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
Inhalation Toxicology. 2008 May;20(7):723-32 [Link]
Dodson RF, Hammar SP, Poye LW.
Dodson Environmental Consulting, Inc., and ERI Analytical, Tyler, Texas, USA.
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 (15,000×) identifies significant numbers of asbestos fibers that are not identified by SEM at 1000×. 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.
