Fate and Transport of Uranium in the Rhizosphere: The Role of Plant Exudates and Hydrological Processes
Abstract
Uranium contamination of the subsurface environment results from both anthropogenic activities and natural occurrence. Human and ecological concerns are related to the fate and transport of uranium in soils and groundwater resources. Therefore, understanding how the geochemical and hydrological conditions and processes govern the fate and transport of uranium in the rhizosphere is critical to forecasting human and ecosystem exposure and health risk assessment to these radionuclides. The objectives of this research are to determine the effects of plant exudates (citrate, oxalate, and tannic acid) and phenomena of water infiltration in the rhizosphere on the fate and transport of uranium (uranyl-phosphate, doped with U-235). Flow and transport experiments were conducted in two-dimensional tanks. ASTM sand was uniformly packed in tanks and radioactive sources of uranyl-phosphate, doped with U-235, were placed in the sand. We examined the effects of plant exudates dispensed as artificial rainfall infiltrating sand under unsaturated conditions on the mobility of the radioactive materials in two-dimensional tanks. U-235 is a gamma ray emitting isotope, thus we were able to monitor the transport of radionuclides in the tank using an automated gamma scanner consisting of a spectroscopic gamma detector mounted on a two-dimensional linear axis system controlled by National Instruments LabVIEW 2015. This monitoring system allowed us to quantify the radionuclides and map their distribution in variably saturated porous media over time. The light transmission method (LTM) was used to examine the effects of plant exudates on the soil hydrological processes by measuring water contents and visualizing infiltration patterns in porous media in the two-dimensional tanks. Effluent from two dimensional tanks was also captured and analyzed using a liquid scintillation counter. The coupling of non-intrusive measurements and breakthrough curve analyses allowed for the characterization of the fate and transport of uranyl-phosphate in the vadose zone, and in particular the effect of plant exudates on uranyl-phosphate dissolution rates and patterns.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.H31J2041D
- Keywords:
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- 1829 Groundwater hydrology;
- HYDROLOGYDE: 1831 Groundwater quality;
- HYDROLOGYDE: 1832 Groundwater transport;
- HYDROLOGYDE: 1847 Modeling;
- HYDROLOGY