Transport of vanadium (V) in saturated porous media: effects of pH,ionic-strength and clay mineral

Vanadium, a hazardous pollutant, has been frequently detected in soil and groundwater, however, its transport behavior in porous media were not clearly understood. In this study, the effects of solution pH, ionic strength (IS) and the effect of clay mineral on the transport of vanadium in saturated porous media were investigated. Laboratory experiments using a series of columns packed with quartz sand were carried out to explore the retention and transport of vanadium with a range of ionic-strength (0.001–0.1 M) and pH (4–8) and two different types of clay minerals montmorillonite and kaolinite. Results of the breakthrough experiments showed that vanadium was highly mobile in the saturated porous media. The increase in pH rendered a higher transport of vanadium in saturated porous media. The study also indicated an easier transfer of vanadium with an increase in IS. Montmorillonite enhanced the mobility of vanadium in the column when compared to kaolinite. A mathematical model based on advection-dispersion equation coupled with equilibrium and kinetic reactions was used to describe the retention and transport of vanadium in the columns very well.     

Inhibitory effect of molybdenum and vanadium salts on aflatoxin B1 synthesis by Aspergillus flavus

The effects of the elements zinc, manganese, iron, copper, molybdenum, and vanadium, added in various salt forms, on mycelial weights and aflatoxin B1 accumulation in the mycelium of Aspergillus flavus were investigated in liquid shake cultures. Ammonium heptamolybdate, when added to a complete medium at concentrations of 50-100 mg/L, appreciably reduced aflatoxin B1 accumulation without affecting growth of the fungus. Sodium molybdate and sodium monovanadate also reduced aflatoxin B1 yields without affecting mycelial growth but to a lesser extent. The addition of zinc sulphate stimulated aflatoxin B1 production in all media used. The influence of the other trace elements on aflatoxin production depended on the level of trace elements present in the basal medium. In general, manganese chloride had a stimulatory effect, whereas copper sulphate depressed yields. Mycelial levels of aflatoxin had peaked and then declined before mycelial dry weights had reached maximum. High yields of aflatoxin B1 were obtained in media having a final pH as low as pH 2.8.     

Mutants of Streptococcus faecalis sensitive to alkaline pH lack Na(+)-ATPase.

Alkali-sensitive mutants which grow at pH 7.5 but not at pH 9.5 in Na(+)-rich media were isolated from Streptococcus faecalis ATCC 9790. One of the mutants, designated Nak1, lacked activities of both Na(+)-stimulated ATPase and KtrII (active K+ uptake by sodium ATPase). These activities were restored in a spontaneous revertant designated Nak1R. Active sodium extrusion from Nak1 was observed at pH 7.0, which allows the cells to generate a proton potential, but not at pH 9.5, which reverses the proton potential, making it positive. Sodium extrusion at pH 7.0 was inhibited by addition of dicyclohexylcarbodiimide and protonophores. Even at pH 9.5, Nak1 did grow well in Na(+)-poor media. In Na(+)-rich media at pH 7.5, growth of Nak1 but not that of 9790 was severely inhibited by a protonophore. These results indicate that mutant Nak1 lacks sodium ATPase but contains a sodium/proton antiporter and that sodium ATPase is essential for the growth of this organism at high pH in Na(+)-rich conditions.     

Removal of Vanadium(III) and Molybdenum(V) from Wastewater Using Posidonia oceanica (Tracheophyta) Biomass

The use of dried and re-hydrated biomass of the seagrass Posidonia oceanica was investigated as an alternative and –low-cost biomaterial for removal of vanadium(III) and molybdenum(V) from wastewaters. Initial characterisation of this biomaterial identified carboxylic groups on the cuticle as potentially responsible for cation sorption, and confirmed the toxic-metal bioaccumulation. The combined effects on biosorption performance of equilibrium pH and metal concentrations were investigated in an ideal single-metal system and in more real-life multicomponent systems. There were either with one metal (vanadium or molybdenum) and sodium nitrate, as representative of high ionic strength systems, or with the two metals (vanadium and molybdenum). For the single-metal solutions, the optimum was at pH 3, where a significant proportion of vanadium was removed (ca. 70%) while there was ca. 40% adsorption of molybdenum. The data obtained from the more real-life multicomponent systems showed that biosorption of one metal was improved both by the presence of the other metal and by high ionic strength, suggesting a synergistic effect on biosorption rather than competition. There data ware used for the development of a simple multi-metal equilibrium model based on the non-competitive Langmuir approach, which was successfully fitted to experimental data and represents a useful support tool for the prediction of biosorption performance in such real-life systems. Overall, the results suggest that biomass of P. oceanica can be used as an efficient biosorbent for removal of vanadium(III) and molybdenum(V) from aqueous solutions. This process thus offers an eco-compatible solution for the reuse of the waste material of leaves that accumulate on the beach due to both human activities and to storms at sea.     

Laboratory-evolved vanadium chloroperoxidase exhibits 100-fold higher halogenating activity at alkaline pH: catalytic effects from first and second coordination sphere mutations

Directed evolution was performed on vanadium chloroperoxidase from the fungus Curvularia inaequalis to increase its brominating activity at a mildly alkaline pH for industrial and synthetic applications and to further understand its mechanism. After successful expression of the enzyme in Escherichia coli, two rounds of screening and selection, saturation mutagenesis of a "hot spot," and rational recombination, a triple mutant (P395D/L241V/T343A) was obtained that showed a 100-fold increase in activity at pH 8 (k(cat) = 100 s(-1)). The increased K(m) values for Br(-) (3.1 mm) and H(2)O(2) (16 microm) are smaller than those found for vanadium bromoperoxidases that are reasonably active at this pH. In addition the brominating activity at pH 5 was increased by a factor of 6 (k(cat) = 575 s(-1)), and the chlorinating activity at pH 5 was increased by a factor of 2 (k(cat) = 36 s(-1)), yielding the "best" vanadium haloperoxidase known thus far. The mutations are in the first and second coordination sphere of the vanadate cofactor, and the catalytic effects suggest that fine tuning of residues Lys-353 and Phe-397, along with addition of negative charge or removal of positive charge near one of the vanadate oxygens, is very important. Lys-353 and Phe-397 were previously assigned to be essential in peroxide activation and halide binding. Analysis of the catalytic parameters of the mutant vanadium bromoperoxidase from the seaweed Ascophyllum nodosum also adds fuel to the discussion regarding factors governing the halide specificity of vanadium haloperoxidases. This study presents the first example of directed evolution of a vanadium enzyme.     

Effects of potassium sorbate and other antibotulinal agents on germination and outgrowth of Clostridium botulinum type E spores in microcultures.

The effects of potassium sorbate, sodium hypophosphite, sodium tripolyphosphate, sodium nitrite, and linoleic acid on the germination and outgrowth of Clostridium botulinum type E spores were studied in microcultures. At pH 5.8 to 6.0 in liver veal agar, the germination rate was decreased to nearly zero with 1.0, 1.5, or 2.0% sorbate. At pH 7.0 t 7.2, these levels of sorbate afforded germination and outgrowth of abnormally shaped cells that were defective in cell division. At the high pH range, 0.5 or 1.0% hypophosphite had effects similar to those of sorbate. The use of 0.05% sodium nitrite with sorbate enhanced the lysis of outgrowing cells at pH 7.2 or lower. Emergence and elongation were inhibited by 0.05% linoleic acid with or without 1.0% sorbate at pH 7.0 to 7.2. The addition of 0.5% tripolyphosphate to media containing 1.5% sorbate at pH 7.1 prevented normal cell growth to an extent greater than with sorbate alone.     

Rapid sodium cyanide depletion in cell culture media: outgassing of hydrogen cyanide at physiological pH

During the course of in vitro studies on cyanide exposure with SH-SY5Y human neuroblastoma cells, we found that sodium cyanide (NaCN) up to a concentration of 10 mM had no significant toxic effect under our culture conditions. Further investigation of this apparent cyanide resistance revealed that the sodium cyanide was being rapidly depleted from the cell culture medium. Cyanide was interacting with constituents of the cell culture medium and was somehow being detoxified or removed from solution. The reaction of cyanide with cell culture media in 96-well culture plates reduced cyanide concentrations rapidly (80-90% in 2 h at 37 degrees C). Running the same reaction in capped tubes significantly reduced cyanide loss from solution. Incubation of cyanide with individual constituents of the cell culture medium in solution showed that glucose, phenol red, and amino acids all acted to detoxify or remove cyanide from solution. When amino acids or buffers were incubated with sodium cyanide in aqueous solution at pH 7.4, hydrogen cyanide (HCN) was found to degas from the solutions. We compared HCN outgassing over a range of pH values. As expected, HCN remained very soluble at high pH, but as the pH was reduced to 7.0, the rate of HCN formation and outgassing increased dramatically. Acid-base reactions involving cyanide and proton donors, such as amino acids and other cell culture media constituents, at physiological pH result in rapid HCN outgassing from solution at 37 degrees C. These results indicate that previous in vitro cyanide toxicity studies done in standard culture media with prolonged incubation times using gas-exchanging culture containers might have to be reevaluated in light of the fact that the effective cyanide concentrations in the culture media were significantly lower than reported.     

INVESTIGATIONS REGARDING THE NATURE OF THE INTERACTION BETWEEN IRON AND MOLYBDENUM OR VANADIUM IN NUTRIENT SOLUTIONS WITH AND WITHOUT A GROWING PLANT

Iron offset the toxicity of molybdenum or vanadium in nutrient solutions more effectively when it was supplied at the same time as the molybdenum or vanadium than when it was given separately in alternate 3-day periods.
Allowing nutrient solutions of pH 4.6 containing high concentrations of iron, with or without vanadium, to stand for 4 days before use did not delay the restoration of colour to chlorotic plants, but even z days' standing reduced the iron content of their roots and the vanadium content of both shoot and root. The presence of vanadium had little effect on iron uptake.
In parallel experiments with molybdenum, standing the solutions for 7–9 days before use delayed colour recovery, but shorter periods had no effect. Standing for z days or longer greatly reduced the iron content of the root, but the molybdenum content was unaffected or increased. High molybdenum greatly increased the iron in the root, but had little effect on that in the shoot.
Precipitation of iron in the nutrient solution was delayed by high concentrations of either ammonium or sodium molybdate if the initial pH was 4.6, but not if it was 6.6. Vanadium had no influence on the precipitation of iron at pH 4.6.
At least part of the compensating action of iron on molybdenum or vanadium toxicity would appear to take place outside the plant.     

Kinetics and mechanism of oxidation of some aldoses by vanadium(v) in perchloric acid medium

The kinetics of oxidation of some aldoses by vanadium(V) in perchloric acid media have been investigated. Each reaction is first order with respect to both [Vanadium(V)] and [Aldose]. The reactions are catalysed by acid. The addition of sodium perchlorate accelerates the rate of reaction. Kinetic evidence for the formation of an intermediate compound between vanadium(V) and aldoses is insignificant, and a mechanism is suggested in which vanadium(V) reacts with the aldoses by a fast step to form a transition state, followed by the decomposition of the latter to give the products of reaction in a slow step. The formation of free-radical intermediates has been demonstrated, and one-electron reduction of vanadium(V) by aldoses seems to be the most plausible mechanism. The oxidation rates follow the order: xyloses arabinose galactose mannose. The activation parameters are reported.     

Cultivation of denitrifying bacteria: optimization of isolation conditions and diversity study

An evolutionary algorithm was applied to study the complex interactions between medium parameters and their effects on the isolation of denitrifying bacteria, both in number and in diversity. Growth media with a pH of 7 and a nitrogen concentration of 3 mM, supplemented with 1 ml of vitamin solution but not with sodium chloride or riboflavin, were the most successful for the isolation of denitrifiers from activated sludge. The use of ethanol or succinate as a carbon source and a molar C/N ratio of 2.5, 20, or 25 were also favorable. After testing of 60 different medium parameter combinations and comparison with each other as well as with the standard medium Trypticase soy agar supplemented with nitrate, three growth media were highly suitable for the cultivation of denitrifying bacteria. All evaluated isolation conditions were used to study the cultivable denitrifier diversity of activated sludge from a municipal wastewater treatment plant. One hundred ninety-nine denitrifiers were isolated, the majority of which belonged to the Betaproteobacteria (50.4%) and the Alphaproteobacteria (36.8%). Representatives of Gammaproteobacteria (5.6%), Epsilonproteobacteria (2%), and Firmicutes (4%) and one isolate of the Bacteroidetes were also found. This study revealed a much more diverse denitrifying community than that previously described in cultivation-dependent research on activated sludge.     

Reduction of vanadium(V) with Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans

Biotechnological leaching has been proposed as a suitable method for extraction of vanadium from spent catalysts and oil ash. In the biological leaching process, the vanadium(V) can be reduced to vanadium(IV), which is a less toxic and more soluble form of the vanadium. The present investigation showed that Acidithiobacillus ferrooxidans efficiently reduced vanadium(V) in the form of vanadium pentaoxide, to vanadyl(IV) ions, and tolerated high concentrations of vanadium(IV) and vanadium(V). A. ferrooxidans was compared with Acidithiobacillus thiooxidans, which has previously been utilized for vanadium leaching and reduction. Vanadium pentaoxide and sodium vanadate were used as model compounds. The results of this study indicate possibilities to develop an economical and technically feasible process for biotechnological vanadium recovery.     

Tiron administration minimizes the toxicity of vanadate but not its insulin mimetic properties in diabetic rats.

Although it has been reported that vanadate is effective in diminishing the expression of diabetes in the rat, the severe toxic side effects noted in the vanadate-treated animals suggest that chronic oral administration of vanadate argues against its use in human diabetes. The present study was conducted to evaluate the effects of the chelator Tiron on the mobilization of vanadium after administration of sodium metavanadate in the drinking water (0.20 mg/ml) of streptozotocin-induced diabetic rats for 35 days. Intraperitoneal treatment with Tiron (300 or 600 mg/kg) was initiated after three weeks of vanadate administration and continued for two weeks. The ameliorative effects of vanadium with respect to diabetes were not diminished by the administration of Tiron, but the accumulation of vanadium in kidney and bone was significantly decreased in the Tiron-treated groups and diabetes associated increases in serum GOT, GPT and cholesterol were diminished with Tiron treatment. It is concluded that the coadministration of metavanadate and Tiron may be of potential value for treatment of diabetes mellitus.     

Extracellular sodium is required for methacholine-induced secretion of mucus glycoconjugates from canine tracheal explants

Extracellular sodium is known to influence secretion by certain secretory cells, possibly by mobilizing calcium from cellular stores or by altering intracellular pH via regulation of a Na(+)-H+ antiport system. Using canine tracheal explants, we determined whether agents which alter sodium fluxes are capable of modulating basal or cholinergically-induced secretion of mucus glycoconjugates. Methacholine, a cholinergic agonist, increased mucus secretion from explants incubated in the presence or absence of calcium, but had no effect on secretion when incubated in sodium-deficient media, indicating (a) that cholinergically-induced secretion can be mediated by mobilization of cellular calcium and (b) that extracellular sodium was required for this stimulatory effect. Several agents which increase intracellular sodium were tested for their effect on mucus secretion. Ouabain, a sodium pump inhibitor, and veratridine, a sodium channel activator, did not significantly affect control or methacholine-induced secretion; gramicidin, a sodium ionophore, also had no effect on basal release. Tetrodotoxin, a sodium channel inhibitor, was also without effect on basal or methacholine-stimulated mucus release. Agents which alter intracellular pH were also examined for their effects on basal or methacholine-induced glycoconjugate secretion. Amiloride, which decreases intracellular pH by inhibiting Na(+)-H+ exchange, produced a 19 per cent increase in basal secretion (not statistically significant), but had no effect on methacholine-induced secretion. An agent, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), which decreases intracellular pH by inhibiting HCO3(-)-Cl- exchange, elicited decreases in both basal and methacholine-induced secretion, but the inhibition did not reach statistical significance.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gill Na(+), K(+)-ATPase in a series of hyper-regulating gammarid amphipods: enzyme characterisation and the effects of salinity acclimation

The enzyme Na(+), K(+)-ATPase was investigated in the gills of selected hyper-regulating gammarid amphipods. Gill Na(+), K(+)-ATPase was characterised with respect to the main cation and co-factor concentrations for the freshwater amphipod Gammarus pulex. The optimum cation and co-factor concentrations for maximal gill Na(+), K(+)-ATPase activity in G. pulex were 100mM Na(+), 15mM K(+), 15mM Mg(2+) and 5mM ATP, at pH 7.2. The effects of salinity acclimation on gill Na(+), K(+)-ATPase activity and haemolymph sodium concentrations was investigated in selected gammarid amphipods from different salinity environments. Maximal enzyme activity occurred in all gammarids when acclimated to the most dilute media. This maximal activity coincided with the largest sodium gradient between the haemolymph and the external media. As the haemolymph/medium sodium gradient decreased, a concomitant reduction in gill Na(+), K(+)-ATPase activity occurred. This implicates the involvement of gill Na(+), K(+)-ATPase in the active uptake of sodium from dilute media in hyper-regulating gammarids.     

Vanadate as factor of cardiovascular regulation by interactions with the catecholamine and nitric oxide systems

The effects of 1 μg/ mL of vanadium, given for 12 mo as sodium metavanadate in drinking water, on cardiovascular and biochemical indices of male rabbits were investigated. At the end of the exposure period, vanadium was more accumulated in bones and kidneys than in spleen and liver; the cardiac ventricles and the aorta contained similar amounts of this element. Blood pressure and heart rate were unchanged in the vanadate-exposed animals since the observed decrease of both cardiac inotropism and stroke volume was counteracted by an increase of peripheral vascular resistance, with reduction of arterial blood flow. The arterial levels of sodium, potassium and aldosterone were unmodified by vanadate which, however, strongly raised those of noradrenaline, adrenaline, L-DOPA, and dopamine. Vanadate caused a marked increase of the activity of monoamine oxidase in renal tubules and liver (probably in relation to the increased plasma catecholamine levels) and a reduction of that of glucose-6-phosphate dehydrogenase in the kidney. There was also evidence that vanadium reduces synthesis and/or release of nitric oxide, the endothelium-derived vasodilating factor, likely through a reduced formation from bradykinin. It was concluded that vanadium may represent an environmental factor of altered cardiovascular homeostasis.     

The brown alga Ascophyllum nodosum contains two different vanadium bromoperoxidases

Haloperoxidases have been detected in a variety of organisms, including bacteria, fungi, algae, and mammals. Mammalian haloperoxidases are known to be directly involved in the oxidative destruction of microorganisms. The algal bromoperoxidases are probably involved in the biosynthesis of bromometabolites, most of which show considerable bactericidal activity. From the brown seaweed Ascophyllum nodosum (order, Fucales) two different bromoperoxidases have been isolated, which both contain vanadium as an essential element for enzymic activity. The location of these two enzymes, determined by activity staining of cross-sections of algal parts, was different. Bromoperoxidase I (which has been described before) was located inside the thallus, particularly around the conceptacles, whereas bromoperoxidase II was present at the thallus surface of the alga. The molecular masses of these bromoperoxidases as judged from sodium dodecyl sulfate-gel electrophoresis were 97 and 106 kDa, respectively. Some of the enzymatic properties (pH optimum and Km for bromide) of the two enzymes were slightly different, whereas the amino acid compositions were more or less equal. The isoelectric point of the two proteins was the same, namely 5.0. On sodium dodecyl sulfate-polyacrylamide gels both enzymes could be stained with periodic acid Schiff's reagent, so both are glycoproteins. Since only bromoperoxidase II could be bound to a concanavalin A-Sepharose column, these enzymes contain different carbohydrates. Both enzymes display a considerable thermostability. However, the chemical stability of the two bromoperoxidases differed. Bromoperoxidase II could also be inactivated by dialysis at low pH and reactivation was only possible with the transition metal vanadium and not with other metal ions. The presence of vanadium in this enzyme could be established with atomic absorption spectrophotometry and electron paramagnetic resonance. The EPR signals of both bromoperoxidases, which were observed after reduction with sodium dithionite, were similar: only minor differences were observed in the hyperfine coupling. In immunoblotting experiments these two bromoperoxidases were found to cross-react, so they have common antigenic determinants.     

Elimination of overgrowth in delayed-incubation membrane filter test for total coliforms by m-ST holding medium.

Two holding media were compared for their effects on total coliform recovery by the delayed-incubation membrane filter procedure. LES-MF holding medium contains tryptone, m-Endo broth, dipotassium hydrogen phosphate, sodium benzoate, sulfanilamide, para-aminobenzoic acid, and cycloheximide (pH 7.0). m-ST holding medium contains ethanol, sodium monophosphate, dipotassium hydrogen phosphate, sulfanilamide, and Tris (pH 8.6). In tests with natural water and wastewater samples from various sources, recovery with LES-MF and m-ST were similar after a 1-day holding period. With LES-MF, however, after a 2- or 3-day holding period, coliform bacteria frequently were partially or totally overgrown by noncoliforms, causing significant reductions in coliform counts. No significant overgrowth was observed with m-ST. We propose that m-ST be used for all holding periods longer than 1 day.     

Elimination of overgrowth in delayed-incubation membrane filter test for total coliforms by m-ST holding medium

Two holding media were compared for their effects on total coliform recovery by the delayed-incubation membrane filter procedure. LES-MF holding medium contains tryptone, m-Endo broth, dipotassium hydrogen phosphate, sodium benzoate, sulfanilamide, para-aminobenzoic acid, and cycloheximide (pH 7.0). m-ST holding medium contains ethanol, sodium monophosphate, dipotassium hydrogen phosphate, sulfanilamide, and Tris (pH 8.6). In tests with natural water and wastewater samples from various sources, recovery with LES-MF and m-ST were similar after a 1-day holding period. With LES-MF, however, after a 2- or 3-day holding period, coliform bacteria frequently were partially or totally overgrown by noncoliforms, causing significant reductions in coliform counts. No significant overgrowth was observed with m-ST. We propose that m-ST be used for all holding periods longer than 1 day.     

Vanadium-enriched chickpea sprout ameliorated hyperglycemia and impaired memory in streptozotocin-induced diabetes rats

Vanadium compounds have been recognized for their hypoglycemic effects; however, potential short and long-term vanadium toxicity has slowed the acceptance for therapeutic use. In the present work, three batches of vanadium-enriched chickpea sprout (VCS) were prepared by incubating chickpea seeds in presence of 200, 100, and 50 mug/ml of sodium orthovanadate (SOV). The effects of oral administration of chickpea sprout (CS) and VCS food for 8 weeks on streptozotocin-induced (STZ) diabetic rats were investigated. Both CS and VCS food was found to ameliorate some hyperglycemic symptoms of the diabetic rats, i.e. improve lipid metabolism, decrease blood glucose level, prevent body weight loss, and reduce impairment of diabetic related spatial learning and memory. Serum insulin was substantially elevated in treated diabetic rats, which is probably one important reason for the hypoglycemic effect. Compared with CS alone, VCS100 food exhibited remarkably enhanced effectiveness in alleviating diabetes induced hyperglycemia and memory loss. Moreover, vanadium-enriched chickpeas appeared to abolish the vanadium induced toxicity associated with administration of this metal for diabetes during the 8-week study period. This study suggested further work of the vanadium speciation in CS and novel hypoglycemic mechanism for the antidiabetic activity of vanadium agents. Vanadium containing (VCS) food could be a dietary supplement for the diabetic status.     

Non-aqueous capillary electrophoresis of drugs: properties and application of selected solvents

The electrophoretic mobility of selected acidic and basic test solutes have been determined in non-aqueous media prepared by adding various combinations of ammonium acetate, sodium acetate, methane sulphonic acid and acetic acid to acetonitrile, propylene carbonate, methanol, formamide, N-methylformamide, N,N-dimethylformamide and dimethylsulphoxide, respectively. The apparent pH (pH*) of these non-aqueous media have been measured and it was found that pH* is an important factor for the separations in non-aqueous capillary electrophoresis. However, in some solvents the concentration of sodium acetate has a strong influence on the mobility despite very small changes in pH*. Due to the fact that a change in one parameter influences a number of other parameters it is very difficult to conduct systematic studies in non-aqueous media and to compare the migration of the species at fixed pH* values from one solvent to another. Thus pH* is only of value for comparison when used with a specific solvent or solvent mixture. The viscosity of the above-mentioned solvents were measured at various temperatures and means to adjust the viscosity of the non-aqueous media used for capillary electrophoresis are discussed and the separation of ibuprofen and its major metabolites in urine is used as an example.