Some observations on the distribution of trace metals in chrysotile asbestos

Our plain-English summary of Some observations on the distribution of trace metals in chrysotile asbestos, by A. Morgan, A.E. Lally, A. Holmes (The Annals of Occupational Hygiene, 1973).

The study

• Authors: A. Morgan, A.E. Lally, A. Holmes
• Journal: The Annals of Occupational Hygiene
• Published: 1973;16(3):231-40
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The distribution of iron, chromium, nickel, cobalt and scandium in a number of samples of chrysotile asbestos, including the standard reference samples prepared under the auspices of the International Union Against Cancer (UICC) was investigated. The composition of material separated magnetically from chrysotile was examined, using radioactive tracer methods. The solubility of these elements was measured by leaching samples of chrysotile in N hydrochloric acid at 25 °C and compared with the solubility of the structural magnesium. These investigations show that all the metals considered can replace magnesium in the brucite layer of chrysotile. In addition, however, with the possible exception of scandium, they are also present in accessory minerals associated with the fibre.

PubMed has no abstract for this study. This is the authors' abstract, copied from the article.

In plain English

This laboratory study did not study people, animals or disease. The authors studied how iron, chromium, nickel, cobalt and scandium were held in chrysotile: the UICC reference samples, the rough milled samples they came from, eight Canadian mine samples and one Cassiar Mine sample. Using radioactive tracers, they measured iron, chromium, cobalt and scandium in magnetically separated material. They leached samples in acid, comparing each metal's dissolving rate with magnesium's, measuring nickel and magnesium by atomic absorption. The text said magnetic separation removed 19 to 53 per cent of the iron; the table lists up to 58. Separation removed 3 to 13 per cent of chromium, 7 to 23 per cent of cobalt and under 1 per cent of scandium (the text says none). The magnetic material was mainly magnetite. Scandium dissolved at a rate closely matching magnesium. Iron, chromium, cobalt and nickel were partly in the fibre, partly in other minerals such as magnetite and probably chromite. The authors concluded the distribution was complex, with most trace metals far more concentrated in mineral and alloy impurities than in the fibre.

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 study of chrysotile samples. It used neutron activation (radioactive tracers) and magnetic separation for iron, chromium, cobalt and scandium. It also used leaching in hydrochloric acid, with atomic absorption measurements of magnesium, iron and nickel.
• Who was studied: Chrysotile asbestos samples, not people. These were the UICC standard reference samples of Rhodesian (UICC A) and Canadian (UICC B) chrysotile, the rough milled samples they were prepared from, eight samples of Canadian chrysotile from different mines (Canadian A to H), and a sample from the Cassiar Mine, British Columbia (Cassiar AAA).
• Exposure: No human or animal exposure was studied. Samples of neutron-irradiated chrysotile of about 20 mg were leached in N hydrochloric acid at 25 degrees C, and magnetic material was separated out, to trace iron, chromium, nickel, cobalt and scandium. Manganese levels are also listed in a table.
• Main results:
  • The text states that the share of total iron removed by magnetic separation varied from 19 to 53 per cent. However, Table 2 lists iron values of 26, 54, 58, 19, 41, 43, 55, 40 and 36 per cent across the samples, reaching 58 per cent for Canadian Mine B. The article does not explain the difference.
  • Magnetic separation also removed 3 to 13 per cent of the chromium and 7 to 23 per cent of the cobalt. For scandium, the text says none was removed in any sample, while Table 2 lists less than 1 per cent.
  • The magnetically separated material consisted mainly of irregular particles of magnetite, generally less than 50 micrometres across.
  • Magnesium in UICC chrysotile B dissolved in acid more rapidly than magnesium in UICC chrysotile A.
  • Milling increased magnesium solubility: the UICC reference samples dissolved more readily than the rough milled samples they were made from. However, rough milled B dissolved faster than fine milled A, so the authors judged that other factors also matter.
  • Canadian sample B was reported by another study (Wagner et al.) to contain 20 per cent brucite. In this sample, the intercept of the leaching curve rose to about 35 per cent of the total magnesium.
  • In all samples, scandium dissolved at a rate closely matching magnesium. The authors read this as scandium occurring almost entirely as a substitute for magnesium within the fibre structure.
  • Some iron sat in the brucite layer of the fibre and dissolved with the magnesium. Most of the rest was accounted for by magnetite, which was relatively insoluble under these conditions.
  • In Canadian samples A, D, E and F, only part of the undissolved chromium could be accounted for by magnetite. Chromium-rich particles were seen, which the authors said probably represent chromite.
  • In the Rhodesian reference sample, Cassiar AAA and Canadian samples C, D and G, most of the cobalt was in the fibre's octahedral layer.
  • In Canadian samples A, D, E and especially H, part of the cobalt was present as a relatively soluble impurity.
  • Nickel generally behaved like cobalt.
• The authors' conclusion: The authors concluded that the distribution of trace metals in commercial chrysotile is complex. All the metals examined can substitute for magnesium in the fibre, and scandium appears to be present almost only in this form. In most samples the metals were also present in associated minerals and alloys, some relatively insoluble (magnetite and chromite) and others relatively soluble. The concentration of most trace metals was much greater in these mineral and alloy impurities than in the fibre itself.
• Limitations the authors state:
  • The chromium-rich particles seen after dissolving the fibre were not identified. The authors only said they probably represent chromite.
  • The acid treatment used to prepare standards for atomic absorption did not dissolve all the chromium in certain samples.
  • Measured weight loss during leaching appeared greater than the theoretical value. The authors attributed this to colloidal silica that centrifuging did not separate.

Mines named here

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

• Cassiar mine, British Columbia

All asbestos mines

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile, UICC, Brucite Layer, Accessory Mineral.

Related studies

• Asbestos fibers and trace metals in the blood of cattle grazing in fields inundated by asbestos-rich sediments — H. Schreier, J.A. Shelford, et al. (1986)
• Determination of iron, chromium, cobalt, nickel, and scandium in asbestos by neutron activation analysis — A. Holmes, A. Morgan, et al. (1971)
• Occurrence of heavy metal-resistance in microflora from serpentine soil of Andaman — A. Pal, S. Dutta, et al. (2005)
• Health effects of natural dust: role of trace elements and compounds — A.G. Cook, P. Weinstein, et al. (2005)
• Major and trace element compositions of the UICC standard asbestos samples — D.R. Bowes, C.M. Farrow (1997)
• Some observations on the in vitro cytotoxicity of chrysotile prepared by the wet dispersion process — I.P. Gormley, R.E. Bolton, et al. (1983)

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