New detoxification processes for asbestos fibers in the environment

Our plain-English summary of New detoxification processes for asbestos fibers in the environment, by F. Turci, M. Colonna, M. Tomatis, et al (Journal of Toxicology and Environmental Health. Part a, 2010).

The study

• Authors: F. Turci, M. Colonna, M. Tomatis, S. Mantegna, G. Cravotto, B. Fubini
• Journal: Journal of Toxicology and Environmental Health. Part a
• Published: 2010;73(5):368-77
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Airborne asbestos fibers are associated with many serious detrimental effects on human health, while the hazard posed by waterborne fibers remains an object of debate. In adopting a precautionary principle, asbestos content in water needs to be kept as low as possible and polluting waters with asbestos should be avoided. Turci et al. (2008) recently reported a method for the decontamination of asbestos-polluted waters or landfill leachates from chrysotile that combines power ultrasound (US) with oxalic acid (Ox), an acidic chelating molecule. In the previous study, the occurrence of antigorite, a polymorph of serpentine, the mineral group encompassing chrysotile asbestos, acted as a confounding factor for complete removal of chrysotile from water. The effects of US + Ox on pure chrysotile asbestos from Val Malenco, Italian Central Alps, were examined in this investigation. In the absence of mineral contaminants, a more rapid removal of pure chrysotile from water was undertaken with respect to the previous specimen. After only 12 h of combined US + Ox acid treatment, imaging (SEM) of mineral debris indicated complete loss of fibrous habit. In addition, crystallography and vibrational features of chrysotile were not detectable (x-ray powder diffraction [XRPD] and micro-Raman spectroscopy) and elemental analysis showed a low Mg/Si ratio, i.e., the loss of the brucitic layer in chrysotile (x-ray fluorescence, XRF). Some nanometric rod-shaped debris, observed in the previous study and tentatively recognized as serpentine antigorite, was now found to be made of amorphous silica, which is relatively safe and noncarcinogenic to humans, providing further assurance regarding the safety of treated product. Thus, data indicated the proposed method was effective in detoxifying waterborne chrysotile asbestos fibers.

In plain English

In a laboratory experiment, the authors tried to break down chrysotile asbestos in water, using pure chrysotile from Val Malenco (Italian Central Alps) and, for comparison, commercial chrysotile from Balangero, Italy. Fibers were treated with power ultrasound, oxalic acid, or both, for 12 or 21 hours, then examined by microscopy and chemical and crystal-structure analyses. Oxalic acid alone left Val Malenco fibers fibrous and morphologically unaltered, apart from some small debris. Ultrasound alone shortened them but largely kept them fibrous. Combined treatment turned Val Malenco fibers into non-fibrous debris. Chrysotile's crystal and spectral signatures disappeared, and magnesium oxalate was the only crystalline reaction product detected, apart from reactor steel debris. Treated Balangero fibers still showed serpentine features, attributed to resistant antigorite. The Val Malenco magnesium-to-silicon ratio fell from 1.47 (plus or minus 0.03) to 0.2 (plus or minus 0.2) after 12 hours of combined treatment. Treated Balangero fibers stayed significantly higher, at 0.83 (plus or minus 0.02). Rod-shaped nanoparticles were judged likely amorphous silica. The authors concluded the product was noncarcinogenic for humans and the process diminishes toxicity. This study ran no toxicity tests.

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 experiment on mineral samples, with no people or animals. Chrysotile fibers were treated by ultrasound plus oxalic acid, by ultrasound alone, or by oxalic acid alone. They were then analyzed by SEM imaging, x-ray powder diffraction, micro-Raman spectroscopy and x-ray fluorescence.
• Who was studied: Two chrysotile samples: a pure chrysotile specimen with limited iron contamination from Val Malenco (Italian Central Internal Alps), and a commercial sample (classified 6D) from the San Vittore out-of-use asbestos mine (Balangero, Italy), used for comparison
• Exposure: 500 mg chrysotile in 50 ml ultrapure water or 50 ml of 0.5 M oxalic acid, sonicated at 19.2 kHz and about 150 W for 12 or 21 h, kept below 50°C. Oxalic acid leaching alone was done at 50°C with mild mixing.
• Main results:
  • Val Malenco chrysotile leached with oxalic acid alone for 21 h kept its fibrous habit and was morphologically unaltered, though some small debris was seen
  • Ultrasound alone in pure water for 21 h strongly reduced fiber length, but fibrous habit was largely preserved and fibers stayed in the micrometric range
  • Combined oxalic acid and ultrasound for 12 h and 21 h produced micrometric non-fibrous debris (Val Malenco sample)
  • X-ray diffraction of Val Malenco fibers after combined treatment for 12 and 21 h showed the serpentine crystal features suppressed, with only magnesium oxalate reflections recorded. Some oxalate reflections overlapped with a signal from steel debris from the ultrasonic reactor.
  • In the Balangero sample treated with ultrasound plus oxalic acid for 21 h, serpentine crystal features were still visible. The authors attributed this to antigorite resistant to the treatment.
  • Micro-Raman spectra of Val Malenco fibers after 21 h combined treatment showed no chrysotile peaks, only magnesium oxalate. Antigorite was not detected in this sample.
  • Mg/Si ratio of Val Malenco fibers (means ± SEM) was 1.47 ± 0.03 untreated versus 1.24 ± 0.03 after ultrasound in pure water, a significant change. Balangero fibers were not significantly changed by ultrasound alone.
  • Combined oxalic acid and ultrasound for 12 h almost completely removed magnesium from the Val Malenco sample (Mg/Si 0.2 ± 0.2)
  • The Balangero sample after combined treatment had an Mg/Si ratio of 0.83 ± 0.02, significantly higher than the Val Malenco sample. The authors attributed this likely to antigorite that does not fully dissolve.
  • Rod-shaped nanometric particles were seen after treatment and had previously been thought to be antigorite. They also occurred in the antigorite-free Val Malenco chrysotile, which the authors took to mean they are likely amorphous silica.
• The authors' conclusion: The authors concluded that the treated material was noncarcinogenic for humans and that the process is effective in diminishing toxicity. They also concluded that it further validated their earlier method for removing chrysotile from water suspensions.
• Limitations the authors state:
  • No toxicity testing of the treated product was done. The authors stated that in vitro tests may add further evidence of safety, which could eventually be validated in vivo.
  • The authors noted that other studies have reported some nanosized amorphous silicas inducing pulmonary inflammation in mice and some cytotoxicity in vitro
  • X-ray powder diffraction could not distinguish chrysotile from antigorite
  • Some diffraction signals overlapped with signals from steel debris shed by the ultrasonic reactor

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: Precautionary Principle, Chrysotile, Ultrasound, Antigorite, Serpentine Group, Confounding, Fibrous Habit, Elemental Analysis.

Related studies

• 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)
• Artificial geochemical barriers for additional recovery of non-ferrous metals and reduction of ecological hazard from the mining industry waste — V. Chanturiya, V. Masloboev, et al. (2011)
• Evidence of arsenic release promoted by disinfection by-products within drinking-water distribution systems — S.S. Andra, K.C. Makris, et al. (2014)
• An update on the detoxification processes for silica particles and asbestos fibers: successess and limitations — M. Gulumian (2005)
• Chrysotile asbestos detoxification with a combined treatment of oxalic acid and silicates producing amorphous silica and biomaterial — A. Valouma, A. Verganelaki, et al. (2016)
• The combination of oxalic acid with power ultrasound fully degrades chrysotile asbestos fibres — F. Turci, M. Tomatis, et al. (2007)

Browse more research in Journal of Toxicology and Environmental Health. Part a, or return to medical research.