation based on the "amphibole hypothesis." Thus, chrysotile should be considered as having the biologic ability to produce cancers, including mesotheliomas, based on the extensive use of this material as a standard reference material.

In plain English

This article reported a laboratory analysis of UICC chrysotile B, a widely used reference sample of chrysotile asbestos that the article describes as a mixture from eight Canadian mines. The authors searched it specifically for tremolite, a fiber some researchers had proposed as the real cause of disease attributed to chrysotile. Other researchers, cited by the authors, had earlier reported mesotheliomas in rats exposed to this same material. This study did not test animals. The authors combined 10 subsamples from the Pneumoconiosis Research Unit in Johannesburg. They examined fibers by electron microscopy, electron diffraction and x-ray analysis, and examined a separate 10-mg portion by polarized light microscopy. All of the following were identified as chrysotile: 500 randomly selected fibers, 20,000 additional consecutive fibers, and 50 fibers chosen because they looked amphibole-like. No tremolite was found. The authors concluded that the sample was uncontaminated by tremolite, at least below their methods' detection limits, and that chrysotile therefore must be able to produce mesotheliomas. They also concluded that their finding does not support the 'amphibole hypothesis.' They did not examine the 8% of nonfibrous material reported by another group.

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: Laboratory mineral analysis of a reference asbestos sample using electron microscopy (with electron diffraction and x-ray energy-dispersive spectroscopy) and polarized light microscopy; no human or animal subjects
• Who was studied: Aliquots of UICC chrysotile B reference asbestos obtained from the Pneumoconiosis Research Unit, Johannesburg; a representative sample was made by combining 10 separate subsamples, plus an additional 10-mg aliquot for polarized light microscopy
• Exposure: UICC chrysotile B, described as a mixture of chrysotile from eight Canadian mines, examined for tremolite contamination; fibers were compared against a NIST SRM 1867 tremolite asbestos standard
• Main results:
  • 500 randomly selected fibers were identified as chrysotile by morphology and electron diffraction, with x-ray spectroscopy as additional confirmation
  • 20,000 additional consecutive fibers examined by electron microscopy across five grids were all determined to be chrysotile
  • The data were never consistent with those from the NIST tremolite asbestos standard
  • 50 fibers deliberately selected because of their amphibole-like shape all gave chrysotile electron diffraction patterns
  • No tremolite fibers were identified among more than 20,000 fibers evaluated by transmission electron microscopy or in a 10-mg aliquot evaluated by polarized light microscopy
• The authors' conclusion: The authors concluded that the UICC chrysotile B sample was uncontaminated by tremolite, at least below the detection limits of their methods. They concluded that chrysotile therefore must be capable of producing mesotheliomas, given earlier animal studies using this material, and that the lack of tremolite does not support the amphibole hypothesis.
• Limitations the authors state:
  • The study did not examine the 8% of nonfibrous materials reported in the sample by Kohyama et al.
  • The finding of no tremolite applies only above the detection limits of the methods; polarized light microscopy had a detection limit of approximately 1 µm with dispersion staining

Topics

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

Medical terms in this study, explained in our Lexicon: Carcinogenic, Tremolite, UICC, Chrysotile, Tremolite Contamination, Polarized Light Microscopy (PLM), dispersion staining, Pathology.

Related studies

• 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)
• Comparison of Calidria chrysotile asbestos to pure tremolite: inhalation biopersistence and histopathology following short-term exposure — D.M. Bernstein, J. Chevalier, et al. (2003)
• Chrysotile and tremolite asbestos fibres in the lungs and parietal pleura of Corsican goats — P. Dumortier, F. Rey, et al. (2002)
• Chrysotile, tremolite, and mesothelioma — J.C. McDonald, A.D. McDonald (1995)
• 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)
• Malignant peritoneal mesothelioma in a 17-year-old boy with evidence of previous exposure to chrysotile and tremolite asbestos — A. Andrion, S. Bosia, et al. (1994)

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