Interaction of Selected Actinides (U, Cm) with Bacteria Relevant to Nuclear Waste Disposal


Interaction of Selected Actinides (U, Cm) with Bacteria Relevant to Nuclear Waste Disposal

Lütke, L.

To assess the safety of a site destined for storage of nuclear waste enhanced research effort is demanded to investigate the complex interactions of released radionuclides with parts of the environment that includes indigenous microorganisms.
As part of a BMWi-funded project this work aimed at assessing the interactions of two bacterial strains with the actinides uranium and curium with a focus on thermodynamics to provide stability constants of the actinide bacteria species formed usable for modelling the distribution of these actinides in the environment. The influences of Pseudomonas fluorescens (CCUG 32456A) isolated from the granitic aquifers at Äspö (Sweden) and a novel isolate from Mont Terri Opalinus clay (Switzerland), Paenibacillus sp. MT-2.2, were investigated. A combined approach using microbiological and spectroscopic techniques as well as potentiometry was employed to characterize the U(VI) and Cm(III) binding onto the cell surface functional groups structurally and thermodynamically. Further, due to its similar ionic radius to Cm(III) also Eu(III) was studied as non-radioactive analog.
The results evidenced that U(VI) and Cm(III) binding onto the cells is strongly pH-dependent. Both strains displayed high U(VI) binding capacities. In view of the versatile possible interaction mechanisms between microbes and actinides, it was found that both investigated strains display besides direct also indirect interaction in the form of a pronounced pH-dependent phosphatase activity and concomitant phosphate release which was drastically decreased in presence of U(VI). A moderate to strong interaction of U(VI) and Cm(III) (Eu(III)) with carboxylic and phosphoryl sites of the bacterial surfaces could be proven. Based on the determined stability constants of the different U(VI) phosphoryl and the U(VI) carboxyl surface complexes it could be shown that U(VI) is bound thermodynamically more stable to phosphoryl sites than to carboxylic ones. U(VI) speciation calculations indicated a dominant binding of U(VI) to the bacterial surface functional groups up to pH 7. For Eu(III) interaction with the bacterial surfaces the complexes R-O-PO3H-Eu2+ and R-COO-Eu2+ were identified and characterized thermodynamically. Spectroscopic results on Cm(III) binding onto Paenibacillus sp. cells indicated that binding occurred to H-phosphoryl surface sites over a wide pH range while sorption was found to be fully reversible. The identified complex R­-O-­PO3H-­Cm2+ was characterized spectroscopically and thermodynamically.
The stability constants calculated in the present work are valuable for modelling the U(VI), Cm(III) and Eu(III) speciation and distribution in the environment.

Keywords: U(VI); Cm(III); Eu(III); Pseudomonas fluorescens; Paenibacillus sp; Äspö; Mont Terri; Opalinus clay; potentiometry; TRLFS; EXAFS

  • Doctoral thesis
    TU Dresden, 2013
    133 Seiten

Permalink: https://www.hzdr.de/publications/Publ-18389
Publ.-Id: 18389