AVAIBILITY OF NUTRIENT AND ENERGETIC SOURCES FOR BACTERIAL DEVELOPMENT IN DEEP CLAY ENVIRONMENTS 1 Introduction: Clayey materials: Observation by DRX Loïc ESNAULT 1, Marie LIBERT 1, Christian MUSTIN 2, Michel JULLIEN 1 ; 1 Laboratoire de Modélisation des Transferts dans l’Environnement, CEA Cadarache, St Paul lez Durance - France 2 LIMOS UMR 7137 CNRS-UHP Nancy I - Faculté des Sciences - BP Vandoeuvre les Nancy cedex – France It is now acknowledged that highly adapted bacteria are present in deep environments and will probably play a very important role in geochemical cycles, but a question is arising about the persistence of microbial activity in deep clay environments and in such extreme conditions. The availability of nutrients and energetic sources able to be used by deep biosphere is a key point to understand microbial subsurface life. However the introduction of nuclear waste (metal containers) in a deep geological disposal will lead to a new inventory of nutrients and energetic sources for microbial activity in this particular environment. An inventory of nutrients, energetic sources and possible thermodynamically reactions has been realised in the case of the specific french geological disposal of nuclear waste based on a multibarrier system involving a host rock: argillite. Different reservoirs of energetic nutrients have been identified to be able to support bacterial activity. That is to say: minerals of the host rock, organic matter of the host rock, nutrients of the interstitial water of argillite and hydrogen. H 2 is known as one of the most energetic substrates for deep terrestrial subsurface environments. High amount of H 2 gas will be produced within nuclear deep waste repository (originated from radiolysis or corrosion processes of metallic components in anoxic conditions) and consequently will improved microbial activity in this specific environment. Dissolution of Fe in argillite of Tournemire is mainly due to a phenomenum of microbial Fe(III) reduction. Al released is very weak compared to Fe and Si release. First release is due to a destabilization of clay structure by microbial reduction, then, second release is due to dissolution by alteration of argillite. This phenomena has already been showed by O’Reilly, 2006 on nontronite mineral. Bio-dissolution evidence of the Tournemire argillite, 40°C Goldschmidt Conclusion and perspectives Acknowledgements: This study was funded by the CEA in collaboration with IRSN References: BEAUCAIRE, C. MICHELOT, J. L. SAVOYE, S. & CABRERA, J. (2008). Groundwater characterisation and modelling of water-rock interaction in an argillaceous formation (Tournemire, France). Applied Geochemistry 23(8), LIN, L. H. SLATER, G. F. LOLLAR, B. S. LACRAMPE-COULOUME, G. & ONSTOTT, T. C. (2005). The yield and isotopic composition of radiolytic H-2, a potential energy source for the deep subsurface biosphere. Geochimica et Cosmochimica Acta 69(4), STROES-GASCOYNE, S. & GASCOYNE, M. (1998). The introduction of microbial nutrients into a nuclear waste disposal vault during excavation and operation. Environmental Science & Technology 32(3), O'REILLY, S. E., Y. FURUKAWA and S. NEWELL (2006). Dissolution and microbial Fe(III) reduction of nontronite (NAu-1). Chemical Geology 235 (1-2), In this specific environment several metabolisms of bacteria could occur. Among them, some microorganisms are able to use structural Fe (III) of the clayey host-rock as electron acceptor and H 2 as electron donor. In a complex environment as argillite of Tournemire, microbial Fe(III) reduction is observed. This Fe(III) respiration coupled with carbon oxidation or H 2 by anaerobic containers corrosion are preceded by a dissolution of minerals in our system. According to other authors, microbial reduction improve the potential of mineral dissolution and transformation. A. Chemical composition of water in equilibrium with the argillite (simulated with the code CHESS), in equilibrium with air, (in moles / l). C. Corrosion of containers: new energetic sources B. Bio reduction, alteration of clay minerals Fe 0 + 2H 2 O Fe H 2 + 2OH - Fe 3 O 4 (magnetite) Fe 3 O 4 + 2H 2 Fe 3+ + Fe H + Bacterial activity Chemical analysis of Tournemire groundwater 7-8 Chemical analysis of Tournemire argillite (weight % ) 2 Nutritional and energy sources in the argillite Nutrients and energetic sources Bioavailability of these sources ? Structural Fe (III) availability for bacteria? ChloriteIllite/SmectiteKaolinite Sample NameNet Area Control experiment-2Months162.4 Shewanella -Tournemire-1Month118.4 Shewanella -Tournemire-2Months101.9 High destabilization of argillite is mainly focused on smectite phase during reactivity with bacteria. Observation of bacteria-clay interaction by SEM Nutrients Corrosion process is depending on pH parameter. The increase of H 2 concentration in the system is observed with a Fe production in solution. Then, there is a precipitation of magnetite which is following by a weaker production of H 2. So, in batch system a process of passivation of iron is observed. 3 Experimental data of microbial development: Case of deep geological storage e- Acceptor SO 4 2- : Not limiting for sulfate reducing bacteria development e- Acceptor HCO 3 - : Not limiting for sulfate reducing bacteria development e- Acceptor Fe(III): During nuclear waste storage, a first step will be under oxidised and saturated conditions leading to a high proportion of Fe(III) available for bacterial respiration. Then in reduced environments, the amount of Fe(III) decrease until become limiting. Could we have another source of Fe(III) for Iron reducing bacteria in this deep clayey environment ? Aqueous anaerobic corrosion, 40°C Argillite - Fe3 + + (αH2 or organic compounds) Argillite’ + βH + + Fe 2+ Electrons donorsElectrons acceptors reducing agentsOxidizing agents H2H2 O2O2 HCO 3 - SO 4 2  Fe (II)Fe (III) Mati è re organique