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In nuclear waste repositories, citric acid may be present due to microbial activity or due to degradation of organic material in the waste. As citrate is able to complex a multitude of lanthanide and actinide ions as readily water soluble complexes and thus increase their mobility, additional investigations are necessary to understand whether the mobility of the radionuclides is affected in case of a water ingress into the repository. Because of the repository’s concrete infrastructure, high-pH conditions may form due to leaching. For low-pH systems, interaction of U(VI) with citrate has been studied extensively[1], however complexation data at higher pH is scarce. This study aims to understand the interactions of U(VI) and citrate in alkaline media. Interactions with the geotechnical barrier, in the form of bentonite (potential backfill material) are also investigated. This study utilizes nuclear magnetic resonance (NMR) spectroscopy, UV-Vis spectroscopy, and time-resolved laser-induced fluorescence spectroscopy (TRLFS) to obtain information about the aqueous U(VI) citrate complexes as well as U(VI) retention on Ca-bentonite. NMR spectroscopy allows for gathering of structural information regarding the ligand. Complementary, TRLFS can show structural information about the complex from the metal ion’s perspective. Together with UV-Vis data, these give insight on the complexes’ structures. Complexation experiments have been conducted in the pH range 9.0 - 12.4. TRLFS as well as NMR show three distinct species: presumably two trinuclear species of different U:Cit ratio, and a mononuclear uranyl hydroxo citrate complex species. The trinuclear complexes decrease in concentration with increasing pH, where the monomeric complex becomes dominant. For pH > 11.5 and citrate concentration and/or Cit:U ratio sufficiently low (≤ 10 mM) the monomeric citrate complex begins to be displaced by citrate-free uranyl hydroxo species (likely UO2(OH)3− and UO2

Radionuclides (RNs) that are released in the environment for instance from contaminated sites or due to accident scenarios, can migrate in groundwater to the surface soil where they can interact with indigenous microorganisms and plants, entering the food chain and posing a health risk to humans. An accurate modeling of the RN uptake by plants requires an understanding of the processes involved in RN accumulation, including the influence of soil microorganisms. RNs as well as root exudates can affect the soil microbial community, causing changes in its composition and activity [1, 2]. In addition, exudates of both plants and microorganisms can modify the RN speciation, thus influencing their mobility and bioavailability [3, 4]. In the present work, we study the impact of uranium (U) and malic acid as representative of root exudates on the microbial community in a reference soil. Furthermore, selected microorganisms are isolated from the soil, cultivated, and identified to study their interaction behavior with U. The aim is to improve the knowledge about the interaction of RNs with soil microorganisms and root exudates on a molecular level and to assess the impact of these processes on the bioavailability of RNs. This contributes to the improvement of radioecological models for the assessment of the RN transport and transfer in the environment up to the food chain. The microbial community in a reference soil (Refesol 01-A, Fraunhofer IME) and its changes in the presence of U, malic acid or both were characterized by 16S rRNA gene analyses. The result of this analysis from a control soil and U-treated soil (50 µM U(VI)) after an exposure time of 0 and 28 days showed a high diverse microbial community in the soil. The most abundant phyla were Actinobacteria, Firmicutes, Proteobacteria, Chloroflexi, and Planctomycetota constituting more than 70% of the total relative abundance. Although the populations from control and U exposed soil were similar, some slight difference

Technetium (Tc) is an element originating mostly from the fission of ²³⁵U and ²³⁹Pu with a yield of 6%.¹ Therefore, ⁹⁹Tc is mainly found in high-level radioactive waste, e.g. from nuclear power or reprocessing plants.² The waste disposal is the subject of numerous studies due to the long half-life of many radionuclides (e.g. ⁹⁹Tc: 2.1 · 10⁵ years)¹ and their high radiotoxicity. One of the most widely accepted strategies is the deep geological underground repository. This approach relies on a multi-barrier system designed to minimize the risk of a worst-case scenario, where water intrusion could lead to the corrosion of the waste canister and the subsequent release of radionuclides. For the long-term safety, including the construction of effective barriers, it is essential to study the interaction of radionuclides with the various minerals present in the repository at a fundamental level. Tc poses a particular challenge due to its complex redox chemistry high mobility in its oxidized form TcO₄¯, under oxidising conditions. However, Tc migration decreases significantly when Tc(VII) is reduced to Tc(IV), as it then forms precipitates or becomes immobilized by mineral surfaces such as Fe(II) minerals.³ Vivianite (Fe₃(PO₄)₂ · 8 H₂O) is a naturally occurring Fe(II) mineral under reducing conditions⁵ and can be formed by microorganisms.⁶ Phosphate phases are already being considered as an immobilisation matrix for other radionuclides relevant in deep geological repositories (e.g. ²³⁵U, ²³⁷Np, ²³⁹Pu, ²⁴³Am).⁷ ⁸ This study investigates the retention of Tc by synthetic vivianite particles as a function of pH, Tc concentration and ionic strength on a macroscopic and molecular scale. In addition, Tc(IV) reoxidation experiments were performed.⁴ The synthesis of vivianite was carried out by precipitation from a solution mixture of an iron(II) sulphate and ammonium hydrogen phosphate, as described by Roldán et al..⁹ The product was characterised by Raman microscopy, Mössbauer spec

Unser Ziel ist es, ein molekulares Prozessverständnis für die Interaktion zwischen Ln/An und Pflanzen zu gewinnen: von der initialen Exposition über die Aufnahme und Speziation in unterschiedlichen Teilen des Wurzelgewebes, der Translokation über Pflanzensäfte bis hin zur Ablagerung in Spross und Blättern.

Clay rock is considered a suitable host rock for the long-term storage of high-level radioactive waste, with bentonite used as backfill material. In the event of a worst-case scenario where water enters the repository, naturally occurring microorganisms might interact with the radionuclides, potentially altering their chemical speciation or inducing redox reactions. Among various sulfate-reducing bacteria, Desulfosporosinus species are significant members of the microbial communities in both clay rock and bentonite. Desulfosporosinus hippei DSM 8344T, closely related to a bacterium isolated from bentonite, was selected for a detailed investigation into uranium(VI) interactions with naturally occurring microorganisms from deep geological layers. Time-dependent experiments in artificial Opalinus Clay pore water (100 µM uranium(VI), pH 5.5) demonstrated a substantial removal of uranium from the supernatants within a short period. UV/Vis studies of the dissolved cell pellets provided clear evidence of partial reduction of uranium(VI) to uranium(IV). These findings suggest a combined association-reduction process as the mechanism of interaction. TEM images showed uranium aggregates forming on the cell surface. Moreover, cells released membrane vesicles, possibly as a defense mechanism against cell encrustation. Additionally, HERFD-XANES measurements confirmed the reduction of uranium(VI) and revealed the presence of uranium(V) in the cell pellets, marking the first evidence of the involvement of uranium(V) in uranium(VI) reduction by sulfate-reducing microorganisms. Subsequent EXAFS measurements identified different cell-related uranium species. This study enhances our understanding of the complexity of redox processes in the environment and contributes to the safety concept for nuclear repositories in clay rock. Moreover, it presents new insights into the uranium(VI) reduction mechanisms of sulfate-reducing bacteria.

When radionuclides (RN) enter the food chain and are ingested by humans, they pose a potential health risk due to their radio- and chemotoxicity. In order to accurately assess the health risk af-ter oral ingestion and to apply effective decontamination methods, it is essential to understand the processes of (bio)chemistry and speciation of RN at the molecular level. To minimize the health risk, chelating agents, which are usually strong complexants, are used after the accidental incorporation of RN for decorporation, that means to increase RN excretion. To date, however, only the aminopolycarboxylate diethylenetriaminepenta-acetic acid (DTPA) is approved and used commercially, although it is only effective for trivalent actinides. Alternative potential decorporation agents such as the hydroxypyridinone 3,4,3-(LI-1,2-HOPO) (HOPO) are being developed [1], but are not yet ready for commercial use. We experimentally investigated the speciation of trivalent lanthanides and actinides (Ln(III)/An(III)) as well as hexavalent uranium (U(VI)) in model fluids of the digestive tract in the absence and presence of chelating agents. The artificial biofluids saliva, gastric juice, pan-creatic juice, and bile were synthesized according to the international Unified Bioaccessibility Method (UBM) of the Bioaccessibility Research Group of Europe (BARGE) [2]. As chelating agents we used DTPA and alternative aminocarboxylates like ethylene diamine tetraacetic acid (EDTA) or ethyleneglycol tetraacetic acid (EGTA) [3], as well as some promising new chelators like HOPO [1] and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), which was formerly used as a pharmaceutical. The solutions were spiked with Eu(III) as a non-radioactive analogue for An(III) as well as with the actinides Cm(III) and U(VI). Samples were analyzed multi-spectroscopically, mainly using time-resolved laser-induced luminescence spectroscopy (TRLFS) combined with parallel factor analysis (PARAFAC) as well as nuclear magnet

Isostructural trivalent lanthanide and actinide amidinates bearing the N,N'-bis(isopropyl)benzamidinate (iPr2BA) ligand [LnIII/AnIII(iPr2BA)3] (Ln = La, Nd, Sm, Eu, Yb, Lu; An = U, Np) have been synthesized and characterized in both solid and solu-tion states. All compounds were examined in the solid state utilizing single crystal X-ray diffraction (SC-XRD), revealing a nota-ble deviation in the actinide series with shortened bond lengths compared to the trend in the lanthanide series, suggesting a non-ionic contribution to the actinide–ligand bonding. Quantum-chemical bonding analysis further elucidated the nature of these inter-actions, highlighting increased covalency within the actinide series, as evidenced by higher delocalization indices and greater 5f orbital occupation, except for Th(III) and Pa(III), which demonstrated substantial 6d orbital occupancies. An in-depth paramag-netic NMR study in solution also shed light on the covalent character of actinide–ligand bonding, with the separation of pseudo-contact (PCS) and contact shift (FCS) contributions employing the BLEANEY and REILLEY method. This analysis unveiled signifi-cant contact contributions in the actinide complexes, indicating enhanced covalency in actinide–ligand bonding. To corroborate these observations, an accurate PCS calculation method based on the KUPROV equation, incorporating both the distribution of electronic spin density and magnetic susceptibility obtained from CASSCF calculations, was applied and compared with experi-mental values

A series of isostructural early actinide AnIV complexes was synthesized in order to investigate the influence of a conjugated framework in the ligand backbone on An bonding. Therefore, the AnIV complexes [An(pyrophen)2] (An = Th, U, Np, and Pu) with the pure N donor ligand bis(2-pyrrolecarbonylaldehyde)-o-phenylenediamine referred to as pyrophen, were synthesized and characterized. Solid state analysis via single-crystal X-ray diffraction (SC-XRD) reveals two sets of ligands binding in an almost orthogonal arrangement to the actinide center. For the larger actinides Th and U, the coordination sphere allows for additional coordination by a solvent molecule. Nuclear magnetic resonance spectroscopy (NMR) studies show the presence of highly symmetrical complexes in solution in good agreement with the solvent-free solid structures. While SC-XRD suggests mainly ionic binding, an analysis of paramagnetic NMR contributions and quantum chemical bond analysis hint towards significant covalency in the U, Np, and Pu compounds. This series of An complexes allowed for a thorough structural and theoretical comparison of a conjugated system to a closely related N-donor ligand (pyren)[1], as well as to the mixed N,O Schiff base ligands salophen (conjugated) and salen (non-conjugated).

When radionuclides (RN) enter the food chain and are ingested by humans, they pose a potential health risk due to their radio- and chemotoxicity. To minimize the health risk, decorporation agents (DA), which are usually strong complexants, are used after the accidental incorporation of RN to increase their excretion. In order to accurately assess the health risk after oral ingestion and to apply effective decontamination methods, it is essential to understand the processes of (bio)chemistry and speciation of RN at the molecular and cellular level. Within the joint research project RADEKOR: “Speciation and transfer of radionuclides in the human organism especially taking into account decorporation agents”, molecular speciation studies of RN in artificial biofluids of the digestive system of humans and cytotoxicity studies with respective human and rat renal cell lines in vitro both in the absence and presence of DA were performed. As DA we investigated i) aminopolycarboxylate diethylenetriaminepentaacetic acid DTPA as the only approved and commercially used DA and ii) some promising new chelators like the hydroxypyridinone 3,4,3-(LI-1,2-HOPO) (HOPO) and 1-hydroxy-ethylidene-1,1-diphosphonic acid (HEDP), which was formerly used as a pharmaceutical. First, the complex formation of the non-radioactive An(III) analogue Eu(III) with HEDP in aqueous solution and cell culture medium was studied. Second, Eu(III) and Am(III) cytotoxicity onto kidney cells was investigated in absence and presence of DTPA and HOPO. Finally, the molecular speciation of Eu(III) and Am/Cm(III) with and w/o DTPA and HOPO was studied in both cell culture medium and exposed renal cells. The results of this work contribute to a better understanding of the effect of DA after RN incorporation at the molecular level and support making them more effective in the future.

The chemistry of actinides (An) is an ongoing subject of current research, particularly with regard to their environmental behaviour and nuclear waste disposal. From a fundamental point of view, the properties of these 5f elements differ significantly from their lanthanide homologues, where the 4f electrons are strongly shielded. Especially for the early actinides Th – Pu, a variety of oxidation states is accessible, ranging from +I to +VII. Furthermore, the 5f electrons are involved in chemical bonding. This results in characteristic magnetic and spectroscopic properties. Yet, exploration of the coordination chemistry of the actinides significantly lags behind that of transition metals and lanthanides. As such, a fundamental understanding of the binding properties in actinide compounds is still leaving many open questions, as can be illustrated by the limited number of structurally characterized An compounds. Furthermore, previous studies have mainly focused on Th and U and hard donor ligands according to the HSAB principle, such as alkoxides or amines. In order to expand knowledge of the electronic and magnetic properties of the 5f elements, systematic studies of An complexes with different donor atoms on a fundamental level are necessary. Previous studies have shown that with sulphur as a soft donor, higher covalent contributions can be found in the U-ligand bonds. For the systematic investigation of the An–S binding properties, we synthesized a series of AnIV complexes with the bidentate ligand pyridine-2-thiolate (PyS‾). Using the complex [U(PyS)₄(THF)] presented by Neu et al. as a blueprint, we established two synthetic routes for the complexation of tetravalent An with PyS‾: a salt metathesis reaction with KPyS and a reaction with PyS–SiMe₃. The obtained compounds of the types [An(PyS)₄(THF)] (An: Th, U, Np, Pu) and K[An(PyS)₅] (An: Th, U) were comprehensively characterized in solution and in solid phase, by single-crystal X-ray diffraction, NMR spectroscopy

Lanthanides (Ln) are essential for various industrial and scientific applications and serve as inactive analogs for trivalent actinides (An) such as curium and americium. Understanding the bioaccumulation behavior of non-essential metals like Ln and An in plants is crucial for food safety and the development of effective phytoremediation strategies. Our aim is to gain a mechanistic understanding of the interaction between Ln/An and plants. Using laser spectroscopy and chemical microscopy in combination with factor analysis, liquid chromatography, thermodynamic modelling, autoradiography, biochemical methods and inductively coupled plasma mass spectrometry, we followed the path of Eu(III) through sand oat (Avena strigosa). We determined Eu(III) concentration and speciation change in the hydroponic medium due to root exudate release. We identified apoplastic (71%) and symplastic (10%) fractions of Eu(III) in the roots and visualized the metal’s microscopic species distribution in root tissue and cells. From a macroscopic point of view, we demonstrated that over 99.35% of bioassociated Eu(III) accumulated in the root through a multistage bioassociation process. The translocation into green plant parts is thereby realized by xylem sap via a Eu(III) malate or citrate complex. Furthermore, we visualized the distribution of the radionuclide in roots and leaves in experiments with Eu-152.

Lanthanides (Ln) are crucial in various industrial and scientific applications. Their intense exploitation opens the door to a multitude of possible entry paths into the environment. Plants have the ability to take up and accumulate non-essential metals, so it is vital to understand the fate of Ln in the biosphere and, in particular, their bioaccumulation behavior. This study aimed to elucidate the process of interaction between Ln and plants, from the initial exposure and cellular uptake, through internal distribution, to the translocation into and deposition in aboveground parts.

When radionuclides (RN) enter the food chain and are ingested by humans, they can present significant health risks due to their radiotoxic and chemotoxic properties. To mitigate these risks, decorporation agents (DA), which are typically strong chelators, are employed after accidental RN exposure to facilitate their removal from the body. A thorough understanding of the (bio)chemical behavior and speciation of RN at both the molecular and cellular levels is essential for assessing health impacts and applying effective decontamination techniques. In the joint BMBF project RADEKOR, studies were conducted to investigate the molecular speciation of RN in artificial digestive biofluids, alongside with in vitro cytotoxicity assessments using human and rat kidney cell lines, with and without DA. As DA we investigated i) aminopolycarboxylate diethylenetriaminepentaacetic acid (DTPA) as the only approved and commercially used DA, ii) alternative aminocarboxylates like ethylenediaminetetraacetic acid (EDTA) or ethyleneglycoltetraacetic acid (EGTA), and iii) some promising new chelators like the hydroxypyridinone 3,4,3-(LI-1,2-HOPO) (HOPO) and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), which was formerly used as a pharmaceutical. The complex formation of Eu(III) as a non-radioactive analogue for An(III) with EGTA was studied along with its molecular speciation in simulated body fluids in presence and absence of DTPA, EGTA, and HOPO. Furthermore, the molecular speciation of U(VI) in simulated body fluids and cell culture medium as well as its cytotoxicity onto kidney cells was investigated in absence and presence of DTPA, HEDP, and HOPO. The results of this work contribute to a better understanding of the effect of DA after RN incorporation at the molecular level and support making them more effective in the future.

Long-term safety analyses of potential repositories for high-level radioactive waste require the consideration of accident scenarios in which groundwater enters the repository and radionuclides (RN) are released into the groundwater. By this RN contamination of the soil occurs, followed by plant uptake and thus entrance to the human food chain. For humans, RN pose a risk to health (Hall et al., 2021) and for plants, RN are non-essential elements, which affect physiology, development and metabolism (Serre et al., 2019). To protect themselves from stress, plants release root exudates into the rhizosphere to model their environment in the favour of the plant. Additionally, root exudates are important for example to influence bacterial communities, to facilitate nutrient uptake, however root exudates also influence the bioavailability of RN by changing their speciation (Chen et al., 2021). A long list of chemical components, including organic acids, phenolic compounds like flavonoids, DNA, RNA, proteins, amino acids, and many more, can be excreted into the rhizosphere by plants (Lui et al,. 2023). In this study the exposure of Phaseolus vulgaris, a widely used crop plant, with Eu(III) as analogue for trivalent actinides, e.g. Am(III) and Cm(III), is studied in hydroponic culture. The accumulation and translocation of Eu(III) is investigated as a function of time and Eu(III) concentration. In addition, the Eu(III) speciation in hydroponic solution is analyzed by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and chemical microscopy. The RN speciation depends on various parameters, e.g. pH, redox potential and the presence of chelating agents, which can be released by plants as root exudates and may influence the bioavailability of RN (Chen et al., 2021). To characterize their effect on the Eu(III) speciation, root exudates of P. vulgaris plants are isolated from the solutions and characterized by high performance liquid chromatography (HPLC). The bioassoci

Uranium (U) is of radioecological relevance owing to its natural occurrence, but also with regard to legacies of former U mining activities and to the long-term safety assessment for high-level radioactive waste repositories. It is a radiotoxic and chemotoxic actinide with a greater risk of chemical toxicity. In biogeosphere context, the two forms of importance are tetravalent U(IV) and hexavalent U(VI). U(IV) prevails in anaerobic environments, is hardly water soluble and hence less mobile and less toxic. Conversely, U(VI) is the most stable form of U, in aqueous media forming the uranyl(VI) ion, UO22+, being soluble and thus highly mobile and, eventually, much better bioavailable. Malic acid (MA), along with citric and succinic acid, is one of the most abundant exudates of plants. It plays several critical roles in plant metabolism and homeostasis, including respiration and energy generation, plant nutrition, nitrogen fixation, metal tolerance, and serving as a signaling molecule for beneficial microbes [1, 2]. MA is a hydroxydicarboxylic acid, forming two stereoisomers, D- and L-isomer, the latter of which naturally occurring in biological systems [3]. The pKa values for the carboxyl groups are 3.4 and 5.1, while the pKa value for the hydroxyl group is approximately 14.5 [4-6]. MA is a notable chelating agent for a wide variety of metal ions [7]. Therefore, interactions between actinides, such as U, and MA are expected when they coexist in the soil. The complexation of uranyl(VI) with MA has been studied and characterized, revealing that the most common uranyl(VI)-MA complex exhibits a dinuclear structure [8]. The complexation of U(VI) with MA significantly impacts U solubility in soil, its potential uptake into plants and interaction with microorganisms. For the prediction of the U(VI)–MA complexation, reliable thermodynamic data based on a molecular process understanding are necessary. These data will contribute to a reliable assessment of the transport and tra

IR spectra NMR spectra QCC results SC-XRD results PCS cone calculations

The transport and transfer of radionuclides (RNs) in the environment is a safety concern both in the remediation of contaminated sites as well as in the safety assessment of nuclear waste repositories. For example, RNs can reach the soil via the groundwater path, where they are taken up by plants and thus enter the food chain and pose a health risk for humans. RNs are non-essential elements for plants, but change their physiology, development and metabolism. Plants release root exudates, including organic acids, phenolic compounds like flavonoids, DNA, RNA, proteins, and amino acids, into the rhizosphere to adapt the environment. Root exudates are able to impact the bioavailability of RNs. The aim of this study is to gain a better understanding of the bioassociation of Eu(III), as analogue for trivalent actinides, e.g. Am(III) and Cm(III), with the widely used crop plant Phaseolus vulgaris (common bean). In addition to the accumulation and translocation of Eu(III) in the plants, the speciation of Eu(III) in hydroponic solution is studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS). High-performance liquid chromatography (HPLC) is used to detect root exudates and their variation induced by the presence of Eu(III) in the medium. In P. vulgaris plants, the bioassociation of Eu(III) depends on time and Eu(III) concentration available to the plant. After 72 h of exposure to 20 or 200 µM Eu(III), bean plants show a strong Eu(III) bioassociation. Eu(III) enters the roots, however less than 1% of Eu(III) present in the root is transported into the leaves. TRLFS spectra indicate the time dependent change of the Eu(III) speciation in solution. At least two Eu(III) species are formed in hydroponic solution. HPLC results display, that root exudates are released into the hydroponic culture by P. vulgaris. Together with previous publications on Brassica napus plants (Jessat et al., 2023), this study contributes to a better understanding of the interaction of

The safety assessment of repositories for high-level radioactive waste, mostly spent nuclear fuel, requires a detailed understanding of the interactions of radionuclides with corroded phases in the near-field of a given repository. Zirconia (ZrO2), the main corrosion product of the zircaloy cladding material of nuclear fuel rods, constitutes a first barrier against the release of radionuclides into the environment. A multimethod approach was pursued to gain a thorough understanding of the Np(V) sorption processes at the water−zirconia interface. For the macroscopic description, pH-dependent batch sorption experiments (varying ionic strength, Np(V) concentration, and solid-to-liquid ratio) as well as sorption isotherms experiments at pH 4.5 and 6.0 were performed. The uptake of Np(V) was pH-dependent, with an increased sorption starting from pH 3 and being at a maximum at pH 6 and above. The Np(V) sorption was independent of ionic strength, suggesting the predominance of Np(V) inner-sphere complexes on the zirconia surface. This was supported by electrokinetic measurements in the absence and presence of neptunium, where Np(V) caused a shift to higher pH values of the isoelectric point of the neat ZrO2. The Np(V) sorption edge was shifted towards lower pH values with increasing solid-to-liquid ratio, indicating the presence of different kinds of sorption sites (strong and weak), which was also corroborated by the shape of the sorption isotherms. Molecular level information was derived from in situ attenuated total reflection Fourier-transform infrared spectroscopy and extended X-ray absorption fine structure spectroscopy (EXAFS), which confirmed the presence of Np(V) inner-sphere complexes. EXAFS experiments revealed the formation of a bidentate inner-sphere surface complex in the weak sorption site regime. The derived information at the macroscopic and molecular levels was used to parametrize a charge distribution multi-site complexation (CD-MUS

The IRE is one of the ten institutes of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Our research ac-tivities are mainly integrated into the program “Nuclear Waste Management, Safety and Radiation Research (NUSAFE)” of the Helmholtz Association (HGF) and fo-cus on the topics “Safety of Nuclear Waste Disposal” and “Safety Research for Nuclear Reactors”. The program NUSAFE, and therefore all work which is done at IRE, belong to the research field “Energy” of the HGF.

Diatoms and bacteria play a vital role in investigating the ecological effects of heavy metals in the environment. Despite separate studies on metal interactions with diatoms and bacteria, there is a significant gap in research regarding heavy metal interactions within a diatom-bacterium system, which closely mirrors natural conditions. In this study, we aim to address this gap by examining the interaction of uranium(VI) (U(VI)) with Achnanthidium saprophilum freshwater diatoms and their natural bacterial community, primarily consisting of four successfully isolated bacterial strains (Acidovorax facilis, Agrobacterium fabrum, Brevundimonas mediterranea, and Pseudomonas peli) from the diatom culture. Uranium (U) bio-association experiments were performed both on the xenic A. saprophilum culture and on the four bacterial isolates. Scanning electron microscopy and transmission electron microscopy coupled with spectrum imaging analysis based on energy-dispersive X-ray spectroscopy revealed a clear co-localization of U and phosphorus both on the surface and inside A. saprophilum diatoms and the associated bacterial cells. Time-resolved laser-induced fluorescence spectroscopy with parallel factor analysis identified similar U(VI) binding motifs both on A. saprophilum diatoms and the four bacterial isolates. This is the first work providing valuable microscopic and spectroscopic data on U localization and speciation within a diatom-bacterium system, demonstrating the contribution of the co-occurring bacteria to the overall interaction with U, a factor non-negligible for future modeling and assessment of radiological effects on living microorganisms.

High-level radioactive waste needs to be stored for long-term and safe in a deep geological repository (DGR) by using a multi-barrier system. Different materials with desirable properties are combined in this system to prevent an early release of radionuclides into the biosphere. For this reason, it is necessary to select suitable barrier materials, which ideally combine long-term stability and integrity. In this study, we combined different container materials (copper and cast iron) and pore waters (Opalinus Clay pore water and cap rock solution) with a Bavarian bentonite in static batch experiments to investigate the microbial influenced corrosion. The increasing concentration of iron and copper in solution as well as detected corrosion products on the metal surface are indicative for an occurring anaerobic corrosion of the respective metals during an incubation of 400 days at 37°C. However, although the intrinsic microbial bentonite community was stimulated with either lactate or H2, an acceleration of cast iron- and copper corrosion did not occur. Furthermore, neither corrosive bacteria nor conventional bacterial corrosion products, such as metal-sulfides, were detected in any of the analyzed samples. The analyses of geochemical parameters (e.g. ferrous iron-, iron-, copper- and potassium concentration as well as redox potential) showed significant changes in some cast iron- and copper-containing setups, but these changes do not correlate with the microbial community structure in respective microcosms, as confirmed by statistical analyses. Thus, we assume that the analyzed Bavarian bentonite (type B25) shows no significant contribution to cast iron and copper corrosion under the applied conditions after long incubation of 400 days. From this perspective, bentonite B25 could be a suitable candidate as geotechnical barrier in future DGRs.

Dinuclear metal complexes present a well-known substance class in the chemistry of the transition metals with a wide variety of applications. However, for the 5f elements, the actinides, such complexes are still rare, with a focus on uranium complexes for the activation of small molecules. Due to their interesting electronic properties, however, the actinides differ greatly from other metals in the periodic table, and the possibility of having two of these metal ions in close proximity in a well-defined molecular framework might provide fascinating insights into the fundamental properties of these elements. The rigid, ambidentate phthalimidinyl anion is a promising ligand for the synthesis of bimetallic complexes The synthesis of such bimetallic actinide complexes can be achieved by reacting the respective actinide tetrachlorides, UCl₄, [ThCl₄(DME)₂], [NpCl₄(DME)₂], and [PuCl₄(DME)₂] (DME = 1,2-dimethoxyethane), with the antimony compound phenyldi(phthalimidinyl)antimony. The antimony reagent bears two advantages over common salt metatheses reactions. 1) The Sb–N bond is quite weak resulting in an easy transfer of the phthalimidinyl ligand to the actinide, and 2) antimony is a highly chlorophilic element that can abstract the chloride ions from the actinide salts to form soluble antimony chloride compounds such as PhSbCl₂. The synthesis was carried out in the coordinating solvent pyridine which leads to the formation of well-defined dinuclear species by saturating the coordination sphere of the metals and prevents the formation of polymeric species. The compounds crystallize readily from the reaction solution in pyridine after standing for a few days in a nitrogen-filled glovebox. This easy synthetic route proved to be effective for a series of tetravalent actinides, enabling the preparation of an isostructural series ranging from thorium to plutonium. The comparably close proximity (i.e. ~4.65 Å) of the two paramagnetic metal ions (in case of U, Np and Pu) lends it

Lanthanides and actinides are emerging contaminants, but little is known about their uptake and distribution by plants and their interactions in the rhizosphere. To better understand the fate of these metals in plants, we assessed the bioassociation of 2, 20 and 200 µM Eu(III) by five hydroponically grown crops endemic to Europe. The metal’s concentration and its speciation was monitored by inductively coupled plasma mass spectrometry and laser spectroscopy, whereas root exudation was investigated by chromatographic methods. It has been shown, that Eu(III) bioassociation is a two-stage process, involving rapid biosorption followed by accumulation in root tissue and distribution to the stem and leaves. Within 96 h of exposure time, the plant induces a change of Eu(III) speciation in the liquid medium, from a predominant Eu(III) aquo species, as calculated by thermodynamic modelling, to a species with longer luminescence lifetime. Root exudates such as citric, malic, and fumaric acid were identified in the cultivation medium and affect Eu(III) speciation in solution, as was shown by a change in the thermodynamic model. These results contribute to a comprehensive understanding of the fate of lanthanides in the biosphere and provide a basis for further investigations with the chemical analogues Cm(III) and Am(III).

As the number of decommissioning projects increases worldwide, meticulous disposal strategies are needed for the growing quantity of potentially radioactive waste. Among these waste materials, structural components represent millions of tons of rubbles, of which over 90% is non-radioactive. The concrete biological shield surrounding the reactor pressure vessel absorbs neutrons during reactor operation. It is the structural element most prone to activation and classification as radioactive waste, presenting activity above the clearance levels. To reduce the time-consuming and costly experimental analyses for waste classification, numerical simulations are used to develop a reactor-specific model, predicting the activity distribution within the concrete structure. A precise model validation by a comprehensive radionalytical analysis is necessary. Further valuable insights are provided by a thorough structural characterization of the radionuclides within the cement structure. Combined analysis and calculation campaigns were conducted on the unit 2 of the Greifswald nuclear power plant in Germany. Samples were taken from the biological shield in two positions of highest expected activity. A depth activation profile was constructed with gamma-spectrometry measurements. In parallel, calculations were run with a Monte-Carlo N-Particle code and the model was refined with precise geometry and composition information. For decommissioning, the relevant radionuclides within the biological shield include 60Co, 152Eu and 154Eu, exhibiting half-lives ranging from 5 to 20 years. 152Eu was found to be the limiting radionuclide for dismantling operations, showing activities above the German clearance level up to 35 cm of depth in the biological shield. The computational model demonstrated excellent agreement with the experimental measurements and accurate enough so that the activity distribution in the rest of the biological shield could be reliably predicted. Additionally, we invest

If radionuclides (RN) enter the food chain and are ingested by humans, they pose a potential health risk due to their radio- and chemotoxicity. In order to accurately assess the health risk after oral ingestion of RN in food and beverages and to apply effective decontamination methods, it is essential to understand the processes of (bio)chemistry and speciation of RN at the molecular level. To minimize the health risk, decorporation agents, which are usually strong complexones, are used after the accidental incorporation of RN in order to increase excretion. To date, however, only the aminopolycarboxylate diethylenetriaminepentaacetic acid (DTPA) has been used commercially, although it is only effective for trivalent actinides. Alternative potential decorporation agents such as the hydroxypyridinone 3,4,3-LI-HOPO (HOPO) are being developed,1 but they are not yet ready for commercial use. Our group experimentally investigated the speciation of trivalent lanthanides and actinides (Ln(III)/An(III)) as well as uranium (U(VI)) in model fluids of the digestive tract in the absence and presence of decorporation agents. This work is part of the German joint project "Speciation and transfer of radionuclides in the human organism with special consideration of decorporation agents (RADEKOR)". The artificial biofluids saliva, gastric juice, pancreatic juice and bile were synthesized according to the international Unified Bioaccessibility Method (UBM) of the Bioaccessibility Research Group of Europe (BARGE).2 The solutions were spiked with the lanthanide Eu(III) as a non-radioactive analogue for trivalent actinides as well as the actinides Cm(III) and U(VI). Samples were analysed spectroscopically, mainly using time-resolved laser-induced luminescence spectroscopy (TRLFS). By analysing the spectra with parallel factor analysis (PARAFAC) and comparing them with the luminescence spectra of the individual components of the biofluids, we were able to determine the speciation of the

Structural and QC data for all compounds described in the manuscript "Structure, covalency, and paramagnetism of homoleptic actinide and lanthanide amidinate complex"

Technetium (Tc) is an element originating mostly from the fission of ²³⁵U and ²³⁹Pu with a yield of 6%.¹ Therefore, ⁹⁹Tc is mainly found in high-level radioactive waste, e.g. from nuclear power or reprocessing plants.² The waste disposal is the subject of numerous studies due to the long half-life of many radionuclides (e.g. ⁹⁹Tc: 2.1 · 10⁵ years)¹ and their high radiotoxicity. One of the most accepted concepts is the deep geological underground repository. A multiple barrier system is planned to reduce the risk of a worst-case scenario, when water ingress could induce the corrosion of the canister containing the waste and, thus, radionuclide release. For the long-term safety, including the construction of effective barriers, the interaction of the radionuclides with different minerals present in the repository needs to be studied at a fundamental level. Tc shows a complex redox chemistry and is considered very mobile compared to cationic radionuclides, due to the presence of the negatively charged TcO₄⁻ under oxidising conditions. However, Tc migration decreases when Tc(VII) is reduced to Tc(IV) since it forms precipitates or is immobilized by mineral surfaces, e.g. with Fe(II) minerals (Fig. 1).³ Vivianite (Fe₃(PO₄)₂ · 8 H₂O) is a naturally occurring Fe(II) mineral under reducing conditions⁵ and can be formed by microorganisms.⁶ Phosphate phases are already being considered as an immobilisation matrix for other radionuclides relevant in deep geological repositories (e.g. ²³⁵U, ²³⁷Np, ²³⁹Pu, ²⁴³Am).⁷ ⁸ This study investigates the retention of Tc by synthetic vivianite particles as a function of pH, Tc concentration and ionic strength on a macroscopic and molecular scale. In addition, Tc(IV) reoxidation experiments were performed.⁴ The synthesis of vivianite was carried out by precipitation from a solution mixture of an iron(II) sulphate and ammonium hydrogen phosphate, as described by Roldán et al..⁹ The product was characterised by Raman microscopy, Mössbauer spec

Our aim is to gain a molecular process understanding of the interaction between Ln and plants: from initial exposure, uptake and speciation in different parts of the root tissue, translocation via plant sap to deposition in shoots and leaves. Therefore, we used hydroponically grown Avena strigosa, a grass cultivated as animal feed in many countries. A. strigosa was exposed to europium, which serves as inactive analog for trivalent actinides (An) such as curium and americium.

Publication of bioassociation, spectroscopic, chromatographic and thermodynamically modelled data obtained in hydroponic plant experiments with Eu(III).

High-energy-resolution fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy was used to investigate the reduction of U(VI) by the sulfate-reducing bacterium Desulfosporosinus hippei DSM 8344T, confirming the partial reduction of U(VI) and the presence of U(V).

Characterizing the physicochemistry and microbial diversity of U mine water is a key prerequisite for understanding the biogeochemical processes occurring in these water mass and for the design of an efficient bioremediation strategy. This study has collected and analysed in reference date measurements water samples from two former U-mines (Schlema-Alberoda and Pöhla, Wismut GmbH) in East Germany. The samples from both mines are pH-circumneutral (7.3 and 6.6) and show reducing conditions (EH: +139 and –91 mV). Interestingly, the U and sulphate concentrations of Schlema-Alberoda mine water (U: 1 mg/L; SO42−: 335 mg/L) are 2 and 3 order of magnitude higher than those of the Pöhla samples (U: 0.01 mg/L; SO42−: 0.5 mg/L), respectively. U, SO42− and Fe seem to shape the differential microbial diversity of the water from both mines. Microbial diversity analysis revealed the distribution of bacteria with U(VI)-reducing capacity and the ability to maintain the stability of reduced U-species (e.g., Desulfurivibrio, Gallionella and Sulfuricurvum). In addition, water from the mines harbour wood-degrading fungal communities (e.g., composed of Cadophora and Acremonium) providing potential electron donors which promote the growth of U-reducing bacteria. For the design of a bioremediation strategy, we conducted a preliminary U-bioreduction experiment to screen for suitable electron donors (glycerol, vanillic acid and gluconic acid). We also observed that high levels of soluble U (initially present as Ca2UO2(CO3)3(aq) and UO2(CO3)34−), Fe and SO42− were removed by 98, 95 and 53%, respectively from the mine water by using glycerol as electron donor. The remaining U concentrations after bioreduction meet regulatory standards for beneficial reuse of U mine water. As a whole, the results reveal the che

Zirconia (ZrO₂), the main corrosion product of the zircaloy cladding material of nuclear fuel rods, might potentially act as the first barrier for radionuclides. Thus, the interactions of radionuclides, such as the long-lived actinide neptunium, with zirconia have to be considered in the safety assessment process of a repository for radioactive waste. The sorption of Np(V) onto zirconia (ZrO₂) was investigated in the absence of carbonate at the macroscopic and molecular scale. For the macroscopic description, pH-dependent batch sorption experiments under varying ionic strength (0.1 and 0.01 mol∙L⁻¹ NaCl), Np(V) concentration (1∙10⁻⁶ or 6∙10⁻⁶ mol∙L⁻¹) and solid-to-liquid ratio (m/V = 0.5 or 4 g∙L⁻¹ ZrO₂) were conducted. Np(V) sorption isotherms at pH 4.5 and 6.0 were additionally obtained at 0.01 mol∙L⁻¹ NaCl. The Np(V) uptake on zirconia strongly depends on pH, with sorption starting from acidic pH and maximum sorption was reached at pH 6 and above. Increasing the m/V ratio caused a significant shift of the sorption edge towards lower pH values. This indicates the presence of different kinds of sorption sites, which was supported by the results of the Np(V) sorption isotherms, where the shape of the isotherm suggested the presence of strong and weak sorption sites. The Np(V) uptake was independent of ionic strength, suggesting the presence of inner-sphere Np(V) surface complexes on zirconia. This was also supported by zeta potential measurements where a shift of the isoelectric point of the pristine zirconia towards higher pH values in the presence of Np(V) was observed. Molecular level investigations by means of spectroscopic techniques, namely in situ attenuated total reflection Fourier transform Infrared Spectroscopy (ATR FT-IR) and extended X-ray absorption fine structure spectroscopy (EXAFS), confirmed the predominant presence of Np(V) inner-sphere complexes on the zirconia surface. EXAFS experiments conducted in the weak sorption site regime revealed the form

Heavy metals pose a potential health risk to humans when they enter the organism. Renal excretion is one of the elimination pathways and, therefore, investigations with kidney cells are of particular interest. In the present study, the effects of Ba(II), Eu(III), and U(VI) on rat and human renal cells were investigated in vitro. A combination of microscopic, biochemical, analytical, and spectroscopic methods was used to assess cell viability, cell death mechanisms, and intracellular metal uptake of exposed cells as well as metal speciation in cell culture medium and inside cells. For Eu(III) and U(VI), cytotoxicity and intracellular uptake are positively correlated and depend on concentration and exposure time. An enhanced apoptosis occurs upon Eu(III) exposure whereas U(VI) exposure leads to enhanced apoptosis and (secondary) necrosis. In contrast to that, Ba(II) exhibits no cytotoxic effect at all and its intracellular uptake is time-independently very low. In general, both cell lines give similar results with rat cells being more sensitive than human cells. The dominant binding motifs of Eu(III) in cell culture medium as well as cell suspensions are (organo-) phosphate groups. Additionally, a protein complex is formed in medium at low Eu(III) concentration. In contrast, U(VI) forms a carbonate complex in cell culture medium as well as each one phosphate and carbonate complex in cell suspensions. Using chemical microscopy, Eu(III) was localized in granular, vesicular compartments near the nucleus and the intracellular Eu(III) species equals the one in cell suspensions. Overall, this study contributes to a better understanding of the interactions of Ba(II), Eu(III), and U(VI) on a cellular and molecular level. Since Ba(II) and Eu(III) serve as inactive analogs of the radioactive Ra(II) and Am(III)/Cm(III), the results of this study are also of importance for the health risk assessment of these radionuclides.

The IRE is one of the ten institutes of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Our research ac-tivities are mainly integrated into the program “Nuclear Waste Management, Safety and Radiation Research (NUSAFE)” of the Helmholtz Association (HGF) and fo-cus on the topics “Safety of Nuclear Waste Disposal” and “Safety Research for Nuclear Reactors”. The program NUSAFE, and therefore all work which is done at IRE, belong to the research field “Energy” of the HGF.

Herein, Eu(III) was representatively used as 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 bioassociation behavior and spatial distribution of Eu(III) in plant cells.