Selenate Se Research Articles

Stability of selenium compounds in aqueous extracts of dietary supplements during storage

The stability of two inorganic (selenite Se (IV) and selenate Se(VI)) as well as four organic (selenomethionine (SeMet), selenocystine (SeCys2), selenomethylocysteine (MeSeCys) and selenomethionine selenoxide (SeMetO)) selenium species were investigated in standard solutions and aqueous extracts of dietary supplements. All of the samples were without any stabilizer addition. The effect of the sample solvent pH and the storage temperature was investigated using hydrophilic interaction liquid chromatography coupled to mass spectrometry detection (HILIC-MS). It was proven that sample solvent has a great impact on the selenium stability. The lowest stability of selenium compounds is observed in ammonium acetate samples. Acidification of the solution increase the selenium stability (with the exception of SeMet in yeast sample). The results of the stability of selenium compounds obtained for the standard solutions are different than those for supplement samples, which shows the enormous influence of the sample matrix on the stability of selenium compounds. Light does not affect selenium stability in standard solutions as well as in supplements extracts.

Selenate Se(VI) reduction to elemental selenium on heterojunctioned rutile/brookite nano-photocatalysts with enhanced charge utilization

Newly synthesized nanocrystalline TiO2 mixed-phase photocatalysts are shown to surpass in Selenium (VI) reduction effectiveness the commercial P25 nanoTiO2 photocatalyst Heterojunctioned rutile (63 %)/brookite (37 %) (designated as R/b) nanoTiO2 is found to be the most effective photocatalyst achieving 95 % photo-assisted reductive deposition vs. 25 % only by the benchmark P25 composed of anatase (80 %) and rutile (A/r). This is attained at very high photocharge utilization with at least 5-fold less formic acid as hole scavenger. The superior performance of R/b is attributed to a favorable band alignment at the heterojunction and its 1D-dominated nanocrystal orientation enabling efficient co-adsorption and enhanced charge separation. The deposition of elemental Se further “auto-catalyzes” the photocatalytic process by enabling visible light activity with simultaneous suppression of charge recombination. In-depth probing of the R/b photocatalyst after selenium removal provides evidence of a 2-step mechanism involving (a) reductive adsorption of Se(VI)aq → Se(IV)surf with the participation of co-adsorbed formate and Ti3+ defects, and photoreduction of Se(IV)surf → Se(0)surf.

Selected antioxidant properties of alfalfa, radish, and white mustard sprouts biofortified with selenium

The aim of this study was to evaluate the effect of application of two mineral selenium forms (selenite Se<sup>4+</sup> or selenate Se<sup>6+</sup>) on the accumulation of this element by alfalfa (<em>Medicago sativa</em>), radish (<em>Raphanus sativus</em> var. <em>sativus</em>), and white mustard (<em>Sinapis alba</em>) at early stages of plant development for biofortification of sprouts with selenium, and the impact of this process on selected phytochemical traits. For this purpose, selenium-biofortified sprouts were analyzed for the contents of l-ascorbic acid and anthocyanin as well as their antioxidant activity. Additionally, the concentration of selenium in the biomass was determined. It was demonstrated that the application of selenium contributed to increased bioaccumulation of the element in the sprouts, constituting an effective method for the production of selenium-biofortified food. Selenate was accumulated less efficiently than was selenite. It was found that a concentration of 20 µmol L<sup>−1</sup> Se in the form of both selenate and selenite was an optimal dose for enrichment of the sprouts with this element. Biofortification of the experimental species with selenium (20 µmol L<sup>−1</sup>) generally increased accumulation of anthocyanins but did not significantly alter the level of l-ascorbic acid and free radical scavenging activity. Therefore, it seems that consumption of selenium-biofortified sprouts can be an effective way to supplement low-selenium diets with this element.

Speciation analysis of Se-enriched strawberries (Fragaria ananassa Duch) cultivated on hydroponics by HPLC-TR-HG-AFS

High-performance liquid chromatography (HPLC) has been coupled to atomic fluorescence spectroscopy (AFS) for speciation of inorganic Se (selenite Se(IV) and selenate Se(VI)) and selenoaminoacids (Se–methionine SeMet, Se–cystine SeCyst and Se–methylselenocisteine SeMeSeCys). A thermoreduction (TR) step is included before hydride generation (HG) to obtain the volatile hydrides of the selenium species before AFS detection. The instrumental coupling HPLC-TR-HG-AFS has been applied for Se speciation in strawberries collected from plants grown on hydroponics and exposed to inorganic Se (Se(IV) and Se(VI)) and one selenoaminoacid (SeMet). Application of Se was performed by foliar spray and root irrigation at concentrations between 0.5–500mgL−1. Of the three Se species applied by root irrigation, only Se(VI) was uptaken by the roots, with no significant biotransformation, followed by a sharp disaccumulation after stopping the selenate application. When selenite was applied by foliar spraying at a high concentration, a significant biotransformation was observed, mainly as SeMet. The results indicated that for strawberries, foliar spray is a more suitable route for Se uptake and biotransformation than root irrigation.

The role of counter ions in nano-hematite synthesis: Implications for surface area and selenium adsorption capacity

Nano metal oxides are of interest for aqueous selenium (Se) remediation, and as such, nano-hematite (nα-Fe2O3) was examined for use as a Se adsorbent. The effect of surface area on adsorption was also studied. nα-Fe2O3 particles were synthesized from Fe(NO3)3 and FeCl3 via forced hydrolysis. The resulting particles have similar sizes, morphologies, aggregate size, pore size, and PZC. The nα-Fe2O3 from FeCl3 (nα-Fe2O3-C) differs from the nα-Fe2O3 from Fe(NO3)3 (nα-Fe2O3-N) with a ∼25±2m2/g greater surface area. Selenite Se(IV) adsorption capacity on nα-Fe2O3 has a qmax ∼17mg/g for the freeze-dried and re-suspended nα-Fe2O3. The Δqmax for nα-Fe2O3 from Fe(NO3)3 and FeCl3 that remained in suspension was 4.6mg/g. For selenate Se(VI), the freeze-dried and re-suspended particles realize a Δqmax= 1.5mg/g for nα-Fe2O3 from Fe(NO3)3 and FeCl3. The nα-Fe2O3 from Fe(NO3)3 and FeCl3 that remained in suspension demonstrated Se(VI) Δqmax=5.4mg/g. In situ ATR–FTIR isotherm measurements completed for Se(VI) at a pH 6 suggest that Se(VI) forms primarily outer–sphere complexes with nα-Fe2O3 synthesized from both salts.

A comment on “Selenite adsorption and desorption in main Chinese soils with their characteristics and physicochemical properties.” J Soils Sediments 15(5):1150–1158 (2015), doi:10.1007/s11368-015-1085-7

Dear Editors-in-Chief: I would like to point out chemical inconsistency errors in the paper entitled BSelenite adsorption and desorption in main Chinese soils with their characteristics and physicochemical properties^ by Z. Li, N. Man, S. Wang, D. Liang, and J. Liu published in the Journal of Soils and Sediments (2015; 15(5):1150–1158) which invalidate almost the entire paper starting with the title. The authors assert that they were studying Se(IV) not Se(VI) adsorption, yet they prepared their Se solutions from Na2SeO4, clearly a hexavalent Se(VI) salt. Therefore, the authors were, in fact, studying the adsorption of Se(VI). Required corrections start with the title where the word Bselenite^ must be replaced by the word Bselenate^ or Bselenium^ to correctly reflect the chemistry of the Se solutions that were used in the investigation. The authors did not speciate their experimental Se solutions, but instead analyzed for total Se using hydride generation–atomic fluorescence spectrophotometry. If a Se speciation analysis had been carried out, the error in redox state would have become apparent. Throughout the manuscript, the authors compared their Se(VI) adsorption measurements to literature data for Se(IV) adsorption. Such comparisons are clearly invalid, especially since the adsorption behavior of Se(VI) on soils has been shown to be very different from that of Se(VI) by various authors (Neal et al. 1987a, b; Neal and Sposito 1989; Goldberg et al. 2008; Gabos et al. 2014; Goldberg 2014). Several of these investigations were cited by the authors in their current work. While the experimental data of Se(VI) adsorption on Chinese soils is valid and may potentially be publishable, especially given the small number of Se(VI) sorption studies currently in the literature, the title, figure captions, and virtually all discussion in the current publication are invalidated by the mislabeling of the Se species . The cur ren t manuscr ip t i s not va l id . Publication of an erratum will be insufficient to address these issues. The required corrections are so extensive that a new manuscript is warranted, necessitating the retraction of the current publication. The new manuscript must clearly state throughout that selenate Se(VI) adsorption is being investigated. Since the tables and figures in the current paper refer to elemental Se, they can be retained in the corrected submission.

Yeast as a model system to study metabolic impact of selenium compounds.

Inorganic Se forms such as selenate or selenite (the two more abundant forms in nature) can be toxic in Saccharomyces cerevisiae cells, which constitute an adequate model to study such toxicity at the molecular level and the functions participating in protection against Se compounds. Those Se forms enter the yeast cell through other oxyanion transporters. Once inside the cell, inorganic Se forms may be converted into selenide through a reductive pathway that in physiological conditions involves reduced glutathione with its consequent oxidation into diglutathione and alteration of the cellular redox buffering capacity. Selenide can subsequently be converted by molecular oxygen into elemental Se, with production of superoxide anions and other reactive oxygen species. Overall, these events result in DNA damage and dose-dependent reversible or irreversible protein oxidation, although additional oxidation of other cellular macromolecules cannot be discarded. Stress-adaptation pathways are essential for efficient Se detoxification, while activation of DNA damage checkpoint and repair pathways protects against Se-mediated genotoxicity. We propose that yeast may be used to improve our knowledge on the impact of Se on metal homeostasis, the identification of Se-targets at the DNA and protein levels, and to gain more insights into the mechanism of Se-mediated apoptosis.

TESTING OF SELENIUM INHIBITION EFFECT ON SELECTED CHARACTERISTICS OF GARDEN PEA

Phytotoxicity effect of sodium selenite Se(IV) and selenate Se(VI) was followed on selected characteristics of garden pea ( Pisum sativum) , such as germination, growth, chlorophyll production, content of dry material and water in the seedlings. Laboratory experiments were established in the Petri dishes, which were treated with sodium selenate (Na 2 SeO 4 ) and sodium selenite pentahydrate (Na 2 SeO 3 .5 H 2 O) on the selenium concentration levels 5.0; 20.0; 100.0; 300.0 and 500.0 mg Se/l. Phytotoxicity was tested by the tests of chronic phytotoxicity and the results obtained were evaluated as IC 50 values (half maximal inhibitory concentration) by probit analysis. Treatment of seedlings with the solutions of Se(IV) and Se(VI) on the concentration levels 5 mg and 20 mg/l resulted in enhanced growth of shoots and roots, especially after application of Se(IV), where the growth exceeded control for about 70 %. The IC 50 value was higher for the growth of shoots as well as for roots after application of Se(VI), what means that the growth inhibition in early growth stages of garden pea can be observed only in the high selenium concentrations (over 200 mg Se/l). Se(IV) showed more significant inhibition of chlorophyll production in the shoots of peas seedlings than Se(VI). Lower concentrations of Se(IV) and Se(VI) (below 100 mg Se/l) did not show significant differences between the water contents, but the higher concentrations (300 mg Se(IV)/l and 500 mg Se(VI)/l) resulted in significant differences, more than 9-times higher in roots.

Selenium speciation in Lower Cambrian Se-enriched strata in South China and its geological implications

To understand the impact of Selenium (Se) into the biogeochemical cycle and implications for palaeo-redox environment, a sequential extraction method was utilized for samples including black shales, cherts, a Ni–Mo–Se sulfide layer, K-bentonite and phosphorite from Lower Cambrian Se-enriched strata in southern China. Seven species (water-soluble, phosphate exchangeable, base-soluble, acetic acid-soluble, sulfide/selenide associated, residual Se) and different oxidation states (selenate Se(VI), selenite Se(IV), organic Se, Se (0) and mineral Se(-II)) were determinated in this study. We found that the Ni–Mo–Se sulfide layer contained a significantly greater amount of Se(-II) associated with sulfides/selenides than those in host black shales and cherts. Furthermore, a positive correlation between the degree of sulfidation of iron (DOS) and the percentage of the sulfide/selenide-associated Se(-II) was observed for samples, which suggests the proportion of sulfide/selenide-associated Se(-II) could serve as a proxy for palaeo-redox conditions. In addition, the higher percentage of Se(IV) in K-bentonite and phosphorite was found and possibly attributed to the adsorption of Se by clay minerals, iron hydroxide surfaces and organic particles. Based on the negative correlations between the percentage of Se(IV) and that of Se(-II) in samples, we propose that the K-bentonite has been altered under the acid oxic conditions, and the most of black shale (and cherts) and the Ni–Mo–Se sulfide layer formed under the anoxic and euxinic environments, respectively. Concerning Se accumulation in the Ni–Mo–Se sulfide layer, the major mechanism can be described by (1) biotic and abiotic adsorption and further dissimilatory reduction from oxidized Se(VI) and Se(IV) to Se(-II), through elemental Se, (2) contribution of hydrothermal fluid with mineral Se(-II).

Selenium accumulation in the floral tissues of two Brassicaceae species and its impact on floral traits and plant performance

Selenium (Se) is a metalloid that can occur naturally in soils from the Cretaceous shale deposits of a prehistoric inland sea in the western United States. Agricultural irrigation and runoff solubilizes Se from these shales, causing buildups of toxic levels of selenate (SeO 4 2−) in water and soil. Our main objective was to investigate the accumulation of Se in two Brassicaceae species chosen for their potential as phytoremediators of Se contaminated soils. We tested the hypothesis that Se will accumulate in the pollen and nectar of two plant species and negatively affect floral traits and plant reproduction. Certain species of Brassicaceae can accumulate high concentrations of Se in their leaf tissues. In this study Se accumulation in plant tissues was investigated under greenhouse conditions. Se accumulator ( Brassica juncea) and Se hyperaccumulator ( Stanleya pinnata) plants were irrigated in sand culture with 0 μM selenate (control), 8 μM selenate, and 13 μM selenate. Nectar and pollen in S. pinnata contained up to 150 μg Se mL −1 wet weight and 12900 μg Se g −1 dry weight when irrigated with 8 μM selenate. Se levels in nectar (110 μg Se mL −1 wet weight) and pollen (1700 μg Se g −1 dry weight) were not as high in B. juncea. Floral display width, petal area and seed pod length were significantly reduced in the 13 μM selenate Se treatment in B. juncea. S. pinnata floral traits and seeds were unaffected by the Se treatments. This study provides crucial information about where some of the highest concentrations of Se are found in two phytoremediators, and may shed light on the potential risks pollinators may face when foraging upon these accumulating plants. In the field, duration of the plant's exposure, Se soil and water concentrations as well as other environmental factors may also play important roles in determining how much Se is accumulated into the leaf and floral tissues. Our greenhouse study shed light on two species’ ability to accumulate Se, as well as determined the specific plant tissues where Se concentrations are highest.

Simultaneous speciation of arsenic (As(III), MMA, DMA, and As(V)) and selenium (Se(IV), Se(VI), and SeCN−) in petroleum refinery aqueous streams

High-performance liquid chromatography (HPLC) coupled to an ICP-MS with an octapole reaction system (ORS) has been used to carry out quantitative speciation of selenium (Se) and arsenic (As) in the stream waters of a refining process. The argon dimers interfering with the (78)Se and (80)Se isotopes were suppressed by pressurizing the octapole chamber with 3.1 mL min(-1) H(2) and 0.5 mL min(-1) He. Four arsenic species arsenite--As(III), arsenate (As(V)), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA)--and three inorganic Se species--selenite Se(IV), selenate Se(VI), and selenocyanate (SeCN(-))--were separated in a single run by ion chromatography (IC) using gradient elution with 100 mmol L(-1) NH(4)NO(3), pH 8.5, adjusted by addition of NH(3), as eluent. Repeatabilities of peak position and of peak area evaluation were better than 1% and about 3%, respectively. Detection limits (as 3sigma of the baseline noise) were 81, 56, and 75 ng L(-1) for Se(IV), Se(VI), and SeCN(-), respectively, and 22, 19, 25, and 16 ng L(-1) for As(III), As(V), MMA, and DMA, respectively. Calibration curve R (2) values ranged between 0.996 and 0.999 for the arsenic and selenium species. Column recovery for ion chromatography was calculated to be 97 +/- 6% for combined arsenic species and 98 +/- 3% for combined selenium species. Because certified reference materials for As and Se speciation studies are still not commercially available, in order to check accuracy and precision the method was applied to certified reference materials, BCR 714, BCR 1714, and BCR 715 and to two different refinery samples--inlet and outlet wastewater. The method was successfully used to study the quantitative speciation of selenium and arsenic in petroleum refinery wastewaters.

SELENIUM UPTAKE IN CEREALS GROWN IN LOWER AUSTRIA

In order to ensure optimum trace element supply via cereals, the uptake of selenium from a selenate containing NPK fertilizer (20:8:8, with 20 mg/kg selenate Se) was tested. A series of fi eld and pot experiments were run on a cambisol, a clay soil, a calcareous phaeozem, and a chernozem within the physiologically feasible range in 3 subsequent years. Selenate addition led to a signifi cant increase in all kinds of cereals investigated, and the memory in subsequent years was poor. The transfer of added selenium to the grains ranged between 0,7 and 4,7% in the fi eld conditions, and between 1,6 and 5,4 % from the pots. In the grains, selenium was specifi ed mainly as seleno-methionine. The selenium addition did not affect the contents of the other essential trace elements. Uptake from pot and fi eld experiments was different.

Bioaccumulation of waterborne selenium in the Asiatic clam Corbicula fluminea: influence of feeding-induced ventilatory activity and selenium species

A set of experiments was performed to investigate the bioavailability and the effect of Se on the ventilatory activity of the bivalve Corbicula fluminea, under different conditions of both algal cell densities and dissolved Se chemical forms and concentrations. A first set of experiments was conducted without selenium to investigate the changes in the ventilatory flow rate as a function of the concentration of the unicellular alga Chlamydomonas reinhardtii (10 5–10 6 cells mL −1). For algal concentrations below 2–3 × 10 5 cells mL −1, ventilatory activity was highly stimulated whereas it was independent of algal densities for higher values (up to 10 6 cells mL −1). To investigate the influence of this first ventilatory drive on selenium contamination process, bivalves were exposed to waterborne selenium at two different algal concentrations, selected to provide contrasting reference ventilatory activities. Three different selenium forms were studied [selenite Se(+IV), selenate Se(+VI) and selenomethionine SeMet] and were added into the water at concentrations of 50 and/or 500 μg L −1. Each selenium form induced a specific behavioural response, an increase, a decrease or no change of ventilation being observed for Se(+IV), SeMet and Se(+VI), respectively. Selenium accumulation by the organisms was investigated at the organ level for the different exposure conditions. Selenomethionine was the most bioaccumulated form, followed by selenate and selenite, respectively. Despite the bivalves displaying different ventilatory behaviours at low or high algal density, there was no evidence showing reduction or enhancement of Se uptake in the chemical domain investigated.

Effects of nano-Ag particles loading on TiO 2 photocatalytic reduction of selenate ions

The photocatalytic reduction of selenate Se(VI) ions was studied using unmodified TiO 2 and Ag-loaded TiO 2 (Ag-TiO 2) photocatalysts. In the presence of formic acid, both the TiO 2 and Ag-TiO 2 photocatalysts were effective in reducing Se(VI). The reaction proceeded through the reduction of Se(VI) ions to elemental selenium Se and then to hydrogen selenide gas (H 2Se). When unmodified TiO 2 photocatalyst was used, the Se formed from the reduction of Se(VI) was further reduced to Se 2− in the form of H 2Se upon the exhaustion of Se(VI) in solution. In the presence of the Ag-TiO 2 photocatalysts, hydrogen selenide gas was generated simultaneously with the reduction of Se(VI). It was found that the maximum Se(VI) reduction rate occurred at pH 3.5 and at a 0.5 at.% Ag loading while the maximum hydrogen selenide gas generation occurred at pH 3.5 and at 2.0 at.% Ag loading. The simultaneous reduction of Se(VI) to hydrogen selenide gas can be attributed to efficient charge separation due to the mediation of photogenerated electrons by the Ag particles. A mechanism is proposed in terms of the TiO 2-Ag-Se electronic interaction during UV irradiation.

Selenium content of barley as influenced by selenite and selenate‐enriched fertilizers

Abstract This study was conducted under field conditions to determine the effect of selenite as compared to selenate sources of Se added at the rates of 10, 20 and 40 g Se ha‐1, on Se concentration in barley. Rates of 10 g Se ha‐1, in the form of sodium selenate, were quite sufficient to enrich the barley grain to 234 μg Se kg‐1. Increasing the rates of selenate Se to 40 g ha‐1 raised the grain Se level to 959 μg kg‐1. With either calcium or sodium selenite, the high rate of 40 g Se ha‐1 was ineffective in raising the grain Se concentration. The grain Se concentration at 20 μg kg‐1 in the Se treated plots during the second year was similar to those in the control treatments regardless of the rate or source of Se used. Therefore, yearly applications of 10 g Se ha‐1 in the form of selenate fertilizer are recommended to enrich the cereal grain ‘to protect livestock from Se deficiency.

ASSIMILATION, DISTRIBUTION, AND METABOLISM OF (75Se)-SELENITE, SELENATE, AND SELENOAMINO ACIDS BYESCHERICHIA COLI

Abstract Assimilation of selenium (Se) by Escherichia coli as (75Se)-selenite, selenate, selenomethionine, selenocystine and Se‒CH3-selenocystine revealed that (a) selenoamino acids from a culture media are more completely assimilated than selenite or selenate and (b) that the amount of selenite is assimilated three to four times selenate. Most (>95%) of the Se assimilated by E. coli could not be solubilized by sonication and ethanol extraction but much (28% to 70%) of the Se, except Se from selenomethionine, was removed by alkaline dialysis. Se from selenocystine and from Se‒CH3-selenocystine dialyzed from intact cells, whereas Se from selenite and selenate did not. Dialyzable Se is that Se probably present in selenotrisulfide (R‒S‒Se‒S‒R) bonds or bound nonspecifically. Analysis of the soluble Se metabolites from selenite, selenate, selenomethionine and selenocystine showed that E. coli produces at least one major metabolic product common to all substrates which upon chromatography appeared to be selenocysteic acid. In monogastric animals selenite and selenate Se does not enter the primary protein structure as amino acids yet metabolites of selenite, selenate and selenocystine produced by E. coli could enter the primary protein structure of animals in minute amounts.