A comparison of light microscopy and transmission electron microscopy results in the evaluation of the occupational exposure to airborne chrysotile fibres

Our plain-English summary of A comparison of light microscopy and transmission electron microscopy results in the evaluation of the occupational exposure to airborne chrysotile fibres, by A. Marconi, E. Menichini, L. Paoletti (The Annals of Occupational Hygiene, 1984).

The study

• Authors: A. Marconi, E. Menichini, L. Paoletti
• Journal: The Annals of Occupational Hygiene
• Published: 1984;28(3):321-31
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

A comparison has been made between light microscope (LM) and transmission electron microscope (TEM) counts of airborne chrysotile fibres, collected on 30 membrane filters from different working processes. For TEM counts, fibres of length l > 5 µm were classified according to diameter d, namely 0.3 µm < d < 3 µm (microscopic fibres) and d ≤ 0.3 µm (submicroscopic fibres); short fibres, l ≤ 5 µm, were taken into account separately. A very good correlation has been found between LM and TEM counts, both for microscopic and total (microscopic + submicroscopic, l > 5 µm) fibres, for densities 40-500 fibres mm-2. The median of the ratios between TEM and LM counts has been found to be 1.1 for microscopic fibres and 1.2 for total fibres. From TEM counts, submicroscopic fibres have been found to account for about 10% of total l > 5 µm fibres. The mean ratio between short fibres and those with l > 5 µm was in the range 0.8-3.6, depending on the working process. These results suggest the possibility of adopting factors, varying with the kind of working process, to be applied to LM counts in order to estimate the exposure to all the asbestos fibres considered important for a comprehensive evaluation of the risk.

PubMed has no abstract for this study. This is the authors' abstract, copied from the article.

In plain English

This study compared two ways of counting airborne chrysotile asbestos fibres on the same filters. One was light microscopy (LM), the routine workplace method; the other was transmission electron microscopy (TEM), which can see thinner fibres. The authors examined 30 filters: 8 from a brake and clutch factory and 22 from a railway workshop handling asbestos tapes and paperboards and sanding asbestos-cement boards. Seven filters with very low or very high fibre densities were considered separately. In the remaining 23, TEM counts of LM-visible fibres over 5 micrometres long closely matched LM counts (correlation coefficient 0.90). The median TEM-to-LM ratio was 1.1 for LM-visible fibres and 1.2 when submicroscopic fibres were added. Submicroscopic fibres averaged about 10% of long fibres, though values varied widely. The mean short-to-long fibre ratio varied by process: 0.8 for brake and clutch work, 3.0 for tapes and paperboards, 3.6 for asbestos-cement sanding. The authors concluded that conversion factors for each process might allow a rough estimate of total fibres from LM counts. They also said factors from other surveys should not be used and more studies are needed.

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 methods-comparison study: portions of the same workplace air-sample filters were counted by light microscopy and by transmission electron microscopy
• Who was studied: 30 membrane-filter air samples: 8 from a brake and clutch factory and 22 from a railway maintenance and repair workshop. The authors worked in Rome, Italy; dates of sampling are not given.
• Exposure: Airborne chrysotile fibres from three work processes: brake and clutch manufacture, handling asbestos tapes and paperboards, and sanding asbestos-cement boards. TEM counts were split into microscopic fibres (longer than 5 micrometres, diameter between 0.3 and 3 micrometres), submicroscopic fibres (longer than 5 micrometres, diameter at or below 0.3 micrometres) and short fibres (5 micrometres or shorter).
• Main results:
  • In 4 of the 5 samples with an LM density below 20 fibres per square millimetre, TEM detected no fibres in the area examined.
  • These low-density samples and the 2 samples above 1000 fibres per square millimetre (7 in all) were considered separately in the overall analysis.
  • For the 23 samples with an LM density of 40 to 1000 fibres per square millimetre, the correlation coefficient was 0.90 between LM counts and TEM counts of microscopic fibres only (longer than 5 micrometres, diameter between 0.3 and 3 micrometres).
  • The median ratio of TEM to LM counts was 1.1 for microscopic fibres and 1.2 for total long fibres (microscopic plus submicroscopic).
  • When submicroscopic fibres were included, TEM detected up to 60% more fibres than LM (mean value for each process); the median increase for all the samples was 20%.
  • By TEM, submicroscopic fibres averaged about 10% of total fibres longer than 5 micrometres, with a wide distribution of values.
  • The mean ratio of short fibres (5 micrometres or less) to fibres longer than 5 micrometres ranged from 0.8 to 3.6 across work processes. These are process means, not the range across individual filters.
  • Table 5 gives the process means for the short-to-long ratio: 3.6 (standard deviation 3.4) for asbestos-cement board sanding, 3.0 (standard deviation 3.1) for tapes and paperboards (listed as insulation), and 0.8 (standard deviation 0.4) for brake and clutch.
  • Agreement between the two methods was greatest for the asbestos tapes and paperboards samples, which generally lacked non-fibrous particulate matter.
  • Agreement was lowest for the asbestos-cement samples.
  • Compared with earlier chrysotile studies, this study found a lower percentage of submicroscopic fibres among fibres longer than 5 micrometres than any other author.
• The authors' conclusion: The authors concluded that the two techniques agreed very well. They suggested that conversion factors derived for each work process could allow a rough evaluation of the total number of airborne chrysotile fibres from LM results, since LM cannot detect all fibres considered harmful.
• Limitations the authors state:
  • The authors stated that conversion factors derived from other surveys should not be used to determine exposure to all harmful fibres.
  • Results from different studies disagree, and few studies and samples exist. For these reasons the authors said generally valid conclusions about the percentage of submicroscopic fibres cannot yet be drawn.
  • The percentages of submicroscopic and short fibres were widely distributed across samples.
  • The authors said further systematic studies on more samples from different work processes are needed to determine conversion factors.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Chrysotile.

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

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