TY - JOUR
T1 - Organic complexation of U(VI) in reducing soils at a natural analogue site
T2 - Implications for uranium transport
AU - Fuller, Adam J.
AU - Leary, Peter
AU - Gray, Neil D.
AU - Davies, Helena S.
AU - Mosselmans, J. Frederick W.
AU - Cox, Filipa
AU - Robinson, Clare H.
AU - Pittman, Jon K.
AU - McCann, Clare M.
AU - Muir, Michael
AU - Graham, Margaret C.
AU - Utsunomiya, Satoshi
AU - Bower, William R.
AU - Morris, Katherine
AU - Shaw, Samuel
AU - Bots, Pieter
AU - Livens, Francis R.
AU - Law, Gareth T.W.
N1 - Funding Information:
This work was funded as part of the LO-RISE ( Long-lived Radionuclides in the Surface Environment ; NE/L000202/1 ) consortium under the UK NERC RATE programme (Radioactivity and the Environment), co-funded by the UK Environment Agency and Radioactive Waste Management Ltd. Synchrotron data was collected at Diamond Light Source on beamline B18 (SP10163 and SP12767), I18 (SP12477), and at the MARS beamline, Synchrotron Soleil (20150125). Law also thanks the UK STFC and NERC for funding through the Environmental Radioactivity Network ( ST/K001787/1 ) and grant NE/M014088/1 . We thank Paul Lythgoe and Alastair Bewsher for assistance with geochemical analysis, Dr Stephen Parry, Dr Pier Lorenzo Solari, Dr Akhil Tayal, Herve Hermange, and Richard Doull for assistance with XAS data collection, Dr Hannah Roberts for advice on HERFD-XANES analysis, and Dr Rosemary Hibberd for assistance with sample collection and manuscript proofing. We thank the European Synchrotron Radiation Facility for access to beamline ID26 (20-01-790).
Funding Information:
This work was funded as part of the LO-RISE (Long-lived Radionuclides in the Surface Environment; NE/L000202/1) consortium under the UK NERC RATE programme (Radioactivity and the Environment), co-funded by the UK Environment Agency and Radioactive Waste Management Ltd. Synchrotron data was collected at Diamond Light Source on beamline B18 (SP10163 and SP12767), I18 (SP12477), and at the MARS beamline, Synchrotron Soleil (20150125). Law also thanks the UK STFC and NERC for funding through the Environmental Radioactivity Network (ST/K001787/1) and grant NE/M014088/1. We thank Paul Lythgoe and Alastair Bewsher for assistance with geochemical analysis, Dr Stephen Parry, Dr Pier Lorenzo Solari, Dr Akhil Tayal, Herve Hermange, and Richard Doull for assistance with XAS data collection, Dr Hannah Roberts for advice on HERFD-XANES analysis, and Dr Rosemary Hibberd for assistance with sample collection and manuscript proofing. We thank the European Synchrotron Radiation Facility for access to beamline ID26 (20-01-790).
Publisher Copyright:
© 2020 The Authors
PY - 2020/9
Y1 - 2020/9
N2 - Understanding the long-term fate, stability, and bioavailability of uranium (U) in the environment is important for the management of nuclear legacy sites and radioactive wastes. Analysis of U behavior at natural analogue sites permits evaluation of U biogeochemistry under conditions more representative of long-term equilibrium. Here, we have used bulk geochemical and microbial community analysis of soils, coupled with X-ray absorption spectroscopy and μ-focus X-ray fluorescence mapping, to gain a mechanistic understanding of the fate of U transported into an organic-rich soil from a pitchblende vein at the UK Needle's Eye Natural Analogue site. U is highly enriched in the Needle's Eye soils (∼1600 mg kg−1). We show that this enrichment is largely controlled by U(VI) complexation with soil organic matter and not U(VI) bioreduction. Instead, organic-associated U(VI) seems to remain stable under microbially-mediated Fe(III)-reducing conditions. U(IV) (as non-crystalline U(IV)) was only observed at greater depths at the site (>25 cm); the soil here was comparatively mineral-rich, organic-poor, and sulfate-reducing/methanogenic. Furthermore, nanocrystalline UO2, an alternative product of U(VI) reduction in soils, was not observed at the site, and U did not appear to be associated with Fe-bearing minerals. Organic-rich soils appear to have the potential to impede U groundwater transport, irrespective of ambient redox conditions.
AB - Understanding the long-term fate, stability, and bioavailability of uranium (U) in the environment is important for the management of nuclear legacy sites and radioactive wastes. Analysis of U behavior at natural analogue sites permits evaluation of U biogeochemistry under conditions more representative of long-term equilibrium. Here, we have used bulk geochemical and microbial community analysis of soils, coupled with X-ray absorption spectroscopy and μ-focus X-ray fluorescence mapping, to gain a mechanistic understanding of the fate of U transported into an organic-rich soil from a pitchblende vein at the UK Needle's Eye Natural Analogue site. U is highly enriched in the Needle's Eye soils (∼1600 mg kg−1). We show that this enrichment is largely controlled by U(VI) complexation with soil organic matter and not U(VI) bioreduction. Instead, organic-associated U(VI) seems to remain stable under microbially-mediated Fe(III)-reducing conditions. U(IV) (as non-crystalline U(IV)) was only observed at greater depths at the site (>25 cm); the soil here was comparatively mineral-rich, organic-poor, and sulfate-reducing/methanogenic. Furthermore, nanocrystalline UO2, an alternative product of U(VI) reduction in soils, was not observed at the site, and U did not appear to be associated with Fe-bearing minerals. Organic-rich soils appear to have the potential to impede U groundwater transport, irrespective of ambient redox conditions.
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U2 - 10.1016/j.chemosphere.2020.126859
DO - 10.1016/j.chemosphere.2020.126859
M3 - Article
C2 - 32957279
AN - SCOPUS:85084215210
VL - 254
JO - Chemosphere
JF - Chemosphere
SN - 0045-6535
M1 - 126859
ER -
