Can microwave radiation at high temperatures reduce the toxicity of fibrous crocidolite asbestos?

Our plain-English summary of Can microwave radiation at high temperatures reduce the toxicity of fibrous crocidolite asbestos?, by M. Gulumian, Z.L. Nkosibomvu, K. Channa, et al (Environmental Health Perspectives, 1997).

The study

• Authors: M. Gulumian, Z.L. Nkosibomvu, K. Channa, H. Pollak
• Journal: Environmental Health Perspectives
• Published: 1997;105 Suppl 5(Suppl 5):1041-4
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Exposure of animals and humans to crocidolite asbestos fibers produces fibrosis and two types of cancers: bronchogenic carcinoma and mesothelioma. It is therefore desirable to reduce toxicity of these fibers without affecting their other characteristics. In this study, commercial crocidolite asbestos fibers were radiated with microwave radiation at different temperatures. Radiated fibers and nonradiated original fibers were then studied by Mössbauer spectroscopy to quantify the amount of ferric and ferrous ions present at structurally different sites in each crocidolite sample. They were also studied for their ability to initiate the peroxidation of linoleic acid to assess the effect of radiation on this process. Results showed that microwave radiation reduced the total Fe2+/Fe3+ ratio. This reduction produced a concomitant decrease in the ability of the radiated samples to peroxidize linoleic acid.

In plain English

This was a laboratory study of crocidolite asbestos fibers. No people, animals or cells were tested. The authors microwaved crushed South African commercial crocidolite for 20 minutes at 300°C, or under carbon dioxide at 110 or 165°C. Using Mössbauer spectroscopy, they found that the 300°C treatment changed the ferrous-to-ferric iron ratio from 1.34 to 0.89 by converting ferrous to ferric iron at one crystal site (M1). In test-tube tests of fat breakdown (linoleic acid peroxidation), untreated crocidolite raised two hydroperoxides by factors of 3.40 and 2.47 versus no fiber. Fibers treated at 300°C changed these only nonsignificantly. Those fibers produced the same aldehyde products as untreated fibers, but at levels less significantly different from no-fiber controls (p = 0.28 for hexanal, p = 0.05 for 4-hydroxynonenal). Fibers treated at the lower temperatures produced significantly lower aldehyde levels than untreated fibers. The authors concluded that changing iron's oxidation state, especially at M1, can change the fibers' activity, and that the decrease in peroxidation may indicate reduced toxicity. They noted they could not separate the effects of heat and microwaves, and that cell tests are still needed.

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 experiment on mineral fibers (spectroscopy and cell-free lipid peroxidation tests); no humans, animals or cells
• Who was studied: Samples of local South African commercial crocidolite asbestos obtained from GENCOR (Griqualand Exploration and Finance, Kuruman, South Africa), crushed to about 3 micrometers in diameter and 5 to 10 micrometers in length
• Exposure: Microwave radiation (2.3 GHz at 7.5 kW) of crocidolite fibers for 20 min at 300°C. Other samples were radiated for 20 min under carbon dioxide at 110 or 165°C. All were compared with nonradiated original fibers.
• Main results:
  • In fibers radiated at 300°C, the ferrous iron population at the M1 site fell from 25% to 16%, and the ferric population at M1 rose from 22% to 32%
  • Radiation at 300°C changed the overall Fe2+/Fe3+ ratio from 1.34 (original fibers) to 0.89 (radiated fibers) by converting ferrous to ferric ions at the M1 site
  • Compared with fiber-free controls, original (untreated) crocidolite increased 9-HPODE by a factor of 3.40 (p = 0.003) and 13-HPODE by a factor of 2.47 (p = 0.0009)
  • Crocidolite radiated at 300°C produced only a small nonsignificant increase in 9-HPODE (1.4-fold, p = 0.131) and a nonsignificant decrease in 13-HPODE (p = 0.255) compared with controls
  • Original crocidolite increased the aldehyde end products hexanal (p = 0.0008) and 4-hydroxynonenal (p = 0.0005) compared with controls
  • Crocidolite radiated at 300°C produced the same aldehyde end products as the original crocidolite, but at levels less significantly different from fiber-free controls (p = 0.28 for hexanal, p = 0.05 for 4-hydroxynonenal)
  • Crocidolite radiated at 110 and 165°C under carbon dioxide produced significantly lower aldehyde concentrations than the original crocidolite fibers
• The authors' conclusion: The authors concluded that changing the oxidation state of iron, especially at the M1 site, can change the activity of crocidolite fibers. They stated that the decreased ability to initiate lipid peroxidation may be an indication of reduced toxicity.
• Limitations the authors state:
  • The experiments did not distinguish the role of heat from that of microwave radiation in converting ferrous to ferric ions
  • Mössbauer measurements for the samples radiated at 110 and 165°C were still in progress
  • Further tests on cells in culture are required to confirm reduced toxicity of radiated fibers
  • Fiber suspensions were harder to prepare from radiated samples than from original fibers, though only at the initial stages

Topics

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

Medical terms in this study, explained in our Lexicon: Crocidolite, Fibrosis, Bronchogenic Carcinoma, Mesothelioma.

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