Adapting to new challenges in medical education: a three-step digitization approach for blended learning.

This research work focuses on evaluating the development of our three-step digitization approach, designed to transform traditional lectures into engaging digital learning experiences. Aimed at offering an easy-to-use solution for educators, this approach addresses the pressing challenges of modern educational environments by enhancing accessibility, engagement, and effectiveness of learning through digital means.Quantitative analysis demonstrated a notable increase in knowledge gain for students engaged with the digital format (t(230) = -2.795, p = 0.006) over traditional methods. Additionally, it was observed that the online setting significantly improved concentration levels (t(230) = -5.801, p < .001) and reduced distractions (t(230) = 2.848, p = 0.005). Emotional assessments, based on the Achievement Emotions Questionnaire (AEQ), indicated an elevation in enjoyment (t(230) = -4.717, p < .001) and a reduction in anxiety (t(230) = 9.446, p < .001) within the digital learning environment. A substantial preference for the digital course format was expressed by 61.0% of participants, with 71.4% acknowledging its superior efficiency compared to 14.3% for traditional lectures.Qualitative feedback underscored the digital format's flexibility, comprehensive learning experience, and immediate feedback as key benefits. Nevertheless, nuances such as a preferred understanding in face-to-face interactions and the absence of a social component in digital settings were noted.To conclude, the findings from this study illuminate the significant advantages of the three-step digitization approach in meeting contemporary educational challenges. By facilitating an enhanced knowledge acquisition and fostering a supportive emotional climate, this approach signifies a promising direction for the future of medical education and beyond, fusing the convenience of digital solutions with the depth and engagement of traditional learning methodologies.

Rethinking Learning Experience: How Generally Perceived Life Stress Influences Students' Course Perceptions in Different Learning Environments.

Previous research work has already demonstrated that both the form of teaching as well as different teaching methods directly influence students' learning experience along with their psychobiological responses at the endocrine and autonomic level. Aiming to gain deeper insights into the constitution of the learning experience, this study examined the influence of external factors such as generally perceived life stress and self-efficacy on the immediate learning experience in different learning environments. Therefore, a randomized experimental field study was conducted in which both psychological constructs and physiological data (heart rate variability) were collected from healthy first-year medical students (n = 101) during the COVID-19 pandemic. In an effort to determine the consistency of the effects across various teaching formats, the same content of a practical histology course was carried out in a face-to-face setting as well as in passive and active online teaching. While self-efficacy was a strong predictor for positive course perceptions in all learning conditions (Pearson's r = 0.41-0.58), generally perceived worries correlated with higher anxiety during passive online learning and face-to-face learning (Pearson's r = 0.21-0.44), a finding supported by the negative correlation between the level of perceived life demands and enjoyment during the learning unit (Pearson's r = -0.40--0.43). Here, we additionally report initial evidence pointing towards the role of reduced general life stress as a resilience factor for the expression of physiological stress parameters in an academic context (small-sized effect; Pearson's r = 0.18). The data gathered in this study illustrate the relevance of emerging emotional manifestations-either aversive; negative effect or positive; protective effect-for the immediate learning process and thus establish a connection between medical education and the importance of mental health and wellbeing-especially discussed against the background of current social and political challenges in increasingly complex societal structures.

Quality Assessment and Modulating Factors on Self-Regulatory Behavior in Peer-Assisted Medical Learning.

OBJECTIVES: Standardized extracurricular skills labs courses have been developed in recent decades and are important approaches in peer-assisted medical learning (PAL). To provide high quality training and achieve effective learning strategies, continuous evaluations and quality assessments are essential. This research aims to evaluate quality data from medical students participating in extracurricular skills labs courses at Ruhr-University Bochum to prospectively optimize concepts and didactical training and standardize processes. Additionally, we set out to assess and quantify drivers that are influencing factors of the self-reflection of competencies. METHODS: The analysis was based on a routine assessment of n = 503 attendees of the PAL courses in the skills labs in three consecutive semesters, who voluntarily participated in the evaluation. We analyzed the effects of age, semester and their interaction on the self-reflection of competencies in technical skills courses using moderated regression and simple slope analyses, as previously published. A univariate analysis of variance (ANOVA) with post hoc Tukey HSD testing was used to analyze group means in estimated competencies using IBM SPSS Statistics V.28. RESULTS: An analysis of variance revealed a significant increase in self-assessed competencies when comparing pre- vs. post-course evaluation data in all 35 depicted items (all p < 0.001). A total of 65.5% of the items were adjusted significantly differently, revealing modified self-reflected pre-course levels compared to those stated before. A moderated regression analysis revealed that age (R2 = 0.001, F(1;2347) = 1.88, p < 0.665), semester of study (∆R2 = 0.001, ∆F (1;2346) = 0.012, p < 0.912) and their interaction (∆R2 = 0.001, ∆F (1;2345) = 10.72, p < 0.227) did not explain a significant amount of the variance in self-reflection variance. A simple slope analysis of earlier (b = 0.07, t = 0.29, p < 0.773) and later semesters of study (b = 0.06, t = 0.07, p < 0.941) did not differentiate from zero. CONCLUSIONS: The presented evaluation paradigm proved to be a useful tool to encourage students to initiate self-regulatory and self-reflective behavior. The cohesive evaluation of the large cohort of attendees in extracurricular, facultative skills labs courses was helpful in terms of quality assessments and future adaptations. Further evaluation paradigms should be implemented to assess other influencing factors, such as gender, on self-reflection, since age and semester did not explain significant differences in the model.

Dynamically Changing Mental Stress Parameters of First-Year Medical Students over the Three-Year Course of the COVID-19 Pandemic: A Repeated Cross-Sectional Study.

Numerous research results have already pointed towards the negative influence of increased mental stress on educational processes and motivational criteria. It has also been shown that the global public health crisis induced by COVID-19 was related to anxiety symptoms and elevated levels of distress. To holistically elucidate the dynamics of the pandemic-related mental stress of first-year medical students, the associated parameters of three different cohorts were measured at the beginning of the pandemic-related restrictions on university life in Germany (20/21), at the peak of the COVID-19-related restrictions (21/22) and during the easing of the restrictions in the winter term 22/23. In a repeated cross-sectional study design, the constructs of worries, tension, demands and joy were collected from first-year medical students (n = 578) using the Perceived Stress Questionnaire. The results demonstrate significantly increased values of the constructs worries (p < 0.001), tension (p < 0.001) and demands (p < 0.001) at the peak of the pandemic related restrictions compared to the previous and following year as well as significantly decreasing values of general joy of life during the observed period of 3 years (all p-values < 0.001). A confirmatory factor analysis was performed to verify the questionnaire's factor structure regarding the addressed target group during the pandemic (CFI: 0.908, RMSEA: 0.071, SRMR: 0.052). These data, collected over a period of three years, provide information regarding dynamically manifesting mental stress during the COVID-19 pandemic, and refer to new areas of responsibility for the faculties to adequately counteract future crisis situations.

Modelling the Effect of Age, Semester of Study and Its Interaction on Self-Reflection of Competencies in Medical Students.

Objectives: Accurate self-assessment and -reflection of competencies are crucial skills for all health professions. The National Competence-Based Learning Objectives Catalogue (NKLM) guiding medical faculties in Germany points out reflection as a non-technical skill and competency-based medical education (CBME) as important approaches. In this context, the role and structure of curricula and skills labs evolved. Especially in peer-assisted trainings, reflection of competencies is important to improve self-regulated learning. Traditionally, we assume self-reflection skills to evolve automatically with learners' experience. This approach aims to find empirical evidence for this assumption and implements self-reflection of competencies in clinical skills education. Here, we quantify the influence of age and semester of study and its interaction on the concordant self-reflection of students' own competencies. Methods: Investigation was based on a retrospective analysis of evaluation data from peer-assisted "first aid" and "physical examination" courses in the skills labs of the medical faculty at the Ruhr-University Bochum, Germany. Participants were asked for self-assessed competencies before (pre) and after (post) the course. Additionally, they were asked to retrospectively re-rate their "before" competencies after completing the course (post-pre). Differences between pre and post-pre competencies were assessed as the concordant self-reflection in a moderated regression analysis. Group means and standard deviation were depicted using univariate analysis of variance (ANOVA) with post-hoc Tukey HSD testing in IBM SPSS Statistics V.28. Moderated regression and simple slope analyses were conducted to calculate interaction effects of age and semester of study on the concordant self-reflection. Results: As expected, participants (n = 168) showed significant progress in subjective self-assessment (pre vs. post) in all 18 assessed domains in the course (all p < 0.001). Additionally, participants self-assessed their previous competencies after the course (post-pre) differently than before the course (pre) in 11 out of 18 domains. Hereby, the interaction of age and semester of study explained a significant part of variance in the first aid course (∆R2 = 0.008, ∆F (1;1020) = 8.53, p < 0.005) and in the physical examination course (ΔR2 = 0.03, ΔF (1;10,280) = 10.72, p < 0.001). Conclusions: We quantified that interaction of age and semester has a significant influence on concordant self-reflection skills using a moderated regression analysis. Assumed as an indicator, we conclude that advanced and older students show less differences in pre- vs. post-pre-ratings. This has implications for curriculum development, postulating that an exposure to self-reflection as a metacognitive process should be introduced early in order to train competencies in health professionals. Prospective studies with competency-based assessments are necessary to validate findings.

Mechanistic understanding of Curium(III) sorption on natural K-feldspar surfaces.

To assess a reliable safety case for future deep underground repositories for highly active nuclear waste the retention of radionuclides by the surrounding host rock must be understood comprehensively. Retention is influenced by several parameters such as mineral heterogeneity and surface roughness, as well as pore water chemistry (e.g., pH). However, the interplay between those parameters is not yet well understood. Therefore, we present a correlative spectromicroscopic approach to investigate sorption of the actinide Cm(III) on: 1) bulk K-feldspar crystals to determine the effect of surface roughness and pH (5.5 and 6.9) and 2) a large feldspar grain as part of a complex crystalline rock system to observe how sorption is influenced by the surrounding heterogeneous mineralogy. Our findings show that rougher K-feldspar surfaces exhibit increased Cm(III) uptake and stronger complexation. Similarly, increasing pH leads to higher surface loading and stronger Cm(III) binding to the surface. Within a heterogeneous mineralogical system sorption is further affected by neighboring mineral dissolution and competitive sorption between mineral phases such as mica and feldspar. The obtained results express a need for investigating relevant processes on multiple scales of dimension and complexity to better understand trivalent radionuclide retention by a potential repository host rock.

Nano Geochemistry.

It is our great pleasure to briefly introduce our motivation to collect scientific contributions for this Special Issue, entitled "Nano Geochemistry" [...].

Radionuclide geochemistry evolution in the Long-term In-situ Test (LIT) at Grimsel Test Site (Switzerland).

The Long-term In-situ Test (LIT) of the Colloid Formation and Migration project (CFM) at the Grimsel Test Site, investigates the generation of bentonite colloids and, hence, radionuclide mobilization within a well-defined and controlled shear zone in a crystalline rock. In this context, the determination of radionuclide aqueous speciation is essential to understand whether radionuclides are easily transported or immobilized by precipitation or uptake processes in the bentonite barrier included in a repository concept for nuclear waste, and mimic in the LIT experiment. The objective of this work is to determine the aqueous speciation of seven radionuclides (i.e. 75Se(VI), 99Tc(VII),233U(VI), 237Np(V), 241Am(III), Th(IV) and 242Pu(IV)) by thermodynamic calculations in different water compositions representing the geochemical evolution through the LIT. A comparison of the results obtained from two different modelling groups allows the identification of the geochemical key parameters affecting radionuclide mobility in this context and the corresponding numerical and conceptual uncertainties. Particularly, silicate complexes of trivalent actinides and uranium(VI) carbonato complexes (i.e. CanUO2(CO3)3(4-2n) n = 1 or 2) seem to be crucial in these environments, even at reducing conditions. Conceptual uncertainties like inclusion/exclusion of tetravalent actinide-bearing colloids formation and polyselenides have clearly been identified.

Metal adaptation and transport in hyphae of the wood-rot fungus Schizophyllum commune.

Fungi living in heavy metals and radionuclides contaminated environments, namely the Chernobyl Exclusion Zone need to be able to cope with these pollutants. In this study, the wood-rot fungus Schizophyllum commune was investigated for its metal tolerance mechanisms, and for its ability to transport such metals through its hyphae. Effects of temperature and pH on tolerance of Cs, Sr, Cd, and Zn were tested. At concentrations allowing for half-maximal growth, adapted strains were raised. The strontium-adapted strain, S. commune 12-43 Sr, showed transport of specifically Sr over distances on a cm-scale using split plates. The adaptation did not yield changes in cell or colony morphology. Intracellular metal localization was not changed, and gene expression profiles under metal stress growing on soil versus artificial medium showed a higher impact of a structured surface for growth on soil than with different metal concentrations. In the transcriptome, transporter genes were mostly down-regulated, while up-regulation was seen for genes involved in the secretory pathway under metal stress. A comparison of wildtype and adapted strains could confirm lower cellular stress levels leading to lack of glutathione S-transferase up-regulation in the adapted strain. Thus, we could show metal transport as well as specific mechanisms in metal stress avoidance.

Spider web biomonitoring: A cost-effective source apportionment approach for urban particulate matter.

Elevated levels of particulate matter (PM) in urban atmospheres are one of the major environmental challenges of the Anthropocene. To effectively lower those levels, identification and quantification of sources of PM is required. Biomonitoring methods are helpful tools to tackle this problem but have not been fully established yet. An example is the sampling and subsequent analysis of spider webs to whose adhesive surface dust particles can attach. For a methodical inspection, webs of orb-weaving spiders were sampled repeatedly from 2016 to 2018 at 22 locations in the city of Jena, Germany. Contents of Ag, Al, As, B, Ba, Ca, Cd, Co, Cr, Cs, Cu, Fe, K, La, Li, Mg, Mn, Mo, Na, Ni, P, Pb, Rb, S, Sb, Si, Sn, Sr, Th, Ti, V, Y, Zn and Zr were determined in the samples using inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma-optical emission spectroscopy (ICP-OES) after aqua regia digestion. Multivariate statistical methods were applied for a detailed evaluation. A combination of cluster analysis and principal component analysis allows for the clear identification of three main sources in the study area: brake wear from car traffic, abrasion of tram/train tracks and particles of geogenic origin. Quantitative source contributions reveal that high amounts of most of the metals are derived from a combination of brake wear and geogenic particles, the latter of which are likely resuspended by moving vehicles. This emphasizes the importance of non-exhaust particles connected to road traffic. Once a source identification has been performed for an area of interest, classification models can be applied to assess air quality for further samples from within the whole study area, offering a tool for air quality assessment. The general validity of this approach is demonstrated using samples from other locations.

Removal of chromate ions from leachate-contaminated groundwater samples of Khan Chandpur, India, using chitin modified iron-enriched hydroxyapatite nanocomposite.

Chromite ore processing residues (COPR) are real environmental threats, leading to CrO42-, i.e., Cr (VI) leaching into groundwater. It is of serious concern as Cr (VI) is proven to be carcinogenic. Here we emphasize the application of novel and eco-friendly chitin functionalized iron-enriched hydroxyapatite nanocomposite (HAP-Fe0-Ct) in the remediation of Cr (VI)-contaminated groundwater samples collected from Khan Chandpur, India, where the level of Cr (VI) is found to be 11.7 mg/L in a complex aqueous matrix having 793 mg/L of total dissolved solids. Chitin functionality in the composite has resulted in positive zeta potential at circum-neutral pH, favoring electrostatic attraction of chromate ions and resulting in its bulk surface transport. The HAP-Fe0-Ct showed faster kinetics of removal with efficiency (qm = 13.9 ± 0.46 mg/g) for Cr (VI). The composite has shown sorption equilibrium and 100% removal of Cr (VI) within 3 h of interaction time in groundwater samples. No Cr (VI) leaching in the acid wash process at pH 3.5 also suggests chromium's strong chemisorption onto nanocomposite. During the interaction in aqueous solutions, the reduced iron (Fe0) on the nanocomposite becomes oxidized, suggesting the probable simultaneous reduction of Cr (VI) and its co-precipitation. Continuous column extraction of chromate ions was also efficient in both spiked solutions (39.7 ± 0.04 mg/g) and COPR contaminated water (13.2 ± 0.09 mg/g). Reusability up to three cycles with almost complete Cr (VI) removal may be attributed to surface protonation, new binding sites generation, and electron transfer from Fe0 core through defects. The study concludes that HAP-Fe0-Ct could be utilized for continuous Cr (VI) removal from COPR contaminated complex groundwater matrices.

Impact of long-term storage of various redox-sensitive supported nanocomposites on their application in removal of dyes from wastewater: Mechanisms delineation through spectroscopic investigations.

For the prevention of freshwater reservoirs from contamination through industrial effluents, eco-friendly adsorbents with minimal aging impact are required. Here, redox-sensitive nanoscale zero-valent iron(nZVI) particles were supported on four different surfaces with varying bentonite(B)/charcoal(C) ratio to mimic layered and porous surfaces. Different dyes, i.e. rhodamine-B(RB) and methylene blue(MB) were reacted with redox-sensitive supported nZVI composites, and degradation mechanisms were delineated using FT-IR spectroscopic analysis of reaction precipitates. A 300-day exposure to open-air was provided to the composites to comparatively evaluate the impact of aging on their reactivity for dyes in wastewater. Results interpret that dyes removal was a combination of different interfacial chemical processes, i.e., reduction or organic degradation probably through Fenton like processes, along with sorption. These mechanisms were found to be surface dependent, i.e., nZVI on charcoal enriched porous surfaces, degrade dyes through organic degradation while on layered clay surfaces, MB gets removed through reduction with limited and slower RB removal. Nanocomposites show a minimal impact of aging with removal capacities >100 mg/g for BC-1/3-nZVI and C-nZVI for MB and 50-75 mg/g for RB with significant removal in wastewater. Overall, the study concludes C-nZVI and novel BC-1/3-nZVI as two efficient dye adsorbents with minimal aging impact.

The Influences of Cement Hydration and Temperature on the Thixotropy of Cement Paste.

The rheological properties of fresh cement paste are highly influenced by a large number of parameters, among which the most important factors are the applied shear stress, and the shear history, the age of the sample and the temperature. The effects of these parameters on the yield stress (designated as structural limit stress in this work), the viscosity and the structural recovery rate (i.e., the change in dynamic viscosity with time at rest) were studied. In parallel, the changes in ion composition of the carrier liquid, mineral phase content and granulometry were investigated. The results reveal that all investigated rheological parameters exhibit an approximated bi-linear trend with respect to the degree of hydration, with a period of quasi-constant properties until a degree of hydration of approximately 0.07, followed by a non-linear increase. This increase could be attributed to the formation of calcium hydroxide (CH) and calcium-silicate-hydrate (C-S-H) via calorimetry results. With regard to the effect of the shear history of the sample on the rheological properties, the structural limit stress showed a minor dependency on the shear history immediately after the end of shearing, which, however, vanished within the first minute at rest. The same is true for the structural recovery rate. The presented results give detailed insights into the influences of hydration and shear on the rheological properties-especially the thixotropy-of fresh cement pastes.

Differential allosteric modulation within dopamine D2R - neurotensin NTS1R and D2R - serotonin 5-HT2AR receptor complexes gives bias to intracellular calcium signalling.

Proceeding investigations of G protein-coupled receptor (GPCR) heterocomplexes have demonstrated that the dopamine D2 receptor (D2R), one of the hub receptors in the physiology of schizophrenia, interacts with both the neurotensin NTS1 (NTS1R) and the serotonin 5-HT2A receptor (5-HT2AR) in cell lines and rodent brain tissue. In situ proximity ligation assay and BRET-based saturation experiments confirmed interacting receptor assemblies in HEK293T and neuronal HT22 cells. The NTS1R agonist NT(8-13) reduces the Gαq-mediated calcium signal in the NTS1R-D2R complex compared to the NTS1R monomer which could be reversed by D2R antagonists. The bivalent ligand CS148 (NTS1R-agonistic, D2R-antagonistic) increased the calcium response addressing the dimer, consistent with the effect of the monovalent ligands suggesting an allosteric D2R-mediated modulation. In contrast, the 5-HT2AR-D2R heteromer did not show a calcium-altering receptor-receptor interaction. Despite their common coupling-preference for Gαq, 5-HT2AR and NTS1R supposedly interact with D2R each in a unique mode. This remarkably diverse ligand-mediated signalling in two different D2R heteroreceptor complexes illustrates the complexity of receptor-receptor interactions and their potential of modifying cell responses to external stimuli. Therefore, GPCR heteromers may provide a very promising novel target for the therapy of neuropsychiatric disorders.

Telemedicine Improves Continuous Positive Airway Pressure Adherence in Stroke Patients with Obstructive Sleep Apnea in a Randomized Trial.

BACKGROUND: The prevalence of obstructive sleep apnea (OSA) is very high in stroke patients, whereas the acceptance of positive airway pressure (PAP) therapy is low. Although telemedicine offers new options to increase acceptance, effective concepts and patient groups are not yet known. OBJECTIVE: The aim of this study was to investigate the effect of a telemedicine concept consisting of telemonitoring and support when usage time drops. METHODS: PAP naive stroke patients with apnea-hypopnea index (AHI) >15 were randomized in a prospective parallel design comparing home therapy with standard care (SC) as opposed to telemedicine care (TC) over a period of 6 months. The TC group received a standardized phone call to offer help and advice if the average weekly usage of PAP fell below 4 h/night. RESULTS: Eighty patients were included, 5 were lost to follow-up, 75 (20 females, age: 57.0 ± 9.9, body mass index: 30.9 ± 6.0 kg/m2, AHI: 39.4 ± 18.6) were evaluated. While inpatient usage was similar in both groups, a significant difference was identified after 6 months of receiving home therapy (TC: 4.4 ± 2.5 h, SC: 2.1 ± 2.2 h; p < 0.000063). On average, 4.7 ± 3.1 interventional phone calls were needed (173 calls in total, ranging from 0 to 10 calls per patient), primarily for the purpose of motivation (61.3%), mask problems (16.2%), nasopharyngeal complaints or humidification issues (11.2%), and technical questions (10.6%). Sleepiness (Epworth Sleepiness Scale [ESS]) differed significantly (TC: 3.7 + 3.2, SC: 6.1 + 4.1; p = 0.008), as well as systolic blood pressure, which was available in a subgroup of 55 patients (TC: 129.5 + 15.2 mm Hg, SC: 138.8 + 16.1 mm Hg; p = 0.034). CONCLUSION: A concept of telemonitoring and short telephone calls from the sleep lab raised PAP therapy adherence significantly in a group of stroke patients with moderate to severe OSA.

Ultratrace Determination of 99Tc in Small Natural Water Samples by Accelerator Mass Spectrometry with the Gas-Filled Analyzing Magnet System.

In the frame of studies on the safe disposal of nuclear waste, there is a great interest for understanding the migration behavior of 99Tc. 99Tc originating from nuclear energy production and global fallout shows environmental levels down to 107 atoms/g of soil (∼2 fg/g). Extremely low concentrations are also expected in groundwater after diffusion of 99Tc through the bentonite constituting the technical barrier for nuclear waste disposal. The main limitation to the sensitivity of the mass spectrometric analysis of 99Tc is the background of its stable isobar 99Ru. For ultratrace analysis, the Accelerator Mass Spectrometry (AMS) setup of the Technical University of Munich using a Gas-Filled Analyzing Magnet System (GAMS) and a 14 MV Tandem accelerator is greatly effective in suppressing this interference. In the present study, the GAMS setup is used for the analysis of 99Tc in samples of the seawater reference material IAEA-443, a peat bog lake, and groundwater from an experiment of in situ diffusion through bentonite in the controlled zone of the Grimsel Test Site (GTS) within the Colloid Formation and Migration (CFM) project. With an adapted chemical preparation procedure, measurements of 99Tc concentrations at the fg/g levels with a sensitivity down to 0.5 fg are accomplished in notably small natural water samples. The access to these low concentration levels allows for the long-term monitoring of in situ tracer tests over several years and for the determination of environmental levels of 99Tc in small samples.

Molecular Identification of Cr(VI) Removal Mechanism on Vivianite Surface.

Experimental and theoretical studies were conducted to identify the molecular-scale reaction mechanism for Cr(VI) removal by a ferrous phosphate mineral, vivianite. The surface-normalized rate constant for Cr(VI) removal in a vivianite suspension at pH 7 was higher than those obtained for other Fe(II)-containing minerals (i.e., magnetite and pyrite). The highest rate constant was obtained at pH 5, which was 35- and 264-times higher than those obtained at pH 7 and 9, respectively, indicating the dramatic acceleration of removal kinetics with decreasing pH of suspension. The X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) spectroscopy revealed that Cr(VI) removal involved reduction of Cr(VI) to Cr(III) coupled with oxidation of Fe(II) to Fe(III) on the vivianite surface. In addition, the density functional theory (DFT)-optimized structure of the Cr(VI)-vivianite complex was consistent with that obtained from extended X-ray absorption fine structure (EXAFS) spectroscopy and revealed the transformation of vivianite to amorphous Fe(III) phosphate. We also demonstrated that both Cr(VI) species, HCrO4̅ and CrO42-, can effectively bind to the vivianite surface, particularly on the Fe sites having 6 neighboring Fe molecules with 4 H2O and 2 PO4 moieties. Our results show that Cr(VI) is readily reduced to Cr(III) by vivianite via adsorption and inner-sphere complexation, suggesting that in anoxic iron-phosphate-enriched environments, vivianite may significantly influence the fate and transport of Cr(VI).

Incorporation of Metals into Calcite in a Deep Anoxic Granite Aquifer.

Understanding metal scavenging by calcite in deep aquifers in granite is of importance for deciphering and modeling hydrochemical fluctuations and water-rock interaction in the upper crust and for retention mechanisms associated with underground repositories for toxic wastes. Metal scavenging into calcite has generally been established in the laboratory or in natural environments that cannot be unreservedly applied to conditions in deep crystalline rocks, an environment of broad interest for nuclear waste repositories. Here, we report a microanalytical study of calcite precipitated over a period of 17 years from anoxic, low-temperature (14 °C), neutral (pH: 7.4-7.7), and brackish (Cl: 1700-7100 mg/L) groundwater flowing in fractures at >400 m depth in granite rock. This enabled assessment of the trace metal uptake by calcite under these deep-seated conditions. Aquatic speciation modeling was carried out to assess influence of metal complexation on the partitioning into calcite. The resulting environment-specific partition coefficients were for several divalent ions in line with values obtained in controlled laboratory experiments, whereas for several other ions they differed substantially. High absolute uptake of rare earth elements and U(IV) suggests that coprecipitation into calcite can be an important sink for these metals and analogousactinides in the vicinity of geological repositories.

Multiactinide Analysis with Accelerator Mass Spectrometry for Ultratrace Determination in Small Samples: Application to an in Situ Radionuclide Tracer Test within the Colloid Formation and Migration Experiment at the Grimsel Test Site (Switzerland).

The multiactinide analysis with accelerator mass spectrometry (AMS) was applied to samples collected from the run 13-05 of the Colloid Formation and Migration (CFM) experiment at the Grimsel Test Site (GTS). In this in situ radionuclide tracer test, the environmental behavior of 233U, 237Np, 242Pu, and 243Am was investigated in a water conductive shear zone under conditions relevant for a nuclear waste repository in crystalline rock. The concentration of the actinides in the GTS groundwater was determined with AMS over 6 orders of magnitude from ∼15 pg/g down to ∼25 ag/g. Levels above 10 fg/g were investigated with both sector field inductively coupled plasma mass spectrometry (SF-ICPMS) and AMS. Agreement within a relative uncertainty of 50% was found for 237Np, 242Pu, and 243Am concentrations determined with the two analytical methods. With the extreme sensitivity of AMS, the long-term release and retention of the actinides was investigated over 8 months in the tailing of the breakthrough curve of run 13-05 as well as in samples collected up to 22 months after. Furthermore, the evidence of masses 241 and 244 u in the CFM samples most probably representing 241Am and 244Pu employed in a previous tracer test demonstrated the analytical capability of AMS for in situ studies lasting more than a decade.