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Berlin Brandenburg

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  • 1
    Language: English
    In: Environmental science & technology, 18 February 2014, Vol.48(4), pp.2281-9
    Description: Organosulfur-coordinated As(III) and realgar (α-As4S4) have been identified as the dominant As species in the naturally As-enriched minerotrophic peatland Gola di Lago, Switzerland. In this study, we explored their oxidation kinetics in peat exposed to atmospheric O2 for up to 180 days under sterile and nonsterile conditions (25 °C, ∼ 100% relative humidity). Anoxic peat samples were collected from a near-surface (0-38 cm) and a deep peat layer (200-250 cm) and studied by bulk As, Fe, and S K-edge X-ray absorption spectroscopy as well as selective extractions as a function of time. Over 180 days, only up to 33% of organosulfur-coordinated As(III) and 44% of realgar were oxidized, corresponding to half-life times, t1/2, of 312 and 215 days, respectively. The oxidation of both As species was mainly controlled by abiotic processes. Realgar was oxidized orders of magnitude slower than predicted from published mixed-flow reactor experiments, indicating that mass-transfer processes were rate-limiting. Most of the As released (〉97%) was sequestered by Fe(III)-(hydr)oxides. However, water-extractable As reached concentrations of 0.7-19 μmol As L(-1), exceeding the WHO drinking water limit by up to 145 times. Only a fraction (20-36%) of reduced S(-II to I) was sensitive to oxidation and was oxidized faster (t1/2 = 50-173 days) than organosulfur-coordinated As(III) and realgar, suggesting a rapid loss of reactive As-sequestering S species following a drop in the water table. Our results imply that wetlands like Gola di Lago can serve as long-term sources for As under prolonged oxidizing conditions. The maintenance of reducing conditions is thus regarded as the primary strategy in the management of this and other As-rich peatlands.
    Keywords: Arsenic -- Chemistry ; Arsenicals -- Chemistry ; Soil -- Chemistry ; Sulfides -- Chemistry ; Sulfur Compounds -- Chemistry
    ISSN: 0013936X
    E-ISSN: 1520-5851
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  • 2
    Language: English
    In: Geochimica et Cosmochimica Acta, 01 December 2017, Vol.218, pp.237-256
    Description: The formation of realgar (As S ) has recently been identified as a prominent As sequestration pathway in the naturally As-enriched wetland soil at the Mokrsko geochemical anomaly (Czech Republic). Here we used bulk soil and pore water analyses, synchrotron X-ray absorption spectroscopy, S isotopes, and DNA extractions to determine the distribution and speciation of As as a function of soil depth and metabolic properties of microbial communities in wetland soil profiles. Total solid-phase analyses showed that As was strongly correlated with organic matter, caused by a considerable As accumulation (up to 21 g kg ) in an organic-rich soil horizon artificially buried in 1980 at a depth of ∼80 cm. Extended X-ray absorption fine structure spectroscopy revealed that As in the buried organic horizon was predominantly present as realgar occurring as nanocrystallites (50–100 nm) in millimeter-scale deposits associated with particulate organic matter. The realgar was depleted in the S isotope by 9–12.5‰ relative to the aqueous sulfate supplied to the soil, implying its biologically induced formation. Analysis of the microbial communities by 16S rDNA sequencing showed that realgar deposits formed in strictly anaerobic organic-rich domains dominated by sulfate-reducing and fermenting metabolisms. In contrast, realgar deposits were not observed in similar domains with even small contributions of oxidative metabolisms. No association of realgar with specific microbial species was observed. Our investigation shows that strongly reducing microenvironments associated with buried organic matter are significant biogeochemical traps for As, with an estimated As accumulation rate of 61 g As m yr . Nevertheless the production of biologically induced realgar in these microenvironments is too slow to lower As groundwater concentrations at our field site (∼6790 mg L ). Our study demonstrates the intricate link between geochemistry and microbial community dynamics in wetland soils, and provides insights into the conditions necessary to promote As sulfide precipitation in engineered wetlands for the treatment of As-rich waters.
    Keywords: Arsenic Speciation ; Realgar ; Wetland Soil ; X-Ray Absorption Spectroscopy ; Sulfur Isotopes ; Microbial Communities ; Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 3
    Language: English
    In: Environmental Science and Technology, 01 April 2016, Vol.50(8)
    Description: Here, peatlands have received significant atmospheric inputs of As and S since the onset of the Industrial Revolution, but the effect of S deposition on the fate of As is largely unknown. It may encompass the formation of As sulfides and organosulfur-bound As, or the indirect stimulation of As biotransformation processes, which are presently not considered as important As immobilization pathways in wetlands. To investigate the immobilization mechanisms of anthropogenically derived As in peatlands subjected to long-term atmospheric pollution, we explored the solid-phase speciation of As, Fe, and S in English peat bogs by X-ray absorption spectroscopy. Additionally, we analyzed the speciation of As in pore- and streamwaters. Linear combination fits of extended X-ray absorption fine structure (EXAFS) data imply that 62–100% (average: 82%) of solid-phase As (Astot: 9–92 mg/kg) was present as organic As(V) and As(III). In agreement with appreciable concentrations of organoarsenicals in surface waters (pH: 4.0–4.4, Eh: 165–190 mV, average Astot: 1.5–129 μg/L), our findings reveal extensive biotransformation of atmospheric As and the enrichment of organoarsenicals in the peat, suggesting that the importance of organometal(loid)s in wetlands subjected to prolonged air pollution is higher than previously assumed.
    Keywords: Environmental Sciences ; Engineering ; Environmental Sciences
    ISSN: 0013-936X
    E-ISSN: 1520-5851
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  • 4
    Language: English
    In: Environmental science & technology, 2013, Vol.47(21), pp.12165-73
    Description: The speciation of As in wetlands is often controlled by natural organic matter (NOM), which can form strong complexes with Fe(III). Here, we elucidated the molecular-scale interaction of arsenite (As(III)) with Fe(III)-NOM complexes under reducing conditions. We reacted peat (40-250 μm size fraction, 1.0 g Fe/kg) with 0-15 g Fe/kg at pH 〈2, removed nonreacted Fe, and subsequently equilibrated the Fe(III) complexes formed with 900 mg As/kg peat at pH 7.0, 8.4, and 8.8. The solid-phase speciation of Fe and As was studied by electron paramagnetic resonance (Fe) and X-ray absorption spectroscopy (As, Fe). Our results show that the majority of Fe in the peat was present as mononuclear Fe(III) species (RFe-C = 2.82-2.88 Å), probably accompanied by small Fe(III) clusters of low nuclearity (RFe-Fe = 3.25-3.46 Å) at high pH and elevated Fe contents. The amount of As(III) retained by the original peat was 161 mg As/kg, which increased by up to 250% at pH 8.8 and an Fe loading of 7.3 g/kg. With increasing Fe content of peat, As(III) increasingly formed bidentate mononuclear (RAs-Fe = 2.88-2.94 Å) and monodentate binuclear (RAs-Fe = 3.35-3.41 Å) complexes with Fe, thus yielding direct evidence of ternary complex formation. The ternary complex formation went along with a ligand exchange reaction between As(III) and hydroxylic/phenolic groups of the peat (RAs-C = 2.70-2.77 Å). Our findings thus provide spectroscopic evidence for two yet unconfirmed As(III)-NOM interaction mechanisms, which may play a vital role in the cycling of As in sub- and anoxic NOM-rich environments such as peatlands, peaty sediments, swamps, or rice paddies.
    Keywords: Arsenites -- Metabolism ; Ferric Compounds -- Chemistry ; Soil -- Chemistry ; Soil Pollutants -- Metabolism
    ISSN: 0013936X
    E-ISSN: 1520-5851
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  • 5
    Language: English
    In: Nature Geoscience, 1/2012, Vol.5(1), pp.66-73
    Description: Wetlands cover more than 6% of the global ice-free land area, and have been recognized as important sinks for arsenic. Wetland soils and sediments are subject to frequent changes in redox conditions, driven by fluctuations in the water table and shifts in biological activity. Under oxic conditions, natural organic matter promotes arsenic release from metal-(hydr)oxides, thereby enhancing arsenic mobility. Under strongly reducing conditions, however, organic matter triggers the formation of arsenic-sequestering sulphides, leading to a reduction in arsenic mobility. Furthermore, the sorption of arsenic to natural organic matter is increasingly thought to suppress arsenic mobility, but the binding mechanisms have remained elusive. Here we use X-ray absorption spectroscopy to analyse the speciation of solid-phase arsenic in peat samples collected from a naturally arsenic-enriched peatland in Switzerland. We show that natural organic matter can completely sequester arsenic through the formation of covalent bonds between trivalent arsenic and organic sulphur groups, which have an average arsenic–sulphur bond distance of 2.26 Å. We suggest that by binding arsenic in this way, natural organic matter plays an active role in arsenic immobilization in sulphur-enriched, anoxic wetlands.
    Keywords: Geology;
    ISSN: 1752-0894
    E-ISSN: 1752-0908
    Source: Nature Publishing Group (via CrossRef)
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  • 6
    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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  • 7
    Language: English
    In: Environ. Sci. Technol, 18 November 2014, Vol.48((22) ; 11, 2014)
    Description: Iron-rich organic flocs are frequently observed in surface waters of wetlands and show a high affinity for trace metal(loid)s. To date, spectroscopic speciation analyses of Fe and trace elements in these mineral-organic matter (OM) associations are missing. In this study, we investigated the speciation and distribution of Fe and As in flocs collected from low-flow streams (pH 5.3-6.3) of the naturally As-enriched peatland Gola di Lago (Switzerland) using ... Mossbauer spectroscopy and synchrotron X-ray techniques. The flocs were rich in acid carbohydrates and contained up to 22.1 wt % Fe, 34.9 wt % C, and 2620 mg/kg As. Mossbauer analyses revealed small quantities (〈5%) of Fe(II) and Fe(III)-OM complexes and the predominance of ferrihydrite (..., 51-59%) and lepidocrocite (...-FeOOH, 34-46%). The latter was not observed by synchrotron X-ray diffraction, implying a coherent scattering domain size of 〈10 nm. Iron X-ray absorption spectroscopy (XAS) confirmed the Mossbauer results, and bulk As XAS indicated the prevalence of arsenate (71-84%) in the flocs. Shell-fit analyses showed that As was entirely sorbed to Fe(III)-(oxyhydr)oxides and that both arsenate and arsenite exclusively formed monodentate-binuclear ("bridging") complexes (... = 3.31-3.34 ...). Microfocused X-ray fluorescence spectrometry documented a strong correlation between As and Fe in the flocs. These analyses also revealed intense As hotspots coinciding with abundant freshwater green algae (Closterium spp.). Microfocused As X-ray absorption near-edge structure spectra collected at algae-specific points identified up to 29% As(III), which, in combination with ~5% As(III) detected at Fe-rich points, suggests As(V) bioreduction in the algae. Our findings imply that floc (bio)organics serve primarily as nucleation sites for the precipitation of nanocrystalline Fe(III)-(oxyhydr)oxides, rendering flocs effective sorbents for trace metal(loid)s. Thus, Fe-rich freshwater flocs likely play a pivotal role for the speciation and cycling of trace elements in wetlands. (ProQuest: ... denotes formulae/symbols omitted.)
    Keywords: X-Rays ; Absorption Spectroscopy ; Hot Spots ; Aquatic Plants ; Wetlands ; Diffraction ; Arsenates ; Iron ; Trace Elements ; Trace Elements in Precipitation ; Spectral Analysis ; Correlations ; Environmental Sciences ; Precipitation ; Spectroscopy ; Spectrometry ; Nucleation ; Wetlands ; Diffraction ; Trace Elements in River Water ; Trace Elements in Surface Waters ; Algae ; Peatlands ; Fluorescence ; Surface Water ; Arsenates ; Spectroscopy ; Streams ; Trace Elements ; Spectrometry ; Sorbents ; Absorption Spectroscopy ; Wetlands ; Carbohydrates ; Iron ; Ph ; Speciation ; X-Rays ; Arsenic ; Absorption ; Trace Elements ; Wetlands ; Spectroscopy ; Streams ; Iron ; Speciation ; X-Rays ; Arsenic ; Absorption ; Trace Elements ; Wetlands ; Spectroscopy ; Streams ; Iron ; Closterium ; Switzerland ; Swamps, Marshes (556.56) ; Water Pollution ; Water Resources and Supplies ; Data Acquisition ; Methods and Instruments;
    ISSN: 0013936X
    E-ISSN: 15205851
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  • 8
    Language: English
    In: Environ. Sci. Technol, 14 February 2014, Vol.48((1) ; 01, 2014)
    Description: Arsenic is a toxic trace element, which commonly occurs as contaminant in riverine floodplains and associated wetlands affected by mining and ore processing. In this study, we investigated the solid-phase speciation of As in river floodplain soils characterized by circumneutral pH (5.7-7.1) and As concentrations of up to 40.3 g/kg caused by former mining of arsenopyrite-rich ores. Soil samples collected in the floodplain of Ogosta River (Bulgaria) were size-fractionated and subsequently analyzed using a combination of X-ray fluorescence (XRF) spectrometry, powder X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and selective chemical extraction of poorly crystalline mineral phases. Arsenic and Fe were found to be spatially correlated and both elements were strongly enriched in the fine soil particle size fractions (〈2 mu m and 2-50 mu m). Between 14 and 82% of the total As was citrate-ascorbate extractable. Molar As/Fe ratios were as high as 0.34 in the bulk soil extracts and increased up to 0.48 in extracts of the fine particle size fractions. Arsenic K-edge XAS spectra showed the predominance of As(V) and were well fitted with a reference spectrum of As(V) adsorbed to ferrihydrite. Whereas no As(III) was detected, considerable amounts of As(-I) were present and identified as arsenopyrite originating from the mining waste. Iron K-edge XAS revealed that in addition to As(V) adsorbed to ferrihydrite, X-ray amorphous As(V)-rich hydrous ferric oxides ("As-HFO") with a reduced number of corner-sharing FeO sub(6) octahedra relative to ferrihydrite were the dominating secondary As species in the soils. The extremely high concentrations of As in the fine particle size fractions (up to 214 g/kg) and its association with poorly crystalline Fe(III) oxyhydroxides and As-HFO phases suggest a high As mobilization potential under both oxic and anoxic conditions, as well as a high bioaccessibility of As upon ingestion, dermal contact, or inhalation by humans or animals.
    Keywords: Particle Size ; Absorption Spectroscopy ; Arsenic ; Flood Plains ; Ores ; River Discharge ; Wetlands ; Diffraction ; Mining ; Ph of Soil ; Flood Plains ; Trace Elements in Soil ; Environmental Sciences ; Weathering ; Wetlands ; Diffraction ; Spectroscopy ; Soil Particles ; Trace Elements in River Water ; Spectrometry ; Particle Size ; Arsenic ; Fluorescence ; Ingestion ; Trace Elements ; Soil ; Absorption Spectroscopy ; Flood Plains ; Mining Wastes ; Weathering ; Wetlands ; Mining ; Chemical Extraction ; Iron ; Rivers ; Flood Plains ; X-Rays ; Arsenic ; Soil Contamination ; Water Analysis ; Particle Size ; Wetlands ; Mine Wastes ; Rivers ; Flood Plains ; X-Rays ; Arsenic ; Soil Contamination ; Water Analysis ; Particle Size ; Wetlands ; Mine Wastes ; Bulgaria ; Freshwater ; Toxicology & Environmental Safety ; Runoff (556.16) ; Freshwater Pollution ; Water Resources and Supplies ; Data Acquisition ; Mechanical and Natural Changes;
    ISSN: 0013936X
    E-ISSN: 15205851
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