Nano/bio treatment of polychlorinated biphenyls with evaluation of comparative toxicity.

The persistence of polychlorinated biphenyl (PCB) Aroclor 1248 in soils and sediments is a major concern because of its toxicity and presence at high concentrations. In this study, we developed an integrated remediation system for PCBs using chemical catalysis and biodegradation. The dechlorination of Aroclor 1248 was achieved by treatment with bimetallic nanoparticles Pd/nFe under anoxic conditions. Among the 32 PCB congeners of Aroclor 1248 examined, our process dechlorinated 99%, 92%, 84%, and 28% of tri-, tetra-, penta-, and hexachlorinated biphenyls, respectively. The resulting biphenyl was biodegraded rapidly by Burkholderia xenovorans LB400. Benzoic acid was detected as an intermediate during the biodegradation process. The toxicity of the residual PCBs after nano-bio treatment was evaluated in terms of toxic equivalent values which decreased from 33.8×10(-5)µgg(-1) to 9.5×10(-5)µgg(-1). The residual PCBs also had low cytotoxicity toward Escherichia coli as demonstrated by lower reactive oxygen species levels, lower glutathione peroxidase activity, and a reduced number of dead bacteria.

Fermentation and hydrogen metabolism affect uranium reduction by clostridia.

Previously, it has been shown that not only is uranium reduction under fermentation condition common among clostridia species, but also the strains differed in the extent of their capability and the pH of the culture significantly affected uranium(VI) reduction. In this study, using HPLC and GC techniques, metabolic properties of those clostridial strains active in uranium reduction under fermentation conditions have been characterized and their effects on capability variance of uranium reduction discussed. Then, the relationship between hydrogen metabolism and uranium reduction has been further explored and the important role played by hydrogenase in uranium(VI) and iron(III) reduction by clostridia demonstrated. When hydrogen was provided as the headspace gas, uranium(VI) reduction occurred in the presence of whole cells of clostridia. This is in contrast to that of nitrogen as the headspace gas. Without clostridia cells, hydrogen alone could not result in uranium(VI) reduction. In alignment with this observation, it was also found that either copper(II) addition or iron depletion in the medium could compromise uranium reduction by clostridia. In the end, a comprehensive model was proposed to explain uranium reduction by clostridia and its relationship to the overall metabolism especially hydrogen (H2) production.

Effect of exogenous electron shuttles on growth and fermentative metabolism in Clostridium sp. BC1.

In this study, the influence exogenous electron shuttles on the growth and glucose fermentative metabolism of Clostridium sp. BC1 was investigated. Bicarbonate addition to mineral salts (MS) medium accelerated growth and glucose fermentation which shifted acidogenesis (acetic- and butyric-acids) towards solventogenesis (ethanol and butanol). Addition of ferrihydrite, anthraquinone disulfonate, and nicotinamide adenine dinucleotide in bicarbonate to growing culture showed no significant influence on fermentative metabolism. In contrast, methyl viologen (MV) enhanced ethanol- and butanol-production by 28- and 12-fold, respectively with concomitant decrease in hydrogen, acetic- and butyric-acids compared to MS medium. The results show that MV addition affects hydrogenase activity with a significant reduction in hydrogen production and a shift in the direction of electron flow towards enhanced production of ethanol and butanol.

Toxicity of various anions associated with methoxyethyl methyl imidazolium-based ionic liquids on Clostridium sp.

We investigated the effects on the growth of the anaerobic bacterium, Clostridium sp., of the ionic liquid, 1-methoxyethyl-3-methyl imidazolium [MOEMIM](+), derived from imidazolium cation and paired with one of a variety of counter-ions, viz., tetrafluoroborate [BF4]⁻, hexafluorophosphate [PF6]⁻(,) trifluoroacetate [CF3COO]⁻, bis(trifluoromethane)sulfonamide [Tf2N]⁻, methane sulfonate [OMS], and 1-butyl-3-methyl imidazolium tetrafluoroborate [BMIM][BF4]. These anions, in association with [MOEMIM](+) lowered the growth rate of the bacterium, showing the following trend: [Tf2N]⁻ ≧ [PF6]⁻ > [BF4]⁻ > [CF3COO]⁻ > [OMS]⁻. Anions incorporating fluorine were more toxic than those without it, and their toxicity rose with an increase in the number of fluorine atoms. Also, [MOEMIM](+)[BF4]⁻ was less toxic than [BMIM](+)[BF4]⁻, probably due to the presence of a methoxyethyl functional group integrated in the cation side chain.

Bioreduction of U(VI)-phthalate to a polymeric U(IV)-phthalate colloid.

Phthalic acid, a ubiquitous organic ligand, formed soluble mono- and biligand complexes with a uranyl ion that was then reduced to a U(IV)-phthalate by a Clostridium species under anaerobic conditions. We confirmed the reduction of the hexavalent uranium to the tetravalent oxidation state by UV-vis absorption and X-ray absorption near edge structure spectroscopy. Sequential micro- and ultrafiltration of the solution revealed that the bioreduced uranium was present as a colloid with particles between 0.03 and 0.45 microm. Analysis with extended X-ray absorption fine structure revealed the association of the reduced uranium with the phthalic acid as a repeating biligand 1:2 U(IV):phthalic acid polymer. This is the first report of the formation of a U(IV) complexed to two phthalic acid molecules in the form of a polymeric colloid. Although it was proposed that the bioreduction and the precipitation of uranium might be an invaluable strategy to immobilize uranium in contaminated environments, our results suggest that the organic ligands present there might hinder the precipitation of the bioreduced uranium under anaerobic conditions and, thereby, enhance its environmental mobility as uranium organic complexes or colloids.

Uranium phases in contaminated sediments below Hanford's U tank farm.

Macroscopic and spectroscopic investigations (XAFS, XRF, and TRLIF) on Hanford contaminated vadose zone sediments from the U-tank farm showed that U(VI) exists as different surface phases as a function of depth below ground surface (bgs). Secondary precipitates of U(VI) silicate precipitates (boltwoodite and uranophane) were present dominantly in shallow-depth sediments (15-16 m bgs), while adsorbed U(VI) phases and polynuclear U(VI) surface precipitates were considered to dominate in intermediate-depth sediments (20-25 m bgs). Only natural uranium was observed in the deeper sediments (> 28 m bgs) with no signs of contact with tank wastes containing Hanford-derived U(VI). Across all depths, most of the U(VI) was preferentially associated with the silt and clay size fractions of sediments. Strong correlation between U(VI) and Ca was found in the shallow-depth sediments, especially for the precipitated U(VI) silicates. Because U(VI) silicate precipitates dominate in the shallow-depth sediments, the released U(VI) concentration by macroscopic (bi)carbonate leaching resulted from both desorption and dissolution processes. Having different U(VI) surface phases in the Hanford contaminated sediments indicates that the U(VI) release mechanism could be complicated and that detailed characterization of the sediments using several different methods would be needed to estimate U(VI) fate and transport correctly in the vadose zone.

Interaction of uranium(VI) with phthalic acid.

Phthalic acid, a ubiquitous organic compound found in soil, water, and in domestic and nuclear wastes can affect the mobility and bioavailability of metals and radionuclides. We examined the complexation of uranium with phthalic acid by potentiometric titration, electrospray ionization-mass spectroscopy (ESI-MS), and extended X-ray absorption fine structure (EXAFS) analysis. Potentiometric titration of a 1:1 U/phthalic acid indicated uranyl ion bonding with both carboxylate groups of phthalic acid; above pH 5 the uranyl ion underwent hydrolysis with one hydroxyl group coordinated to the inner-sphere of uranium. In the presence of excess phthalic acid, ESI-MS analysis revealed the formation of both 1:1 and 1:2 U/phthalic acid complexes. EXAFS studies confirmed the mononuclear biligand 1:2 U/phthalic acid complex as the predominant form. These results show that phthalates can form soluble stable complexes with uranium and may affect its mobility.

Reduction of uranium(VI) to uranium(IV) by clostridia.

Several different species of clostridia reduced U(VI) to U(IV) to various degrees. The optimal pH for U(VI) reduction is 5 to 6 in most cases; a Clostridium sp. showed the highest rate at pH 4. Nitrate did not affect U(VI) reduction, indicating that this process in clostridia is nitrate independent.

Reductive dissolution of Pu(IV) by Clostridium sp. under anaerobic conditions.

An anaerobic, gram positive, spore-forming bacterium Clostridium sp., common in soils and wastes, capable of reduction of Fe(III) to Fe(II), Mn(IV) to Mn(II), Tc(VII) to Tc(IV), and U(VI) to U(IV), reduced Pu(IV) to Pu(III). Addition of 242Pu (IV)-nitrate to the bacterial growth medium at pH 6.4 resulted in the precipitation of Pu as amorphous Pu(OH)4 due to hydrolysis and polymerization reactions. The Pu (1 x 10(-5) M) had no effect upon growth of the bacterium as evidenced by glucose consumption; carbon dioxide and hydrogen production; a decrease in pH of the medium from 6.4 to 3.0 due to production of acetic and butyric acids from glucose fermentation; and a change in the Eh of the culture medium from +50 to -180 mV. Commensurate with bacterial growth, Pu was rapidly solubilized as evidenced by an increase in Pu concentration in solution which passed through a 0.03 microm filtration. Selective solvent extraction of the culture by thenoyltrifluoroacetone (TTA) indicated the presence of a reduced Pu species in the soluble fraction. X-ray absorption near edge spectroscopic (XANES) analysis of Pu in the culture sample at the Pu LIII absorption edge (18.054 keV) showed a shift of -3 eV compared to a Pu(IV) standard indicating reduction of Pu(IV) to Pu(III). These results suggestthat, although Pu generally exists as insoluble Pu(IV) in the environment, under appropriate conditions, anaerobic microbial activity could affect the long-term stability and mobility of Pu by its reductive dissolution.

Interactions of uranium with polyphosphate.

Inorganic polyphosphates (PolyP) are simple linear phosphate (PO(4)(3-)) polymers which are produced by a variety of microorganisms. One of their functions is to complex metals resulting in their precipitation. We investigated the interaction of phosphate and low-molecular-weight PolyP (1400-1900Da) with uranyl ion at various pHs. Potentiometric titration of uranyl ion in the presence of phosphate showed two sharp inflection points at pHs 4 and 8 due to uranium hydrolysis reaction and interaction with phosphate. Titration of uranyl ion and PolyP revealed a broad inflection point starting at pH 4 indicating that complexation of U-PolyP occurs over a wide range of pHs with no uranium hydrolysis. EXAFS analysis of the U-HPO(4) complex revealed that an insoluble uranyl phosphate species was formed below pH 6; at higher pH (> or = 8) uranium formed a precipitate consisting of hydroxophosphato species. In contrast, adding uranyl ion to PolyP resulted in formation of U-PolyP complex over the entire pH range studied. At low pH (< or = 6) an insoluble U-PolyP complex having a monodentate coordination of phosphate with uranium was observed. Above pH 6 however, a soluble bidentate complex with phosphate and uranium was predominant. These results show that the complexation and solubility of uranium with PO(4) and PolyP are dependent upon pH.

Chemical speciation and association of plutonium with bacteria, kaolinite clay, and their mixture.

We investigated the interactions of Pu(VI) with Bacillus subtilis, kaolinite clay, and a mixture of the two to determine and delineate the role of the microbes in regulating the environmental mobility of Pu. The bacteria, the kaolinite, and their mixture were exposed to a 4 x 10(-4) M Pu(VI) solution at pH 5.0. The amount of Pu sorbed by B. subtilis increased with time, but had not reached equilibrium in 48 h, whereas equilibrium was attained in kaolinite within 8 h. After 48 h, the oxidation state of Pu in the solutions exposed to B. subtilis and the mixture had changed to Pu-(V), whereas the oxidation state of Pu associated with B. subtilis and the mixture was Pu(IV). Exudates released from B. subtilis reduced Pu(VI) to Pu(V). In contrast, there was no change in the oxidation state of Pu in the solution or on kaolinite after exposure to Pu(VI). Scanning electron microscopy-energy dispersive spectrometry analysis indicated that most of the Pu in the mixture was associated with B. subtilis. These results suggest that Pu-(IV) is preferably sorbed to bacterial cells in the mixture and that Pu(VI) is reduced to Pu(V) and Pu(IV).

Thermodynamics and the structural aspects of the ternary complexes of Am(III), Cm(III) and Eu(III) with Ox and EDTA + Ox.

The stability constants and the associated thermodynamic parameters of formation of the binary and the ternary complexes of Am(3+), Cm(3+) and Eu(3+) were determined by a solvent extraction to measure the variation in the distribution coefficient with temperature (0-60 degrees C) for aqueous solutions of I = 6.60 m (NaClO(4)). The formation of ternary complexes is favored by both the enthalpy (exothermic) and the entropy (endothermic) values. (13) C NMR, TRLFS and EXAFS spectral data was used to study the coordination modes of the ternary complexes. In the formation of the complex M(EDTA)(Ox)(3-), the EDTA retained all its coordination sites with Ox binding via two carboxylates and with one water of hydration remaining attached to the M(3+). In the complex M(EDTA)(Ox)(2)(5-), one carboxylate, either from EDTA or Ox, is not bounded to M(3+) and there were no water of hydration attached to these cations.

Association of europium(III), americium(III), and curium(III) with cellulose, chitin, and chitosan.

The association of trivalent f-elements-Eu(III), Am(III), and Cm(III)--with cellulose, chitin, and chitosan was determined by batch experiments and time-resolved, laser-induced fluorescence spectroscopy (TRLFS). The properties of these biopolymers as an adsorbent were characterized based on speciation calculation of Eu(III). The adsorption study showed that an increase of the ionic strength by NaCl did not affect the adsorption kinetics of Eu(III), Am(III), and Cm(III) for all the biopolymers, but the addition of Na2CO3 significantly delayed the kinetics because of their trivalent f-element complexation with carbonate ions. It also was suggested from the speciation calculation study that all the biopolymers were degraded under alkaline conditions, leading to their masking of the adsorption of Eu(III), Am(III), and Cm(III) on the nondegraded biopolymers. The masking effect was higher for cellulose than for chitin and chitosan, indicating that of the three, cellulose was degraded most significantly in alkaline solutions. Desorption experiments suggested that some portion of the adsorbed Eu(III) penetrated deep into the matrix, being isolated in a cavity-like site. The TRLFS study showed that the coordination environment of Eu(III) is stabilized mainly by the inner spherical coordination in chitin and by the outer spherical coordination in chitosan, with less association in cellulose in comparison to chitin and chitosan. These results suggest that the association of these biopolymers with Eu(III), Am(III), and Cm(III) is governed not only by the affinity of the functional groups alone but also by other factors, such as the macromolecular steric effect. The association of degraded materials of the biopolymers also should be taken into consideration for an accurate prediction of the influence of biopolymers on the migration behavior of trivalent f-elements.

Determination of stability constants of U(VI)-Fe(III)-citrate complexes.

Ion-exchange experiments were performed to evaluate the formation of the uranium-citrate and uranium-iron-citrate complexes over a wide concentration range; i.e., environmentally relevant concentrations (e.g., 10(-6) M in metal and ligand) and concentrations useful for spectroscopic investigations (e.g., 10(-4) M in metal and ligand). The stability of the well-known uranium-citrate complex was determined to validate the computational and experimental methods applied to the more complex system. Values of the conditional stability constants for these species were obtained using a chemical equilibrium model in FITEQL. At a pH of 4.0, the stability constant for uranium-citrate complex (log beta1,1) was determined to be 8.71+/-0.6 at I = 0. Analysis of the results of ion-exchange experiments for the U-Fe-citric acid system indicates the formation of the 1:1:1 and 1:1:2 ternary species with stability constants (log beta) of 17.10+/-0.41 and 20.47+/-0.31, respectively, at I= 0.

Competitive inhibition and selectivity enhancement by Ca in the uptake of inorganic elements (Be, Na, Mg, K, Ca, Sc, Mn, Co, Zn, Se, Rb, Sr, Y, Zr, Ce, Pm, Gd, Hf) by carrot (Daucus carota cv. U.S. harumakigosun).

We investigated the uptake of inorganic elements (Be, Na, Mg, K, Ca, Sc, Mn, Co, Zn, Se, Rb, Sr, Y, Zr, Ce, Pm, Gd, and Hf) and the effect of Ca on their uptake in carrots (Daucus carota cv. U.S. harumakigosun) by the radioactive multitracer technique. The experimental results suggested that Na, Mg, K, and Rb competed for the functional groups outside the cells in roots with Ca but not for the transporter-binding sites on the plasma membrane of the root cortex cells. In contrast, Y, Ce, Pm, and Gd competed with Ca for the transporters on the plasma membrane. The selectivity, which was defined as the value obtained by dividing the concentration ratio of an elemental pair, K/Na, Rb/Na, Be/Sr, and Mg/Sr, in the presence of 0.2 and 2 ppm Ca by that of the corresponding elemental pair in the absence of Ca in the solution was estimated. The selectivity of K and Rb in roots was increased in the presence of Ca. The selectivity of Be in roots was not affected, whereas the selectivity of Mg was increased by Ca. These observations suggest that the presence of Ca in the uptake solution enhances the selectivity in the uptake of metabolically important elements against unwanted elements.