A comprehensive review on environmental transformation of selenium: recent advances and research perspectives

Insight into selenium biofortification and the selenite metabolic mechanism of Monascus ruber M7

Monascus species are functional fermentation fungi with great potential for selenium (Se) supplementation. This study investigated the effects of Se bio-fortification on the growth, morphology, and biosynthesis of Monascus ruber M7. The results demonstrated a significant increase in the yield of orange and red Monascus pigments (MPs) in red yeast rice (RYR) by 38.52% and 36.57%, respectively, under 20 μg/mL of selenite pressure. Meanwhile, the production of citrinin (CIT), a mycotoxin, decreased from 244.47 μg/g to 175.01 μg/g. Transcriptome analysis revealed significant upregulation of twelve genes involved in MPs biosynthesis, specifically MpigE, MpigF, and MpigN, and downregulation of four genes (mrr3, mrr4, mrr7, and mrr8) associated with CIT biosynthesis. Additionally, three genes encoding cysteine synthase cysK (Log2FC = 1.6), methionine synthase metH (Log2FC = 2.2), and methionyl-tRNA synthetase metG (Log2FC = 1.8) in selenocompound metabolism showed significantly upregulated. These findings provide insights into Se biotransformation and metabolism in filamentous fungi.

Effect of inorganic arsenic in paddy soil on the migration and transformation of selenium species in rice plants

Selenium (Se) in paddy rice is one of the significant sources of human Se nutrition. However, the effect of arsenic (As) pollution in soil on the translocation of Se species in rice plants is unclear. In this research, a pot experiment was designed to examine the effect of the addition of 50 mg As/kg soil as arsenite or arsenate on the migration of Se species from soil to indica Minghui 63 and Luyoumingzhan. The results showed that the antagonism between inorganic As and Se was closely related to the rice cultivar and Se oxidation state in soil. Relative to the standalone selenate treatment, arsenite significantly (p < 0.05) decreased the accumulation of selenocystine, selenomethionine and selenate in the roots, stems, sheaths, leaves, brans and kernels of both cultivars by 21.4%-100.0%, 40.0%-100.0%, 41.0%-100%, 5.4%-96.3%, 11.3%-100.0% and 26.2%-39.7% respectively, except for selenocystine in the kernels of indica Minghui 63 and selenomethionine in the leaves of indica Minghui 63 and the stems of indica Luyoumingzhan. Arsenate also decreased (p < 0.05) the accumulation of selenocystine, selenomethionine and selenate in the roots, stems, brans and kernels of both cultivars by 34.9%-100.0%, 30.2%-100.0%, 11.3%-100.0% and 5.6%-39.6% respectively, except for selenate in the stems of indica Minghui 63. However, relative to the standalone selenite treatment, arsenite and arsenate decreased (p < 0.05) the accumulation of selenocystine, selenomethionine and selenite only in the roots of indica Minghui 63 by 45.5%-100.0%. Our results suggested that arsenite and arsenate had better antagonism toward Se species in selenate-added soil than that in selenite-added soil; moreover, arsenite had a higher inhibiting effect on the accumulation of Se species than arsenate.

Changes in Cerebrospinal Fluid Concentrations of Selenium Species Induced by Tofersen Administration in Subjects with Amyotrophic Lateral Sclerosis Carrying SOD1 Gene Mutations

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting the brain and spinal cord motor neurons. On 25 April 2023, the drug tofersen, an antisense oligonucleotide, received the US Food and Drug Administration approval for treating ALS in adults carrying mutations of the SOD1 gene. We aimed at assessing whether cerebrospinal fluid concentrations of selenium, an element of both toxicological and nutritional interest possibly involved in disease etiology and progression, are modified by tofersen administration. We determined concentrations of selenium species by anion exchange chromatography hyphenated to inductively coupled plasma-dynamic reaction cell-mass spectrometry and overall selenium by using inductively coupled plasma sector-field mass spectrometry, at baseline and 6 months after active tofersen treatment in ten Italian ALS patients carrying the SOD1 gene mutation. Concentrations of total selenium and many selenium species substantially increased after the intervention, particularly of inorganic (tetravalent and hexavalent) selenium and of the organic species selenomethionine and a compound co-eluting with the selenocystine standard. Overall, these findings suggest that tofersen treatment markedly alters selenium status and probably the redox status within the central nervous system, possibly due to a direct effect on neurons and/or the blood-brain barrier. Further studies are required to investigate the biological and clinical relevance of these findings and how they might relate to the pharmacological effects of the drug and to disease progression.

Selenium Species in Diabetes Mellitus Type 2

Selenium is an important trace element for humans and animals as it plays a key role in several major metabolic pathways. Several studies were conducted to better understand the role of selenium against diabetes mellitus (DM), particularly type 2 (T2DM), but the obtained conclusions are contradictory. A simple linear relationship does not exist between the risk of T2DM and selenium levels but is best represented in a dose-dependent manner, getting often the U-graph. This relation also depends on selenium chemical forms that are present in a diet or supplements. Both too low and too high selenium intakes could increase the risk of diabetes. Moreover, the baseline status of Se should be taken into consideration to avoid over-supplementation. The focus of this brief overview is to report the recent updates concerning selenium participation in diabetes mellitus.

Identification and functional characterization of ABC transporters for selenium accumulation and tolerance in soybean

ATP-binding cassette (ABC) transporters were crucial for various physiological processes like nutrition, development, and environmental interactions. Selenium (Se) is an essential micronutrient for humans, and its role in plants depends on applied dosage. ABC transporters are considered to participate in Se translocation in plants, but detailed studies in soybean are still lacking. We identified 196 ABC genes in soybean transcriptome under Se exposure using next-generation sequencing and single-molecule real-time sequencing technology. These proteins fell into eight subfamilies: 8 GmABCA, 51 GmABCB, 39 GmABCC, 5 GmABCD, 1 GmABCE, 10 GmABCF, 74 GmABCG, and 8 GmABCI, with amino acid length 121-3022 aa, molecular weight 13.50-341.04 kDa, and isoelectric point 4.06-9.82. We predicted a total of 15 motifs, some of which were specific to certain subfamilies (especially GmABCB, GmABCC, and GmABCG). We also found predicted alternative splicing in GmABCs: 60 events in selenium nanoparticles (SeNPs)-treated, 37 in sodium selenite (Na2SeO3)-treated samples. The GmABC genes showed differential expression in leaves and roots under different application of Se species and Se levels, most of which are belonged to GmABCB, GmABCC, and GmABCG subfamilies with functions in auxin transport, barrier formation, and detoxification. Protein-protein interaction and weighted gene co-expression network analysis suggested functional gene networks with hub ABC genes, contributing to our understanding of their biological functions. Our results illuminate the contributions of GmABC genes to Se accumulation and tolerance in soybean and provide insight for a better understanding of their roles in soybean as well as in other plants.

Factors controlling accumulation and bioavailability of selenium in paddy soils: A case study in Luxi County, China

Selenium (Se) accumulation in rice (Oryza sativa L.) has become a major global concern. Se offers multiple health benefits in humans; however, its inadequate or excessive intake can be harmful. Therefore, determining the factors driving Se abundance and bioavailability in paddy soils is essential to ensure the safety of human Se intake. This study investigated the accumulation, bioavailability, and distribution of Se in 820 paddy soil and rice grain samples from Luxi County, China to assess how soil properties (soil organic matter [SOM], cation exchange capacity [CEC], and pH), geographical factors (parent materials, elevation, and mean annual precipitation [MAP] and temperature [MAT]), and essential micronutrients (copper [Cu], zinc [Zn], and manganese [Mn]) govern Se accumulation and bioavailability in paddy soils. Results showed that the average soil Se content was 0.36 mg kg-1, which was higher than that in China (0.29 mg kg-1). Alternatively, the average rice grain Se content was 0.032 mg kg-1, which was lower than the minimum allowable content in Se-rich rice grains (0.04 mg kg-1). Five studied parent materials all had a significant effect on soil Se content but had little effect on Se bioavailability (p < 0.05). CEC, elevation, and SOM, as well as the soil contents of Cu, Zn, and Mn were positively correlated with soil Se content, but pH, MAP, and MAT were negatively correlated. Correspondingly, Se bioavailability was negatively correlated with SOM and soil Zn content, but positively correlated with MAP and grain contents of Cu, Zn, and Mn. Furthermore, partial least squares path analysis revealed the interactive impacts of the influencing factors on Se accumulation and bioavailability in soils. On this basis, prediction models were established to predict Se accumulation and bioavailability in paddy soils, thereby providing theoretical support for developing efficient control measures to meet Se challenges in agriculture.

Reaction Pattern and Mechanistic Aspects of Iodine and Iodine-Based Reagents in Selenylation of Aliphatic, Aromatic, and (Hetero)Cyclic Systems

Organoselenium compounds have been the subject of extensive research since the discovery of the biologically active compound ebselen. Ebselen has recently been found to show activity against the main protease of the virus responsible for COVID-19. Other organoselenium compounds are also well-known for their diverse biological activities, with such compounds exhibiting interesting physical properties relevant to the fields of electronics, materials, and polymer chemistry. In addition, the incorporation of selenium into various organic molecules has garnered significant attention due to the potential of selenium to enhance the biological activity of these molecules, particularly in conjunction with bioactive heterocycles. Iodine and iodine-based reagents play a prominent role in the synthesis of organoselenium compounds, being valued for their cost-effectiveness, non-toxicity, and ease of handling. These reagents efficiently selenylate a broad range of organic substrates, encompassing alkenes, alkynes, and cyclic, aromatic, and heterocyclic molecules. They serve as catalysts, additives, inducers, and oxidizing agents, facilitating the introduction of different functional groups at alternate positions in the molecules, thereby allowing for regioselective and stereoselective approaches. Specific iodine reagents and their combinations can be tailored to follow the desired reaction pathways. Here, we present a comprehensive review of the progress in the selenylation of organic molecules using iodine reagents over the past decade, with a focus on reaction patterns, solvent effects, heating, microwave, and ultrasonic conditions. Detailed discussions on mechanistic aspects, such as electrophilic, nucleophilic, radical, electrochemical, and ring expansion reactions via selenylation, multiselenylation, and difunctionalization, are included. The review also highlights the formation of various cyclic, heterocyclic, and heteroarenes resulting from the in situ generation of selenium intermediates, encompassing cyclic ketones, cyclic ethers, cyclic lactones, selenophenes, chromones, pyrazolines, pyrrolidines, piperidines, indolines, oxazolines, isooxazolines, lactones, dihydrofurans, and isoxazolidines. To enhance the reader's interest, the review is structured into different sections covering the selenylation of aliphatic sp2/sp carbon and cyclic sp2 carbon, and then is further subdivided into various heterocyclic molecules.

Soil Geobacteraceae are the key predictors of neurotoxic methylmercury bioaccumulation in rice

Contamination of rice by the potent neurotoxin methylmercury (MeHg) originates from microbe-mediated Hg methylation in soils. However, the high diversity of Hg methylating microorganisms in soils hinders the prediction of MeHg formation and challenges the mitigation of MeHg bioaccumulation via regulating soil microbiomes. Here we explored the roles of various cropland microbial communities in MeHg formation in the potentials leading to MeHg accumulation in rice and reveal that Geobacteraceae are the key predictors of MeHg bioaccumulation in paddy soil systems. We characterized Hg methylating microorganisms from 67 cropland ecosystems across 3,600 latitudinal kilometres. The simulations of a rice-paddy biogeochemical model show that MeHg accumulation in rice is 1.3-1.7-fold more sensitive to changes in the relative abundance of Geobacteraceae compared to Hg input, which is recognized as the primary parameter in controlling MeHg exposure. These findings open up a window to predict MeHg formation and accumulation in human food webs, enabling more efficient mitigation of risks to human health through regulations of key soil microbiomes.

The beneficial and toxic effects of selenium on zebrafish. A systematic review of the literature

Selenium is an important and essential trace element in organisms, but its effects on organisms are also a "double-edged sword". Selenium deficiency or excess can endanger the health of humans and animals. In order to thoroughly understand the nutritional value and toxicity hazards of selenium, researchers have conducted many studies on the model animal zebrafish. However, there is a lack of induction and summary of relevant research on which selenium acts on zebrafish. This paper provides a review of the reported studies. Firstly, this article summarizes the benefits of selenium on zebrafish from three aspects: Promoting growth, Enhancing immune function and anti-tumor ability, Antagonizing some pollutants, such as mercury. Then, three aspects of selenium toxicity to zebrafish are introduced: nervous system and behavior, reproductive system and growth, and damage to some organs. This article also describes how different forms of selenium compounds have different effects on zebrafish health. Finally, prospects for future research directions are presented.

Cross-species apical microinjected selenomethionine toxicity in embryo-larval fishes

Selenium (Se) is an essential micronutrient that becomes toxic when exposures minimally exceed those that are physiologically required. Studies on Se contaminated aquatic environments have identified that embryo-larval fishes are at particular risk of Se toxicity, primarily due to maternal Se transfer to developing eggs during oogenesis. This study emulated these exposures in embryo-larval fathead minnow (FHM), rainbow trout (RBT), white sucker (WSu), and white sturgeon (WSt) using embryonic selenomethionine (SeMet) microinjections. Adverse Se-outcomes observed across these species included spinal and edematous deformities, total individuals deformed, and reduced survival. Spinal deformity was the most sensitive sublethal endpoint and developed at the lowest concentrations in WSt (10 % effects concentration (EC10) = 12.42 μg (total) Se/g dry weight (d.w.)) followed by WSu (EC10 = 14.49 μg Se/g d.w.) and FHM (EC10 = 18.10 μg Se/g d.w.). High mortality was observed in RBT, but SeMet influences were confounded by the species' innate sensitivity to the microinjections themselves. 5 % hazardous concentrations derived across exposure type data subsets were ∼49 % higher when derived from within-species maternal transfer exclusive data as opposed to all, or within-species microinjection exclusive, data. These results support the current exclusion of SeMet microinjections during regulatory guideline derivation and their inclusion when studying mechanistic Se toxicity across phylogenetically distant fishes.

Modelling selenium behavior in aquatic systems: a review of status, challenges, and opportunities

Selenium (Se) is an essential element for aquatic organisms as well as humans. It can be toxic to organisms depending on its concentration and chemical speciation; thus, considerable efforts have been made to unravel the biogeochemical cycling of Se in aquatic systems. Mathematical models provide an important tool to better understand the fate of Se in different environment compartments. However, a comprehensive review of modeling Se in aquatic systems with current challenges and opportunities is missing. To fill this gap, we firstly summarize the processes governing Se cycling in aquatic systems, including particle adsorption and desorption, diffusion, biological uptake, redox reactions, and volatilization. Then, we critically review the available models, identifying the compartments modelled, environmental factors considered, and the Se species and geochemical processes used in each model, providing an assessment of their advantages and limitations. Data availability for modeling studies is investigated, highlighting how to better quantify the redox reactions, estimate of Se loadings, and mass balance. For the modeling of Se cycling in aquatic systems, the ability of the models to link sources to biota concentrations under a range of hydrodynamic conditions and with mechanistic representations of transport, transformation, and uptake processes is required. The majority of the current models can conduct this task; however, to better present the uptake processes of Se in the food web, two-way coupling of the Se cycling model with a food web model is recommended.

Selenite (IV) and selenate (VI) uptake and accumulation capacity of Lemna minor L. from an aquatic medium

The uptake of sodium selenite (Se(IV)) and sodium selenate (Se(VI)) from aqueous medium by Lemna minor L. and the influence of different Se concentrations on its growth, morphological and ultrastructural characteristics were studied. L. minor was grown at different concentrations (1, 3, 5 and 10 mg L-1) of Se(IV) and Se(IV). The Se(IV) concentration in the plant tissue ranged between 77.7 (± 4.3) to 453 (± 0) mg kg-1 DW. The Se(VI) concentration in plant tissues ranged between 117 (± 11) to 417 (± 2) mg kg-1 DW. The highest bioconcentration factor for Se(VI) was 127 (± 7) at 3 mg/L, with a Se removal efficiency of 44%. For Se(IV), the highest bioconcentration factor was 77.7 (± 4.3) at 1 mg L-1, which had a Se removal efficiency of 23%. Growth of L. minor was suppressed at 10 mg L-1 Se in both forms. The addition of Se promoted the formation of starch granules in L. minor which occupied a chloroplast area of 74% for Se(IV) and 77% for Se(VI). The efficient uptake of both Se forms by L. minor indicates the potential application of this species for phytoremediation of Se laden wastewaters and its use as an alternative feedstock in biofuel production.

Environmental selenium and human longevity: An ecogeochemical perspective

Selenium (Se) has been called the "longevity element" by the scientific community because it has anti-cancer, anti-inflammatory, and anti-oxidant activity in humans. The geochemical properties and biological functions of Se have been widely studied in various fields, including geology, agriculture, and medicine. Bama Yao Autonomous County (Bama), a typical township in China with high longevity among the population, was selected as the research area. The present study organically combines the geological background, dietary structure, absorption and metabolism, and other biogeochemical aspects to comprehensively analyze the anti-aging properties of Se under high-Se conditions and a fiber-rich polysaccharide diet. Biogeochemical samples of surface soil, food, human hair, and urine were systematically collected from the environment and the residents, and the content and speciation of Se were analyzed. Concentrations of Se in the soil were moderate to high for Bama, with high-Se soil in 77.21% of the samples. Water-soluble Se concentrations were also high, 90% of the samples with moderate to high Se, and had a significant positive correlation with Se concentrations in crops. With both high total and high available Se, dietary samples from the study area showed Se-enriched characteristics. Accordingly, Se intake was also high (82.54 μg/d) in the population, strongly maintaining the normal bodily functions of the elderly. Accumulation and metabolism of Se in the population were assessed based on concentrations of Se in the hair and urine of residents over 60 years old. Continuous accumulation of Se was found to occur from 71 to 80 years of age. Concentrations of Se in residents under 71 years old and over 80 years old were in a state of loss. Overall, Se absorption and metabolism are maintained at the optimal physiological state, which is one of the primary factors maintaining the health and longevity of the elderly people in the study area.

A critical review on selenium removal capacity from water using emerging non-conventional biosorbents

Anthropogenic-driven selenium (Se) contamination of natural waters has emerged as severe health and environmental concern. Lowering Se levels to safe limits of 40 μg-L-1 (recommended by WHO) presents a critical challenge for the scientific community, necessitating reliable and effective methods for Se removal. The primary obectives of this review are to evaluate the efficiency of different biosorbents in removing Se, understand the mechanism of adsorption, and identify the factors influencing the biosorption process. A comprehensive literature review is conducted to analyze various studies that have explored the use of modified biochars, iron oxides, and other non-conventional biosorbents for selenium removal. The assessed biosorbents include biomass, microalgae-based, alginate compounds, peats, chitosan, and biochar/modified biochar-based adsorbents. Quantitative data from the selected studies analyzed Se adsorption capacities of biosorbents, were collected considering pH, temperature, and environmental conditions, while highlighting advantages and limitations. The role of iron impregnation in enhancing the biosorption efficiency is investigated, and the mechanisms of Se adsorption on these biosorbents at different pH levels are discussed. A critical literature assessment reveals a robust understanding of the current state of Se biosorption and the effectiveness of non-conventional biosorbents for Se removal, providing crucial information for further research and practical applications in water treatment processes. By understanding the strengths and limitations of various biosorbents, this review is expected to scale-up targeted research on Se removal, promoting the development of innovative and cost-effective adsorbents, efficient and sustainable approaches for Se removal from water.

Effect of Dietary Selenium on the Growth and Immune Systems of Fish

Dietary selenium (Se) is an essential component that supports fish growth and the immune system. This review attempts to provide insight into the biological impacts of dietary Se, including immunological responses, infection defense, and fish species growth, and it also identifies the routes via which it enters the aquatic environment. Dietary Se is important in fish feed due to its additive, antioxidant, and enzyme properties, which aid in various biological processes. However, excessive intake of it may harm aquatic ecosystems and potentially disrupt the food chain. This review explores the diverse natures of dietary Se, their impact on fish species, and the biological methods for eliminating excesses in aquatic environments. Soil has a potential role in the distribution of Se through erosion from agricultural, industrial, and mine sites. The research on dietary Se's effects on fish immune system and growth can provide knowledge regarding fish health, fish farming strategies, and the health of aquatic ecosystems, promoting the feed industry and sustainable aquaculture. This review provides data and references from various research studies on managing Se levels in aquatic ecosystems, promoting fish conservation, and utilizing Se in farmed fish diets.

A quantitative review of the effects of Se application on the reduction of Hg concentration in plant: a meta-analysis

Mercury (Hg) is a highly toxic heavy metal entering the human body through the food chain after absorption by plant. Exogenous selenium (Se) has been suggested as a potential solution to reduce Hg concentration in plants. However, the literature does not provide a consistent picture of the performance of Se on the accumulation of Hg in plant. To obtain a more conclusive answer on the interactions of Se and Hg, 1,193 data records were collected from 38 publications for this meta-analysis, and we tested the effects of different factors on Hg accumulation by meta-subgroup analysis and meta-regression model. The results highlighted a significant dose-dependent effect of Se/Hg molar ratio on the reduction of Hg concentration in plants, and the optimum condition for inhibiting Hg accumulation in plants is at a Se/Hg ratio of 1-3. Exogenous Se significantly reduced Hg concentrations in the overall plant species, rice grains, and non-rice species by 24.22%, 25.26%, and 28.04%, respectively. Both Se(IV) and Se(VI) significantly reduced Hg accumulation in plants, but Se(VI) had a stronger inhibiting effect than Se(IV). Se significantly decreased the BAF_Grain in rice, which indicated that other physiological processes in rice may be involved in restricting uptake from soil to rice grain. Therefore, Se can effectively reduce Hg accumulation in rice grain, which provides a strategy for effectively alleviating the transfer of Hg to the human body through the food chain.

Transcriptomics and metabolomics provide insight into the anti-browning mechanism of selenium in freshly cut apples

Enzymatic browning has a considerable negative impact on the acceptability and marketability of freshly cut apples. However, the molecular mechanism by which selenium (Se) positively affects freshly cut apples in this regard is not yet clear. In this study, 0.75 kg/plant of Se-enriched organic fertilizer was applied to "Fuji" apple trees during the young fruit stage (M₅, May 25), the early fruit enlargement stage (M₆, June 25), and the fruit enlargement stage (M₇, July 25), respectively. The same amount of Se-free organic fertilizer was applied as a control. Herein, the regulatory mechanism by which exogenous Se exerts its anti-browning effect in freshly cut apples was investigated. The results showed that the M₇ treatment applied in Se-reinforced apples could remarkably inhibit their browning at 1 h after being freshly cut. Additionally, the expression of polyphenol oxidase (PPO) and peroxidase (POD) genes treated with exogenous Se was significantly reduced compared to controls. Moreover, the lipoxygenase (LOX) and phospholipase D (PLD) genes, which are involved in membrane lipid oxidation, were expressed at higher levels in the control. The gene expression levels of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST), and ascorbate peroxidase (APX) were upregulated in the different exogenous Se treatment groups. Similarly, the main metabolites measured during the browning process were phenols and lipids; thus, it could be speculated that the mechanism by which exogenous Se produces its anti-browning effect may be by reducing phenolase activity, improving the antioxidant capacity of the fruits, and alleviating membrane lipid peroxidation. In summary, this study provides evidence regarding and insight into the response mechanism employed by exogenous Se to inhibit browning in freshly cut apples.

A critical analysis of sources, pollution, and remediation of selenium, an emerging contaminant

Selenium (Se) is an essential metalloid and is categorized as emerging anthropogenic contaminant released to the environment. The rise of Se release into the environment has raised concern about its bioaccumulation, toxicity, and potential to cause serious damages to aquatic and terrestrial ecosystem. Therefore, it is extremely important to monitor Se level in environment on a regular basis. Understanding Se release, anthropogenic sources, and environmental behavior is critical for developing an effective Se containment strategy. The ongoing efforts of Se remediation have mostly emphasized monitoring and remediation as an independent topics of research. However, our paper has integrated both by explaining the attributes of monitoring on effective scale followed by a candid review of widespread technological options available with specific focus on Se removal from environmental media. Another novel approach demonstrated in the article is the presentation of an overwhelming evidence of limitations that various researchers are confronted with to overcome achieving effective remediation. Furthermore, we followed a holistic approach to discuss ways to remediate Se for cleaner environment especially related to introducing weak magnetic field for ZVI reactivity enhancement. We linked this phenomenal process to electrokinetics and presented convincing facts in support of Se remediation, which has led to emerge 'membrane technology', as another viable option for remediation. Hence, an interesting, innovative and future oriented review is presented, which will undoubtedly seek attention from global researchers.

A synthetic community of siderophore-producing bacteria increases soil selenium bioavailability and plant uptake through regulation of the soil microbiome

Dietary selenium (Se) is an effective strategy to meet Se requirement of human body, and Se biofortification in crops in seleniferous soils with selenobacteria represents an eco-friendly biotechnique. In this study, we tested the effectiveness of siderophore-producing bacterial (SPB) synthetic communities (SynComs) in promoting plant Se uptake in a subtropical seleniferous soil where the fixation of Se by ferric-oxides is severe. The results indicated that SPB SynComs drastically elevated soil bioavailable Se content by up to 68.7 %, and significantly increased plant Se concentration and uptake by up to 83.1 % and 92.2 %, respectively. Seven out of ten SPB isolates in the SynComs were enriched in soils after 120 days of inoculation. Additionally, variation partitioning analysis (VPA) revealed that the contribution of soil bacterial community (up to 42.8 %) to the increased plant Se uptake was much greater than that of soil bioavailable Se (up to 5.1 %), suggesting a direct pathway other than the pathway of mobilizing Se. The relative abundances of some operational taxonomic units (OTUs) showed significantly positive relationship with plant Se status but not with soil Se status, which supports the results of VPA. Network analysis indicates that some inoculated SPB isolates promoted plant Se uptake by regulating the native bacterial taxa. Taken together, this study demonstrates that SPB can be used in Se biofortification in crops, especially in subtropical soils.

Coexposure to multiple metals and renal tubular damage: a population-based cross-sectional study in China's rural regions

Previous studies have indicated that exposure to a single toxic metal can cause renal tubular damage, while evidence about the effects of multimetal exposure on renal tubular damage is relatively limited. We aimed to evaluate the relationships of multimetal coexposure with renal tubular damage in adults in heavy metal-polluted rural regions of China. A cross-sectional study of 1918 adults in China's heavy metal-contaminated rural regions was conducted. Inductively coupled plasma-mass spectrometry (ICP-MS) was used to measure the plasma levels of 18 metals in participants, and immune turbidimetry was used to measure sensitive biological indicators, reflecting renal tubular damage (including retinol-binding protein and β2-microglobulin). Least absolute shrinkage and selection operator (LASSO) penalized regression analysis, logistic and linear regression analysis, restricted cubic spline (RCS) regression analysis and the Bayesian kernel machine regression (BKMR) method were used to explore associations of multimetal coexposure with renal tubular damage risk or renal tubular damage indicators. Plasma selenium, cadmium, arsenic, and iron were identified as the main plasma metals associated with renal tubular damage risk after dimensionality reduction. Multimetal regression models showed that selenium was positively associated, and iron was negatively associated with renal tubular damage risk or its biological indicators. Multimetal RCS analyses additionally revealed a non-linear relationship of selenium with renal tubular damage risk. The BKMR models showed that the metal mixtures were positively associated with biological indicators of renal tubular damage when the metal mixtures were above the 50th percentile of concentration. Our findings indicated that natural exposure to high levels of multimetal mixtures increases the risk of renal tubular damage. Under the conditions of multimetal exposure, selenium was positively associated, and iron was negatively associated with renal tubular damage risk or its biological indicators.

Accumulation, translocation, and transformation of two CdSe/ZnS quantum dots in rice and pumpkin plants

As a widely applied semiconductor nanomaterial, quantum dots (QDs) have drawn considerable interest. In this study, pumpkin and rice seedlings were hydroponically exposed to two core/shell CdSe/ZnS QDs coated with cysteamine (CdSe/ZnS-CA) and polyethylene glycol-carboxy (CdSe/ZnS-PEG-COOH) for 10 days to analyze their time-varying uptake, translocation, and transformation behaviors in plants. Both QDs were mainly adsorbed/absorbed by the roots in the particulate state, and more CdSe/ZnS-CA accumulated than CdSe/ZnS-PEG-COOH. For CdSe/ZnS-CA-treated plants, the Se and Cd concentrations (CSe and CCd) associated with the roots were 561 ± 75 and 580 ± 73 μg/g (dw) for rice and 474 ± 49 and 546 ± 53 μg/g (dw) for pumpkin, respectively, on day 10. For CdSe/ZnS-PEG-COOH-treated plants, the concentrations of Se and Cd associated with roots were 392 ± 56 and 453 ± 56 μg/g (dw) for rice and 363 ± 52 and 417 ± 52 μg/g (dw) for pumpkin, respectively. The surface charges and coatings significantly affected the accumulation of QDs at the beginning of exposure; however, the impaction decreased with time. The ratios between the Cd and Se concentrations (CCd/CSe) in the stems and leaves varied from those of the QD standards, indicating the transformation of the QDs in the exposure system. Se and Cd were more likely to translocate in CdSe/ZnS-PEG-COOH-treated plants than in CdSe/ZnS-CA-treated plants. The vertical translocation of Se was greater than that of Cd. Rice showed greater abilities of accumulation and translocation of Se and Cd from both QDs than pumpkin. These findings improve our understanding of the interference of QDs with plants and their environmental fate.

Alterations of selenium level and speciation during milling and cooking in different wheat cultivars

BACKGROUND

Selenium (Se) deficiency is a recognized problem that threatens the health of people worldwide, and wheat is grown worldwide and is one of the major sources of dietary Se. Since there are few studies that have investigated the changes in Se content and speciation of different varieties of Se-enriched wheat from primary to deep processing, we studied four naturally Se-enriched kinds of wheat and two Se-fertilized kinds of wheat.

RESULTS

Glutenin- and albumin-bound Se accounted for the highest proportion of protein-bound Se in refined wheat flour (7.29 ± 0.19 to 10.82 ± 0.50% and 6.16 ± 0.34 to 8.45 ± 0.07%); water-soluble polysaccharide-bound Se accounted for the highest proportion of polysaccharide-bound Se in refined wheat flour (12.02 ± 0.54 to 24.62 ± 1.87%). Coarse bran Se content was significantly higher than refined wheat flour (137.94 ± 7.80 to 174.55 ± 5.09% for unpeeled wheat, 147.27 ± 10.96 to 187.72 ± 17.70% for peeled wheat). The peeling and processing of wheat into flour had different effects on Se the content and speciation dependent on the particular wheat variety. Whole wheat flour enabled better retention of selenomethionine (101.64 ± 2.32 to 138.41 ± 2.84% for unpeeled wheat, 158.59 ± 13.72 to 250.20 ± 4.94% for peeled wheat). The cooking process had no significant effect on Se content, but Se species were possibly interconverted.

CONCLUSION

The organic Se content of different varieties of Se-enriched wheat was different, but the milling and cooking process retained the total Se and Se speciation better, which could be used for daily Se supplementation for Se-deficient people. © 2022 Society of Chemical Industry.

Genetic mechanisms for Se(VI) reduction and synthesis of trigonal 1-D nanostructures in Stenotrophomonas bentonitica: Perspectives in eco-friendly nanomaterial production and bioremediation

Selenate (Se(VI)) is one of the most soluble and toxic species of Se. Microbial Se(VI) reduction is an efficient tool for bioremediation strategies. However, this process is limited to a few microorganisms, and its molecular basis remains unknown. We present detailed Se(VI)-resistance mechanisms under 50 and 200 mM, in Stenotrophomonas bentonitica BII-R7, coupling enzymatic reduction of Se(VI) to formation of less toxic trigonal Se (t-Se). The results reveal a concentration-dependent response. Despite the lack of evidence of Se(VI)-reduction to Se(0) under 50 mM Se(VI), many genes were highly induced, indicating that Se(VI)-resistance could be based on intracellular reduction to Se(IV), mainly through molybdenum-dependent enzymes (e.g. respiratory nitrate reductase), and antioxidant activity by enzymes like glutathione peroxidase. Although exposure to 200 mM provoked a sharp drop in gene expression, a time-dependent process of reduction and formation of amorphous (a), monoclinic (m) and t-Se nanostructures was unravelled: a-Se nanospheres were initially synthesized intracellularly, which would transform into m-Se and finally into t-Se nanostructures during the following phases. This is the first work describing an intracellular Se(VI) reduction and biotransformation process to long-term stable and insoluble t-Se nanomaterials. These results expand the fundamental understanding of Se biogeochemical cycling, and the effectiveness of BII-R7 for bioremediation purposes.

Selenite Ameliorates Cadmium-induced Cytotoxicity Through Downregulation of ROS Levels and Upregulation of Selenoprotein Thioredoxin Reductase 1 in SH-SY5Y Cells

Cadmium (Cd) as a ubiquitous toxic heavy metal in the environment, causes severe hazards to human health, such as cellular stress and organ injury. Selenium (Se) was reported to reduce Cd toxicity and the mechanisms have been intensively studied so far. However, it is not yet crystal clear whether the protective effect of Se against Cd-induced cytotoxicity is related to selenoproteins in nerve cells or not. In this study, we found that Cd inhibited selenoprotein thioredoxin reductase 1 (TrxR1; TXNRD1) and decreased the expression level of TrxR1, resulting in cellular oxidative stress, and Se supplements ameliorated Cd-induced cytotoxicity in SH-SY5Y cells. Mechanistically, the detoxification of Se against Cd is attributed to the increase of the cellular TrxR activity and upregulated TrxR1 protein level, culminating in strengthened antioxidant capacity. Results showed that Se supplements attenuated the ROS production and apoptosis in SH-SY5Y cells, and significantly mitigated Cd-induced SH-SY5Y cell death. This study may be a valuable reference for shedding light on the mechanism of Cd-induced cytotoxicity and the role of TrxR1 in Se-mitigated cytotoxicity of Cd in neuroblast cells, which may be helpful for understanding the therapeutic potential of Cd and Se in treating or preventing neurodegenerative diseases, like Alzheimer's disease (AD) and Parkinson's disease (PD).

Comparative physiological and transcriptome analysis reveals the potential mechanism of selenium accumulation and tolerance to selenate toxicity of Broussonetia papyrifera

Broussonetia papyrifera is an important fodder tree that is widely distributed in China. Enhancing the selenium (Se) content in B. papyrifera may help to improve the nutritional value of the feed. In this study, sodium selenite and selenate were foliar applied to investigate the mechanisms of Se tolerance and accumulation in B. papyrifera. The results showed that both Se forms significantly increased the total Se content, and the proportion of organic Se was significantly higher in the sodium selenite treatment than in the control. In addition, the soluble sugar, phenolic acid and flavonoid contents and antioxidant enzyme activities were increased by exogenous Se. The de novo RNA sequencing results showed that 644 and 1804 differentially expressed genes were identified in the selenite and selenate comparison groups, respectively. Pathway enrichment analysis demonstrated that 24 of the 108 pathways were significantly enriched, of which sulfur assimilation genes in the sodium selenite-treated groups were upregulated, whereas Se conjugation and transporter genes, such as SBP1, PCS, GSTs, ABCs and GPX, were significantly induced under selenate treatment. The hub genes identified by weighted-gene co-expression network analysis further confirmed that sulfur assimilation, conjugation and transporter genes might play a vital role in Se assimilation and tolerance. From this, a model of Se metabolism in B. papyrifera was proposed based on the above physiological and RNA sequencing data. This study is the first study to report that B. papyrifera has a strong ability to accumulate and tolerate exogenous Se, thereby providing a foundation for further characterization of the accumulation and tolerance mechanism of B. papyrifera. Our findings can provide technical support for producing Se-enriched fodder.

Highland barley grain and soil surveys reveal the widespread deficiency of dietary selenium intake of Tibetan adults living along Yalung Zangpo River

Objective

In order to assess selenium (Se) flux through the soil-plant-human chain in Tibet plateau and explore the reason why local Tibetan adult residents from large scale agricultural production areas in Tibet lacked daily Se intake.

Methods

A total of 210 intact highland barley plants and their corresponding cultivated topsoil samples were collected in fields of 14 agricultural counties along Yalung Zangpo River and quantitative dietary data were collected from a cross-sectional survey using a cultural-specific food frequency questionnaire that contained all local Tibetan foods in 2020.

Results

The mean value of The estimated daily Se dietary intake by each participant was 17.1 ± 1.9 μg/day/adult, the Se concentration in topsoil and highland barley grain were 0.128 ± 0.015 mg/kg and 0.017 ± 0.003 mg/kg, respectively. Although highland barley was the first contributor of dietary Se in local adult residents (34.2%), the dietary Se intake provided by highland barley only about 10% of the EAR value (50 μg/day/adult) currently. A significantly positive relationship was determined between soil total Se content (STSe), available Se content (SASe) and highland barley grain Se content (GSe). The amount of Se in food system depends on a number of soil properties (TOC, pH, clay content, Fe/Mn/Al oxides), climate variables (MAP, MAT) and terrain factor (altitude).

Conclusion

To sum up, it can be inferred that the insufficient dietary Se intake of Tibetan adult population living along Yalung Zangbo River is mainly caused by the low Se content in highland barley grain, which was result from the low Se content in cultivated soil. In order to enable adult participants in the present study to achieve recommended dietary Se-intake levels, agronomic fortification with selenised fertilizers applied to highland barley could be a great solution. It is necessary to combine the influencing factors, and comprehensively consider the spatial variation of local soil properties, climatic and topographic conditions, and planting systems.

Foliar Application of Reaction Products Derived from Selenite Removal by Iron Monosulfide for Brassica rapa ssp. Chinensis L

The extensive application of FeS in environmental remediation requires the recovery and reuse of reaction products between FeS and pollutants. Therefore, foliar application of reaction products derived from selenite [Se(IV)] removal by FeS for pak choi was performed. The removal rate of Se(IV) by 100 mg/L FeS was 0.047 h^-1. 93.2% of Se(IV) was reduced to Se(0), and FeS was correspondingly oxidized to goethite (78.9%), lepidocrocite (21.1%), and S(0) (91.5%) based on the analysis of X-ray absorption fine structure. The reaction products promoted the growth of pak choi in terms of fresh biomass, vitamin C, and protein, ascribed to the key roles of Fe and S in enhancing the electron transfer rate and light conversion rate. Furthermore, the application of reaction products decreased by 64% of disease incidence as compared with the pathogen Pseudomonas syringae pv. maculicola-infected control. The total Se content in plants increased to 576 μg/kg and was composed of 11.9% of SeMeCys, 29.8% of SeMet, and 58.3% of SeCys after exposure to reaction products, which is beneficial to the human dietary intake from pak choi. This study demonstrated that the reaction products between FeS and Se(IV) could be recovered and applied as a nano-enabled strategy to prevent crop insecurity.

Can As concentration in crop be controlled by Se fertilization? A meta-analysis and outline of As sequestration mechanisms

Arsenic (As) is a pollutant with a strong toxic effect on animals, plants and human beings. Exogenous selenium (Se) has been suggested to reduce the accumulation of As in crops, but contradictory results were found in the published literature. In order to clarify the possible processes, we collected the literature that reports on the effects of Se application on As uptake and accumulation in crops, analyzed the data by meta-analysis, and tested the effects of different factors on As accumulation by meta-regression model and subgroup analysis. The results highlighted a significant dose-dependent reduction of As content in crops after Se addition. Exogenous Se can significantly reduce As concentrations in grains by 18.76%. The reduction was dose-dependent for rice grains under aerobic soil conditions but not for rice grains under anoxic soil conditions. Se-enriched soils (greater than 0.5 mg kg^-1) significantly reduced As concentrations in grains. Selenium significantly decreased the transfer factor of As from root to shoot. Moreover, selenite had a stronger inhibiting effect on the transport of As from root to shoot than selenate. The inhibition of selenium fertilization on As concentrations seems to take place in root and soil, while physiological processes in rice may be involved in restricting uptake and transport from root to shoot. These findings provide new ideas for effectively alleviating the transfer of As to the human body through the food chain.

Investigating diffusion mechanism for HTO and Se(IV)/Se(VI) in compacted Tamusu clay rock with different column lengths

Due to continuous self-sealing and good mechanical properties, the Tamusu clay rock of Inner Mongolia has been identified as the pre-selected site for high-level radioactive waste geological disposal site in China. The study of chemical behaviors related to Tamusu clay rock, such as nuclide migration, will be an important content of the performance assessment and safety assessment of the disposal repository in the future. The diffusion behavior of HTO and Se(IV)/Se(VI) with different compacted column lengths in Tamusu clay rock is discussed by the through-diffusion method. The diffusion coefficient, rock capacity factor, effective porosity, and other diffusion parameters closely related to nuclide migration are calculated, and the mechanism of nuclide diffusion is preliminarily discussed. The results show that D a (6.23 × 10−11∼17.96 × 10−11 m2 s−1), D e (1.62 × 10−11∼4.67 × 10−11 m2 s−1) for HTO increase with the increase of the compacted column length, and it is proposed that the diffusion process of HTO is affected by the change of geometrical factor and path tortuosity. D a (7.29 × 10−13∼1.74 × 10−13 m2 s−1), D e (5.15 × 10−12∼2.15 × 10−12 m2 s−1) for Se(IV), D a (3.11 × 10−12∼1.09 × 10−12 m2 s−1), D e (2.53 × 10−12∼1.09 × 10−12 m2 s−1) for Se(VI), which decrease with the increase of the compacted column length, it is mainly due to the existence of anion repulsion effect.

A Bibliometric Analysis of Research on Selenium in Drinking Water during the 1990-2021 Period: Treatment Options for Selenium Removal

A bibliometric analysis based on the Scopus database was carried out to summarize the global research related to selenium in drinking water from 1990 to 2021 and identify the quantitative characteristics of the research in this period. The results from the analysis revealed that the number of accumulated publications followed a quadratic growth, which confirmed the relevance this research topic is gaining during the last years. High research efforts have been invested to define safe selenium content in drinking water, since the insufficient or excessive intake of selenium and the corresponding effects on human health are only separated by a narrow margin. Some important research features of the four main technologies most frequently used to remove selenium from drinking water (coagulation, flocculation and precipitation followed by filtration; adsorption and ion exchange; membrane-based processes and biological treatments) were compiled in this work. Although the search of technological options to remove selenium from drinking water is less intensive than the search of solutions to reduce and eliminate the presence of other pollutants, adsorption was the alternative that has received the most attention according to the research trends during the studied period, followed by membrane technologies, while biological methods require further research efforts to promote their implementation.

Treatment technologies for selenium contaminated water: A critical review

Selenium is an indispensable trace element for humans and other organisms; however, excessive selenium in water can jeopardize the aquatic environment. Investigations on the biogeochemical cycle of selenium have shown that anthropogenic activities such as mining, refinery, and coal combustion mainly contribute to aquatic selenium pollution, imposing tremendous risks on ecosystems and human beings. Various technologies thus have been developed recently to treat selenium contaminated water to reduce its environmental impacts. This work provides a critical review on the applications, characteristics, and latest developments of current treatment technologies for selenium polluted water. It first outlines the present status of the characteristics, sources, and toxicity of selenium in water. Selenium treatment technologies are then classified into three categories: 1) physicochemical separation including membrane filtration, adsorption, coagulation/precipitation, 2) redox decontamination including chemical reduction and catalysis, and 3) biological transformation including microbial treatment and constructed wetland. Details of these methods including their overall efficiencies, applicability, advantages and drawbacks, and latest developments are systematically analyzed and compared. Although all these methods are promising in treating selenium in water, further studies are still needed to develop sustainable strategies based on existing and new technologies. Perspectives on future research directions are laid out at the end.

Safety of selenium exposure and limitations of selenoprotein maximization: Molecular and epidemiologic perspectives

Recent evidence from laboratory and epidemiologic studies has shed a different light on selenium health effects and its recommended range of environmental exposure, compared with earlier research. Specifically, epidemiologic studies in Western populations have shown adverse effects of selenium exposure at low levels, sometimes below or slightly above selenium intakes needed to maximize selenoprotein expression and activity. In addition, three recent lines of evidence in molecular and biochemical studies suggest some potential drawbacks associated with selenoprotein maximization: 1) the possibility that selenoprotein upregulation is a compensatory response to oxidative challenge, induced by selenium itself or other oxidants; 2) the capacity of selenoproteins to trigger tumor growth in some circumstances; and 3) the deleterious metabolic effects of selenoproteins and particularly of selenoprotein P. The last observation provides a toxicological basis to explain why in humans selenium intake levels as low as 60 μg/day, still in the range of selenium exposure upregulating selenoprotein expression, might start to increase risk of type 2 diabetes. Overall, these new pieces of evidence from the literature call into question the purported benefit of selenoprotein maximization, and indicate the need to reassess selenium dietary reference values and upper intake level. This reassessment should clarify which range of selenoprotein upregulation follows restoration of adequate selenium availability and which range is driven by a compensatory response to selenium toxicity and oxidative stress.

Trace Element Selenium Effectively Alleviates Intestinal Diseases

Selenium (Se) is an essential trace element in the body. It is mainly used in the body in the form of selenoproteins and has a variety of biological functions. Intestinal diseases caused by chronic inflammation are among the most important threats to human health, and there is no complete cure at present. Due to its excellent antioxidant function, Se has been proven to be effective in alleviating intestinal diseases such as inflammatory bowel diseases (IBDs). Therefore, this paper introduces the role of Se and selenoproteins in the intestinal tract and the mechanism of their involvement in the mediation of intestinal diseases. In addition, it introduces the advantages and disadvantages of nano-Se as a new Se preparation and traditional Se supplement in the prevention and treatment of intestinal diseases, so as to provide a reference for the further exploration of the interaction between selenium and intestinal health.

Lead, mercury, and selenium alter physiological functions in wild caimans (Caiman crocodilus)

Environmental contaminants affect ecosystems worldwide and have deleterious effects on biota. Non-essential mercury (Hg) and lead (Pb) concentrations are well documented in some taxa and are described to cause multiple detrimental effects on human and wildlife. Additionally, essential selenium (Se) is known to be toxic at high concentrations but, at lower concentrations, Se can protect organisms against Hg toxicity. Crocodilians are known to bioaccumulate contaminants. However, the effects of these contaminants on physiological processes remain poorly studied. In the present study, we quantified Hg, Pb and Se concentrations in spectacled caimans (Caiman crocodilus) and investigated the effects of these contaminants on several physiological processes linked to osmoregulatory, hepatic, endocrine and renal functions measured through blood parameters in 23 individuals. Mercury was related to disruption of osmoregulation (sodium levels), hepatic function (alkaline phosphatase levels) and endocrine processes (corticosterone levels). Lead was related to disruption of hepatic functions (glucose and alanine aminotransferase levels). Selenium was not related to any parameters, but the Se:Hg molar ratio was positively related to the Na⁺ and corticosterone concentrations, suggesting a potential protective effect against Hg toxicity. Overall, our results suggest that Hg and Pb alter physiological mechanisms in wild caimans and highlight the need to thoroughly investigate the consequences of trace element contamination in crocodilians.

A consistent model for estimating the partitioning of Am, Pu and Se in agricultural soils

The component additive model UNiSeCs II for simulating the physicochemical behaviour of the radionuclides americium, plutonium and selenium in agricultural soils is presented. The model is validated by estimating the distribution coefficients (Kd) of these elements measured in batch experiments from the literature. For all three elements, the resulting average relative deviations from the experimental values are smaller than a factor of 2.5. This indicates that the model has the potential to significantly improve the predictions of radioecological models that normally use tabulated Kd values from the IAEA which are known to have large uncertainties. Using UNiSeCs II, the soil solution parameters most important for the partitioning of Am, Pu and Se are identified by single parameter variations.

Highly stable selenium nanoparticles: Assembly and stabilization via flagellin FliC and porin OmpF in Rahnella aquatilis HX2

Microorganisms play a critical role in the reduction of the more toxic selenite and selenate to the less toxic elemental selenium. However, the assembly process and stability of selenium nanoparticles (SeNPs) remain understudied. The plant growth-promoting rhizobacterium Rahnella aquatilis HX2 can reduce selenite to biogenic SeNPs (BioSeNPs). Two main proteins, namely flagellin FliC and porin OmpF were identified in the BioSeNPs. The fliC and ompF gene mutation experiments demonstrated that the FliC and OmpF could control the assembly of BioSeNPs in vivo. At the same time, the expressed and purified FliC and OmpF could control the assembly of SeNPs in vitro. BioSeNPs produced by R. aquatilis HX2 exhibited high stability under various ionic strengths, while the chemically synthesized SeNPs (CheSeNPs) showed a high level of aggregation. The in vitro experiments verified that FliC and OmpF could prevent the aggregation of the CheSeNPs under various ionic strengths. This work reports the preparation of highly stable BioSeNPs produced by strain R. aquatilis HX2 and verifies that FliC and OmpF both could control the assembly and stability of BioSeNPs. BioSeNPs with high stability could be suitable as nutritional supplement to remedy selenium deficiency and in nanomedicine applications.

Cadmium uptake and translocation: selenium and silicon roles in Cd detoxification for the production of low Cd crops: a critical review

Cadmium (Cd) is a primary contaminant in agricultural soils of the world. The ability of Cd uptake, transport, detoxification, and accumulation varies among different plant species and genotypes. Cd is translocated from soil to root by different transporters which are used for essential plant nutrient uptake. A number of strategies have been suggested for decreasing Cd toxicity in Cd contaminated soils. Recently, a lot of research have been carried out on minimizing Cd uptake through selenium (Se) and silicon (Si) applications. Both Se and Si have been reported to mitigate Cd toxicity in different crops. Vacuolar sequestration, formation of phytochelatins, and cell wall adsorption have been reported as effective mechanisms for Cd detoxification. The present review discussed past and current knowledge of literature to better understand Cd toxicity and its mitigation by adopting different feasible and practical approaches.

Environmental Impacts of Selenium Contamination: A Review on Current-Issues and Remediation Strategies in an Aqueous System

In both aquatic and terrestrial environment, selenium contamination may exist at concentrations above the micronutrient limit. Since there is such a narrow bandwidth between which selenium concentration is acceptable, the health of the public may be at risk of selenium toxicity once the concentration increases beyond a threshold. Selenium contamination in an aqueous environment can occur due to anthropogenic activities and/or from natural sources. This study presents a review of the forms of selenium, inorganic and organic selenium contamination, mobilization, analytical methods for various forms of selenium and remediation strategies. The review also provides recent advances in removal methods for selenium from water including bioremediation, precipitation, coagulation, electrocoagulation, adsorption, nano-zerovalent iron, iron co-precipitation and other methods. A review of selenomethionine and selenocysteine removal strategy from industrial wastewaters is presented. Selenium resource recovery from copper ore processing has been discussed. Various analytical methods used for selenium and heavy metal analysis were compared. Importantly, existing knowledge gaps were identified and prospective areas for further research were recommended.

Simultaneous Removal of Selenite and Selenate by Nanosized Zerovalent Iron in Anoxic Systems: The Overlooked Role of Selenite

The application of nanosized zerovalent iron (nZVI) for reductive immobilization of selenite (Se(IV)) or selenate (Se(VI)) alone has been extensively investigated. However, as the predominant species, Se(IV) and Se(VI) usually coexist in the environment. Thus, it is essential to remove both species simultaneously in the solution by nZVI. Negligible Se(VI) removal (∼7%) by nZVI was observed in the absence of Se(IV). In contrast, the Se(VI) was completely removed in the presence of Se(IV), and the removal rate and electron selectivity of Se(VI) increased from 0.12 ± 0.01 to 0.29 ± 0.02 h^-1 and from 1% to 4.5%, respectively, as the Se(IV) concentration increased from 0.05 to 0.20 mM. Se(IV) was rapidly removed by nZVI, and Se(VI) exerted minor influence on Se(IV) removal. Se(IV) promoted the generation of corrosion products that were mainly composed of magnetite (26%) and lepidocrocite (67%) based on the Fe K-edge XANES spectra and k³-weighted EXAFS analysis. Fe(II) released during the Se(IV) reduction was not the main reductant for Se(VI) but accelerated the transformation of F(0) to magnetite and lepidocrocite. The formation of lepidocrocite contributed to the enrichment of Se(VI) on the nZVI surface, and magnetite promoted electron transfer from Fe(0) to Se(VI). This study demonstrated that Se(IV) acted as an oxidant to activate nZVI, thus improving the reactivity of nZVI toward Se(VI), which displays a potential application of nZVI in the remediation of Se(IV)- and Se(VI)-containing water.

Selenium volatilization from tundra soils in maritime Antarctica

Maritime Antarctica harbors a large number of penguins and seals that provide considerable input of selenium (Se) originating as guano into terrestrial ecosystems. Subsequent Se emissions via biomethylation and volatilization from these sources of Se have not been studied. Here, penguin colony soils (PCS) and adjacent tundra marsh soils (TMS), seal colony soils (SCS) and adjacent tundra soils (STS), and normal upland tundra soils (NTS) were collected in maritime Antarctica. For the first time, Se volatilization and speciation were investigated in these soils through incubation experiments using chemo-trapping method. The Se contents in PCS, SCS, STS and TMS were highly enriched compared with NTS, with organic matter-bound Se accounting for 70%-80%. Laboratory incubations yielded the greatest Se volatilization rates (VR_Se) in PCS (0.20 ± 0.01 μg kg^-1 d^-1), followed by SCS (0.14 ± 0.01 μg kg^-1 d^-1) at low temperature (4 °C). Soil frozen-thawing induced 1-4 fold increase in VR_Se, and the VR_Se continuously increased until the soils fully thawed. The VR_Se showed a significant positive correlation (R² = 0.96, p < 0.01) with soil temperature. Methylated Se species were dominated by dimethylselenide (DMSe) in PCS and dimethyldiselenide (DMDSe) in SCS. Our results imply that the combination of climate warming, frozen-thawing processes, and high-Se inputs from sea animals will significantly increase tundra soil Se volatilization in maritime Antarctica. High VR_Se from penguin colony soils, and significantly elevated Se levels in the mosses close to penguin colony, suggest that volatilization of Se from penguin colony soils play an important role in the mobilization and regional biogeochemical cycling of Se in maritime Antarctica.

Combined use of arbuscular mycorrhizal fungus and selenium fertilizer shapes microbial community structure and enhances organic selenium accumulation in rice grain

Selenium (Se) deficiency is a public health concern that is mainly caused by inadequate intake of Se from staple crops. The purpose of this study is to investigate the effects of inoculation with different arbuscular mycorrhizal fungus (AMF) strains, including Funneliformis mosseae (Fm) and Glomus versiforme (Gv), and fertilization with selenite or selenate on the accumulation and speciation of Se in rice. The results showed that using both AMF inoculation and Se fertilization could promote organic Se accumulation in rice grain than using only Se fertilization. Moreover, grain of rice inoculated with Fm and grown in soil fertilized with selenate had the highest accumulation of Se, of which selenomethionine was the dominant Se species. The AMF inoculation also led to high content of available Se and high relative abundance of Firmicutes in soil. The high concentration of available Se in soil suggests that the AMF inoculation may modify the microbial community, which then causes the Se uptake of rice to increase, in turn causing the amount of organic Se accumulated in rice to increase. Based on these results, using AMF inoculation combined with Se fertilization can be a promising strategy for Se biofortification in rice.

Selenium Biofortification and Interaction With Other Elements in Plants: A Review

Selenium (Se) is an essential element for humans and animals and its deficiency in the diet is a global problem. Crop plants are the main source of Se for consumers. Therefore, there is much interest in understanding the factors that govern the accumulation and distribution of Se in the tissues of crop plants and the mechanisms of interaction of Se absorption and accumulation with other elements, especially with a view toward optimizing Se biofortification. An ideal crop for human consumption is rich in essential nutrient elements such as Se, while showing reduced accumulation of toxic elements in its edible parts. This review focuses on (a) summarizing the nutritional functions of Se and the current understanding of Se uptake by plant roots, translocation of Se from roots to shoots, and accumulation of Se in grains; and (b) discussing the influence of nitrogen (N), phosphorus (P), and sulfur (S) on the biofortification of Se. In addition, we discuss interactions of Se with major toxicant metals (Hg, As, and Cd) frequently present in soil. We highlight key challenges in the quest to improve Se biofortification, with a focus on both agronomic practice and human health.

Selenosis in Ruminants

Selenium (Se) is a metalloid that exists as a red amorphous powder, reddish crystal, silver-gray crystal, or brown-black solid. Its potency as a nutrient and a toxicant is such that few people have seen the pure element. It is easy to lose sight of the narrow margin between too little and too much. The most common cause of selenosis is accidental or intentional overuse of supplements. Many target organs and effects of Se toxicity are similar to those of Se deficiency, so laboratory confirmation is necessary. Prevention consists of minimizing exposure to seleniferous feedstuffs and optimizing dietary factors that might aggravate selenosis.

Selenium and Nano-Selenium Biofortification for Human Health: Opportunities and Challenges

Selenium is an essential micronutrient required for the health of humans and lower plants, but its importance for higher plants is still being investigated. The biological functions of Se related to human health revolve around its presence in 25 known selenoproteins (e.g., selenocysteine or the 21st amino acid). Humans may receive their required Se through plant uptake of soil Se, foods enriched in Se, or Se dietary supplements. Selenium nanoparticles (Se-NPs) have been applied to biofortified foods and feeds. Due to low toxicity and high efficiency, Se-NPs are used in applications such as cancer therapy and nano-medicines. Selenium and nano-selenium may be able to support and enhance the productivity of cultivated plants and animals under stressful conditions because they are antimicrobial and anti-carcinogenic agents, with antioxidant capacity and immune-modulatory efficacy. Thus, nano-selenium could be inserted in the feeds of fish and livestock to improvise stress resilience and productivity. This review offers new insights in Se and Se-NPs biofortification for edible plants and farm animals under stressful environments. Further, extensive research on Se-NPs is required to identify possible adverse effects on humans and their cytotoxicity.

Selenium deficiency risk in central Kenya highlands: an assessment from the soil to the body

Selenium (Se) deficiency is associated with increased risk of clinical disorders. Yet, it has not been considered as an important public health issue in Africa. The health burden of this 'hidden hunger' remains largely unknown. Using a case study of central Kenya highlands, a cross-sectional survey assesses Se status of agricultural soils, foods, hair, and actual average dietary Se intake of the local population and investigates the soil-food Se concentration and Se intake-individual Se status relationships. The survey examines eight locations characterized by different agricultural soil types and assesses average dietary Se intake among 159 children and 111 women based on 24-h dietary recall data. Soil Se concentration does not explain Se concentration in foods, which instead is associated with soil's pH, organic matter, and P and Fe content. Cereal grains, beans and potato/green banana form a large portion of the local diet while intake of animal-based foods is limited. This results in Se intake of 15 and 33 µg p^-1 d^-1 for children and women, respectively. On average, 87% of children and 97% of women have inadequate average daily dietary Se intake, and the hair Se concentration of 92% children and 94% women is below the reference values. Soil's characteristics contribute to variation in Se concentration in foods and consequently the dietary Se intake. A low diversified diet is a key contributing factor to inadequate dietary Se intake in the region. These findings call for the need to investigate potential intervention measure and the health burden of Se deficiency.