35 Search Results

Microbial communities from riparian sediments contaminated with high levels of Ni and U were examined for metal-tolerant microorganisms. Isolation of four aerobic Ni-tolerant, Gram-positive heterotrophic bacteria indicated selection pressure from Ni. These isolates were identified as Arthrobacter oxydans NR-1, Streptomyces galbus NR-2, Streptomyces aureofaciens NR-3, and Kitasatospora cystarginea NR-4 based on partial 16S rDNA sequences. A functional gene microarray containing gene probes for functions associated with biogeochemical cycling, metal homeostasis, and organic contaminant degradation showed little overlap among the four isolates. Fifteen of the genes were detected in all four isolates with only two of these related to metal resistance, specifically to tellurium. Each of the four isolates also displayed resistance to at least one of six antibiotics tested, with resistance to kanamycin, gentamycin, and ciprofloxacin observed in at least two of the isolates. Further characterization of S. aureofaciens NR-3 and K. cystarginea NR-4 demonstrated that both isolates expressed Ni tolerance constitutively. In addition, both were able to grow in higher concentrations of Ni at pH 6 as compared with pH 7 (42.6 and 8.5 mM Ni at pH 6 and 7, respectively). Tolerance to Cd, Co, and Zn was also examined in these two isolates; a similar pH-dependent metal tolerance was observed when grown with Co and Zn. Neither isolate was tolerant to Cd. These findings suggest that Ni is exerting a selection pressure at this site for metal-resistant actinomycetes.

No abstract prepared.

Evaporation ponds in the San Joaquin Valley (SJV), CA, used for the containment of irrigation drainage waters contain elevated levels of uranium (U) resulting from the extensive leaching by carbonate-rich irrigation waters of the local agricultural soils that contain low levels of naturally-occurring U. The SJV ponds are subjected to changes in redox chemistry with cycles of drying and flooding. Past studies have shown that U in the SJV Pont 14 surface sediments is present as mostly the oxidized and soluble form, U(VI). However, the authors were uncertain whether the U in the soil was only present as a U oxide of mixed stoichiometry, such as U{sub 3}O{sub 8(s)} (pitchblende) or other species. Here they present characterization information, which includes wet chemical and in situ spectroscopic techniques (X-ray absorption near-edge structure (XANES) and low temperature time-resolved luminescence spectroscopies) for samples from two SJV Pond sediments. Surface sediments from SJV Pont 16 were characterized for average oxidation state of U with XANES spectroscopy. The wet chemical extractions and in situ spectroscopic techniques provided fundamental and basic knowledge about the fraction of U(IV) to U(VI), the speciation of luminescent U(VI), and the susceptibility of the sediment U species to leaching.

The hydrolysis of Fe-Si systems with Si/Fe ratios between 0 and 4 leads to the formation of poorly crystalline or, more frequently, of long-range disorganized precipitates. The increase of Si/Fe molar ratios results in a dramatic change of Fe polymerization. The formation of double and single corner-sharing Fe linkages is reduced compared to pure Fe hydrolysis products. The growth regime depends on the Si concentration in the system. Three-dimensional and two-dimensional growth of Fe colloids occurs at low and high Si/Fe ratios, respectively, systems with Si/Fe ratios around 1 representing a crossover between these two regimes. Though Si neighbors cannot be detected unequivocally by Fe K-edge EXAFS, their presence in the close environment of Fe atoms is evident from the change in Fe speciation.

Batch equilibrations were performed to investigate the ability of hydroxyapatite (Ca{sub 5}(PO{sub 4}){sub 3}OH) to chemically immobilize U in two contaminated sediment samples having different organic carbon contents. Apatite additions lowered aqueous U to near proposed drinking water standards in batch equilibrations of two distinct sediment strata having total U concentrations of 1703 and 2100 mg kg{sup {minus}1}, respectively. Apatite addition of 50 g kg{sup {minus}1} reduced the solubility of U to values less than would be expected if autunite was the controlling solid phase. A comparison of the two sediment types suggests that aqueous phase U may be controlled by both the DOC content through complexation and the equilibrium pH for a given apatite application rate. Sequential chemical extractions demonstrated that apatite amendment transfers U from more chemically labile fractions, including water-soluble, exchangeable, and acid-soluble fractions, to the Mn-occluded fraction. This suggests that apatite amendment redirects solid-phase speciation with secondary U phosphates being solubilized due to the lower pH of the Mn-occluded extractant, despite the lack of significant quantities of Mn oxides within these sediments. Energy dispersive X-ray (EDX) analysis conducted in a transmission electron microscope (TEM) confirmed that apatite amendment sequesters some U in secondary Al/Fe phosphate phases.

Batch and column techniques were used to evaluate the in situ Cr(VI) reduction and immobilization using Fe(II) solutions within the sediments of the Atlantic Coastal Plain. Remediation treatments included Cr-free groundwater and buffered and unbuffered Fe(II) solutions as either FeCl{sub 2} and FeSO{sub 4}. The slow release of Cr(VI) from the Fe-oxide rich subsurface sediment following exposure to Cr-free solutions indicated that simple pump-and-treat procedures would require extended operation time to meet regulatory standards. In situ reduction was confirmed by the loss of Cr(VI) and Fe(II) from solution and a drop in pH compared to control systems. Batch and column-effluent Cr(VI) decreased with increasing Fe(II), generally failing below detection limits as the persistence of Fe(II) occurred. However, Cr{sub Dissolved}, presumably Cr(III), exceeded regulatory limits due to the low pH ({approx}3.0) induced by oxidation and hydrolysis of Fe(II). Acetate-buffered Fe(II) solutions maintained an elevated pH in the presence of Cr(VI) reduction, making the treatment effective at lowering Cr{sub Dissolved} in batch evaluations. Acetate increased Cr(VI) mobility in columns ahead of the reactive Fe(II) front, suggesting that in situ reduction using soluble chemical additives may be somewhat ineffective due to the enhanced migration of Cr, either Cr(III) or Cr(VI), induced by the treatment solution.

'Cesium (137) is a major component of high level weapons waste. At Hanford, single shell tanks (SST''s) with high level wastes (HLW) have leaked supernate containing over 10{sup 6} Ci of 137 Cs and other co-contaminants into the vadose zone. In select locations, 137 Cs has migrated further than expected from retardation experiments and performance assessment calculations. Deep 137 Cs migration has been observed beneath the SX tank farm at Hanford with REDOX wastes as the carrier causing regulatory and stakeholder concern. The causes for expedited migration are unclear. This research is investigating how the sorption chemistry of Cs on Hanford vadose zone sediments changes after contact with solutions characteristic of HLW. The central scientific hypothesis is that the high Na concentration of HLW will suppress surface-exchange reactions of Cs, except those to highly-selective frayed edge sites (FES) of the micaceous fraction. The authors further speculate that the concentrations, ion selectivity, and structural aspects of the FES will change after contact with HLW and that these changes will be manifest in the macroscopic sorption behavior of Cs. The authors believe that migration predictions of Cs can be improved substantially if such changes are understood and quantified. The research has three objectives: (1.) identify how the multi-component surface exchange behavior of Cs on Hanford sediments changes after contact with HLW simulants that span a range of relevant chemical (Na, OH, Al, K) and temperature conditions (23-80 C); (2) reconcile changes in sorption chemistry with microscopic and molecular changes in site distribution, chemistry, mineralogy, and surface structure of the micaceous fraction; (3) integrate mass-action-solution exchange measurements with changes in the structure/site distribution of the micaceous fraction to yield a multicomponent exchange model relevant to high ionic strength and hydroxide for prediction of environmental Cs sorption.'

Spatially resolved XAS and X-ray fluorescence spectroscopic studies were conducted to investigate the distribution and chemical speciation of uranium (U) in contaminated soils and sediments prior to and following chemical extraction. This approach provided direct information on the chemical speciation of uranium in micro-regions of contaminated soils and sediments sampled at the Fernald Environmental Management Project Site and the Savannah River Site. Using X-ray absorption near edge structure (XANES) spectroscopy, the predominant oxidation state of uranium in the contaminated sediments was determined. A calibration method was developed which enhanced the ability to collect oxidation state information at much lower concentrations in a reasonable time frame and allowed for the generation of oxidation state distribution maps at a 20 {mu}m spatial resolution. Additional experiments conducted on mixed uranium containing mineral phases confirmed the ability of the method to accurately delineate proportions of uranium in different oxidation states. Furthermore, a method of imbedding particles in a nonreactive silicon polymer was developed such that individual particles could be examined before and after extraction with a wide range of chemicals used in sequential extraction techniques and others proposed for chemical intervention technologies. Studies revealed that the sodium carbonate treatment proposed to extract U from soils efficiently removed U(VI), except when present as a phosphate phase, and was inefficient at extracting U(IV) phases. The results of these studies demonstrated the utility of spatially resolved XAS methods for in situ chemical speciation of U and other metals and metalloids.

Evaporation ponds in the San Joaquin Valley (SJV), CA, used for the disposal of irrigation drainage waters, contain elevated levels of uranium. The ponds are filled periodically and support algae which upon evaporation become incorporated in the sediments as layers of decaying organic matter. This rich source of organic matter promotes reducing conditions in the sediments. Our research was conducted to characterize oxidation/reduction reactions that affect soluble and sediment U(IV)/U(VI) concentrations in the SJV ponds. Studies were done to (1) determine soluble U(Vl)/U(IV) in waters in contact with a pond sediment subjected to changes in redox status, (2) observe U solid oxidation state as a reducing pond sediment underwent (in vitro) oxidation, and (3) determine U solid oxidation state with respect to depth in pond surface sediment layers. Low pressure ion-exchange chromatography with an eluent of 0.125 M H{sub 2}C{sub 2}O{sub 4}/0.25 M HNO{sub 3} was used for the separation of U(IV) and U(VI) oxidation states in the drainage waters. Soluble U(VI) and U(IV) coexisted in sediment suspensions exposed to changes in redox potential (Eh) (-260 mV to +330 mV), and U(VI) was highly soluble in the oxidized, surface pond sediments. X-ray near edge absorption spectroscopy (XANES) showed that the U solid phases were 25% U(IV) and 75% U(VI) and probably a mixed solid [U{sub 3}O{sub 8}{sub (s)}] in highly reducing pond sediments. Sediment U(IV) increased slightly with depth in the surface pond sediment layers suggesting a gradual reduction of U(VI) to U(IV) with time. Under oxidized conditions, this mixed oxidation-state solid was highly soluble. 59 refs., 6 figs., 1 tab.

A major obstacle in developing realistic environmental risk assessment or in designing environmentally sound, yet cost effective chemical and biological remediation strategies has been the ability to properly characterize the distribution and chemical speciation of a contaminant metal or radionuclide in an environmental sample or waste form. Synchrotron based X-ray fluorescence spectroscopy (SXRF) and X-ray absorption spectroscopy (XAS) are non-invasive techniques that can be used to examine the distribution and chemical speciation of elements (Z {ge} 20) in moist heterogeneous samples under ambient temperature and pressure. Using a dedicated micro-probe beam line (X-26A) at the National Synchrotron Light Source, Brookhaven National Lab, we have conducted spatially resolved XAS studies on a variety of environmental samples and on samples produced in waste isolation and processing activities. Spatially resolved SXRF spectroscopy has been used to generate elemental distribution maps on a 5 {mu}m scale, providing information on elemental distributions and associations. In addition, spatially resolved X-ray absorption near edge structure (XANES) spectroscopy has provided detailed information on the oxidation states of U, Cr, Se, and other metals and metalloids in contaminated soils, biological samples, and in waste forms on regions as small as 40 Pin, with minimal sample manipulation. Furthermore, qualitative information on bonding environments of many of these contaminants has been deduced based upon the {open_quote}fingerprint{close_quote} or multiple scattering regions of the XANES spectra coupled with the elemental distribution maps generated by SXRF spectroscopy.