Publications by authors named "Matthew Ginder-Vogel"

42 Publications

Investigation of ICP-MS/MS for total sulfur quantification in freshwater dissolved organic matter.

J Environ Qual 2021 Sep 24. Epub 2021 Sep 24.

Department of Civil and Environmental Engineering, Environmental Chemistry and Technology Program, University of Wisconsin - Madison, 660 N Park St., Madison, Wisconsin, 53705, United States.

Sulfur-containing functional groups in dissolved organic matter (DOM) interact with trace metals, which in turn affects trace metal mobility and bioavailability in aquatic environments. Typical methods for identification and quantification of sulfur in DOM are costly, complex, and time intensive. Triple quadrupole inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) is capable of part per billion level sulfur quantification in environmental samples and is a more accessible analytical technique compared to other available methods. To date, this study is the first published investigation of ICP-MS/MS for the direct quantification of sulfur in freshwater dissolved organic matter. Sulfur ( S) detection occurs at a mass-to-charge ratio of 48 as S O after removal of interferences and reaction with oxygen gas. We compare three commonly used dissolved organic matter preparation methods to assess variability among replicate samples. Preparation of freshwater DOM samples by solid phase extraction followed by evaporation overnight and dissolution in 2% nitric acid results in the most accurate quantification of sulfur. Analysis of sulfur in Suwannee River Fulvic Acid standard serves as method validation, measuring a carbon normalized sulfur concentration that is approximately 20% higher than previously reported methods. We apply the ICP-MS/MS analysis method to determine sulfur concentrations in DOM from nine lakes in the Northern Midwest. Carbon normalized sulfur concentrations in the selected lakes are in general agreement with previously reported percentages of sulfur-containing formulas in DOM found by Fourier transform-ion cyclotron resonance-mass spectroscopy. This article is protected by copyright. All rights reserved.
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http://dx.doi.org/10.1002/jeq2.20291DOI Listing
September 2021

Selective Reactivity and Oxidation of Dissolved Organic Matter by Manganese Oxides.

Environ Sci Technol 2021 09 25;55(17):12084-12094. Epub 2021 Aug 25.

Environmental Chemistry and Technology Program, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States.

Dissolved organic matter (DOM) varies widely across natural and engineered systems, but little is known about the influence of DOM composition on its reactivity with manganese oxides. Here, we investigate bulk and molecular transformations of 30 diverse DOM samples after reaction with acid birnessite (MnO), a strong oxidant that may react with DOM in Mn-rich environments or engineered treatment systems. The reaction of DOM with acid birnessite reduces Mn and forms DOM that is generally more aliphatic and lower in apparent molecular weight. However, the extent of reaction depends on the water type (e.g., wastewater, rivers) and highly aromatic DOM undergoes greater changes. Despite the variability in reactivity due to the DOM composition, aqueous products attributable to the oxidation of phenolic precursors are identified in waters analyzed by high-resolution mass spectrometry. The number of matched product formulas correlates significantly with indicators of DOM aromaticity, such as double-bond equivalents ( = 2.43 × 10). At the molecular level, highly aromatic, lignin-like carbon reacts selectively with acid birnessite in all samples despite the variability in initial DOM composition, resulting in the formation of a wide range of aqueous products. These findings demonstrate that DOM oxidation occurs in diverse waters but also suggest that reactivity with acid birnessite and the composition of the resulting aqueous DOM pool are composition-dependent and linked to the DOM source and initial aromaticity.
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http://dx.doi.org/10.1021/acs.est.1c03972DOI Listing
September 2021

Simultaneous Kinetics of Selenite Oxidation and Sorption on δ-MnO in Stirred-Flow Reactors.

Int J Environ Res Public Health 2021 03 12;18(6). Epub 2021 Mar 12.

College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China.

Selenium (Se) is an essential and crucial micronutrient for humans and animals, but excessive Se brings negativity and toxicity. The adsorption and oxidation of Se(IV) on Mn-oxide surfaces are important processes for understanding the geochemical fate of Se and developing engineered remediation strategies. In this study, the characterization of simultaneous adsorption, oxidation, and desorption of Se(IV) on δ-MnO mineral was carried out using stirred-flow reactors. About 9.5% to 25.3% of Se(IV) was oxidized to Se(VI) in the stirred-flow system in a continuous and slow process, with the kinetic rate constant k of 0.032 h, which was significantly higher than the apparent rate constant of 0.0014 h obtained by the quasi-level kinetic fit of the batch method. The oxidation reaction was driven by proton concentration, and its rate also depended on the Se(IV) influent concentration, flow rate, and δ-MnO dosage. During the reaction of Se(IV) and δ-MnO, Mn(II) was produced and adsorbed strongly on Mn oxide surfaces, which was evidenced by the total reflectance Fourier transform infrared (ATR-FTIR) results. The X-ray photoelectron spectroscopy (XPS) data indicated that the reaction of Se(VI) on δ-MnO produced Mn(III) as the main product. These results contribute to a deeper understanding of the interface chemical process of Se(IV) with δ-MnO in the environment.
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http://dx.doi.org/10.3390/ijerph18062902DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7998768PMC
March 2021

Identifying the mechanisms of cation inhibition of phenol oxidation by acid birnessite.

J Environ Qual 2020 Nov 22;49(6):1644-1654. Epub 2020 Sep 22.

Environmental Chemistry and Technology Program, Univ. of Wisconsin-Madison, 660 N. Park St., Madison, WI, 53706, USA.

Many phenolic compounds found as contaminants in natural waters are susceptible to oxidation by manganese oxides. However, there is often variability between oxidation rates reported in pristine matrices and studies using more environmentally relevant conditions. For example, the presence of cations generally results in slower phenolic oxidation rates. However, the underlying mechanism of cation interference is not well understood. In this study, cation co-solutes inhibit the transformation of four target phenols (bisphenol A, estrone, p-cresol, and triclosan) by acid birnessite. Oxidation rates for these compounds by acid birnessite follow the same trend (Na > K > Mg > Ca) when cations are present as co-solutes. We further demonstrate that the same trend applies to these cations when they are absent from solution but pre-exchanged with the mineral. We analyze valence state, surface area, crystallinity, and zeta potential to characterize changes in oxide structure. The findings of this study show that pre-exchanged cations have a large effect on birnessite reactivity even in the absence of cation co-solutes, indicating that the inhibition of phenolic compound oxidation is not due to competition for surface sites, as previously suggested. Instead, the reaction inhibition is attributed to changes in aggregation and the mineral microstructure.
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http://dx.doi.org/10.1002/jeq2.20144DOI Listing
November 2020

Neutralization of high pH and alkalinity effluent from recycled concrete aggregate by common subgrade soil.

J Environ Qual 2020 Jan 17;49(1):172-183. Epub 2020 Feb 17.

Dep. of Civil and Environmental Engineering, Geological Engineering and Environmental Chemistry and Technology Programs, Univ. of Wisconsin-Madison, Madison, WI, 53706, USA.

Use of recycled concrete aggregate (RCA) as highway basecourse material conserves virgin aggregate, reduces energy consumption and CO emissions, and may also decrease costs during construction. However, concerns remain over possible negative environmental impacts associated with high pH (>11) effluent from RCA in contact with water. This study examines the reactive transport of high-pH and high-alkalinity water, modeled on RCA leachate, through model subgrade soils. By developing an understanding of the reactions controlling effluent neutralization, this study aims to quantify the change in pH from the discharge site through surrounding subgrade soils. Four types of subgrade soils with a range of mineral composition, Atterberg limits, and cation exchange capacities (CECs) are examined. They include a clayey sand (SC10), low-plasticity clays (M14, SC25), and a high-plasticity clay (CH38). Batch reaction experiments are used to develop kinetic parameters describing the neutralization of high-pH and -alkalinity leachate by clay minerals through mineral dissolution and reprecipitation. Given this information, a reactive transport model incorporating advection, diffusion, and reaction is used to model the change in pH as a function of distance traveled through model subgrade soils and is applied to laboratory-scale column experiments. The rate at which the high pH front travels is directly related to a soil's clay mineral content. Soils with high CECs effectively delay the propagation of hydroxide front by the dissolution of clay minerals. This study demonstrates that common subgrade soils with moderate clay content will effectively neutralize high pH leachate initially produced by RCA.
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http://dx.doi.org/10.1002/jeq2.20008DOI Listing
January 2020

Recycled concrete aggregate in base course applications: Review of field and laboratory investigations of leachate pH.

J Hazard Mater 2020 03 2;385:121562. Epub 2019 Nov 2.

Department of Civil and Environmental Engineering, Geological Engineering Program, University of Wisconsin - Madison, United States; Department of Civil and Environmental Engineering, Environmental Chemistry and Technology Program, University of Wisconsin-Madison, United States. Electronic address:

The prevalence of construction and demolition (C&D) waste and the concurrent demand for construction aggregate presents the opportunity to recycle C&D waste materials as substitutes for virgin aggregate. Commonly, recycled concrete aggregate (RCA) is used as base course in pavement construction. Environmentally responsible applications of RCA must consider the high pH leachate and trace element leaching risks reported in the literature. This review presents the methodology, results, and limitations of existing laboratory and field investigations of RCA leachate chemistry. Long-term highway field studies of RCA leachate illustrate that an initially high leachate pH approaches neutral within approximately one to two years of construction. Conversely, laboratory investigations of RCA leachate pH using batch reactor leaching tests and column leaching tests measure consistently high leachate pH (pH > 10). The discrepancies between field and laboratory measurements of RCA leachate pH suggest that the current laboratory methodology inadequately describes leachate conditions in the field. The authors recommend that future laboratory investigations consider intermittent wetting and drying cycles, eliminate particle abrasion, employ relevant contact times, and consider additional environmental processes that reduce leachate pH such as soil acidity and carbonation.
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http://dx.doi.org/10.1016/j.jhazmat.2019.121562DOI Listing
March 2020

Effects of Co(II) ion exchange, Ni(II)- and V(V)-doping on the transformation behaviors of Cr(III) on hexagonal turbostratic birnessite-water interfaces.

Environ Pollut 2020 Jan 24;256:113462. Epub 2019 Oct 24.

Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River) Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China. Electronic address:

Natural birnessite-like minerals are commonly enriched in various transitional metals (TMs), which greatly modify the mineral structure and properties. However few studies are yet conducted systematically on the effects of TM doping on birnessite reactivity towards Cr(III) oxidation. In the present study, the transformation behaviors of Cr(III) on Co-, Ni-, V-containing birnessites were investigated. Co and Ni doping generally decrease the mineral crystalline sizes and hydrodynamic sizes (D) while V-doping greatly decreases the crystalline sizes but not the D, owing to particle aggregation. Co and Ni firstly decrease and then increase the mineral zeta potentials (ζ) at pH4 while V decreases ζ. Electrochemical specific capacitances for Co-containing birnessites are gradually reduced, while those for Ni-doped birnessites are slightly reduced and for V-doped birnessites increased, which have a positively linear relationship with the amounts of Cr(III) oxidized by these samples. Cr(III) removal efficiencies from solution by these Co-, Ni- and V-containing birnessites are 26-51%, ∼62-72% and ∼96-100%, respectively, compared to ∼92% by pure birnessite. Cr(III) oxidation kinetics analysis demonstrates the gradual decrease of Mn(IV) and concurrent increase of Mn(III) and the adsorption of mainly Cr(III) on mineral surfaces. A negatively linear relationship exists between birnessite lateral sizes and the proportions of Mn(IV/III) consumed to oxidize Cr(III). Apparent initial Cr(III) oxidation rate (k) for Co-containing birnessites are greatly reduced, while those for Ni-doped samples moderately decreased and for V-doped samples first increased and then decreased. A positively or negatively linear relationship exists between k or the amount of Mn(II) released and the mineral Mn(IV) content respectively. Cr(III) oxidation probably initiates from layer edge sites of Ni-doped birnessites but the vacancies of Co- and V-containing birnessites. These results provide insights into the reaction mechanisms of Cr(III) with natural birnessite-like minerals.
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http://dx.doi.org/10.1016/j.envpol.2019.113462DOI Listing
January 2020

Impact of bisphenol A influent concentration and reaction time on MnO transformation in a stirred flow reactor.

Environ Sci Process Impacts 2019 Jan;21(1):19-27

Environmental Chemistry and Technology Program, University of Wisconsin-Madison, 660 N. Park St., Madison, WI 53706, USA.

Bisphenol A (BPA) is an endocrine disrupting compound commonly found in natural waters at concentrations that are considered harmful for aquatic life. Manganese(iii/iv) oxides are strong oxidants capable of oxidizing organic and inorganic contaminants, including BPA. Here we use δ-MnO2 in stirred flow reactors to determine if higher influent BPA concentrations, or introduction rates, lead to increased polymer production. A major BPA oxidation product, 4-hydroxycumyl alcohol (HCA), is formed through radical coupling, and was therefore used as a metric for polymer production in this study. The influent BPA concentration in stirred flow reactors did not affect HCA yield, suggesting that polymeric production is not strongly dependent on influent concentrations. However, changes in influent BPA concentration affected BPA oxidation rates and the rate of δ-MnO2 reduction. Lower aqueous Mn(ii) production was observed in reactors at higher BPA introduction rates, suggesting that single-electron transfer and polymer production are favored under these conditions. However, an examination of Mn(ii) sorption during these reactions indicated that the length of the reaction, rather than BPA introduction rate, caused enhanced aqueous Mn(ii) production in reactors with low introduction rates and longer reaction times due to increased opportunity for disproportionation and comproportionation. This study demonstrates the importance of investigating both the organic and inorganic reactants in the aqueous and solid phases in this complex reaction.
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http://dx.doi.org/10.1039/c8em00451jDOI Listing
January 2019

Stability of Ferrihydrite-Humic Acid Coprecipitates under Iron-Reducing Conditions.

Environ Sci Technol 2018 11 8;52(22):13174-13183. Epub 2018 Nov 8.

Department of Geoscience , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States.

Recent studies have suggested the potential for release of iron (hydr)oxide-bound organic carbon (OC) during dissimilatory iron oxide reduction (DIR). However, the stability of iron (hydr)oxide-bound OC in the presence of a natural microbial consortium capable of driving both OC metabolism and DIR has not been resolved. Pure ferrihydrite (Fhy) and Fhy-humic acid coprecipitates (Fhy-HA) were inoculated with a small quantity of freshwater sediment and incubated under anoxic conditions in the presence and absence of H or glucose as electron donors for DIR. H promoted DIR led to release of ca. 1 mM dissolved organic carbon (DOC). However, comparable amounts of DOC were released from both pure Fhy and Fhy-HA, similar to DOC levels in mineral-free, inoculum-only controls. These results suggest that the observed DOC release during H-promoted DIR originated from OC contained in the inoculum as opposed to the much larger pool (ca. 38 mM) of OC in the Fhy-HA. Thus, DIR preferentially released sorbed OC with low aromaticity (inoculum OC) versus highly aromatic OC (HA) coprecipitated with iron oxide. Our findings provide new insight into the extent and mechanisms by which DIR is likely to influence aqueous/solid-phase OC partitioning in anoxic soils and sediments.
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http://dx.doi.org/10.1021/acs.est.8b03615DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8381759PMC
November 2018

Use of Routine Soil Tests to Estimate Pb Bioaccessibility.

Environ Sci Technol 2018 11 24;52(21):12556-12562. Epub 2018 Oct 24.

Department of Soil Science , University of Wisconsin , 1525 Observatory Drive , Madison , Wisconsin 53706 , United States.

Soil lead (Pb) hazard level is contingent on bioavailability, but existing assays that estimate Pb bioavailability for human health risks are too expensive or otherwise inaccessible to many people that are impacted by Pb-contaminated soil. This study investigated the use of routine soil nutrient tests to estimate soil-Pb bioaccessibility as a surrogate measure of Pb bioavailability. A silt loam soil was spiked to a target concentration of 2000 mg Pb kg with Pb(NO) and amended with HPO (varying P-to-Pb molar ratios) and KCl (Cl-to-P molar ratio of 2:5) to generate soils with similar total Pb concentrations but a range of Pb bioavailability (and bioaccessibility). Soils were extracted using Mehlich 3, Mehlich 1, Bray P1, Olsen, and  micronutrient (DTPA) methods, and the results were compared to U.S. Environmental Protection Agency method 1340 data as well as to extended X-ray absorption fine structure (EXAFS) spectroscopy. The Mehlich 3 and method 1340 treatment effect ratios were well-correlated ( r = 0.88, p ≤ 0.05), whereas Bray P1, DTPA, and Olsen results were more reflective of EXAFS data. Preliminary animal-feeding trials suggest that the Mehlich 3 is as effective as method 1340 at predicting the impact of P treatment on Pb relative bioavailability; however, both methods over-estimated the Pb hazard to mice in P-amended soil. Other routine soil tests that have heightened sensitivity to P amendment (e.g., Bray P1) may be promising candidates for Pb bioaccessibility assessment.
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http://dx.doi.org/10.1021/acs.est.8b02633DOI Listing
November 2018

Dual Role of Humic Substances As Electron Donor and Shuttle for Dissimilatory Iron Reduction.

Environ Sci Technol 2018 05 24;52(10):5691-5699. Epub 2018 Apr 24.

Department of Geoscience , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States.

Dissimilatory iron-reducing bacteria (DIRB) are known to use humic substances (HS) as electron shuttles for dissimilatory iron reduction (DIR) by transferring electrons to HS-quinone moieties, which in turn rapidly reduce Fe(III) oxides. However, the potential for HS to serve as a source of organic carbon (OC) that can donate electrons for DIR is unknown. We studied whether humic acids (HA) and humins (HM) recovered from peat soil by sodium pyrophosphate extraction could serve as both electron shuttles and electron donors for DIR by freshwater sediment microorganisms. Both HA and HM served as electron shuttles in cultures amended with glucose. However, only HA served as an electron donor for DIR. Metagenomes from HA-containing cultures had an overrepresentation of genes involved in polysaccharide and to a lesser extent aromatic compound degradation, suggesting complex OC metabolism. Genomic searches for the porin-cytochrome complex involved in DIR resulted in matches to Ignavibacterium/Melioribacter, DIRB capable of polymeric OC metabolism. These results indicate that such taxa may have played a role in both DIR and decomposition of complex OC. Our results suggest that decomposition of HS coupled to DIR and other anaerobic pathways could play an important role in soil and sediment OC metabolism.
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http://dx.doi.org/10.1021/acs.est.7b06574DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6211804PMC
May 2018

Coordination geometry of Zn on hexagonal turbostratic birnessites with different Mn average oxidation states and its stability under acid dissolution.

J Environ Sci (China) 2018 Mar 7;65:282-292. Epub 2017 Mar 7.

Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River) Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China. Electronic address:

Hexagonal turbostratic birnessite, with the characteristics of high contents of vacancies, varying amounts of structural and adsorbed Mn, and small particle size, undergoes strong adsorption reactions with trace metal (TM) contaminants. While the interactions of TM, i.e., Zn, with birnessite are well understood, the effect of birnessite structural characteristics on the coordination and stability of Zn on the mineral surfaces under proton attack is as yet unclear. In the present study, the effects of a series of synthesized hexagonal turbostratic birnessites with different Mn average oxide states (AOSs) on the coordination geometry of adsorbed Zn and its stability under acidic conditions were investigated. With decreasing Mn AOS, birnessite exhibits smaller particle sizes and thus larger specific surface area, higher amounts of layer Mn and thus longer distances for the first MnO and MnMn shells, but a low quantity of available vacancies and thus low adsorption capacity for Zn. Zn K-edge EXAFS spectroscopy demonstrates that birnessite with low Mn AOS has smaller adsorption capacity but more tetrahedral Zn (Zn) complexes on vacancies than octahedral (Zn) complexes, and Zn is more unstable under acidic conditions than that adsorbed on birnessite with high Mn AOS. High Zn loading favors the formation of Zn complexes over Zn complexes, and the release of Zn is faster than at low loading. These results will deepen our understanding of the interaction mechanisms of various TMs with natural birnessites, and the stability and thus the potential toxicity of heavy metal pollutants sequestered by engineered nano-sized metal oxide materials.
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http://dx.doi.org/10.1016/j.jes.2017.02.017DOI Listing
March 2018

Decreased Electron Transfer between Cr(VI) and AH2DS in the Presence of Goethite.

J Environ Qual 2018 Jan;47(1):139-146

9,10-Anthraquinone-2,6-disulfonic acid (AQDS) is commonly used as a model species to examine the influence of quinones on different biogeochemical cycles. The reduced form of this quinone, AHDS, can donate electrons to the toxic metal species Cr(VI), leading to the precipitation of less soluble Cr(III) phases. Due to the environmental abundance of Fe(III) (oxyhydr)oxides, such as goethite (α-FeOOH), it is important to study the role of these mineral phases on the electron transfer reaction between AHDS and Cr(VI). In this study, this electron transfer reaction is examined in the presence and absence of goethite at three different ratios of AHDS/Cr(VI). Ultraviolet-visible spectroscopy is used to qualitatively assess the oxidation state of AQDS during reactions with goethite. Iron K-edge and Cr K-edge X-ray absorption spectroscopy are used to examine the role of goethite in electron transfer and identify Cr(III) phases that form. Goethite inhibits the extent of Cr(VI) reduction to Cr(III), most notably at the highest ratio of AHDS/Cr(VI) investigated. Production of semiquinone radical species may limit electron transfer and decrease the yields of Fe(II) and Cr(III), both in the presence and absence of goethite. Understanding abiotic electron transfer reactions that occur in systems with multiple redox active species is important to determine the contribution of abiotic redox reactions to Fe biogeochemical cycling in natural soils.
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http://dx.doi.org/10.2134/jeq2017.08.0316DOI Listing
January 2018

Colonization Habitat Controls Biomass, Composition, and Metabolic Activity of Attached Microbial Communities in the Columbia River Hyporheic Corridor.

Appl Environ Microbiol 2017 08 1;83(16). Epub 2017 Aug 1.

Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin, USA

Hydrologic exchange plays a critical role in biogeochemical cycling within the hyporheic zone (the interface between river water and groundwater) of riverine ecosystems. Such exchange may set limits on the rates of microbial metabolism and impose deterministic selection on microbial communities that adapt to dynamically changing dissolved organic carbon (DOC) sources. This study examined the response of attached microbial communities ( colonized sand packs) from groundwater, hyporheic, and riverbed habitats within the Columbia River hyporheic corridor to "cross-feeding" with either groundwater, river water, or DOC-free artificial fluids. Our working hypothesis was that deterministic selection during colonization would dictate the response to cross-feeding, with communities displaying maximal biomass and respiration when supplied with their native fluid source. In contrast to expectations, the major observation was that the riverbed colonized sand had much higher biomass and respiratory activity, as well as a distinct community structure, compared with those of the hyporheic and groundwater colonized sands. 16S rRNA gene amplicon sequencing revealed a much higher proportion of certain heterotrophic taxa as well as significant numbers of eukaryotic algal chloroplasts in the riverbed colonized sand. Significant quantities of DOC were released from riverbed sediment and colonized sand, and separate experiments showed that the released DOC stimulated respiration in the groundwater and piezometer colonized sand. These results suggest that the accumulation and degradation of labile particulate organic carbon (POC) within the riverbed are likely to release DOC, which may enter the hyporheic corridor during hydrologic exchange, thereby stimulating microbial activity and imposing deterministic selective pressure on the microbial community composition. The influence of river water-groundwater mixing on hyporheic zone microbial community structure and function is an important but poorly understood component of riverine biogeochemistry. This study employed an experimental approach to gain insight into how such mixing might be expected to influence the biomass, respiration, and composition of hyporheic zone microbial communities. Colonized sands from three different habitats (groundwater, river water, and hyporheic) were "cross-fed" with either groundwater, river water, or DOC-free artificial fluids. We expected that the colonization history would dictate the response to cross-feeding, with communities displaying maximal biomass and respiration when supplied with their native fluid source. By contrast, the major observation was that the riverbed communities had much higher biomass and respiration, as well as a distinct community structure compared with those of the hyporheic and groundwater colonized sands. These results highlight the importance of riverbed microbial metabolism in organic carbon processing in hyporheic corridors.
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http://dx.doi.org/10.1128/AEM.00260-17DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5541231PMC
August 2017

Structural Transformation of MnO during the Oxidation of Bisphenol A.

Environ Sci Technol 2017 Jun 8;51(11):6053-6062. Epub 2017 May 8.

Department of Chemistry, Seattle University , Seattle, Washington 98122, United States.

Bisphenol A (BPA) is an endocrine-disrupting compound widely used in the plastic industry and found in natural waters at concentrations considered harmful for aquatic life. BPA is susceptible to oxidation by Mn(III/IV) oxides, which are commonly found in near-surface environments. Here, we quantify BPA oxidation rates and the formation of its predominant product, 4-hydroxycumyl alcohol (HCA), in tandem with transformation of a synthetic, Mn(III)-rich δ-MnO. To investigate the effect of Mn oxide structural changes on BPA oxidation rate, 12 sequential additions of 80 μM BPA are performed at pH 7. During the additions, BPA oxidation rate decreases by 3 orders of magnitude, and HCA yield decreases from 40% to 3%. This is attributed to the accumulation of interlayer Mn(II/III) produced during the reaction, as observed using X-ray absorption spectroscopy, as well as additional spectroscopic and wet chemical techniques. HCA is oxidized at a rate that is 12.6 times slower than BPA and accumulates in solution. These results demonstrate that BPA degradation by environmentally relevant Mn(III/IV) oxides is inhibited by the buildup of solid-phase Mn(II/III), specifically in interlayer sites. Nevertheless, Mn oxides may limit BPA migration in near-surface environments and have potential for use in drinking and wastewater treatment.
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http://dx.doi.org/10.1021/acs.est.6b05904DOI Listing
June 2017

Influence of Oxygen and Nitrate on Fe (Hydr)oxide Mineral Transformation and Soil Microbial Communities during Redox Cycling.

Environ Sci Technol 2016 Apr 21;50(7):3580-8. Epub 2016 Mar 21.

Environmental Chemistry and Technology Program, Department of Civil and Environmental Engineering, The University of Wisconsin-Madison , 660 North Park Street, Madison, Wisconsin 53706, United States.

Oscillations between reducing and oxidizing conditions are observed at the interface of anaerobic/oxic and anaerobic/anoxic environments, and are often stimulated by an alternating flux of electron donors (e.g., organic carbon) and electron acceptors (e.g., O2 and NO3(-)). In iron (Fe) rich soils and sediments, these oscillations may stimulate the growth of both Fe-reducing bacteria (FeRB) and Fe-oxidizing bacteria (FeOB), and their metabolism may induce cycling between Fe(II) and Fe(III), promoting the transformation of Fe (hydr)oxide minerals. Here, we examine the mineralogical evolution of lepidocrocite and ferrihydrite, and the adaptation of a natural microbial community to alternating Fe-reducing (anaerobic with addition of glucose) and Fe-oxidizing (with addition of nitrate or air) conditions. The growth of FeRB (e.g., Geobacter) is stimulated under anaerobic conditions in the presence of glucose. However, the abundance of these organisms depends on the availability of Fe(III) (hydr)oxides. Redox cycling with nitrate results in decreased Fe(II) oxidation thereby decreasing the availability of Fe(III) for FeRB. Additionally, magnetite is detected as the main product of both lepidocrocite and ferrihydrite reduction. In contrast, introduction of air results in increased Fe(II) oxidation, increasing the availability of Fe(III) and the abundance of Geobacter. In the lepidocrocite reactors, Fe(II) oxidation by dissolved O2 promotes the formation of ferrihydrite and lepidocrocite, whereas in the ferrihydrite reactors we observe a decrease in magnetite stoichiometry (e.g., oxidation). Understanding Fe (hydr)oxide transformation under environmentally relevant redox cycling conditions provides insight into nutrient availability and transport, contaminant mobility, and microbial metabolism in soils and sediments.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5066396PMC
http://dx.doi.org/10.1021/acs.est.5b05519DOI Listing
April 2016

A critical review of the reactivity of manganese oxides with organic contaminants.

Environ Sci Process Impacts 2014 May;16(6):1247-66

University of Wisconsin-Madison, Department of Civil and Environmental Engineering, 660 N. Park St., Madison, WI, USA.

Naturally occurring manganese (Mn(iii/iv)) oxides are ubiquitous in a wide range of environmental settings and play a key role in numerous biogeochemical cycles. In addition, Mn(iii/iv) oxides are powerful oxidants that are capable of oxidizing a wide range of compounds. This review critically assesses the reactivity of Mn oxides with organic contaminants. Initial work with organic reductants employed high concentrations of model compounds (e.g., substituted phenols and anilines) and emphasized the reductive dissolution of the Mn oxides. Studies with lower concentrations of organic contaminants demonstrate that Mn oxides are capable of oxidizing a wide range of compounds (e.g., antibacterial agents, endocrine disruptors, and pesticides). Both model compounds and organic contaminants undergo similar reaction mechanisms on the oxide surface. The oxidation rates of organic compounds by manganese oxides are dependent upon solution conditions, such as pH and the presence of cations, anions, or dissolved organic matter. Similarly, physicochemical properties of the minerals used affect the rates of organic compound oxidation, which increase with the average oxidation state, redox potential, and specific surface area of the Mn oxides. Due to their reactivity with contaminants under environmentally relevant conditions, Mn oxides may oxidize contaminants in soils and/or be applied in water treatment applications.
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http://dx.doi.org/10.1039/c3em00703kDOI Listing
May 2014

Chromium(III) oxidation by three poorly-crystalline manganese(IV) oxides. 1. Chromium(III)-oxidizing capacity.

Environ Sci Technol 2012 Nov 19;46(21):11594-600. Epub 2012 Oct 19.

Plant and Soil Sciences Department, Delaware Environmental Institute, University of Delaware, 152 Townsend Hall, Newark, Delaware 19716, USA.

The Cr(III)-oxidizing capacity of three layered poorly crystalline Mn(IV)O(2) phases, i.e. δ-MnO(2), Random Stacked Birnessite (RSB), and Acid Birnessite (AB), was determined in real-time and in situ, using Quick X-ray Absorption Fine Structure Spectroscopy (Q-XAFS). The results obtained with this technique, which allows the measurement of the total amount of Cr(VI) produced in the system, indicated that the Cr(III) oxidation reaction had ceased between 30 min and 1 h under most experimental conditions. However, this cessation was not observed with a traditional batch technique, which only allows the measurement of Cr(VI) present in solution and thus neglects the amount of Cr(VI) that may be sorbed to Mn(IV)O(2). This study also demonstrated that the Mn(IV)O(2) phase oxidizing the highest amount of Cr(III), which is positively charged in solution, was the mineral featuring the most negatively charged surface. Also, the results indicated that the presence of Mn(II) and/or Mn(III) impurities inside the Mn(IV)O(2) structure could enhance the mineral's capacity to oxidize Cr(III). The information provided in this study will be useful in predicting the capabilities of naturally occurring Mn oxide minerals, which are similar to the three synthetic Mn(IV)O(2) investigated, to oxidize Cr(III) to toxic and mobile Cr(VI) in the soil of contaminated sites.
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http://dx.doi.org/10.1021/es302383yDOI Listing
November 2012

Chromium(III) oxidation by three poorly crystalline manganese(IV) oxides. 2. Solid phase analyses.

Environ Sci Technol 2012 Nov 19;46(21):11601-9. Epub 2012 Oct 19.

Plant and Soil Sciences Department, Delaware Environmental Institute, University of Delaware, 152 Townsend Hall, Newark, Delaware 19716, USA.

Layered, poorly crystalline Mn(IV)O(2) phases are abundant in the environment. These mineral phases may rapidly oxidize Cr(III) to more mobile and toxic Cr(VI) in soils. There is still, however, little knowledge of how Cr(III) oxidation by Mn(IV)O(2) proceeds at the microscopic and molecular levels. Therefore, the sorption mechanisms of Cr(III) and Cr(VI) on Random Stacked Birnessite (RSB), δ-MnO(2), and Acid Birnessite (AB) were determined by Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS). These three synthetic Mn(IV)O(2), which are poorly crystalline phases and have layered structures, were reacted with 50 mM Cr(III) at pH 2.5, 3, and 3.5 before being analyzed by EXAFS. The results indicated that Cr(VI) was loosely sorbed as an outer-sphere complex on Mn(IV)O(2), while Cr(III) was tightly sorbed as an inner-sphere complex. Further research is needed to understand why Cr(III) stopped being significantly oxidized by Mn(IV)O(2) after 30 min. This study, however, demonstrated that the formation of a Cr surface precipitate is not necessarily responsible for the cessation in Cr(III) oxidation. Indeed, no Cr surface precipitate was detected at the microscopic and molecular levels on Mn(IV)O(2) surfaces reacted with Cr(III) for 1 h, although the Cr(III) oxidation ceased before 1 h of reaction at most employed experimental conditions.
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http://dx.doi.org/10.1021/es302384qDOI Listing
November 2012

Synthesis and evaluation of substrate analogue inhibitors of trypanothione reductase.

J Enzyme Inhib Med Chem 2012 Dec 15;27(6):784-94. Epub 2011 Nov 15.

Department of Chemistry, Carleton College, Northfield, MN 55057, USA.

Trypanothione reductase (TR) is found in the trypanosomatid parasites, where it catalyses the NADPH-dependent reduction of the glutathione analogue, trypanothione, and is a key player in the parasite's defenses against oxidative stress. TR is a promising target for the development of antitrypanosomal drugs; here, we report our synthesis and evaluation of compounds 3-5 as low micromolar Trypanosoma cruzi TR inhibitors. Although 4 and 5 were designed as potential irreversible inhibitors, these compounds, as well as 3, displayed reversible competitive inhibition. Compound 3 proved to be the most potent inhibitor, with a K(i) = 2 µM.
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http://dx.doi.org/10.3109/14756366.2011.604319DOI Listing
December 2012

Arsenite oxidation by a poorly-crystalline manganese oxide. 3. Arsenic and manganese desorption.

Environ Sci Technol 2011 Nov 12;45(21):9218-23. Epub 2011 Oct 12.

Department of Plant and Soil Sciences, Delaware Environmental Institute, University of Delaware, 152 Townsend Hall, Newark, Delaware 19716, United States.

Arsenic (As) mobility in the environment is greatly affected by its oxidation state and the degree to which it is sorbed on metal oxide surfaces. Manganese oxides (Mn oxides) have the ability to decrease overall As mobility both by oxidizing toxic arsenite (As(III)) to less toxic arsenate (As(V)), and by sorbing As. However, the effect of competing ions on the mobility of As sorbed on Mn-oxide surfaces is not well understood. In this study, desorption of As(V) and As(III) from a poorly crystalline phyllomanganate (δ-MnO(2)) by two environmentally significant ions is investigated using a stirred-flow technique and X-ray absorption spectroscopy (XAS). As(III) is not observed in solution after desorption under any conditions used in this study, agreeing with previous studies showing As sorbed on Mn-oxides exists only as As(V). However, some As(V) is desorbed from the δ-MnO(2) surface under all conditions studied, while neither desorptive used in this study completely removes As(V) from the δ-MnO(2) surface.
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http://dx.doi.org/10.1021/es201281uDOI Listing
November 2011

Speciation and release kinetics of cadmium in an alkaline paddy soil under various flooding periods and draining conditions.

Environ Sci Technol 2011 May 22;45(10):4249-55. Epub 2011 Apr 22.

Department of Plant and Soil Sciences, University of Delaware, 152 Townsend Hall, Newark, Delaware 19716, USA.

This study determined Cd speciation and release kinetics in a Cd-Zn cocontaminated alkaline paddy soil, under various flooding periods and draining conditions, by employing synchrotron-based techniques, and a stirred-flow kinetic method. Results revealed that varying flooding periods and draining conditions affected Cd speciation and its release kinetics. Linear least-squares fitting (LLSF) of bulk X-ray absorption fine structure (XAFS) spectra of the air-dried, and the 1 day-flooded soil samples, showed that at least 50% of Cd was bound to humic acid. Cadmium carbonates were found as the major species at most flooding periods, while a small amount of cadmium sulfide was found after the soils were flooded for longer periods. Under all flooding and draining conditions, at least 14 mg/kg Cd was desorbed from the soil after a 2-hour desorption experiment. The results obtained by micro X-ray fluorescence (μ-XRF) spectroscopy showed that Cd was less associated with Zn than Ca, in most soil samples. Therefore, it is more likely that Cd and Ca will be present in the same mineral phases rather than Cd and Zn, although the source of these two latter elements may originate from the same surrounding Zn mines in the Mae Sot district.
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http://dx.doi.org/10.1021/es103971yDOI Listing
May 2011

Arsenite oxidation by a poorly crystalline manganese-oxide. 2. Results from X-ray absorption spectroscopy and X-ray diffraction.

Environ Sci Technol 2010 Nov 26;44(22):8467-72. Epub 2010 Oct 26.

Department of Plant and Soil Sciences, Delaware Environmental Institute, University of Delaware, Newark, Delaware 19716, USA.

Arsenite (As(III)) oxidation by manganese oxides (Mn-oxides) serves to detoxify and, under many conditions, immobilize arsenic (As) by forming arsenate (As(V)). As(III) oxidation by Mn(IV)-oxides can be quite complex, involving many simultaneous forward reactions and subsequent back reactions. During As(III) oxidation by Mn-oxides, a reduction in oxidation rate is often observed, which is attributed to Mn-oxide surface passivation. X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) data show that Mn(II) sorption on a poorly crystalline hexagonal birnessite (δ-MnO₂) is important in passivation early during reaction with As(III). Also, it appears that Mn(III) in the δ-MnO₂ structure is formed by conproportionation of sorbed Mn(II) and Mn(IV) in the mineral structure. The content of Mn(III) within the δ-MnO₂ structure appears to increase as the reaction proceeds. Binding of As(V) to δ-MnO₂ also changes as Mn(III) becomes more prominent in the δ-MnO ₂ structure. The data presented indicate that As(III) oxidation and As(V) sorption by poorly crystalline δ-MnO₂ is greatly affected by Mn oxidation state in the δ-MnO₂ structure.
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http://dx.doi.org/10.1021/es102016cDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2987725PMC
November 2010

Arsenite oxidation by a poorly crystalline manganese-oxide 1. Stirred-flow experiments.

Environ Sci Technol 2010 Nov;44(22):8460-6

Department of Plant and Soil Sciences, Delaware Environmental Institute, University of Delaware, Newark, Delaware 19716, USA.

Manganese-oxides (Mn-oxides) are quite reactive, with respect to arsenite (As(III)) oxidation. However, studies regarding the pathways of As(III) oxidation, over a range of time scales, by poorly crystalline Mn-oxides, are lacking. In stirred-flow experiments, As(III) oxidation by δ-MnO₂ (a poorly crystalline form of hexagonal birnessite) is initially rapid but slows appreciably after several hours of reaction. Mn(II) is the only reduced product of δ-MnO₂ formed by As(III) oxidation during the initial, most rapid phase of the reaction. There seems to be evidence that the formation of Mn(III) observed in previous studies is a result of conproportionation of Mn(II) sorbed onto Mn(IV) reaction sites rather than from direct reduction of Mn(IV) by As(III).The only evidence of arsenic (As) sorption during As(III) oxidation by δ-MnO₂ is during the first 10 h of reaction, and As sorption is greater when As(V) and Mn(II) occur simultaneously in solution. Our findings indicate that As(III) oxidation by poorly crystalline δ-MnO₂ involves several simultaneous reactions and reinforces the importance of studying reaction mechanisms over time.
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http://dx.doi.org/10.1021/es102013pDOI Listing
November 2010

Significant association between sulfate-reducing bacteria and uranium-reducing microbial communities as revealed by a combined massively parallel sequencing-indicator species approach.

Appl Environ Microbiol 2010 Oct 20;76(20):6778-86. Epub 2010 Aug 20.

Center for Microbial Ecology, Michigan State University, East Lansing, MI 48824-1325, USA.

Massively parallel sequencing has provided a more affordable and high-throughput method to study microbial communities, although it has mostly been used in an exploratory fashion. We combined pyrosequencing with a strict indicator species statistical analysis to test if bacteria specifically responded to ethanol injection that successfully promoted dissimilatory uranium(VI) reduction in the subsurface of a uranium contamination plume at the Oak Ridge Field Research Center in Tennessee. Remediation was achieved with a hydraulic flow control consisting of an inner loop, where ethanol was injected, and an outer loop for flow-field protection. This strategy reduced uranium concentrations in groundwater to levels below 0.126 μM and created geochemical gradients in electron donors from the inner-loop injection well toward the outer loop and downgradient flow path. Our analysis with 15 sediment samples from the entire test area found significant indicator species that showed a high degree of adaptation to the three different hydrochemical-created conditions. Castellaniella and Rhodanobacter characterized areas with low pH, heavy metals, and low bioactivity, while sulfate-, Fe(III)-, and U(VI)-reducing bacteria (Desulfovibrio, Anaeromyxobacter, and Desulfosporosinus) were indicators of areas where U(VI) reduction occurred. The abundance of these bacteria, as well as the Fe(III) and U(VI) reducer Geobacter, correlated with the hydraulic connectivity to the substrate injection site, suggesting that the selected populations were a direct response to electron donor addition by the groundwater flow path. A false-discovery-rate approach was implemented to discard false-positive results by chance, given the large amount of data compared.
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http://dx.doi.org/10.1128/AEM.01097-10DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2953039PMC
October 2010

Cation effects on the layer structure of biogenic Mn-oxides.

Environ Sci Technol 2010 Jun;44(12):4465-71

Department of Plant and Soil Sciences, Delaware Environmental Institute, University of Delaware, 152 Townsend Hall, Newark, Delaware 19716, USA.

Biologically catalyzed Mn(II) oxidation produces biogenic Mn-oxides (BioMnO(x)) and may serve as one of the major formation pathways for layered Mn-oxides in soils and sediments. The structure of Mn octahedral layers in layered Mn-oxides controls its metal sequestration properties, photochemistry, oxidizing ability, and topotactic transformation to tunneled structures. This study investigates the impacts of cations (H(+), Ni(II), Na(+), and Ca(2+)) during biotic Mn(II) oxidation on the structure of Mn octahedral layers of BioMnO(x) using solution chemistry and synchrotron X-ray techniques. Results demonstrate that Mn octahedral layer symmetry and composition are sensitive to previous cations during BioMnO(x) formation. Specifically, H(+) and Ni(II) enhance vacant site formation, whereas Na(+) and Ca(2+) favor formation of Mn(III) and its ordered distribution in Mn octahedral layers. This study emphasizes the importance of the abiotic reaction between Mn(II) and BioMnO(x) and dependence of the crystal structure of BioMnO(x) on solution chemistry.
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http://dx.doi.org/10.1021/es1009955DOI Listing
June 2010

Ni(II) sorption on biogenic Mn-oxides with varying Mn octahedral layer structure.

Environ Sci Technol 2010 Jun;44(12):4472-8

Department of Plant and Soil Sciences, Delaware Environmental Institute, University of Delaware, 152 Townsend Hall, Newark, Delaware 19716, USA.

Biogenic Mn-oxides (BioMnO(x)), produced by microorganisms, possess an extraordinary ability to sequester metals. BioMnO(x) are generally layered structures containing varying amounts of Mn(III) and vacant sites in the Mn layers. However the relationship between the varying structure of BioMnO(x) and metal sorption properties remains unclear. In this study, BioMnO(x) produced by Pseudomonas putida strain GB-1 was synthesized at either pH 6, 7, or 8 in CaCl(2) solution, and Ni(II) sorption mechanisms were determined at pH 7 and at different Ni(II) loadings, using isotherm and extended X-ray absorption fine structure (EXAFS) spectroscopic analyses. Our data demonstrate that Ni(II) sorbs at vacant sites in the interlayer of the BioMnO(x) and the maximum Ni(II) sorption capacity increases as the formation pH of BioMnO(x) decreases. This relation indicates that the quantity of BioMnO(x) vacant sites increases as formation conditions become more acidic, which is in good agreement with our companion study. Contents of the vacant sites were quantitatively estimated based on maximum Ni(II) sorption capacity. Additionally, this study reveals that imidazole groups are involved in Ni(II) binding to biomaterials, and have a higher Ni(II) sorption affinity, but a lower site density compared to carboxyl groups.
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http://dx.doi.org/10.1021/es9037066DOI Listing
June 2010

Responses of microbial community functional structures to pilot-scale uranium in situ bioremediation.

ISME J 2010 Aug 18;4(8):1060-70. Epub 2010 Mar 18.

Institute for Environmental Genomics and Department of Botany and Microbiology, University of Oklahoma, Norman, OK, USA.

A pilot-scale field test system with an inner loop nested within an outer loop was constructed for in situ U(VI) bioremediation at a US Department of Energy site, Oak Ridge, TN. The outer loop was used for hydrological protection of the inner loop where ethanol was injected for biostimulation of microorganisms for U(VI) reduction/immobilization. After 2 years of biostimulation with ethanol, U(VI) levels were reduced to below drinking water standard (<30 microg l(-1)) in the inner loop monitoring wells. To elucidate the microbial community structure and functions under in situ uranium bioremediation conditions, we used a comprehensive functional gene array (GeoChip) to examine the microbial functional gene composition of the sediment samples collected from both inner and outer loop wells. Our study results showed that distinct microbial communities were established in the inner loop wells. Also, higher microbial functional gene number, diversity and abundance were observed in the inner loop wells than the outer loop wells. In addition, metal-reducing bacteria, such as Desulfovibrio, Geobacter, Anaeromyxobacter and Shewanella, and other bacteria, for example, Rhodopseudomonas and Pseudomonas, are highly abundant in the inner loop wells. Finally, the richness and abundance of microbial functional genes were highly correlated with the mean travel time of groundwater from the inner loop injection well, pH and sulfate concentration in groundwater. These results suggest that the indigenous microbial communities can be successfully stimulated for U bioremediation in the groundwater ecosystem, and their structure and performance can be manipulated or optimized by adjusting geochemical and hydrological conditions.
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http://dx.doi.org/10.1038/ismej.2010.31DOI Listing
August 2010

Kinetic and mechanistic constraints on the oxidation of biogenic uraninite by ferrihydrite.

Environ Sci Technol 2010 Jan;44(1):163-9

Department of Environmental Earth System Science, Stanford University, Stanford, California 94305, USA.

The oxidation state of uranium plays a major role in determining uranium mobility in the environment. Under anaerobic conditions, common metal respiring bacteria enzymatically reduce soluble U(VI) to U(IV), resulting in the formation of sparingly soluble UO(2(bio)) (biogenic uraninite). The stability of biologically precipitated uraninite is critical for determining the long-term fate of uranium and is not well characterized within soils and sediments. Here, we demonstrate that biogenic uraninite oxidation by ferrihydrite, an environmentally ubiquitous, disordered Fe(III) (hydr)oxide, appears to proceed through a soluble U(IV) intermediate and results in the concomitant production of Fe(II) and dissolved U(VI). Uraninite oxidation rates are accelerated under conditions that increase its solubility and decrease uraninite surface passivation, which include high bicarbonate concentration and pH values deviating from neutrality. Thus, our results demonstrate that UO(2(bio)) oxidation by Fe(III) (hydr)oxides is controlled by the rate of uraninite dissolution and that this process may limit uranium(IV) sequestration in the presence of Fe(III) (hydr)oxides.
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http://dx.doi.org/10.1021/es902452uDOI Listing
January 2010

Molecular scale assessment of methylarsenic sorption on aluminum oxide.

Environ Sci Technol 2010 Jan;44(2):612-7

Department of Plant and Soil Sciences, Delaware Environmental Institute, University of Delaware, Newark, Delaware 19716, USA.

Methylated forms of arsenic (As), monomethylarsenate (MMA) and dimethylarsenate (DMA), have historically been used as herbicides and pesticides. Because of their large application to agriculture fields and the toxicity of MMA and DMA, the sorption of methylated As to soil constituents requires investigation. MMA and DMA sorption on amorphous aluminum oxide (AAO) was investigated using both macroscopic batch sorption kinetics and molecular scale extended X-ray absorption fine structure (EXAFS) and Fourier transform infrared (FTIR) spectroscopic techniques. Sorption isotherm studies revealed sorption maxima of 0.183, 0.145, and 0.056 mmol As/mmol Al for arsenate (As(V)), MMA, and DMA, respectively. In the sorption kinetics studies, 100% of added As(V) was sorbed within 5 min, while 78% and 15% of added MMA and DMA were sorbed, respectively. Desorption experiments, using phosphate as a desorbing agent, resulted in 30% release of absorbed As(V), while 48% and 62% of absorbed MMA and DMA, respectively, were released. FTIR and EXAFS studies revealed that MMA and DMA formed mainly bidentate binuclear complexes with AAO. On the basis of these results, it is proposed that increasing methyl group substitution results in decreased As sorption and increased As desorption on AAO.
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http://dx.doi.org/10.1021/es9027502DOI Listing
January 2010
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