Iron mineralogy and uranium-binding environment in the rhizosphere of a wetland soil.
Wetlands mitigate the migration of groundwater contaminants through a series of biogeochemical gradients that enhance multiple contaminant-binding processes. The hypothesis of this study was that wetland plant roots contribute organic carbon and release O2 within the rhizosphere (plant-impact soil zone) that promote the formation of Fe(III)-(oxyhydr)oxides. In turn, these Fe(III)-(oxyhydr)oxides stabilize organic matter that together contribute to contaminant immobilization. Mineralogy and U binding environments of the rhizosphere were evaluated in samples collected from contaminated and non-contaminated areas of a wetland on the Savannah River Site in South Carolina. Based on Mössbauer spectroscopy, rhizosphere soil was greatly enriched with nanogoethite, ferrihydrite-like nanoparticulates, and hematite, with negligible Fe(II) present. X-ray computed tomography and various microscopy techniques showed that root plaques were tens-of-microns thick and consisted of highly oriented Fe-nanoparticles, suggesting that the roots were involved in creating the biogeochemical conditions conducive to the nanoparticle formation. XAS showed that a majority of the U in the bulk wetland soil was in the +6 oxidation state and was not well correlated spatially to Fe concentrations. SEM/EDS confirm that U was enriched on root plaques, where it was always found in association with P. Together these findings support our hypothesis and suggest that plants can alter mineralogical conditions that may be conducive to contaminant immobilization in wetlands.
Savannah River National Laboratory, Aiken, SC 29808, United States. Electronic address: daniel.kaplan@srnl.doe.gov.
Daniel I
DI
Kaplan
Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99354, United States.
Ravi
R
Kukkadapu
Savannah River Ecology Laboratory, University of Georgia, Aiken, SC 29802, United States.
John C
JC
Seaman
Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99354, United States.
Bruce W
BW
Arey
Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99354, United States.
Alice C
AC
Dohnalkova
Savannah River Ecology Laboratory, University of Georgia, Aiken, SC 29802, United States.
Shea
S
Buettner
Savannah River National Laboratory, Aiken, SC 29808, United States.
Dien
D
Li
Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99354, United States.
Tamas
T
Varga
US Environmental Protection Agency, National Risk Management Research Laboratory, Cincinnati, OH 45224, United States.
Kirk G
KG
Scheckel
Princeton University, Princeton, NJ 08540, United States.
Peter R
PR
Jaffé
D005290:Ferric Compounds / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D058441:Rhizosphere; D012987:Soil / Q000737:chemistry*; D013022:South Carolina; D014501:Uranium / Q000032:analysis; D053833:Wetlands
D005290:Ferric Compounds; D012987:Soil; D014501:Uranium; D007501:Iron
Iron nanoparticles; Mössbauer; Root; X-ray absorption spectroscopy