Higher Se Concentrations Research Articles

Extreme enrichment of selenium in the Apliki Cyprus-type VMS deposit, Troodos, Cyprus

ABSTRACTThe Troodos ophiolite Cyprus hosts the type locality for Cyprus-type, mafic volcanogenic massive sulfide (VMS) deposits. Regional soil geochemical data for Troodos are highly variable with the Solea graben, one of three regional graben structures on Cyprus, showing enrichment in Te and Se. Of the three VMS sampled within the Solea graben, Apliki exhibits the most significant enrichment in Se. Samples from the South Apliki Breccia Zone; a zone of hematite-rich breccia containing euhedral pyrite and chalcopyrite, contain up to 4953 and 3956 ppm Se in pyrite and chalcopyrite, respectively. Four paragenetic stages are identified at Apliki and different generations of pyrite are distinguishable using trace-element chemistry analysed via laser ablation inductively coupled plasma mass spectrometry. Results indicate stage I pyrite formed under reduced conditions at high temperatures >280°C and contains 182 ppm (n = 22 σ = 253) Se. Late stage III pyrite which is euhedral and overprints chalcopyrite and hematite is enriched in Se (averaging 1862 ppm; n = 23 σ = 1394). Sulfide dissolution and hematite formation displaced large amounts of Se as hematite cannot accommodate high concentrations of Se in its crystal structure. The mechanisms proposed to explain the pronounced change in redox are twofold. Fault movement leading to localized seawater ingress coupled with a decreasing magmatic flux that generated locally oxidizing conditions and promoted sulfide dissolution. A Se/S ratio of 9280 indicates a probable magmatic component for late stage III pyrite, which is suggested as a mechanism explaining the transition from oxidizing back to reduced conditions. This study highlights the significance of changes in redox which promote sulfide dissolution, mobilization and enrichment of Se.

Activity and Stability Relationship for Anion Doped CoSxSe2-X Dichalcogenides for the Hydrogen Evolution Reaction

As an ideal clean energy carrier, hydrogen can be produced through polymer electrolyte membrane (PEM) electrolysis by generating H2 from H2O. However, noble platinum group metals (PGM) remain the most common electrocatalysts for hydrogen evolution reaction (HER). The expense and scarcity of these catalytic materials obstruct the wide-spread adoption of electrochemical fuel generation technologies 1. Sulfur based transition metal dichalcogenides (TMDs) have emerged as a promising alternative to PGM HER electrocatalysts as they are abundant, inexpensive, and exhibit a low HER overpotential in acidic environment 2,3. Here we present a systemic assessment of the compositional dependent HER activity and stability for Co-based mixed chalcogen, CoSxSe2-x, pyrite TMDs. We observe a decrease in HER activity from the single chalcogen TMDs, CoS2 and CoSe2, to mixed chalcogen TMDs, as shown in Figure 1. This observed compositional trend in HER activity can be explained by the unique combination of compositional dependent hydrogen adsorption free energy (ΔGHad) and bulk resistivity/conductivity of the pyrite TMD. With near thermoneutral ΔGHad, the highest resistivity among the compositions was observed. The following increase in Se content leads to the decrease in HER activity due to a steady movement away from optimal ΔGHad. As the composition approaches CoSe2, however, it is observed that HER activity again increases at higher Se contents, with CoSe2 exhibiting similar activity to CoS2. This highlights the convolution of ΔGHad and material conductivity in determining the HER activity. Furthermore, through stability tests under constant potential HER electrolysis, as shown in Figure 2, Se-rich Co-based pyrite TMDs are found to be more durable than S-rich samples. Therefore, with an HER activity matching that of CoS2, but with a dramatic improvement in stability, CoSe2 breaks away from the traditional inverse activity/stability relationship and represents a promising material for non-PGM HER electrocatalysis in acidic based PEM electrolyzers. Wang, J. et al. Mater. 28, (2016) 215-230.Chhowalla, H. et al. Nature Chemistry 5, (2013) 263-275.Jaramillo, T. et al. Science 317, (2007) 100-102. Figure 1

Toxicity and Translocation of Selenium in Phaseolus vulgaris L.

Selenium (Se) is not considered an essential nutrient for plants, although trace amounts of this element can enhance the growth and yield of some plant species. The application of sodium selenate in staple foods has been proposed as an alternative to minimize Se deficiency in the human diet. However, the threshold between deficiency and toxicity for Se is very narrow. Different plant species vary considerably in the absorption and accumulation of Se in shoots and other edible parts, and also in the tolerance to high Se concentrations in the soil. Therefore, this study aimed to evaluate the Se toxicity in common bean plants grown under high doses of sodium selenate, and the Se translocation of contaminated bean seeds to next generation grains. The study was carried out on a field experiment with the application of four rates of sodium selenate (0, 50, 500 and 5000 g/ha) to the soil were common bean crop was grown. Following, greenhouse conditions were used to investigate the translocation of Se from enriched seeds to the grains. The common bean showed tolerance to sodium selenate rates up to 500 g/ha, with reduction of yield observed at rate of 5000 g/ha. Even with no symptoms of toxicity the application rates of 500 g/ha of sodium selenate to the soil produced grains with concentrations of Se that surpass the limit established by Brazilian food law. The seeds enriched with Se can translocate this nutrient to the next generation.

Evaluation of trace elements in U.S. coals using the USGS COALQUAL database version 3.0. Part II: Non-REY critical elements

Coal is a potential source of some valuable elements. In this work, concentrations of 25 critical elements in U.S. coals were evaluated using the COALQUAL Database Version 3.0 aiming to identify best coal sources for potential recovery of critical element. A method was proposed to calculate the mean concentrations of critical elements in U.S. coals, including Li (11.5 ppm), Be (1.9 ppm), Ti (721 ppm), V (21.6 ppm), Mn (50.8 ppm), Co (4.5 ppm), Ga (5.1 ppm), Ge (7.2p pm), Se (2.4 ppm), Zr (30.4 ppm), Nb (3.3 ppm), Sn (1.8 ppm), Sb (1.0 ppm), Ba (266 ppm), Hf (0.77 ppm), and Ta (0.19 ppm).Based on the calculated mean concentrations, a rough estimate indicates that U.S. coals contain a large amount of critical elements that are enough to meet U.S. demands for many years to come, if these elements can be commercially extracted. By comparing with the suggested cut-off grades, we found that 5.8% of the coal samples have Ga concentrations higher than the suggested cut-off grade. The percentages of promising coal samples (higher than cut-off grades) of other elements are below 3%. Results further indicate that despite some variations among elements, bituminous coals from the Appalachian region are likely to have high concentrations of Li, Ga, Be, Se, and Sb which make them a potential source of these critical elements. Bituminous coals from the Interior Coal Province, both Eastern and Western, were found to have relatively high probabilities of having high Ge concentrations. Very limited coal samples were found from mixed regions to have V and Zr concentrations higher than the corresponding suggested cut-off grades.

Selenium Distribution for Soils Derived from Mancos Shale in Gunnison and Uncompahgre River Basins, West-Central Colorado

ABSTRACTSelenium (Se) is an essential micronutrient for humans and animals and can be toxic when present in high concentrations in soil and water. Many soils in Gunnison and Uncompahgre River Basins in West-Central Colorado are formed from deposits derived mainly from weathered Mancos shale that have high concentration of Se and salts. Elevated concentrations of Se and salts were detected in streams and rivers in this area. The objectives were to determine the amount and distribution of different forms of Se and relationships with physical and chemical properties for soils derived from Se-rich Mancos shale. The information may help to improve land management practices and minimize the environmental impact on natural water resources. A total of 48 topsoil samples and soils from horizons in 9 pedons were investigated. The total and water-soluble Se and other elements as well as physical and chemical properties were determined in soils. The total Se ranged from 330 to 5,673 µg/kg with a mean of 2,224 µg/kg. The water-soluble Se ranged from a minimum of 4.95 µg/kg to a maximum of 2,415 µg/kg and a mean of 338 µg/kg. A highly significant correlation was detected between the total and water-soluble Se in soils. Both the total organic carbon (TOC) and CaCO3% had significant positive correlations with the total Se. A highly significant correlation was also found between the water-soluble Se and electric conductivity (EC), as well as with the water-soluble chloride, sulfate, nitrate, molybdenum, and sodium in soils. For the pedons tested, in general, both the total and water-soluble Se increased with depth. However, the water-soluble Se concentrations were greater in shallow than deep pedons where most Se was removed from soils with drainage water. It could be concluded that Se leaching from topsoils and that dissolving from Se-rich parent materials would be a major source of elevated Se concentrations in streams/rivers for the West-Central Colorado area. To minimize the impact on water quality, an appropriate land/water management practices should be followed to minimize Se leaching from soils derived from Mancos shale.

Comparative effects on nutritional quality and selenium metabolism in two ecotypes of Brassica rapa exposed to selenite stress

The metalloid selenium (Se) is one of the important micronutrients for humans and plant growth. However, high Se concentrations in the soil is toxicity to normal plants. Therefore, research on Se metabolism in plants and its biological impacts on plant growth is very important. The vegetable Brassica rapa (B. rapa), known as a Brassicaceae Se accumulator, is a very important organic Se source for humans. In the present study, to investigate the Se metabolism in B. rapa under selenite (SeIV) stress, two species of B. rapa, B. rapa var. perviridis (Br. perv) and B. rapa var. purpuraria (Br. purp), have been selected as model plants. We grew the two B. rapa ecotypes in different Se(IV) concentrations and monitored biomass, physiological phenotypes, Se distribution and transport rates. The results reveal that low concentration Se(IV) can improve the nutritional quality of both B. rapa species, but Se can more significantly affect the biomass of Br. purp than Br. perv. And the Se content in Br. purp was up to 2 times higher than in Br. perv. Furthermore, expression levels of genes from Se metabolism-related gene families, such as APS, APR, SAT, SMT, CysD and MMT, were analyzed using qRT-PCR assays. The qRT-PCR results show that Br. purp was more tolerant to Se(IV) treatment than Br. perv. The present study is very important for further characterize the Se uptake and translocation metabolism in different ecotypes of B. rapa.

Soil Selenium (Se) Biofortification Changes the Physiological, Biochemical and Epigenetic Responses to Water Stress in Zea mays L. by Inducing a Higher Drought Tolerance.

Requiring water and minerals to grow and to develop its organs, Maize (Zea mays L.) production and distribution is highly rainfall-dependent. Current global climatic changes reveal irregular rainfall patterns and this could represent for maize a stressing condition resulting in yield and productivity loss around the world. It is well known that low water availability leads the plant to adopt a number of metabolic alterations to overcome stress or reduce its effects. In this regard, selenium (Se), a trace element, can help reduce water damage caused by the overproduction of reactive oxygen species (ROS). Here we report the effects of exogenous Se supply on physiological and biochemical processes that may influence yield and quality of maize under drought stress conditions. Plants were grown in soil fertilized by adding 150 mg of Se (sodium selenite). We verified the effects of drought stress and Se treatment. Selenium biofortification proved more beneficial for maize plants when supplied at higher Se concentrations. The increase in proline, K concentrations and nitrogen metabolism in aerial parts of plants grown in Se-rich substrates, seems to prove that Se-biofortification increased plant resistance to water shortage conditions. Moreover, the increase of SeMeSeCys and SeCys2 forms in roots and aerial parts of Se-treated plants suggest resistance strategies to Se similar to those existing in Se-hyperaccumulator species. In addition, epigenetic changes in DNA methylation due to water stress and Se treatment were also investigated using methylation sensitive amplified polymorphism (MSAP). Results suggest that Se may be an activator of particular classes of genes that are involved in tolerance to abiotic stresses. In particular, PSY (phytoene synthase) gene, essential for maintaining leaf carotenoid contents, SDH (sorbitol dehydrogenase), whose activity regulates the level of important osmolytes during drought stress and ADH (alcohol dehydrogenase), whose activity plays a central role in biochemical adaptation to environmental stress. In conclusion, Se-biofortification could help maize plants to cope with drought stress conditions, by inducing a higher drought tolerance.

The influence of selenium on expression levels of the rbcL gene in Chlorella vulgaris.

In this study, the effects of selenium on the microalgae Chlorella vulgaris were examined. Four groups of C. vulgaris were cultivated using Bristol medium: group I (control), no sodium selenite (Se); group II, 1µM Se; group III, 10µM Se; and group IV, 100µM Se. Algal biomass samples were collected for biochemical evaluation and gene expression studies on the 21st day of cultivation. The following parameters were investigated: chlorophyll a (Cla), chlorophyll b (Clb) and total carotene content, total protein, and total glutathione (GSH) and malondialdehyde (MDA) levels. Gene expression levels of large subunits of Rubisco (rbcL) were analyzed using real-time quantitative polymerase chain reaction. Total Cla and total carotene in C. vulgaris decreased in high concentrations of Se (100µM) (around 23 and 42%, respectively) when compared to controls while, Clb content increased by about 10%. 10µM of Se led to increased GSH levels (3.04 ± 0.02µg GSH/mg protein) and decreased MDA levels (2.02 ± 0.1µmol MDA/mg protein) when compared to control groups (1.18 ± 0.04µg GSH/mg protein and 0.94 ± 0.23µmol MDA/mg protein), while a significant decrease in GSH and an increase in MDA levels in the presence of 100µM Se showed the opposite effect. rbcL gene expression increased 1.76 ± 1.37-fold and 0.86 ± 1.33-fold in 10and 100µM selenium experiments when compared to control groups. Our results suggest both pro-oxidant and antioxidant activities of Se on C. vulgaris and upregulation of the rbcL gene for the first time. Treatment with low concentrations of Se improves the antioxidant features of the microalgae, C. vulgaris.

Effect of selenium doping on the crystallization behaviors of GeSb for phase-change memory applications

We investigated the effect of Se doping on the physical and electrical properties of Ge10Sb90 films prepared by sputtering. We examined the crystal structure, chemical bonding, electrical and thermal properties, and volume shrinkage during the crystallization of Ge10Sb90 films doped concentrations of Se between 0 and 20 at.%. X-ray diffraction patterns showed that incorporating Se leads to phase separation at high Se concentrations. As the Se concentration increased, both the crystallization temperature (Tc) and the sheet resistance increased in both the amorphous and crystalline states. In contrast, the melting temperature (Tm) and grain size both decreased with the increasing Se. The volume shrinkage of the Se-doped Ge10Sb90 films was analyzed by X-ray reflectivity measurements. Our results demonstrate that Se-doped Ge10Sb90 films show a favorably low operation current and good thermal and mechanical stability, which strongly indicate their feasibility for phase-change memory applications.

Selenium and hazardous elements distribution in plant–soil–water system and human health risk assessment of Lower Cambrian, Southern Shaanxi, China

The natural selenium poisoning due to toxic Se levels in food chain had been observed in humans and animals in Lower Cambrian outcrop areas in Southern Shaanxi, China. To find out the distribution pattern of selenium and other hazardous elements in the plant, soil and water of Lower Cambrian in Southern Shaanxi, China, and their possible potential health risk, a total of 30 elements were analyzed and the health risk assessment of 18 elements was calculated. Results showed that the soil, plant and natural water of Lower Cambrian all had relatively high Se levels. In Lower Cambrian, the soil was enriched with Se, As, Ba, Cu, Mo, Ni, Zn, Ga, Cd and Cr (1.68<Igeo<4.48, Igeo; geo-accumulation index). In same plants, the contents of Se, Cd and Zn (except Cd in corn and rice, Zn in potato and corn) of Lower Cambrian were higher than that of the other strata. Ba and Ga in natural water were higher than that of the other strata, while K and Cs were opposite. The health risk assessment results showed that the people living in outcrop areas of Lower Cambrian had both high total non-carcinogenic risk of 18 elements (HI=16.12, acceptable range: <1) and carcinogenic risk of As (3.98E-04, acceptable range: 10-6-10-4). High contents of Se, As, Mo and Tl of Lower Cambrian may pose a health risk to local people, and food intake was the major pathway. For minimizing potential health risk, the local inhabitants should use the mix-imported food with local growing foods.

ANTIOXIDANT ACTIVITY, SE DEPOSITION AND GROWTH PERFORMANCE OF BROILERS AS AFFECTED BY SELENIUM-ENRICHED YEAST

The purpose of this investigation was to study effects of using selenium-enriched yeast on productive performance, carcass composition, Se deposition in meat, some blood constituents and antioxidant activity of broiler chickens. One hundred fifty chicks of commercial broiler strain were divided into five groups, each group comprised five replicates (6 birds per replicate). The groups received a basal diet complemented with 0.2 (control), 0.3, 0.4, 0.5, or 0.6 ppm selenium (Se)/ kg diet. The experiment continued from one-day-old to five weeks of age. Data obtained illustrated that dietary treatments had insignificant effect on growth performance. Selenium (Se) concentration in breast muscles was increased by increasing Se-enriched yeast level in the diet, where the highest content of Se was in birds fed diet supplemented with 0.6 ppm Se/ kg (being 0.48 ppm /kg). Also, supplementing broiler diets with Se-enriched yeast resulted in higher activities of catalase (CAT), glutathione peroxidase (GPx) and superoxide dismutase (SOD) than in control group. Conversely, plasma malondialdehyde (MDA) levels were significantly declined by increasing dietary Se levels. Concerning total antioxidant capacity (TAC) levels, groups received 0.3 and 0.4 ppm Se/ kg diet appeared significantly similar to control group. Levels of triglyceride (TG), total cholesterol (TC), as well as low-density lipoprotein (LDL-C) in plasma were decreased in all treated groups compared to control group. In conclusion, complementing broiler diets with Se-enriched yeast might be recommended to improve the antioxidant status and blood lipid profile.

Dopaminergic dysregulation and impaired associative learning behavior in zebrafish during chronic dietary exposure to selenium

A growing body of evidence indicates that exposure to selenium (Se) can cause neurotoxicity, and this can occur because of its interference with several neurotransmitter systems in humans and animals. Dopamine is a critical modulator of a variety of brain functions and a prime target for environmental neurotoxicants. However, effects of environmentally relevant concentrations of Se on dopaminergic system and its neurobehavioral effects are still largely unknown. For this purpose, we exposed zebrafish, a model organism, to different concentrations of dietary l-selenomethionine (control, 3.5, 11.1, 27.4, and 63.4 μg Se/g dry weight) for a period of 60 days. Cognitive performance of fish was evaluated using a plus maze associative learning paradigm. Oxidative stress, as the main driver of Se neurotoxicity, was assessed by measuring the ratio of reduced to oxidized glutathione (GSH:GSSG), lipid peroxidation (LPO) levels, and mRNA expression of several antioxidant enzymes in the zebrafish brain. Dopamine levels in the brain and the expression of genes involved in dopamine synthesis, storage, reuptake, metabolism, and receptor activation were examined. Moreover, transcription of several synaptic plasticity-related immediate-early and late response genes was determined. Overall, fish fed with the two highest concentrations of dietary Se displayed impaired associative learning. Se exposure also induced oxidative stress in the zebrafish brain, as indicated by a reduction in GSH:GSSG ratio, increased LPO levels, and up-regulation of antioxidant genes in fish treated with the two highest concentrations of Se. An increase in brain dopamine levels associated with altered expression of dopaminergic cell markers was evident in different treatment groups. Moreover, Se exposure led to the down-regulation of immediate-early and late response genes in fish that exhibiting learning impairment. Taken together, the results of this study imply that the induction of oxidative stress and dysregulation of dopaminergic neurotransmission may underlie Se-induced impairment of associative learning in zebrafish.

A QTL located on chromosome 3D enhances the selenium concentration of wheat grain by improving phytoavailability and root structure

Background and aimsAs an essential mineral element, selenium (Se) plays a critical role in human health. Given the low concentrations (<100 mg Se kg–1) of Se in staple crops, the identification of genetic resources with enriched Se, as well as the genes controlling Se concentration, is valuable for the marker-assisted selection of Se-rich varieties.MethodsWe determined the chromosomal quantitative trait (QTL) for Se concentration over two consecutive plant growth cycles using recombinant inbred lines (RILs) treated with two different concentrations of Se under both field-grown and hydroponic conditions.ResultsSeveral QTL for Se concentration were detected across the different treatments. Significant genotypic variation in the tissues of the RIL was found at Se-deficicencycondition. Notably, a QTL located on 3D (interval 214.00–218.00, Qse.sau-3D) affected root length and Se concentration in the leaves and grains, suggesting the existence of the same allele with distinctly different functions. However, the QTL for the agronomic traits measured (plant height, flowering time, and tillering number) and Se concentration were not found to be located on the same chromosomal regions, suggesting that marker-assisted selection for both traits is feasible. Se concentrations in the grains were primarily determined by the mineral transport efficiency of the lines, and the line with the highest Se concentration in the grains always possessed larger, more fibrous root systems. The concentrations of Se in the plant tissues were in the order of: root > stem > grain.ConclusionsThis is the first study to document a Se-rich synthetic wheat line, and root structure and Se grain concentration was strongly affected by QTL located on 3D.

In vitro bioaccessibility and speciation changes of selenium in Pleurotus eryngii during the growing stage.

The production of Pleurotus eryngii by selenium (Se) biofortification is an effective way to improve the demand for Se in humans. In order to investigate the Se bioaccessibility and speciation of Se-enriched P. eryngii during the growing stage, the Se distribution in biochemical fractions, and the molecular weight and the Se species of Se-containing compounds derived from in vitro simulated gastrointestinal fluids were analyzed by size exclusion and anion exchange-high performance liquid chromatography and inductively coupled plasma mass spectrometry. The results showed that albumin had the highest Se content among biochemical fractions, approximately 34.40% of total Se, followed by glutelin, globulin and gliadins. Selenomethionine that was proved to be the major Se species would increase with P. eryngii growing from 45.85% to 59.32%, while selenocysteine would decrease from 40.68% to 15.17% of total Se. In conclusion, selenocysteine would gradually convert to selenomethionine, and thus the bioaccessibility of Se was greater in mature P. eryngii than in younger mushrooms.

Impact of stoichiometry and disorder on the electronic structure of the PbBi2Te4−xSex topological insulator

Detailed comparative theoretical and experimental study of electronic properties and spin structure was carried out for a series of Pb-based quaternary compounds ${\mathrm{PbBi}}_{2}{\mathrm{Te}}_{4\ensuremath{-}x}{\mathrm{Se}}_{x}$. For all values of $x$, these compounds are theoretically predicted to be topological insulators, possessing at high Se content a remarkably large band gap and a Dirac point isolated from bulk states. Using spin- and angle-resolved photoemission spectroscopy, it was shown that the ${\mathrm{PbBi}}_{2}{\mathrm{Te}}_{2}{\mathrm{Se}}_{2}$ and ${\mathrm{PbBi}}_{2}{\mathrm{Te}}_{1.4}{\mathrm{Se}}_{2.6}$ compounds are characterized by well-defined spin-polarized topological surface state in the bulk gap. To define the probable distribution of atoms over the atomic sites for these samples, we performed ab initio calculations in ordered and disordered configurations of the unit cell. We found that theoretical calculations better reproduce photoemission data when Te atoms are placed in the outermost layers of the septuple layer block.

Chemical composition and heavy metals in bottled mineral drinking waters in Bandar Abbas

Introduction: In recent years, attraction toward drinking bottled mineral water has increased. Therefore, chemical composition and safety of these waters considering trace elements and heavy metals should confirm the national or international standard limits. The aim of this study was to evaluate and comparison of the mineral and heavy metal composition of bottled waters in Bandar Abbas with Iranian national standard range. Methods: A total of 125 samples from 25 bottled mineral water brands were analyzed for 17 elements including Zn, Cu,Ca, Mg, Na, K, Al, Mn, As, Pb, Cr, Se, Cd, Co, Ni, Mo, Ba using ICP-OES technique. Concentrations were compared to the desirable and permissible limits of Iran national standard. Results: Zn, Cu, Ca and Mg were lower than desirable limits. Na concentration in all brands was lower than maximum permissible limit. Concentrations of Cr and Se were higher than maximum permissible limit in 7 brands. As, Pb, Cd, Co, Ni, Mo and Ba concentrations were lower than maximum permissible limit in all brands. Conclusion: The results showed that the studied mineral waters could not provide clinically important dietary intake of Ca, Mg, Cu and Zn. Low Na concentration was a proper characteristic. Except for 7 brands with high Cr and Se concentrations, other bottled mineral waters were safe for daily intake.

Induction of oxidative stress and cell apoptosis by selenium: the cure against oral carcinoma.

Oral carcinoma (OC) remains one of the most difficult malignancies to cure. selenium (Se) is an essential trace mineral for human and animals, but high concentrations of Se induce apoptosis and oxidative effects. Although cell apoptosis has been evidenced as a critical mechanism mediating the anticancer activity of Se, the underlying molecular mechanisms remain elusive. To explore the role of Se in rat OC, we examined the weather the oxidative stress-mediated apoptotic pathway induced by Se was involved in the development of OC. In this study, we successfully constructed the OC rat model by 4-Nitroquinoline-1-oxide (4-NQO) exposure which reflected from histopathological observations. Se-induced the productions of methane dicarboxylic aldehyde (MDA) and reactive oxygen species (ROS), which was accompanied by the inhibition of superoxide dismutase (SOD) both in vivo and vitro. The anti-apoptotic gene (Bcl-2) was down-regulated and pro-apoptosis members (Bax, Bak, Cyt-c, caspase9 and caspase3) were up-regulated by Se in OC cells. Meanwhile, we also found that Se could strongly inhibited the cell proliferation of OC lines in vitro. These results suggested that excessive Se could effectively cause oxidative stress and induce apoptosis in OC cells, as a result the OC was also inhibited to some extent. Therefore, the information presented in this study is believed to be helpful in supplementing data for further therapy of OC.

Metal endowment reflected in chemical composition of silicates and sulfides of mineralized porphyry copper systems, Urumieh-Dokhtar magmatic arc, Iran

The present work attempts to discriminate between the geochemical features of magmatic-hydrothermal systems involved in the early stages of mineralization in high grade versus low grade porphyry copper systems, using chemical compositions of silicate and sulfide minerals (i.e., plagioclase, biotite, pyrite and chalcopyrite). The data indicate that magmatic plagioclase in all of the porphyry copper systems studied here has high An% and Al content with a significant trend of evolution toward AlAl3SiO8 and □Si4O8 endmembers, providing insight into the high melt water contents of the parental magmas. Comparably, excess Al and An% in the high grade deposits appears to be higher than that of selected low grade deposits, representing a direct link between the amounts of exsolving hydrothermal fluids and the potential of metal endowment in porphyry copper deposits (PCDs). Also, higher Al contents accompanied by elevated An% are linked to the increasing intensity of disruptive alteration (phyllic) in feldspars from the high grade deposits. As calculated from biotite compositions, chloride contents are higher in the exsolving hydrothermal fluids that contributed to the early mineralization stages of highly mineralized porphyry systems. However, as evidenced by scattered and elevated log (fH2O)/(fHF) and log (fH2O)/(fHCl) values, chloride contents recorded in biotite could be influenced by post potassic fluids. Geothermometry of biotite associated with the onset of sulfide mineralization indicates that there is a trend of increasing temperature from high grade to low grade porphyry systems. Significantly, this is coupled with a sharp change in copper content of pyrite assemblages precipitated at the early stages of mineralization such that Cu decreased with increasing temperature. Based on EMPA and detailed WDS elemental mapping, trace elements do not exhibit complex compositional zoning or solid solution in the sulfide structure. Nevertheless, significant amounts of Cu and Au are contained in pyrite assemblages as micro- to nano-sized inclusions, especially in the high grade fertile porphyry deposits. However, unexpectedly high concentrations of Te, Se, and Re may be associated with early stage of sulfide mineralization, especially when there is no epithermal lithocap. This may highlight the significance of trace metals partitioning in the sulfides formed at the early stages of mineralization in PCDs.

Effect of Se dopping on the structural and electronic properties, charge redistribution and efficiency of the Cu2ZnSnS4 solar cells

ABSTRACTIn this study, we systematically investigated the doping effects of Se in CZTS, the crystal structure, electronic structure, and electron charge redistribution properties of Cu2ZnSn(SxSe1-x)4 with different concentrations were calculated using density functional theory. Se doping causes very gentle lattice distortion and induces crystal expansion in all concentrations. The calculated formation energies show that Cu2ZnSn(SxSe1-x)4 alloys are highly miscible with positive formation energy and it costs additional energy to replace Se with S anions to form the Cu2ZnSn(SxSe1-x)4 .The band gaps of the Cu2ZnSn(SxSe1-x)4 alloy decrease with the increase of Se content.Our results show that Solar cells based on Cu2ZnSn(SxSe1-x)4 alloys with high Se concentration can have higher efficiency than those with low Se content. The results can be helpful to determine the optimal alloy composition to achieve high efficiency Cu2ZnSn(SxSe1-x)4-based solar cells.

The selenium isotopic variations in chondrites are mass-dependent; Implications for sulfide formation in the early solar system

Element transfer from the solar nebular gas to solids occurred either through direct condensation or via heterogeneous reactions between gaseous molecules and previously condensed solid matter. The precursors of altered sulfides observed in chondrites are for example attributed to reactions between gaseous hydrogen sulfide and metallic iron grains. The transfer of selenium to solids likely occurred through a similar pathway, allowing the formation of iron selenides concomitantly with sulfides. The formation rate of sulfide however remains difficult to assess. Here we investigate whether the Se isotopic composition of meteorites contributes to constrain sulfide formation during condensation stages of our solar system. We present high precision Se concentration and δ82/78Se data for 23 chondrites as well as the first δ74/78Se, δ76/78Se and δ77/78Se data for a sub-set of seven chondrites. We combine our dataset with previously published sulfur isotopic data and discuss aspects of sulfide formation for various types of chondrites.Our Se concentration data are within uncertainty to literature values and are consistent with sulfides being the dominant selenium host in chondrites. Our overall average δ82/78Se value for chondrites is −0.21±0.43‰ (n=23, 2 s.d.), or −0.14±0.21‰ after exclusion of three weathered chondrites (n=20, 2 s.d.). These average values are within uncertainty indistinguishable from a previously published estimate. For the first time however, we resolve distinct δ82/78Se between ordinary (−0.14±0.07‰, n=9, 2 s.d.), enstatite (−0.27±0.05‰, n=3, 2 s.d.) and CI carbonaceous chondrites (−0.01±0.06‰, n=2, 2 s.d.). We also resolve a Se isotopic variability among CM carbonaceous chondrites. In addition, we report on δ74/78Se, δ76/78Se and δ77/78Se values determined for 7 chondrites. Our data allow evaluating the mass dependency of the δ82/78Se variations. Mass-independent deficits ro excesses of 74Se, 76Se and 77Se are calculated relative to the observed 82Se/78Se ratios, and were observed negligible. This rules out poor mixing of nucleosynthetic components to account for the δ82/78Se variability and implies that the mass dependent Se isotopic variations were produced in a once-homogeneous disk.The mass-dependent isotopic difference between enstatite and ordinary chondrites may reflect the contribution of a kinetic sulfidation process at anomalously high H2S–H2Se contents in the region of enstatite chondrite formation. Experimental studies showed that high H2S contents favor the formation of compact sulfide layers around metallic grains. This decreases the reactive surface, which tends to inhibit the continuation of the sulfidation reaction. Under these conditions sulfide growth likely occurs under isotopic disequilibrium and favors the trapping of light S and Se isotopes in solids; This hypothesis provides an explanation for our Se isotope as well as for previously published S isotope data. On the other hand, high δ82/78Se values in carbonaceous chondrites may result from sample heterogeneities generated by parent body aqueous alteration, or could reflect the contribution of ices carrying photo-processed Se from the outer solar system.