Acid leaching studies of neutron-irradiated chyrsotile asbestos

Our plain-English summary of Acid leaching studies of neutron-irradiated chyrsotile asbestos, by A. Morgan, R.J. Talbot (The Annals of Occupational Hygiene, 1997).

The study

• Authors: A. Morgan, R.J. Talbot
• Journal: The Annals of Occupational Hygiene
• Published: 1997;41(3):269-79
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Samples of chrysotile from Quebec (UICC B and Jeffrey 4T-30) and from the Coalinga region of California (Calidria RG-144) were irradiated with thermal neutrons in a reactor. The main activation products induced were 46Sc, 51Cr, 59Fe and 60Co. Accurately weighed samples of the irradiated materials were dispersed in N HCl by hand shaking for 10 s. After leaching for predetermined periods at 25 degrees C, the samples were filtered and the concentrations of Mg determined in the filtrates by inductively-coupled plasma atomic emission spectrometry (IPC-AES) and the activities of the four radionuclides by high resolution gamma-ray spectrometry. Similar measurements were made on solutions obtained by refluxing samples of irradiated chrysotile with 2N HCl for 2 h. The specific activities of each of the four activation products were calculated in arbitrary units and, as the concentrations of Sc, Cr, Fe and Co in the UICC B sample had already been determined, it was possible to estimate the concentrations of these elements in the other two samples. Similarities in the leaching patterns of magnesium and of the activation products showed that with all samples, high proportions of the parent trace elements were present in the form of isomorphous substitutes for magnesium in structural brucite. Agreement was closest with the Calidria chrysotile in which all the radionuclides had a similar pattern. With the Jeffrey and UICC B samples, the presence of a high proportion of the iron as relatively insoluble magnetite accounted for the observed discrepancy in behaviour between 59Fe and Mg. More detailed calculation of leaching rates over specific time intervals showed that, initially, 51Cr and 60Co dissolved more rapidly than Mg but that this was followed by a period in which the opposite was the case. It was concluded that the Calidria RG-144 sample is an ideal candidate for studies of magnesium dissolution in vivo.

In plain English

This was a laboratory study of chrysotile asbestos samples. It did not study people or health effects. The authors used three samples: UICC B, a reference sample blended from eight mines (seven in Quebec, one in British Columbia); Jeffrey 4T-30, from the Jeffrey mine in Quebec; and Calidria RG-144, from the Coalinga region of California. The samples were irradiated with neutrons in a reactor, which made trace scandium, chromium, iron and cobalt radioactive. They were then left in hydrochloric acid for set times at 25°C, and the authors compared how fast magnesium and these radioactive traces dissolved. The patterns were broadly similar, which the authors took to mean that most of the trace elements sat in place of magnesium in the fiber structure. The exception was iron in the UICC B and Jeffrey samples. Only about 50% of it had dissolved when virtually all the magnesium had, and the authors linked this to magnetite. Chromium and cobalt dissolved faster than magnesium in the first 2 minutes, but more slowly between 1 and 20 hours. Most measurements were single ones. The authors concluded that Calidria RG-144 would be an ideal candidate for studies of magnesium dissolution in vivo (in the living body).

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 (in vitro) acid-leaching experiment on neutron-irradiated chrysotile samples
• Who was studied: Three chrysotile samples, two portions (about 200 mg) of each: UICC B Standard Reference Sample (bulked from eight mines, seven in Quebec and one in British Columbia), Jeffrey 4T-30 (Jeffrey mine, Quebec) and Calidria RG-144 (Calidria mine, Coalinga region, California). They were irradiated in the University of London reactor at Silwood Park.
• Exposure: Chrysotile irradiated with thermal neutrons for a total of 120 h, producing radioactive forms of the trace elements scandium, chromium, iron and cobalt. Portions were then leached in N HCl at 25°C for set times. Magnesium was measured by ICP-AES and the radioactive traces by gamma-ray spectrometry. Total contents were measured by refluxing in 2N HCl for 2 h.
• Main results:
  • The total magnesium measured was slightly lower (95-98%) than in the authors' previous study. The magnesium leaching curves were very similar to those reported before for the same samples, so the authors judged that neutron irradiation had not significantly affected magnesium solubility.
  • Estimated trace element contents were Fe 2.8%, Cr 455 ppm, Co 45 ppm and Sc 6 ppm for Jeffrey 4T-30, and Fe 1.6%, Cr 1690 ppm, Co 65 ppm and Sc 6 ppm for Calidria RG-144. The Calidria sample had less iron than is generally found in Quebec samples and about three times more chromium.
  • In all samples, the similar leaching patterns of magnesium and the radioactive traces indicated that, in most cases, high proportions of the trace elements were present as substitutes for magnesium in the fiber structure.
  • In the UICC B and Jeffrey samples, only about 50% of the radioactive iron (59Fe) had been leached when virtually all the magnesium had dissolved, which the authors linked to iron present as magnetite. In Calidria RG-144, iron behaved much more like magnesium, which the authors put down to the virtual absence of magnetite.
  • In all samples, radioactive chromium and cobalt dissolved faster than magnesium in the first 2 minutes. Rates were similar between 2 minutes and 1 hour, and magnesium dissolved faster between 1 hour and 20 hours. At later times the rates were similar within experimental error.
  • After refluxing, filtered-to-unfiltered activity ratios were mostly below 1 for all radionuclides except 59Fe. This indicated that small fractions of the other radionuclides stayed undissolved.
• The authors' conclusion: The authors concluded that Calidria RG-144 chrysotile would be an ideal candidate for studies of magnesium dissolution in vivo, because of its low levels of non-fibrous impurities and because its radioactive chromium and cobalt dissolved in a pattern similar in overall shape to magnesium. Whether the method works for less pure Quebec materials would need further study.
• Limitations the authors state:
  • Because little irradiated material was available, most data points were single measurements.
  • Because most leaching-rate points were individual measurements, no indication of errors could be given.
  • Scandium that dissolves in vivo is partly retained in organs, which limits its usefulness as a stand-in for magnesium.
  • Trial intratracheal instillation studies indicated that the radioactivity achieved was too low, and higher specific activities would be needed for in vivo studies.
  • Applying the method to less pure Quebec materials would require further studies.

Mines named here

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

• Jeffrey mine, Asbestos, Quebec
• Santa Rita mine, Joaquin Ridge near Coalinga, California

All asbestos mines

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, UICC, Calidria, Brucite.

Related studies

• Acid leaching studies of chrysotile asbestos from mines in the Coalinga region of California and from Quebec and British Columbia — A. Morgan (1997)
• Determination of iron, chromium, cobalt, nickel, and scandium in asbestos by neutron activation analysis — A. Holmes, A. Morgan, et al. (1971)
• Asbestiform minerals in ophiolitic rocks of Calabria (southern Italy) — A. Campopiano, A. Olori, et al. (2018)
• Chrysotile, tremolite, and mesothelioma — J.C. McDonald, A.D. McDonald (1995)
• Mineralogical and exposure determinants of pulmonary fibrosis among Québec chrysotile miners and millers — A. Nayebzadeh, B.W. Case, et al. (2006)
• Characterization of Lone Pine, California, tremolite asbestos and preparation of research material — M. Harper, B. Van Gosen, et al. (2015)

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