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

• Published in: Environmental science & technology 2018-11, Vol.52 (22), p.13089-13098
• Main Authors: El Hayek, Eliane, Torres, Chris, Rodriguez-Freire, Lucia, Blake, Johanna M, De Vore, Cherie L, Brearley, Adrian J, Spilde, Michael N, Cabaniss, Stephen, Ali, Abdul-Mehdi S, Cerrato, José M
• Format: Article
• Language: English
• Subjects: Bioaccumulation; Bioavailability; Biological Availability; Brassica; Calcium; Cell walls; Energy transmission; Experiments; Hydrogen-Ion Concentration; Kinetics; Mapping; Microscopy; Motivation; New Mexico; pH effects; Plant Roots; Plant sciences; Precipitates; Scanning electron microscopy; Scanning transmission electron microscopy; Spectrometry; Spectroscopy; Stream banks; Transmission electron microscopy; Uranium
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.8b02724

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 (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–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.