Release Of Selenium Research Articles

The Leaching Characteristics of Selenium from Coal Fly Ashes

The leaching characteristics of selenium from several bituminous and subbituminous coal fly ashes under different pH conditions were investigated using batch methods. Results indicated that pH had a significant effect on selenium leaching from bituminous coal ash. The minimum selenium leaching occurred in the pH range between 3 and 4, while the maximum selenium leaching occurred at pH 12. The release of selenium from subbituminous coal ashes was very low for the entire experimental pH range, possibly due to the high content of calcium which can form hydration or precipitation products as a sink for selenium. The adsorption results for different selenium species indicated that Se(VI) was hardly adsorbable on either bituminous coal ashes or subbituminous coal ashes at any pH. However, Se(IV) was highly adsorbed by bituminous coal ashes under acidic pH conditions and was mostly removed by subbituminous coal ashes across the entire pH range. This result suggests that the majority of selenium released from the tested fly ashes was Se(IV). A speciation-based model was developed to simulate the adsorption of Se(IV) on bituminous coal fly ash, and the pH-independent adsorption constants of HSeO3* and SeO3 2* were determined. The modeling approach is useful for understanding and predicting the release process of selenium from fly ash.

The release and behavior of mercury, selenium, and boron in coal combustion

The release of mercury, selenium and boron from coal is investigated at high temperatures using a drop tube furnace and a coal combustion test facility. The results show that under combustion conditions, most of the mercury and selenium are released from the coal and did not remain in the fly ash at high temperatures, but some of the boron remains in the fly ash at high temperature. Under reducing conditions, all of the mercury is released from the coal, and some of the selenium and most of the boron remains in the coal char at 1473 K. This indicates that oxidation reaction contributes to the release of selenium and boron from coal. The transfer of these elements from gas to fly ash in coal combustion is tested as a function of temperature. The results show that mercury and selenium are captured on fly ash below 773 K, and the capture ratio increases as the temperature decreases. The transfer of boron from gas to fly ash is small between 393 K and 1273 K.

A thermodynamical approach to the formation reactions of sodium-doped Cu(In,Ga)Se 2

This work describes the influence of sodium doping on the formation reactions of the semiconductor material Cu(In,Ga)Se 2. Assuming the sodium dopant to act as a surface catalyst by formation of sodium polyselenides, we estimate the shift in the reaction enthalpies for the formation of binary selenides. Since the release of selenium from sodium polyselenides is an endothermic process, five of six possible reactions resulting in copper selenides are energetically suppressed whereas all indium and gallium selenides can still be formed exothermically. Furthermore, we have applied the effective heat of formation model on the ternary Cu–In–Se system to predict the first compound being formed during the selenisation of the metallic precursor. Our model predicts that sodium doping does not influence which selenide compound will be formed at first, but that influences consecutive reactions by shifting their reaction enthalpies.

Spatial and time-dependent patterns of selenium (Se) release from selected Se fertiliser granules

The spatial and time-dependent patterns of selenium (Se) release from similar-sized granules of 4 Se fertilisers, 3 containing sodium selenate (Unitech Agsel, Ravensdown A, and Ravensdown B) and the fourth containing sodium selenate and barium selenate (Selcote Ultra), were evaluated using ryegrass grown on a Se-deficient soil under glasshouse conditions. Four granules (2–3 mm diameter) from each of the 4 fertiliser types having uniform shape and similar weight were placed on the soil surface of trays (0.51 m length, 0.42 m width, 0.15 m depth) at a distance 0.10 m from 2 adjacent sides of the trays, and the Se content of herbage in concentric rings around each granule was periodically measured over 1 year. The amount of Se applied to the trays, calculated by adding herbage Se to the residual fertiliser Se in soil at the end of the trial, was 12–31 g Se/ha. Soil Se concentration at the end of the trial for the Selcote Ultra and Ravensdown A treatments and herbage Se concentration at 10 harvests for all fertiliser treatments decreased exponentially with increased distance from the granules. Herbage Se concentration reached the level considered deficient to animals (0.05 mg/kg) at the centre of the tray (0.12 m from the granules) 4 months after Unitech Agsel application (7% of paddock area). By 9 months all plants in this treatment became deficient in Se. In contrast, 7% of the sward area in the Ravensdown A treatment, and 41% of the sward area in the Ravensdown B and Selcote Ultra treatments, were deficient in Se at this time, but the average herbage Se concentration for the entire tray was above the deficiency level for these 3 fertiliser treatments. The efficiency of the fertilisers in increasing herbage Se concentration per unit weight of Se applied for the first 3 months was: Unitech Agsel ≥ Ravensdown B ≥ Ravensdown A > Selcote Ultra. During the last 3 months, this order was: Selcote Ultra = Ravensdown A > Ravensdown B > Unitech Agsel.

Enhancement of enzymatic digestion of Antarctic krill and successive extraction of selenium organic compounds by ultrasound treatment

In a previous work we described the isolation of selenium organic species from Antarctic krill after enzymatic hydrolysis. In this paper we present the results of the influence of ultrasonication on the enzymatic treatment and the successive isolation of selenomethionine. We showed that ultrasound-assisted enzymatic digestion leads to quantitative release of selenium in the soluble fraction and recovery of selenomethionine from the krill protein within a time 2 orders of magnitude shorter. The solubilised sample was analysed by size-exclusion chromatography and the selenomethionine content was quantified by high-performance liquid chromatography-inductively coupled plasma mass spectrometry. In total, 99% of the selenomethionine in the krill hydrolysate was recovered from the chromatographic fractions. It corresponds to 35% of the total selenium content in Antarctic krill. Monitoring by microscopy of the changes in the structure of the krill samples during ultrasonication suggested that the enhancement of the ultrasound-assisted enzymatic reaction was mainly due to decrease of mass transfer limitations. A reference experiment for ultrasound-assisted enzymatic digestion of cell-free protein in a homogeneous system does not exclude direct influence of the ultrasound energy on the enzyme-substrate interaction.

An Investigation on the Structure of Polyselenocyanogen [Se 2 (CN) 2 ] x

The structure of polyselenocyanogen [Se2(CN)2] x is analogous to that of polythiocyanogens, which have the general formula [S y (CN)2)] x (y=1,2,3,...). This result is based on the surprising fact that the FT-IR spectrum of the former compound is similar to the spectra of the latter class of compounds and on other experimental data. Thus, the proposed structure for polyselenocyanogen involves polyazomethine chains connected together by selenium bridges. Selenocyanogen Se2(CN)2 polymerizes when treated with certain organic solvents. The polymerization was followed by electronic spectroscopy and involves the formation of peculiar absorption bands in the visible and near infrared portion of the spectrum. Alternatively, selenocyanogen polymerization is promoted by thermal treatment in high boiling solvents like xylenes and decalin. The resulting polymer shows an FT-IR spectrum comparable to that of polythiocyanogens. The thermal stability of selenocyanogen has been studied by thermogravimetric analysis (TGA) in conjunction with differential thermal analysis (DTA). Heating of Se2(CN)2 under N2 to 650°C causes conversion into paracyanogen (CN) x with the release of selenium.

Selenium-dependent metabolism of purines: A selenium-dependent purine hydroxylase and xanthine dehydrogenase were purified from Clostridium purinolyticum and characterized.

During purification of the selenium-dependent xanthine dehydrogenase (XDH) from Clostridium purinolyticum, another hydroxylase was uncovered that also contained selenium and exhibited similar spectral properties. This enzyme was purified to homogeneity. It uses purine, 2OH-purine, and hypoxanthine as substrates, and based on its substrate specificity, this selenoenzyme is termed purine hydroxylase (PH). The product of hydroxylation of purine by PH is xanthine. A concomitant release of selenium from the enzyme and loss of catalytic activity on treatment with cyanide indicates that selenium is essential for PH activity. Selenium-dependent XDH, also purified from C. purinolyticum, was found to be insensitive to oxygen during purification and to use both potassium ferricyanide and 2,6-dichloroindophenol as electron acceptors. Selenium is required for the xanthine-dependent reduction of 2, 6-dichloroindophenol by XDH. Kinetic analyses of both enzymes revealed that xanthine is the preferred substrate for XDH and purine and hypoxanthine are preferred by PH. This characterization of these selenium-requiring hydroxylases involved in the interconversion of purines describes an extension of the pathway for purine fermentation in the purinolytic clostridia.

Selenium contamination, redistribution and remobilisation in sediments of Lake Macquarie, NSW

This paper examines the history of selenium pollution in Lake Macquarie, NSW, Australia, and three factors that may affect the redistribution and remobilisation of particle bound selenium: changes in redox state, bioturbation, and bioaccumulation by macrobenthos and bacteria. Sediment cores were taken from Nords Wharf, a relatively unpolluted area, and from Mannering Bay near the Vales Point coal-fired power station. The age profile at the unpolluted site seems to indicate that mild selenium pollution has been occurring for over 100 years, however, some mixing of the sediments has occurred. At the polluted site, the age profile indicated that major contamination has occurred in the last 30 years, due to a fly ash dam associated with nearby electric power generation facilities. The contamination chronology suggests that remobilisation and reduction processes have affected the selenium profile. Changing the redox state of Lake Macquarie sediment results in a release of selenium under oxidising conditions and immobilisation under reducing conditions. The sediment-bound selenium was associated with the operationally defined ‘organic/sulfide’ fraction under reducing conditions, and as the redox potential increases this moves into the ‘exchangeable’ and ‘iron/manganese oxyhydroxide’ phases to a limited extent. Bioturbation by the animals Marphysa sanguinea and Spisula trigonella caused increases in the redox potential and pore water selenium concentrations in surficial sediments relative to unbioturbated controls. Both animals accumulated significantly more selenium when exposed to contaminated sediment than when exposed to uncontaminated control sediments. Selenium concentrations in molluscs from Mannering Bay were all significantly higher than those collected from Nords Wharf. Most of the selenium in the mollusc tissues was found to be associated with the protein fraction. Selenium isolated from hydrolysed muscle tissue was not present as selenate or selenite but as selenomethionine and an unidentified compound. Seven types of bacteria were isolated from Lake Macquarie sediment. All seven isolates were able to transform selenite quantitatively to elemental selenium as evidenced by a red precipitate and identified by X-ray diffraction. Six isolates grew on media containing selenate but no elemental selenium was formed. Mass balances showed that for three isolates total selenium was conserved, selenate decreased and selenium (0; II-) increased indicating the production of non-volatile organic selenium compounds. For two isolates both total selenium and selenate decreased with no increase in selenium (0; II-), therefore, loss of selenium occurred from the media. Selenium is immobile in anoxic reduced sediments but may become available to benthos and fish as a consequence of sediment oxidation associated with bioturbation leading to bioaccumulation and transformation by macrobenthos and bacteria. These mechanisms can be invoked as possible transport pathways to explain the presence of selenium above background concentrations in preindustrial sediments, but further work dating the sediments in which elevated concentrations of selenium are found is needed to confirm this hypothesis.

Enzymatic digestion-high-pressure homogenization prior to slurry introduction graphite furnace atomic absorption spectrometry for selenium determination in plant and animal tissues.

Homogenization using a new flat valve homogenizer in combination with enzymatic digestion with a crude protease was investigated as a means of releasing Se compounds from zoological and botanical matrixes prior to slurry introduction GFAAS. Timed trials with four zoological certified reference materials (CRMs), three botanical reference materials (RMs), and a food crop indicated that Se release into 5% (v/v) ethanol-0.03 M TRIS containing 20 mg of protease was quantitative after homogenization or became quantitative within 1 h of digestion at 60 degrees C. For each of the zoological RMs (whole egg powder, dogfish muscle, and dogfish liver), three passes through the homogenizer in the presence of protease provided a quantitative release of selenium, and incubation with the enzyme was not necessary. No separation of the Se between the liquid phase and the particulate phase was evident even after several days of subsequent storage at 4 degrees C. The botanical matrixes (three milled wheat RMs and a rapeseed sample) were more resistant to selenium release and required up to 1 h of digestion with protease at 60 degrees C. Alternatively, 10 passes through the homogenizing valve (in the presence of the enzyme) resulted in the quantitative release of analyte.

Release of selenium and tin from the graphite support in the presence of tungsten and palladium modifiers

Electrothermal at. absorption spectrometry is applied to study the release of the selenium and tin atoms from pyrocoated graphite support. The Coats and Redfern and Sturgeon approaches were used for estn. of the apparent activation energies of atom release. The addn. of tungsten and palladium modifiers leads to enhancement of the activation energies and changes the kind of the vaporizing species for analytes. [on SciFinder (R)]

The effect of a zinc, cobalt and selenium soluble glass bolus on immune function in Lambs

Trace element deficiencies are common in many countries and affect animal health, productivity and welfare. Trace elements that can be limiting in animal nutrition include copper, cobalt, selenium and zinc. Deficiency diseases may be manifested as a consequence of a single or a multiple element deficiency. Deficiency in any of the above trace elements can result in an increased disease susceptibility and a decreased immune function. A soluble glass bolus has been developed for the sustained release of zinc, cobalt and selenium to sheep, using the same technology as the commercially available copper, cobalt and selenium bolus (Cosecure). The aim of this experiment was to observe whether the trace elements released from the bolus would have an effect on the immune function of sheep, as measured by the humoral immune response to a novel antigen.

Studies on the Pharmacokinetics of Ebselen in Rats (3): Absorption, Distribution and Excretion after Administration of 75Se-labelled Compound.

In order to clarify whether ebselen, 2-phenyl-1, 2-benzisoselenazol-3(2H)-one is metabolized to liberate its selenium atom as an inorganic compound(s) or not in vivo, blood level of radioactivity and excretion of radioactivity in urine and feces were determined, and whole body autoradiograms were prepared after oral administration of 75Se-ebselen (50 mg/kg) or intravenous injection of Na275SeO3, an inorganic selenium compound, as a control (1 mg/kg) to male rats. Following results were obtained: 1. For 75Se-ebselen dosing group, the mean blood levels of radioactivity reached the Cmax of 29.17 nmol eq. to ebselen/ml (8.00 μg eq./ml) at 1 hr and declined with a half-life, t1/2 of 7.6 hr from 2 to 24 hr after dosing. For Na275SeO3 dosing group, the blood level of radioactivity was 57.75 nmol eq. to Na275SeO3/ml (9.99 μgeq./ml) at the first sampling time and thereafter declined slowly with a half-life, t1/2 of 190 hr from 24 to 168 hr after dosing. 2. For 75Se-ebselen dosing group, the highest levels of radioactivity were observed in the gastric and intestinal contents, followed by fat, brown fat and liver, showing higher radioactivity than that in blood. The overall distribution of radioactivity decreased with time and the radioactivity was not detected at 168 hr after dosing. For Na275SeO3 dosing group, high levels of radioactivity remained in liver, kidney and blood even at 168 hr after dosing. 3. For 75Se-ebselen dosing group, within 168 hr after dosing, 53.8% of the dosed radioactivity was excreted in urine, and 45.8% of that in feces. The residual radioactivity in the carcass was not detected. For Na275SeO3 dosing group, within 168 hr after dosing, 44.8% of the dosed radioactivity was excreted in urine, and 8.0% of that in feces. The radioactivity remained in the carcass, being 41.1% of the dose. From the results above, the extent of inorganic selenium release from ebselen was estimated to be 0.0% of the dose.

Mobilization of selenium by a selenium-dependent bacterium

A selenium-dependent bacterium, Bacillus sp., failed to grow on selenium-free media. However, it is able to grow at high concentrations of sodium selenite containing media up to 3% (w/v). It accumulated extraordinary high quantities of selenium, 432 ppm/mL. The bacterium generated the transformation of inorganic selenium into volatile selenium form(s) into the atmosphere. The biological release of volatile selenium basically depended on several factors: incubation temperature, pH, incubation periods, and substrate concentration. Maximal quantity of the volatile selenium form was obtained at 30 degrees C, pH 7, and 1% (w/v) sodium selenite.

Grouted Waste Leach Tests: Pursuit of Mechanisms and Data for Long-Term Performance Assessment

ABSTRACTAt Hanford, low-level liquid nuclear waste is being mixed with cementitious materials (grout) to form leach-resistant solid waste. Prior to grouting each liquid waste, an assessment must be performed to evaluate the long-term environmental impact. These predictions rely upon a diffusioncontrolled release model and short-term laboratory leach data on small grout samples. This paper describes size scale-up and inventory scale-up experiments that evaluate whether diffusion does in fact control the release of contaminants. The results of the volume scale-up test suggest that tests on grout cylinders between the sizes 3 cm dia. by 3 cm length and 30 cm dia. by 29 cm length yield comparable results. These data and other available literature suggest that extrapolation of leach results to large blocks of solidified waste is defensible.The inventory scale-up tests for 125I and selenium show a constant effective diffusivity regardless of the original inventory. This suggests that diffusion processes do in fact control the release of iodide and selenium from grout. The 99Tc effective diffusivities may not remain constant with changes in inventory.

The efficacy of intraruminal pellets composed of elemental selenium and iron in sheep

Commercial selenium pellets, manufactured after CSIRO workers drew attention to the significance of grain size on the rate of release of selenium, were tested in 27 sheep grazing a low-selenium New Zealand pasture. The pellets were shown by microscopy to contain mainly 10-20 pm particles of selenium, often agglomerated into larger lumps. There was a considerable variation in the length of time pellets maintained blood selenium levels above the deficiency level of 250 nmol/e (20 microg/l). Whereas four animals given pellets had blood levels below 250 nmol/l after only 343 days, two animals had levels of 375 and 400 nmol/l after 651 days when the level in control sheep was 125 +/- 32 nmol/l. The pellets were recovered from all but one animal and had varying degrees of surface coating which was assumed to be mainly calcium phosphate. Two pellets recovered from sheep at 386 and 484 days, when blood selenium levels were 175 and 1813 nmol/l respectively, were sectioned and examined by light and electron microscopy. Both pellets still contained unreacted selenium but differed in the degree of surface coating. The pellet recovered at 386 days had a solid and continuous coating whereas the coating on the pellet recovered at 484 days was not continuous and consisted of an open lattice of interlocking needles. It appears that it is the extent of this coating which limits the effective life of the pellet in sheep.

Reaction cements as materials for the sustained release of trace elements into the digestive tract of cattle and sheep. II. Release of cobalt and selenium.

Acid-base reaction cements, containing salts of copper, cobalt and selenium, were placed in the reticulum of sheep and cattle, and the rate of release of cobalt and selenium from them was measured. The rate of release of cobalt decreased with time but was sufficient to provide adequate supplementation for at least 6 months. After an initial rate of release of 4 mg Se/day for 1-2 weeks, the mean subsequent rate of release of selenium over a period of 4 months was 0.1 mg Se/day (identical to 5 micrograms Se/day/cm2 surface area). Field trials in lambs and growing steers showed that the cement increased the selenium concentration of their blood throughout a summer grazing period.

Studies with the intraruminal selenium pellet. 2. The effect of grain size of selenium on the functional life of pellets in sheep

Grain size of elemental selenium is a major factor controlling the long-term effectiveness of intraruminal selenium pellets. Microscope studies of polished sections of new and used selenium pellets showed that two commercially manufactured pellets contained selenium with average grain sizes about 4 and 40 �m respectively. Plasma selenium concentrations in sheep treated with pellets containing the coarse-grained selenium were maintained at higher levels over longer periods of time than those measured for sheep treated with pellets with fine-grained selenium. Pellets removed from sheep after 2, 4, 8, 16 and 28 days showed a progressive increase in the degree of alteration of selenium to a compound of average composition (g/100 g) iron, 33.7; selenium, 51.3 ; oxygen, 15.0. After 28 days only a small percentage of elemental selenium remained in pellets with fine-grained selenium, whereas about 50% remained in pellets with coarse-grained selenium. CSIRO prototype pellets, for which long-term effectiveness had been established, also contained coarse-grained selenium, and remnants of selenium were found in pellets that had been in sheep for periods up to 3 years. Selenium, administered in gelatin capsules or as sachets containing glass-selenium mixtures, was stable under the pH-Eh conditions of the rumen, but was rendered unstable in selenium pellets or iron-selenium mixtures by the presence of iron. It is probable that the most rapid release of selenium to the sheep occurs as a result of a chemical reaction involving the oxidation of iron and concomitant alteration of elemental selenium to iron selenide.

Purification and properties of glutathione peroxidase from human placenta

Glutathione peroxidase (glutathione--H2O2 oxidoreductase; EC 1.11.1.9) was purified to homogeneity from human placenta by using (NH4)2SO4 precipitation, ion-exchange chromatography, Sephadex gel filtration and preparative polyacrylamide-disc-gel electrophoresis. Glutathione peroxidase from human placenta is a tetramer, having 4g-atoms of selenium/mol of protein. The molecular weight of the enzyme is about 85000 with a subunit size of about 22,000. Kinetic properties of the enzyme are described. On incubation with cyanide, glutathione peroxidase is completely and irreversibly inactivated and selenium is released as a low-molecular-weight fragment. Reduced glutathione, beta-mercaptoethanol and dithiothreitol protect the enzyme from inactivation by cyanide and the release of selenium. Properties of human placental glutathione peroxidase are similar to those of isoenzyme A reported earlier by us from human erythrocytes. The presence of isoenzyme, B, reported earlier by us in human erythrocytes, was not detected in placenta. Also selenium-independent glutathione peroxidase (isoenzyme II), which is specific for cumene hydroperoxide, was not present in human placenta.

Interaction between cadmium and selenium in rat plasma.

The metabolism of (75)Se-labeled SeO(3) (2-) and its conversion by intact rat erythrocytes in vitro to a form which complexes with Cd and plasma proteins were studied. By utilizing both excess SeO(3) (2-) and N-ethylmaleimide to lower erythrocyte reduced glutathione (GSH) concentrations, it was shown that the uptake and metabolism of SeO(3) (2-) were GSH-dependent, the probable intermediate being glutathione selenotrisulfide (GSSeSG). Secondary release of selenium by rat erythrocytes had no relation to the erythrocyte transport of oxidized glutathione (GSSG). While fluoride depressed and chromate increased GSSG transport, chromate, a glutathione reductase inhibitor, decreased selenium release. This release appeared to be secondary to a reaction catalyzed by glutathione reductase. The similarity of I(50) values for chromate's inhibition of glutathione reductase and for the inhibition of selenium release further suggested a relationship between these two events. H(2)Se or a similar product of GSSeSG reduction is proposed to be the active product of SeO(3) (2-) metabolism by rat erythrocytes. By use of gel-filtration and ion-exchange methods it was noted that the incubation of H(2)Se with cadmium and plasma produced a Cd-Se complex indistinguishable from that produced by incubation of Cd, SeO(3) (2-), plasma, and erythrocytes in vitro, or that noted following the administration of Cd and SeO(3)in vivo. A mechanism whereby the tissue distribution and toxicity of cadmium are altered by selenium is suggested.

Glutathione peroxidase: Inhibition by cyanide and release of selenium

Treatment of highly purified ovine erythrocyte glutathione peroxidase with KCN resulted in loss of enzyme activity and release of selenium from the enzyme. The inactivation by cyanide was time-dependent and the rate was strongly influenced by temperature, concentration of cyanide, oxidation state of the enzyme, and pH. The pH effect could be explained on the basis of the increasing proportion of cyanide ion with increasing pH. Inhibition could be prevented by prior reduction of the purified enzyme with glutathione, dithiothreitol, or dithionite. Oxidation with cumene hydroperoxide was necessary to demonstrate cyanide inhibition of glutathione peroxidase activity in rat liver cytosol. These observations explain why cyanide inhibition of glutathione peroxidase has not been noted previously and provide new approaches for studying the chemical nature of the enzyme-selenium.