News - 2008
- 12/12/08 - Hybrid Numerical Methods Improve Computer
Modeling of Geochemical Processes. Geochemically important reactions governing the transport of
contaminants in groundwater are often influenced by processes occurring
at very small scales (microscales). Simulating these phenomena and extrapolating
to larger scales becomes computationally inefficient because the microscale
descriptions must be extended across the entire computational domain. Hybrid
numerical methods allow the coupling of microscale process models with
coarser scale models only where needed thereby improving computational
efficiency. Researchers at PNNL, INL and the University of California/San
Diego describe the use of hybrid numerical methods to simulate mineral
precipitation in a mixing front between two geochemical reactive solutions.
The results have important implications for linking microscale mechanisms
influencing the mobility and reactivity of contaminants in groundwater
to field scale predictions of contaminant transport. This work is jointly
funded by BER and ASCR under the SciDAC program.
Reference: SIAM JOURNAL ON SCIENTIFIC COMPUTING, 2008, 30 (6): 2799-2816. - 10/23/08 - New Genome-Based Tools Improve Description
of Uranium Bioreduction in the Environment. Environmental microbes play an important role in the
remediation of contaminants such as uranium by converting them from mobile
to immobile forms. However, we do not have accurate or reliable tools to
predict the role that microbes will play in remediation of contaminants
at a site. Researchers at the University of Massachusetts have developed
a genome-enabled approach for assessing the metal-reducing activity of
members of the Geobacter family involved in acetate stimulated uranium
reduction in the environment. This new approach couples laboratory studies
with in silico modeling of microbial metabolism and gene expression (mRNA)
analyses from the dominant Geobacter species at a site to explain how the
microbes respond to acetate injected into the subsurface to stimulate uranium
reduction. The new tools can, for example, provide crucial data on rates
of acetate uptake useful in mechanistic, in silico, models of microbial
growth and activity. The current study is an example of how genome-enabled
studies of environmentally-relevant microbes can lead to more mechanistic
descriptions of microbial metabolism in the environment.
Reference: Microbiology, 2008, vol 154:2589-2599. - 9/10/08 - New Modeling Approach Integrates Geochemical Processes into Field-Scale Simulation of Uranium Mobility in Groundwater at the Hanford Site. Uranium is a persistent groundwater contaminant at many DOE sites due to its adsorption onto mineral surfaces and/or precipitation of various uranium minerals within subsurface materials. These molecular-scale processes often exert a profound influence on uranium mobility at the field scale. One challenge in simulating uranium transport in the subsurface is the difficulty in coupling molecular-scale geochemical processes controlling uranium concentrations with groundwater transport processes occurring at the field-scale. Researchers at PNNL examining uranium sorption in column experiments have developed a modeling approach that incorporates laboratory-derived geochemical and reaction kinetic information on uranium adsorption with transport information obtained from tracer experiments to describe uranium mobility. The approach couples molecular-scale, laboratory-derived characterization of uranium geochemical properties with field-scale descriptions of transport processes obtained from tracer experiments. The new approach will be tested in conjunction with laboratory studies and field-scale tracer experiments examining uranium transport as part of the Integrated Field-Scale Subsurface Research Challenge (IFC) site at the Hanford 300 Area (http://ifchanford.pnl.gov/). Reference: Liu, C. Zachara, JM, Qafoku, NP, Wang, Z. (2008), Scale-dependent desorption of uranium from contaminated subsurface sediments. Wat. Resour. Res. vol. 44 (W08413), doi:10.1029/2007WR006478.
- 8/18/08 - Processes influencing technetium-99 mobility
in the environment. Technetium-99 (Tc-99) is a long-lived radioactive fission product of uranium
processing and a high priority contaminant at DOE sites such as Hanford.
Tc-99 is highly mobile in groundwater but can be reduced to an insoluble
(and immobile) solid by reduced iron found in many minerals in the environment.
Researchers at PNNL evaluated the reaction kinetics at mineral surfaces
containing reduced iron to understand both the mechanism and products of
Tc-99 reduction. Mineral surface-catalyzed reactions increased the rate
of Tc-99 reduction compared to reactions in aqueous solution indicating
the importance of surface-associated geochemistry in controlling Tc-99
reduction. Also, the solid-phase products of Tc-99 reduction differed depending
on the nature of the mineral surface tested. The results add to a growing
body of literature on Tc-99 fate and transport properties in natural environments,
information needed to construct conceptual models for Tc-99 mobility and/or
remediation at contaminated sites.
Reference: Environmental Science & Technology, 2008, vol 42(15):5499-5506. -
8/1/08 SciDAC Review. Science for Problems Under the Surface. Processes in Earth's subsurface are central players in several critical, interrelated energy and environmental issues. Leadership-class computing will soon be brought to bear on understanding and predicting these processes across a wide range of time and space scales. Read about it online or download the pdf.
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7/18/08 Summary Report for the biomodeling workshop, which will be published in EOS. Download the pdf here. The full report (pdf) is online as referenced in the summary report.
- 7/10/08 - BER Researchers at LBNL win R&D 100 Award for Phylochip. Development. Tools for rapid characterization of complex microbial communities are needed to detect and indentify microorganisms in a variety of environmental samples. LBNL researchers have developed a microarray technique known as the Phylochip that can detect and identify thousands of different species of microorganisms very rapidly. The Phylochip allows unprecedented detection and identification capability in a device about the size of a quarter. The Phylochip was developed by Gary Andersen, Todd DeSantis, Eoin Brodie and Yvette Piceno from LBNL’s Earth Sciences Division. The device has been used to identify airborne bacterial species as part of a biodefense project, to assess microbial communities involved in environmental cleanup projects and will help advance the understanding of microbial processes involved in biofuel production and carbon sequestration. The prestigious R&D 100 awards are given in recognition of the top 100 significant technological advances over the past year.
- 7/2/08 - Geochemical Research Sheds Light on Plutonium Mobility in the Environment. There is a concern that the mobility of plutonium (Pu) in the environment at some DOE legacy waste sites may be increased due to the formation of complexes with the metal-complexing compound ethylenediaminetetraacetic acid (EDTA), which was co-disposed with Pu. At issue is whether EDTA enhances the solubility and therefore the mobility of Pu(IV). Researchers at Pacific Northwest National Laboratory examined the mobility of Pu(IV)-EDTA complexes under common environmental conditions and found that they are not as mobile as previously assumed. The complexation of Pu(IV) with EDTA is affected by competitive complexation reactions with other common inorganic species such as Fe, Al, Ca and Mg. EDTA also readily adsorbs to geologic materials and is biodegraded by microorganisms commonly found in the environment. These other competitive reactions ultimately reduce the potential for EDTA to complex and mobilize Pu in the environment suggesting that Pu(IV)-EDTA complexes are not responsible for the observed mobility of Pu in the environment. Reference: Journal of Solution Chemistry, 2008, vol. 37:957-986.
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6/12/08 Special Issue of Geobiology Outlines Recent Advances in Understanding Extracellular Electron Transport and Microbe-Mineral Interactions. Numerous ERSP researchers contributed to a special issue of Geobiology dedicated to the memory of Terry Beveridge, a world-renowned geomicrobiologist and long-time NABIR-ERSP grantee. This special issue is a review of the current state-of-the-science in understanding microbe-metal interactions and a fitting tribute to a respected colleague whose scientific breadth spanned this entire area of science. Advances made over the last few years in understanding microbial metabolism at the microbe-mineral interface are detailed in this special issue. Several groups of bacteria are capable of respiring (breathing) solid phase materials that reside outside the cell. How cells accomplish this feat is a topic under intensive investigation within DOE's Office of Biological and Environmental Research (BER). Microbes with the ability to reduce inorganic materials extracellularly also reduce electrodes in microbial fuel cells, produce soluble organics with electrochemical properties, and influence mineral precipitation in novel ways. These unique traits have implications for understanding the processes that influence contaminant transport, bioenergy production, microbial biofilm formation, intercellular communication and biomineral production.
Reference: Geobiology, Vol 6(3), June 2008. http://www.blackwell-synergy.com/toc/gbi/6/3 - 6/9/08 - Practical Gas Sampling Method Allows Rapid Evaluation of Microbial Processes in Groundwater. Researchers at Oak Ridge National Laboratory developed a practical method to sample dissolved gases present in groundwater. Concentrations of dissolved gases such as oxygen, hydrogen, methane, nitrous oxide, carbon monoxide and others yield important information on microbial processes occurring at depth. Microorganisms profoundly affect the transport of contaminants in the subsurface and these methods can help identify which microbial processes are active in the subsurface. The new method is a significant improvement over other methods because no pumping of groundwater is required. The sampling device is suspended in the well until equilibration with ambient conditions then removed for analysis in the laboratory. The technique is highly sensitive for trace level analysis of gases of interest and can provide researchers and modelers with information on active microbial processes in the subsurface in order to refine simulations of contaminant transport, understand bioremediation or natural attenuation processes or devise new techniques to intercept and immobilize contaminants. Reference: Environmental Science & Technology, 2008, vol 42(10):3766-3772.
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4/16/2008. Jenny Druhan, Graduate Student at UC Berkeley was given an "Outstanding Student Paper Award" from the Hydrology Section of the American Geophysical Union for her paper "Sulfur isotopes as indicators of bacterial sulfate processes influencing field scale uranium bioremediation" with authors: Jennifer L. Druhan, Mark E. Conrad, Kenneth Hurst Williams, Lucie N'Guessan, Philip E. Long and Susan S. Hubbard. The paper was presented at the American Geophysical Union Fall Meeting, in San Francisco in December 2007. The award announcement was published in the April 16, 2008 edition of EOS (vol. 89, no. 15). Congratulations, Jenny!
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3/7/2008. Craig Criddle ERSP-funded research identified as a “Most Cited Article” for 2006 by the journal Environmental Science & Technology. The published manuscript details results obtained from the in situ stimulation of uranium reduction at the Oak Ridge Y-12 site. Congratulations to the Oak Ridge National Laboratory and Stanford University team!
Pilot-Scale in Situ Bioremedation of Uranium in a Highly Contaminated Aquifer. 2. Reduction of U(VI) and Geochemical Control of U(VI) Bioavailability
Wu, W.-M.; Carley, J.; Gentry, T.; Ginder-Vogel, M. A.; Fienen, M.; Mehlhorn, T.; Yan, H.; Caroll, S.; Pace, M. N.; Nyman, J.; Luo, J.; Gentile, M. E.; Fields, M. W.; Hickey, R. F.; Gu, B.; Watson, D.; Cirpka, O. A.; Zhou, J.; Fendorf, S.; Kitanidis, P. K.; Jardine, P. M.; Criddle, C. S. Environ. Sci. Technol.
(Article); 2006; 40(12); 3986-3995.DOI: 10.1021/es051960u
(http://pubs.acs.org/journals/esthag/promo/most/most_cited/2006.html) - John Zachara, long-time NABIR/ERSP investigator wins DOE's E.O. Lawrence Award, Congratulations John!!
