Submitted to: World Congress of Soil Science
Publication Type: Abstract Only
Publication Acceptance Date: February 15, 2006
Publication Date: July 10, 2006
Citation: Tappero, R., Chaney, R.L., Sparks, D.L. 2006. Spectromicroscopic investigation of co speciation in a ni/co hyperaccumulator plant used for phytoremediation and phytomining [abstract]. World Congress of Soil Science. Abstract 12480.
Metal contamination of surface and subsurface environments is a worldwide concern. Unique metallophyte plants (hyperaccumulators) accumulate high concentrations of trace metals in their harvestable biomass, and thereby offer a sustainable method for treatment of metal-contaminated sites (phytoremediation) and an opportunity to mine metal-rich soils (phytomining). Several species of Alyssum (Brassicacea family) have the ability to simultaneously hyperaccumulate Ni and Co in a mixed-contaminant system. Information on the localization, speciation, and associations of accumulated metals with other elements in hyperaccumulator plants can provide insight into the physiological and biochemical mechanisms of metal tolerance and accumulation. Synchrotron-based techniques such as microfocused X-ray absorption fine structure (XAFS) and X-ray fluorescence (XRF) spectroscopy and computed microtomography (CMT) enable the investigation of metal reactions and processes in natural systems at the micron scale. SXRF and CMT were utilized to observe in situ metal localization and compartmentalization in the Ni/Co hyperaccumulator A. murale. SXRF images revealed preferential localization of Co at leaf tips and margins and a relatively uniform distribution of Ni in A. murale leaves. CMT cross-sectional images revealed aqueous Co was primarily limited to the plant vascular system, while Ni was enriched in vascular and epidermal tissue. Cobalt speciation in plant tissue was investigated in situ with bulk and '-XAFS. Primary Co species in the roots and leaves were aqueous metal complexes with organic and amino acids (e.g. malate and histidine). Preliminary '-XAFS investigations indicated the Co deposited at leaf tips and margins formed a Co(OH)2-nH2O precipitate with some degree of short range order. Results suggest A. murale utilizes different metal detoxification and sequestration mechanisms to tolerate elevated concentrations of Co and Ni in plant tissue.