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Redox roll-front mobilization of geogenic uranium by nitrate input into aquifers: Risks for groundwater resources Wolfgang van Berk, and Yunjiao Fu Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b01569 • Publication Date (Web): 07 Dec 2016 Downloaded from http://pubs.acs.org on December 12, 2016
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Environmental Science & Technology
Redox conditions are seen as the key to controlling aqueous uranium concentrations (cU(aq)). Groundwater data collected by a state-wide groundwater quality monitoring study in Mecklenburg-Western Pomerania (Germany) reveal peak cU(aq) (up to 75 µg L–1), but low background uranium concentration (median cU(aq) < 0.5 µg L–1). To characterize the hydrogeochemical processes causing such groundwater contamination by peak cU(aq), we evaluated redox potentials, concentrations of uranium, nitrate and sulfate together with their depth distribution and performed semi-generic 2D reactive mass transport modeling which is based on chemical thermodynamics. The combined interpretation of modeling results and measured data reveals that high cU(aq) and its depth-specific distribution depending on redox conditions is a result of a nitrate-triggered roll-front mobilization of geogenic uranium in the studied aquifers which are unaffected by nuclear activities. The modeling results show that groundwater recharge containing (fertilizer-derived) nitrate drives the redox transition from originally reducing towards oxidizing environments, when nitrate input has consumed the reducing buffering capacity of the aquifers, which is present as pyrite, degradable organic carbon, and geogenic U(IV) minerals. These redox reactions control the uranium roll-front mobilization and consequently, result in high cU(aq) within the redoxcline. Moreover, cU(aq) in extracted raw water will increase with ongoing nitrate input. 159x104mm (300 x 300 DPI)
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Environmental Science & Technology
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Redox roll-front mobilization of geogenic uranium by nitrate input into aquifers: Risks for
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groundwater resources
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Wolfgang van Berk*,† and Yunjiao Fu†
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†
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Clausthal-Zellerfeld, Germany
Institute of Geology and Paleontology, Clausthal University of Technology, Leibnizstraße 10, 38678
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ABSTRACT
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Redox conditions are seen as the key to controlling aqueous uranium concentrations (cU(aq)).
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Groundwater data collected by a state-wide groundwater quality monitoring study in Mecklenburg-
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Western Pomerania (Germany) reveal peak cU(aq) up to 75 µg L–1, but low background uranium
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concentrations (median cU(aq)
