Microorganisms and Their Influence on Radionuclide Migration in Igneous Rock Environments

Microorganisms interact with their surroundings and in some cases they greatly modify the characteristics of theirenvironment. Several such interactions may have a significant influence on the behaviour of radionuclidespossibly escaping from underground radioactive waste repositories. Microbes can mobilise trace elements.Unattached microbes may act as large colloids, transporting radionuclides on their cell surfaces with the groundwaterflow. Many microbes produce ligands that can mobilise trace elements from solid phases and that caninhibit trace element sorption to solid phases. Bacterial species from the deep subsurface have demonstrated asignificant effect on the mobilization of 59Fe(III), 147Pm(III), 234Th(IV) and 241Am(III) under varying redox conditions.The extent of bacterial immobilisation of radionuclides has been investigated under in situ conditions.Experiments have demonstrated this effect with 60Co, 147Pm, 234Th, 237Np, and 232U. A large group of microbescatalyse the formation of iron oxides from dissolved ferrous iron in groundwater that reaches an oxidising environment.Such biological iron oxide systems (BIOS) will have a retardation effect on many radionuclides.Microorganisms execute an important influence on the chemical situation in groundwater. Especially, they maycatalyse reactions that stabilise the redox potential in groundwater at a low and, therefore, beneficial level for aradioactive waste repository