SREL Reprint #3766

Uranium biogeochemistry in the rhizosphere of a contaminated wetland

Daniel I. Kaplan1, Maxim I. Boyanov2,3, Nathaniel A. Losey4, Peng Lin1, Chen Xu5, Edward J. O’Loughlin2,
Peter H. Santschi5, Wei Xing1, Wendy W. Kuhne4, and Kenneth M. Kemner2

1Savannah River Ecology Laboratory, University of Georgia, Aiken, South Carolina 29802, USA
2Argonne National Laboratory, Lemont, Illinois 60439, USA
3Chemical Engineering, Bulgarian Academy of Sciences, Sofia 1040, Bulgaria
4Savannah River National Laboratory, Aiken, South Carolina 29808, USA
5Marine & Coastal Environmental Science, Texas A&M University-Galveston, Galveston, Texas 77553, USA

Abstract: The objective of this study was to determine if U sediment concentrations in a U-contaminated wetland located within the Savannah River Site, South Carolina, were greater in the rhizosphere than in the nonrhizosphere. U concentrations were as much as 1100% greater in the rhizosphere than in the nonrhizosphere fractions; however and importantly, not all paired samples followed this trend. Iron (but not C, N, or S) concentrations were significantly enriched in the rhizosphere. XAS analyses showed that in both sediment fractions, U existed as UO22+ coordinated with iron(III)-oxides and organic matter. A key difference between the two sediment fractions was that a larger proportion of U was adsorbed to Fe(III)-oxides, not organic matter, in the rhizosphere, where significantly greater total Fe concentrations and greater proportions of ferrihydrite and goethite existed. Based on 16S rRNA analyses, most bacterial sequences in both paired samples were heterotrophs, and population differences were consistent with the generally more oxidizing conditions in the rhizosphere. Finally, U was very strongly bound to the whole (unfractionated) sediments, with an average desorption Kd value (Usediment/Uaqueous) of 3972 ± 1370 (mg-U/kg)/(mg-U/L). Together, these results indicate that the rhizosphere can greatly enrich U especially in wetland areas, where roots promote the formation of reactive Fe(III)-oxides.

Keywords: XAFS, roots, oxidation state, 16S rRNA, speciation

SREL Reprint #3766

Kaplan, D. I., M. I. Boyanov, N. A. Losey, P. Lin, C. Xu, E. J. O'loughlin, P. H. Santschi, W. Xing, W. W. Kuhne, and K. M. Kemner. 2024. Uranium biogeochemistry in the rhizosphere of a contaminated wetland. Environmental Science & Technology (58): 6381-6390.

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