X-ray synchrotron microtomography: a new technique for characterizing chrysotile asbestos

Our plain-English summary of X-ray synchrotron microtomography: a new technique for characterizing chrysotile asbestos, by A. Bloise, C. Ricchiuti, G. Lanzafame, et al (The Science of the Total Environment, 2020).

The study

• Authors: A. Bloise, C. Ricchiuti, G. Lanzafame, R. Punturo
• Journal: The Science of the Total Environment
• Published: 2020;703:135675
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Over the last decades, many studies have been conducted on rocks containing Naturally Occurring Asbestos (NOA) to determine the potential health risks to exposed neighboring populations. It is difficult to accurately characterize the asbestos fibres contained within the rocks as conventional techniques are not effective and have drawbacks associated with the disturbance of the sample under study. X-ray synchrotron microtomography (SR-μCT) supplemented with polarized light microscope (PLM), scanning electron microscopy analysis combined with energy dispersive spectrometry (SEM/EDS), electron probe micro-analysis (EPMA) were used for identifying asbestos fibres in a mineral matrix. As a case study, we analyzed a representative set of veins and fibrous chrysotile that fills the veins, taken from massive serpentinite outcrops (Southern-Italy). We were able to identify respirable chrysotile fibres (regulated asbestos) within the serpentinite matrix. SR-μCT of NOA veins achieved the resolution and reconstructed 3D structures of infill chrysotile asbestos fibres and other phase structures that were not resolvable with PLM, SEM or EPMA. Moreover, due to differences in chemical composition between veins and matrix, the data obtained enabled us to evaluate the vein shapes present in the massive serpentinite matrix. In particular, iron and aluminum distribution variations between veins and matrix induce different radiation absorption patterns thus permitting a detailed image-based 3D geometric reconstruction. The advantages of the SR-μCT technique as well as limitation of conventional methods are also discussed. These analytical approaches will be used for conducting future research on NOA of other minerals, which exhibit asbestiform and non-asbestiform habits within veins, including asbestos amphiboles.

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In plain English

This laboratory study tested whether X-ray synchrotron microtomography (SR-μCT), a non-destructive 3D imaging method, could characterize chrysotile asbestos inside rock without grinding or crushing the sample. The authors examined seven serpentinite rocks from an abandoned quarry in the Gimigliano-Mount Reventino Unit in Calabria, southern Italy. They used light microscopy, electron microscopy and chemical microanalysis, and scanned two samples with SR-μCT. The study examined rock samples, not people or disease. In the vein chrysotile, averages were 2.45 wt% aluminum oxide (Al2O3) and 2.00 wt% iron oxide (FeO). In the surrounding rock matrix, averages were 0.72 wt% Al2O3 and 3.67 wt% FeO. These differences let the 3D images separate veins from the rock. The scans showed four vein shapes and small veins not visible at the mesoscopic scale. Chrysotile fibres were 10 to 300 μm long, all longer than 5 μm with aspect ratios greater than 3:1. The authors said these fibres matched the size of regulated asbestos. The method could not measure fibres shorter than 2 μm. The authors concluded that SR-μCT was a valuable and promising technique for analysing vein chrysotile in serpentinite.

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 mineralogical study of rock samples comparing analytical techniques. It used non-destructive 3D imaging by X-ray synchrotron microtomography (SR-μCT) alongside polarized light microscopy, SEM/EDS and electron probe microanalysis (EPMA).
• Who was studied: Seven serpentinite rock samples from an abandoned quarry in the Gimigliano-Mount Reventino Unit (Calabria, Southern Italy). Two samples with class T2 veins (T2_GMRU2 and T2_GMRU12) were scanned by SR-μCT at the Elettra synchrotron laboratory in Trieste.
• Exposure: Naturally occurring chrysotile asbestos fibres filling veins in serpentinite rock. No human exposure was studied.
• Main results:
  • From ten measurements on each of 50 veins, the authors defined four vein-width classes: T1 (average width less than 0.3 mm), T2 (0.3 to 1 mm), T3 (1 to 2 mm) and T4 (more than 2 mm). Most veins were T1 (37%) or T2 (41%). The two wider classes made up 22%, 11% each.
  • Aluminum was higher in the vein chrysotile than in the surrounding matrix. Spot analyses gave an average of 2.45 wt% in vein chrysotile and 0.72 wt% in the matrix. Tables 1 and 2 report these as oxide weight percent (Al2O3).
  • Iron was lower in the vein chrysotile than in the matrix. The average was 2.00 wt% in the vein infill and 3.67 wt% in the matrix, almost twice as high. Tables 1 and 2 report these as oxide weight percent (FeO).
  • The SR-μCT 3D renderings showed four vein shapes: sub-parallel side, lens-shape, V-shape and irregular-shape.
  • SR-μCT showed smaller class T1 veins within the matrix that were not visible at the mesoscopic scale. The maximal vein thickness was 0.580 mm in sample T2_GMRU2 and 0.566 mm in sample T2_GMRU12.
  • Chrysotile fibre lengths in all the samples ranged from 10 to 300 μm. All fibres (100%) were longer than 5 μm, with aspect ratios greater than 3:1.
  • The authors reported that the fibre dimensions, measured without grinding or milling, all matched the size of regulated asbestos under European law (Directive 2003/18/CE).
• The authors' conclusion: The authors concluded that SR-μCT was a valuable and promising technique for analysing chrysotile asbestos filling veins in massive serpentinite. They said that, combined with conventional techniques, it could help characterize chrysotile-filled veins and identify naturally occurring asbestos in serpentinite rocks.
• Limitations the authors state:
  • SR-μCT could not measure fibres shorter than 2 μm, because they fall below its resolution.
  • The authors stated that some veins are hard to tell apart from the matrix with SR-μCT. These are veins formed at greater depth and temperature, whose chemistry differs little from the matrix.

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile, naturally occurring asbestos (NOA), Scanning Electron Microscopy (SEM), Serpentinite, Regulated Asbestos, Asbestiform, Non-Asbestiform, Habit.

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