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DETERMINING COPPER AND LEAD BINDING IN LARREA TRIDENTATA THROUGH CHEMICAL MODIFICATION AND X-RAY ABSORPTION SPECTROSCOPY

We determined, through chemical modification of carboxyl groups with methanol, that these functional groups are responsible for a portion of copper binding. In contrast, lead binding was minimally affected by modification of carboxyl groups. Additionally, chemical modification of sulfhydryl and amino groups minimally affected either copper or lead binding. X-ray absorption spectroscopic studies conducted at Stanford Synchrotron Radiation Laboratory (SSRL) further support copper binding to oxygen-coordinated ligands and also imply that the binding is not due to phytochelatins.

The EXAFS data indicates the presence of both Cu-O and Cu-S backscatters, no short Cu-Cu interactions, but with significant Cu-Cu backscattering at 3.7Å (unlike phytochelatins with predominantly Cu-S coordination and short Cu-Cu interactions at 2.7Å). Cu EXAFS of roots and leaves also vary depending on the level of heavy metal contamination environment from which the various creosote samples were obtained. Spectra are consistent, however, with the presence of both cuprous and cupric copper in both the roots and leaves, with a larger fraction of cuprous copper in the leaf tissue.

Contrastly, Pb XANES data of roots and leaves of creosote collected from different contaminated sites indicate no difference in valence states or ligand coordination. Additional XANES and EXAFS of copper and lead binding will be presented.

Key words: Larrea tridentata, phytoremediation, creosote bush, x-ray absorption