Arsenic sequestration by nitrate respiring microbial communities in urban lake sediments. Chemosphere, 70(2), 329-336
Department of Microbiology, University of Massachusetts, Amherst, MA 01003, USA. Chemosphere
(Impact Factor: 3.34).
12/2007; 70(2):329-36. DOI: 10.1016/j.chemosphere.2007.05.094
Changes in microbial community composition and activity were related to geochemical conditions favoring arsenic sequestration in sediments collected from the urban, arsenic-contaminated Upper Mystic Lake. After amendment with nitrate, >94% total soluble arsenic is sequestered by Fe(III)-(oxy)hydroxides generated in live sediments. Of this sequestered arsenic, >75% existed as As(III), indicating As redox state alone is not responsible for changes in mobility. Arsenic sequestration was concurrent with the microbial respiration of nitrate as indicated by steady state hydrogen concentration and the presence of organisms similar to nitrate-reducing, iron-oxidizing bacteria belonging to the genus Dechloromonas in 16S rDNA clone libraries.
Available from: Jing Sun
- "carbon . Nitrate is known to strongly influence Fe and accordingly As , and also meditates As ( III ) oxidation to As ( V ) ( Gibney and Nusslein , 2007 ; Hohmann et al . , 2011 ; Senn and Hemond , 2002 "
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ABSTRACT: Magnetite strongly retains As, and is relatively stable under Fe(III)-reducing conditions common in aquifers that release As. Here, laboratory microcosm experiments were conducted to investigate a potential As remediation method involving magnetite formation, using groundwater and sediments from the Vineland Superfund site. The microcosms were amended with various combinations of nitrate, Fe(II) (aq) (as ferrous sulfate) and lactate, and were incubated for more than 5 weeks. In the microcosms enriched with 10 mM nitrate and 5 mM Fe(II) (aq), black magnetic particles were produced, and As removal from solution was observed even under sustained Fe(III) reduction stimulated by the addition of 10 mM lactate. The enhanced As retention was mainly attributed to co-precipitation within magnetite and adsorption on a mixture of magnetite and ferrihydrite. Sequential chemical extraction, X-ray absorption spectroscopy and magnetic susceptibility measurements showed that these minerals formed at pH 6-7 following nitrate-Fe(II) addition, and As-bearing magnetite was stable under reducing conditions. Scanning electron microscopy and X-ray diffraction indicated that nano-particulate magnetite was produced as coatings on fine sediments, and no aging effect was detected on morphology over the course of incubation. These results suggest that a magnetite based strategy may be a long-term remedial option for As-contaminated aquifers.
Available from: Huaming Guo
- "Meanwhile, in oxic conditions , adsorption of As on aquifer sediments occurs in the alluvial fans, which leads to low As concentrations in Cluster III (Fig. 6c), although the grains are coarse in the alluvial fans with low adsorption capacity for As (Stumm, 1992). Other researchers have also indicated that the reductive dissolution of Fe (hydr)oxides is largely suppressed because that NO 3 strongly buffers the redox potential and As would be adsorbed on Fe minerals in the NO 3 reduction environment (Guo et al., 2011; Kim et al., 2009; Nickson et al., 2000; Senn and Hemond, 2002; Gibney and Nüsslein, 2007). As free oxygen is consumed along the flow path, NO 3 becomes the first to be electron acceptor in the process of organic matter oxidation by microorganisms, which leads to the decrease in NO 3 concentration (Guo et al., 2011). "
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ABSTRACT: Although high As groundwater has been observed in shallow groundwater of the Hetao basin, little is known about As distribution in deep groundwater. Quantitative investigations into relationships among chemical properties and among samples in different areas were carried out. Ninety groundwater samples were collected from deep aquifers of the northwest of the basin. Twenty-two physicochemical parameters were obtained for each sample. Statistical methods, including principal component analysis (PCA) and hierarchical cluster analysis (HCA), were used to analyze those data. Results show that As species were highly correlated with Fe species, NH4-N and pH. Furthermore, result of PCA indicates that high As groundwater was controlled by geological, reducing and oxic factors. The samples are classified into three clusters in HCA, which corresponded to the alluvial fans, the distal zone and the flat plain. Moreover, the combination of PCA with HCA shows the different dominant factors in different areas. In the alluvial fans, groundwater is influenced by oxic factors, and low As concentrations are observed. In the distal zone, groundwater is under suboxic conditions, which is dominated by reducing and geological factors. In the flat plain, groundwater is characterized by reducing conditions and high As concentrations, which is dominated by the reducing factor. This investigations indicate that deep groundwater in the alluvial fans mostly contains low As concentrations but high NO3 and U concentrations, and needs to be carefully checked prior to being used for drinking water sources.
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