BER Research Highlights

Search Date: June 27, 2017

6 Records match the search term(s):


August 10, 2012

Improved Approach for Modeling Pu Behavior in the Environment

The presence of plutonium (Pu) in the environment due to anthropogenic activity remains a serious problem. Predicting Pu transport and fate requires an understanding of biogeochemical processes that are particularly complicated in the case of Pu. Detailed Pu characterization is difficult because its very low environmental concentrations make most experimental approaches difficult to use. Extrapolation from higher Pu concentration studies in the laboratory are subject to concentration-related artifacts. Researchers at Lawrence Livermore National Laboratory recently explored an alternate course of ab initio simulations to study aqueous actinide ions. They tested a number of approaches to simulate the highly insoluble species Pu (IV), using a comparison of ab initio electronic structure methods applied to a benchmark case under environmentally relevant concentrations and neutral pH. They proposed the use of the extension of density functional theory that explicitly includes onsite interactions as a method to improve the calculation. The application of this method combined with additional derived parameters was proposed as an overall approach for largescale dynamical simulations of Pu (IV) chemistry.

Reference: Huang, P., M. Zavarin, and A. B. Kersting. 2012. "Ab initio Structure and Energetics of Pu(OH)4 and Pu(OH)4(H2O)n Clusters: Comparison Between Density Functional and Multi-Reference Theories," Chemical Physics Letters 543, 193–98. (Reference link)

Contact: Arthur Katz, SC-23.2, (301) 903-4932
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


August 01, 2012

How Iron in Minerals Affects Subsurface Uranium

Subsurface minerals help control the chemical form of contaminants such as uranium (U). The redox (reduction and oxidation) state of soils and sediments exists on a continuum from oxidized to reduced and can affect the mobility of uranium plumes. Under oxidized conditions, U is rather soluble as a uranyl ion in the U6+ valence state, whereas under reducing conditions U can become immobilized in the less-soluble U4+ valence state. Researchers at the University of Iowa and Argonne National Laboratory have found that a complex mixture of ferrous iron (Fe2+)-bearing minerals in a naturally reduced soil is capable of reducing and immobilizing uranium. Using Mössbauer spectroscopy at the University of Iowa and synchrotron x-ray absorption spectroscopy at the Advanced Photon Source at Argonne, the researchers found that uranium was reduced by Fe2+ in clay minerals and by a less-common, transient, and highly reactive Fe2+-mineral called green rust. The researchers also observed that the reduced U4+ atoms formed a product different from the uraninite mineral (UO2) commonly observed in laboratory studies, providing evidence for the diversity in chemical speciation of reduced U in natural systems. This study provides detailed information necessary for understanding toxic and radioactive contaminant mobility which will contribute to the long-term stewardship of U.S. Department of Energy legacy sites.

Reference: Latta, D. E., M. I. Boyanov, K. M. Kemner, E. J. O'Loughlin, and M. M. Scherer. 2012. "Abiotic Reduction of Uranium by Fe(II) in Soil," Applied Geochemistry 27, 1512–24. (Reference link)

Contact: Roland F. Hirsch, SC-23.2, (301) 903-9009
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


August 01, 2012

Novel Bioremediation Strategy for Degrading Contaminants

Microbes continue to offer surprises by their range of capabilities and versatility. When studying a microbe in its natural environment for a particular application, scientists often find that it also does something quite different and useful. A new study of the basic biological processes of methane-producing bacteria (methanotrophs) found that Methylocystis strain SB2 can also grow on acetate or ethanol and degrade a wide range of halogenated hydrocarbons. A specific pollutant-degrading protein, particulate methane monooxygenase (pMMO), attacked pollutants of interest while the bacteria used ethanol to grow. Ethanol added to contaminated groundwater enhances the ability of the groundwater to “flush” pollutants such as trichloroethylene and tetrachloroethylene. The authors suggest that the resulting aqueous ethanol-pollutant solution can be passed through a methanotrophic bioreactor where both ethanol and the pollutants are removed by a bacterium like Methylocystis strain SB2. The study, which began as a project to understand how methanotrophs that produce a metal-binding compound (methanobactin) affect the behavior of copper and mercury in the environment, led to new discoveries that could provide novel bioremediation strategies.

Reference: Jagadevan, S., and J. D. Semrau. 2012. “Priority Pollutant Degradation by the Facultative Methanotroph, Methylocystis Strain SB2,” Applied Microbiology and Biotechnology, DOI: 10.1007/s00253-012-4310-y. (Reference link).

Contact: Arthur Katz, SC-23.2, (301) 903-4932
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


June 08, 2012

Bacteria Affect Rock Weathering

In their effort to derive energy from iron, bacteria may set off a cascade of reactions that reduce rocks to soil and free biologically important minerals. These findings from a team at the Environmental Molecular Sciences Laboratory (EMSL) at Pacific Northwest National Laboratory are based on a model microbial community called the Straub culture, a lithotrophic culture or literally an “eater of rock,” that can turn non-carbon sources such as iron into energy. This energy is produced via a biochemical pathway driven by a series of electron exchanges, which, in the case of the Straub culture, is initiated by taking an electron from, or oxidizing, iron. To gain insight into how lithotrophs behave in the environment, the Straub culture was incubated with media containing fine particles of an iron-rich mica called biotite. After two weeks, Mössbauer spectroscopy was used to compare a biotite control to biotite incubated with the Straub culture to quantify how much iron exists in what oxidation states in the sample. In the biotite, Mössbauer confirmed that the microbes did oxidize iron from Fe(II) to Fe(III). Transmission electron microscopy revealed that this oxidation affected the biotite structure, leading to changes that resemble those observed in nature. This work offers new insight into the roles of microbes in soil production and in the biogeochemical cycling of minerals (e.g., iron oxidation) and suggests that microbes have a direct effect on rock weathering.

Reference: Shelobolina, E. S., H. Xu, H. Konishi, R. K. Kukkadapu, T. Wu, M. Blothe, and E. E. Roden. 2012. "Microbial Lithotrophic Oxidation of Structural Fe(II) in Biotite," Applied and Environmental Microbiology 78(16), 5746–52. DOI: 10.1128/AEM.01034-12. (Reference link)

Contact: Paul E. Bayer, SC-23.1, (301) 903-5324
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 10, 2012

Electron Gradients in Biofilms

Microbes play a key role in determining the chemical form of metal and radioactive contaminants in the environment. They shuttle electrons back and forth with metal ions, often over long distances. Researchers at the University of Minnesota have found new evidence for how this happens by examining how the thickness of a biofilm produced by Geobacter sulfurreducens affects electron transfer. They used spectroscopic methods involving ultraviolet and visible light with a potentiometric system that exposes the biofilm to a controlled voltage. The investigators discovered that a gradient of electrons developed if the biofilm grew beyond a few cell thicknesses. This gradient was identified when an increased potential, i.e., an increased pull on the electrons produced by a more positive electrode, could not increase the rate electrons travelled out of the thicker biofilm. Unlike thin biofilms where only a small percentage of cytochromes retained electrons, the thicker biofilm showed a substantial number of cytochromes still retained electrons, even when subjected to increased voltage. These results will be helpful in developing new interaction models of metallic contaminants with microbial communities in the environment, particularly in light of the fact that previous studies have led to significantly different descriptions of how the electron transfer process works.

Reference: Liu, Y., and D. R. Bond. 2012. “Long-Distance Electron Transfer by G. sulfurreducens Biofilms Results in Accumulation of Reduced c-Type Cytochromes,” ChemSusChem 5(6), 1047–1053. DOI: 10.1002/cssc.201100734. (Reference link)

Contact: Arthur Katz, SC-23.2, (301) 903-4932
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 10, 2012

Mercury Methylating Bacteria Widespread in Contaminated Streams

Mercury has become a global pollutant due to its release into the atmosphere during coal burning and into freshwater systems as part of agricultural runoff and direct industrial discharge. Once in freshwater systems, specific types of microorganisms are known to transform mercury into methylmercury (MeHg), a highly toxic form of mercury. Scientists from Oak Ridge National Laboratory (ORNL) recently examined the microbial communities from the sediments of six different surface streams in Oak Ridge, Tennessee, to identify bacteria that could be contributing to MeHg production. Using 16S rRNA pyrosequencing, the researchers correlated the presence of a group of known MeHg producers, the Deltaproteobacteria, with MeHg in all of the Hg contaminated streams. Within the Deltaproteobacteria group, Desulfobulbus species are considered to be prime candidates for being involved in Hg methylation in these streams.

Reference: Mosher, J. J., T. A. Vishnivetskaya, D. A. Elias, M. Podar, S. C. Brooks, S. D. Brown, C. C. Brandt, and A. V. Palumbo. 2012. "Characterization of the Deltaproteobacteria in Contaminated and Uncontaminated Stream Sediments and Identification of Potential Mercury Methylators," Aquatic Microbial Ecology 66, 271–82. (Reference link)

Contact: Paul E. Bayer, SC-23.1, (301) 903-5324
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER