Susanne Sachs

Understanding the behavior of contaminants in soils and their transport in water is crucial. This study focuses on the mobility of uranium (U) in a buried contaminated sediment layer, deposited in a wetland 70 years ago by the first U mining activities in France. U mobilization is kinetically limited in the contaminated layer with a small fraction of labile U as deduced from laboratory desorption-based studies and in situ studies performed by DET (Diffusive Equilibration in Thin films)/DGT (Diffusive Gradients in Thin films) passive sampler data monitored over time. The smart-K_d approach, combined with a comprehensive system characterization, identified this labile fraction as U(VI) primarily adsorbed on 2:1 clay minerals, which is in line with X-ray Absorption Spectroscopy (XAS) data. The inert fraction was found to correspond to U minerals and adsorbed U(IV) and U(VI) species exhibiting desorption hysteresis. Combining laboratory and field studies, this multiscale approach allows to connect molecular processes to operational K_d(labile) parameters.

A multi-method approach allowed unambiguous determination of aqueous speciation in a uranyl( vi )–malic acid system in the pH range 1.5–5.5, highlighting the predominance of dinuclear complexes even at U( vi ) concentrations as low as 10 µM.

Diatoms are essential bio-indicators for assessing the impact of heavy metals and hazardous materials on aquatic ecosystems. This study seeks to advance our understanding of the interaction between uranium (U) and the freshwater diatom species Achnanthidium saprophilum, employing macroscopic, microscopic, and spectroscopic approaches. Bio-association experiments with hexavalent U (U(VI)) were conducted during various diatom growth phases and revealed time- and concentration-dependent U retention by the diatoms. U bio-association was observed by scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDX), indicating co-localization of U with phosphorus (P). Time-resolved laser-induced fluorescence spectroscopy on U(VI)-associated diatoms suggested the formation of two adsorbed U(VI) species, whose proportions depend on the diatom growth phase. Fourier-transform infrared spectroscopy confirmed the interaction of U(VI) dominated by carboxyl groups on diatoms, while the contribution of silanol groups from the diatom frustule appeared insignificant. U bio-association experiments revealed also U incorporation into diatom cells, confirmed by transmission electron microscopy coupled with EDX. Co-localization of U with P within the vacuole was evident, suggesting co-precipitation of various metals, including U, in form of phosphates. The results of this study highlight not only the adsorption but also the internalization of U by diatoms, which influences the fate of U in aquatic ecosystems and affects its mobility and bioavailability. These findings are highly relevant for the further development of radioecological models.

The extensive use of lanthanides in science, industry and high-technology products is accompanied by an anthropogenic input of rare earth elements into the environment. Knowledge of a metal's environmental fate is essential for reasonable risk assessment and remediation approaches. In the present study, Eu(III) was representatively used as a luminescent probe to study the chemical environment and to elucidate the molecular interactions of lanthanides with a suspension cell culture of Nicotiana tabacum BY-2. Biochemical methods were combined with luminescence spectroscopy, two-dimensional microspectroscopic mappings, and data deconvolution methods to resolve the bioassociation behavior and spatial distribution of Eu(III) in plant cells. BY-2 cells were found to gradually take up the metal after exposure to 100 μM Eu(III) without significant loss of viability. Time-resolved luminescence measurements were used to specify the occurrence of Eu(III) species as a function of time, revealing the transformation of an initial Eu(III) species into another after 24 h exposure. Chemical microscopy and subsequent iterative factor analysis reveal the presence of four distinct Eu(III) species located at different cellular compartments, e.g., the cell nucleus, nucleolus and cell walls, which could be assigned to intracellular binding motifs. In addition, a special type of bioaccumulation occurs through the formation of a Eu(III)-containing oxalate biomineral, which is already formed within the first 24 hours after metal exposure. Oxalate crystals were also obtained in analogous experiments with Gd and Sm. These results indicate that tobacco BY-2 cells induce the precipitation of metal oxalate biominerals for detoxification of lanthanides, although they also bind to other cellular ligands at the same time.

Studying the toxicity of chemical compounds using isothermal microcalorimetry (IMC), which monitors the metabolic heat from living microorganisms, is a rapidly expanding field. The unprecedented sensitivity of IMC is particularly attractive for studies at low levels of stressors, where lethality-based data are inadequate. We have revealed via IMC the effect of low dose rates from radioactive β⁻-decay on bacterial metabolism. The low dose rate regime (−1) is typical of radioactively contaminated environmental sites, where chemical toxicity and radioactivity-mediated effects coexist without a predominance or specific characteristic of either of them. We found that IMC allows distinguishing the two sources of metabolic interference on the basis of “isotope-editing” and advanced thermogram analyses. The stable and radioactive europium isotopes ¹⁵³Eu and ¹⁵²Eu, respectively, were employed in monitoring Lactococcus lactis cultures via IMC. β⁻-emission (electrons) was found to increase initial culture growth by increased nutrient uptake efficiency, which compensates for a reduced maximal cell division rate. Direct adsorption of the radionuclide to the biomass, revealed by mass spectrometry, is critical for both the initial stress response and the “dilution” of radioactivity-mediated damage at later culture stages, which are dominated by the chemical toxicity of Eu.