Comparative uptake, translocation, and plant mediated transport of Tc-99, Cs-133, Np-237, and U-238 in Savannah River Site soil columns for the grass species Andropogon virginicus.

This study examines the ability of the grass species Andropogon virginicus to alter the subsurface transport and redistribution of a suite of radionuclides (Tc, Cs (stable analog for Cs and Cs), Np, U) with varying chemical behaviors in a Savannah River Site soil via the use of vegetated and unvegetated soil columns. After an acclimation period, a small volume of solution containing all radionuclides was introduced into the columns via Rhizon© pore water sampling tubes. Plants were grown for an additional 4 weeks before shoots were harvested, and columns were prepared for sampling. Plant presence led to decreased radionuclide release from the columns, mainly due to radionuclide specific combinations of system hydrology differences resulting from plant transpiration as well as plant uptake. For the most mobile radionuclides, Tc followed by Np, plant presence resulted in significantly different soil concentration profiles between vegetated and unvegetated columns, including notable upward migration for Np in columns with plants. Additionally, plant uptake of Tc was the greatest of all the radionuclides, with plant tissues containing an average of 44 % of the Tc, while plant uptake only accounted for <2 % of Np and <0.5 % of Cs and U in the system. Although overall plant uptake of Cs and U were similar, the majority of Cs taken up by plants was associated with Cs already available in the aqueous phase while U uptake was mainly associated with the solid phase, meaning that plant activity resulted in a fraction of the native U being mobilized and thus, made available for plant uptake. Overall, this study quantified the influence of several plant-mediated physical and biogeochemical factors that have significant influence on radionuclide mobility and transport in this complex system which can be further utilized in future system or site-specific environmental transport and risk assessment models.