Evaluation and application of a plasma ashing method for STEM fiber analysis in human lung tissue

A preparation technique for fiber analysis in human lung tissue has been developed that involves freeze-drying and low-temperature ashing. Analysis is made in the analytical scanning transmission electron microscope at a magnification of 10,000 x. With the use of a special counting method, the sensitivity is approximately 80,000 fibers per gram dry tissue with lengths less than 5 microns and 40,000 fibers per gram dry tissue with lengths greater than or equal to 5 microns. In spite of the leaching and contamination effects described in the literature--even for chrysotile fibrils taken from the lung, elemental spectra do not differ essentially from the asbestos standard. In order to carry out a complete check of the preparation method, a suspension of standard crocidolite fibers in water was gelatinated. No changes in length, diameter or aspect ratio distribution occurred. After preparation, at least 40% of the fibers were recovered. Compared to the wide range of fiber concentrations observed in human lung tissue, these recovery rates appear adequate for fiber analysis in lung dust for medical or legal purposes. To date, 70 lung dust specimens have been analyzed. These are discussed in the paper.