Characterization and assessment of the potential toxicity/pathogenicity of fibrous glaucophane

Our plain-English summary of Characterization and assessment of the potential toxicity/pathogenicity of fibrous glaucophane, by D. Di Giuseppe, M. Harper, M. Bailey, et al (Environmental Research, 2019).

The study

• Authors: D. Di Giuseppe, M. Harper, M. Bailey, B. Erskine, G. Della Ventura, M. Ardit, L. Pasquali, G. Tomaino, R. Ray, H. Mason, M.D. Dyar, M. Hanuskova, C. Giacobbe, A. Zoboli, A.F. Gualtieri
• Journal: Environmental Research
• Published: 2019;178:108723
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In California, the metamorphic blueschist occurrences within the Franciscan Complex are commonly composed of glaucophane, which can be found with a fibrous habit. Fibrous glaucophane's potential toxicity/pathogenicity has never been determined and it has not been considered by the International Agency for Research on Cancer (IARC) as a potential carcinogen to date. Notwithstanding, outcrops hosting fibrous glaucophane are being excavated today in California for building/construction purposes (see for example the Calaveras Dam Replacement Project - CDRP). Dust generated by these excavation activities may expose workforces and the general population to this potential natural hazard. In this work, the potential toxicity/pathogenicity of fibrous glaucophane has been determined using the fibre potential toxicity index (FPTI). This model has been applied to a representative glaucophane-rich sample collected at San Anselmo, Marin County (CA, USA), characterized using a suite of experimental techniques to determine morphometric, crystal-chemical parameters, surface reactivity, biodurability and related parameters. With respect to the asbestos minerals, the FPTI of fibrous glaucophane is remarkably higher than that of chrysotile, and comparable to that of tremolite, thus supporting the application of the precautionary approach when excavating fibrous glaucophane-rich blueschist rocks. Because fibrous glaucophane can be considered a potential health hazard, just like amphibole asbestos, it should be taken into consideration in the standard procedures for the identification and assessment of minerals fibres in soil and air samples.

Copyright © 2019 Elsevier Inc. All rights reserved.

In plain English

This laboratory study examined one blueschist rock sample collected at San Anselmo, Marin County, California, to estimate how harmful its fibrous glaucophane, an amphibole mineral, might be. No people, animals or cells were tested. The sample was 86.7% glaucophane by weight. The authors measured 244 glaucophane particles, choosing only those more than three times as long as they were wide; these single fibres averaged 4 micrometres long and 0.2 micrometres wide. The authors calculated a fibre potential toxicity index (FPTI). This is a scoring model based on fibre size, chemistry, iron content, durability in a simulated lung fluid test, and surface properties. Glaucophane scored 2.77 (error 0.25), compared with 2.23 (0.21) for chrysotile from Balangero (Italy) and 2.88 (0.43) for tremolite asbestos from Val d'Ala (Italy). Its estimated fibre lifetime in the dissolution test, 55 years, was comparable to amphibole asbestos. The short fibre length lowered its score. The authors concluded that its potential was markedly greater than chrysotile's and comparable to amphibole asbestos, supporting a precautionary approach during excavation. They called for in vitro testing to confirm this.

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 mineral characterization of a rock sample, with the hazard estimated by a calculated scoring model (the fibre potential toxicity index, FPTI); no toxicity testing in cells, animals or people
• Who was studied: A blueschist rock sample collected at San Anselmo, Marin County, California, about 24 km north of San Francisco, in the Franciscan Complex. Electron microscopy was used to measure 244 single glaucophane particles that had a length-to-width ratio above 3.
• Exposure: Fibrous glaucophane (a sodic amphibole). By weight, the sample was 86.7% glaucophane, 6.4% clinochlore, 5.1% unclassified amphibole and 1.7% quartz
• Main results:
  • Only single glaucophane particles with a length-to-width ratio above 3 were measured: 244 particles in total
  • The measured single glaucophane fibres were 1 to 16 micrometres long (average 4 micrometres). Diameters were 0.04 to 2 micrometres (average 0.2 micrometres).
  • FPTI score (with error): chrysotile from Balangero 2.23 (0.21); tremolite asbestos from Val d'Ala 2.88 (0.43); fibrous glaucophane 2.77 (0.25)
  • The glaucophane FPTI was smaller than that of the other fibrous amphibole species compared. The authors attributed this to the short mean fibre length of 4.1 micrometres, below a 5 micrometre threshold.
  • In the acellular dissolution test, the estimated glaucophane fibre lifetime was 55 years. For comparison: 49 years for Val d'Ala tremolite asbestos, 66 for UICC crocidolite, 74 for UICC amosite, 245 for UICC anthophyllite asbestos and 0.3 for UICC chrysotile. The authors described glaucophane as comparable to the asbestos amphiboles.
  • Zeta potential (a measure of surface electrical charge) was negative across pH 2 to 10, with values similar to crocidolite
  • The fibres had relatively high ferrous iron (FeO above 1 weight %) and total iron (above 10 weight %)
  • Arsenic, cobalt, copper, nickel and vanadium in the blueschist exceeded recommended limits. The authors stated this should not be a concern because the mineral's biodurability prevents their release in the body.
  • In a hypothetical calculation assuming fibres longer than 20 micrometres, the glaucophane score would exceed those of anthophyllite asbestos, crocidolite and fibrous fluoro-edenite
• The authors' conclusion: The authors concluded that the calculated toxicity/pathogenicity potential of fibrous glaucophane is markedly greater than that of chrysotile and comparable to that of amphibole asbestos. They said this supports a precautionary approach when excavating glaucophane-rich blueschist, including at the Calaveras Dam Replacement Project.
• Limitations the authors state:
  • Some parameters were measured on the whole sample, including minerals other than glaucophane
  • Airborne particles released by disturbing the rock may differ from the bulk material analysed
  • Glaucophane from the Calaveras Dam site may differ from the Marin County sample
  • The index result has not been confirmed experimentally; the authors called for in vitro testing
  • The unidentified amphibole in the sample needs a separate study

Topics

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

Medical terms in this study, explained in our Lexicon: Fibrous Habit, IARC, Surface Reactivity, Asbestos, Chrysotile, Tremolite, Amphibole Asbestos.

Related studies

• In vitro toxicity of fibrous glaucophane — A.F. Gualtieri, A. Zoboli, et al. (2021)
• Towards a quantitative model to predict the toxicity/pathogenicity potential of mineral fibers — A.F. Gualtieri (2018)
• Potential toxicity of nonregulated asbestiform minerals: balangeroite from the western Alps. Part 1: Identification and characterization — C. Groppo, M. Tomatis, et al. (2005)
• Iron from a geochemical viewpoint. Understanding toxicity/pathogenicity mechanisms in iron-bearing minerals with a special attention to mineral fibers — A.F. Gualtieri, G.B. Andreozzi, et al. (2019)
• Size- and type-specific exposure assessment of an asbestos products factory in China — M.N. Courtice, D.W. Berman, et al. (2016)
• Potential toxicity of nonregulated asbestiform minerals: balangeroite from the western Alps. Part 3: Depletion of antioxidant defenses — E. Gazzano, C. Riganti, et al. (2005)

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