The uptake and degradation of perchlorate by three woody plants (willow (Salix ssp.), Cottonwoods (Populus ssp.) and Eucalyptus cineria) species was investigated. Perchlorate was removed by willow from bioreactors dosed with 10,20 and 100 mg/L of perchlorate to below the method detectionlimit of 2 #mu#g/L by willows and Eucalyptus. Non-woody plants, such as spinach, French tarragon, and Myriophyllum (an aquatic plant) also removed perchlorate from the contaminated water. Two phytoprocesses identified as important in the remediation of perchlorate-contaminated water included: (1) uptake and phytodegradation in the plant organs, and (2) rhizodegradation. Experiments conducted with growth media taken from the rhizosphere of willow trees confirmed that rhizosphere-associated microorganisms mediated the rhizodegradation of perchlorate to chloride. High nitrate concentrations interfered with the rhizodegradation of perchlorate because nitrate acted as a competing terminal electron acceptor (TEA). Uptake of perchlorate by woody plants was minimized in medium with ammonium as the N-source. Since perchlorate does not volatilize from water readily, a perchlorate remediation scheme may involve an intensively cultivated plantation of trees with phraetophytic characteristics, and irrigation with the contaminated water.
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