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Reference Number NE/D00473X/1
Title The environmental behaviour of redox active radionuclides - a combined biogeochemical and geomicrobiological approach.
Status Completed
Energy Categories NUCLEAR FISSION and FUSION(Nuclear Fission, Nuclear supporting technologies) 100%;
Research Types Basic and strategic applied research 100%
Science and Technology Fields PHYSICAL SCIENCES AND MATHEMATICS (Chemistry) 50%;
ENVIRONMENTAL SCIENCES (Earth Systems and Environmental Sciences) 50%;
UKERC Cross Cutting Characterisation Not Cross-cutting 75%;
Sociological economical and environmental impact of energy (Environmental dimensions) 25%;
Principal Investigator Dr K (Katherine ) Morris
No email address given
Earth, Atmospheric and Environmental Sciences
University of Manchester
Award Type R&D
Funding Source NERC
Start Date 01 October 2006
End Date 30 September 2009
Duration 36 months
Total Grant Value £208,784
Industrial Sectors Power
Region North West
Programme Standard
 
Investigators Principal Investigator Dr K (Katherine ) Morris , Earth, Atmospheric and Environmental Sciences, University of Manchester (99.997%)
  Other Investigator Professor F Livens , Chemistry, University of Manchester (0.001%)
Dr I (Ian ) Burke , School of Earth and Environment, University of Leeds (0.001%)
Professor JR (Jonathan ) Lloyd , Earth, Atmospheric and Environmental Sciences, University of Manchester (0.001%)
Web Site
Objectives Objectives. To produce new mechanistic insights into the environmental behaviour of U, Tc, Np and Pu, we will integrate three complementary workpackages: (1) geomicrobiology studies with selected pure culture systems will characterise the potential range of enzymatic and indirect mechanisms mediated by prokaryotes in reducing and reoxidising conditions; (2) biogeochemical studies will use more complex microcosm experiments with sediments from nuclear licensed sites to track radionuclide fate on reduction and reoxidation; and (3) molecular ecology techniques will be used to define the microbial populations driving key biogeochemical cycles in contaminated sediments and will link workpackages (1) and (2). These three work packages will be repeated in two workprogrammes on bioreduction andoxidation. Our specific objectives are to: 1. Quantify the mechanisms of enzymatic bioreduction processes affecting redox active radionuclides in model, pure culture geomicrobiological experiments using appropriate, well characterised nitrate-, metal-, sulfate-reducing and methanogenic microorganisms (JRL) 2. Understand the biogeochemical processes affecting the behaviour of redox active radionuc lides in sediments from nuclear sites in selected incubations undergoing microbial reduction (KM) 3. Understand the geomicrobiological mechanism of nitrate reoxidation processes affecting Tc, U, Np and Pu in pure culture experiments and with stable, fully characterised microbial consortia in defined media (JRL) 4. Understand how reoxidation processes affect the biogeochemistry of Tc, U, Np andPu when reduced radiolabelled sediments are reoxidised with both air and nitrate (KM) 5. Use molecular ecology (JRL) techniques to define key microbes and their enzymes affectingredox cycling in sediments and isolate pure cultures of key microbes involved in mineral cycling from contaminated sediments. These microorganisms will be used to refine our understanding of radionuclide behaviour duringred ox cycling using model systems with defined media and mineral phases (JRL, KM)
Abstract The UK has a substantial legacy of contaminated nuclear industry sites. Two of the principle sites are at Sellafield and and Dounreay, and the soils and groundwaters at these sites have been contaminated with radioactivity. Indeed, groundwater contamination with radionuclides is a global problem, and decommissioning of nuclear facilities will require control and removal of the contamination. However, little is currently understood of the way that sub-surface microorganisms affect the mobility and behaviour of radionuclides in contaminated land. We have identified four radionuclides that are of particular relevance to radionuclide contamination: technetium; uranium; neptunium; and plutonium. All of these radionuclides are long-lived, and U and Tc are currently priority pollutants at a number of sites throughout the world and are reported as contaminants at Sellafield, whilst Np and Pu will be significant medium term environmental contaminants in radioactive wastes and in contaminated land. Additionally, they are all redox active and are commonly more mobile in their oxidised states when compared to their reduced forms. This project focuses on understanding the interactions of these radionuclides with microorganisms and sediments from contaminated nuclear sites in the UK during 'redox cycling' as reducing conditions developand as reduced systems are reoxidised. In sub-surface environments, microorganisms control redox chemistry, and many recent studies have highlighted the fact that microorganisms can interact with redox active radionuclides. In turn these interactions may affect the environmental behaviour of Tc, U, Np and Pu by altering their redox state (or speciation). The radionuclide-microbe interactions that occur can be split into two groups: 1. Direct interactions, where the microbe is enzymatically mediating changes in the radionuclide speciation and; 2. indirect interactions, where reduced products of microbial metabolism such as Fe(II), or sulfide can cause abiotic changes in speciation. Currently, there is a relatively poor understanding of both the direct and indirect mechanisms of microbial interactions with radionuclides, and how the balance between enzymatic and abiotic reactionscontrols radionuclide redox cycling in contaminated environments. Understanding the fundamental mechanisms of these radionuclide-microbe interactions isthe focus of this proposal, and we will tackle this problem using three different approaches. As U and Tc are less radiologically hazardous than Np and Pu, we will focus the majority of our experiments on U and Tc, limiting our Np and Pu work to several key systems. We will use geomicrobiology techniques to examine the enzymatic transformations of Tc, U, Np and Pu with key microorganisms found in sub-surface environments and in reducing and reoxidising systems. In addition, we will take sediments from DY and SF, and use biogeochemistry techniques to examine the behaviour of the radionuclides in complex sedimentary environments as reducing conditions develop, and when we reoxidise the sediments. We will also use molecular ecology techniques to identify key microorganisms controlling thebiogeochemistry of the sediments. In turn we will isolate pure cultures of key microbes involved in redox cycling in the sediments, and use these microorganisms to investigate radionuclide behaviour during reduction and reoxidation in model systems. These experiments will bridge between the pure culture systems designed to understand enzymatic transformations, and the complex sediment experimentsdesigned to examine transformations in real sedimentary environments. These multidisciplinary approaches will allow substantial advances in understanding the redox cycling behaviour of the radionuclides technetium, uranium, neptunium and plutonium.
Publications (none)
Final Report (none)
Added to Database 15/09/08