Mineralogy and textures of riebeckitic asbestos (crocidolite): The role of single versus agglomerated fibres in toxicological experiments

Our plain-English summary of Mineralogy and textures of riebeckitic asbestos (crocidolite): The role of single versus agglomerated fibres in toxicological experiments, by S. Yao, G. Iezzi, G. Della Ventura, et al (Journal of Hazardous Materials, 2017).

The study

• Authors: S. Yao, G. Iezzi, G. Della Ventura, F. Bellatreccia, C. Petibois, A. Marcelli, M. Nazzari, F. Lazzarin, M. Di Gioacchino, C. Petrarca
• Journal: Journal of Hazardous Materials
• Published: 2017;340:472-485
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos may cause adverse effects, but relationship between mineralogy and texture of fibres versus toxicity is still lacking. Toxicological studies can be interpreted and compared only if quantitative features of fibres are determined. Here, riebeckitic ("crocidolite") amphibole fibres were analysed by XRPD, FTIR, SEM-EDS and EMP-WDS; only crystals with stochiometry A□BNa2C(Fe2+2.5Mg0.5)CFe3+2TSi8O22W(OH)2 are present in the starting material used for the experiments. Fibres deposited from solutions of 0.1, 1, 10, 25, 50, 75 and 100mg/L were counted by image analysis using SEM images. At 0.1 and 1mg/L the fibres are well separated, whereas between 1 and 10mg/L they start to agglomerate. In-vitro tests performed on fibres deposited at the same mg/L concentrations show that the toxic potential follows a curvilinear increasing trend with a decreasing rate. Since the range of sizes of single fibres and their mineralogy are constant, this decreasing rate can be only attributed to the increasing amount of agglomerated fibres. Hence, single versus agglomerated fibre population is a factor that cannot be neglected in defining the final adverse effects of asbestos. The analytical protocol proposed here is valuable for any aero-dispersed dust, in polluted environments, as well as in the interpretation of experimental studies.

Copyright © 2017 Elsevier B.V. All rights reserved.

In plain English

This laboratory study examined a sample of crocidolite asbestos (the amphibole mineral riebeckite) from Buchanawald, South Africa, held in the collection of a Paris museum. The authors used several mineral-analysis methods to confirm the sample's composition. They then dispersed the fibres in liquid at seven concentrations, from 0.1 to 100 mg/L, and counted and measured the deposited fibres in electron microscope images. They also exposed A549 lung tumor cells to the same concentrations for 24 hours and measured cell viability with three tests. The fibres had a very uniform composition. At 1 mg/L or less the fibres lay separately. At 10 mg/L and above, many fibres clumped into networks, and only about 15% to 30% of counted objects were single fibres. Cell death generally rose with concentration. In the MTT test, however, the rise slowed, and 50 to 100 mg/L gave the same toxic response. The authors suggested that the MTT results were mainly controlled by the amount of single fibres rather than by the total weight of fibres. They cautioned that fibres in air could be much less clumped than in their experiments.

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 study: mineralogical and textural characterization of a crocidolite (riebeckite) fibre sample combined with in-vitro cell toxicity tests
• Who was studied: A crocidolite sample from the Museum National d'Histoire Naturelle of Paris, labelled as from Buchanawald (South Africa), file #134-86; cell tests used the A549 type II epithelial lung tumor cell line
• Exposure: Riebeckitic (crocidolite) fibres dispersed at 0.1, 1, 10, 25, 50, 75 and 100 mg/L; cells were exposed for 24 hours to amounts across the range 0.1-100 mg/L
• Main results:
  • Three independent mineralogical methods showed the fibres had very low variability in composition, close to the nominal riebeckite formula
  • Single fibres were less than 1.0 µm wide; most were about 5-10 µm long, with maximum lengths of about 60-70 µm
  • At 1 mg/L or less, all counted objects had an aspect ratio above 5:1 (single fibres). At 10 mg/L or more, many objects had aspect ratios between 1:1 and 5:1, indicating clumped networks of touching fibres
  • At 1 mg/L all fibres were single objects. At 10, 25 and 50 mg/L only 25% to 15% of objects were single fibres, and at 75 and 100 mg/L about 30% were
  • Increasing fibre concentration generally increased cell deaths in the cell tests, except at 10 mg/L in the cytometry test
  • In the MTT test, toxicity rose very steeply from 0.1 to 10 mg/L, then more gently, and concentrations from 50 to 100 mg/L induced the same toxic response
• The authors' conclusion: The authors concluded that an increasing amount of fibres may not produce a proportional increase in toxicity, because toxicity also depends on how much the fibres clump together. They suggested that the MTT results were mainly controlled by the amount of single fibres.
• Limitations the authors state:
  • The authors cautioned that the results should be applied to real situations with caution, because fibres in air could be much less clumped than in these experiments
  • Image analysis missed some fibres whose grey levels were close to the silicon holder or that were very small
  • Networks of fibres aligned along their length could not be distinguished from single fibres, though the authors said these were few
  • Very few electron microprobe point analyses could be collected because the fibres are so narrow
  • The fibre concentrations used were high compared to recommended limits

Topics

Medical terms in this study, explained in our Lexicon: Mineralogy, Crocidolite, Amphibole Group.

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