Assessment of occupational exposure to asbestos fibers: Contribution of analytical transmission electron microscopy analysis and comparison with phase-contrast microscopy

Our plain-English summary of Assessment of occupational exposure to asbestos fibers: Contribution of analytical transmission electron microscopy analysis and comparison with phase-contrast microscopy, by C. Eypert-Blaison, A. Romero-Hariot, F. Clerc, et al (Journal of Occupational and Environmental Hygiene, 2018).

The study

• Authors: C. Eypert-Blaison, A. Romero-Hariot, F. Clerc, R. Vincent
• Journal: Journal of Occupational and Environmental Hygiene
• Published: 2018;15(3):263-274
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

From November 2009 to October 2010, the French general directorate for labor organized a large field-study using analytical transmission electron microscopy (ATEM) to characterize occupational exposure to asbestos fibers during work on asbestos containing materials (ACM). The primary objective of this study was to establish a method and to validate the feasibility of using ATEM for the analysis of airborne asbestos of individual filters sampled in various occupational environments. For each sampling event, ATEM data were compared to those obtained by phase-contrast optical microscopy (PCOM), the WHO-recommended reference technique. A total of 265 results were obtained from 29 construction sites where workers were in contact with ACM. Data were sorted depending on the combination of the ACM type and the removal technique. For each "ACM-removal technique" combination, ATEM data were used to compute statistical indicators on short, fine and WHO asbestos fibers. Moreover, exposure was assessed taking into account the use of respiratory protective devices (RPD). As in previous studies, no simple relationship was found between results by PCOM and ATEM counting methods. Some ACM, such as asbestos-containing plasters, generated very high dust levels, and some techniques generated considerable levels of dust whatever the ACM treated. On the basis of these observations, recommendations were made to measure and control the occupational exposure limit. General prevention measures to be taken during work with ACM are also suggested. Finally, it is necessary to continue acquiring knowledge, in particular regarding RPD and the dust levels measured by ATEM for the activities not evaluated during this study.

In plain English

This French field study, organised by the general directorate of labour from November 2009 to October 2010, measured asbestos fibers in personal air samples taken during work on asbestos-containing materials. Samples from 71 sites, covering 29 combinations of material and removal technique, gave 265 results analysed by analytical transmission electron microscopy (ATEM). For 196 of these, phase-contrast optical microscopy (PCOM) counts on the same filters were available. Short asbestos fibers were considerably more numerous than WHO fibers or thin fibers, and for each fiber class the mean serpentine concentration exceeded the mean amphibole concentration. Asbestos-containing plaster produced the highest dust levels. After allowing for respirator protection, the estimated maximum exposure to WHO plus thin fibers exceeded 10 fibers per litre for more than half the site types. On average, ATEM counted about 4 times more WHO fibers than PCOM, and about 15 times more when thin fibers were included. No simple relationship allowed results to be converted between the two methods. The authors concluded that ATEM monitoring was technically feasible and that PCOM underestimates dust levels compared with ATEM. They noted that only about half the planned results were collected and the analysis was descriptive.

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: Field measurement campaign using personal air sampling during work on asbestos-containing materials, with ATEM counts compared to PCOM counts on the same filters (descriptive analysis)
• Who was studied: Workers on 71 French work sites covering 29 material-technique combinations, sampled November 2009 to October 2010; 265 ATEM results
• Exposure: Airborne asbestos fibers (serpentine and amphibole; chrysotile the most common type identified) released during removal or other work on asbestos-containing materials such as plaster, sprayed-applied asbestos, asbestos cement, floor and wall tile adhesives, paints and coatings, and pipe insulation, using techniques such as scraping, grinding-sanding, chiseling, cutting and very high or ultrahigh pressure hydroblasting. Fibers were classed as WHO fibers, thin asbestos fibers (TAF) and short asbestos fibers (SAF).
• Main results:
  • Across all samples, concentrations of short asbestos fibers (SAF) were greater than those of WHO fibers and thin fibers (TAF).
  • The number of thin fibers (TAF) was slightly higher than the number of WHO fibers.
  • For every fiber class, the mean amphibole concentration was lower than the mean serpentine concentration. Results were highly variable, with extreme values above 250,000 fibers per litre for serpentine short fibers.
  • Asbestos-containing plaster produced the highest concentrations of thin and short fibers, and the highest mean and maximum WHO plus thin fiber levels.
  • Very high pressure and ultrahigh pressure removal techniques produced the highest mean WHO plus thin fiber concentration, above 11,000 fibers per litre.
  • After dividing measurements by the assigned protection factor of the respirators worn, the estimated maximum WHO plus thin fiber exposure exceeded 10 fibers per litre for more than half of the site types.
  • Removal of materials considered non-friable, such as fiber cement roofing or indoor-outdoor surface coatings, produced high dust levels: greater than 2000 fibers per litre on average and in some cases up to 8580 fibers per litre.
  • 390 filters were assessed by PCOM, allowing direct comparison with 196 ATEM results.
  • On average, ATEM gave 4-fold higher counts of WHO fibers than PCOM, and the ratio rose to 15 when thin fibers were included. Table 5 gives mean ratios of 4.56 for WHO fibers and 15.21 for WHO plus thin fibers, across 196 samples.
  • For amphibole fibers, the ratio of ATEM to PCOM counts was lower, often less than 1.
  • For asbestos-containing plaster, paints and surface coatings, PCOM considerably underestimated fiber numbers compared with ATEM.
  • Statistical tests (Pearson R of 0.86, adjusted R2 of 0.43) led the authors to conclude that no simple relationship allows results to be converted between the two counting techniques.
• The authors' conclusion: The authors concluded that monitoring asbestos in occupational settings by ATEM is technically feasible whatever the dust level, that PCOM is unsuitable for characterising asbestos fiber aerosols at work, and that PCOM underestimates dust levels compared with ATEM.
• Limitations the authors state:
  • Only slightly more than half of the planned results were collected.
  • Only 77% of ATEM results could be directly compared with PCOM results.
  • The statistical analysis was descriptive only.
  • The small number of sites surveyed made statistically significant results impossible.
  • The respirator protection factors used were derived from PCOM analysis in the 1990s and need reassessment by ATEM.
  • Few sporadic intervention situations were assessed, so more data are needed for these operations.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Analytical Transmission Electron Microscopy (ATEM).

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