The decontamination of perchlorate-contaminated water by woody plants was i
nvestigated in sand and hydroponic bioreactors. Willow trees were found to
be the most favorable woody plants with phraetophytic characteristics in co
mparative screen tests with eastern cottonwoods and Eucalyptus cineria. Wil
lows decontaminated aqueous solutions dosed with 10-100 mg/L of perchlorate
to below the method detection limit of 2 mu g/L. Two phytoprocesses were i
dentified as important in the remediation of perchlorate-contaminated water
: (a) uptake and phytodegradation of perchlorate in the tree branches and l
eaves and (b) rhizodegradation. Exposure of rooted willow trees to perchlor
ate-dosed media stimulated rhizodegradation. Homogeneous degradation studie
s using media from the root zone of dosed willow trees confirmed that rhizo
sphere-associated microorganisms mediated the degradation of perchlorate to
chloride. Experiments conducted with varying ranges of nitrate concentrati
ons clearly indicated that high nitrate concentrations interfered with rhiz
odegradation of perchlorate. This study provides evidence that the efficacy
of phytoremediation of perchlorate-contaminated environments may depend on
the concentration of competing terminal electron accepters, such as nitrat
e, and the nitrogen source of the nutrient solution. Since perchlorate does
not volatilize from water readily, a perchlorate remediation scheme may in
volve an intensively cultivated plantation of trees with phraetophytic char
acteristics and irrigation with the contaminated water.