Form Of Selenite Research Articles

Selenium leaching behaviors from MSWI fly ash and its control

A large number of fly ash samples from mechanical grate furnaces at a municipal solid waste incineration (MSWI) plant were examined including Se speciation and content. Se leaching behaviors before and after solidification/stabilization(S/S) treatment were comparatively studied. The results showed that Se in the MSWI fly ash was present mainly in the form of selenite with small amounts of physically adsorbed SeO2(s). Se in the low alkalinity ash (pH ∼ 7) tended to be more leachable than that in the high alkalinity ash (pH ∼ 12). The chelation treatment would further raise the risk of Se leaching into the environment from the low alkalinity ash (pH ∼ 7). Three Fe-containing additives (zero-valent iron (ZVI)、α-Fe2O3 and Fe3O4) were introduced, respectively in attempt to immobilize Se in the low alkalinity MSWI fly ash. A strong positive effect was found with ZVI addition in terms of Se leaching from low alkalinity chelated MSWI ash. Comparatively, iron oxides showed no obvious effect. The adjustment to ash alkalinity (CaO addition) exhibited a comparable effect to ZVI addition, which provided another option to control Se leaching from low alkalinity chelated ash.

Foraging for selenium: a comparison between hyperaccumulator and non-accumulator plant species

Selenium (Se) hyperaccumulators are a unique group of plants that can accumulate this element in their aerial parts at concentrations exceeding 100 mg kgDW−1. These plants actively search for Se in the soil, a phenomenon known as root foraging, reported to date only by few studies. In this study, the effect of localized Se enrichment, in the form of selenite and selenate, was investigated on the root architecture of two Se-hyperaccumulators (Stanleya pinnata and Astragalus bisulcatus) and two non-accumulators (Brassica juncea and Medicago sativa). Rhizoboxes were divided into two halves: one half was filled with control soil while the other with selenate or selenite (30 mg kgDW−1) spiked soil. Seedling were transferred into the interface of the two soils and allowed to grow for three weeks under controlled light and temperature conditions. Staneya pinnata exhibited equal root density in both halves of the rhizobox when grown in control/control and selenite/control soil treatments. However, in the presence of selenate, S. pinnata developed 76% of the roots towards the selenate-enriched half, indicating an active root foraging. In contrast, A. bisulcatus and the non-accumulators B. juncea and M. sativa did not show any preferential distribution of roots. This study revealed that only S. pinnata showed the ability to detect and forage for Se when provided as selenate. Non-accumulators did not show any morphological or Se-accumulation difference associated with the presence of Se in soil in either form.

Microbiota-Liver-Bile Salts Axis, a Novel Mechanism Involved in the Contrasting Effects of Sodium Selenite and Selenium-Nanoparticle Supplementation on Adipose Tissue Development in Adolescent Rats.

Adolescence is a period during which body composition changes deeply. Selenium (Se) is an excellent antioxidant trace element related to cell growth and endocrine function. In adolescent rats, low Se supplementation affects adipocyte development differently depending on its form of administration (selenite or Se nanoparticles (SeNPs). Despite this effect being related to oxidative, insulin-signaling and autophagy processes, the whole mechanism is not elucidated. The microbiota-liver-bile salts secretion axis is related to lipid homeostasis and adipose tissue development. Therefore, the colonic microbiota and total bile salts homeostasis were explored in four experimental groups of male adolescent rats: control, low-sodium selenite supplementation, low SeNP supplementation and moderate SeNPs supplementation. SeNPs were obtained by reducing Se tetrachloride in the presence of ascorbic acid. Supplementation was received orally through water intake; low-Se rats received twice more Se than control animals and moderate-Se rats tenfold more. Supplementation with low doses of Se clearly affected anaerobic colonic microbiota profile and bile salts homeostasis. However, these effects were different depending on the Se administration form. Selenite supplementation primarily affected liver by decreasing farnesoid X receptor hepatic function, leading to the accumulation of hepatic bile salts together to increase in the ratio Firmicutes/Bacteroidetes and glucagon-like peptide-1 (GLP-1) secretion. In contrast, low SeNP levels mainly affected microbiota, moving them towards a more prominent Gram-negative profile in which the relative abundance of Akkermansia and Muribaculaceae was clearly enhanced and the Firmicutes/Bacteroidetes ratio decreased. This bacterial profile is directly related to lower adipose tissue mass. Moreover, low SeNP administration did not modify bile salts pool in serum circulation. In addition, specific gut microbiota was regulated upon administration of low levels of Se in the forms of selenite or SeNPs, which are properly discussed. On its side, moderate-SeNPs administration led to great dysbiosis and enhanced the abundance of pathogenic bacteria, being considered toxic. These results strongly correlate with the deep change in adipose mass previously found in these animals, indicating that the microbiota-liver-bile salts axis is also mechanistically involved in these changes.

Research on migration and transformation behavior of selenium during the dual-alkali wet flue gas deacidification process in the simulated flue gas

Selenium easily escapes from the existing air pollution control devices (APCDs) used in municipal waste solid incineration (MSWI), which poses a threat to both the ecosystem and human health. Dual-alkali wet flue gas deacidification (DAWFGD) has been recently applied in MSWI power plants to improve the purification of flue gas. This technology provides a new route for the coordinated control of selenium in the DAWFGD device, which removes acidic gas simultaneously. In this study, a laboratory-scale DAWFGD system was constructed to investigate the migration and transformation behavior of selenium during the absorption and regeneration process in the DAWFGD system. The results showed that the Na2CO3 solution could effectively absorb SeO2, and the absorption efficiency could reach up to 97.09% by increasing the Na2CO3 concentration. High-concentration CO2 has less of an absorption inhibition effect on gaseous selenium compared to low-concentration HCl and SO2. The absorption of SeO2 was adversely affected by the decrease in pH value of the absorption solution caused by an increase in SO2 concentration. However, the addition of a small amount of alkali solution (OH–) into the absorption solution could well recover its absorption performance for SeO2. During the regeneration process, the precipitation ratio of selenium from the aqueous phase to the solid phase increased with the molar ratio of Ca/S increasing. Besides, selenium was found to be in the form of selenite during both the absorption and regeneration processes. This study helps to evaluate the potential of DAWFGD in MSWI power plants for removing SeO2 from flue gas and provides a theoretical reference for the treatment of gas-phase selenium in the waste incineration process.

The Effects of BSA-Stabilized Selenium Nanoparticles and Sodium Selenite Supplementation on the Structure, Oxidative Stress Parameters and Selenium Redox Biology in Rat Placenta.

The chemical element selenium (Se) is a nonmetal that is in trace amounts indispensable for normal cellular functioning. During pregnancy, a low Se status can increase the risk of oxidative stress. However, elevated concentrations of Se in the body can also cause oxidative stress. This study aimed to compare the effects of BSA-stabilized Se nanoparticles (SeNPs, Se0) (BSA-bovine serum albumin) and inorganic sodium selenite (NaSe, Se+4) supplementation on the histological structure of the placenta, oxidative stress parameters and the total placental Se concentration of Wistar rats during pregnancy. Pregnant females were randomized into four groups: (i) intact controls; (ii) controls that were dosed by daily oral gavage with 8.6% bovine serum albumin (BSA) and 0.125 M vit C; (iii) the SeNP group that was administered 0.5 mg of SeNPs stabilized with 8.6% BSA and 0.125 M vit C/kg bw/day by oral gavage dosing; (iv) the NaSe group, gavage dosed with 0.5 mg Na2SeO3/kg bw/day. The treatment of pregnant females started on gestational day one, lasted until day 20, and on day 21 of gestation, the fetuses with the placenta were removed from the uterus. Our findings show that the mode of action of equivalent concentrations of Se in SeNPs and NaSe depended on its redox state and chemical structure. Administration of SeNPs (Se0) increased fetal lethality and induced changes in the antioxidative defense parameters in the placenta. The accumulation of Se in the placenta was highest in SeNP-treated animals. All obtained data indicate an increased bioavailability of Se in its organic nano form and Se0 redox state in comparison to its inorganic sodium selenite form and Se+4 redox state.

Engineering Ni(OH)x/(Ni, Cu)Se2 heterostructure nanosheet arrays for highly-efficient water oxidation

The development of efficient and inexpensive alkaline oxygen evolution reaction (OER) catalysts is crucial for electrochemical water splitting. Cu-doped NiSe2 has good electrical conductivity and OER activity, but (Ni, Cu)Se2 will dissolve a large amount of Se during the OER process and adsorb on the surface of the catalyst in the form of selenite, which seriously affects its OER stability. Here, heterostructure electrocatalysts composed of crystalline (Ni, Cu)Se2 and amorphous Ni(OH)x are designed. The Ni(OH)x/(Ni, Cu)Se2 exhibits an distinguished catalytic performance for OER, needing only an overpotential of 200 mV at the current density of 10 mA cm−2 with a Tafel slope of 62 mV dec−1 in 1 M KOH. Combining the experimental and theoretical results, electronic interactions at the coupled interface optimize the free energy of the oxygen-containing intermediate and weaken the Ni-*O bond, which leads to enhanced OER activity and stability. This work of amorphous core-shell interface engineering to improve OER activity and stability may provide a strategy for the rational design of advanced non-precious metal electrocatalysts.

Parental exposure to waterborne selenite induces transgenerational development toxicity in zebrafish offspring.

Excessive selenium (Se), especially selenite form exerts great toxicity to fish. Most studies have attached considerable attention to the adverse effects of Se on parental fish. However, the transgenerational toxicity of Se on fish has been rarely reported. In the present study, zebrafish embryos were exposed to environmentally relevant concentrations of Na₂SeO₃ (0, 12.5, 25, 50, and 100μg/L) for 120 days. And the exposed zebrafish (F0) were allowed to spawn with normal zebrafish after sexual maturity. Subsequently, the offspring (F1) were cultured in clean water for 5 days. In the F0 generation, exposure to 100μg/L Na₂SeO₃ significantly increased the Se content in the tissues (liver, brain and gonad) and decreased the body length and weight. After parental exposure to 100μg/L Na₂SeO₃, the increased mortality, elevated malformation rate and reduced body length were measured in F1 zebrafish. The Se content was only significantly increased in F1 larvae derived from exposed females in the 100μg/L exposure group. The contents of thyroid hormones (THs), growth hormone (GH) and insulin-like growth factor (IGF) significantly decreased in F0 and F1 zebrafish. The transcriptional levels of genes along the hypothalamic-pituitary-thyroid (HPT) axis and growth hormone/insulin-like growth factor (GH/IGF) axis were detected to further explore the possible mechanisms of Se-induced thyroid and growth hormone disruption. The results suggest that the toxicity of Se in zebrafish can be markedly transmitted to offspring. And the transgenerational development toxicity might be different due to the differences in gender of exposed parents.

Comparative study of efficacy of prepartum injection of multivitamins and selenium- vitamin E (ά-tocopherol)-combination on post-partum clinical findings, serum steroids, calf and placental weights, and milk antioxidant biomarkers changes in female dromedary camel.

All concentrates given to camels were enriched in selenium (Se) in selenite form. The impacts of Se supplementation on lactating female health, milk, and Se/antioxidant statuses received no research interest. The current study aimed to compare the efficacy of long-term prepartum injection of Se-vitamin E combination and multivitamins on maternal post-calving clinical findings, serum steroid hormones, milk antioxidants, milk somatic cell count (SCC) status, calf body weight, placental weight (PW), and vaginal wash isolates. From three equal groups of postpartum she-camels (n = 45), one group received no treatment and served as control group (Cont.; n = 15). For 3 months prepartum, one group had received a combination of vitamin E (ά-tocopherol) and Se (VitE-Se-; n = 15), and the third one received multivitamins (Multi-; n = 15). All dams were subjected to clinical and laboratory assays including milk total antioxidant capacity (TAC), Se, vitamin E, and milk SCC on Days 14, 21, and 28 post-calving. Steroid hormones and calf and PW were estimated at birth (Day 0). The study reported higher efficacy of Se-vitamin E combination comparing with that of multivitamins as a long-term prepartum injection in recently calved she-camels that was reflected through significant changes in steroids hormones (Drop), i.e., progesterone (P4) and estradiol (E2), the milk antioxidant biomarkers (Elevation), i.e., TAC, Se, vitamin E, and milk SCCs (Reduction). Both two therapeutic regimens had a more powerful effect that the control one. The applied therapeutic supplements had no significant effect on clinical and hematological changes as well as calves' body weights and PWs. Body weights were significantly higher in male camel calves than those of female calves either in Cont., VitE-Se-, or Multi-.

Modeling of selenite toxicity to wheat root elongation using biotic ligand model: Considering the effects of pH and phosphate anion.

It has not been well understood that the binding affinity and potential toxicity of different chemical forms of selenite (Se(IV)), which are predominant forms of selenium with plant availability. The influences of pH and major anions on Se(IV) toxicity to wheat root elongation were determined in solutions and modeled based on the biotic ligand model (BLM) and free ion activity model (FIAM) concepts. Results showed that EC50[Se(IV)]T values increased from 164 to 273μM as the pH raised from 4.5 to 8.0, indicating the increase of pH induced weakened Se(IV) toxicity. The EC50{SeO32-} values increased from 0.019 to 71.3μM while the EC50{H2SeO3} values sharply decreased from 2.08μM to 0.760nM with the pH increasing from 4.5 to 8.0. The effect of pH on Se(IV) toxicity could be explained by the changes of Se(IV) species in different pH solutions as H2SeO3, HSeO3- and SeO32- were differently toxic to wheat root elongation. The toxicity of Se(IV) decreased with increasing H2PO4- activity but not for SO42-, NO3- and Cl- activities, indicating that only H2PO4- had a competitive effect with Se(IV) on the binding sites. A site-specific BLM was developed to count in effects of pH and H2PO4-, and stability constants of H2SeO3, HSeO3-, SeO32- and H2PO4- to the binding sites were obtained: log [Formula: see text] =4.96, log [Formula: see text] =3.47, log [Formula: see text] =2.56 and log [Formula: see text] =2.00. Results implied that BLM performed much better than FIAM in the wheat root elongation prediction when coupling toxic species H2SeO3, HSeO3-, SeO32-, and the competitions of H2PO4- for the binding sites while developing the Se(IV)-BLM.

Transcription response of Tetranychus cinnabarinus to plant-mediated short-term and long -term selenium treatment

Selenium is a trace element necessary for living organisms. It exists mainly in the form of selenite in nature. In plants, selenium can enhance defenses against pests. In this study, transcriptome sequencing technology was used to analyze the response mechanism of Tetranychus cinnabarinus to plant-mediated selenium treatment. We tested four sodium selenite treatments (5, 20, 50, and 200 μM) that were the same for short (2 d) and long (30 d) treatment durations. The results showed that the number of differentially expressed genes (DEGs) in the short-term treatment was greater than in the long-term treatment. This indicated that the gene expression of spider mites gradually stabilized during the selenium treatment. Regardless of the long-term and short-term conditions, spider mites had the largest response to the 20 μM sodium selenite treatment. The functional annotation classification of DEGs showed no significant difference under different concentrations and treatment durations. A total of 25 genes were differentially expressed in all eight treatments, including four down-regulated cytochrome P450 genes and one up-regulated chitinase gene. We speculate that selenium may have the potential to enhance the activity of chemical acaricides. Transcriptome sequencing of sodium selenite treatment at different concentrations and different times revealed the response mechanism of spider mites under plant-mediated selenium treatment. At the same time, it also provides new clues for the development of methods for preventing and controlling spider mites with selenium.

Synthesis of Se-polysaccharide mediated by selenium oxychloride: Structure features and antiproliferative activity

Selenium oxychloride (SOC) was employed as a highly reactive selenide reagent to synthesize selenized Artemisia sphaerocephala polysaccharides (SeASP). Se content of SeASP was significantly increased (∼22,400 μg/g) as compared to HNO3/H2SeO3 selenylation method (1703 μg/g). Furthermore, selenized ASP was prepared by using microwave-assisted synthesis which obviously enhanced selenylation kinetics. FT-IR, Raman, XPS and NMR results exhibited seleno-group was substituted at C6 position in the form of selenite (Se4+). SEC-MALLS suggested SOC system could effectively avoid the degradation of polysaccharide chain. Meanwhile, MALLS calculation, MB spectrophotometric method and AFM observation showed SeASP appeared spherical and rod-shaped conformation after selenylation. Seleno-groups were more likely to affect the conformational transformation of polysaccharide chains. Moreover, SeASP could significantly enhance antiproliferative activity against three tumor cells, of which the IC50 value of HepG2 was calculated as 24.35 μg/mL. It was found that higher Se content could effectively improve the antitumor activities of Se-polysaccharides in vitro.

Dietary supplementation of nano-selenium improves reproductive performance, sexual behavior and deposition of selenium in the testis and ovary of Japanese quail.

Objective:Selenium (Se), as the form of selenite, is commonly supplemented in poultry diet, which has low bioavailability and high toxicity. Here, we compared the effects of the supplementation of the diet with Se nanoparticles (nano-Se) on the growth, sexual behavior, and reproductive performance (gonad size, sperm quality traits, and plasma testosterone levels for males and egg production for females) of Japanese quail (Coturnix coturnix japonica).Materials and Methods:Quail chicks (n = 300) aging 14 days were divided into three groups: Group 1 (basal diet and Se at 0.2 mg/kg ration), Group 2 (basal diet and nano-Se at 0.2 mg/kg ration), and Group 3 (basal diet and nano-Se at 0.1 mg/kg ration). Several parameters relating to body weight and egg were measured. Sexual behaviors of the birds were observed by continuous visual scanning. The sperm viability, sperm morphology, and concentration of spermatozoa were determined after staining and microscopic examination. The plasma testosterone levels were determined by indirect enzyme immunoassay assay. The Se concentrations in the testicular, ovarian, and ration samples were measured by flame emission atomic absorption spectrophotometer.Results:The type or concentration of nano-Se administration had no impact on body weight, feed efficiency, egg production, or egg weight. However, the total feed intake throughout the experiment was reduced in Group 2 at 0.2 mg/kg. Nano-Se supplementation significantly increased the sexual behavior. In general, the deposition of Se in the testicular and ovarian tissues increased with increasing supplement concentration. At the same supplement concentration, the tissue deposition of nano-Se was more enhanced than that of inorganic Se. Nano-Se supplementation improved the testicular functions by enhancing plasma testosterone level and sperm quality traits (sperm count, motility, and viability). This improvement was found more prominent with the lower supplement concentration (when comparing 0.1 vs. 0.2 mg/kg diet).Conclusion:It is concluded that the use of nano-Se (at 0.1 mg/kg) in the ration of Japanese quail improves several reproductive performance parameters.

Effect of foliar selenium application on the infestation of the perennial ryegrass Lolium perenne L. and tall fescue Festuca arundinacea Schreb. by fungal pathogen Fusarium culmorum (W.G. Sm.) Sacc.

1 SUMMARY Selenium is considered an essential element for the life of animals, including humans. Anyway, its necessity and function in the plant organism have not been fully explained yet. The aim of the work was to investigate an effect of foliar application of selenium on the infestation of the perennial ryegrass and tall fescue by fungal pathogen Fusarium culmorum based on a determination of ergosterol in plant biomass. Two major species of grass (perennial ryegrass and tall fescue) cultivated under defined climate chamber conditions were included in the experiment. Within 5 weeks from their germination, a solution of selenium in the form of selenite or selenate, corresponding to 4 mg/m2 Se, was foliarily applied onto the plants. After 14 days of spraying, a solution containing conidia of Fusarium culmorum was applied to the plants. Subsequently, samples of green matter were taken at 14-day intervals, and the content of ergosterol and selenium were determined there. The content of ergosterol, which was selected as a marker of fungal pathogens, was found to be significantly higher (P<0.05) on the 28th day after the selenite and selenate application in both grass species. This increase was conclusive (P<0.05), when compared to the control group. No difference was observed between the selenium forms used. From our experiment, it is clear the plants of the perennial ryegrass and tall fescue were more easily attacked by fungal pathogen Fusarium culmorum after the application of selenium. Thus, it is possible to assume the application of selenium acts as stress a factor to plants.

Kinetic and mechanistic aspects of selenite oxidation by chlorine, bromine, monochloramine, ozone, permanganate, and hydrogen peroxide

Selenium (mainly in the forms of selenite (Se(IV)) and selenate (Se(VI)) is a regulated drinking water contaminant, but there is little information on the kinetics and mechanisms of Se(IV) oxidation during water treatment. Species-specific and apparent second-order rate constants for the oxidation of Se(IV) at pH 7.0 were determined in buffered solutions and they decrease in the order bromine (5.8 ± 0.3 × 103 M−1 s−1) > ozone (O3, 513.4 ± 10.0 M−1 s−1) > chlorine (61.0 ± 3.6 M−1 s−1) > permanganate (2.1 ± 0.1 M−1 s−1), monochloramine (NH2Cl, (1.3 ± 0.1) × 10−3 M−1 s−1), and hydrogen peroxide (H2O2, (2.3 ± 0.1) × 10−5 M−1 s−1). The reaction stoichiometries for the reactions of Se(IV) with bromine, O3, chlorine, NH2Cl, and H2O2 are 1:1. For Mn(VII), the stoichiometries varied with pH and were 5:2, 3:2, and 1:2 for acidic, neutral, and alkaline conditions, respectively. Based on the reaction orders and stoichiometries, the corresponding Se(IV) oxidation mechanisms for various oxidants are discussed. The role of bromide for Se(IV) oxidation was also investigated during chlorination and ozonation of Se(IV)-containing water. During chlorination, bromide-catalysis enhances the rate of the oxidation of Se(IV) to Se(VI) from 50% to nearly 90% with bromide concentrations of 50 μg L−1 and 200 μg L−1, respectively, at pH 7.0 and a chlorine dose of 2.0 mg L−1 (within 15 min). During ozonation, bromide had no effect on Se(IV) oxidation. Based on the determined second order rate constants, the oxidation of Se(IV) by chlorine and ozone were successfully predicted in a natural water by a kinetic model. The second order rate constants for the same oxidants were also investigated and/or evaluated for other related anions, such as arsenite (As(III)) and sulfite (S(IV)). They decreased in the order S(IV) > As(III) > Se(IV).

Effects of different water management on absorption and accumulation of selenium in rice

Rice is the staple food for more than half of the world's population, but selenium (Se) is low in many rice growing countries. Water management model affects rice soil pH and Eh, and then affects the bioavailability of Se in soil. A pot experiment was conducted to investigate the effects of water management on soil Se species, dynamics and selenium uptake by rice plants. Sodium selenite was added to the soil so that the soil selenium content reached 0.5 mg kg−1 to study the effects of 3 different water management modes on soil selenium uptake by rice plants. These three modes are flood irrigation (F), aerobic irrigation (A) and alternate flood and aerobic irrigation (AFA). The results showed that flooded irrigation treatment increased the soil soluble selenium concentration, and the selenium in soil solution mainly existed in the form of selenite and selenomethionine selenium oxide. The content of selenium in grain was 2.44 and 1.84 times that of flooded irrigation treatment under A and AFA respectively. The content of selenium in straw was 1.32 and 1.58 times that of flooded treatment under A and AFA respectively. After rice grain enzyme hydrolysis, HPLC-ICP-MS analysis showed that Selenomethionine was the main selenium speciation in rice grains. This study showed that aerobic flooded treatment is one of the most effective ways to increase selenium content in rice field.

Flow injection determination of Se in dietary supplements using TiO2 mediated ultraviolet-photochemical volatile species generation

This paper proposes a method for determination of selenium content in samples of dietary supplements using TiO2 mediated UV-photochemical vapor generation with quartz furnace atomic spectrometric detection. The flow-injection method was optimized for determination of selenium in the form of selenite or selenate ions. The limits of detection of the proposed method are 0.89ngmL−1 and 0.68ngmL−1 for selenite and selenate, respectively. Extraction in neutral medium was used for the leaching of selenate and NaOH solution was used for the leaching of selenite. The methods accuracy was verified against the declared amounts of Se in five different samples of over-the-counter dietary supplements and on NIST SRM 3280. The method was also compared to results achieved with determination by electrothermal atomization atomic absorption spectrometry following microwave decomposition. The recovery of selenium during sample preparation was tested by spiking the tablets prior to extraction and estimated to be approximately 100%. An interference study has been carried out to estimate the effect of concomitant elements on the methods accuracy.

Effect of different forms of selenium on the plant–soil–earthworm system

AbstractSelenium (Se) is an essential micronutrient for humans, animals, and certain lower plants, but at higher concentrations Se becomes toxic to organisms. The boundary between the Se beneficial effect and its toxicity is narrow and depends on its chemical form, applied concentration, and other environmentally regulating factors. Due to the potential risk of toxicity in higher concentration, the aim of this study was to estimate the impact of increased concentrations of different forms of Se on the response of the wheat–soil–earthworm system. Soil, earthworms, and wheat grains were exposed to the Se in form of selenite and selenate in concentrations of 0.01, 0.1, and 1 mg kg−1. As an indicator of oxidative stress in wheat, lipid peroxidation levels (LPO) and total H2O2 content were determined, while antioxidative response was determined by catalase (CAT), glutathione peroxidase (GPX), and glutathione reductase (GR) activities. The biomarker responses in earthworms were determined by acetylcholinesterase (AChE), carboxylesterase (CES), and antioxidative enzymes (CAT and glutathione S‐transferase) activities. Selenite and selenate increased Se content in the wheat and earthworms, while selenate application was more efficient, indicating higher bioaccumulation of this Se form. Both Se forms did not cause significant changes in the LPO level and H2O2 content, while GPX activities were elevated in all treatments, suggesting that oxidative stress was not induced in wheat. In earthworms, Se significantly reduced activities of AChE and CAT at some concentrations, while CES activity was increased at all concentrations applied. This study showed significant impact of Se on measured biochemical responses in wheat and earthworms, indicating the disruption of homeostasis. Obtained results can serve as basis for further studies on Se effects and will help in including different aspects necessary for understanding of Se impact on different components of soil ecosystems.

Sorption and speciation of selenium in boreal forest soil

Sorption and speciation of selenium in the initial chemical forms of selenite and selenate were investigated in batch experiments on humus and mineral soil samples taken from a 4–m deep boreal forest soil excavator pit on Olkiluoto Island, on the Baltic Sea coast in southwestern Finland. The HPLC–ICP-MS technique was used to monitor any possible transformations in the selenium liquid phase speciation and to determine the concentrations of selenite and selenate in the samples for calculation of the mass distribution coefficient, Kd, for both species. Both SeO32− and SeO42− proved to be resistant forms in the prevailing soil conditions and no changes in selenium liquid phase speciation were seen in the sorption experiments in spite of variations in the initial selenium species, incubation time or conditions, pH, temperature or microbial activity. Selenite sorption on the mineral soil increased with time in aerobic conditions whilst the opposite trend was seen for the anaerobic soil samples. Selenite retention correlated with the contents of organic matter and weakly crystalline oxides of aluminum and iron, solution pH and the specific surface area. Selenate exhibited poorer sorption on soil than selenite and on average the Kd values were 27–times lower. Mineral soil was more efficient in retaining selenite and selenate than humus, implicating the possible importance of weakly crystalline aluminum and iron oxides for the retention of oxyanions in Olkiluoto soil. Sterilization of the soil samples decreased the retention of selenite, thus implying some involvement of soil microbes in the sorption processes or a change in sample composition, but it produced no effect for selenate. There was no sorption of selenite by quartz, potassium feldspar, hornblende or muscovite. Biotite showed the best retentive properties for selenite in the model soil solution at about pH 8, followed by hematite, plagioclase and chlorite. The Kd values for these minerals were 18, 14, 8 and 7 L/kg, respectively. It is proposed that selenite sorption is affected by the structural Fe(II) in biotite, which is capable of inducing the reduction of SeO32− to Se(0). Selenite probably forms a surface complex with Fe(III) atoms on the surface of hematite, thus explaining its retention on this mineral. None of the minerals retained selenate to any extent.

Influence of Se concentrations and species in hydroponic cultures on Se uptake, translocation and assimilation in non-accumulator ryegrass

The success of biofortification and phytoremediation practices, addressing Se deficiency and Se pollution issues, hinges crucially on the fate of selenium in the plant media in response to uptake, translocation and assimilation processes. We investigate the fate of selenium in root and shoot compartments after 3 and 6 weeks of experiment using a total of 128 plants grown in hydroponic solution supplied with 0.2, 2, 5, 20 and 100 mg L−1 of selenium in the form of selenite, selenate and a mixture of both species. Selenate-treated plants exhibited higher root-to-shoot Se translocation and total Se uptake than selenite-treated plants. Plants took advantage of the selenate mobility and presumably of the storage capacity of leaf vacuoles to circumvent selenium toxicity within the plant. Surprisingly, 28% of selenate was found in shoots of selenite-treated plants, questioning the ability of plants to oxidize selenite into selenate. Selenomethionine and methylated organo-selenium amounted to 30% and 8% respectively in shoots and 35% and 9% in roots of the identified Se, suggesting that selenium metabolization occurred concomitantly in root and shoot plant compartments and demonstrating that non-accumulator plants can synthesize notable quantities of precursor compound for volatilization. The present study demonstrated that non-accumulator plants can develop the same strategies as hyper-accumulator plants to limit selenium toxicity. When both selenate and selenite were supplied together, plants used selenate in a storage pathway and selenite in an assimilation pathway. Plants might thereby benefit from mixed supplies of selenite and selenate by saving enzymes and energy required for selenate reduction.

Selenite is More Efficient than Selenate in Alleviation of Salt Stress in Lettuce Plants

Abstract There is increasing evidence showing that low selenium (Se) concentrations may increase tolerance of crop plants to several environmental stresses. The aim of this study was to compare the influence of two chemical forms of Se (selenite or selenate) at different concentrations (2 or 6 μM) on the resistance of butterhead lettuce (Lactuca sativa L. var. capitata) cv. Justyna to NaCl-induced stress (40 mM NaCl). Plant growth was negatively affected by salinity, but the level of photosynthetic pigments was not reduced. Se application at a concentration of 2 μM significantly improved the growth of salt-stressed plants, but selenite was much more effective than selenate in enhancing salt-tolerance of lettuce. The growth-promoting effect of Se was also noted at 6 μM of selenite, but did not appear at 6 μM of selenate. The beneficial effect of Se in salt-stressed lettuce could be due to antioxidative activity of Se, root system growth stimulation, and/or increase in photosynthetic pigment concentration after Se supplementation; however, it was not related to either increase in proline accumulation or reduction in foliar Na+ or Cl− concentration. These results imply that Se application, especially in the form of selenite, can enhance antioxidant defense of lettuce under salt stress, and Se supplementation may be recommended for areas of lettuce cultivation with excessive salt accumulation.