Program One
Tuesday, May 20, 1997

Metals Kansa A


    3

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

 
L.A. Polette, J.L. Gardea-Torresdey, and R.R. Chianelli; Department of Chemistry, The University of Texas at El Paso, El Paso, TX 79968, and I. Pickering and G. George, Stanford Synchrotron Radiation Laboratory, Bldg 120, 2575 Sandhill Rd, Menlo Park, CA 94025 Metal contamination in soils has become a widespread problem. Emerging technologies, such as phytoremediation, may offer low cost cleanup methods. We have identified a desert plant, Larrea tridentata (creosote bush) which naturally grows and uptakes copper and lead from a contaminated area near a smelting operation. In an effort to understand its potential use as a phytoremediating shrub, the role of carboxyl, sulfhydryl, and amino groups on copper and lead binding were examined.

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 3.7 (unlike phytochelatins with predominantly Cu-S coordination and short Cu-Cu interactions at 2.7). 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



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Tuesday, May 20, 1997

Metals Kansa A

Remediation of Munitions Compounds Kansa B

Analytical Methods Kansa C/D

General Topics Kansa B


Wednesday, May 21, 1997

Metals Kansa A

Zero-Valent Metals Kansa A

Remediation Kansa A

Vegetation-based Remediation Kansa B

Partnerships & Innovative Technologies Kansa C/D

Nonaqueous Phase Liquids Kansa C/D


Thursday, May 22, 1997

Biofilms & Barriers Kansa A

Bioremediation Kansa B

Partnerships & Technology Innovations Kansa C/D

Remediation Kansa C/D


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