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Journal Articles

Nagasaki sediments reveal that long-term fate of plutonium is controlled by select organic matter moieties

Lin, P.*; Xu, C.*; Kaplan, D. I.*; Chen, H.*; Yeager, C. M.*; Xing, W.*; Sun, L.*; Schwehr, K. A.*; Yamazaki, Hideo*; Kokubu, Yoko; et al.

Science of the Total Environment, 678, p.409 - 418, 2019/08

 Times Cited Count:13 Percentile:52.02(Environmental Sciences)

Nagasaki sediments containing bomb-derived Pu provided a unique opportunity to explore the long term geochemical behavior of Pu. Through a combination of selective extractions and molecular characterization via electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry, we determined that 55 $$pm$$ 3% of the $$^{239,240}$$Pu was preferentially associated with more persistent organic matter compounds in Nagasaki sediments, particularly those natural organic matter (NOM) stabilized by Fe oxides. Other organic matter compounds served as a secondary sink of these $$^{239,240}$$Pu (31 $$pm$$ 2% on average), and less than 20% of the $$^{239,240}$$Pu was immobilized by inorganic mineral particles. While present long-term disposal and environmental remediation modeling assume that solubility limits and sorption to mineral surfaces control Pu subsurface mobility, our observations suggest that NOM undoubtedly plays an important role in sequestering Pu. Ignoring the role of NOM in controlling Pu fate and transport is not justified in most environmental systems.

Journal Articles

Speciation of iodine isotopes inside and outside of a contaminant plume at the Savannah River Site

Schwehr, K. A.*; Otosaka, Shigeyoshi; Merchel, S.*; Kaplan, D. I.*; Zhang, S.*; Xu, C.*; Li, H.-P.*; Ho, Y.-F.*; Yeager, C. M.*; Santschi, P. H.*; et al.

Science of the Total Environment, 497-498, p.671 - 678, 2014/11

 Times Cited Count:14 Percentile:39.86(Environmental Sciences)

A new, accurate and simple pH-dependent solvent extraction method combined with accelerator mass spectrometry (AMS) measurement for $$^{129}$$I/$$^{127}$$I isotopes and iodine speciation (iodide, iodate, and organo-I) quantification in liquids of any ionic strength has been developed. We then validated the AMS method for activity concentration measurements with a recently developed gas chromatography mass spectrometry method for $$^{129}$$I concentrations of 1 Bq/L or higher. This technique was applied to $$^{129}$$I-contaminated groundwater from the Savannah River Site, USA, and demonstrated changes of $$^{129}$$I and $$^{127}$$I concentrations and speciation along a pH, redox potential, and organic carbon gradient. The data suggest that $$^{129}$$I/$$^{127}$$I and species distribution is strongly pH dependent. The new method can now be applied to a wide range of chemically-diverse aquatic systems, including uncontaminated environments.

Journal Articles

Bacterial production of organic acids enhances H$$_{2}$$O$$_{2}$$-dependent iodide oxidation

Li, H.-P.*; Yeager, C. M.*; Brinkmeyer, R.*; Zhang, S.*; Ho, Y.-F.*; Xu, C.*; Jones, W. L.*; Schwehr, K. A.*; Otosaka, Shigeyoshi; Roberts, K. A.*; et al.

Environmental Science & Technology, 46(9), p.4837 - 4844, 2012/03

 Times Cited Count:49 Percentile:77.28(Engineering, Environmental)

In order to develop an understanding of the role that microorganisms play in the transport of $$^{129}$$I in soil-water systems, naturally occurring bacteria isolated from the F-area subsurface of the Savannah River Site (SRS) were assessed for iodide oxidizing activity. Spent liquid medium from a number of SRS bacterial cultures enhanced iodide oxidation 2-10 fold in the presence of hydrogen peroxide (H$$_{2}$$O$$_{2}$$). From a time-series measurements of peroxidase activities and organic acid concentrations, it was hypothesized that microbial organic acid exudate promoted iodide oxidation via following mechanisms; (1) organic acids interact with H$$_{2}$$O$$_{2}$$ to form strong iodide oxidizing agents, peroxy carboxylic acids, and (2) organic acid secretion led to enhanced rates of H$$_{2}$$O$$_{2}$$-dependent iodide oxidation by lowering the pH of the culture medium.

Journal Articles

Sequestration and remobilization of radioiodine ($$^{129}$$I) by soil organic matter and possible consequences of the remedial action at Savannah River Site

Xu, C.*; Miller, E. J.*; Zhang, S.*; Li, H.-P.*; Ho, Y.-F.*; Schwehr, K. A.*; Kaplan, D. I.*; Otosaka, Shigeyoshi; Roberts, K. A.*; Brinkmeyer, R.*; et al.

Environmental Science & Technology, 45(23), p.9975 - 9983, 2011/12

 Times Cited Count:63 Percentile:82.65(Engineering, Environmental)

In order to investigate accumulation process of iodine-129 ($$^{129}$$I) in a contaminated F-Area groundwater plume of the US Savannah River Site, soil resuspension experiments simulating surface runoff and erosion events were conducted. Results showed that 72$$sim$$77% of the newly-introduced iodide was irreversibly sequestered into the organic-rich soil, while the rest was transformed into colloidal and dissolved organo-iodine by the soil. Laboratory iodination of the soil indicated a preferential incorporation of inorganic iodine into soil organic matter (SOM) at acidic pH (3$$sim$$4), except for the iodination catalyzed by lactoperoxidase, which favors more alkaline conditions. From this result, we concluded that under very acidic conditions, abiotic iodination of SOM was predominant, while under less acidic conditions (pH $$geq$$5), microbial enzymatically-assisted iodination took over.

Journal Articles

Is soil natural organic matter a sink or source for mobile radioiodine ($$^{129}$$I) at the Savannah River Site?

Xu, C.*; Zhang, S.*; Ho, Y.-F.*; Miller, E. J.*; Roberts, K. A.*; Li, H.-P.*; Schwehr, K. A.*; Otosaka, Shigeyoshi; Kaplan, D. I.*; Brinkmeyer, R.*; et al.

Geochimica et Cosmochimica Acta, 75(19), p.5716 - 5735, 2011/10

 Times Cited Count:61 Percentile:83.93(Geochemistry & Geophysics)

In order to understand the effect of soil organic matter (SOM) on the mobility of iodine in the vicinity of the F-area seepage basin at the U.S. Department Energy's Savannah River Site (SRS), relationships between radioiodine/iodine concentration and properties of SOM (e.g., degree of humification, aromaticity, and molecular weight) were examined. Analyses were carried out for four sequential extracts of SOM (freshwater, alkaline, glycerol, and citric-alkaline solutions). Iodine in SOM was selectively bound to a small-size aromatic subunit (less than 10 kDa), and majority of water soluble $$^{129}$$I was associated with a low molecular weight amphiphilic organic carrier (13.5-15 kDa). From these results, it was suggested that (1) SOM behaved as a sink as well as a source for iodine at the SRS, and (2) the function of SOM varies with groundwater chemistry.

Journal Articles

Factors controlling mobility of $$^{127}$$I and $$^{129}$$I species in an acidic groundwater plume at the Savannah River Site

Otosaka, Shigeyoshi; Schwehr, K. A.*; Kaplan, D. I.*; Roberts, K. A.*; Zhang, S.*; Xu, C.*; Li, H.-P.*; Ho, Y.-F.*; Brinkmeyer, R.*; Yeager, C. M.*; et al.

Science of the Total Environment, 409(19), p.3857 - 3865, 2011/09

 Times Cited Count:60 Percentile:82.65(Environmental Sciences)

Spatial distributions of concentrations and speciation of radioiodine ($$^{129}$$I) and stable iodine ($$^{127}$$I) in groundwater in the vicinity of the F-area seepage basin at the U.S. Department Energy of Savannah River Site were investigated. $$^{129}$$I concentration in groundwater was 8.6 Bq/L immediately downstream of the seepage basin (well FSB-95DR), and decreased with distance from the infiltration basin. $$^{127}$$I concentration decreased similarly to that of $$^{129}$$I. Although there was no potential $$^{127}$$I source in wastes in the basin, $$^{127}$$I also showed a similar gradient to that of $$^{129}$$I. High concentrations of $$^{127}$$I or $$^{127}$$I were not detected in groundwater collected from wells located outside of the mixed waste plume of this area. The high iodide concentrations in groundwater near the basin were presumed to be caused by dissolution of iodide from soil due to gradually increasing of pH values in the last decade.

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