Activation of UICC crocidolite: the effect of conversion of some ferric ions to ferrous ions

Our plain-English summary of Activation of UICC crocidolite: the effect of conversion of some ferric ions to ferrous ions, by M. Gulumian, D.J. Bhoolia, R.S. Du Toit, et al (Environmental Research, 1993).

The study

• Authors: M. Gulumian, D.J. Bhoolia, R.S. Du Toit, R.E. Rendall, H. Pollak, J.A. van Wyk, M. Rhempula
• Journal: Environmental Research
• Published: 1993;60(2):193-206
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos fibers catalyze the generation of oxygen-centered radicals in the presence of oxygen or hydrogen peroxide. The amount of iron in asbestos fibers, its oxidation state, and its availability to specific chelating agents determine their ability to catalyze the aforementioned reactions. In the present study, the activation of UICC crocidolite was achieved by converting some of the ferric ions into ferrous ions. The activation process did not interfere with the size distribution, surface area, or crystal structure of these fibers. Although oxygen-centered radicals generated and lipid peroxidation produced by asbestos fibers are reported to play an important role in their toxicity, factors such as size, surface area, and durability are considered to be crucial determinants of fiber toxicity and carcinogenicity. The employment of the activated crocidolite in animal experiments to help further elucidate the importance of oxygen free radicals and lipid peroxidation in fiber-induced diseases is therefore proposed.

In plain English

This was a laboratory study of UICC reference crocidolite fibers, which the authors chemically modified ('activated') by passing pure hydrogen over packed fibers at 320°C and then characterised the treated and untreated fibers. Using Mössbauer spectroscopy, the authors reported that conversion of ferric to ferrous ions reached 57% in M1 sites and 82% in M2 sites, and that total ferrous ions across all cationic sites was 87% in the activated fibers compared with 46% in the native crocidolite; metallic iron was also formed. With the chelating agent, about five times more ferrous iron was mobilised from activated than from native crocidolite, and this was still possible 3 months after activation. In cell-free ESR and oxygen-uptake tests, the activated fibers reduced oxygen more, produced a higher level of hydroxyl radicals in a Fenton-type reaction, and completed lipid peroxidation in 1 day versus 3 days for native crocidolite. Fiber length and diameter distributions did not differ significantly between the samples. The authors proposed using such activated fibers in animal experiments.

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, cell-free) experimental study characterising chemically activated asbestos fibers
• Who was studied: UICC reference crocidolite fiber samples, native and hydrogen-activated; no humans or animals studied
• Exposure: activation of UICC crocidolite by heating packed fibers under flowing pure hydrogen, raised to 320°C over a 2-hr period and maintained for a further 16 hr, converting some ferric ions to ferrous ions
• Main results:
  • In the activated fibers, conversion of ferric to ferrous ions was 57% in M1 sites and 82% in M2 sites (Mössbauer spectroscopy)
  • Total ferrous ions in all cationic sites: 87% in activated crocidolite versus 46% in native crocidolite
  • With the chelating agent, five times more ferrous iron was mobilised from activated than from native UICC crocidolite
  • Mobilisation was still possible 3 months after activation of the fibers
  • Oxygen reduction by activated UICC crocidolite exceeded that by an equal concentration of native crocidolite (ESR with DMPO and formate)
  • Activated crocidolite produced a higher level of hydroxyl radicals than native fiber in a Fenton-type reaction with hydrogen peroxide
  • Activated crocidolite completed lipid peroxidation within 1 day, compared with 3 days for native crocidolite
  • Length and diameter distributions of activated and native fibers did not differ significantly (paired t tests)
  • The authors reported that activation increased surface activity, correlated to ferrous ion content, without altering physical characteristics of the fiber
• The authors' conclusion: The authors proposed that these activated fibers could be employed to further elucidate the role of surface active sites in cancer and other crocidolite asbestos-induced diseases

Topics

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

Medical terms in this study, explained in our Lexicon: UICC, Crocidolite, Crystal Structure.

Related studies

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• Crocidolite-induced lipid peroxidation in rat lung microsomes. I. Role of different ions — M. Gulumian, T.A. Kilroe-Smith (1987)
• Using in vitro iron deposition on asbestos to model asbestos bodies formed in human lung — Z. Shen, D. Bosbach, et al. (2000)
• Can microwave radiation at high temperatures reduce the toxicity of fibrous crocidolite asbestos? — M. Gulumian, Z.L. Nkosibomvu, et al. (1997)
• Microsomal lipid peroxidation and oxy-radicals formation are induced by insoluble iron-containing minerals — M. Fontecave, M. Jaouen, et al. (1990)

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