New Mexico Geological Society Annual Spring Meeting — Abstracts

Phytoremediation of U-contaminated soils has been extensively explored in Ohio and other temperate U.S. areas. These studies have used soil amendments such as EDTA or citric acid to stimulate plant U hyperaccumulation. Arid and semi-arid soils are however significantly different from temperate U.S. soils as they generally have a higher pH, higher calcium carbonate content, and less organic carbon. As pH increases, oxidized U (VI) becomes less soluble and adsorbs to the Fe and Mn oxhydroxides. These soil treatments become less effective and cost-effective in areas with diffuse contamination and alkaline soils.

For phytoremediation to work, it is important to find U-accumulating plants that can grow well in the local environment. Uranium geobotanical studies for the Four Corners area have found preliminary evidence of native plant accumulation of uranium. These studies documented a wide variety of plant species under varying site conditions. The response of multiple plant species involves a more detailed analysis of site conditions.

Two unremediated mine sites (with U to 10^-4 Rem levels) and a uranium-bearing surface outcrop were evaluated for plant concentrations of uranium and for the soil availability of uranium. Initial results indicate that the winter annual, Descurainia obtusa, and the grass Oryzopsis hymenoides may be natural U accumulators. The end goal is identifying semi-arid plant species that will naturally accumulate uranium. Natural accumulators will then be further investigated through greenhouse and field application studies to identify the most useful U phytoremediation species in semi-arid soil.