Processing conditions applied during food production could affect food component contents and bioaccessibility. Here, possible changes in Hg and Se total and species contents and bioaccessibility have been tracked in each stage of the production chain of processed fish-derived products. Therefore, Se:Hg molar ratio and Selenium Health Benefit Value (HBVSe) were calculated for final products and raw materials, resulting favorable in all cases, suggesting the safety of surimi-based products regarding mercury. Speciation studies revealed the presence of SeMeSeCys and SeMet in all samples. Thus, the integrity of the selenium species seems to be maintained. Moreover, in vitro gastrointestinal digestion model evidenced that Se bioaccessibility ranged between 20-39 % for all samples, while in case of Hg was between 8-37 %. Additionaly, SeMeSeCys and SeMet were also identified in the gastrointestinal extracts. Finally, no cytotoxicity was observed after exposure of Caco-2 cells to the gastrointestinal extracts.

In the present work, liposomes have been used as nanocarriers in the biofortification of wheat plants with selenium (Se) through foliar application. Liposomal formulations were prepared using 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and Phospholipon®90H (P90H) (average size <100 nm), loaded with different concentrations of inorganic Se (selenite and selenate) and applied twice to the plants in the stage of vegetative growth. Liposomes enhanced Se uptake by wheat plants compared to direct application. The highest Se enrichment was achieved using the phospholipid DPPC and a concentration of 1000 μmol·L-1 of Se without affecting the biomass, chlorophylls, carotenoids, and the concentration of mineral nutrients of the plants. The chemical speciation of Se in the plants was further investigated by X-ray absorption spectroscopy (XAS). The results from XAS spectra revealed that most of the inorganic Se was transformed to organic Se and that the use of liposomes influenced the proportion of C-Se-C over C-Se-Se-C species.

An in-depth understanding of Se uptake and metabolism in plants is necessary for developing Se biofortification strategies. Thus, hydroponic experiments were conducted to investigate the associated processes and mechanisms of organic Se (selenomethionine (SeMet) and selenomethionine-oxide (SeOMet)) uptake, translocation, transformation and their interaction in wheat, in comparison to inorganic Se. The results showed that Se uptake by the roots and the root-to-shoot translocation factor under the SeMet treatment were higher than those under the selenite, selenate and SeOMet treatments. The uptake and translocation of SeMet were higher than those of SeOMet within 72 h, although the differences gradually narrowed with time. The uptake of SeMet and SeOMet was also sensitive to the aquaporin inhibitor: AgNO3 addition resulted in 99.5% and 99.9% inhibitions of Se in the root in the SeMet and SeOMet treatments, respectively. Once absorbed by the root, they rapidly assimilated to other Se forms, and SeMet and Se-methyl-selenocysteine (MeSeCys) were the dominant species in SeMet- and SeOMet-treated plants, while notably, an unidentified Se form was also found in the root and xylem sap under the SeMet treatment. In addition, within 16 h, SeOMet inhibited the uptake and translocation of SeMet, while the inhibition was weakened with longer treatment time. Taken together, the present study provides new insights for the uptake and transformation processes of organic Se within plants.

The roles of Ca/Fe phases on selenium (Se) enrichment behavior in fly ash during coal combustion were investigated by examining the Ca/Fe mineralogy of various ash samples, exploring the binding forms of Se in fly ashes, and performing bench-scale adsorption experiments (150-1000 ℃). The results indicated that Se capture by fly ash is a function of flue gas temperature, particle size, and more importantly, the contents and form of Ca/Fe in combustion ash. Physical condensation/adsorption was mainly determined by temperature and particle size, contributing to less than 25% of total Se in fly ash. The remaining Se in fly ash was captured by chemical reactions of Se with ash components. Calcium in ash mostly was present as Ca-aluminosilicates, Ca-silicates, gypsum, or complex Ca-Al-Si-Fe-O mixed phases. Iron mainly occurred as Fe-silicates and some crystalline minerals including hematite, magnetite, and maghemite. Although adsorption experiments found that only CaO was able to capture SeO2 (g) at high temperature (> 900 ℃), the roles of lime as well as Fe2+-/Fe3+-silicates (conclusion from previous literature) can be excluded, as inferred from the small amount of CaO in ash and the lack of correlation between Fe-silicate and Se. Sequential extraction experiments and electron microscopy analysis revealed that Fe-bound Se was dominant and iron oxides might be the critical phase for Se retention. Simulated adsorption experiments demonstrated that magnetite had the best Se capture ability among the iron minerals. The extraction of Fe-bound Se from coal fly ash required more stringent conditions than that of physiosorbed-Se and Ca-bound Se. Therefore, pretreatment methods including magnetic separation, flotation, size segregation, etc. were suggested to be used prior to acid leaching. This study can provide scientific basis for developing high-efficiency Se recovery methods or Se emission control techniques for high-Se coal utilization in thermal power stations.

This study reports the development and validation of a new analytical method for simultaneous speciation analysis of Se and Hg in fish muscle. For this purpose, four Se species (selenite/Se(IV), selenate/Se(VI), selenomethionine/SeMet, and selenocysteine/SeCys) and two Hg species (inorganic mercury/iHg and methylmercury/MeHg) were extracted simultaneously by microwave-assisted enzymatic hydrolysis and then separated by HPLC in less than 15 min by using a column with both anion and cation exchange mechanisms and a mobile phase consisting of a mixture of methanol 5% (v/v), 45 mM HNO3, 0.015% 2-mercaptoethanol, and 1.5 mM sodium 3-mercapto-1-propanesulfonate. The separated species of Hg and Se were detected online by inductively coupled plasma-mass spectrometry (ICP-MS). The speciation analysis method was validated by means of the accuracy profile approach by carrying out three series of measurements in duplicate on three different days over a time-span of 3 weeks. The limits of quantification (LOQ) are in the range of 0.010-0.013 mg/kg wet weight (ww) for all selenium species, except for Se(IV) (0.15 mg/kg ww), while the coefficient of variation in terms of intermediate reproducibility (CVR) was < 7%. The LOQ for MeHg was 0.006 mg/kg ww, while the CVR was 3%. The method was successfully applied to the analysis of muscle samples from four different fish species: rainbow trout, tuna, swordfish, and dogfish.

Selenium (Se) inhibits cadmium (Cd) root-to-shoot translocation and accumulation in the shoots of pak choi; however, the mechanism by which Se regulates Cd retention in roots is still poorly understood. A time-dependent hydroponic experiment was conducted to compare the effects of selenite and selenate on Cd translocation and retention in the roots. The underlying mechanisms were investigated regarding Se biotransformation and metal transportation in roots using HPLC and transcriptome analyses. Selenite showed reducing effects on Cd translocation and accumulation in shoots earlier than selenate. Selenite is mainly biotransformed into selenomethionine (80% of total Se in roots) at 72 h, while SeO42- was the dominant species in the selenate treatments (68% in shoots). Selenite up-regulated genes involved in the biosynthesis of lignin, suberin, and phytochelatins and those involved in stress signaling, thereby helping to retain Cd in the roots, whereas essentially, selenate had opposite effects and impaired the symplastic and apoplastic retention of Cd. These results suggest that cell-wall reinforcement and Cd retention in roots may be the key processes by which Se regulates Cd accumulation, and faster biotransformation into organic seleno-compounds could lead to earlier effects.

An appropriate selenium intake can be beneficial for human health. Se-biofortified food in Se-deficient regions is becoming an increasingly common practice but there are still issues to be addressed regarding the observed Se-induced toxicity to the plant. In this respect, plant biostimulants are used to enhance nutrition efficiency, abiotic stress tolerance and crop quality. In this work, the efficacy of a plant biostimulant to counteract the Se-induced stress in wheat plants is experimentally assessed. The co-application of different Se-biofortification treatments and the biostimulant at different growth stages (tillering or heading stage) was investigated. The use of micro focused X-ray spectroscopy allows us to confirm organic Se species to be the main Se species found in wheat grain and that the proportion of organic Se species is only slightly affected by the Se application stage. Our study proves that the biostimulant had a key role in the enhancement of both the amount of grains produced per spike and their dry biomass without hindering Se enrichment process, neither diminishing the Se concentration nor massively disrupting the Se species present. This information will be useful to minimize both plant toxicity and economic cost towards a more effective and plant healthy selenium supplementation.

Selenite and phosphate share similar uptake mechanisms, as a phosphate transporter is involved in the selenite uptake process. However, the mechanism by which selenium (Se) transformation in plants is mediated by phosphorus (P) remains unclear. In this hydroponic study, the absorption, translocation, and biotransformation of Se in selenite-treated rice (Oryza sativa L.) seedlings were investigated under varying P nutrient status. The results showed that P-deficient cultivation increased the Se concentration in roots with Se-only treatment by 2.1 times relative to that of the P-normal condition. However, co-treating roots with additional P caused the Se concentration to decline by 20 and 73% compared to Se treatment alone under P-normal and P-deficient cultivation, respectively. A similar pattern was also observed in Se uptake by rice roots. With an Se-transfer factor elevated by 4.4 times, the shoot Se concentration was increased by 44% with additional P supply compared to the concentration under Se-only treatment of P deficiency; however, no significant differences were observed regarding P-normal cultivation. P deficiency increased the Se percentage by 28% within the cell wall, but reduced it by 60% in the soluble fraction of Se-only treated roots relative to that of the P-normal condition. Contrarily, compared with the Se-only treatment under P deficiency, additional P supply enhanced Se storage in the root soluble fraction by 1.3 times. The opposite tendency was observed for rice shoots. Moreover, P deficiency reduced the proportion of SeMet by 22%, but increased MeSeCys by 1.3 times in Se-only treated roots compared to those under the P-normal condition. Interestingly, MeSeCys was not detected when additional P was added to the two cultivation conditions. Unlike in the roots, only SeMet was generally detected in the rice shoots. The results demonstrate that the P nutrient status strongly affects the Se biofortification efficiency in rice seedlings by altering the Se subcellular distribution and speciation.

Selenium (Se) is essential to most animals, whereas the gap between necessity and toxicity is narrow. Our previous work showed constructed wetlands were a promising solution to Se contamination in aquatic habitats. This study further examined effects of organic amendments and hydrologic regimes on Se removal by constructed wetlands. Our results suggest the removal efficiency exceeded 94% within 8 days for the systems with moderate and low organic carbon contents in the substrate, as a 98% removal of Se was obtained in three weeks for the system subjected to the 2-day wet/dry cycle. To mimic field wetlands, a litter layer was added to the cattail treatment system, which reduced waterborne Se much more rapidly than control, achieving a 77% removal of Se within 4 days. XAS results show all sediment Se was transformed to Se0 in the presence of litter, as SeMet (47%) dominated the Se adsorbed by the litter. The findings indicate the Se removal capacity of a constructed wetland would improve over time, especially via Se volatilization into the atmosphere and Se stabilization in the sediment with litter accumulating at the surface. Another mesocosm experiment showed the cattail floating system effectively removed Se, particularly selenate, by 99% in 48 h. To confirm that high performance, seven constructed wetland types were set up for comparison. The results show the cattail floating system was most effective in Se removal (93-100% at around 35 °C in summer and 51-100% at about 5 °C in winter). More research is needed to test the floating system under more field conditions and investigate the biomagnification and biotransformation of the removed Se along food chains. Seven constructed wetland types were set up for comparison.

There are a lack of systematic studies comparing the effects of foliar-applied selenium (Se) with different Se sources at different growth stages in wheat. Herein, we biofortified wheat via the foliar application of selenite and selenate at different rates and different stages under field conditions. Results showed that foliar-applied selenate and selenite had no significant effect either on wheat biomass or grain yield (p < 0.05). Selenium distribution in different parts of wheat plant ranked decrease as leaf > root > grain > glume > stem with selenite treatment, and it appeared in the decline order as leaf > grain > glume > stem > root with selenate treatment. These results suggested that biofortification with selenate caused, relatively to selenite, a higher accumulation of Se in grains. Foliar application of Se of either selenate or selenite at pre-filling stage was superior in improving the Se concentration of wheat grains than application at pre-flowering stage. Meanwhile, organic Se comprised about 72-93% of total Se in wheat grains, which was reduced by 5.8% at high Se rate (100 g ha-1), irrespective of the forms of Se or stages applied. The organic Se proportion in wheat grains was 9% higher with the selenate treatment than with the selenite treatment. Selenomethionine (SeMet) was the main organic species (67-86%) in wheat grains, followed by selenocysteine (SeCys2). In summary, our results indicate that Se biofortification of wheat is most effective with 20 g ha-1 selenate foliar-applied at pre-filling stage.