Selenium nanoparticles (SeNPs) are gaining importance in the field of medicine owing to their antibacterial and anticancer properties. SeNPs are biocompatible and non-toxic compared to the ...counterparts, selenite (SeO₃ ⁻²) and selenate (SeO₄ ⁻²). They can be synthesized by physical, chemical, and biological methods and have distinct bright orange-red color. Biogenic SeNPs are stable and do not aggregate owing to natural coating of the biomolecules. Various hypotheses have been proposed to describe the mechanism of microbial synthesis of SeNPs. It is primarily a two-step reduction process from SeO₄ ⁻² to SeO₃ ⁻² to insoluble elemental selenium (Se⁰) catalyzed by selenate and selenite reductases. Phenazine-1-carboxylic acid and glutathione are involved in selenite reduction. Se factor A (SefA) and metalloid reductase Rar A present on the surface of SeNPs confer stability to the nanoparticles. SeNPs act as potent chemopreventive and chemotherapeutic agents. Conjugation with antibiotics enhances their anticancer efficacy. These also have applications in nanobiosensors and environmental remediation.
The reduction of selenate, SeO42−(aq),in 0.1 M HClO4 solutions, induced by underpotential deposition, UPD, of Cu on polycrystalline Au electrodes was investigated using the rotating ring-disk ...electrode, RRDE, technique. Design and implementation of electrode potential-rotation rate protocols made it possible to determine the rates of SeO42−(aq)reduction as a function of Cu coverage, θCu, as determined by the Bruckenstein method (Swathirajan et al. J. Phys. Chem.1982,86, 2480-2485). In agreement with the results reported recently for Au(111) film electrodes (Strobl et al. Electrochimica Acta2024,493, 144298), the reaction was found to proceeds only for θCu above a critical value, i.e. ca. 0.39, in this case, and that the mechanism is consistent with an initial reversible formation of an adsorbed Cu|SeO42−(ads),followed by its subsequent irreversible reduction, to yield a yet to be identified species denoted as Cu|Se(ads), as the rate determining step. Best fits of the kinetic model yielded values of the equilibrium constant for adduct formation, K, and first order rate constant for adduct reduction, kET, in the range (2.4 – 45) × 106 cm3 mol−1 and (0.55 – 30) × 10−3 s−1, respectively, which are close to those found for Au(111). This unique electrocatalytic effect has been attributed to a shift in the potential of zero charge of the bare substrate toward more negative values, induced by the metal UPD, which promotes the adsorption of the oxyanion at potentials more negative than those found for the bare substrate, making it possible to access overpotentials large enough for its further reduction to ensue.
In this paper we report an investigation into the phases formed on dehydration of Na2M(SO4)2−x(SeO4)x·2H2O (0 ≤ x ≤ 1; M = Mn, Fe, Co and Ni). For the Fe series, all attempts to dehydrate the samples ...doped with selenate resulted in amorphous products, and it is suspected that a side redox reaction involving the Fe and selenate may be occurring leading to phase decomposition and hence the lack of a crystalline product on dehydration. For M = Mn, Co, Ni, the structure observed was shown to depend upon the transition metal cation and level of selenate doping. An alluaudite phase, Na3M1.5(SO4)3-1.5x(SeO4)1.5x, was observed for the selenate doped compositions, with this phase forming as a single phase for x ≥ 0.5M = Co, and x = 1.0M = Ni. For M = Mn, the alluaudite structure is obtained across the series, albeit with small impurities for lower selenate content samples. Although the alluaudite-type phases Na2+2y(Mn/Co)2−y(SO4)3 have recently been reported 1,2, doping with selenate appears to increase the maximum sodium content within the structure. Moreover, the selenate doped Ni based samples reported here are the first examples of a Ni sulfate/selenate containing system exhibiting the alluaudite structure.
The refined crystal structure of alluaudite-type Na3Co1.5(SO4)1.5(SeO4)1.5 (Tetrahedra = S/SeO4; Co (and mixed Co/Na site) at the centre of octahedra, Spheres = Na) Display omitted
•The highest reported sodium content for an alluaudite phase constructed from sulfate/selenate tetrahedra.•Demonstration of a correlation between structure and cation size.•The first report of a nickel alluaudite phase.
Methane oxidation coupled to selenate reduction has been suggested as a promising technology to bio-remediate selenium contaminated environments. However, the effect of dissolved oxygen (DO) on this ...process remained unclear. Here, we investigate the feasibility of selenate removal at two distinct DO concentrations. A membrane biofilm reactor (MBfR) was initially fed with ∼5 mg Se/L and then lowered to ∼1 mg Se/L of selenate, under anoxic condition containing ∼0.2 mg/L of influent DO. Selenate removal reached approximately 90% without selenite accumulation after one-month operation. Then 6–7 mg/L of DO was introduced and showed no apparent effect on selenate reduction in the subsequent operation. Electron microscopy suggested elevated oxygen exposure did not affect microbial shapes. 16S rDNA sequencing showed the aerobic methanotroph Methylocystis increased, while possible selenate reducers, Ignavibacterium and Bradyrhizobium, maintained stable after oxygen boost. Gene analysis indicated that nitrate/nitrite reductases positively correlated with selenate removal flux and were not remarkably affected by oxygen addition. Reversely, enzymes related with aerobic methane oxidation were obviously improved. This study provides a potential technology for selenate removal from oxygenated environments in a methane-based MBfR.
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•Influent 6–7 mg/L DO had no inhibition on selenate reduction in a CH4-based MBfR.•Aerobic methanotroph Methylocystis remarkably increased after DO elevating.•Likely selenate reducers Ignavibacterium and Bradyrhizobium weren't affected by DO.
The objective of the present study was to evaluate agronomic biofortification with nitrogen (N) and selenium (Se) with the aim of increasing the daily Se intake by the population and the nutritional ...quality of the grain. A randomized block experimental design with a 5 × 2 factorial scheme was used; the factors were the five levels of N (0, 20, 40, 80, and 120 kg ha−1), applied as topdressing fertilization, and the two levels of Se (0 and 25 g ha−1). The reserve protein fractions in the seeds, glutelin, and globulin increased significantly when Se application was combined with N fertilization. Grain Se content varied from 0.03 to 0.35 mg kg−1, which was within the food safety limit of 0.3 mg kg−1 established by the Codex Alimentarius. The estimated daily Se intake originating from Se-biofortified rice varied between 2.05 and 24.7 μg per day, representing an increase from 3.72% to 44.9% of the daily Se requirement. Because the recommended Se daily intake for adults is 55 μg per day, the present study presents relevant information about agronomic biofortification to increase Se concentrations in edible plant parts, with possible benefits to human health.
•Se and N increase the albumin and glutelin in rice seeds.•The combination of Se and N enhances the daily Se intake.•25 g ha−1 of Se achieves the Se levels in seeds as suggested by the Codex Alimentarius.•Se combined with N reduces the lipid peroxidation in rice leaves.•Agronomic biofortification improves the Se level in rice seeds.
Selenium pollution has become an increasingly serious global concern. Methane-fed selenate reduction has proven to be of great interest for the bioremediation of selenate-contaminated waters even ...with the coexistence of nitrate and dissolved oxygen. However, it is unclear if the common concurrent sulfate anion affects selenate removal. To address this question, we first introduced selenate (SeO42-) as the sole influent electron acceptor in a CH4-fed membrane biofilm reactor (CH4-MBfR); then we added different concentrations of sulfate (SO42-). The initial selenate removal efficiency (∼90%) was decreased by 50% in the presence of 15.6 μM of sulfate and completely inhibited after loading with 171.9 μM of sulfate. 16S rRNA gene sequencing showed that the selenate-reducing bacteria decreased after the addition of sulfate. Metagenomic sequencing showed that the abundance of genes encoding molybdenum (Mo)-dependent selenate reductase reduced by >50% when exposed to high concentrations of sulfate. Furthermore, the decrease in the total genes encoding all Mo-oxidoreductases was much greater than that of the genes encoding molybdate transporters, suggesting that the inhibition of selenate reduction by sulfate was most likely via the direct competition with molybdate for the transport system, leading to a lack of available Mo for Mo-dependent selenate reductases and thus reducing their activities. This result was confirmed by a batch test wherein the supplementation of molybdate mitigated the sulfate effect. Overall, this study shed light on the underlying mechanism of sulfate inhibition on selenate reduction and laid the foundation for applying the technology to practical wastewaters.
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•Influent 171.9 μM of sulfate completely inhibited selenate reduction in a CH4-MBfR.•Sulfate suppressed selenate reductase by competing for molybdate transporters.•The supplementation of molybdate restored the selenate reduction ability.
The aim of this review is to synthesize current knowledge of selenium (Se) transport and metabolism in plants, with a focus on implications for biofortification and phytoremediation. Selenium is a ...necessary human micronutrient, and around a billion people worldwide may be Se deficient. This can be ameliorated by Se biofortification of staple crops. Selenium is also a potential toxin at higher concentrations, and multiple environmental disasters over the past 50 years have been caused by Se pollution from agricultural and industrial sources. Phytoremediation by plants able to take up large amounts of Se is an important tool to combat pollution issues. Both biofortification and phytoremediation applications require a thorough understanding of how Se is taken up and metabolized by plants. Selenium uptake and translocation in plants are largely accomplished via sulfur (S) transport proteins. Current understanding of these transporters is reviewed here, and transporters that may be manipulated to improve Se uptake are discussed. Plant Se metabolism also largely follows the S metabolic pathway. This pathway is reviewed here, with special focus on genes that have been, or may be manipulated to reduce the accumulation of toxic metabolites or enhance the accumulation of nontoxic metabolites. Finally, unique aspects of Se transport and metabolism in Se hyperaccumulators are reviewed. Hyperaccumulators, which can accumulate Se at up to 1000 times higher concentrations than normal plants, present interesting specialized systems of Se transport and metabolism. Selenium hyperaccumulation mechanisms and potential applications of these mechanisms to biofortification and phytoremediation are presented.
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•Plants are both critical sources of dietary selenium and tools for phytoremediation of selenium contaminated soils.•Plant sulfate transporters interact with selenate and can be manipulated to increase selenium uptake and translocation.•Selenium is toxic to plants, but nontoxic metabolites can be produced, especially in selenium hyperaccumulators.
Aims
Taking into account the relevance of biofortification of crop plants with selenium (Se) - an essential element for humans and animals -, this study assessed the effect of adding Se in the soil ...(as selenate) on: i) rice grains yield; ii) Se contents in polished rice grains; iii) physiological traits in rice leaves; and, iv) spatial distribution of Se and other elements in biofortified grains.
Methods
A field trial was conducted using five Se rates (12, 21, 38, 68, and 120 g ha
−1
). Physiologic and enzymatic evaluations were carried out in rice leaves. Rice grain yield and Se contents were assessed. Spatial distributions of Se and other elements were visualized mapping the biofortified rice grains with μXRF at Brazilian Synchrotron Light Source.
Results
Results showed that soil Se application was effective in producing rice grains with higher Se contents, yet no effects were verified on rice yield. Antioxidant enzyme activities and gas exchanges in rice leaves changed following the application of Se. The spatial distribution of different elements in biofortified grains varied, with Se being accumulated mainly in the rice endosperm.
Conclusion
Our results suggest that soil application of 47 and 36 g ha
−1
of Se (as sodium selenate) may guarantee the production of rice grains with adequate Se levels for human consumption in Brazil and worldwide, respectively.
Iron oxyhydroxides are widely spread in soils and sediments. They can considerably affect the migration of selenate in the environment, due to their high affinity towards oxyanions. To assess the ...sorptive properties of one of the most common oxyhydroxides, the selenate sorption onto goethite and its effects on goethite's structural properties during its crystallization were investigated. The sorption kinetics of selenate onto goethite at different pH revealed the presence of a desorption phase that had manifested extensively, especially at higher pH values. Also, an isotherm study indicated that the selenate sorption onto goethite is multi-layered at higher concentrations. Phosphate, which is one of the common naturally occurring oxyanions, affected selenate sorption onto goethite significantly, while chloride and sulfate influenced sorption only marginally. The Mössbauer spectrometry showed no structural changes after iron oxyhydroxides crystallization in the presence of selenate. However, changes outside the goethite lattice were manifested by the alterations in distributions of hyperfine magnetic fields obtained from Mössbauer spectra analyses, as well as by the changes in values of the selenate-treated samples' surface charge.
•Detailed analysis of selenate sorption kinetics in range of pH 3–7 are provided.•Sorption of Se onto goethite is 3-step process and includes rapid desorption phase.•Desorption phase is highly dependent on initial pH.•Se sorption onto goethite is multilayered, and well described by sigmoidal isotherm.•During co-precipitation only marginal effects of Se on goethite lattice were noted.
Underpotential deposited Cu on the low index faces of single crystal Au electrodes has been found to promote the reduction of selenate, SeO42−(aq),in 0.1 M HClO4 solutions, a behavior analogous to ...that reported earlier in our laboratory for polycrystalline Au (Strobl et al. J. Electrochem. Soc.2016,163 (13), H1066). Sequential potential step-linear scan voltammetry data collected for Au(111) film electrodes in solutions containing Cu2+(aq) in the μM range afforded evidence that the onset for the electrocatalytic activity occurs for Cu(UPD) coverages, θCu ≈ 0.18, the same value at which complementary microgravimetric data displayed a clear increase in mass. On this basis, a reaction mechanism has been proposed involving the initial reversible formation of an adsorbed adduct, we denote as Cu|SeO42−(ads), followed by a first order irreversible reduction to yield a yet to be identified species, which we denote as Cu|Se(ads), as the rate determining step. Support for this reaction scheme was obtained from numerical solutions of the coupled differential equations that govern the time evolution of Cu|SeO4−(ads) and Cu|Se(ads), yielding best agreement with the experimental data for values of the equilibrium constant for adduct formation and the adduct reduction rate constant of 2.5 × 106 cm3 mol−1, and 9.1 × 10−3 s−1, respectively. This unique electrocatalytic effect has been attributed to a shift in the potential of zero charge of the bare Au substrates induced by Cu(UPD), which promotes the adsorption of HSeO4−(aq) at potentials more negative than those found for the bare substrates, allowing access to overpotentials high enough for its activation and further reduction to ensue.
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