Nils Baumann

Uranium speciation in biofilms studied by laser fluorescence techniques

AbstractBiofilms may immobilize toxic heavy metals in the environment and thereby influence their migration behaviour. The mechanisms of these processes are currently not understood, because the complexity of such biofilms creates many discrete geochemical microenvironments which may differ from the surrounding bulk solution in their bacterial diversity, their prevailing geochemical properties, e.g. pH and dissolved oxygen concentration, the presence of organic molecules, e.g. metabolites, and many more, all of which may affect metal speciation. To obtain such information, which is necessary for performance assessment studies or the development of new cost-effective strategies for cleaning waste waters, it is very important to develop new non-invasive methods applicable to study the interactions of metals within biofilm systems. Laser fluorescence techniques have some superior features, above all very high sensitivity for fluorescent heavy metals. An approach combining confocal laser scanning microscopy and laser-induced fluorescence spectroscopy for study of the interactions of biofilms with uranium is presented. It was found that coupling these techniques furnishes a promising tool for in-situ non-invasive study of fluorescent heavy metals within biofilm systems. Information on uranium speciation and uranium redox states can be obtained. FigureSpectroscopic information, e.g. different oxidation states, can be visualized and spectroscopically identified within a confocal volume by a combination of confocal laser scanning microscopy (CLSM) and laser-induced fluorescence spectroscopy (LIFS)

Boltwoodite [K(UO2)(SiO3OH)(H2O)1.5] and compreignacite K2[(UO2)3O2(OH)3]2·7H2O characterized by laser fluorescence spectroscopy

Synthetically prepared boltwoodite and compreignacite were characterized with time-resolved laser-induced fluorescence spectroscopy (TRLFS). The obtained TRLFS emission spectra of both synthesized uranium minerals differ from each other in their positions of the vibronic peak maxima and in their fluorescence lifetimes. Also, the shapes of the spectra and their respective intensities are different. The TRLFS-spectrum of boltwoodite showed well-resolved sharp vibronic peaks at 485.1, 501.5, 521.2, 543.0, 567.4, and 591.4nm with deep notches between them and compreignacite is characterized by two broad peaks with various shoulders. Here five emission bands were identified at 500.7, 516.1, 532.4, 554.3, and 579.6nm. The shape of the TRLFS spectra of compreignacite is typical for uranium in a hydroxide coordination environment. For both minerals two fluorescence lifetimes were extracted. The two species of boltwoodite and compreignacite, respectively, showed the same positions of the peak maxima showing that the coordination environments are similar, but differ in the chemistry and number of possible quenchers, e.g. water molecules and hydroxide groups. For boltwoodite fluorescence lifetimes of 382 and 2130ns, and for compreignacite shorter ones of 202 and 914ns, respectively, were determined. The spectroscopic signatures of the two uranyl minerals reported here could be useful for identifying uranyl(VI) mineral species as colloids, as thin coatings on minerals, as minor component in soils, or as alteration products of nuclear waste.

The copper spoil heap Knappenberg, Austria, as a model for metal habitats - Vegetation, substrate and contamination.

Historic mining in the Eastern Alps has left us with a legacy of numerous spoil heaps hosting specific, metal tolerant vegetation. Such habitats are characterized by elevated concentrations of toxic elements but also by high irradiation, a poorly developed substrate or extreme pH of the soil. This study investigates the distribution of vascular plants, mosses and lichens on a copper spoil heap on the ore bearing Knappenberg formed by Prebichl Layers and Werfener Schist in Lower Austria. It serves as a model for discriminating between various ecological traits and their effects on vegetation. Five distinct clusters were distinguished: (1) The bare, metal rich Central Spoil Heap was only colonised by highly resistant specialists. (2) The Northern and (3) Southern Peripheries contained less copper; the contrasting vegetation was best explained by the different microclimate. (4) A forest over acidic bedrock hosted a vegetation overlapping with the periphery of the spoil heap. (5) A forest over calcareous bedrock was similar to the spoil heap with regard to pH and humus content but hosted a vegetation differing strongly to all other habitats. Among the multiple toxic elements at the spoil heap, only Cu seems to exert a crucial influence on the vegetation pattern. Besides metal concentrations, irradiation, humidity, humus, pH and grain size distribution are important for the establishment of a metal tolerant vegetation. The difference between the species poor Northern and the diverse Southern Periphery can be explained by the microclimate rather than by the substrate. All plant species penetrating from the forest into the periphery of the spoil heap originate from the acidic but not from the calcareous bedrock.

Speciation of Uranium in Seepage and Pore Waters of Heavy Metal-Contaminated Soil

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) is a very helpful tool with an extremely low detection limit for analyzing speciation of certain radioactive heavy metal ions like uranium(VI). Thus this technique is preferentially appropriate for detection of speciation from that ions in environmental relevant concentrations. So TRLFS can be useful in safety assessment concerning migration behavior of radioactive elements. In this chapter, TRLFS was used to analyze the uranium speciation in naturally occurring seepage water samples, and in soil water samples, all samples collected from test site “Gessenwiese” close to Ronneburg in Eastern Thuringia (Germany). This test site was installed as a part of a research program of the Friedrich Schiller University Jena for investigations within the area of recultivated former uranium mining heaps. The TRLFS measurements on water samples collected within test site Gessenwiese revealed that the uranium speciation in that seepage water is dominated by the hydrolyzed and monomer uranium(VI) sulfate species UO2SO4(aq). The results presented here are a convincing example for the suitability of TRFLS in analyzing the speciation of uranium from naturally occurring water samples with pH values between 3.2 and 4.0.