Speciation of bioaccumulated uranium(VI) by Euglena mutabilis cells obtained by laser fluorescence spectroscopy

Euglena mutabilis cells were used to study the influence of eukaryotic microorganisms on the migration behavior of uranium in acid mine drainage (AMD) environments. Batch sorption experiments at pH 3 and 4 were performed in Na2SO4 background solutions to mimic AMD conditions and in NaClO4 background solutions for comparison, respectively. It was found that axenic cultures of Euglena mutabilis were able to bioaccumulate more than 94 % of uranium from a 1×10­5 mol/L uranium solution. Laser induced fluorescence spectroscopy, used to identify the speciation of uranium, indicated that the bioaccumulated uranium species forming in Euglena cells or on euglenid pellicles were related to carboxylic groups and/or organophosphate groups.
In similar experiments using sterile filtrated AMD waters, obtained from a former uranium mine, reduced uranium immobilization rates for Euglena mutabilis cells were observed. However, the identified uranium speciation in both experiments was identical. The reduced rates were attributed to the competition by other cations for available sorption sites on or in the Euglena cells. The results showed that Euglena mutabilis or components of it are able to immobilize aqueous uranium and thus may be used in future as promising agent for immobilizing uranium in low pH waste water environments.