QUANTIFYING PERCENT AMPHIBOLE ASBESTOS BY POWDER X-RAY DIFFRACTION AND POLARIZING LIGHT MICROSCOPY: USING SOILS FROM LIBBY, MONTANA AND EL DORADO HILLS, CALIFORNIA USA

Six soil samples, three from Libby, Montana and three from El Dorado Hills, California, were collected and analyzed for percent asbestiform and percent non-asbestiform amphiboles. Powder X-ray Diffraction (XRD) and polarized light microscopy (PLM) were used in concert in this study. Quantitative XRD was used to quantify bulk amphibole content, while the mineralogical definition of asbestiform was used to differentiate the growth habit of asbestos from non-asbestos habits. XRD detected and quantified amphiboles in each soil. The percent amphibole for the Libby samples ranged from 1.4 to 7.9 weight percent (%), while the EL Dorado Hills samples ranged from 0.7 to 10.7 %. The Libby soils analyzed also contained appreciable amounts of vermiculite. Fifty amphibole particles were observed per sample to determine morphology. The portion of amphiboles that were asbestiform for the Libby soils was 22 %, 26 %, and 32 %, respectively in the three samples. These data are consistent with other researchers. In contrast the El Dorado Hills soils contained no observed asbestiform amphiboles. Total percent asbestiform amphibole for the Libby samples is 0.3 to 2.5 weight percent and for the El Dorado Hills zero percent.

Using the proposed definition developed by the California Air Resources Board (CARB) to define asbestos in soils. Specifically: optical properties within a specified range, fiber aspect ratio of 3:1 or greater, width < 3.0 mm, no length criteria, acicular or needle-like crystal habit, cleavage planes bounding fragments, irregular shapes (i.e., square terminations and non-parallel or jagged sides) CARB 2009. Based on these criteria, results for the Libby samples exhibited an increase asbestos content of 0.68 to 4.76 % and the El Dorado Hills samples increases to 0.04 to 3.41 %. Thus there is a major discrepancy between their proposed definition of asbestos and the actual asbestiform amphibole content of these soils.