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The magnesium chalcogenide spinel MgSc2Se4 with high Mg‐ion room‐temperature conductivity has recently attracted interest as solid electrolyte for magnesium ion batteries. Its ionic/electronic mixed‐conducting nature and the influence of the spinel composition on the conductivity and Mg2+ migration barrier are yet not well understood. Here, results from a combined experimental and computational study on four MgB2Se4 spinels (B = Sc, Y, Er, Tm) are presented. The room‐temperature ionic conductivities (σion = 2 × 10−5–7 × 10–5 S cm−1) of the spinels are accurately measured, as electron transport is effectively suppressed by purely Mg‐ion conducting electrode interlayers. Using the same approach, reversible Mg plating/stripping as well as good electrochemical stability are achieved. Driven by the good accordance of the computationally and experimentally obtained Mg2+ migration barriers Ea(th) and Ea, respectively, further periodic density functional calculations are performed on the MgB2Se4 spinel system, revealing the role of trigonal distortion on the migration path geometry and Ea(th). These findings provide deeper understanding how to reach small Mg2+ migration barriers Ea in the MgB2Se4 spinels. [ABSTRACT FROM AUTHOR]

Magnesium batteries offer promising potential as next‐generation sustainable energy‐storage solutions due to the high theoretical capacity of the magnesium metal anode. Facilitating dendrite‐free operation of metal anodes necessitates the development of solid electrolytes with high magnesium‐ion conductivity. While the chalcogenide spinel MgSc2Se4 is predicted to exhibit high magnesium ion mobility, unequivocal experimental evidence for magnesium ion conduction beyond short‐range motion is still missing. This study confirms magnesium‐ion transport in MgSc2Se4 through two independent electrochemical methods: electrochemical deposition of magnesium metal and reversible magnesium plating/stripping cycling. To overcome the difficulty of measuring the ionic conductivity of the mixed conducting MgSc2Se4 spinel, a pure ion conducting interlayer is employed in a symmetric transference cell. This approach effectively suppresses the electron transport, allowing accurate characterization of the ionic conductivity. The experimental results confirm a low migration barrier of (386 ± 24) meV for magnesium ion transport in MgSc2Se4 and demonstrate one of the best performances at room temperature among the reported inorganic magnesium solid electrolytes. The findings open a new door for exploring additional mixed magnesium ion conductors and highlight the potential of magnesium chalcogenide spinels as a promising class of magnesium solid electrolytes. [ABSTRACT FROM AUTHOR]

The precise detection of the toxic gas H2S requires reliable sensitivity and specificity of sensors even at minute concentrations of as low as 10 ppm, the value corresponding to typical exposure limits. CuO can be used for H2S dosimetry, based on the formation of conductive CuS and the concomitant significant increase in conductance. In theory, at elevated temperature the reaction is reversed and CuO is formed, ideally enabling repeated and long‐term use of one sensor. Yet, the performance of CuO tends to drop upon cycling. Utilizing defined CuO nanorods we thoroughly elucidated the associated detrimental chemical changes directly on the sensors, by Raman and electron microscopy analysis of each step during sensing (CuO→CuS) and regeneration (CuS→CuO) cycles. We find the decrease in the sensing performance is mainly caused by the irreversible formation of CuSO4 during regeneration. The findings allowed us to develop strategies to reduce CuSO4 formation and thus to substantially maintain the sensing stability even for repeated cycles. We achieved CuO‐based dosimeters possessing a response time of a few minutes only, even for 10 ppm H2S, and prolonged life‐time. [ABSTRACT FROM AUTHOR]

• Total suspended solids correlated linearly with PAHs and musk fragrances in a river during a storm event. • Total concentrations of hydrophobic compounds and their cytotoxicity increased with increasing total suspended solids. • Cytotoxicity per mass of particles and volume of water remained stable throughout storm events. Storm events lead to mobilization of particles as well as organic contaminants that can pose a risk to river ecosystems. Assessment of total loads of particle-bound and dissolved contaminants in rivers is challenging, especially during rain events since multiple, often unknown contamination sources may be triggered, among them tributaries, combined sewer overflows, direct soil and road runoff, and the riverbed sediment. We investigated whether cytotoxicity (i.e., reduction of the cell viability of human cell lines) could be used as a proxy for the total chemical mixture to assess the transport of organic contaminant mixtures either in particle-associated form or in the aqueous phase. Time-proportional composite samples were collected in the Ammer River (Southwestern Germany) during two storm events in June 2021. All samples were screened for 127 organic contaminants and cytotoxicity in the water and particle phase separately. In total, 56 organic compounds were found, of which 14 and 34 were detected only in the water and particle extracts, respectively, and eight compounds were present in both phases. Thermodynamic equilibrium between the aqueous phase and suspended solids was observed for four compounds namely triphenyl phosphate, octocrylene, galaxolide, and p -chlorocresol. Substances that were not in equilibrium were mainly constituents of plastics and tire rubber, and their high concentrations in the particle phase were probably due to extractions from the particles themselves. Linear correlations between TSS and total compound concentrations were found for 17 PAHs and two musk fragrances, suggesting stable particle loadings and aqueous concentrations over the course of the rain event, most likely due to particle delivery from a particle source with a constant degree of contamination. The total cytotoxicity of water plus particles in the river correlated linearly with TSS during storm events. Inflowing water and particles from all sources appeared to be integrated, such that the total cytotoxicity of all contaminants per mass of particles and volume of water in the river was stable throughout storm events. From this relationship, a threshold of 0.5 g L-1 TSS was derived, above which particle-facilitated transport exceeded dissolved cumulative contaminant transport in the Ammer River, indicating the relevance of particle-facilitated contaminant transport. [ABSTRACT FROM AUTHOR]

• Catchment morphology of tidal creeks is a controlling factor for the submarine groundwater discharge (SGD). • Tidal creeks act as a link between the terrestrial aquifer and the ocean. • High amount of freshwater drains into the sea during spring tide via the tidal creek. Coastal ecosystem health and sustainability is tightly coupled to submarine groundwater discharge (SGD) and associated nutrient, carbon and pollutant fluxes. However, there are few studies that systematically analyse the interaction between the terrestrial aquifer system, catchment morphology and coastal SGD. The objective of this study was to evaluate the role of catchment morphology and how this influences the spatial distribution, timing and volume of the SGD flux to a branched tidal creek system, on the barrier island Spiekeroog, Germany. The subsurface salinity was mapped using electrical resistivity tomography (ERT) and a hydrogeochemical survey of the shallow groundwater. Temporal and spatial analysis of geochemical tracers (radon-222, chloride) in the tidal creek water was integrated into a transient 222Rn mass balance model for quantification of SGD rates during two field campaigns that encompassed spring and neap tides. The ERT mapping indicated that fresh groundwater dominated under the dune ridges down to about 15 m depth, but became progressively more brackish seawards. This is likely due to frequent tidal and storm flooding of low-lying areas. The highest groundwater fluxes into the creek were indicated by high 222Rn activities (average 468 Bq m−3) towards the dune ridge. Chloride concentrations (up to 17.3 g L−1) increased seawards showing the progressive salinization of water in the creek. The freshwater component of SGD was highly variable in time but was highest at low tide, while the total SGD flux (saline + fresh) was highest when tides changed from inflow to outflow as the rapid pressure release on the local aquifer caused a large hydraulic gradient towards the creek. Comparing the freshwater component of mean daily SGD to the creek with estimated groundwater recharge rates in the catchment (665 m3 d−1) shows that the fresh groundwater discharge exceeds fresh recharge during spring tides (~120%) but is was lower than recharge during neap tides (~27%). In this study we show that tidal creeks and their relation to catchment morphology are relevant for understanding the spatial and temporal exchange of fresh and saline water between the catchment and coastal zone. [ABSTRACT FROM AUTHOR]

Organic micropollutants enter rivers mainly with discharges of wastewater treatment plants (WWTP) and pose a risk to aquatic ecosystems and water quality. A considerable knowledge gap exists for disentangling overlapping processes and driving conditions that control the fate of these pollutants. Thus, the aim of this study was to identify the driving parameters for attenuation of selected pharmaceuticals (carbamazepine, diclofenac, tramadol and venlafaxine) under field conditions. The presented study was performed at a small river (Ammer River, mean discharge 0.87 m3 s−1) which is hydrologically complex due to karstification, numerous artificial discharges, and engineered modifications of the channel. We applied a Lagrangian sampling scheme at two sequential river reaches. In general, for the investigated compounds and over the length of the tested reaches, the absolute net attenuation representative for 24 h was low (≤ 23% net attenuation), yet calculated half-lives were comparable to literature. Photodegradation is specifically relevant for the first river reach characterized by a higher net attenuation of the photosensitive compound diclofenac (14.5% ±11.3%) compared to the second section (9.8% ±13.7%). This is likely due to a spatial difference in canopy shading, which is supported by significant correlations (R2 ≥ 0.8) of the temporally changing 'temperature' and 'solar radiation' with time-specific degradation rate constants of photosensitive compounds for consecutive hourly water parcels. In general, the presented spatially and temporally resolved approach is a suitable tool to determine the attenuation of organic micropollutants and to narrow down the interpretation of net attenuation to a few reasonable processes. Unlabelled Image • Integrated investigation combining field approaches and chemical analysis in a small river • River water influenced by (diffuse) groundwater inflow and wastewater • Application of a mass balance approach based on Lagrangian sampling • Determination of temporal and spatial variability in attenuation of organic micropollutants • Photodegradation identified as major attenuation mechanism in the studied river [ABSTRACT FROM AUTHOR]

Characterization of groundwater-surface water interactions remains challenging,especially in anthropogenically affected and geologically complex river systems. In thisstudy, groundwater inflow into the Ammer River was quantified by optimizingexfiltration rates in an implicit numerical model (FINIFLUX) to measured data ofseveral environmental tracers (e.g., sulfate (SO42−), radon (222Rn)) and organicconservative pollutants like carbamazepine and sulfamethoxazole emitted via awastewater treatment plant (WWTP). Modelling results of the selected tracers werecompared. The investigated Ammer River is strongly karstified and anthropogenically modified (millcanals, weirs, numerous artificial inputs) but representative for many small river systems inEurope. 222Rn activities in the river ranged from 500 to 3300 Bq m−3 and SO42−concentrations from 224 to 291 mg L−1. Concentrations of carbamazepine (90-130 ng L−1)and sulfamethoxazole (55-100 ng L−1) in the river water result from effluents of aWWTP. All tracers indicate major local groundwater inflows over the 6 km riverreach. Additional high peaks mainly observed in 222Rn activities indicate inputsalong geological fault lines, whereby increasing concentrations of carbamazepineand sulfamethoxazole may be attributed to inputs of groundwater contaminated byinfiltration of wastewater from a nearby WWTP. 222Rn-based calculations showed thebest optimization performance (R2=0.90) and result in a reasonable cumulativegroundwater inflow of 0.274 m3 s−1 (28.5% of total discharge) for the investigated reach.Poor optimizations for the other tracers may be due to the diurnal pattern of ionconcentrations induced by the WWTP and measurement uncertainties and the smallconcentration differences between river water and groundwater for carbamazepine andsulfamethoxazole. In our case study, 222Rn seems to be the most suitable environmental tracer despiteuncertainties in degassing and determination of the groundwater endmember concentration.However, only a multi tracer approach can account for the complexity of the investigatedriver system and may thus be indispensable for future investigations aiming to understandgroundwater-surface water interactions. [ABSTRACT FROM AUTHOR]

Anthropogenic organic micropollutants enter river systems mainly via wastewater treatment plants (WWTP). Characterization of turnover processes and fate of these compounds including temporal and spatial resolution at the same time remains challenging. Still, published results rely frequently on grab samples that do not account adequately for advection, dispersion and transformation along the studied reach. This study aims to compare degradation rates calculated from a Lagrangian Sampling concept in two different sequential reaches with calculations from arbitrary grab samples.Field investigations took place at two sequential reaches at the Ammer River close to Tübingen in the southwest of Germany that differ in (hydro-) morphology, slope and amount of groundwater inflow. Time-series measurements of organic chemical compounds (target screening), accompanied by electrical conductivity (EC), and conservative ions were conducted over a period of 24 hours. A lumped parameter model approach accounting for advection and dispersion was applied to the time-series measurements to calculate degradation rate constants affecting water parcels entering and leaving the same reach. In an alternative approach, degradation rate constants were calculated from arbitrary grab samples of the time series, representative for samples not properly considering travel time of water in the river. The influence of dilution caused by tributary and groundwater inflow was included for the overall attenuation rate in both approaches. The Lagrangian sampling approach integrates temporal dynamics such as the changed solar radiation or input of the WWTP into the river throughout the whole day and thus leads to representative degradation rates and characterization of turnover processes. In contrast, results from arbitrary grab samples may be misleading and indicating unrealistic processes and rates.The different results of the tested approaches show the relevance of identifying and including temporal and spatial aspects of river systems for characterization of the fate of organic micropollutants. They highlight the need to consider hydrological processes in the river for future field-based attenuation investigations. [ABSTRACT FROM AUTHOR]

Organic micropollutants of anthropogenic origin in river waters may impair aquatic ecosystem health and drinking water quality. To evaluate micropollutant fate and turnover on a catchment scale, information on input source characteristics as well as spatial and temporal variability is required. The influence of tributaries from agricultural and urban areas and the input of wastewater were investigated by grab and Lagrangian sampling under base flow conditions within a 7.7‐km‐long stretch of the Ammer River (southwest Germany) using target screening for 83 organic micropollutants and 4 in vitro bioassays with environmentally relevant modes of action. In total, 9 pesticides and transformation products, 13 pharmaceuticals, and 6 industrial and household chemicals were detected. Further, aryl hydrocarbon receptor induction, peroxisome proliferator–activated receptor activity, estrogenicity, and oxidative stress response were measured in the river. The vast majority of the compounds and mixture effects were introduced by the effluent of a wastewater‐treatment plant, which contributed 50% of the total flow rate of the river on the sampling day. The tributaries contributed little to the overall load of organic micropollutants and mixture effects because of their relatively low discharge but showed a different chemical and toxicological pattern from the Ammer River, though a comparison to effect‐based trigger values pointed toward unacceptable surface water quality in the main stem and in some of the tributaries. Chemical analysis and in vitro bioassays covered different windows of analyte properties but reflected the same picture. Environ Toxicol Chem 2020;39:1382–1391. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Secondary batteries using multivalent cations as ionic charge carriers have attracted increasing attention in recent years due to the high theoretical energy density provided by multi‐electron redox reactions. However, the high charge density of these cations inevitably leads to sluggish kinetics of ion migration at room temperature, which poses a challenge for the development of solid‐state batteries using multivalent ions. Here, a magnesium ion conducting hybrid solid electrolyte (HSE) is prepared, consisting of a new NASICON‐structured material, Mg0.5Sn2(PO4)3, and a small amount of magnesium ionic liquid. The HSE shows superior room‐temperature ionic conductivity of 1.11 × 10−4 S cm−1 and an activation energy of 0.36 eV. Due to the good compatibility of the HSE with the magnesium metal anode, symmetric MgǀHSEǀMg cells show stable magnesium plating and stripping behavior at room temperature. Using in situ electrochemical scanning electron microscopy measurements, the room temperature growth‐induced fracture of the HSE is observed, giving unequivocal evidence for magnesium deposition. These results may serve as a starting point for understanding the magnesium deposition mechanism on solid electrolytes in solid‐state batteries. [ABSTRACT FROM AUTHOR]

First order streams drain considerable proportions of river catchments and as they are normally well connected to shallow groundwater they are among the first receptors of agricultural effluents. Understanding the processes governing the water quality in agricultural areas requires identifying sources of potential pollutants, hotspots of biogeochemical reactivity and defining the different hydrologic flowpaths connecting sources, reactive hotspots and streams. In the present study, we have equipped an agricultural drainage system (Schönbrunnen) in south-western Germany with 23 piezometers in the shallow aquifer and 4 measurement stations along the stream. In order to identify hydrological flowpaths, sources of different groundwater bodies and to quantify the hydrologic turnover, data were collected covering an entire annual cycle from July 2017 to August 2018, applying hydrological and hydrochemical parameters as well as environmental and artificial tracers.The 550 m long test segment of the Schönbrunnen stream, features an alternation of gaining and loosing reaches with strong seasonal variabilities: more than 15% of its volumetric discharge was lost in downstream direction during warmer periods, causing the relative hydrologic turnover to be larger. We hypothesized that when groundwater levels are high, the whole stream would get exfiltrating groundwater and vice versa. By contrast, this behavior only occurred on the lower segment under wetter conditions (especially during the winter months), when it was gaining from the groundwater bodies at both sides of the stream, which showed contrasting chemical signature. Also, a larger fraction of upstream water was remaining in the lowermost segment of the stream during this period, i.e. the hydrologic turnover was smaller than during summer months. Groundwater contour maps were interpolated on a monthly basis and indicated shifting groundwater flow directions. During the summer period, groundwater flowpaths run basically parallel to both streams, meaning that there is only a little fraction of exfiltrating groundwater into the stream, whereas in winter months the head contours showed the characteristic inversed-V shapes, especially towards the downstream end. The use of geochemical tracers proved that the different contributions from both groundwater bodies drive the stream chemistry. Furthermore, the alternating gaining/loosing situation affects streamwater composition and it may change the turnover capacity of the agricultural pollutants along the transition zone. In conclusion, hydrological turnover, i.e. exchanges with surrounding groundwater bodies, has been found to strongly influence streamwater chemistry of low order streams – an effect which is often overlooked. [ABSTRACT FROM AUTHOR]