Mobilisation of Radionuclides by Ligands Produced by Bacteria from the Deep Subsurface
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0RELOLVDWLRQRI5DGLRQXFOLGHVE\/LJDQGV3URGXFHGE\%DFWHULDIURPWKH'HHS6XEVXUIDFH Johanna Arlinger1, Anna Oskarsson1, Yngve Albinsson2, Thomas Andlid3 and Karsten Pedersen1 1 Göteborg University, CMB, Microbiology, Box 462, SE-405 30 Göteborg, Sweden 2 Chalmers University of Technology, Department of Food Science, Box 5401, SE-402 29 Göteborg, Sweden 3 Chalmers University of Technology, Nuclear chemistry-Department of Materials and Surface chemistry, SE-412 96 Göteborg, Sweden $%675$&7 Microbial processes can influence retention of radionuclides directly or indirectly in several different ways. Many microorganisms produce various kinds of ligands or chelating compounds to increase the bioavailability of essential elements needed for metabolism. These ligands are not always highly specific, and several of them will also mobilise other elements such as heavy metals and radionuclides. Three bacterial species (6KHZDQHOODSXWUHIDFLHQV3VHXGRPRQDV IOXRUHVFHQVand 3VHXGRPRQDVVWXW]HULL , isolated from the deep subsurface, and four radionuclides, 59Fe(III), 147Pm(III), 234Th(IV) and 241Am(III), were selected for this study. The microbes were cultured in the laboratory, separated from their exudates by centrifugation, and the supernatants were collected. The supernatants were mixed with radionuclide and solid phase (TiO2 or SiO2). The pH ranged from 7.5-9.0. All three bacterial species produced ligands that were able to complex up to 90% of the radionuclides in competition with the solid phases. High performance liquid chromatography analysis detected four Fe-complexing substances in the supernatant from 3IOXRUHVFHQV and two peaks and one peak, respectively, from 3VWXW]HULL and 6SXWUHIDFLHQV All substances eluted from the column varied in retention times, indicating that the microbes studied produced several metabolites that have different chelating abilities. ,1752'8&7,21 Many countries plan to store their high-level nuclear waste in underground repositories where the environment will be anaerobic. Studies have been and are being made on inorganic processes affecting the migration of radionuclides in these repositories but it is becoming increasingly evident that biological processes may be of importance as well [1, 2]. Microbial processes can significantly alter the mobility of radionuclides in the environment [3, 4]. Multidisciplinary research combining microbial physiology, ecology and molecular biology with nuclear chemistry, geochemistry and geology therefore plays an important role in the exploration of such processes. Table I summarises microbial processes that can influence radionuclide speciation and thereby their migration behaviour. Microbial processes will act immobilising or mobilising, depending on the type of process and the state of the microbes. Microbes in biofilms will, with the exception of those who produce complexing agents, be immobilising.
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7DEOH,. Microbial processes can influence retention of radionuclides directly or indirectly in several different ways. The most important v
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