Temporal evolution of Pu and Cs sediment contamination in a seasonally stratified pond.

There remains a lack of knowledge regarding ecosystem transfer, transport processes, and mechanisms, which influence the long-term mobility of Pu-239 and Cs-137 in natural environments. Monitoring the distribution and migration of trace radioisotopes as ecosystem tracers has the potential to provide insight into the underlying mechanisms of geochemical cycles. This study investigated the distribution of anthropogenic radionuclides Pu-239 and Cs-137 along with total organic carbon, iron, and trace element in contaminated sediments of Pond B at the Savannah River Site (SRS).

Redox Cycling Driven Transformation of Layered Manganese Oxides to Tunnel Structures.

Mn oxides are among the most ubiquitous minerals on Earth and play critical roles in numerous elemental cycles in biotic/abiotic loops as the key redox center. Yet, it has long puzzled geochemists why the laboratory synthesis of todorokite, a tunnel-structured Mn oxide, is extremely difficult while it is the dominant form over other tunneled phases in low-temperature natural environments. This study employs a novel electrochemical method to mimic the cyclic redox reactions occurring over long geological time scales in an accelerated manner.

Microbial Fe(II) oxidation by Sideroxydans lithotrophicus ES-1 in the presence of Schlöppnerbrunnen fen-derived humic acids.

Controlled laboratory experiments were combined with field measurements to better understand the interactions between dissolved organic matter (DOM) and reduced iron in organic-rich peatlands. Addition of peat-derived humic acid extract (HA) to Sideroxydans lithotrophicus ES-1 liquid cultures led to higher cell numbers and up to 1.4 times higher Fe(II) oxidation rates compared to chemical controls.

Effect of Manganese Oxide Aging and Structure Transformation on the Kinetics of Thiol Oxidation.

The kinetics and mechanism of thiol oxidation by Mn oxides undergoing dynamic structural transformation under environmentally relevant conditions remain poorly understood. In this study, thiol/disulfide pair concentrations were simultaneously determined in situ using voltammetric microelectrodes during the interaction of four common thiols (cysteine, homocysteine, cysteamine, and glutathione) with fresh and aged δ-MnO at pH 7.0.

Microbial manganese(III) reduction fuelled by anaerobic acetate oxidation.

Soluble manganese in the intermediate +III oxidation state (Mn ) is a newly identified oxidant in anoxic environments, whereas acetate is a naturally abundant substrate that fuels microbial activity. Microbial populations coupling anaerobic acetate oxidation to Mn reduction, however, have yet to be identified. We isolated a Shewanella strain capable of oxidizing acetate anaerobically with Mn as the electron acceptor, and confirmed this phenotype in other strains.

Simultaneous Transformation of Commingled Trichloroethylene, Tetrachloroethylene, and 1,4-Dioxane by a Microbially Driven Fenton Reaction in Batch Liquid Cultures.

Unlabelled: Improper disposal of 1,4-dioxane and the chlorinated organic solvents trichloroethylene (TCE) and tetrachloroethylene (also known as perchloroethylene [PCE]) has resulted in widespread contamination of soil and groundwater. In the present study, a previously designed microbially driven Fenton reaction system was reconfigured to generate hydroxyl (HO˙) radicals for simultaneous transformation of source zone levels of single, binary, and ternary mixtures of TCE, PCE, and 1,4-dioxane. The reconfigured Fenton reaction system was driven by fed batch cultures of the Fe(III)-reducing facultative anaerobe Shewanella oneidensis amended with lactate, Fe(III), and contaminants and exposed to alternating anaerobic and aerobic conditions.

Microbial community responses to organophosphate substrate additions in contaminated subsurface sediments.

Background: Radionuclide- and heavy metal-contaminated subsurface sediments remain a legacy of Cold War nuclear weapons research and recent nuclear power plant failures. Within such contaminated sediments, remediation activities are necessary to mitigate groundwater contamination. A promising approach makes use of extant microbial communities capable of hydrolyzing organophosphate substrates to promote mineralization of soluble contaminants within deep subsurface environments.

Siderophores are not involved in Fe(III) solubilization during anaerobic Fe(III) respiration by Shewanella oneidensis MR-1.

Shewanella oneidensis MR-1 respires a wide range of anaerobic electron acceptors, including sparingly soluble Fe(III) oxides. In the present study, S. oneidensis was found to produce Fe(III)-solubilizing organic ligands during anaerobic Fe(III) oxide respiration, a respiratory strategy postulated to destabilize Fe(III) and produce more readily reducible soluble organic Fe(III).

Shewanella oneidensis MR-1 mutants selected for their inability to produce soluble organic-Fe(III) complexes are unable to respire Fe(III) as anaerobic electron acceptor.

Recent voltammetric analyses indicate that Shewanella putrefaciens strain 200 produces soluble organic-Fe(III) complexes during anaerobic respiration of sparingly soluble Fe(III) oxides. Results of the present study expand the range of Shewanella species capable of producing soluble organic-Fe(III) complexes to include Shewanella oneidensis MR-1. Soluble organic-Fe(III) was produced by S.

Microbial colonization of an in situ sediment cap and correlation to stratified redox zones.

In situ capping is a management technique for contaminated sediments involving the placement of clean material at the sediment-water interface. This work combined porewater geochemical profiling with quantitative microbial data to investigate the intrinsic microbial colonization of a sand cap. Geochemical characterization using voltammetric microelectrodes indicated vertical stratification of biogeochemical processes within a capped sediment column.

Spatial and temporal evolution of biogeochemical processes following in situ capping of contaminated sediments.

In situ capping has recently emerged as a remedial method for contaminated sediments and involves placing a layer of clean material at the sediment-water interface. The biogeochemical response of native sediment following capping, as well as the redoxenvironmentsthatdevelopwithinthe cap, are currently unknown. Column experiments were performed using voltammetric microelectrodes to characterize spatial and temporal distributions of biogeochemical processes in capped sediments under stagnant and upflow conditions.

Remote in situ voltammetric techniques to characterize the biogeochemical cycling of trace metals in aquatic systems.

The contamination of aquatic ecosystems by natural and anthropogenic metals has lead to a need to better characterize their impact in the environment. To a large extent, the fate and the (eco)toxicity of these elements in aquatic systems are related to their chemical speciation, which may vary continuously in space and time. Detailed measurements of the fraction of specific metal species or groups of homologous metal species and their variation as a function of the bio-physicochemical conditions of the natural media are thus of prime importance.

Aerobic uranium (VI) bioprecipitation by metal-resistant bacteria isolated from radionuclide- and metal-contaminated subsurface soils.

In this study, the immobilization of toxic uranium [U(VI)] mediated by the intrinsic phosphatase activities of naturally occurring bacteria isolated from contaminated subsurface soils was examined. The phosphatase phenotypes of strains belonging to the genera, Arthrobacter, Bacillus and Rahnella, previously isolated from subsurface soils at the US Department of Energy's (DOE) Oak Ridge Field Research Center (ORFRC), were determined. The ORFRC represents a unique, extreme environment consisting of highly acidic soils with co-occurring heavy metals, radionuclides and high nitrate concentrations.

Uranium biomineralization as a result of bacterial phosphatase activity: insights from bacterial isolates from a contaminated subsurface.

Uranium contamination is an environmental concern at the Department of Energy's Field Research Center in Oak Ridge, Tennessee. In this study, we investigated whether phosphate biomineralization, or the aerobic precipitation of U(VI)-phosphate phases facilitated by the enzymatic activities of microorganisms, offers an alternative to the more extensively studied anaerobic U(VI) bioreduction. Three heterotrophic bacteria isolated from FRC soils were studied for their ability to grow and liberate phosphate in the presence of U(VI) and an organophosphate between pH 4.

Shewanella putrefaciens produces an Fe(III)-solubilizing organic ligand during anaerobic respiration on insoluble Fe(III) oxides.

The mechanism of Fe(III) reduction was investigated using voltammetric techniques in anaerobic incubations of Shewanella putrefaciens strain 200 supplemented with Fe(III) citrate or a suite of Fe(III) oxides as terminal electron acceptor. Results indicate that organic complexes of Fe(III) are produced during the reduction of Fe(III) at rates that correlate with the reactivity of the Fe(III) phase and bacterial cell density. Anaerobic Fe(III) solubilization activity is detected with either Fe(III) oxides or Fe(III) citrate, suggesting that the organic ligand produced is strong enough to destabilize Fe(III) from soluble or solid Fe(III) substrates.

The effect of tidal forcing on biogeochemical processes in intertidal salt marsh sediments.

Background: Early diagenetic processes involved in natural organic matter (NOM) oxidation in marine sediments have been for the most part characterized after collecting sediment cores and extracting porewaters. These techniques have proven useful for deep-sea sediments where biogeochemical processes are limited to aerobic respiration, denitrification, and manganese reduction and span over several centimeters. In coastal marine sediments, however, the concentration of NOM is so high that the spatial resolution needed to characterize these processes cannot be achieved with conventional sampling techniques.

Scanning electrochemical microscopy imaging of rhodochrosite dissolution using gold amalgam microelectrodes.

Gold/mercury amalgam (Au/Hg) microelectrodes with a diameter of 25 microm were developed for the detection of environmentally relevant analytes such as manganese and iron by scanning electrochemical microscopy (SECM), and applied to investigate the controlled dissolution of manganese carbonate (MnCO(3); rhodochrosite) in acidic conditions. Characterization of the amalgam electrode geometry via approach curves recorded during SECM experiments revealed Au/Hg microelectrodes with sphere cap geometry. Quantitative determination of Mn(2+) has been achieved by calibration of the Au/Hg microelectrode in bulk solution experiments.

A dynamic numerical model to characterize labile metal complexes collected with diffusion gradient in thin films devices.

The speciation of metal species extracted by diffusion gradient in thin films (DGT) devices during experimental deployments in simple metal-ligand synthetic solutions was numerically modeled, analyzed at steady state, and simulated in the dynamic regime. The modeled speciation of two well-known complexes (Cu-citrate and Cu-EDTA) are in good agreement with experimental data obtained in NaNO3 solutions. For any metal complex, the rate at which the metal accumulates on the chelating resin is proportional to the concentration of free metal in solution plus a fraction of the metal complex concentration in solution equivalent to xiD(ML)/D(M).

Evidence for a dynamic cycle between Mn and Co in the water column of a stratified lake.

The geochemical behavior of Co in aquatic systems has often been related to the presence of Fe and Mn particles. A few studies have shown that Co is exclusively associated with particulate Mn, but the dynamics of Co and Mn cycling have never been determined in real time under natural conditions. In this study, we used a combination of analytical techniques to study the temporal and spatial evolution of Mn microparticles (MnOx) over 2 weeks in the water column of a shallow stratified lake (Paul Lake, MI).