A biomimetic approach to the chemical inactivation of chrysotile fibres by lichen metabolites

Our plain-English summary of A biomimetic approach to the chemical inactivation of chrysotile fibres by lichen metabolites, by F. Turci, S.E. Favero-Longo, M. Tomatis, et al (Chemistry, 2007).

The study

• Authors: F. Turci, S.E. Favero-Longo, M. Tomatis, G. Martra, D. Castelli, R. Piervittori, B. Fubini
• Journal: Chemistry
• Published: 2007;13(14):4081-93
• Cited by: 26 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Some lichens were recently reported to modify the surface state of asbestos. Here we report some new insight on the physico-chemical modifications induced by natural chelators (lichen metabolites) on two asbestos samples collected in two different locations. A biomimetic approach was followed by reproducing in the laboratory the weathering effect of lichen metabolites. Norstictic, pulvinic and oxalic acid (0.005, 0.5 and 50 mM) were put in contact with chrysotile fibres, either in pure form (A) or intergrown with balangeroite, an iron-rich asbestiform phase (B). Mg and Si removal, measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), reveals an incongruent dissolution for pure chrysotile (A), with Mg removal always exceeding that of Si, while chrysotile-balangeroite (B) follows a congruent dissolution pattern in all cases except in the presence of 50 mM oxalic acid. A much larger removal of Mg than Si in the solutions of 0.5 and 50 mM oxalic acid with chrysotile (A) suggests a structural collapse, which in the case of chrysotile-balangeroite (B) only occurs with 50 mM oxalic acid; in these cases both samples are converted into amorphous silica (as detected by X-ray diffraction (XRD)). Subsequent to incubation, some new phases (Fe(2)O(3), CaMg(CO(3))(2), Ca(C(2)O(4)) x H(2)O and Mg(C(2)O(4))2 x H(2)O), similar to those observed in the field, were detected by XRD and micro-Raman spectroscopy. The leaching effect of lichen metabolites also modifies the Fenton activity, a process widely correlated with asbestos pathogenicity: pure chrysotile (A) activity is reduced by 50 mM oxalic acid, while all lichen metabolites reduce the activity of chrysotile-balangeroite (B). The selective removal of poorly coordinated, highly reactive iron ions, evidenced by NO adsorption, accounts for the loss in Fenton activity. Such fibres were chemically close to the ones observed in the field. Chrysotile-rich rocks, colonised by lichens, could be exposed to a natural bioattenuation and considered as a transient environmental hazard.

In plain English

This was a laboratory experiment on mineral samples. The authors tried to reproduce how lichens weather asbestos by soaking two Italian chrysotile samples for 35 days in solutions of lichen chemicals: oxalic acid (0.005, 0.5 and 50 millimolar), norstictic acid and pulvinic acid. One sample was relatively pure chrysotile. The other, from the Balangero asbestos mine, was chrysotile intergrown with balangeroite, an iron-rich asbestiform mineral. In the pure chrysotile, 0.5 and 50 millimolar oxalic acid leached out 59% and 84% of the magnesium. Both samples were completely transformed after 50 millimolar oxalic acid. The authors measured hydroxyl radical release from hydrogen peroxide (Fenton activity), which they describe as widely correlated with asbestos pathogenicity. For pure chrysotile it fell significantly only after 50 millimolar oxalic acid. For chrysotile–balangeroite it fell after norstictic acid, pulvinic acid and 0.5 millimolar oxalic acid. After 50 millimolar oxalic acid it showed a variable but significant restoration. The authors concluded that lichens are possible bioattenuating organisms for asbestos-polluted rocks.

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 (biomimetic) experiment on asbestos mineral samples incubated with lichen metabolites; no human or animal subjects
• Who was studied: Two asbestos samples from Italian outcrops. (A) A relatively pure chrysotile from Val Malenco, Sondrio. (B) Chrysotile intergrown with iron-rich asbestiform balangeroite (ratio about 3:2) from the Balangero asbestos mine, Val di Lanzo, Torino.
• Exposure: Fibres were incubated for 35 days at 25 degrees C in the dark in lichen metabolite solutions. Oxalic acid was used at 0.005, 0.5 and 50 millimolar, norstictic acid at about 0.004 millimolar and pulvinic acid at about 0.003 millimolar. Water was used as a blank.
• Main results:
  • Pure chrysotile: after 0.5 and 50 millimolar oxalic acid, the magnesium leached was 59% (149 mg per litre) and 84% (212 mg per litre) of the sample's total magnesium content (252 mg per litre).
  • Chrysotile–balangeroite: only 50 millimolar oxalic acid produced deeper leaching, up to 64 mg per litre of silicon and 152 mg per litre of magnesium.
  • Both samples were completely transformed (X-ray diffraction showed an amorphous residue) after 50 millimolar oxalic acid. They kept their crystallinity with the other treatments.
  • In untreated samples, chrysotile–balangeroite released significantly fewer hydroxyl radicals than pure chrysotile.
  • Pure chrysotile: hydroxyl radical release (Fenton activity) was significantly decreased only after 50 millimolar oxalic acid, with wide variability. Other treatments were not significantly different from the water blank.
  • Chrysotile–balangeroite: Fenton activity was significantly reduced after norstictic acid, pulvinic acid and 0.5 millimolar oxalic acid, compared with the blank. 0.005 millimolar oxalic acid did not affect it.
  • Chrysotile–balangeroite leached with 50 millimolar oxalic acid showed a variable but significant restoration of Fenton activity.
  • In the leached chrysotile–balangeroite samples, nitric oxide adsorption no longer detected the trinitrosyl signal. The authors attribute this signal to the least-coordinated, most reactive surface iron, and its loss to removal of that iron.
• The authors' conclusion: The authors concluded that the study confirms lichens as possible bioattenuating microorganisms for asbestos-polluted rocks, modifying fibre reactivity and ultimately turning fibres into amorphous non-toxic silica debris. They also concluded that the effect was more pronounced on chrysotile–balangeroite than on pure chrysotile. They suggested that 50 millimolar oxalic acid could represent very long-term bioweathering.
• Limitations the authors state:
  • Only a single ICP-AES analysis was performed on each solution.
  • Iron concentrations in the solutions were not reported because iron hydroxides precipitate at some of the working pH values.
  • Leached pure chrysotile samples were not analysed by nitric oxide adsorption, because the activation step modified the surface structure.
  • Leaching varied from fibre to fibre, which the authors say likely caused the wide error bars.

Mines named here

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

• Balangero mine, Balangero, about 20 km north of Turin, Piedmont

All asbestos mines

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Balangeroite, Asbestiform, Scanning Electron Microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-Ray Diffraction (XRD).

Related studies

• Chrysotile asbestos is progressively converted into a non-fibrous amorphous material by the chelating action of lichen metabolites — S.E. Favero-Longo, F. Turci, et al. (2005)
• Lichens on asbestos-cement roofs: bioweathering and biocovering effects — S.E. Favero-Longo, D. Castelli, et al. (2009)
• Interactions of sterile-cultured lichen-forming ascomycetes with asbestos fibres — S.E. Favero-Longo, M. Girlanda, et al. (2007)
• Role of associated mineral fibres in chrysotile asbestos health effects: the case of balangeroite — F. Turci, M. Tomatis, et al. (2009)
• The combination of oxalic acid with power ultrasound fully degrades chrysotile asbestos fibres — F. Turci, M. Tomatis, et al. (2007)
• Long-term instillation to four natural representative chrysotile of China induce the inactivation of P53 and P16 and the activation of C-JUN and C-FOS in the lung tissues of Wistar rats — Y. Luo, J. Deng, et al. (2020)

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