Two complimentary spectroscopic techniques, X-ray absorption and fluorescence spectroscopy have been conducted at spatial scales of 1 to 25 ~tm on uranium contaminated soil sediments collected from two former nuclear materials processing facilities of the DOE: Fernald, OH and Savannah River Site, SC. A method of imbedding particles in a non-reactive Si polymer was developed such that individual particles could be examined before and after extraction with a wide range of chemicals typically used in sequential extraction techniques and others proposed for ex situ chemical intervention technologies. Using both the micro-X-ray fluorescence (XRF) and micro-X-ray Absorption Near Edge Structure (XANES) techniques, both elemental and oxidation state distribution maps were generated on individual particles before and following chemical extraction. XANES can determine the relative proportion of U(VI) and U(IV) in phases comprising individual particles before and after extraction and showed that greater than 85% of the uranium existed as hexavalent U(VI). Fluorescence spectra of contaminated particles containing mainly U(VI) revealed populations of uranyl hydroxide phases and demonstrated the relative efficacy and specificity of each extraction method. Correlation of XAS and fluorescence data at micron scales provides information of U oxidation state as well as chemical form in heterogeneous samples.
Shell fragments from turtles collected in a wetland receiving outfall from coal combustion ash basins were elevated in a number of contaminants, notably Se and As. Micro-XANES analysis of the epithelial layer on the shell and of the bone tissue revealed that the keratin associated Se was present exclusively in seleno-amino acid coordination environments, whereas Se in the bone tissue was a mixture of selenate and proteinaceous Se. Elemental distribution maps of hyperaccumulating plants generated by XRF reveal a heterogeneous distribution of Se and Cr, with Se being concentrated within the nuclei of cells and Cr within discrete aggregates in the cytoplasm. Micro-XANES measurements taken on these same regions demonstrated the total loss of the CrWI) diagnostic pre-edge feature, indicating the complete reduction of the Cr(V1) to CrfJII) after uptake by the plants.
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