Biodurability and release of metals during the dissolution of chrysotile, crocidolite and fibrous erionite

Our plain-English summary of Biodurability and release of metals during the dissolution of chrysotile, crocidolite and fibrous erionite, by A.F. Gualtieri, G. Lusvardi, A. Zoboli, et al (Environmental Research, 2019).

The study

• Authors: A.F. Gualtieri, G. Lusvardi, A. Zoboli, D. Di Giuseppe, M. Lassinantti Gualtieri
• Journal: Environmental Research
• Published: 2019;171:550-557
• Cited by: 31 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: The mechanisms by which mineral fibers induce adverse effects in vivo are still not well understood. The mechanisms of fiber dissolution in the lungs and subsequent release of metals in the extracellular/intracellular environment must be taken into account.

Aim: For the first time, the kinetics of release of metals during the acellular in vitro dissolution of chrysotile, crocidolite and fibrous erionite were determined.

Methods: In vitro acellular dissolution of chrysotile, crocidolite, and fibrous erionite-Na was conducted using a solution mimicking the phagolysosome environment active during the phagocytosis process (pH=4.5, at 37 °C). The kinetics of release of a representative selection of metals were determined over a period of three months.

Results: Despite the fact that the difference in Fe content between chrysotile and crocidolite is one order of magnitude, the much faster dissolution rate of chrysotile compared to crocidolite prompts greater release of available active surface Fe in the first weeks of the dissolution experiment and comparable amounts after 90 d. Such active iron may promote the formation of toxic hydroxyl radicals. The fast release of metals like Cr, Ni and Mn from chrysotile is also a source of concern whereas the release of V in solution is negligible.

Conclusion: Because chrysotile undergoes fast dissolution with respect to crocidolite and fibrous erionite, it behaves like a carrier that releases its metals' cargo in the lung environment, mimicking the phenomenon that explains the toxicity of nanoparticles. Hence, the toxicity paradigm of a non biodurable fiber like chrysotile should also take into account the release of toxic metals in the intracellular/extracellular medium during the rapid dissolution process.

Copyright © 2019 Elsevier Inc. All rights reserved.

In plain English

This was a laboratory experiment without cells, animals or people. The authors placed three mineral fibers, Balangero (Italy) chrysotile, UICC South African crocidolite and fibrous erionite-Na from Jersey, Nevada (USA), in a fluid meant to mimic the acidic interior of lung immune cells (pH 4.5, 37 °C). Over three months they measured how much of each fiber dissolved and which metals entered the fluid. After 90 days about 100% of the chrysotile had dissolved, compared with about 20% of the erionite and 18% of the crocidolite. Chrysotile released about one order of magnitude more silicon than the other two fibers. Crocidolite contains far more iron, yet chrysotile released more iron in the first weeks. After 90 days the two fibers had released comparable amounts, about 4000 ppb, and erionite about 1000 ppb. Chrysotile released more than 80 ppb of chromium and nickel and about 180 ppb of manganese. Crocidolite released 80 ppb of manganese. Vanadium release was only a few ppb. The authors concluded that fast-dissolving chrysotile may act as a carrier of harmful metals into the lung environment, similar to an effect proposed for nanoparticles.

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 (in vitro, acellular) dissolution experiment comparing three mineral fibers in a simulated lung fluid over three months
• Who was studied: No people or animals. Three fiber samples: UICC standard crocidolite (South African), chrysotile from Balangero (Torino, Italy) and fibrous erionite-Na from Jersey, Nevada (USA). Fibers were selected under the microscope and cleaned of impurities.
• Exposure: 0.025 g of each fiber was placed in 250 ml of a modified Gamble's solution (alveolar lung fluid, pH 4.5) at 37 °C under continuous agitation. Samples were taken at 24 h, 48 h, 7 d, 14 d and 1, 2 and 3 months. Released Si, Mg, Al, Fe, Cr, Mn, Ni, V, Na, Ca and K were measured.
• Main results:
  • After 90 days the dissolved fraction was about 100% for chrysotile, 20% for erionite and 18% for crocidolite.
  • Chrysotile released about one order of magnitude more silicon than crocidolite and erionite.
  • Chrysotile released more active surface iron than crocidolite in the first weeks. After 90 days the two fibers had released comparable amounts, about 4000 ppb.
  • Fibrous erionite released about 1000 ppb of iron after 3 months. The authors attributed this to impurities on the fiber surface, not to the fiber structure itself.
  • Chrysotile released chromium and nickel at more than 80 ppb.
  • Manganese release was 80 ppb from crocidolite and about 180 ppb from chrysotile.
  • Vanadium release from all three fibers was a few ppb, which the authors judged should not be a concern.
  • Aluminium was released from erionite (and from chrysotile), with no release from the amphibole (crocidolite).
  • After 3 months chrysotile had become amorphous, while crocidolite and erionite were still crystalline.
• The authors' conclusion: The authors concluded that chrysotile is less biodurable than amphibole fibers and is ideally less toxic. Because it dissolves rapidly in the acidic phagolysosome environment, they concluded it may behave like a carrier of harmful metals, mimicking the effect proposed to explain nanoparticle toxicity.
• Limitations the authors state:
  • The authors state the study was not focused on the kinetics of ion release. Dissolution rates were calculated only for elements with sufficiently high concentrations, not for those below 5 ppb.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Crocidolite, erionite, Mineral Fiber, Phagolysosome, Phagocytosis, Hydroxyl Radical.

Related studies

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• Concentrations of asbestos fibers and metals in drinking water caused by natural crocidolite asbestos in the soil from a rural area — B. Wei, B. Ye, et al. (2013)
• New insights into the toxicity of mineral fibres: A combined in situ synchrotron μ-XRD and HR-TEM study of chrysotile, crocidolite, and erionite fibres found in the tissues of Sprague-Dawley rats — A.F. Gualtieri, N. Bursi Gandolfi, et al. (2017)
• Asbestos and erionite fibres can induce mutations in human lymphocytes that result in loss of heterozygosity — K. Both, D.W. Henderson, et al. (1994)
• Metaphase and anaphase analysis of V79 cells exposed to erionite, UICC chrysotile and UICC crocidolite — L.D. Palekar, J.F. Eyre, et al. (1987)
• The in vitro genetic effects of fibrous erionite and crocidolite asbestos — K.T. Kelsey, E. Yano, et al. (1986)

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