Innovative unattended SEM-EDS analysis for asbestos fiber quantification

Our plain-English summary of Innovative unattended SEM-EDS analysis for asbestos fiber quantification, by R. Cossio, C. Albonico, A. Zanella, et al (Talanta, 2018).

The study

• Authors: R. Cossio, C. Albonico, A. Zanella, S. Fraterrigo-Garofalo, C. Avataneo, R. Compagnoni, F. Turci
• Journal: Talanta
• Published: 2018;190:158-166
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Scanning electron microscopy with energy dispersive spectrometry (SEM-EDS) is the only affordable analytical technique that can discriminate both morphology and elemental composition of inorganic fibers. SEM-EDS is indeed required to quantify asbestos in confounding natural matrixes (e.g. ophiolites), but is also time-consuming, operator dependent, and strongly relies on the stochastic distribution of the fibers on the filter surface. The balance between analytical time/cost and the method sensibility allows only about 0.5% of the filter to be analyzed, strongly affecting the statistical significance of results. To improve sensitivity and precision and enhance productivity, an unattended quantitative measurement of the asbestos fibers by SEM-EDS is proposed. The method identifies the particle shape first and determines their chemical composition later, saving EDS analytical time. Our approach was tested on four asbestos standards and the relative error on replicated measurements was < 10%. The proposed unattended method quantifies asbestos in natural confounding matrix, also with a very low asbestos content.

Copyright © 2018 Elsevier B.V. All rights reserved.

In plain English

This laboratory study developed and tested an automated method for counting and identifying asbestos fibers on filters using scanning electron microscopy with energy dispersive spectrometry (SEM-EDS). The method first sorted particles by shape, then checked the chemical makeup of only the fiber-shaped ones. The authors tested it on four reference samples (UICC chrysotile, amosite and crocidolite, and fibrous tremolite from Susa Valley) and three naturally occurring asbestos samples from the Italian Alps containing chrysotile and tremolite. A new shape measure, the "equivalent rectangle", classified 78.66% of counted chrysotile particles and 94.08% of crocidolite particles as fibers. A standard measure (Feret diameters) classified 49.88% and 38.50%. Repeated measurements on amosite and tremolite had relative errors of 6% to 11.5%. On the natural samples, conventional-method results fell within 3 standard deviations of the repeated automated measurements' mean, and within 1 for two samples. Relative error did not exceed 30%, at asbestos concentrations between 500 and 10,000 ppm. The authors concluded this was the first fully automatic SEM-EDS quantification of asbestos fibers. They noted some elongated particles still need manual review.

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 analytical method-development and validation study (automated SEM-EDS fiber counting and identification)
• Who was studied: Four asbestos reference samples (UICC amosite, UICC crocidolite, UICC chrysotile, and fibrous tremolite from Susa Valley, Italy) and three naturally occurring asbestos (NOA) samples. Two came from a deposit near Salbertrand, Susa Valley, and one was a serpentinite from near Lanzada, Val Malenco, Italy.
• Exposure: Asbestos fibers deposited on polycarbonate filters: chrysotile, amosite, crocidolite and tremolite standards, plus natural samples containing both chrysotile and tremolite
• Main results:
  • Particles classified as fibers (WHO respirable-fiber definition) by the equivalent rectangle (ER) method compared with Feret diameters: chrysotile 656 of 834 (78.66%) vs 416 (49.88%); tremolite 1094 of 1165 (93.91%) vs 670 (57.51%); amosite 1907 of 2135 (89.32%) vs 1145 (53.63%); crocidolite 2160 of 2296 (94.08%) vs 884 (38.50%)
  • Precision: relative error on four replicate automated measurements ranged from 6% (amosite) to 11.5% (tremolite)
  • In all three natural samples, values from the conventional method fell within 3 standard deviations of the mean of the replicated automated measures. For NOA2 and NOA3 they fell within 1 standard deviation.
  • In the natural samples, relative error did not exceed 30%, even when only a few tens of fibers were detected
  • Asbestos concentrations detected in the natural samples ranged between 500 and 10,000 ppm
  • In a chemical (principal component) analysis, the first two components accounted for 92.25% of the variance, and the four asbestos standards were distinguished by their chemical composition
• The authors' conclusion: The authors concluded that this was the first use of SEM-EDS for fully automatic quantification of asbestos fibers. They stated that the method quantifies asbestos at low concentration and takes at most 2 hours per sample. They also stated that it showed excellent reproducibility and good precision compared with conventional SEM-EDS.
• Limitations the authors state:
  • Elongated or acicular tremolite particles are hard to assign to asbestos or non-asbestos and may need manual review
  • Precision in real natural samples was slightly lower than with the reference standards
  • The upper and lower threshold levels that separate fibers from other material must be selected manually

Topics

Medical terms in this study, explained in our Lexicon: Scanning Electron Microscopy (SEM), Confounding, Ophiolite, Statistical Significance.

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