Chrysotile: its occurrence and properties as variables controlling biological effects

Our plain-English summary of Chrysotile: its occurrence and properties as variables controlling biological effects, by A.M. Langer, R.P. Nolan (The Annals of Occupational Hygiene, 1994).

The study

• Authors: A.M. Langer, R.P. Nolan
• Journal: The Annals of Occupational Hygiene
• Published: 1994;38(4):427-51, 407
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Chrysotile formation arises through serpentinization of ultramafics and silicified dolomitic limestones. Rock types tend to control the trace metal content and both the nature and amounts of admixed minerals in the ore, such as fibrous brucite (nemalite) and tremolite. Some associated minerals and trace metals are thought to play a role in biological potential. Tremolite, one of the important associated minerals, may occur with different morphological forms, called habits. These habits range from asbestiform (tremolite asbestos) to common blocky or non-fibrous form (tremolite cleavage fragments). The latter is most common in nature. Tremolite in chrysotile ore varies in habit and concentration, both factors determining the degree of risk following inhalation. Tremolite fibre is thought to be important in relation to the occurrence of mesothelioma. Chrysotile fibrils may vary in diameter. Dust clouds generated following manipulation vary in fibre number and surface area. Chrysotile fibres exhibit a range of physical characteristics. The fibre may be non-flexible ('stiff') and low in tensile strength ('brittle'), and may lack an ability to curl. This fibre, referred to as 'harsh', sheds water more quickly than its curly, flexible 'soft' variety. The behaviour of the harsh fibres is more amphibole-like and their splintery nature suggests an enhanced inhalation potential. Slip fibre ore from Canada tends to contain more fibrous brucite (nemalite) than cross-fibre ore in the same mine. Industrial manipulation, which includes chemical treatment, heating and milling, may impart new surface properties to chrysotile dusts. Biological potential may be enhanced (opening of fibre bundles) or reduced (disruption of surface bonds and lessened ability to interact with organic moieties). Leaching of magnesium from chrysotile occurs at a pH less than about 10. Chrysotile has been demonstrated to lose magnesium in vivo and undergo clearance from the lung. The biological potential of magnesium-depleted chrysotile is much reduced, or even eliminated. Reduction of mesothelioma-inducing and cytotoxic potential has been observed and quantified experimentally. Use of chrysotile products in high-temperature environments may heat the mineral to the point where it undergoes alteration of properties, especially by dehydroxylation. Chrysotile ore may vary in properties and associated minerals: it may form aerosols with different size distributions, especially fibre/fibril diameters and surface areas; it may be associated with varying quantities of tremolite (with differing habits); it may be manipulated both industrially and environmentally to yield surfaces with different properties and, hence, differing biological potentials. Chrysotile's properties may vary from place to place and among different user industries.

In plain English

This paper, read at a 1993 workshop on health risks of chrysotile asbestos, was a review of chrysotile's mineralogy and of how its properties might influence its biological effects. The authors described how chrysotile forms from ultramafic rocks or silicified dolomites, and how the source rock shapes the minerals mixed into the ore, such as fibrous brucite (nemalite), magnetite and tremolite. They cited a study by Addison and Davies (1990) that found tremolite in 28 of 81 chrysotile samples, at an average concentration of 0.09%. In the authors' own laboratory, the tremolite found at very low concentrations in ore from the Bell mine, Thetford, Quebec, consisted of cleavage fragments, not asbestos fibres. They stated that any tremolite asbestos present must be below the detection level of about 0.01%. They also reported that soft chrysotile heated to between 200 and 400°C behaved like harsh fibre in water. The review also covered magnesium leaching, surface properties, industrial processing and the UICC chrysotile reference samples. The authors concluded that the mineral nature of chrysotile controls its biological behaviour.

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 chrysotile mineralogy, presented as a workshop paper. It includes a few observations from the authors' own laboratory.
• Who was studied: No human or animal population was studied. The paper reviewed published mineralogical and experimental literature on chrysotile ores from deposits around the world (Canada, Zimbabwe, South Africa, United States and others). The authors' own laboratory examined chrysotile ore from the Bell mine, Thetford, Quebec.
• Exposure: Chrysotile from ultramafic and silicified dolomite deposits, together with minerals mixed into the ore (tremolite, nemalite or fibrous brucite, magnetite and others). The paper also discussed the UICC chrysotile 'A' and 'B' reference samples and the effects of heating, milling and chemical treatment.
• Main results:
  • In a study the authors cited (Addison and Davies, 1990), tremolite was found in 28 of 81 chrysotile samples (about 34%), at an average concentration of 0.09%.
  • In the authors' laboratory, tremolite detected at very low concentrations by transmission electron microscopy in Bell mine ore (Thetford, Quebec) consisted of cleavage fragments, not asbestos fibres.
  • The authors stated that if tremolite asbestos was present in the Bell mine ore, its concentration must be below the detection level of about 0.01%.
  • In the authors' laboratory, soft chrysotile heated to between 200 and 400°C behaved like harsh fibre in water: it settled rapidly and did not form a gel.
  • Literature the authors reviewed reported that magnesium readily leaves the chrysotile fibre surface in dilute acids, or in water at a pH below 10.
  • The authors cited an animal study (Smith, 1974) in which harsh fibre produced a more rapid onset of malignant tumours in laboratory animals than identical amounts of soft fibre given the same way.
  • The authors cited epidemiological studies reporting that mesothelioma incidence was lower among Jeffrey miners and millers in Quebec than among Thetford workers in the same province.
• The authors' conclusion: The authors concluded that the mineral nature of chrysotile controls its biological behaviour, and that these factors must be considered in developing health criteria documents and in resolving health effects that follow exposure to dust.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Bell Asbestos mine, Thetford Mines, Quebec
• Jeffrey mine, Asbestos, Quebec

All asbestos mines

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Serpentinization, Dolomitic Limestone, Brucite, Tremolite, Habit, Asbestiform, Cleavage Fragment.

Related studies

• Reduction of the biological potential of chrysotile asbestos arising from conditions of service on brake pads — A.M. Langer (2003)
• The effects of naturally occurring acids on the surface properties of chrysotile asbestos — E.P. Holmes, L.M. Lavkulich (2014)
• Probing anisotropic surface properties and interaction forces of chrysotile rods by atomic force microscopy and rheology — D. Yang, L. Xie, et al. (2014)
• Peculiarities of the clastogenic properties of chrysotile-asbestos fibers and zeolite particles — A.D. Durnev, N.O. Daugel-Dauge, et al. (1993)
• Assessment of the physicochemical properties of chrysotile-containing brake debris pertaining to toxicity — M.S.P. Boyles, C.A. Poland, et al. (2019)
• How are the physical and chemical properties of chrysotile asbestos altered by a 10-year residence in water and up to 5 days in simulated stomach acid? — K. Seshan (1983)

Browse more research in The Annals of Occupational Hygiene, or return to medical research.