UPTAKE AND FRACTIONATION OF RARE EARTH ELEMENTS BY CRESTED WHEATGRASS IN A SAGEBRUSH STEPPE ECOSYSTEM

We have characterized the ability of crested wheatgrass (Agropyron desertorum) from a sagebrush steppe ecosystem at the Idaho National Engineering and Environmental Laboratory (INEEL) to fractionate rare earth elements (REE). Samples of rhizosphere soil, as well as shoots and roots of crested wheatgrass were collected at an uncontaminated site within the Advance Reactor Area of the INEEL. The samples were collected in early April 2001 during the early growth cycle as nutrients and water were shuttled from the rhizosphere soil and the roots, into the shoots of the plant via the xylem. Samples were oven dried and mechanically processed in preparation for analysis by neutron activation analysis (NAA). Results indicate that partitioning does occur between soils and plants and within different locations of the plant. The REE concentrations were normalized to the North American Shale composite to help identify fractionation trends. Initial analysis of these normalized concentrations in the rhizosphere soil, roots, and shoots indicate that crested wheatgrass does have the ability to fractionally extract REEs from the soil. The data trend indicates that the concentrations of REEs in the roots are higher and have greater variability than the concentrations of REEs in the shoots. The roots fractionate REEs more than do the shoots of the crested wheatgrass plant. The REEs are chemically similar to several transuranics and so REE behavior in shallow vegetated soils can serve as an analog of the behavior of those radioactive elements.