The effects of naturally occurring acids on the surface properties of chrysotile asbestos

Our plain-English summary of The effects of naturally occurring acids on the surface properties of chrysotile asbestos, by E.P. Holmes, L.M. Lavkulich (Journal of Environmental Science and Health. Part A, Toxic/hazardous Substances & Environmental Engineering, 2014).

The study

• Authors: E.P. Holmes, L.M. Lavkulich
• Journal: Journal of Environmental Science and Health. Part A, Toxic/hazardous Substances & Environmental Engineering
• Published: 2014;49(12):1445-52
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Chrysotile asbestos is considered an environmental health hazard. It is postulated that the surface of chrysotile, with its inherent positive charge and chemical content of trace transition metals within the mineral is a causative factor of the concern. Weathering may reduce the negative health effects of chrysotile asbestos, by alteration of the outer brucite layer of the chrysotile. To assess the changes in the surface properties of chrysotile asbestos by simulated weathering, chrysotile was treated with oxalic, hydrochloric, and carbonic acids. Naturally occurring chrysotile, from a mine site and serpentinitic stream sediments from the Sumas River were analyzed and compared. Oxalic acid, a chelating acid, was the most effective at extracting the majority of the trace elements present in the chrysotile, reducing their positive surface charge and producing visible changes at the surface of the fibers as shown by Field Emission Scanning Electron Microsopy (FESEM). Carbonic acid had little effect on the surface properties. Stream environments had minor detectable effects on the surface properties on the chrysotile stream sediments.

In plain English

This was a laboratory study of the surface chemistry of chrysotile asbestos. It did not study people or animals. The authors treated unweathered chrysotile from the Cassiar Mine in British Columbia with carbonic, oxalic or hydrochloric acid to simulate weathering. They compared it with chrysotile-containing sediment collected at four locations along the Sumas River in Washington State. Oxalic acid extracted the most magnesium, chromium, aluminum and iron. Carbonic acid extracted little. Oxalic and hydrochloric acid changed the fibers' surface charge from positive to negative and left a silica-enriched surface. Carbonic acid lowered the charge, but it stayed positive. Under the electron microscope, oxalic-treated fibers looked shorter and altered. The river sediments had magnesium-dominated surfaces, which the authors read as limited weathering. The authors concluded that stream weathering did alter chrysotile's surface properties, but that the extent in terms of environmental or human health effects remains unknown. They cautioned that samples were highly variable.

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 surface chemistry: acid treatment of chrysotile compared with naturally weathered river sediment (no human or animal subjects)
• Who was studied: Nine 0.5 g samples of high-grade, unweathered chrysotile ore from the Cassiar Mine, British Columbia, Canada (Grade AY), and suspended sediment collected over 12 days from four locations along the Sumas River below the Swift Creek landslide on Sumas Mountain, Washington State, USA. Sampling dates were not given.
• Exposure: Chrysotile treated with one of three acids: carbonic acid (pH 3.6), 0.25 M oxalic acid (pH 1.9) or 0.1 M hydrochloric acid (pH 1). Each sample got 25 mL of acid, was shaken for two hours and left overnight. River sediment had been exposed to natural weathering in the stream.
• Main results:
  • Of the three acids, oxalic acid extracted the most magnesium, chromium, aluminum and iron from the Cassiar chrysotile. For example, it extracted 20868 mg/kg of magnesium, compared with 147220 mg/kg in the untreated digested sample. Hydrochloric acid extracted the most nickel and zinc. Carbonic acid was a relatively poor extractor of all elements.
  • Oxalic and hydrochloric acid treatment changed the chrysotile's surface charge (zeta potential) from positive to negative. Oxalic acid gave the lowest charge, hydrochloric acid the second lowest. Carbonic acid gave a lower charge than untreated fiber, but it remained positive.
  • At the fiber surface, the magnesium-to-silicon ratio was lowest after oxalic acid (0.7) and second lowest after hydrochloric acid (10.1). It was 19.8 after carbonic acid and 24.9 in untreated fiber. Oxalic and hydrochloric acid left a silicon-enriched surface.
  • Under the electron microscope, untreated, carbonic acid treated and hydrochloric acid treated fibers looked intact and long. Oxalic acid treated fibers were shorter and appeared modified. Intact fibers were sometimes found next to broken ones in the same sample.
  • The river sediment samples had positive surface charges, which decreased slightly downstream from Swift Creek. Their surfaces were dominated by magnesium, with magnesium-to-silicon ratios of 16.2 to 20, similar to the carbonic acid treated sample. The authors interpreted this as limited weathering in the stream.
  • Across acid-treated and sediment samples, surface charge was positively correlated with the surface magnesium-to-silicon ratio.
• The authors' conclusion: The authors concluded that natural weathering in stream environments did alter the surface properties of chrysotile, but that the extent in terms of environmental or potential human health effects remains unknown. They said their results support the hypothesis that the outer brucite (magnesium) layer governs chrysotile's reactivity and surface charge. They also suggested that reclamation of the Sumas River deposits consider applying organic material such as peat, compost or sawdust.
• Limitations the authors state:
  • There was high natural variability within samples, so the authors cautioned against quantitative interpretation of micro-scale measurements. Differences between sediment sites may not be significant.
  • The river sediments contained minerals other than chrysotile. They were also subject to factors that can affect surface charge, such as adsorbed organic matter, different pH and complexing cations.
  • The sediment from the Border station, next to a dairy farm, was too heterogeneous for surface (ToF-SIMS) analysis.

Mines named here

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

• Cassiar mine, British Columbia

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, Brucite Layer.

Related studies

• The combination of oxalic acid with power ultrasound fully degrades chrysotile asbestos fibres — F. Turci, M. Tomatis, 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)
• 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)
• The effect of weathering on ecopersistence, reactivity, and potential toxicity of naturally occurring asbestos and asbestiform minerals — S. Enrico Favero-Longo, F. Turci, et al. (2009)
• 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)
• Probing anisotropic surface properties and interaction forces of chrysotile rods by atomic force microscopy and rheology — D. Yang, L. Xie, et al. (2014)

Browse more research in Journal of Environmental Science and Health. Part A, Toxic/hazardous Substances & Environmental Engineering, or return to medical research.