Associated minerals in chrysotile deposits and their potential health risks

Our plain-English summary of Associated minerals in chrysotile deposits and their potential health risks, by E.J. Chatfield (Frontiers in Public Health, 2025).

The study

• Author: E.J. Chatfield
• Journal: Frontiers in Public Health
• Published: 2025;13:1583469
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Chrysotile samples from different deposits and the UICC-A and UICC-B standards have been analyzed by a procedure in which the chrysotile is removed by successive treatments in hydrochloric acid and sodium hydroxide, followed by transmission electron microscopy (TEM) examination of the residues. Two separate TEM fiber counts of a minimum of 100 fibers each were made for each sample: fibers longer than 5 μm and fibers with lengths between 0.5 μm and 5 μm. The tremolite/actinolite in each sample was quantified in terms of fibers/gram of chrysotile and as mass fraction in parts per million (ppm). Chrysotile from almost all of the commercial deposits examined was found to contain tremolite/actinolite. In particular, UICC-B Canadian chrysotile was found to contain an average of approximately 180 ppm tremolite/actinolite, equivalent to 1.25 × 107 fibers per gram (longer than 5 μm) of tremolite/actinolite, a proportion of which is asbestiform. The results also showed that both the UICC-B and UICC-A chrysotile standards are contaminated by Amosite. The primary grades of chrysotile from Coalinga, United States, and Minaçu, Brazil, were found to contain substantially less than 1 ppm of tremolite/actinolite. An asbestiform variety of the pyroxene diopside was detected in chrysotile from the Balangero mine in Italy. The asbestiform diopside has a fiber concentration and mass fraction comparable to those of tremolite/actinolite in chrysotile from other sources. Some of the diopside fibers are considerably longer than the tremolite/actinolite fibers found in other sources of chrysotile. Low levels (<4 ppm) of tremolite/actinolite were detected in Balangero chrysotile. No fibers with compositions consistent with Balangeroite were detected. It was found that Balangeroite does not survive the acid-alkali dissolution procedure, and it probably has durability comparable to that of chrysotile. Publications that claim the absence of tremolite/actinolite in UICC-B chrysotile were based on analytical methods that had insufficient sensitivity. Use of these analytical methods permitted only a 1 in 5 chance that a single tremolite/actinolite fiber would be detected. The concentrations of tremolite/actinolite and Amosite found in the reference UICC chrysotile standards raise questions as to the validity of historical biological experiments carried out using these materials.

Copyright © 2025 Chatfield.

In plain English

The author analyzed commercial chrysotile from mines in Canada, the United States, Brazil, Zimbabwe and Italy, plus the UICC-A and UICC-B reference standards. The chrysotile was dissolved in hydrochloric acid and sodium hydroxide, and the residue was examined by electron microscopy. Almost all commercial sources contained tremolite/actinolite. Samples from the Bell mine in Québec had the most, one at 10993.9 ppm (more than 1%). The three UICC-B samples averaged 179.17 ppm tremolite/actinolite, or 1.25 × 10^7 fibers longer than 5 μm per gram, and both UICC standards also contained amosite. Primary grades from Coalinga, California and Minaçu, Brazil had much less than 1 ppm. Chrysotile from Balangero, Italy contained asbestiform diopside fibers and very little tremolite/actinolite. No balangeroite was detected, and in a separate test balangeroite dissolved. Frank and colleagues had earlier found no tremolite in a count of 20,000 UICC-B fibers. The author calculated that such a count had only a 1 in 5 chance of detecting one tremolite fiber at least 0.5 μm long. The author concluded that the findings could raise questions about historical experiments using the UICC standards.

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. Chrysotile was dissolved by acid and alkali treatment, and the residue was examined by transmission electron microscopy (TEM).
• Who was studied: Production-grade commercial chrysotile samples from Canadian, United States, Brazilian, Italian (Balangero) and Zimbabwean mines, plus UICC-A and UICC-B chrysotile reference standards obtained from two separate sources.
• Exposure: Mineral fibers found alongside chrysotile: tremolite/actinolite, amosite, diopside and balangeroite. They were measured as fibers per gram of chrysotile (longer than 5 μm, and 0.5 to 5 μm) and as mass fraction in parts per million.
• Main results:
  • Bell mine chrysotile had the highest tremolite/actinolite content; one sample had a mass fraction of 10993.9 ppm (more than 1%).
  • UICC-B chrysotile (mean of three samples) contained 179.17 ppm tremolite/actinolite, or 1.25 × 10^7 fibers longer than 5 μm per gram.
  • Jeffrey mine chrysotile (mean of three results) contained 64.45 ppm tremolite/actinolite.
  • In UICC-B chrysotile, about 21.4% of tremolite/actinolite fibers longer than 5 μm were extra-criteria fibers. The author took this as confirming a substantial asbestiform proportion.
  • Amosite fibers were detected in both the UICC-A and UICC-B chrysotile standards.
  • Coalinga chrysotile: tremolite/actinolite was detected in 3 of 5 samples, at mass fractions much lower than 1 ppm.
  • Minaçu, Brazil chrysotile: the primary production grade (CB-4 T) had 0.11 ppm tremolite/actinolite. A short grade collected from baghouse filters (CB-7TF) had 14.80 ppm.
  • The two Zimbabwe chrysotile grades had 3.38 ppm and 1.44 ppm tremolite/actinolite.
  • All four Balangero chrysotile samples contained an asbestiform fiber identified as diopside.
  • No balangeroite fibers were detected in the Balangero samples. When a balangeroite sample was put through the same treatment, it did not survive.
  • The author calculated that in an analysis of 20,000 UICC-B chrysotile fibers, as in the Frank et al. report, there was only a 1 in 5 chance of detecting a single tremolite fiber 0.5 μm or longer.
• The authors' conclusion: The author concluded that the tremolite/actinolite content of UICC-B and UICC-A, and the presence of amosite in both standards, could raise questions about the validity or interpretation of historical biological experiments that used these materials.
• Limitations the authors state:
  • It is not known what weight of chrysotile is representative of its amphibole content.
  • Mass fraction values can be affected by a small number of unusually thick fibers.
  • The production dates of the Bell samples analyzed are unknown.
  • The apparent increase over time in tremolite/actinolite in Cassiar chrysotile may reflect different grades rather than time.
  • The Coalinga results were close to the analytical sensitivity of the method.

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: Chrysotile, UICC, Transmission Electron Microscopy (TEM), Tremolite, Actinolite, Fibers Per Gram, Asbestiform, Amosite.

Related studies

• Role of associated mineral fibres in chrysotile asbestos health effects: the case of balangeroite — F. Turci, M. Tomatis, et al. (2009)
• Measurement of elongate mineral particles: What we should measure and how do we do it? — E.J. Chatfield (2018)
• Analysis of amphibole asbestos in chrysotile and other minerals — J. Addison, L.S. Davies (1990)
• Pulmonary fibrosis in workers exposed to non-asbestiform tremolite asbestos minerals — H.Y. Yang, R.H. Shie, et al. (2013)
• Health risk of chrysotile revisited — 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)

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