Combined use of X-ray photoelectron and Mössbauer spectroscopic techniques in the analytical characterization of iron oxidation state in amphibole asbestos

Our plain-English summary of Combined use of X-ray photoelectron and Mössbauer spectroscopic techniques in the analytical characterization of iron oxidation state in amphibole asbestos, by M. Fantauzzi, A. Pacella, D. Atzei, et al (Analytical and Bioanalytical Chemistry, 2010).

The study

• Authors: M. Fantauzzi, A. Pacella, D. Atzei, A. Gianfagna, G.B. Andreozzi, A. Rossi
• Journal: Analytical and Bioanalytical Chemistry
• Published: 2010;396(8):2889-98
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos fibers are an important cause of serious health problems and respiratory diseases. The presence, structural coordination, and oxidation state of iron at the fiber surface are potentially important for the biological effects of asbestos because iron can catalyze the Haber-Weiss reaction, generating the reactive oxygen species *OH. Literature results indicate that the surface concentration of Fe(III) may play an important role in fiber-related radical formation. Amphibole asbestos were analyzed by X-ray photoelectron spectroscopy (XPS) and Mössbauer spectroscopy, with the aim of determining the surface vs. bulk Fe(III)/Fe(tot) ratios. A standard reference asbestos (Union Internationale Contre le Cancer crocidolite from South Africa) and three fibrous tremolite samples (from Italy and USA) were investigated. In addition to the Mössbauer spectroscopy study of bulk Fe(III)/Fe(tot) ratios, much work was dedicated to the interpretation of the XPS Fe2p signal and to the quantification of surface Fe(III)/Fe(tot) ratios. Results confirmed the importance of surface properties because this showed that fiber surfaces are always more oxidized than the bulk and that Fe(III) is present as oxide and oxyhydroxide species. Notably, the highest difference of surface/bulk Fe oxidation was found for San Mango tremolite--the sample that in preliminary cytotoxicity tests (MTT assay) had revealed a cell mortality delayed with respect to the other samples.

In plain English

This laboratory study examined asbestos fibers, not people or animals. The authors analyzed four amphibole asbestos samples: UICC reference crocidolite from South Africa and fibrous tremolite from Ala di Stura and San Mango (Italy) and Montgomery County, Maryland (USA). They compared the share of iron present as Fe(III), an oxidized form, at the fiber surface (by X-ray photoelectron spectroscopy) with that in the bulk (by Mössbauer spectroscopy). In the bulk, Fe(III) was 52% of the iron in crocidolite and 6% to 16% in the tremolites. At the surface, the Fe(III) ratio was 0.80 for crocidolite, 0.65 for San Mango and 0.70 for Maryland tremolite. The Ala di Stura surface iron could not be split into its forms because the sample held too little iron. Much surface Fe(III) was iron oxyhydroxide. San Mango tremolite's surface was ten times more oxidized than its bulk. The authors concluded that fiber surfaces were enriched in Fe(III), most markedly in tremolite. Separate preliminary cell tests, summarized here without methods or numbers, showed significant cell death with all samples, delayed with San Mango tremolite. The authors suggested its oxidized surface iron explained the delay.

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 mineral analysis comparing surface and bulk iron oxidation state of asbestos fibers by X-ray photoelectron spectroscopy and Mössbauer spectroscopy (no human or animal subjects)
• Who was studied: Four amphibole asbestos samples: UICC reference crocidolite from South Africa, and fibrous tremolite from Ala di Stura (Piedmont, Italy), San Mango (Calabria, Italy) and Montgomery County, Maryland (USA)
• Exposure: No human exposure was studied. The materials were crocidolite and fibrous tremolite asbestos. Hematite, maghemite and synthetic magnetite served as iron oxide reference materials.
• Main results:
  • In the bulk (Mössbauer), the tremolite samples were dominated by Fe(II). Their Fe(III) share of total iron ranged from 6% to 16% (corrected values: San Mango 6%, Ala di Stura 12%, Maryland 16%). UICC crocidolite had a corrected Fe(III) share of 52%.
  • At the fiber surface (XPS, second fitting approach), the Fe(III) to total iron ratio was 0.80 for UICC crocidolite, 0.65 for San Mango tremolite and 0.70 for Maryland tremolite.
  • Surface and bulk Fe(III) ratios differed in every sample. The San Mango tremolite surface was ten times more oxidized than its bulk.
  • A significant amount of surface Fe(III) was present as iron oxyhydroxide (FeOOH). The FeOOH share of surface iron was 0.62 for crocidolite, 0.65 for San Mango tremolite and 0.60 for Maryland tremolite.
  • Surface elemental composition agreed with bulk composition for all samples except UICC crocidolite. Its surface iron content was half that of the bulk (5.2 vs 10.7 atomic percent).
  • On the magnetite reference, the second XPS fitting approach gave a Fe(III) ratio of 0.68, against 0.67 by Mössbauer. The first approach gave 0.80. The authors judged the second approach more accurate.
  • The article briefly reported preliminary MTT cytotoxicity results from separate ongoing work (its reference 52). These showed significant mortality of cells kept in contact with the samples, and a delay of mortality for cells in contact with San Mango tremolite compared with the other amphibole asbestos. No methods or numerical results for these tests are given. The authors proposed that the oxidized surface iron could explain the delay.
• The authors' conclusion: The authors concluded that the surfaces of the studied samples were enriched in Fe(III), mainly present as FeOOH. They found the difference between surface and bulk particularly marked in the tremolite samples.
• Limitations the authors state:
  • For Ala di Stura tremolite, the surface iron signal could not be separated into Fe(II) and Fe(III). The sample contained little iron and gave a weak signal.
  • The surface atomic concentrations calculated from XPS were estimated to be accurate to within plus or minus 10%.
  • The first XPS fitting approach gave Fe(III) ratios that did not agree with the Mössbauer data. The authors attributed this to the complexity of fitting many multiplet peaks.

Topics

Medical terms in this study, explained in our Lexicon: Amphibole Asbestos, Reactive Oxygen Species (ROS), Crocidolite, Tremolite.

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