Uranium speciation in biofilms studied by Laser fluorescence techniques

Biofilms may immobilize toxic heavy metals in the environment and thereby influence their migration behavior. The mechanisms of these processes are currently not understood. This is due to the complexity occurring in such biofilms creating many discrete geochemical microenvironments which may differ from the surrounding bulk solution in their bacterial diversity, their prevailing geochemical parameters, e.g. pH and dissolved oxygen concentration, their presence of organic molecules, e.g. metabolites, and many more. All of them may affect the metal speciation. To obtain such information, which are necessary for performance assessments studies or the development of new cost effective strategies for cleaning waste waters, it is however very important to develop new non-invasive methods applicable to study the interactions of metals within biofilm systems. Laser fluorescence techniques possess some superior features above all a very high sensitivity for fluorescent heavy metals. An approach of combining confocal laser scanning microscopy and laser induced fluorescence spectroscopy to study the interactions of biofilms with uranium is presented and it was found that the coupling of these techniques is a promising tool to study in situ in non-invasive fashion fluorescent heavy metals within biofilm systems. Information on uranium speciation and uranium redox states can be generated.