Uptake of uranium into desert plants in an abandoned uranium mine and its implications for phytostabilization strategies

Abstract

This research assessed a variety of native desert plant species for their ability to accumulate toxic elements in an abandoned uranium mine in the Sonoran Desert. Paired soil and plant samples were collected for six species of plants that had naturally re-colonized the mine. The mine soils had a median uranium concentration of 56.0 mg kg−1 (range: MDL to 696) while the plant samples had concentrations of 3.7 mg kg−1 (range: MDL to 20.0). The results showed uranium bioconcentration factors (BCFs) were between 0.051 and 0.234 with the longer-living, woody species having higher concentrations than short-lived herbaceous species. These BCF values were near the high end of values reported in the literature which implies that these desert species were either better at acquiring elements or they have fewer mechanisms to eliminate elements (e.g. litterfall). The life histories of the species were then evaluated on four criteria, namely uranium BCF, inedibility, longevity, and root depth, to assess which species would be best for phytostabilization, which is the use of plants to stabilize the soil to prevent water or wind erosion that might transport contaminants off site. The goal was to select a species that would stabilize the soil without accumulating uranium in the above ground biomass where it could enter the food web and be transported off site. Ultimately, brittlebush (Encelia farinosa A. Gray ex Torr.) was selected because of its low BCF, shallow roots and reasonable longevity.