PHYTOREMEDIATION OF TOXIC WASTE SITES

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The purpose of this program is to explore the use of plants to remediate toxic solvent spills, especially trichloroethylene (TCE), in the environment. Poplars were used as there is an extensive background dealing with this species. The hybrid H-11-11, Populus trichocarpa X P. deltoides, was used as it has favorable cultivation and growth characteristics. The tress were planted at a site designed by Occidental Chemical Corporation with concurrence of the Washington State Department of Ecology. Over the 4-year period 98-99% of the TCE has been removed from the influent water. During 1998 there was no detectable TCE transpired by the trees. Analysis of the planted soil versus controls showed an increase in chloride that was equivalent to the amount of TCE added to the cells. indicating that the TCE has been extensively mineralized. Comparable results were found using carbon tetrachloride and perchloroethylene. The contribution of bacteria to the degradation of the TC was negligible. Under conditions comparable to what exists at our site, poplars will be useful for remediation. Studies with Dr. Mike Hooper (Project #7) have indicated that the detritus from TCE treated poplars is harmless to several insects tested. Future work will use 14C-labeled TCE to measure the rate of uptake and the fate of the carbon of TCE. We will also develop a repertoire of plants that can detoxify a variety of common pollutants in a variety of geographic areas. We have also had preliminary success with the introduction of genes for a degradative enzyme, cytochrome P450 IIE1. These plants formed up to 35 times as much of the first degradative product of TCE. We are in the process of applying for permission to use them at our field test site. We have entered into collaborations with several other investigations to obtain genes that will broaden the range of compounds that can be detoxified by plants.