A technical comparison of evaluating asbestos concentration by phase-contrast microscopy (PCM), scanning electron microscopy (SEM), and analytical transmission electron microscopy (ATEM) as illustrated from data generated from a case report

Our plain-English summary of A technical comparison of evaluating asbestos concentration by phase-contrast microscopy (PCM), scanning electron microscopy (SEM), and analytical transmission electron microscopy (ATEM) as illustrated from data generated from a case report, by R.F. Dodson, S.P. Hammar, L.W. Poye (Inhalation Toxicology, 2008).

The study

• Authors: R.F. Dodson, S.P. Hammar, L.W. Poye
• Journal: Inhalation Toxicology
• Published: 2008;20(7):723-32
• Type of article: Case report
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

As reported in the literature, there are more than 30 different standard methods available for the analysis of asbestos in a variety of situations. The methods include those for determining asbestos concentration in air, water, bulk building materials, surface dust, soil, and lung tissue (Millette, 2006; Dodson, 2006). Knowledge of the various methodologies is essential in determining which methodology is appropriate for any given situation. To better understand the use of various techniques in evaluating asbestos, we use an example of an individual who was a machinist in an auto supply/parts business. His work activity during much of his professional career included grinding, arcing, and drilling brake components. Asbestos has been identified as an important component of friction products, particularly brakes, and exposure to asbestos brake dust is of concern, particularly in workers where grinding, arcing, sanding, and drilling of brake components are recognized as releasing appreciable dust. Various methods can be used to evaluate asbestos in tissue and air. The case reported herein was of an individual who died from a pleural mesothelioma. Paraffin-embedded lung tissue was examined by a laboratory using scanning electron microscopy (SEM) and was reported to contain elevated asbestos body concentrations and five fibers, of which two were asbestos (one chrysotile and one tremolite). Tissue from the same paraffin block was analyzed by the laboratory of one of us (RFD) using analytical transmission electron microscopy (ATEM). While one might think the number of asbestos bodies and fibers would be similar using SEM and ATEM, this was not the case. Slightly elevated numbers of ferruginous asbestos bodies were detected in the digestate by light microscopy. Large numbers of uncoated chrysotile fibers were found by ATEM, but not by SEM. The majority of the chrysotile structures were fibrils whose detection required resolution levels attainable only at higher magnification by ATEM. The findings in this case clearly indicate that analysis of lung tissue digestates by ATEM at a higher magnification (15,000x) identifies significant numbers of asbestos fibers that are not identified by SEM at 1000x. These results further indicate that if causation of an asbestos-induced disease such as mesothelioma is based on asbestos concentration of lung tissue, erroneous conclusions can be made by analyzing tissue only by SEM. Thus, the methodologies that are available to analyze asbestos in lung tissue are extensively discussed here with respect to the type of procedure that should be utilized in various situations.

In plain English

This case report compared methods for measuring asbestos in lung tissue. The patient was a 62-year-old man who died of pleural mesothelioma and worked as a machinist whose work included grinding, drilling and arcing brake components. An earlier laboratory using scanning electron microscopy (SEM) at 1000× reported 10,900 uncoated fibers per gram of wet lung. Of the five fibers it analyzed, one was chrysotile, one tremolite and three talc. The authors examined remaining tissue from the same paraffin block by analytical transmission electron microscopy (ATEM) at 15,000×. They found 92 uncoated fibers, including 84 chrysotile and 4 amosite, equal to 458,333 asbestos fibers per gram of deparaffinized wet tissue. Both laboratories found asbestos bodies above the level the authors cite as the upper limit expected in the general population. The authors calculated that 97% of the chrysotile fibers would not be recognized under a phase-contrast light microscopy count scheme. They concluded that unless tissue or air is analyzed by ATEM at 15,000× or greater, many short fibers and long, thin fibers, mostly chrysotile, will be missed. They noted the report was based on a single case and one tissue block.

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: Case report used as a technical comparison of lung tissue analysis methods (an earlier SEM analysis by another laboratory versus the authors' ATEM analysis)
• Who was studied: One man, 62 years old at death, who had pleural mesothelioma
• Exposure: Work as a machinist that included grinding, drilling and arcing of brake components
• Main results:
  • Earlier analysis (other laboratory, SEM at 1000×): 10,900 uncoated fibers per gram of wet lung
  • Earlier analysis: of the five fibers examined, one was consistent with chrysotile, one with tremolite and three were talc
  • Earlier analysis: light microscopy found 1490 ferruginous bodies per gram of wet tissue
  • Authors' analysis: light microscopy found 7 small asbestos bodies, equivalent to 84 asbestos bodies per gram of deparaffinized wet tissue
  • Both laboratories found asbestos body levels above the level given as the upper limit expected in the general population
  • Authors' ATEM analysis at 15,000×: 92 uncoated fibers (1 silica, 3 talc, 4 amosite, 84 chrysotile)
  • Authors' ATEM analysis: uncoated asbestos fibers were equivalent to 458,333 fibers per gram of deparaffinized wet tissue
  • By ATEM, amosite made up 4% and chrysotile 96% of the asbestos fibers in the tissue
  • Only 7% of the chrysotile fibers were not fibrils (fibrils measured 0.02 to 0.05 μm in diameter)
  • 35% of the uncoated chrysotile fibers were longer than 5 μm
  • Under a count limited to fibers longer than 5 μm, 65% of the 84 chrysotile fibers would not qualify, while all 4 amosite fibers would
  • Under a phase-contrast light microscopy count scheme, 97% of the chrysotile fibers would not be recognized
  • Compared with an earlier 55-case mesothelioma study, this individual would have had the seventh highest asbestos burden
• The authors' conclusion: The authors concluded that unless lung tissue or air is analyzed by ATEM at 15,000× or greater magnification, a significant number of short fibers and long, thin fibers, most of them chrysotile, will be missed
• Limitations the authors state:
  • The report is based on a single case and findings in a single block of tissue

Topics

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

Medical terms in this study, explained in our Lexicon: Scanning Electron Microscopy (SEM), Analytical Transmission Electron Microscopy (ATEM), Settled Dust, Friction Products, Pleural Mesothelioma, Asbestos Body Formation, Chrysotile, Tremolite.

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