BER Research Highlights

Search Date: December 13, 2017

6 Records match the search term(s):


December 24, 2014

Carbonate Minerals Could Immobilize Neptunium in Groundwater

The radioactive metallic element neptunium (Np) is created when uranium (U)-based nuclear fuel is burned in electricity-producing commercial reactors and in plutonium-producing reactors operated for military purposes. Np(V) has been accidentally released to the environment at former Department of Energy (DOE) weapons production sites as well as other locations through a variety of circumstances. Because Np(V) has a high aqueous solubility, it is readily transported in groundwater. Predictions for the transport of Np(V) in groundwater are based on studies of U(VI), in part because U(VI) is easier and cheaper to study. However, there are major differences in the crystal chemistry of Np(V) and U(VI), suggesting they might be incorporated into mineral structures differently, and thereby immobilized in groundwater differently. In a recent study, researchers from the University of Notre Dame and Pacific Northwest National Laboratory examined factors that impact the structural incorporation of Np(V) and U(VI) ions into carbonate and sulfate minerals. Using spectroscopic and imaging instruments in RadEMSL, a radiochemistry facility at DOE’s Environmental Molecular Sciences Laboraty, the team found that carbonate minerals incorporated both ions at far higher levels than sulfate minerals. In addition, they found that Np(V) and U(VI) are incorporated into carbonate minerals at dramatically different levels, and that Np(V) can be readily incorporated into carbonate minerals, thereby reducing its mobility in groundwater.

Reference: Balboni, E., J. M. Morrison, Z. Wang, M. H. Engelhard, and P. C. Burns. 2015. "Incorporation of Np(V) and U(VI) in Carbonate and Sulfate Minerals Crystallized from Aqueous Solution," Geochimica et Cosmochimica Acta 151,133-49. DOI: 10.1016/j.gca.2014.10.027. (Reference link)
(See also)

Contact: Paul E. Bayer, SC-23.1, (301) 903-5324, Roland F. Hirsch, SC-23.2, (301) 903-9009
Topic Areas:

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


September 30, 2014

Visualizing Mercury on Surface of Freshwater Particulates

Suspended particulates are primarily responsible for the transport of mercury and toxic methylmercury in freshwater systems; however, little is known about how mercury interacts with particulates. Mercury interactions with phytoplankton and colloidal minerals, two common types of particulates known to be involved in binding and transporting mercury, were studied by a team of scientists from Oak Ridge National Laboratory and Argonne National Laboratory using X-ray fluorescence (XRF) spectroscopy. Using samples from a mercury-contaminated freshwater system, the team found that mercury is mostly found on the outer surface of phytoplankton cells (diatoms) and that it is heterogeneously distributed on mineral particles rich in iron oxides and natural organic matter (NOM). The findings confirm that suspended particles, especially diatoms and NOM-coated oxide minerals, are important sinks for mercury in freshwater systems.

Reference: Gu, B., B. Mishra, C. Miller, W. Wang, B. Lai, S. C. Brooks, K. M. Kemner, and L. Liang. 2014. “X-Ray Fluorescence Mapping of Mercury on Suspended Mineral Particles and Diatoms in a Contaminated Freshwater System,” Biogeosciences Discussion 11, 7521-40. DOI:10.5194/bgd-11-7521-2014. (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 30, 2014

How Sulfur Affects Chemistry of Iron in the Environment

Substantial amounts of iron are present in many subsurface environments. This element has a significant effect on both the biogeochemical cycling of carbon and the fate and transport of trace environmental contaminants, because it is readily transformed among several reactive species. The interactions of subsurface iron with various naturally occurring bacteria have a major influence on its environmental impacts, but these interactions are not well understood. Scientists at Argonne National Laboratory and three partner universities have identified a key role for sulfur in how bacteria affect the speciation of subsurface iron. They determined that bacteria unable to reduce ferric iron directly under alkaline conditions can do so indirectly. The bacteria do this by reducing elemental sulfur to sulfide ion, which then reduces the ferric iron in the goethite to ferrous iron. In addition, this ferrous iron can reduce other metal species such as uranyl ion, thus affecting their solubility. The researchers determined that this process is common in alkaline environments such aquifers, especially those in arid regions. This new understanding of this environmental role of iron will enable progress in a wide range of areas, from modeling of potential carbon capture systems to understanding speciation of contaminants such as uranium and arsenic.

References: Flynn, T. M., E. J. O’Loughlin, B. Mishra, T. J. DiChristina, and K. M. Kemner. 2014. “Sulfur-Mediated Electron Shuttling During Bacterial Iron Reduction,”, Science 344, 1039-42. DOI: 10.1126/science.1252066. (Reference link)

Friedrich, M. W., and K. W. Finster. 2014. “How Sulfur Beats Iron,” Science 344, 974-75. DOI: 10.1126/science.1255442. (Reference link)

Contact: Roland F. Hirsch, SC-23.2, roland.hirsch@science.doe.gov, 301-903-9009.

Topic Areas:

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


May 15, 2014

Stimulating Bacteria to Immobilize Chromium in Groundwater

Hexavalent chromium is a major contaminant in numerous soil and groundwater systems worldwide, in particular at Department of Energy sites due to former weapons production and reprocessing activities and wastes from electroplating processes, and from industrial efforts to reduce corrosion in steel pipes. Although hexavalent chromium is readily transported in groundwater, reduction to a less mobile form involves the interaction of hexavalent chromium with certain minerals and microorganisms. Specifically, iron-reducing bacteria can convert the oxidized form of iron in clay minerals (ferric iron) into the reduced form of iron (ferrous iron) that can then reduce hexavalent chromium to much less mobile trivalent chromium. Efforts to understand the specific details of this process were recently reported by a team of scientists from Miami University and the Environmental Molecular Sciences Laboratory (EMSL), using EMSL’s ultra-sensitive microscopy and spectroscopy capabilities. Starting with the iron-reducing bacterium Geobacter sulfurreducens and ferric iron-containing clay minerals, the team found that they could provide a specific nutrient to the bacteria that would significantly stimulate the bacteria to reduce ferric to ferrous iron. The resulting ferrous iron was able to reduce hexavalent chromium, and it reduced the chromium even faster as the temperature of the system was increased. In addition to demonstrating a possible way to reduce the transport of hexavalent chromium in groundwater, the team also determined the kinetics of these reactions. These kinetic parameters can now be incorporated into models to improve predictions of the transport of hexavalent chromium in subsurface environments.

Reference: Bishop, M. E., P. Glasser, H. Dong, B. Arey, and L. Kovarik. 2014. “Reduction and Immobilization of Hexavalent Chromium by Microbially Reduced Fe-bearing Clay Minerals,” Geochimica et Cosmochimica Acta 133, 186-203. DOI: 10.1016/j.gca.2014.02.040. (Reference link)

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

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


January 09, 2014

Chemical View of Single Uranium Atoms Attached to Mineral Surfaces

Uranium fission currently provides a significant portion of the world’s low-carbon energy. Mining of uranium ores, fuel processing, nuclear accidents, and spent fuel disposal all have resulted in the release of uranium to the environment. Furthermore, because of its chemistry, uranium is often enriched in fossil fuel ores (e.g., kerogens and black shales). Accurate modelling of uranium transport is paramount to understanding the risks from uranium release in the environment. Current models assume that reduction of U6+ to U4+ in bioreduced sediments results in the precipitation of the insoluble mineral uraninite (UO2). However, researchers at Argonne National Laboratory have shown that mineral surfaces have a significant role in stabilizing U4+ as isolated, adsorbed U4+ atoms at low U:surface ratios that are more typical of contaminated sites. Using two model minerals, rutile (TiO2) and magnetite (Fe3O4), the researchers found that the surface area threshold at which U4+ forms single-atom surface complexes and the stability of these complexes over time is dependent on the mineral chemistry. Adsorbed U4+ was produced by reactions representative of both biotic and abiotic U6+ reduction pathways, suggesting that non-uraninite U4+ associated with minerals may account for a significant portion of the U4+ balance in sediments. The results indicate the need to include such forms of U4+ in reactive transport models to better predict uranium mobility in the environment.

Reference: Latta, D. E., B. Mishra, R. E. Cook, K. M. Kemner, and M. I. Boyanov. 2014. “Stable U(IV) Complexes Form at High-Affinity Mineral Surface Sites,” Environmental Science and Technology 48(3), 1683-91. DOI: 10.1021/es4047389. (Reference link)

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

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


January 03, 2014

Watershed-Scale Fungal Communities in a Co-Contaminated System

The legacy of the Department of Energy’s former weapons production activities includes comingled plumes of uranium and very high levels of nitrate in groundwater and soils. At contaminated sites with high nitrate concentrations, anaerobic microbes are known to reduce the nitrate through metabolic respiration. In contrast, the role and importance of fungi, which are abundant in groundwater and soils and are also metal resistant and involved in biogeochemical cycling of carbon, nutrients and metals, is not well understood. To address this gap in understanding, a team of scientists from the Georgia Institute of Technology, Florida State University, and Oak Ridge National Laboratory used quantitative and semi-quantitative molecular techniques to characterize the abundance, distribution, and diversity of fungi in a nitrate and uranium contaminated watershed. The team found that members of the Ascomycota phylum dominated the watershed, and that the community composition varied as a function of the pH gradient. In addition, they discovered that one fungal species is able to reduce nitrate to nitrous oxide, a potent greenhouse gas.

Reference: Jasrotia, P., S. J. Green, A. Ganion, W. A. Overholt, O. Prakash, D. Wafula, D. Hubbard, D. B. Watson, C. W. Schadt, S. C. Brooks, and J. E. Kostka. 2014. “Watershed-Scale Fungal Community Characterization Along a pH Gradient in a Subsurface Environment Cocontaminated with Uranium and Nitrate,” Applied and Environmental Microbiology 80(6), 1810-20. DOI:10.1128/AEM.03423-13. (Reference link)

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

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