Surface reactivity of amphibole asbestos: a comparison between crocidolite and tremolite

Our plain-English summary of Surface reactivity of amphibole asbestos: a comparison between crocidolite and tremolite, by G.B. Andreozzi, A. Pacella, I. Corazzari, et al (Scientific Reports, 2017).

The study

• Authors: G.B. Andreozzi, A. Pacella, I. Corazzari, M. Tomatis, F. Turci
• Journal: Scientific Reports
• Published: 2017;7(1):14696
• Cited by: 25 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Among asbestos minerals, fibrous riebeckite (crocidolite) and tremolite share the amphibole structure but largely differ in terms of their iron content and oxidation state. In asbestos toxicology, iron-generated free radicals are largely held as one of the causes of asbestos malignant effect. With the aim of clarifying i) the relationship between Fe occurrence and asbestos surface reactivity, and ii) how free-radical generation is modulated by surface modifications of the minerals, UICC crocidolite and fibrous tremolite from Maryland were leached from 1 day to 1 month in an oxidative medium buffered at pH 7.4 to induce redox alterations and surface rearrangements that may occur in body fluids. Structural and chemical modifications and free radical generation were monitored by HR-TEM/EDS and spin trapping/EPR spectroscopy, respectively. Free radical yield resulted to be dependent on few specific Fe2+ and Fe3+ surface sites rather than total Fe content. The evolution of reactivity with time highlighted that low-coordinated Fe ions primarily contribute to the overall reactivity of the fibre. Current findings contribute to explain the causes of the severe asbestos-induced oxidative stress at molecular level also for iron-poor amphiboles, and demonstrate that asbestos have a sustained surface radical activity even when highly altered by oxidative leaching.

In plain English

This was a laboratory experiment on two asbestos fiber samples. No cells, animals or people were studied. The authors soaked a standard UICC crocidolite sample and a fibrous tremolite sample from Montgomery County, Maryland, for 1 day to 1 month in a hydrogen peroxide solution buffered at pH 7.4. They said these conditions were chosen to speed up fiber dissolution, not to mimic the cellular environment. They examined the fibers by electron microscopy and measured two kinds of iron-related free radicals the fibers produced. Untreated, both fibers produced radicals, and crocidolite was slightly less reactive than tremolite for hydroxyl radicals. After soaking, crocidolite's hydroxyl radical output rose to almost double. Tremolite's fell sharply in the first 24 hours and then slowly recovered. Carboxyl radicals appeared only when ascorbic acid was added. Their output became negligible for crocidolite from 48 hours on. For tremolite it fell to zero at 24 hours and rose again after 48 hours. The authors concluded that radical activity depended on specific surface iron sites rather than total iron content, and that it persisted even in highly altered fibers.

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 (cell-free) experiment: asbestos fibers soaked in an oxidative buffered solution for different times, then examined by electron microscopy and tested for free radical generation
• Who was studied: Two fiber samples: the UICC crocidolite (fibrous riebeckite) standard and a fibrous tremolite specimen from Montgomery County, Maryland (USA)
• Exposure: 25 mg of fibers suspended in 2 ml of 0.1 M hydrogen peroxide buffered with potassium phosphate at pH 7.4, for 24 h, 48 h, 168 h (1 week) and 720 h (1 month); untreated (pristine) fibers were also tested
• Main results:
  • Untreated (pristine) crocidolite and tremolite both generated hydroxyl and carboxyl radicals. Crocidolite was slightly less reactive than tremolite in hydroxyl radical release.
  • For both fibers, carboxyl radicals were generated only when ascorbic acid was present.
  • Electron microscopy showed alteration of the outer layers of crocidolite fibers after 24 hours of soaking. Tremolite was virtually unaltered after 24 and 48 hours.
  • Tremolite structure was virtually unaltered after 24 and 48 hours of soaking.
  • Soaked crocidolite produced significantly more hydroxyl radicals than untreated crocidolite, rising to almost double after 24 to 48 hours. Its carboxyl radical production dropped to zero.
  • Crocidolite carboxyl radical yield was measurable only for untreated fibers and fibers soaked for 24 hours, and was negligible from 48 hours onward.
  • Tremolite hydroxyl radical production fell sharply in the first 24 hours of soaking, then slowly recovered up to 1 month.
  • Tremolite carboxyl radical yield was highest in untreated fibers and fell to zero after 24 hours.
  • Tremolite carboxyl radical yield rose again after 48 hours and was sustained up to the longest soaking time.
• The authors' conclusion: The authors concluded that the surface reactivity of crocidolite and tremolite depended on specific surface iron sites rather than total iron content. They also concluded that the amphiboles kept sustained surface radical activity even when highly altered by oxidative soaking.
• Limitations the authors state:
  • The soaking conditions were not intended to mimic the cellular environment. They were chosen to speed up fiber dissolution within a reasonable experimental time.

Topics

Medical terms in this study, explained in our Lexicon: Surface Reactivity, Amphibole Asbestos, Crocidolite, Tremolite, Asbestos, Riebeckite, Amphibole Group, UICC.

Related studies

• Thermal inertization of amphibole asbestos modulates Fe topochemistry and surface reactivity — A. Pacella, M. Tomatis, et al. (2020)
• Iron topochemistry and surface reactivity of amphibole asbestos: relations with in vitro toxicity — A. Pacella, G.B. Andreozzi, et al. (2012)
• Surface chemistry and surface reactivity of fibrous amphiboles that are not regulated as asbestos — M. Fantauzzi, A. Pacella, et al. (2012)
• Surface reactivity and cell responses to chrysotile asbestos nanofibers — F. Turci, M. Colonna, et al. (2012)
• Surface reactivity in the pathogenic response to particulates — B. Fubini (1997)
• Immunological impact of graphene oxide sheets in the abdominal cavity is governed by surface reactivity — A.F. Rodrigues, L. Newman, et al. (2018)

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