SREL Reprint #3292

Uranium immobilization in an iron-rich rhizosphere of a native wetland plant from the Savannah River Site under reducing conditions

Hyun-shik Chang1, Shea W. Buettner1, John. C. Seaman1, Peter R. Jaffé2, Paul. G. Koster van Groos2,
Dien Li3, Aaron D. Peacock4, Kirk G. Scheckel5, and Daniel I. Kaplan3

1Savannah River Ecology Laboratory, University of Georgia, P.O. Drawer E,
Aiken, South Carolina 29802, USA
2Princeton University, Princeton, New Jersey 08540, USA
3Savannah River National Laboratory, Aiken, South Carolina 29808, USA
4Microbial Insights, Inc., Rockford, Tennessee 37853, USA
5U.S. Environmental Protection Agency, Cincinnati, Ohio 45268, USA

Abstract: The hypothesis of this study was that iron plaques formed on the roots of wetland plants and their rhizospheres create environmental conditions favorable for iron reducing bacteria that promote the in situ immobilization of uranium. Greenhouse microcosm studies were conducted using native plants (Sparganium americanum) from a wetland located on the Savannah River Site, Aiken, SC. After iron plaques were established during a 73-day period by using an anoxic Fe(II)-rich nutrient solution, a U(VI) amended nutrient solution was added to the system for an additional two months. Compared to plant-free control microcosms, microcosms containing iron plaques successfully stimulated the growth of targeted iron reducing bacteria, Geobacter spp. Their population continuously increased after the introduction of the U(VI) nutrient solution. The reduction of some of the U(VI) to U(IV) by iron reducing bacteria was deduced based on the observations that the aqueous Fe(II) concentrations increased while the U(VI) concentrations decreased. The Fe(II) produced by the iron reducing bacteria was assumed to be reoxidized by the oxygen released from the roots. Advanced spectroscopic analyses revealed that a significant fraction of the U(VI) had been reduced to U(IV) and they were commonly deposited in association with phosphorus on the iron plaque.

SREL Reprint #3292

Chang, H., S. W. Buettner, J. C. Seaman, P. R. Jaffé, P. Koster van Groos, D. Li, A. D. Peacock, K. G. Scheckel, and D. I. Kaplan. 2014. Uranium immobilization in an iron-rich rhizosphere of a native wetland plant from the Savannah River Site under reducing conditions. Environmental Science and Technology 48(2014): 9270-9278.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).