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Berlin Brandenburg

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  • 1
    Language: English
    In: Soil Science Society of America Journal, March-April, 2006, Vol.70(2), p.541(9)
    Description: Biogenetic polysugars may affect the sorption characteristics of soil mineral particles in the rhizosphere. We hypothesized that polygalacturonate [PGA, ([[C.sub.6][H.sub.7][O.sub.6]).sub.n.sup.-]] coatings on goethite reduce the diffusion of phosphate into the pores of the adsorbent. Goethite was preloaded with PGA (0-10 mg C [g.sup.-1]). The samples were characterized by [N.sub.2] and C[O.sub.2] adsorption, electrophoretic mobility measurements, and scanning electron microscopy/energy dispersive X-ray analysis (SEM-EDX). The phosphate sorption kinetics was studied with batch experiments over 2 wk at pH 5 and an initial phosphate concentration of 250 [micro]M. Pore volume and specific surface area of the goethite samples declined after PGA addition. The PGA coatings reduced the [zeta]-potential of goethite from 42.3 to -39.6 mV at the highest C loading. With increasing PGA-C content and decreasing [zeta]-potential the amount of phosphate sorbed after 2 wk decreased linearly (P 〈 0.001). Sorption of phosphate to pure and PGA-coated goethite showed an initial fast sorption followed by a slow sorption reaction. At the smallest C loading (5.5 mg C [g.sup.-1]) the portion of phosphate retained by the slow reaction was smaller than for the treatment without any PGA, while at higher C loadings the fraction of slowly immobilized phosphate increased. Our results suggest that at low C-loadings PGA impaired the intraparticle diffusion of phosphate. In contrast, the slow step-by-step desorption of PGA (〈52% within 2 wk) or the diffusion of phosphate through PGA coatings or both are rate limiting for the slow phosphate reaction at C loadings 〉 5.5 mg C [g.sup.-1].
    Keywords: Soil Phosphorus -- Research ; Soil Chemistry -- Research ; X-ray Analysis
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 2
    Language: English
    In: Geochimica et Cosmochimica Acta, 2009, Vol.73(7), pp.1795-1812
    Description: The application of stable Fe isotopes as a tracer of the biogeochemical Fe cycle necessitates a mechanistic knowledge of natural fractionation processes. We studied the equilibrium Fe isotope fractionation upon sorption of Fe(II) to aluminum oxide (γ-Al O ), goethite (α-FeOOH), quartz (α-SiO ), and goethite-loaded quartz in batch experiments, and performed continuous-flow column experiments to study the extent of equilibrium and kinetic Fe isotope fractionation during reactive transport of Fe(II) through pure and goethite-loaded quartz sand. In addition, batch and column experiments were used to quantify the coupled electron transfer-atom exchange between dissolved Fe(II) (Fe(II) ) and structural Fe(III) of goethite. All experiments were conducted under strictly anoxic conditions at pH 7.2 in 20 mM MOPS (3-( -morpholino)-propanesulfonic acid) buffer and 23 °C. Iron isotope ratios were measured by high-resolution MC-ICP-MS. Isotope data were analyzed with isotope fractionation models. In batch systems, we observed significant Fe isotope fractionation upon equilibrium sorption of Fe(II) to all sorbents tested, except for aluminum oxide. The equilibrium enrichment factor, , of the Fe(II) –Fe(II) couple was 0.85 ± 0.10‰ (±2 ) for quartz and 0.85 ± 0.08‰ (±2 ) for goethite-loaded quartz. In the goethite system, the sorption-induced isotope fractionation was superimposed by atom exchange, leading to a Fe shift in solution towards the isotopic composition of the goethite. Without consideration of atom exchange, the equilibrium enrichment factor was 2.01 ± 0.08‰ (±2 ), but decreased to 0.73 ± 0.24‰ (±2 ) when atom exchange was taken into account. The amount of structural Fe in goethite that equilibrated isotopically with Fe(II) via atom exchange was equivalent to one atomic Fe layer of the mineral surface (∼3% of goethite-Fe). Column experiments showed significant Fe isotope fractionation with Fe(II) spanning a range of 1.00‰ and 1.65‰ for pure and goethite-loaded quartz, respectively. Reactive transport of Fe(II) under non-steady state conditions led to complex, non-monotonous Fe isotope trends that could be explained by a combination of kinetic and equilibrium isotope enrichment factors. Our results demonstrate that in abiotic anoxic systems with near-neutral pH, sorption of Fe(II) to mineral surfaces, even to supposedly non-reactive minerals such as quartz, induces significant Fe isotope fractionation. Therefore we expect Fe isotope signatures in natural systems with changing concentration gradients of Fe(II) to be affected by sorption.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 3
    Language: English
    In: Environmental science & technology, 07 October 2014, Vol.48(19), pp.11320-9
    Description: Elevated solution concentrations of As in anoxic natural systems are usually accompanied by microbially mediated As(V), Mn(III/IV), and Fe(III) reduction. The microbially mediated reductive dissolution of Fe(III)-(oxyhydr)oxides mainly liberates sorbed As(V) which is subsequently reduced to As(III). Manganese oxides have been shown to rapidly oxidize As(III) and Fe(II) under oxic conditions, but their net effect on the microbially mediated reductive release of As and Fe is still poorly understood. Here, we investigated the microbial reduction of As(V)-bearing ferrihydrite (molar As/Fe: 0.05; Fe tot: 32.1 mM) by Shewanella sp. ANA-3 (10(8) cells/mL) in the presence of different concentrations of birnessite (Mn tot: 0, 0.9, 3.1 mM) at circumneutral pH over 397 h using wet-chemical analyses and X-ray absorption spectroscopy. Additional abiotic experiments were performed to explore the reactivity of birnessite toward As(III) and Fe(II) in the presence of Mn(II), Fe(II), ferrihydrite, or deactivated bacterial cells. Compared to the birnessite-free control, the highest birnessite concentration resulted in 78% less Fe and 47% less As reduction at the end of the biotic experiment. The abiotic oxidation of As(III) by birnessite (k initial = 0.68 ± 0.31/h) was inhibited by Mn(II) and ferrihydrite, and lowered by Fe(II) and bacterial cell material. In contrast, the oxidation of Fe(II) by birnessite proceeded equally fast under all conditions (k initial = 493 ± 2/h) and was significantly faster than the oxidation of As(III). We conclude that in the presence of birnessite, microbially produced Fe(II) is rapidly reoxidized and precipitates as As-sequestering ferrihydrite. Our findings imply that the ability of Mn-oxides to oxidize As(III) in water-logged soils and sediments is limited by the formation of ferrihydrite and surface passivation processes.
    Keywords: Arsenic -- Chemistry ; Ferric Compounds -- Chemistry ; Iron -- Chemistry ; Oxides -- Chemistry ; Shewanella -- Metabolism
    ISSN: 0013936X
    E-ISSN: 1520-5851
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  • 4
    Language: English
    In: Environmental science & technology, 01 April 2014, Vol.48(7), pp.3822-31
    Description: Binding of arsenite (As(III)) to sulfhydryl groups (Sorg(-II)) plays a key role in As detoxification mechanisms of plants and microorganisms, As remediation techniques, and reduced environmental systems rich in natural organic matter. Here, we studied the formation of Sorg(-II)-As(III) complexes on a sulfhydryl model adsorbent (Ambersep GT74 resin) in the absence and presence of ferrihydrite as a competing mineral adsorbent under reducing conditions and tested their stability against oxidation in air. Adsorption of As(III) onto the resin was studied in the pH range 4.0-9.0. On the basis of As X-ray absorption spectroscopy (XAS) results, a surface complexation model describing the pH dependence of As(III) binding to the organic adsorbent was developed. Stability constants (log K) determined for dithio ((AmbS)2AsO(-)) and trithio ((AmbS)3As) surface complexes were 8.4 and 7.3, respectively. The ability of sulfhydryl ligands to compete with ferrihydrite for As(III) was tested in various anoxic mixtures of both adsorbents at pH 7.0. At a 1:1 ratio of their reactive binding sites, R-SH and ≡FeOH, both adsorbents possessed nearly identical affinities for As(III). The oxidation of Sorg(-II)-As(III) complexes in water vapor saturated air over 80 days, monitored by As and S XAS, revealed that the complexed As(III) is stabilized against oxidation (t1/2 = 318 days). Our results thus document that sulfhydryl ligands are highly competitive As(III) complexing agents that can stabilize As in its reduced oxidation state even under prolonged oxidizing conditions. These findings are particularly relevant for organic S-rich semiterrestrial environments subject to periodic redox potential changes such as peatlands, marshes, and estuaries.
    Keywords: Models, Theoretical ; Arsenites -- Chemistry ; Ferric Compounds -- Chemistry ; Sulfhydryl Compounds -- Chemistry
    ISSN: 0013936X
    E-ISSN: 1520-5851
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  • 5
    Language: English
    In: Environ. Sci. Technol, 09 April 2013, Vol.47((7) ; 04, 2013)
    Description: Short-range ordered ferric arsenate (FeAsO4 · xH2O) is a secondary As precipitate frequently encountered in acid mine waste environments. Two distinct structural models have recently been proposed for this phase. The first model is based on the structure of scorodite (FeAsO4 · 2H2O) where isolated FeO6 octahedra share corners with four adjacent arsenate (AsO4) tetrahedra in a three-dimensional framework (framework model). The second model consists of single chains of corner-sharing FeO6 octahedra being bridged by AsO4 bound in a monodentate binuclear (2)C complex (chain model). In order to rigorously test the accuracy of both structural models, we synthesized ferric arsenates and analyzed their local (〈6 Å) structure by As and Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. We found that both As and Fe K-edge EXAFS spectra were most compatible with isolated FeO6 octahedra being bridged by AsO4 tetrahedra (RFe-As = 3.33 ± 0.01 Å). Our shell-fit results further indicated a lack of evidence for single corner-sharing FeO6 linkages in ferric arsenate. Wavelet-transform analyses of the Fe K-edge EXAFS spectra of ferric arsenates complemented by shell fitting confirmed Fe atoms at an average distance of ∼5.3 Å, consistent with crystallographic data of scorodite and in disagreement with the chain model. A scorodite-type local structure of short-range ordered ferric arsenates provides a plausible explanation for their rapid transformation into scorodite in acid mining environments.
    Keywords: X-Ray Absorption Spectroscopy ; Arsenates -- Chemistry ; Ferric Compounds -- Chemistry;
    ISSN: 0013936X
    E-ISSN: 15205851
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  • 6
    Language: English
    In: Environmental Science and Technology, 04 October 2016, Vol.50(19)
    Description: Peatlands frequently serve as efficient biogeochemical traps for U. Mechanisms of U immobilization in these organic matter-dominated environments may encompass the precipitation of U-bearing mineral(oid)s and the complexation of U by a vast range of (in)organic surfaces. The objective of this work was to investigate the spatial distribution and molecular binding mechanisms of U in soils of an alpine minerotrophic peatland (pH 4.7-6.6, Eh = -127 to 463 mV) using microfocused X-ray fluorescence spectrometry and bulk and microfocused U L3-edge X-ray absorption spectroscopy. The soils contained 2.3-47.4 wt % organic C, 4.1-58.6 g/kg Fe, and up to 335 mg/kg geogenic U. Uranium was found to be heterogeneously distributed at the micrometer scale and enriched as both U(IV) and U(VI) on fibrous and woody plant debris (48 plus or minus 10% U(IV), x plus or minus s, n = 22). Bulk U X-ray absorption near edge structure (XANES) spectroscopy revealed that in all samples U(IV) comprised 35-68% of total U (x = 50%, n = 15). Shell-fit analyses of bulk U L3-edge extended X-ray absorption fine structure (EXAFS) spectra showed that U was coordinated to 1.3 plus or minus 0.2 C atoms at a distance of 2.91 plus or minus 0.01 A (x plus or minus s), which implies the formation of bidentate-mononuclear U(IV/VI) complexes with carboxyl groups. We neither found evidence for U shells at ~3.9 A, indicative of mineral-associated U or multinuclear U(IV) species, nor for a substantial P/Fe coordination of U. Our data indicates that U(IV/VI) complexation by natural organic matter prevents the precipitation of U minerals as well as U complexation by Fe/Mn phases at our field site, and suggests that organically complexed U(IV) is formed via reduction of organic matter-bound U(VI).
    Keywords: Engineering ; Environmental Sciences
    ISSN: 0013-936X
    E-ISSN: 1520-5851
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  • 7
    Language: English
    In: Geochimica et Cosmochimica Acta, 2008, Vol.72(4), pp.1128-1142
    Description: Ferrihydrite (Fh) coprecipitated with exopolymers of plants and microbes may differ in its geochemical reactivity from its abiotic counterpart. We synthesized Fh in the presence and absence of acid polysaccharides (polygalacturonic acid (PGA), alginate, xanthan) and characterized the physical and structural properties of the precipitates formed [Mikutta C., Mikutta R., Bonneville S., Wagner F., Voegelin A., Christl I. and Kretzschmar R. (2008) Synthetic coprecipitates of exopolysaccharides and ferrihydrite. Part I: Characterization. ]. In this paper, we focus on the reactivity of PGA and alginate coprecipitates and pure Fh, and studied their interaction with the microbial siderophore desferrioxamine B (DFOB) in the presence and absence of low molecular weight organic (LMWO) acid anions (malate, citrate). Batch adsorption and dissolution experiments were performed in the dark at pH 7 in 10 mM NaClO background electrolyte. In the dissolution experiments, different modes of ligand addition were applied (single, simultaneous, stepwise). With an estimated Langmuir sorption maximum of 15 mmol/mol Fe, a PGA coprecipitate with 11% C sorbed about four times as much DFOB as pure Fh, and the amount of DFOB sorbed was ∼4-fold larger than estimated from the sum of DFOB sorption to pure Fh and PGA alone. The apparent initial dissolution rates, , and pseudo-first order rate coefficients, , of the coprecipitates exceeded those of pure Fh by up to two orders of magnitude. Citrate and malate exerted a strong synergistic effect on the DFOB-promoted dissolution of pure Fh, whereas synergistic effects of both anions were absent or negligible for the coprecipitates. of the citrate and DFOB-promoted dissolution of PGA coprecipitates increased with increasing molar C/Fe ratio of the coprecipitates, independent of the charge of the LMWO ligand. Our results indicate that polyuronates stabilize Fh particles sterically and /or electrostatically, thus increasing the mineral surface area accessible to LMWO ligands. In contrast, pure Fh was coagulated at pH 7 (pH of Fh = 7.1), and hence only a small fraction of the Fh surface underwent dissolution. The increase in ligand-accessible surface area of Fh upon coprecipitation with acid polysaccharides seems to primarily control the kinetics of the ligand-promoted dissolution at neutral pH. In pH environments where the solubility of Fe(III) is very low, dissolution rates of Fe(III) (hydr)oxides in such coprecipitates may therefore exceed those of pure minerals by several orders of magnitude, despite a similar crystallinity of the minerals.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 8
    Language: English
    In: Soil Science Society of America Journal, Nov-Dec, 2004, Vol.68(6), p.1853(10)
    Description: Recent [N.sub.2] adsorption studies have suggested a 'pore clogging' effect on mineral soil phases caused by organic matter coatings. For methodological reasons, this pore clogging effect has been studied only after drying. Our hypothesis was that pore clogging is affected by drying of organic coatings. In our study, we used AlOOH, which has been equilibrated with dissolved organic matter (DOM) and polygalacturonic acid [[PGA; [([C.sub.6][H.sub.8][O.sub.6]).sup.n]]. To test our hypothesis, we determined the porosity of moist and freeze-dried AlOOH samples. Freeze-dried samples were analyzed by [N.sub.2] adsorption, moist samples by [sup.1]H-nuclear magnetic resonance (NMR). In addition, the samples were characterized by environmental scanning electron microscopy--energy dispersive x-ray spectroscopy (ESEM-EDX). Both, DOM and PGA significantly reduced specific surface area (SS[A.sub.BET]) of AlOOH by 34 [m.sup.2][g.sup.-1](15%) and 77 [m.sup.2] [g.sup.-1] (36%). The reduction in SS[A.sub.BET] normalized to the amount of C sorbed was 1.0 [m.sup.2] [mg.sup.-1] DOM-C and 5.9 [m.sup.2] [mg.sup.-1] PGA-C. Dissolved OM reduced the pore volume of micro- and small mesopores 〈3 nm whereas PGA also reduced the volume of larger pores. The [sup.1]H-NMR results of moist samples showed that PGA sorption reduced the amount of water in pores 〈4 nm. In addition, the pore size maximum of AlOOH increased by 150%. Polygalacturonic acid coatings created new interparticle pores of about 10- to 70-nm size that are not stable upon freeze-drying. Porosity changes upon DOM-treatment were not commensurable by [sup.1]H-NMR. Our results indicate that clogging of micro- and small mesopores is not an artifact of freeze-drying. Polygalacturonic acid seems not only to cover the mouth of AlOOH-nanometer pores but also to fill them.
    Keywords: Soil Mineralogy -- Research
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 9
    Language: English
    In: Environmental Science and Technology, 03 June 2016, Vol.50((7) ; 04, 2016)
    Description: Iron-rich organic flocs are frequently observed in surface waters of wetlands and show a high affinity for trace metal(loid)s. Under low-flow stream conditions, flocs may settle, become buried, and eventually be subjected to reducing conditions facilitating trace metal(loid) release. In this study, we reacted freshwater flocs (704-1280 mg As/kg) from a minerotrophic peatland (Gola di Lago, Switzerland) with sulfide (5.2 mM, S(-II).../Fe = 0.75-1.62 mol/mol) at neutral pH and studied the speciation changes of Fe, S, and As at 25 plus or minus 1 ...C over 1 week through a combination of synchrotron X-ray techniques and wet-chemical analyses. Sulfidization of floc ferrihydrite and nanocrystalline lepidocrocite caused the rapid formation of mackinawite (52-81% of Fe... at day 7) as well as solid-phase associated S(0) and polysulfides. Ferrihydrite was preferentially reduced over lepidocrocite, although neoformation of lepidocrocite from ferrihydrite could not be excluded. Sulfide-reacted flocs contained primarily arsenate (47-72%) which preferentially adsorbed to Fe(III)-(oxyhydr)oxides, despite abundant mackinawite precipitation. At higher S(-II)spike/Fe molar ratios (=1.0), the formation of an orpiment-like phase accounted for up to 35% of solid-phase As. Despite Fe and As sulfide precipitation and the presence of residual Fe(III)-(oxyhydr)oxides, mobilization of As was recorded in all samples (As... = 0.45-7.0 ...M at 7 days). Aqueous As speciation analyses documented the formation of thioarsenates contributing up to 33% of As.... Our findings show that freshwater flocs from the Gola di Lago peatland may become a source of As under sulfate-reducing conditions and emphasize the pivotal role Fe-rich organic freshwater flocs play in trace metal(loid) cycling in S-rich wetlands characterized by oscillating redox conditions. (ProQuest: ... denotes formulae/symbols omitted.)
    Keywords: Engineering ; Environmental Sciences
    ISSN: 0013-936X
    E-ISSN: 1520-5851
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  • 10
    Language: English
    In: Environ. Sci. Technol, 18 November 2014, Vol.48((22) ; 11, 2014)
    Description: Floodplain soils are frequently contaminated with metal(loid)s due to present or historic mining, but data on the bioaccessibility (BA) of contaminants in these periodically flooded soils are scarce. Therefore, we studied the speciation of As and Fe in eight As-contaminated circumneutral floodplain soils ( less than or equal to 21600 mg As/kg) and their size fractions using X-ray absorption spectroscopy (XAS) and examined the BA of As in the solids by in-vitro gastrointestinal (IVG) extractions. Arsenopyrite and As(V)-adsorbed ferrihydrite were identified by XAS as the predominant As species. The latter was the major source for bioaccessible As, which accounted for 5-35% of the total As. The amount of bioaccessible As increased with decreasing particle size and was controlled by the slow dissolution kinetics of ferrihydrite in the gastric environment (pH 1.8). The relative BA of As (% of total) decreased with decreasing particle size only in a highly As-contaminated soil -- which supported by Fe XAS -- suggests the formation of As-rich hydrous ferric oxides in the gastric extracts. Multiple linear regression analyses identified Al, total As, Corg, and P as main predictors for the absolute BA of As (adjusted R2 less than or equal to 0.977). Health risk assessments for residential adults showed that (i) nearly half of the bulk soils may cause adverse health effects and (ii) particles 〈5 mu m pose the highest absolute health threat upon incidental soil ingestion. Owing to their low abundance, however, health risks were primarily associated with particles in the 5-50 and 100-200 mu m size ranges. These particles are easily mobilized from riverbanks during flooding events and dispersed within the floodplain or transported downstream.
    Keywords: Flood Plains ; Environmental Sciences ; Regression Analysis ; Spectroscopy ; Particle Size ; Rivers ; Flooded Soils ; Abundance ; Environmental Impact ; Particulates ; Ingestion ; Soil ; Health Risks ; Absorption Spectroscopy ; Flood Plains ; River Banks ; Kinetics ; Ph ; Flood Plains ; Speciation ; Risk ; Arsenic ; Public Health ; Assessments ; Soil Contamination ; Particle Size ; Solids ; Flood Plains ; Speciation ; Risk ; Arsenic ; Public Health ; Assessments ; Soil Contamination ; Particle Size ; Solids ; Freshwater Pollution ; Natural Hazards ; General (556) ; Toxicology & Environmental Safety ; Epidemiology and Public Health ; Water Resources and Supplies ; Data Acquisition;
    ISSN: 0013936X
    E-ISSN: 15205851
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