Improved Method for Analysis of Airborne Asbestos Fibers Using Phase Contrast Microscopy and FTIR Spectrometry

Our plain-English summary of Improved Method for Analysis of Airborne Asbestos Fibers Using Phase Contrast Microscopy and FTIR Spectrometry, by M.R. Azari, A. Yazdian, R. Zendehdel, et al (Tanaffos, 2014).

The study

• Authors: M.R. Azari, A. Yazdian, R. Zendehdel, H. Souri, S. Khodakarim, H. Peirovi, D. Panahi, M. Kazempour
• Journal: Tanaffos
• Published: 2014;13(3):38-45
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Free full text

Abstract

Background: In recent years, some studies have tried to improve Phase Contrast Microscopy (PCM) for counting asbestos fibers. Due to the lack of a universally accepted alternative method, this study aimed to improve PCM for better counting of asbestos fibers.

Materials And Methods: Confirmed asbestos standards were applied using a dust generator for sampling. Sampling from the dust generator was carried out according to the Occupational Safety and Health Administration (OSHA) ID-160 method and 95 samples with diverse densities were prepared to be counted using conventional and modern PCM. All samples were counted single blindly by a co-author of this study and the obtained data were analyzed by paired t-test, correlation coefficient and Bland-Altman analysis. Duplicate samples were prepared for qualitative analysis by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and X ray.

Results: Asbestos densities on filters were in the range of less than 100 to 600 fibers/mm(2). Statistically, significant differences were observed for the count density of the 95 samples counted by the two phase contrast microscopes (P<0.001). Nikon microscope demonstrated higher counts compared to conventional microscope and had a lower coefficient of variation. Samples were analyzed qualitatively using FT-IR and SEM, and the presence of asbestos fibers was confirmed.

Conclusion: The improved PCM and FT-IR methods presented in this study demonstrated more precise and accurate determination of personal exposure to airborne asbestos fibers and subsequent risk assessment.

In plain English

This was a laboratory study from Iran. It compared two ways of counting airborne asbestos fibers with a phase contrast microscope and tested infrared spectroscopy (FT-IR) for identifying chrysotile asbestos. The authors fed chrysotile asbestos into a closed glass dust generator and collected 95 filter samples at six different air flows, following the OSHA ID-160 method. A co-author who did not know which sample was which counted each sample five times on a conventional Leitz microscope and on a Nikon microscope connected to a 12-megapixel camera and 21-inch monitor. The Nikon counted more fibers, a statistically significant difference (P<0.001). The two sets of counts were closely correlated (r2 = 0.962). Average count variability (coefficient of variation) was 0.12 for the Leitz and 0.10 for the Nikon. FT-IR showed that two of three reference samples were pure chrysotile, and SEM confirmed this. Raw materials from brake shoe manufacturers were not identified as chrysotile, but waste from auto brake repairs was. The authors concluded that both methods may be used to measure personal exposure and assess risk.

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 method-comparison study: fiber counts by a conventional phase contrast microscope compared with counts by a modern camera-and-monitor phase contrast microscope, plus qualitative identification of chrysotile by FT-IR, SEM and X-ray diffraction
• Who was studied: 95 air filter samples collected at 6 different sampling flows from a laboratory dust generator (Shahid Beheshti University of Medical Sciences, Tehran, Iran); also bulk raw materials from three brake shoe manufacturers, waste from auto brake repairs, and two personal air samples from auto brake repair workers. Study dates not given.
• Exposure: Airborne chrysotile asbestos produced in a closed dust generator from standard asbestos obtained from Iranian universities. Samples were collected at flows of 0.5 to 1.75 l/m for 30 minutes, and fibers at least 5 microns long with a length-to-width ratio of 3 or more were counted.
• Main results:
  • Across the 95 samples, mean fiber density ranged from 9.6 to 551.8 f/mm2 when counted on the Leitz (conventional) microscope and from 13.8 to 588.5 f/mm2 on the Nikon (modern) microscope.
  • The Nikon microscope counted more fibers than the Leitz microscope, and the difference was statistically significant (P<0.001, paired t-test).
  • In the Bland-Altman agreement analysis, six of the 95 samples fell outside two standard deviations of the mean difference between the two microscopes.
  • Mean coefficient of variation was 0.12 (SD 0.065) for the Leitz microscope and 0.10 (SD 0.047) for the Nikon microscope. In the 0 to 100 f/mm2 range it was 0.19 for the Leitz and 0.15 for the Nikon.
  • Counts by the two microscopes were correlated, with r2 = 0.962.
  • FT-IR found that only two of the three standard asbestos samples from Iranian universities (A and B) were pure chrysotile, and SEM confirmed this. The magnesium to silica ratio for sample A was 1.39.
  • Three raw-material samples from brake shoe manufacturers were not identified as chrysotile asbestos, while a waste sample from auto brake repairs was identified as chrysotile. SEM confirmed both results.
• The authors' conclusion: The authors concluded that the improved phase contrast microscopy and FT-IR analysis presented in the study may be used to determine personal exposure and for subsequent risk assessment.

Topics

Medical terms in this study, explained in our Lexicon: phase contrast microscopy (PCM), OSHA, Infrared Spectroscopy (IR), Scanning Electron Microscopy (SEM).

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