Chrysotile asbestos is progressively converted into a non-fibrous amorphous material by the chelating action of lichen metabolites

Our plain-English summary of Chrysotile asbestos is progressively converted into a non-fibrous amorphous material by the chelating action of lichen metabolites, by S.E. Favero-Longo, F. Turci, M. Tomatis, et al (Journal of Environmental Monitoring, 2005).

The study

• Authors: S.E. Favero-Longo, F. Turci, M. Tomatis, D. Castelli, P. Bonfante, M.F. Hochella, R. Piervittori, B. Fubini
• Journal: Journal of Environmental Monitoring
• Published: 2005;7(8):764-6
• Cited by: 32 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

A natural deactivation of chrysotile asbestos occurs on serpentinite rocks where lichens selectively grow on the fibres and secrete metabolites, including oxalic acid, which, in the long term, turn the fibres into a non-toxic amorphous material.

In plain English

This short communication examined how lichens growing on chrysotile asbestos change the fibres. The authors studied four lichen species on chrysotile-bearing serpentinite rocks around the disused Balangero asbestos mine in Piedmont, Italy, analysing chrysotile from three rock outcrops and one asbestos cement roof. Under the microscope, lichen filaments (hyphae) closely surrounded chrysotile fibres and, in one species, reached 2.5 mm into the rock. Where fibres were in intimate contact with lichens, their relative magnesium oxide content was about 15–20% lower, and calcium oxalate had formed at the lichen–rock interface. In the laboratory, chrysotile soaked for 35 days in dilute oxalic acid (0.005 and 0.5 mM) changed composition in a similar way, and its ability to generate hydroxyl free radicals was progressively suppressed. In the strongest solution (50 mM), the fibres became a powdery, non-fibrous material made mainly of silica. The authors concluded that lichen growth appears to be a possible tool for cleaning up chrysotile in the environment. They noted that lichens grow extremely slowly, so the process would need to be sped up.

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: Short communication combining field observation of lichens on asbestos-bearing rock and roofing with laboratory experiments (chemical analysis of fibres, incubation of chrysotile in oxalic acid, and free-radical testing)
• Who was studied: Chrysotile fibres from three serpentinite rock outcrops and one asbestos cement roof in and around the disused Balangero asbestos mine (Piedmont, Italy), either uncolonized or colonized by four lichen species (Candelariella vitellina, Lecanora rupicola, Neofuscelia pulla, Xanthoparmelia tinctina); no humans or animals were studied
• Exposure: Chrysotile asbestos exposed to lichens in the field, and chrysotile incubated in the laboratory for 35 days in oxalic acid solutions of 0.005, 0.5 and 50 mM
• Main results:
  • Lichen hyphae surrounded chrysotile fibres in close contact; in Lecanora rupicola the hyphae penetrated the rock down to 2.5 mm under the lichen body
  • Chrysotile fibres in intimate contact with the lichen body showed a selective magnesium depletion, with relative MgO content decreasing by about 15–20%
  • X-ray diffraction mostly showed newly formed calcium monohydrate oxalate at the lichen–rock interface, which the authors considered consistent with weathering by oxalic acid secreted by the lichens
  • In the laboratory, incubation in 0.005 and 0.5 mM oxalic acid changed the chemical composition of chrysotile similarly to the changes seen in rock under lichens
  • After incubation in 50 mM oxalic acid, the asbestos fibres were converted into an amorphous powdery material made mainly of pure silica and lost their fibrous nature
  • For fibres incubated in 0.005 and 0.5 mM oxalic acid, the ability to generate hydroxyl radicals from hydrogen peroxide (Fenton activity) was progressively suppressed compared with untreated chrysotile
• The authors' conclusion: The authors concluded that lichen growth appears to be a possible tool for bioremediation of chrysotile in the environment. Based on the leaching experiments, they expected that over the long term lichens would reduce chrysotile to what they described as non-toxic, fibre-free amorphous silica debris.
• Limitations the authors state:
  • Lichens grow extremely slowly, so biotechnological techniques would be needed to speed up the process before it could become a viable decontamination method
  • The 50 mM oxalic acid treatment is assumed, not shown, to mimic conditions under prolonged lichen growth

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, Serpentinite.

Related studies

• A biomimetic approach to the chemical inactivation of chrysotile fibres by lichen metabolites — F. Turci, S.E. Favero-Longo, et al. (2007)
• Chrysotile asbestos detoxification with a combined treatment of oxalic acid and silicates producing amorphous silica and biomaterial — A. Valouma, A. Verganelaki, et al. (2016)
• Lichens on asbestos-cement roofs: bioweathering and biocovering effects — S.E. Favero-Longo, D. Castelli, et al. (2009)
• The combination of oxalic acid with power ultrasound fully degrades chrysotile asbestos fibres — F. Turci, M. Tomatis, et al. (2007)
• The effects of naturally occurring acids on the surface properties of chrysotile asbestos — E.P. Holmes, L.M. Lavkulich (2014)
• A new approach to the decontamination of asbestos-polluted waters by treatment with oxalic acid under power ultrasound — F. Turci, M. Tomatis, et al. (2008)

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