Browsing by Author "Spycher, Nicolas"

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Heavy metal-mineral associations in Coeur d'Alene River sediments: A synchrotron-based analysis
(2009-12) Moberly, James G.; Borch, Thomas; Sani, Rajesh K.; Spycher, Nicolas; Şengör, S. Sevinç; Ginn, Timothy R.; Peyton, Brent M.
Nearly a century of mining activities upstream have contaminated Lake Coeur d’Alene and its tributaries with Pb, Zn, and other heavy metals. Heavy metal concentrations in sediments of the Coeur d’Alene watershed have been shown to be inversely proportional to the sediment size fraction; thus, analysis on a very small scale is essential to determine the mobility and stability of heavy metals in this environment. Micron-scale synchrotron-based methods were used to determine the association of heavy metals with solid phases in sediments of the Coeur d’Alene River. Bulk X-ray diffraction (XRD), extended X-ray absorption fine structure spectroscopy, and synchrotron-based microfocused XRD combined with microfocused X-ray fluorescence mapping indicate the presence of crystalline Pb- and Zn-bearing mineral phases of dundasite [Pb2Al4(CO3)4(OH)8·3H2O], coronadite [PbMn8O16], stolzite [PbWO4], mattheddleite [Pb10(SiO4)3.5(SO4)2Cl2], bindheimite [Pb2Sb2O7], and smithsonite [ZnCO3]. Likely phases for Zn and Pb adsorption were ferrihydrite, diaspore [AlO(OH)], manganite [Mn(III)O(OH)], muscovite [KAl2(Si3Al)O10(OH,F)2], biotite [K(Fe,Mg)3AlSi3O10(F,OH)2], and montmorillonite [Na0.3(Al,Mg)2Si4O10(OH)2·8H2O]. The large predominance of Fe and Mn (hydr)oxides over other sorbent minerals suggests that the metal sorption behavior is dominated by these (hydr)oxide phases.
Impact of different environmental conditions on the aggregation of biogenic U(IV) nanoparticles synthesized by Desulfovibrio alaskensis G20
(2016-12) Şengör, S. Sevinç; Singh, Gursharan; Dohnalkova, Alice; Spycher, Nicolas; Ginn, Timothy R.; Peyton, Brent M.; Sani, Rajesh K.
This study investigates the impact of specific environmental conditions on the formation of colloidal U(IV) nanoparticles by the sulfate reducing bacteria (SRB, Desulfovibrio alaskensis G20). The reduction of soluble U(VI) to less soluble U(IV) was quantitatively investigated under growth and non-growth conditions in bicarbonate or 1,4-piperazinediethanesulfonic acid (PIPES) buffered environments. The results showed that under non-growth conditions, the majority of the reduced U nanoparticles aggregated and precipitated out of solution. High resolution transmission electron microscopy revealed that only a very small fraction of cells had reduced U precipitates in the periplasmic spaces in the presence of PIPES buffer, whereas in the presence of bicarbonate buffer, reduced U was also observed in the cytoplasm with greater aggregation of biogenic U(IV) particles at higher initial U(VI) concentrations. The same experiments were repeated under growth conditions using two different electron donors (lactate and pyruvate) and three electron acceptors (sulfate, fumarate, and thiosulfate). In contrast to the results of the non-growth experiments, even after 0.2 μm filtration, the majority of biogenic U(IV) remained in the aqueous phase resulting in potentially mobile biogenic U(IV) nanoparticles. Size fractionation results showed that U(IV) aggregates were between 18 and 200 nm in diameter, and thus could be very mobile. The findings of this study are helpful to assess the size and potential mobility of reduced U nanoparticles under different environmental conditions, and would provide insights on their potential impact affecting U(VI) bioremediation efforts at subsurface contaminated sites.
Influence of chelating agents on biogenic uraninite reoxidation by Fe(III) (Hydr)oxides
(2013-01) Stewart, B. D.; Giradot, Crystal L.; Spycher, Nicolas; Sani, Rajesh K.; Peyton, Brent M.
Microbially mediated reduction of soluble U(VI) to U(IV) with subsequent precipitation of uraninite, UO2(S), has been proposed as a method for limiting uranium (U) migration. However, microbially reduced UO2 may be susceptible to reoxidation by environmental factors, with Fe(III) (hydr)oxides playing a significant role. Little is known about the role that organic compounds such as Fe(III) chelators play in the stability of reduced U. Here, we investigate the impact of citrate, DFB, EDTA, and NTA on biogenic UO2 reoxidation with ferrihydrite, goethite, and hematite. Experiments were conducted in anaerobic batch systems in PIPES buffer (10 mM, pH 7) with bicarbonate for approximately 80 days. Results showed EDTA accelerated UO2 reoxidation the most at an initial rate of 9.5 Î¼M dayâˆ’1 with ferrihydrite, 8.6 Î¼M dayâˆ’1 with goethite, and 8.8 Î¼M dayâˆ’1 with hematite. NTA accelerated UO2 reoxidation with ferrihydrite at a rate of 4.8 Î¼M dayâˆ’1; rates were less with goethite and hematite (0.66 and 0.71 Î¼M dayâˆ’1, respectively). Citrate increased UO2 reoxidation with ferrihydrite at a rate of 1.8 Î¼M dayâˆ’1, but did not increase the extent of reaction with goethite or hematite, with no reoxidation in this case. In all cases, bicarbonate increased the rate and extent of UO2 reoxidation with ferrihydrite in the presence and absence of chelators. The highest rate of UO2 reoxidation occurred when the chelator promoted both UO2 and Fe(III) (hydr)oxide dissolution as demonstrated with EDTA. When UO2 dissolution did not occur, UO2 reoxidation likely proceeded through an aqueous Fe(III) intermediate with lower reoxidation rates observed. Reaction modeling suggests that strong Fe(II) chelators promote reoxidation whereas strong Fe(III) chelators impede it. These results indicate that chelators found in U contaminated sites may play a significant role in mobilizing U, potentially affecting bioremediation efforts.
The toxicity of lead to Desulfovibrio desulfuricans G20 in the presence of goethite and quartz
(2010-04) Sani, Rajesh K.; Rastogi, Gurdeep; Moberly, James G.; Dohnalkova, Alice; Ginn, Timothy R.; Spycher, Nicolas; Shende, Rajesh V.; Peyton, Brent M.
An aqueous mixture of goethite, quartz, and lead chloride (PbCl2) was treated with the sulfate reducing bacterium, Desulfovibrio desulfuricans G20 (D. desulfuricans G20), in a medium specifically designed to assess metal toxicity. In the presence of 26 Î¼M of soluble Pb, together with the goethite and quartz, D. desulfuricans G20 grew after a lag time of 5 days compared to 2 days in Pb-, goethite-, and quartz-free treatments. In the absence of goethite and quartz, however, with 26 Î¼M soluble Pb, no measurable growth was observed. Results showed that D. desulfuricans G20 first removed Pb from solutions then growth began resulting in black precipitates of Pb and iron sulfides. Transmission electron microscopic analyses of thin sections of D. desulfuricans G20 treated with 10 Î¼M PbCl2 in goethite- and quartz-free treatment showed the presence of a dense deposit of lead sulfide precipitates both in the periplasm and cytoplasm. However, thin sections of D. desulfuricans G20 treated with goethite, quartz, and PbCl2 (26 Î¼M soluble Pb) showed the presence of a dense deposit of iron sulfide precipitates both in the periplasm and cytoplasm. Energy-dispersive X-ray spectroscopy, selected area electron diffraction patterns, or X-ray diffraction analyses confirmed the structure of precipitated Pb inside the cell as galena (PbS) in goethite- and quartz-free treatments, and iron sulfides in treatments with goethite, quartz, and PbCl2. Overall results suggest that even at the same soluble Pb concentration (26 Î¼M), in the presence of goethite and quartz, apparent Pb toxicity to D. desulfuricans G20 decreased significantly. Further, accumulation of lead/iron sulfides inside D. desulfuricans G20 cells depended on the presence of goethite and quartz.