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Abstract: The erosion of legacy coastal municipal solid waste landfill sites will result in the dispersion of particulate material into nearby ecosystems with potential for effects on marine populations. Information on the speciation and solid phase associations of metal(loid) contaminants will help to predict contaminant behaviour and better understand ecosystem risks. Here, we investigate the solid phase composition of, and metal(loid) leaching from, fine fraction materials recovered from three actively eroding coastal landfill sites. High concentrations of a range of potentially toxic elements (As, Cd, Cr, Cu, Pb, Ni and Zn) were present in multiple samples, but metal(loid) leaching rates were very low (≪1 wt%) in both deionised water and seawater solutions. Therefore, particulate dispersion is the most likely mode of contaminant transport occurring at these sites. The fine fraction materials were dominated by fine sand sized (63–180 μm) quartz grains and silt sized (<63 μm) matrix components, which were likely to be poorly retained on beaches and easily transported offshore. Four priority contaminants (As, Cu, Pb and Zn) were found to occur primarily in adsorbed or precipitate forms, as either coatings on other particles or as discrete <10 μm particles. Dilution of these fine-grained contaminated particles within natural pelitic sediments will likely reduce the overall ecosystems impacts; but the risks to filter and bottom feeding organisms, and the potential for biomagnification across trophic levels are poorly understood.

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Abstract: Iron and steel slags have a long history of both disposal and beneficial use in the coastal zone. Despite the large volumes of slag deposited, comprehensive assessments of potential risks associated with metal(loid) leaching from iron and steel by-products are rare for coastal systems. This study provides a national-scale overview of the 14 known slag deposits in the coastal environment of Great Britain (those within 100 m of the mean high-water mark), comprising geochemical characterisation and leaching test data (using both low and high ionic strength waters) to assess potential leaching risks. The seaward facing length of slag deposits totalled at least 76 km, and are predominantly composed of blast furnace (iron-making) slags from the early to mid-20th Century. Some of these form tidal barriers and formal coastal defence structures, but larger deposits are associated with historical coastal disposal in many former areas of iron and steel production, notably the Cumbrian coast of England. Slag deposits are dominated by melilite phases (e.g. gehlenite), with evidence of secondary mineral formation (e.g. gypsum, calcite) indicative of weathering. Leaching tests typically show lower element (e.g. Ba, V, Cr, Fe) release under seawater leaching scenarios compared to deionised water, largely ascribable to the pH buffering provided by the former. Only Mn and Mo showed elevated leaching concentrations in seawater treatments, though at modest levels (<3 mg/L and 0.01 mg/L, respectively). No significant leaching of potentially ecotoxic elements such as Cr and V (mean leachate concentrations <0.006 mg/L for both) were apparent in seawater, which micro-X-Ray Absorption Near Edge Structure (μXANES) analysis show are both present in slags in low valence (and low toxicity) forms. Although there may be physical hazards posed by extensive erosion of deposits in high-energy coastlines, the data suggest seawater leaching of coastal iron and steel slags in the UK is likely to pose minimal environmental risk.

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Abstract: Seismic studies are essential for accurate characterisation of planetary interior structures, but are dependent on modelling for interpretation, requiring data on the elastic properties of likely constituent minerals. With the potential deployment of seismic stations on icy worlds such as Europa and Titan envisioned for the near future, a campaign of study into the elasticity of potential icy ocean world minerals is of paramount importance. In the paper we assess the role of first-principles computer simulations to this problem, in particular focussing on the application of recent advances in simulating dispersion forces in loosely-bonded molecular solids, likely to be the main constituents of icy ocean worlds. This is of particular interest for these kinds of materials, since the complex sample handling, phase transitions and the difficulty of obtaining single crystals often greatly complicates the experimental determination of the full elastic tensor. We focus on CO2, C6H6, MgSO4·7H2O and CaSO4·2H2O as they allow us to benchmark the performance over a wide range of chemical space, structural topologies, crystal symmetries and bonding types, and moreover have accurate experimentally determined unit-cell dimensions, bulk moduli and full elastic tensors for benchmarking purposes. We demonstrate that the dispersion corrected approaches indeed perform superior in modelling the experimental density profiles (mean unsigned differences of merely 0.04 g/cm3 (CO2), 0.02 g/cm3 (C6H6), 0.003 g/cm3 (MgSO4·7H2O) and 0.013 g/cm3 (CaSO4·2H2O)) and may find application in exploring the compressive parameters of candidate materials, which could then be used in rheological models of icy ocean worlds. Moreover, we have assessed if the elastic constants computed by dispersion corrected density functional theory are accurate enough to be used in a reference data base for the seismic exploration of icy ocean worlds. Despite one approach having demonstrated good accuracy compared with the experimental values in modelling the elasticity of CO2, we instead find average differences from expected P and S wave velocities of around 10 to 25% for the elastically more complex title compounds. In part these differences are due to the large temperature difference between the experimental elasticity data (typically near 300 K) and our calculations, which were performed in the athermal limit.

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Abstract: Results are presented from the analysis of aqueous and solid-phase V speciation within samples collected from the Hazeltine Creek catchment affected by the August 2014 Mount Polley mine tailings dam failure, Canada. Electron microprobe and XANES analysis found that V is present as V3+ substituted into magnetite, and V3+ and V4+ substituted into titanite, both of which occur in the spilled Mount Polley tailings. Secondary Fe oxyhydroxides forming in inflow waters and on creek beds have V K-edge XANES spectra exhibiting E½ positions and pre-edge features consistent with the presence of V5+ species, suggesting sorption of this species on these secondary phases. PHREEQC modelling suggests that the stream waters mostly contain V5+, and the inflow and pore waters contain a mixture of V3+ and V5+. These data, and stream, inflow and pore water chemical data, suggest that dissolution of V(III)-bearing magnetite, V(III,IV)-bearing titanite, V(V)-bearing Fe(-Al-Si-Mn) oxhydroxides, V-bearing Al(OH)3 and/or -clay minerals may have occurred. In the circumneutral pH environment of Hazeltine Creek elevated V concentrations are likely naturally attenuated by formation of V(V)-bearing secondary Fe oxyhydroxide, Al(OH)3 or clay mineral colloids, suggesting that the V is not bioavailable. A conceptual model is presented describing the origin and fate of V in Hazeltine Creek that is applicable to other river systems.

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Abstract: Purpose: Chromium, a potentially harmful element, occurs commonly within the urban sediment cascade as a result of abundant industrial and transport-related sources. The risks that Cr-bearing particles pose to ecosystems and humans depend on the solid-phase chemical speciation of Cr and its environmental mobility. In this study, we adopt an integrated geochemical approach to investigate and determine the long-term fate of Cr in the urban sediment cascade. Materials and methods: We use bulk chemical digests, sequential chemical extraction analysis, electron microscopy, electron microprobe and microfocus XANES analysis to describe the solid-phase speciation, geochemical characteristics and potential long-term behaviour of Cr in urban particulate matter from both aquatic sediment and road dust sediment (RDS) in Manchester, UK. Results and discussion: Cr-bearing grains within RDS and aquatic sediment are predominantly iron oxides and alumino-silicate glass grains. Electron microprobe analysis indicates Cr concentrations up to 3300 and 133,400 μg g−1 in the RDS and aquatic grains, respectively. XANES analysis indicates that Cr(III) is the dominant oxidation state, with only trace amounts of Cr(VI). Importantly, Cr speciation does not appear to have changed between sedimentary environments and the dominance of Cr(III) suggests limited bioavailability or toxicity under predominant environmental (anoxic and neutral pH) conditions in the aquatic sediment sink. Furthermore, geochemical analyses suggest the environmental mobility of Cr in the aquatic sediment sink is low (compared to other toxic metals) due to its association mainly with alumino-silicate glass grains and its inclusion as an integral part of the glass structure. Conclusions: Industrial glass grains are a major component of urban sediment worldwide. The speciation and geochemical investigations performed in this study suggest most Cr within the urban sediment cascade may be resistant to environmental processes that could mobilise other toxic metals.