The effect of weathering on ecopersistence, reactivity, and potential toxicity of naturally occurring asbestos and asbestiform minerals

Our plain-English summary of The effect of weathering on ecopersistence, reactivity, and potential toxicity of naturally occurring asbestos and asbestiform minerals, by S. Enrico Favero-Longo, F. Turci, M. Tomatis, et al (Journal of Toxicology and Environmental Health. Part a, 2009).

The study

• Authors: S. Enrico Favero-Longo, F. Turci, M. Tomatis, R. Compagnoni, R. Piervittori, B. Fubini
• Journal: Journal of Toxicology and Environmental Health. Part a
• Published: 2009;72(5):305-14
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The mechanisms underlying asbestos toxicity mainly rely on experiments performed on "laboratory" fibers, but little data is available on naturally occurring asbestos (NOA). Human exposure to NOA is subject to their ecopersistence and the modulation of their potential toxicity following weathering. The effect of weathering on three fibrous minerals from the Italian Western Alps, chrysotile, tremolite, and balangeroite-a Fe-rich asbestiform mineral-was investigated by mimicking more than 100 yr of physical (freezing-thawing/wetting-drying cycles in a climatic chamber) and biochemical forces (incubation with oxalic acid). Ion release, evaluated by means of inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and variation in chemical composition, evaluated by scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS), indicated that weathering modified the fibers in the series: chrysotile > balangeroite > tremolite. Kinetics of ion release from the fibers (Mg, Fe, and Si) revealed different ion removal pathways. Tremolite was poorly affected. Chrysotile preferentially released cations up to a plateau, with physical and biochemical forces acting competitively. Conversely, for balangeroite, upon which weathering forces acted synergistically, the initial loss of ions facilitated further dissolution and more Si than Mg was released, suggesting an ongoing collapse of the crystal structure. Depletion of redox-reactive ions produced a significant reduction in fiber-derived *OH radicals (EPR, spin-trapping technique), but the fibrous nature was always retained. Despite weathered fibers appearing less toxic than "stored/laboratory" ones, NOA is to be considered far from safe because of fibrous nature and residual surface reactivity. Risk assessment needs to consider the effect of weathering on exposures. Both tremolite and balangeroite may contaminate, in some areas, chrysotile asbestos. However, in contrast to tremolite, balangeroite exhibits a low ecopersistence, similar to chrysotile behavior. Any contribution of balangeroite to chrysotile toxicity will thus be related to its quantitative occurrence and not to higher structural stability.

In plain English

This laboratory study used naturally occurring fibers from the Italian Western Alps. Chrysotile and balangeroite, an iron-rich asbestiform mineral, came from the inactive Balangero mine; tremolite came from Jovencaux-Oulx in the Susa valley. No people or animals were studied. To imitate weathering, fibers went through 500 freezing-thawing and wetting-drying cycles, estimated to equal about 100 years of aging. This was done alone or after 35 days in dilute oxalic acid, mimicking attack by organisms such as lichens. With the cycles alone, chrysotile lost the largest share of its magnesium (38.1 millimoles per mole of magnesium present). Balangeroite lost a larger share of its silicon (6.8 millimoles per mole of silicon) than of its magnesium (1.5 per mole of magnesium). Tremolite changed little. All three minerals stayed fibrous. Their ability to generate hydroxyl radicals, a laboratory measure linked to toxicity, fell after most treatments. The authors concluded that weathered fibers may be less reactive than fresh ones but remain fibrous and keep some surface reactivity. They also judged chrysotile and balangeroite much less persistent in the environment than tremolite.

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 simulating environmental weathering of mineral fibers (no human or animal subjects)
• Who was studied: Three fiber samples from the Italian Western Alps: a commercial short-fiber chrysotile sample (6D) and a field sample of balangeroite, both from the inactive Balangero asbestos mine (Lanzo valley), and a tremolite sample from serpentinite outcrops at Jovencaux-Oulx (Susa valley)
• Exposure: Simulated weathering. Fibers received 500 freezing-thawing/wetting-drying cycles (3 h each, with a water wash every 100 cycles), estimated to correspond to about 100 years of aging. This was done alone or after 35 days of incubation in 0.5 mM oxalic acid. Fibers studied were chrysotile, balangeroite and tremolite.
• Main results:
  • All three minerals kept their fibrous nature after every treatment
  • Ion release was expressed as millimoles of each element released per mole of that same element present in the fiber (mmol/mol), so magnesium and silicon figures are fractions of different element contents
  • Chrysotile, cycles only: magnesium release reached a plateau of 38.1 mmol per mol of magnesium in the fiber at the end of the cycles. Silicon release was 0.2 mmol per mol of silicon.
  • Balangeroite, after 500 cycles only: silicon release (6.8 mmol per mol of silicon in the fiber) exceeded magnesium release (1.5 mmol per mol of magnesium in the fiber) by about threefold, the opposite of chrysotile
  • Tremolite, cycles only: silicon release was less than 0.1 mmol/mol after 500 cycles and magnesium release was 1.6 mmol/mol. The Mg/Si and Ca/Si ratios in the fibers were not modified.
  • Oxalic acid incubation: chrysotile released 53 mmol/mol magnesium versus 5.6 mmol/mol silicon. Balangeroite released 26.7 mmol/mol magnesium and 28.6 mmol/mol silicon. Tremolite released 11.5 mmol/mol magnesium and 3.1 mmol/mol silicon.
  • Oxalic acid and the physical cycles acted competitively on chrysotile and cooperatively (synergistically) on balangeroite
  • Hydroxyl radical generation (Fenton-like activity) after the physical cycles alone was significantly reduced for chrysotile and tremolite. Balangeroite showed no significant variation.
  • With oxalic acid followed by the cycles, balangeroite's radical release was significantly reduced to about one half. Tremolite showed no further reduction.
• The authors' conclusion: The authors concluded that weathering alters natural fibers, so results from fresh laboratory fibers do not necessarily apply to naturally occurring asbestos. They stated that weathered fibers may be less reactive, but that fibrous nature is completely preserved and surface reactivity is not fully extinguished. They found chrysotile and balangeroite much less persistent in the environment than tremolite, and judged that small amounts of balangeroite contaminating chrysotile are not likely to play the role claimed for tremolite.
• Limitations the authors state:
  • The authors noted that weathering lowers toxicity only where such climatic events occur. In some arid areas there is little chance these reactions take place.
  • The authors' view that balangeroite is not biopersistent holds unless in vivo tests show otherwise. No in vivo tests were done in this study.

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, Tremolite.

Medical terms in this study, explained in our Lexicon: naturally occurring asbestos (NOA), Asbestiform, Chrysotile, Tremolite, Balangeroite, Scanning Electron Microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Cation.

Related studies

• Potential toxicity of nonregulated asbestiform minerals: balangeroite from the western Alps. Part 2: Oxidant activity of the fibers — F. Turci, M. Tomatis, et al. (2005)
• Potential toxicity of nonregulated asbestiform minerals: balangeroite from the western Alps. Part 3: Depletion of antioxidant defenses — E. Gazzano, C. Riganti, et al. (2005)
• Potential toxicity of nonregulated asbestiform minerals: balangeroite from the western Alps. Part 1: Identification and characterization — C. Groppo, M. Tomatis, et al. (2005)
• Role of associated mineral fibres in chrysotile asbestos health effects: the case of balangeroite — F. Turci, M. Tomatis, et al. (2009)
• Long-term toxicity of naturally occurring asbestos in male Fischer 344 rats — J.M. Cyphert, M.A. McGee, et al. (2016)
• The effects of naturally occurring acids on the surface properties of chrysotile asbestos — E.P. Holmes, L.M. Lavkulich (2014)

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