REDUCTION OF CR(VI) TO CR(III) BY WETLAND PLANTS - POTENTIAL FOR IN-SITU HEAVY-METAL DETOXIFICATION

Reduction of heavy metals in situ by plants may be a useful detoxifica tion mechanism for phytoremediation. Using X-ray spectroscopy, we show that Eichhornia crassipes (water hyacinth), supplied with Cr(VI) in n utrient culture, accumulated nontoxic Cr(III) in root and shoot tissue s. The reduction of Cr(VI) to Cr(III) appeared to occur in the fine la teral roots. The Cr(III) was subsequently translocated to leaf tissues . Extended X-ray absorption fine structure of Cr in leaf and petiole d iffered when compared to Cr in roots. In roots, Cr(III) was hydrated b y water, but in petiole and more so in leaf, a portion of the Cr(III) may be bound to oxalate ligands. This suggests that E. crassipes detox ified Cr(VI) upon root uptake and transported a portion of the detoxif ied Cr to leaf tissues. Cr-rich crystalline structures were observed o n the leaf surface. The chemical species of Cr in other plants, collec ted from wetlands that contained Cr(VI)-contaminated wastewater, was a lso found to be Cr(III). We propose that this plant-based reduction of Cr(VI) by E crassipes has the potential to be used for the in situ de toxification of Cr(VI)-contaminated wastestreams.