Plutonium Immobilization and Remobilization by Soil Mineral and Organic Matter in the Far-Field of the Savannah River Site, U.S.

Xu, Chen; Athon, Matthew; Ho, Yi‐Fang; Chang, Hyun-Shik; Zhang, Saijin; Kaplan, Daniel I.; Schwehr, Kathleen A.; DiDonato, Nicole; Hatcher, Patrick G.; Santschi, Peter H.

doi:10.1021/es404951y

Cited by 31 publications

(49 citation statements)

References 56 publications

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“…4 The majority of the mobile colloidal Pu was contained in a subfraction that was separated via an isoelectric focusing (IEF) electrophoresis experiment and found to concentrate around the IEF range of 4.1−5.6 (defined as "SRS IEF colloid"). 7 Elevated pH values, as a result of the basin closure and remediation strategies, led to Pu remobilization by complexation with colloidal organic matter and subsequent desorption from soil particles in the downstream wetland sediment.…”

Section: ■ Introductionmentioning

confidence: 99%

Substructural Components of Organic Colloids from a Pu-Polluted Soil with Implications for Pu Mobilization

DiDonato

Santschi

et al. 2017

Environ. Sci. Technol.

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Contaminated soil organic matter from the Rocky Flats Environmental Technology Site (RFETS) has been previously shown to accumulate plutonium (Pu) in a colloidal subfraction and is hypothesized to contain cutin-like chemical structures cross-linked with hydroxamate functionality. The present study further characterizes this high Pu affinity subfraction using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) and discovers additional substructural components. The Pu-enriched fraction was extracted and purified through a series of ultrafiltration and isoelectric focusing (IEF) electrophoresis steps. Predominantly low H/C and high double-bond equivalence (DBE) aromatic and condensed aromatic molecular formulas were detected, 66% of which are included in a COO Kendrick mass defect (KMD) homologous series. This suggests the existence of polycarboxylated aromatic and condensed aromatic formulas, with CHON-type COO KMD formulas relatively more abundant in the purified subfraction where Pu had been observed than in the crude soil fractions which had successively lower Pu concentrations. Nitrogen contents increased with the progression of purification (bulk soil → crude colloid → IEF colloid) and coincided with the trend of Pu concentration; thus, we propose that these nitrogen and carboxyl functionalities of aromatic compounds may also impart significant Pu chelation character to the colloid.

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Section: ■ Introductionmentioning

confidence: 99%

Substructural Components of Organic Colloids from a Pu-Polluted Soil with Implications for Pu Mobilization

DiDonato

Santschi

et al. 2017

Environ. Sci. Technol.

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“…Blinova et al 51 argued that Pu−FA complexation will result in more mobile Pu(IV) species at higher pH values (i.e., pH 6), where one would expect lower FA sorption and larger FA fractions remaining in solution. Last, Xu et al 33 determined that, at increasing pH values, larger fractions of Pu became associated with organic-rich colloids compared to the particulate phase of an environmental soil sample.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…31 Second, NOM in solution may control Pu redox chemistry 35 and therefore indirectly affect Pu sorption characteristics (e.g., the relative abundance of Pu(IV) versus Pu(V) in solution will influence Pu sorption affinities). In addition to dissolved NOM, organic-rich colloids can alter Pu partitioning between dissolved, colloidal, and particulate phases and enhance Pu mobility, as has been demonstrated under both laboratory 33 and field conditions. 28,36 Besides dissolved and colloidal organic matter, we believe that the specific role of organic matter coatings, commonly found on mineral surfaces in the environment, 37,38 needs to be taken into account for the evaluation of organic matter effects on Pu mobility.…”

Section: ■ Introductionmentioning

confidence: 85%

“…This effect of solid-phase FA on Pu sorption kinetics may be due to a kinetic transition of Pu surface species from sites associated with the "bare" mineral to sorbed FA, similarily as has been suggested for an organic-rich soil previously. 33 In order to evaluate the influence of solution-versus solidphase FA in precoating experiments, we can compare Pu sorption behavior in precomplexation experiments at 0.5 and 5 mg L −1 initial TOC with the precoating experiment at 50 mg L −1 TOC, which resulted in a similar solution-phase TOC (1.14 mg L −1 ) but in the presence of a high FA surface concentration (10.97 mg TOC g goethite −1…”

Section: Environmental Science and Technologymentioning

confidence: 99%

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Effect of Fulvic Acid Surface Coatings on Plutonium Sorption and Desorption Kinetics on Goethite

Tinnacher

Begg

Mason

et al. 2015

Environ. Sci. Technol.

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The rates and extent of plutonium (Pu) sorption and desorption onto mineral surfaces are important parameters for predicting Pu mobility in subsurface environments. The presence of natural organic matter, such as fulvic acid (FA), may influence these parameters. We investigated the effects of FA on Pu(IV) sorption/desorption onto goethite in two scenarios: when FA was (1) initially present in solution or (2) found as organic coatings on the mineral surface. A low pH was used to maximize FA coatings on goethite. Experiments were combined with kinetic modeling and speciation calculations to interpret variations in Pu sorption rates in the presence of FA. Our results indicate that FA can change the rates and extent of Pu sorption onto goethite at pH 4. Differences in the kinetics of Pu sorption were observed as a function of the concentration and initial form of FA. The fraction of desorbed Pu decreased in the presence of FA, indicating that organic matter can stabilize sorbed Pu on goethite. These results suggest that ternary Pu-FA-mineral complexes could enhance colloid-facilitated Pu transport. However, more representative natural conditions need to be investigated to quantify the relevance of these findings.

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“…Despite the low Kd values of Pu in soils and sediments (McCubbin et al, 2004;Serne, 2007), the potential remobilization of small quantities of the actinide is still a concern (Kersting et al, 1999;Santschi and Roberts, 2002;Xu et al, 2014). Previous work by the current authors has demonstrated that negligible Pu present in environmental contaminated soils (from the AWE Aldermaston site) is released into solution (<0.01%) under induced-reducing conditions, suggesting that little Pu is mobilized despite the inferred dissolution of oxide minerals and presence of microorganisms linked to Pu reduction (Kimber et al, 2012).…”

Section: Introductionmentioning

confidence: 82%

Geochemical association of Pu and Am in selected host-phases of contaminated soils from the UK and their susceptibility to chemical and microbiological leaching

Kimber

Corkhill

Amos

et al. 2015

Journal of Environmental Radioactivity

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Understanding the biogeochemical behaviour and potential mobility of actinides in soils and groundwater is vital for developing remediation and management strategies for radionuclide-contaminated land. Pu is known to have a high Kd in soils and sediments, however remobilization of low concentrations of Pu remains a concern. Here, some of the physicochemical properties of Pu and the co-contaminant, Am, are investigated in contaminated soils from Aldermaston, Berkshire, UK, and the Esk Estuary, Cumbria, UK, to determine their potential mobility. Sequential extraction techniques were used to examine the host-phases of the actinides in these soils and their susceptibility to microbiological leaching was investigated using acidophilic sulphur-oxidising bacteria. Sequential extractions found the majority of (239,240)Pu associated with the highly refractory residual phase in both the Aldermaston (63.8-85.5 %) and Esk Estuary (91.9-94.5%) soils. The (241)Am was distributed across multiple phases including the reducible oxide (26.1-40.0%), organic (45.6-63.6%) and residual fractions (1.9-11.1%). Plutonium proved largely resistant to leaching from microbially-produced sulphuric acid, with a maximum 0.18% leached into solution, although up to 12.5% of the (241)Am was leached under the same conditions. If Pu was present as distinct oxide particles in the soil, then (241)Am, a decay product of Pu, would be expected to be physically retained in the particle. The differences in geochemical association and bioleachability of the two actinides suggest that this is not the case and hence, that significant Pu is not present as distinct particles. These data suggest the majority of Pu in the contaminated soils studied is highly recalcitrant to geochemical changes and is likely to remain immobile over significant time periods, even when challenged with aggressive "bioleaching" bacteria.

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Plutonium Immobilization and Remobilization by Soil Mineral and Organic Matter in the Far-Field of the Savannah River Site, U.S.

Cited by 31 publications

References 56 publications

Substructural Components of Organic Colloids from a Pu-Polluted Soil with Implications for Pu Mobilization

Substructural Components of Organic Colloids from a Pu-Polluted Soil with Implications for Pu Mobilization

Effect of Fulvic Acid Surface Coatings on Plutonium Sorption and Desorption Kinetics on Goethite

Geochemical association of Pu and Am in selected host-phases of contaminated soils from the UK and their susceptibility to chemical and microbiological leaching

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