Analysis and identification of elongated mineral particles in road coated aggregates

Our plain-English summary of Analysis and identification of elongated mineral particles in road coated aggregates, by E. Leocat, C. Rielland, P. Letessier (Toxicology and Applied Pharmacology, 2018).

The study

• Authors: E. Leocat, C. Rielland, P. Letessier
• Journal: Toxicology and Applied Pharmacology
• Published: 2018;361:149-154
• Read it: PubMed · Publisher

Abstract

The issue of Elongated Mineral Particles (EMP) in building materials has been revealed during roadworks in 2013 in France. In fact, road coating aggregates are made of specific rock gravels that can contain Naturally Occurring Asbestos (NOA), which is mainly actinolite. The legislation refers to six regulatory asbestos, that consist in asbestiform habitus of the six minerals. The current technical standard is not adapted for analyzing natural material, as it cannot distinguish the asbestiform fibers and the cleavage fragments fibers. Therefore, the Eichrom Laboratories developed an internal method for analyzing rock gravel and identifying the different kind of EMP. This analytical method is based on an accurate sample preparation and three techniques at different resolutions: a petrological analysis with a stereomicroscope, a mineralogical analysis with a Polarized Light Microscope (PLM) and structural and with a Transmission Electronic Microscope (TEM). This innovative procedure is reinforced by the expertise of geologists, which is not necessary for the manufactured products. Putting the process in a national standard is essential for result homogenization of the asbestos testing laboratories.

Copyright © 2018 Elsevier Inc. All rights reserved.

In plain English

This methods paper from Eichrom Laboratories, France, did not study health effects. The authors described an in-house method for finding naturally occurring asbestos, mainly actinolite, in road coated aggregates. It also aimed to separate asbestiform fibers from non-asbestiform cleavage fragments, which the authors said the current standard cannot do. It combined grinding, stereomicroscope, polarized light and transmission electron microscopy, and geological expertise. Internal standard samples showed a detection limit below 0.1 %, and at least three fibers meeting asbestiform criteria had to be counted to detect asbestos. Of four representative samples, a natural rock sample, a reference road aggregate sample and one road aggregate sample each contained both asbestiform and non-asbestiform fibers. Apart from one anthophyllite fiber, these were calcic amphiboles such as actinolite, tremolite and hornblende. One road aggregate fiber looked asbestiform under the NF X43-050 standard but had an actinolitic hornblende composition, and the procedure could not conclude on its identification. The authors concluded that the method gave coherent and reliable results. They noted that analyses rested on few fibers and that the method does not measure asbestos quantity.

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 methods paper describing an internal method, with application to a small number of representative samples; not a health study
• Who was studied: Four material samples: a reference standard actinolite asbestos (RSA) from the English Health and Safety Laboratories; a naturally occurring asbestos rock (NOA) from a French site known to contain actinolite asbestos; a road coated aggregate reference sample (RSS) from a German inter-laboratory campaign supplied by CRB Analyse Service; and one road coated aggregate sample (RCA) analyzed at Eichrom Laboratories
• Exposure: Elongated mineral particles in road coated aggregates (bituminous coating plus rock gravels): naturally occurring asbestos, mainly actinolite, and non-asbestiform cleavage fragments
• Main results:
  • In the authors' tests, a ball mill ground the material to a particle size of less than 100 micrometres at 450 rounds per minute for 5 minutes
  • Internal standard samples were used to show that the procedure identifies asbestiform fibers with a detection limit of less than 0.1 %
  • The authors' detection limit tests showed that at least three fibers meeting asbestiform criteria had to be counted to detect asbestos in products containing natural material
  • Based on morphology and dimensions, the NOA, RSS and RCA samples each contained both asbestiform and non-asbestiform fibers
  • In the RCA sample, no fiber was longer than 11 micrometres; one curved fiber had an aspect ratio of 65:1
  • All analyzed fibers showed a diffraction pattern confirming a crystalline structure
  • By chemical analysis, one fiber was anthophyllite. All other fibers were calcic amphiboles: actinolite, tremolite or hornblende, plus intermediate minerals such as actinolitic hornblende and ferro-actinolite
  • One fiber in the RCA sample was asbestiform by morphology under the NF X43-050 standard but had an actinolitic hornblende composition; the authors said their procedure could not conclude on the identification of this fiber
• The authors' conclusion: The authors concluded that the method accounts for the heterogeneity of natural materials and distinguishes asbestiform from non-asbestiform elongated mineral particles, and that the three techniques with geological expertise give coherent and reliable results. They called for standard samples and standardized terminology to make laboratory results consistent.
• Limitations the authors state:
  • The procedure is not intended for quantification
  • Analyses are mostly done on a small population of fibers, which the authors called very low for an unambiguous result
  • The method cannot be run routinely as for manufactured products because it requires geological expertise and quantitative analysis
  • With polarized light microscopy, the extinction angle cannot be observed for thin or single fibers, so transmission electron microscopy is needed
  • A conclusion on presence or absence of asbestos requires a fiber population representative of the whole material

Topics

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

Medical terms in this study, explained in our Lexicon: naturally occurring asbestos (NOA), Actinolite, Asbestiform, Cleavage Fragment.

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• The epidemiologic evidence for elongate mineral particle (EMP)-related human cancer risk — P. Boffetta, K.A. Mundt, et al. (2018)
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