DIRECT ANALYSIS OF AMPHIBOLES ON TREE BARK BY SEM UTILIZING BOTH EDS AND EBSD TECHNIQUES FROM LIBBY, MONTANA AND IMPLICATIONS ON PUBLIC PERCEPTION

Tree bark as a reservoir of amphibole asbestos fibers was first recognized by Ward et al. 2006 in areas near the former vermiculite mine outside of Libby Montana. Observed concentration using indirect preparation techniques have been demonstrated for years to inflate fiber counts in standard test methods for asbestos. In order to determine the direct amphibole loading on tree bark in the Libby area 12 sample locations were chosen surrounding the former vermiculite mine where the various tree types bark were sampled. The samples were directly analyzed under variable pressure and amphiboles were characterized by SEM-EDS and a subgroup were relocated and analyzed using EBSD techniques to confirm amphibole is present. Multiple amphibole species were observed that included tremolite, actinolite, magnesio-hornblende, winchite, and richterite and based on composition only a fraction of observed amphiboles can be traced back to the vermiculite mine. Interestingly amphiboles were observed that are consistent with those observed in the 1980 Mount Saint Helens ash. Observed surface loadings of tree bark ranged from none detect to 0.85s/cm². This is contrasted with concentration ranges observed using indirect preparation techniques for tree bark collected by Ward of none detect to 260 million s/cm². The vast difference observed in structure concentration between this study and other studies to date are directly associated to the indirect preparation and associated calculations and uncertainties.