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  • 1
    Language: English
    In: Analytical chemistry, 01 July 2010, Vol.82(13), pp.5534-40
    Description: A novel sequential extraction method for the speciation of As(III) and As(V) in oxic and anoxic mineral soils was developed and tested. The procedure consists of seven extraction steps targeting various As pools ranging from weakly adsorbed to well-crystalline species. Each step was specifically designed to preserve the As(III) and As(V) redox states, e.g., by complexation of As(III) with diethyldithiocarbamate or pyrrolidinedithiocarbamate, using mild reductive (NH(2)OH.HCl) or oxidative (hot HNO(3)) extractions, and complexing (Fe(3+) with Cl(-), acetate, and oxalate) or precipitating (S(2-) with Hg(2+)) matrix elements, which may cause As redox transformations. Using high-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) for the quantification of dissolved As(III) and As(V) in the extracts, the detection limit for each step was in the range of 1.0-75 ng As/g, depending on the extraction matrix. Thus, the procedure is also well-suited for As speciation in soils or sediments with low As concentrations, where analyses by X-ray absorption spectroscopy (XAS) may be difficult. The entire extraction sequence can be performed under normal atmosphere, which greatly simplifies sample handling. The proposed method was tested using model minerals spiked with As(III) or As(V), two strongly As-polluted soil previously characterized for As speciation by XAS, and three less-polluted soils.
    Keywords: Arsenates -- Analysis ; Arsenites -- Analysis ; Chromatography, High Pressure Liquid -- Methods ; Mass Spectrometry -- Methods ; Soil -- Analysis ; Soil Pollutants -- Analysis
    ISSN: 00032700
    E-ISSN: 1520-6882
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  • 2
    Language: English
    In: Geochimica et Cosmochimica Acta, Dec 15, 2013, Vol.123, p.385(18)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.gca.2013.07.017 Byline: Beate Fulda, Andreas Voegelin, Katrin Ehlert, Ruben Kretzschmar Abstract: In periodically flooded soils, interactions of Cu with biogenic sulfide formed during soil reduction lead to the precipitation of sparingly soluble Cu-sulfides. In contaminated soils, however, the amounts of Cu can exceed the amount of sulfate available for microbial reduction to sulfide. In laboratory batch experiments, we incubated a paddy soil spiked to [approximately equal to]4.4mmolkg.sup.-1 (280mgkg.sup.-1) Cu(II) to monitor temporal changes in the concentrations of dissolved Cu and the speciation of solid-phase Cu during 40days of soil reduction and 28days of reoxidation as a function of initially available reducible sulfate (0.06, 2.09 or 5.92mmolkg.sup.-1). Using Cu K-edge EXAFS spectroscopy, we found that a large fraction of Cu(II) became rapidly reduced to Cu(I) (23-39%) and Cu(0) (7-17%) before the onset of sulfate reduction. Combination with results from sequential Cu extraction and chromium reducible sulfur (CRS) data suggested that complexation of Cu(I) by reduced organic S groups (S.sub.org) may be an important process during this early stage. In sulfate-depleted soil, Cu(0) and Cu(I)-S.sub.org remained the dominant species over the entire reduction period, whereas in soils with sufficient sulfate, initially formed Cu(0) and (remaining) Cu(II) became transformed into Cu-sulfide during continuing sulfate reduction. The formation of Cu(0), Cu(I)-S.sub.org, and Cu-sulfide led to an effective decrease in dissolved Cu concentrations. Differences in Cu speciation at the end of soil reduction however affected the dynamics of Cu during reoxidation. Whereas Cu(0) was rapidly oxidized to Cu(II), more than half of the S-coordinated Cu fraction persisted over 14days of aeration. Our results show that precipitation of Cu(0) and complexation of Cu(I) by reduced organic S groups are important processes in periodically flooded soils if sulfide formation is limited by the amount of available sulfate or the duration of soil flooding. The speciation changes of Cu described in this study may also affect the speciation and solubility of other chalcophile metals in redox-dynamic wetland soils. Article History: Received 17 January 2013; Accepted 14 July 2013 Article Note: (miscellaneous) Associate editor: Jon Chorover
    Keywords: Rain ; Sulfides ; Sulfates
    ISSN: 0016-7037
    Source: Cengage Learning, Inc.
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  • 3
    Language: English
    In: Geochimica et Cosmochimica Acta, Sept 15, 2013, Vol.117, p.53(12)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.gca.2013.04.003 Byline: Evert J. Elzinga, Ruben Kretzschmar Abstract: We used in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy to study the impact of Cd(II) on the coordination of orthophosphate to the surface of hematite in the pH range 4.5-9.0, and at aqueous reactant concentrations below saturation with respect to Cd(II)-phosphate precipitates. In the absence of Cd(II), the orthophosphate surface speciation was pH dependent and dominated by two surface species assigned as monodentate monoprotonated complexes dominating at alkaline pH and additional formation of bidentate monoprotonated complexes at pH 〈8.0. Addition of aqueous Cd(II) raised the amount of orthophosphate adsorbed across the pH range, with promotive effects increasing with increasing pH. We observe the formation of two structurally distinct ternary Cd(II)-orthophosphate surface complexes which change proportion with pH. The IR spectra suggest stronger distortion of the orthophosphate tetrahedra involved in the ternary complexes formed at low pH relative to those formed at high pH, indicating differences in protonation state, surface coordination, and/or coordination to surface Cd(II) between the two ternary complexes. Over most of the pH range covered, the two ternary complexes are present simultaneously at the hematite surface, and co-exist with the two binary orthophosphate surface species, with the relative proportions of the various complexes varying with pH. The presence of Cd(II) thus not only raises the extent of orthophosphate adsorption but also the level of complexity of the orthophosphate surface speciation. These results imply that the simultaneous presence of divalent metals and orthophosphate significantly influences the solubility and speciation of these compounds in environmental settings even under conditions where precipitation of metal-phosphates does not occur. Article History: Received 19 September 2012; Accepted 4 April 2013 Article Note: (miscellaneous) Associate editor: Owen Duckworth
    Keywords: Hematite -- Chemical Properties ; Hematite -- Analysis ; Spectroscopy -- Chemical Properties ; Spectroscopy -- Analysis ; Phosphates -- Chemical Properties ; Phosphates -- Analysis ; Rain -- Chemical Properties ; Rain -- Analysis ; Adsorption -- Chemical Properties ; Adsorption -- Analysis
    ISSN: 0016-7037
    Source: Cengage Learning, Inc.
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  • 4
    Language: English
    In: Geochimica et Cosmochimica Acta, 15 September 2013, Vol.117, pp.53-64
    Description: We used attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy to study the impact of Cd(II) on the coordination of orthophosphate to the surface of hematite in the pH range 4.5–9.0, and at aqueous reactant concentrations below saturation with respect to Cd(II)–phosphate precipitates. In the absence of Cd(II), the orthophosphate surface speciation was pH dependent and dominated by two surface species assigned as monodentate monoprotonated complexes dominating at alkaline pH and additional formation of bidentate monoprotonated complexes at pH 〈8.0. Addition of aqueous Cd(II) raised the amount of orthophosphate adsorbed across the pH range, with promotive effects increasing with increasing pH. We observe the formation of two structurally distinct ternary Cd(II)–orthophosphate surface complexes which change proportion with pH. The IR spectra suggest stronger distortion of the orthophosphate tetrahedra involved in the ternary complexes formed at low pH relative to those formed at high pH, indicating differences in protonation state, surface coordination, and/or coordination to surface Cd(II) between the two ternary complexes. Over most of the pH range covered, the two ternary complexes are present simultaneously at the hematite surface, and co-exist with the two binary orthophosphate surface species, with the relative proportions of the various complexes varying with pH. The presence of Cd(II) thus not only raises the extent of orthophosphate adsorption but also the level of complexity of the orthophosphate surface speciation. These results imply that the simultaneous presence of divalent metals and orthophosphate significantly influences the solubility and speciation of these compounds in environmental settings even under conditions where precipitation of metal–phosphates does not occur.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 5
    Language: English
    In: Geochimica et cosmochimica acta, 2013, Vol.117, pp.53-64
    Description: We used in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy to study the impact of Cd(II) on the coordination of orthophosphate to the surface of hematite in the pH range 4.5–9.0, and at aqueous reactant concentrations below saturation with respect to Cd(II)–phosphate precipitates. In the absence of Cd(II), the orthophosphate surface speciation was pH dependent and dominated by two surface species assigned as monodentate monoprotonated complexes dominating at alkaline pH and additional formation of bidentate monoprotonated complexes at pH 〈8.0. Addition of aqueous Cd(II) raised the amount of orthophosphate adsorbed across the pH range, with promotive effects increasing with increasing pH. We observe the formation of two structurally distinct ternary Cd(II)–orthophosphate surface complexes which change proportion with pH. The IR spectra suggest stronger distortion of the orthophosphate tetrahedra involved in the ternary complexes formed at low pH relative to those formed at high pH, indicating differences in protonation state, surface coordination, and/or coordination to surface Cd(II) between the two ternary complexes. Over most of the pH range covered, the two ternary complexes are present simultaneously at the hematite surface, and co-exist with the two binary orthophosphate surface species, with the relative proportions of the various complexes varying with pH. The presence of Cd(II) thus not only raises the extent of orthophosphate adsorption but also the level of complexity of the orthophosphate surface speciation. These results imply that the simultaneous presence of divalent metals and orthophosphate significantly influences the solubility and speciation of these compounds in environmental settings even under conditions where precipitation of metal–phosphates does not occur. ; p. 53-64.
    Keywords: Orthophosphates ; Hematite ; Cadmium ; Adsorption ; Solubility ; Spectroscopy ; Reflectance ; Ph
    ISSN: 0016-7037
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 6
    Language: English
    In: Geochimica et Cosmochimica Acta, Feb 15, 2013, Vol.103, p.316(17)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.gca.2012.10.053 Byline: Anke F. Hofacker (a), Andreas Voegelin (b), Ralf Kaegi (b), Frank-Andreas Weber (c), Ruben Kretzschmar (a) Abstract: Riparian floodplains in temperate regions are affected by pronounced seasonal variations in soil and water temperature. This affects the rates and interplay of microbial and abiotic geochemical processes that control the fate of metals in contaminated floodplain soils, including potential release into surface and groundwater during periodic flooding. Here, we investigated how temperature affects chalcophile trace metal contaminants (Cu, Cd, Pb) upon flooding of a riparian soil contaminated by past mining activities. In soil microcosms incubated at 23, 14, and 5[degrees]C, the reductive dissolution of Mn(III,IV) and Fe(III) (oxyhydr)oxides and the release of dissolved Mn.sup.2+ and Fe.sup.2+ were significantly slower and less intense at the lower temperatures, which was reflected in a decrease of trace metal mobilization via the dissolution of metal oxide sorbents and cation competition for sorption sites. The onset of sulfate reduction was significantly delayed at lower temperatures and the apparent rate of sulfate reduction was decreased, especially at 5[degrees]C. This resulted in elevated high dissolved Cu, Cd, and Pb concentrations over weeks of flooding at 5[degrees]C, whereas colloidal metal sulfide formation dominated Cu, Cd, and Pb pore water dynamics at higher temperatures of 14 and 23[degrees]C due to fast sulfate reduction. Cu K-edge X-ray absorption fine structure spectroscopy revealed metallic Cu(0) as the main colloidal Cu species prior to sulfate reduction at all three temperatures. Analytical electron microscopy showed that Cu(0) particles were associated with suspended bacteria, suggesting biomineralization of Cu(0). Upon onset of sulfate reduction, metallic Cu particles were transformed into Cu.sub.x S with incorporation of smaller amounts of Cd and Pb. Concomitantly, freely dispersed mixed Cu-Cd-Pb sulfide nanoparticles precipitated in the pore water. Other metals with higher metal sulfide solubility products did not react with the limited amounts of biogenic sulfide. The median size of the mixed metal sulfide nanoparticles increased from 21nm at 23[degrees]C to 70nm at 5[degrees]C. During [approximately equal to]30days of soil flooding at 23 and 14[degrees]C, Cu speciation in the soil matrix changed from Cu(II) bound to soil organic matter in the oxic soil to 66% Cu.sub.x S, with intermittent formation of about 14% metallic Cu(0). In contrast, at 5[degrees]C, sulfate reduction and formation of Cu(0) were strongly retarded. After [approximately equal to]30days of flooding at 23 and 14[degrees]C, nearly all Cd and about 25% of total Pb in the soil, were precipitated in mixed metal sulfides. Our results demonstrate that temperature controls trace metal dynamics during soil flooding via its influence on microbial reduction of terminal electron acceptors. Even at low temperatures, soil flooding may trigger the release of chalcophile metals from contaminated floodplain soils by sorbent reduction, competitive sorption, and formation of nanoparticulate metal-bearing colloids. Author Affiliation: (a) Soil Chemistry Group, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, CHN, CH-8092 Zurich, Switzerland (b) Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dubendorf, Switzerland (c) IWW Rheinisch-Westfalisches Institut fur Wasser Beratungs- und Entwicklungsgesellschaft mbH, Regionalstandort Rhein-Main, D-64584 Biebesheim, Germany Article History: Received 13 June 2012; Accepted 30 October 2012 Article Note: (miscellaneous) Associate editor: Jon Chorover
    Keywords: Floods ; Biogeochemistry ; Oxides ; Groundwater ; Sulfates ; Bacteria ; Soil Chemistry ; Nanoparticles ; Sulfides ; Soil Carbon
    ISSN: 0016-7037
    Source: Cengage Learning, Inc.
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  • 7
    Language: English
    In: Journal of Colloid And Interface Science, 01 July 2012, Vol.377(1), pp.313-321
    Description: ► Arsenate and carbonate form bidentate inner-sphere surface complexes on hematite surfaces. ► Highly elevated CO partial pressures lead to decreased arsenic sorption. ► Arsenite sorption is affected by carbonate more strongly than arsenate sorption. The competitive sorption of carbonate and arsenic to hematite was investigated in closed-system batch experiments. The experimental conditions covered a pH range of 3–7, arsenate concentrations of 3–300 μM, and arsenite concentrations of 3–200 μM. Dissolved carbonate concentrations were varied by fixing the CO partial pressure at 0.39 (atmospheric), 10, or 100 hPa. Sorption data were modeled with a one-site three plane model considering carbonate and arsenate surface complexes derived from ATR-FTIR spectroscopy analyses. Macroscopic sorption data revealed that in the pH range 3–7, carbonate was a weak competitor for both arsenite and arsenate. The competitive effect of carbonate increased with increasing CO partial pressure and decreasing arsenic concentrations. For arsenate, sorption was reduced by carbonate only at slightly acidic to neutral pH values, whereas arsenite sorption was decreased across the entire pH range. ATR-FTIR spectra indicated the predominant formation of bidentate binuclear inner-sphere surface complexes for both sorbed arsenate and sorbed carbonate. Surface complexation modeling based on the dominant arsenate and carbonate surface complexes indicated by ATR-FTIR and assuming inner-sphere complexation of arsenite successfully described the macroscopic sorption data. Our results imply that in natural arsenic-contaminated systems where iron oxide minerals are important sorbents, dissolved carbonate may increase aqueous arsenite concentrations, but will affect dissolved arsenate concentrations only at neutral to alkaline pH and at very high CO partial pressures.
    Keywords: Arsenic ; Carbonate ; Competitive Sorption ; Surface Complexation ; Atr-Ftir Spectroscopy ; Iron Oxide ; Hematite ; Arsenate ; Arsenite ; Carbon Dioxide ; Engineering ; Chemistry
    ISSN: 0021-9797
    E-ISSN: 1095-7103
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  • 8
    Language: English
    In: Science of the Total Environment, 01 December 2016, Vol.572, pp.742-754
    Description: Riverine floodplains downstream of active or former metal sulfide mines are in many cases contaminated with trace metals and metalloids, including arsenic (As). Since decontamination of such floodplains on a large scale is unfeasible, management of contaminated land must focus on providing land use guidelines or even restrictions. This should be based on knowledge about how contaminants enter the food chain. For As, uptake by plants may be an important pathway, but the As soil-to-plant transfer under field conditions is poorly understood. Here, we investigated the soil-to-shoot transfer of As and phosphorus (P) in wild populations of herbaceous species growing along an As contamination gradient across an extensive pasture in the mining-impacted Ogosta River floodplain. The As concentrations in the shoots of and reflected the soil contamination gradient. However, the soil-to-shoot transfer factors (TF) were fairly low, with values mostly below 0.07 (TF = As /As ). We found no evidence for interference of As with P uptake by plants, despite extremely high molar As:P ratios (up to 2.6) in Olsen soil extracts of the most contaminated topsoils (0–20 cm). Considering the restricted soil-to-shoot transfer, we estimated that for grazing livestock As intake via soil ingestion is likely more important than intake via pasture herbage.
    Keywords: Pollution ; Plant Uptake ; Holcus Lanatus ; Trifolium Repens ; Apera Spica-Venti ; Food Chain ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 9
    Language: English
    In: Geochimica et Cosmochimica Acta, 15 December 2013, Vol.123, pp.385-402
    Description: In periodically flooded soils, interactions of Cu with biogenic sulfide formed during soil reduction lead to the precipitation of sparingly soluble Cu-sulfides. In contaminated soils, however, the amounts of Cu can exceed the amount of sulfate available for microbial reduction to sulfide. In laboratory batch experiments, we incubated a paddy soil spiked to ∼4.4 mmol kg (280 mg kg ) Cu(II) to monitor temporal changes in the concentrations of dissolved Cu and the speciation of solid-phase Cu during 40 days of soil reduction and 28 days of reoxidation as a function of initially available reducible sulfate (0.06, 2.09 or 5.92 mmol kg ). Using Cu -edge EXAFS spectroscopy, we found that a large fraction of Cu(II) became rapidly reduced to Cu(I) (23–39%) and Cu(0) (7–17%) before the onset of sulfate reduction. Combination with results from sequential Cu extraction and chromium reducible sulfur (CRS) data suggested that complexation of Cu(I) by reduced organic S groups (S ) may be an important process during this early stage. In sulfate-depleted soil, Cu(0) and Cu(I)–S remained the dominant species over the entire reduction period, whereas in soils with sufficient sulfate, initially formed Cu(0) and (remaining) Cu(II) became transformed into Cu-sulfide during continuing sulfate reduction. The formation of Cu(0), Cu(I)–S , and Cu-sulfide led to an effective decrease in dissolved Cu concentrations. Differences in Cu speciation at the end of soil reduction however affected the dynamics of Cu during reoxidation. Whereas Cu(0) was rapidly oxidized to Cu(II), more than half of the S-coordinated Cu fraction persisted over 14 days of aeration. Our results show that precipitation of Cu(0) and complexation of Cu(I) by reduced organic S groups are important processes in periodically flooded soils if sulfide formation is limited by the amount of available sulfate or the duration of soil flooding. The speciation changes of Cu described in this study may also affect the speciation and solubility of other chalcophile metals in redox-dynamic wetland soils.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 10
    Language: English
    In: Geochimica et cosmochimica acta, 2013, Vol.123, pp.385-402
    Description: In periodically flooded soils, interactions of Cu with biogenic sulfide formed during soil reduction lead to the precipitation of sparingly soluble Cu-sulfides. In contaminated soils, however, the amounts of Cu can exceed the amount of sulfate available for microbial reduction to sulfide. In laboratory batch experiments, we incubated a paddy soil spiked to ∼4.4mmolkg⁻¹ (280mgkg⁻¹) Cu(II) to monitor temporal changes in the concentrations of dissolved Cu and the speciation of solid-phase Cu during 40days of soil reduction and 28days of reoxidation as a function of initially available reducible sulfate (0.06, 2.09 or 5.92mmolkg⁻¹). Using Cu K-edge EXAFS spectroscopy, we found that a large fraction of Cu(II) became rapidly reduced to Cu(I) (23–39%) and Cu(0) (7–17%) before the onset of sulfate reduction. Combination with results from sequential Cu extraction and chromium reducible sulfur (CRS) data suggested that complexation of Cu(I) by reduced organic S groups (Sₒᵣg) may be an important process during this early stage. In sulfate-depleted soil, Cu(0) and Cu(I)–Sₒᵣg remained the dominant species over the entire reduction period, whereas in soils with sufficient sulfate, initially formed Cu(0) and (remaining) Cu(II) became transformed into Cu-sulfide during continuing sulfate reduction. The formation of Cu(0), Cu(I)–Sₒᵣg, and Cu-sulfide led to an effective decrease in dissolved Cu concentrations. Differences in Cu speciation at the end of soil reduction however affected the dynamics of Cu during reoxidation. Whereas Cu(0) was rapidly oxidized to Cu(II), more than half of the S-coordinated Cu fraction persisted over 14days of aeration. Our results show that precipitation of Cu(0) and complexation of Cu(I) by reduced organic S groups are important processes in periodically flooded soils if sulfide formation is limited by the amount of available sulfate or the duration of soil flooding. The speciation changes of Cu described in this study may also affect the speciation and solubility of other chalcophile metals in redox-dynamic wetland soils. ; p. 385-402.
    Keywords: Wetland Soils ; Paddy Soils ; Copper ; Aeration ; Sulfur ; Solubility ; Spectroscopy ; Polluted Soils ; Chromium ; Temporal Variation
    ISSN: 0016-7037
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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