Kinetic Model Data: Effect of Calcium on the Bioavailability of Dissolved Uranium (VI) in Plant Roots under Circumneutral pH

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 HCO3 −
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 (V0) 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−CO3 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.