Health Library

Published: April 2016

Evaluation of libby amphibole asbestos in three media sources via polarized light microscopy and transmission electron microscopy

Published By: ProQuest Dissertations & Theses Global

Contributors: McCloskey, Kalli


Studies have shown that the town of Libby, Montana and surrounding forested areas have been contaminated with Libby amphibole asbestos (LA) by activity from the vermiculite mine located northeast of Libby. The mine was in production from the 1920s until its closing in 1990. The United States Environmental Protection Agency (USEPA) created the operable units (OU) within the superfund site due to the LA contamination. In addition to the work completed in this research, previous studies have shown that there is an exposure pathway for the United States Department of Agriculture, Forest Service (USFS) personnel tasked with forest maintenance in and around the Tubb gulch OU3 area. Tree bark, duff, and soil composite samples were collected to characterize the LA contamination in the Tubb Gulch area west of the mine. Composite samples were analyzed first by polarized light microscopy (PLM) (for bark and duff) and second by transmission electron microscopy for all media sources (TEM). The objective was to determine if PLM analysis could be used as a primary analytical tool for bark and duff sampling, since TEM is considerably more expensive and takes longer for the laboratory analysis. Fifteen positive composite samples that were initially analyzed via PLM were selected for further analyses via TEM for bark and duff media types. Bark sampling results revealed positive TEM values in 14 of 15 (93%) of the samples and duff sampling results revealed positive TEM values in 15 of 15 (100%) of the samples. These data suggest that PLM analysis may be a reliable initial analytical screening method. Since the LA concentrations for bark were expressed as fibers per surface area of bark and the LA concentrations for duff were expressed as fibers per gram, statistical correlation analyses could not be performed. A further limitation with this assessment is that bark and duff samples revealing non-detect values via PLM analysis were not selected for TEM analysis; therefore, the potential for false negative results via PLM was not assessed. The results of this study were valuable in further characterizing the Tubb Gulch area. All bark and duff composite samples revealed the presence of asbestos structures via TEM with the exception of one bark sample. Based on these source media results, there is a potential for LA exposure to USFS personnel or members of the public when working or recreating in the Tubb Gulch area. It is important to note that the results did not follow a concentration gradient in that some of the lowest concentrations were detected closest to the mine. These data suggest that LA contamination was dispersed not only from the mining activities but during transportation of the vermiculite concentrate to Libby and to the train loading facility.

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