Abstract
We integrated field measurements, hydroponic experiments, microscopy, and spectroscopy to investigate the effect of Ca(II) on dissolved U(VI) uptake by plants in 1 mM HCO(3)(-) solutions at circumneutral pH. The accumulation of U in plants (3.1-21.3 mg kg(-1)) from the stream bank of the Rio Paguate, Jackpile Mine, New Mexico served as a motivation for this study. Brassica juncea was the model plant used for the laboratory experiments conducted over a range of U (30-700 μg L(-1)) and Ca (0-240 mg L(-1)) concentrations. The initial U uptake followed pseudo-second-order kinetics. The initial U uptake rate ( V(0)) ranged from 4.4 to 62 μg g(-1) h(-1) in experiments with no added Ca and from 0.73 to 2.07 μg g(-1) h(-1) in experiments with 12 mg L(-1) Ca. No measurable U uptake over time was detected for experiments with 240 mg L(-1) Ca. Ternary Ca-U-CO(3) complexes may affect the decrease in U bioavailability observed in this study. Elemental X-ray mapping using scanning transmission electron microscopy-energy-dispersive spectrometry detected U-P-bearing precipitates within root cell walls in water free of Ca. These results suggest that root interactions with Ca and carbonate in solution affect the bioavailability of U in plants. This study contributes relevant information to applications related to U transport and remediation of contaminated sites.