Surface chemistry and surface reactivity of fibrous amphiboles that are not regulated as asbestos

Our plain-English summary of Surface chemistry and surface reactivity of fibrous amphiboles that are not regulated as asbestos, by M. Fantauzzi, A. Pacella, J. Fournier, et al (Analytical and Bioanalytical Chemistry, 2012).

The study

• Authors: M. Fantauzzi, A. Pacella, J. Fournier, A. Gianfagna, G.B. Andreozzi, A. Rossi
• Journal: Analytical and Bioanalytical Chemistry
• Published: 2012;404(3):821-33
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Three fibrous amphiboles that are not regulated as asbestos--two from Biancavilla (Sicily, Italy) and one from Libby (MT, USA)--were studied in order to establish relationships between surface chemistry and surface reactivity. The three fibrous samples, plus one prismatic fluoro-edenite from Biancavilla that was used for comparison, were investigated by X-ray photoelectron spectroscopy (XPS) in order to obtain their quantitative surface compositions and to determine the chemical environment of the Fe in each case. In particular, the Fe 2p(3/2) peak was fitted and, for the first for these materials, the binding energies of Fe(II) oxide, Fe(III) oxide and Fe(III) oxyhydroxide were identified. Bulk chemistries and Fe oxidation states were obtained from previous studies for the samples from Biancavilla, and were investigated in the present work by electron microprobe (EMP) and (57)Fe Mössbauer spectroscopy (MS) for the sample from Libby. Comparison between surface and bulk data revealed that the sample with the lowest bulk Fe oxidation state was the one most affected by surface oxidation, while the samples with bulk highly-oxidised Fe were showing very high signal of Fe (III) oxy-hydroxide probably due to weathering. The surface reactivities of the fibrous amphiboles were investigated by measuring the production of the [DMPO, HO]• radical adduct using electron paramagnetic resonance (EPR) spectroscopy. Notably, significant chemical reactivity was observed; it was found to be comparable with--or, for the Libby sample, even higher than--that of fibrous tremolite (one of the six asbestos minerals). A positive linear correlation was observed when the production of HO• radical was plotted versus the Fe(II) content on the fibre surface. Data on fibrous tremolite obtained from previous studies were added to substantiate the correlation. These results provide evidence that Fe(II) at the fibre surface controls the production of radicals at the fibre surface. The observed relationship provides further confirmation that Fe topochemistry is strictly related to--though not solely responsible for--the toxicity of asbestos and other fibrous amphiboles that are not regulated as asbestos.

In plain English

This laboratory study examined mineral samples, not people or animals. The authors analyzed three fibrous amphiboles that are not regulated as asbestos. Two came from Biancavilla in Sicily, Italy, and one from the vermiculite mine at Libby, Montana, USA. A non-fibrous (prismatic) fluoro-edenite from Biancavilla was included for comparison. The authors measured the chemistry of the fiber surfaces, especially the form of iron present. They also tested how much of a reactive chemical, the hydroxyl radical, the fibers produced in a hydrogen peroxide solution. Less-oxidized iron, Fe(II), was found on the surfaces of Biancavilla sample 1 and the Libby sample. Only oxidized iron was found on the surface of Biancavilla sample 4. Radical production by the fibrous samples was comparable to that of fibrous tremolite from earlier studies, or higher for the Libby sample. It was markedly lower than that of UICC crocidolite. Radical production did not correlate well with total iron but tracked surface Fe(II). The authors concluded that iron chemistry is related to, though not solely responsible for, asbestos toxicity.

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 mineral samples: surface chemistry by X-ray photoelectron spectroscopy, bulk chemistry of the Libby sample by electron microprobe and Mössbauer spectroscopy, and hydroxyl radical production measured by electron paramagnetic resonance spectroscopy
• Who was studied: Four mineral samples: two fibrous amphiboles from Biancavilla, Sicily, Italy (samples 1 and 4), one fibrous amphibole from the vermiculite mine of Libby, Montana, USA, and one prismatic fluoro-edenite from Biancavilla (FB-p) used for comparison
• Exposure: Fibrous amphiboles not regulated as asbestos. The Biancavilla fibrous samples had average compositions in the tremolite region, with fluoro-edenite and winchite components. The Libby sample's mean composition corresponded to richterite, with minor winchite components.
• Main results:
  • In the Libby fibrous sample, iron in the bulk mineral was 68% Fe(III) based on measured spectral area and 64% after correction. Bulk values for the Biancavilla samples were taken from previous studies: 54% for sample 1, 94% for sample 4 and 92% for the prismatic fluoro-edenite.
  • Fe(II) was present on the surfaces of sample 1 (0.13 of surface iron) and the Libby sample (0.30). Fe(III) was the only form of surface iron on sample 4 and the prismatic fluoro-edenite.
  • For Biancavilla sample 1, surface iron was more oxidised than iron in the bulk mineral. Only very small surface-to-bulk differences were seen for sample 4, Libby and the prismatic fluoro-edenite.
  • Iron, magnesium and calcium were depleted on the surfaces of all the fibrous samples compared with the bulk.
  • Hydroxyl radical production by the fibrous samples was at least comparable with that of fibrous tremolite (data from previous studies) for the Biancavilla fibres, and higher for the Libby fibres. The authors described it as markedly lower than that of UICC crocidolite.
  • Radical production did not correlate very well with total iron content.
  • Radical production correlated with Fe(II) content at the fiber surface, including when data from fibrous tremolite samples in previous studies were added.
• The authors' conclusion: The authors concluded that surface Fe(II) controls hydroxyl radical production by these fibers, and that iron topochemistry is strictly related to, though not solely responsible for, the toxicity of asbestos and of fibrous amphiboles not regulated as asbestos.
• Limitations the authors state:
  • The authors said they did not have enough information to determine why sample 1 showed strong surface oxidation while the Libby sample did not. They suggested possibly different geological or weathering histories.
  • The correlation line between radical production and surface Fe(II) did not clearly pass through zero (intercept 6, uncertainty 4), meaning some activity appeared at zero surface Fe(II). The authors tentatively explained this by surface measurements being made on unaltered fibres, while radical measurements were made after incubation, during which fibres may dissolve slightly.

Mines named here

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

• Libby vermiculite mine, Montana

All asbestos mines

Topics

Medical terms in this study, explained in our Lexicon: Surface Reactivity, Amphibole Group, Biancavilla, fluoro-edenite, Electron Microprobe Analysis, Tremolite, Asbestos.

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