The essential toxin: the changing perception of selenium in environmental sciences

Hydraulic retention time (HRT) extension and nitrate addition mitigate Se(VI) inhibition and enhance selenium removal in constructed wetlands: Potential role of nitrate and Fe/Mn pumps

Selenate (Se(VI)) and nitrate as co-contamination pose significant threats to both environment and human health. This study intends to examine the effects of the addition of Se(VI) on nitrogen removal in iron/manganese ore and wood based two-stage vertical flow constructed wetlands (B-CWs and C-CWs), as well as the feasibility of simultaneous removal. The results indicated that low Se(VI) concentration (0.5 mg/L) caused acute inhibition for nitrogen removal. Increasing nitrate concentration and prolonging HRT resulted in simultaneous and efficient removal of Se(VI) and nitrogen in B-CWs and C-CWs, with C-CWs having a higher total selenium removal. However, nitrogen removal was inhibited when further increasing Se(VI) concentration (1 mg/L) in C-CWs, but Se(VI) removal remained efficient. High concentrations of Se(VI) (5 mg/L) had a long-term inhibition for Se(VI) and nitrogen removal, which was not recoverable. Se(0) was the main reduction end product, accompanied by some Se(IV) production. High abundance of denitrifying/Se(VI)-reducing bacteria coupled with iron/manganese cycling pumps promoted efficient Se(VI) bioreduction.

Microbial diversity and community assembly in heavy metal-contaminated soils: insights from selenium-impacted mining areas

The mining industry in China plays a pivotal role in economic development but also leads to severe environmental issues, particularly heavy metal pollution in soils. Heavy metal pollution significantly impacts soil microbial communities due to its persistence and long-term residual effects. We assessed changes in microbial diversity, community structure, and assembly mechanisms in selenium-impacted soils. This study investigates the impacts of selenium (Se) and other heavy metals on soil microbial communities in selenium-rich mining areas using full-length 16S rRNA gene sequencing. Our results showed that Se and other heavy metal contamination significantly altered microbial community composition, favoring metal-tolerant phyla such as Proteobacteria, Actinobacteriota and Firmicutes, while reducing the abundance of sensitive groups like Acidobacteriota and Chloroflexi. Microbial diversity decreased as Se and other heavy metal concentrations increased. Mantel test analysis revealed that soil total potassium (TK), soil organic carbon, total nitrogen, and several other metals, including zinc, niobium, titanium (Ti), manganese, rubidium, barium, potassium, cobalt, gallium (Ga), Se, chromium (Cr), vanadium, and copper were significantly and positively correlated with microbial community composition across all soil samples. Random forest analysis showed that soil TK and multiple elements [Cr, Ti, nickel (Ni), Ga and Se] were the most important predictors of bacterial diversity, emphasizing the role of multiple elements in shaping microbial communities. Co-occurrence network analysis revealed that Se and other heavy metal contamination reduced network complexity and stability, with high Se-contaminated soils exhibiting fragmented microbial networks. Community assembly was primarily driven by drift in control soils, whereas dispersal limitation became more prominent in Se-contaminated soils due to heavy metal toxicity. These findings highlight the ecological consequences of heavy metal pollution on microbial communities and offer valuable insights for effective soil management and remediation strategies.

Theoretical Study of the Reaction of Hydrogen Selenide with the Cl• Atom and the •OH Radical, and Differences with the Behavior of Other Hydrogen Chalcogenides

Hydrogen selenide, H2Se, is the third-row analog of hydrogen sulfide, H2S, and water, H2O. While there is ample thermochemical and kinetic information about the reactions of the latter two species, few experimental or theoretical data are available on H2Se. In this work, we use high-level post-Hartree-Fock methods to study the reaction of H2Se with two of the most abundant atmospheric radical species, the Cl• atom and the •OH radical, H2Se + Cl• → HSe• + HCl H2Se + •OH → HSe• + H2O We used the SVECV-f12 composite quantum chemical method to study the stability of adducts and transition states, as well as the barriers for the transformations. It was found that a correct representation of the barrierless adduct is crucial for a correct description of the reaction's kinetics, and we present in this paper the first theoretical determination of the reaction coefficient of H2Se with Cl• in the literature, obtaining a value of 5.7 × 10-10 cm3 molecule-1 s-1, in excellent agreement with the experimental determination of 5.5 × 10-10 cm3 molecule-1 s-1 at room temperature Additionally, using the same procedure, we obtained a value of 6.4 × 10-11 cm3 molecule-1 s-1 for the reaction with •OH, in this case slightly smaller than the only previous estimation of 7.2 × 10-11 cm3 molecule-1 s-1 obtained indirectly from similar reactions for sulfur compounds, in all cases at 298.15 K. Judging from the agreement of the theoretical and experimental rate coefficients in the case of the reaction with chlorine, we suggest that our value for the reaction with the hydroxyl radical is more accurate than the estimated one. A comparison of the dependence of the rate coefficients for H2S and H2Se as a function of the temperature shows some noticeable differences. A convex behavior of the T-dependence for the Cl• reaction at high temperatures was found, instead of the concave behavior found for sulfur. Nevertheless, this is not important in atmospheric chemistry conditions, and a sufficiently linear region was found with the expression, k(Cl•) = 1.6 × 10-10 exp (0.7/RT) cm3 molecule-1 s-1. The reaction with •OH is even more complicated, with nonlinear tail at high (combustion) and low (stratosphere) temperatures, while the region important in tropospheric chemistry could be fitted with the Arrhenius equation k(•OH) = 5.9 × 10-12 exp (1.4/RT) cm3 molecule-1 s-1. Using our theoretically determined kinetic data, we were also able to calculate the atmospheric lifetime of H2Se as 2.6 h, considerably shorter than that of H2S (12.2 h).

Interactions between selenium species and pyrogenic carbonaceous materials in water and soil relevant to selenium control and remediation: A molecular-level perspective

In the environment, selenium (Se) has dual impacts on living organisms, as it is an essential element but high concentrations can be toxic. Current technologies for treating Se in real applications are not cost effective. Pyrogenic carbonaceous materials (PCM) with high surface area and redox properties have been proposed to remove Se. The objective of this review is to evaluate recent developments in fabrication of PCM and functionalized PCM for Se sorption and reduction in environmental remediation, as well as their potential impacts on crop growth. The sorptive removal of Se by PCM depends on the combined effects of electrostatic interactions, steric constraints, and complexation with metal species. The reduction property of PCM facilitates the conversion the ionic Se into solid state. The sorption of Se on PCM can also find applications in crop growth and the inhibition of heavy metal ions. We provide an outlook of terminal treatment of Se on PCM including immobilizing Se as solid species or applying PCM with sorbed Se as micronutrient soil amendment.

Biogenic selenium nanoparticles: a comprehensive update on the multifaceted application, stability, biocompatibility, risk, and opportunity

Biogenic selenium nanoparticles (SeNPs) have emerged as promising area of research due to their unique properties and potential multifaceted applications. The biosynthesis of SeNPs through biological methods, such as using microorganism, plant extracts, etc., offers a safe, eco-friendly, and biocompatible approach, compared to traditional chemical synthesis. Recent several studies demonstrated that multifaceted application of SeNPs includes a broad area such as antibacterial, anticancer, antioxidant, antiviral, anti-inflammatory, antidiabetic, and excellent wound healing activity. On the other hand, SeNPs have also shown promising application in sensing of inorganic toxic metals, electrochemistry, agro-industries, aqua-cultures, and in fabrication of solar panels. Additionally, SeNPs capability to enhance the efficacy of traditional antibiotics and act as effective agents against multidrug-resistant pathogens has shown their potential in addressing critical health challenges. Although, the SeNPs exhibit wide applicability, the potential toxicity of Se, particularly in its various oxidative states, necessitates careful assessment of the environmental and health impacts associated with their use. Therefore, understanding the balance between their beneficial properties and potential risks is crucial for its safe applications. This review focuses exclusively on SeNPs synthesized via eco-friendly process, excluding research utilizing other synthesis processes. Moreover, this review aims to offer an overview of the diverse applications, potential risks, stability requirement, and cytocompatibility requirement, and multifaceted opportunities associated with SeNPs. Ultimately, the review bridges a gap in knowledge by providing an updated details of multifaceted applications of SeNPs.

In situ formed Se-TiO2 as a highly reusable photocatalyst for selenium reduction and removal from industrial wastewater

Selenium (Se) release from anthropogenic activities such as mining, power generation, and agriculture poses considerable environmental and ecological risks. Increasing prevalence and awareness of Se-related issues have driven the development of many innovative Se treatment technologies. Photocatalysis has shown promise towards Se removal from industrial wastewaters with minimal residuals, and is generally considered a low-cost, robust, non-toxic, and potentially solar-powered method. Despite this, its real-world application towards environmental remediation remains extremely limited. This is because research into practical considerations, such as photocatalyst stability and reusability, is often overlooked or understudied in favor of developing academically interesting but impractical materials. In this work, commercial anatase TiO2 is stress tested through fifteen cycles of reuse towards the photocatalytic reduction and removal of selenate in synthetic mining-influenced brine (SMIB) without washing or regeneration. Remarkably, selenate removal exceeds 99.3% throughout all cycles. In situ Se-TiO2 heterojunction formation, and changes to its properties including Se loading, particle size, and crystal phase, are characterized through X-ray absorption spectroscopy, scanning transmission electron microscopy, and diffuse reflectance UV/vis, while their effects on catalyst performance are elucidated. This work underscores the importance of catalyst recyclability for practical photocatalytic environmental remediation and discusses the effects of extensive use on photocatalyst performance.

Research progress of edible mushroom polysaccharide-metal trace element complexes

Metal trace elements are crucial for human health, and the complexes of edible mushroom polysaccharides with metal trace elements are currently a research hotspot in the field of food science. This article reviews the preparation methods, structural characterization, and physiological activities of edible mushroom polysaccharide-metal trace element complexes, including iron, selenium, and zinc. Research has shown that iron complexes obtained through Co-thermal synthesis of the FeCl3 method exhibit excellent antioxidant and anti-anemia functions; selenium complexes prepared via selenium-enriched cultivation significantly enhance immunological and anti-cancer properties; zinc complexes improve lipid-lowering, liver protection, and antioxidant capabilities. However, there is an imbalance in research among different metal elements, particularly with a high density of studies on selenium complexes. These studies provide a foundation for the future development of edible mushroom polysaccharide-metal trace element complexes.

Application of selenium isotopes to define selenium bioreduction in coal waste rock: Elk Valley, British Columbia

Anthropogenic sources of selenium (Se), including coal mining, can release Se to the environment and raise Se concentrations in receiving waters above drinking water and aquatic limits. Selenium bioreduction can be an important control to reduce dissolved selenate concentrations. This extensive study investigated the application of Se stable isotope ratios (δ82Se) of dissolved selenate to identify Se bioreduction in saturated and unsaturated mine rock piles (MRPs) located in the Elk Valley, Canada. The study included in situ and laboratory column experiments, where methanol was added to promote bioreduction. Results showed that selenate concentrations often are not reliable indicators of bioreduction. However, elevation of δ82Se relative to the selenate sources in all environments provided a robust indicator of widespread selenate bioreduction. Native microbes were shown to use both methanol and natural carbon sources as an electron donor for selenate bioreduction. Variability in the magnitude of apparent isotopic fractionation in column experiments was attributed to physical and microbiological heterogeneity, while variability in apparent isotopic fractionation from in situ experiments was attributed to the entrainment of small masses of background selenate into the experiment. Due to the uncertainty in apparent epsilon values, the extent of bioreduction can only be estimated with limited confidence. Despite uncertainties, however, the application of δ82Se is valuable in guiding the management of Se in mine environments.

Volatile Substances, Quality and Non-Targeted Metabolomics Analysis of Commercially Available Selenium-Enriched Rice

Selenium is an essential trace element for the human body. However, its intake is usually low. Therefore, the production and utilization of selenium-enriched food are currently a research hotspot. Despite the remarkable scientific interest in this topic, only a few of the numerous studies focus on commercially available products. This study examined the nutritional quality, physical and chemical properties, cooking characteristics, and eating quality of four commercially available hot-selling rice types, both selenium-enriched and non-selenium-enriched, and discovered that selenium-enriched rice outperforms ordinary rice in terms of both nutritional quality and taste. In addition, we employed the gas chromatography-ion mobility spectrometry (GC-IMS) technique to evaluate the volatile chemicals of rice. Some of the chemicals that made selenium-rich rice taste different from regular rice were pentanal, (E)-2-Hexen-1-ol, ethyl-3-methyl butanoate, 2-furan methanol acetate, ethyl heptanoate, ethyl hexanoate, methyl hexanoate, isopentyl pentanoate, and ethyl butyrate. We looked into the metabolite profiles of rice using LC-MS-based untargeted metabolomics to obtain a better idea of the different metabolites that are found in selenium-enriched rice compared to regular rice. We identified a total of 522 metabolites and screened 182, 227, and 100 differential metabolites in selenium-enriched (A) vs. non-selenium-enriched rice (B/C/D) groups, respectively. This study revealed that selenium primarily influenced the metabolism of D-amino acids, starch, sucrose, and linoleic acid in rice. This study systematically analyzed the quality differences between selenium-enriched and non-selenium-enriched rice available on the market. For consumers, it is essential to understand the quality of selenium-rich rice on the market to guide the purchase of rice.

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.

Aerobic Se(IV) reducing bacteria and their reducing characteristics in estuarine sediment

Microorganisms play a critical role in the biogeochemical cycling of selenium in natural ecosystems, particularly in reducing selenite (Se(IV)) to element selenium (Se(0)) which reduces its mobility and bioavailability. However, Se(IV)-reducing bacteria and their reducing characteristics in estuarine sediments remain inadequately understood. In this study, the reduction of Se(IV) was confirmed to be microbially driven through the cultivation of a mixture of estuarine sediment and Se(IV) under aerobic conditions. Community analysis indicates that Bacillus was primarily involved in the reduction of Se(IV). A strain with high salt tolerance (7.5 % NaCl) and Se(IV) resistance (up to 200 mM), Bacillus cereus SD1, was isolated from an estuarine sediment. The reduction of Se(IV) occurred concomitantly with the onset of microbial growth, and reduction capacity increased approximately 5-fold by adjusting the pH. In addition, Se(IV) reduction in Bacillus cereus SD1 was significantly inhibited by sulfite, and the key enzyme activity tests revealed the possible presence of a sulfite reductase-mediated Se(IV) reduction pathway. These research findings provide new insights into the bioreducing characteristics and the biogeochemical cycling of selenium in estuarine environments.

Selenate bioreduction in a large in situ field trial

Removing selenium (Se) from mine effluent is a common challenge. A long-term, in situ experiment was conducted to bioremediate large volumes (up to 7500 mc d-1) of Se(VI)-contaminated water (mean 87 μg L-1) by injecting the water into a saturated waste rock fill (SRF) at a coal mining operation in Elk Valley, British Columbia, Canada. To stimulate/maintain biofilm growth in the SRF, labile organic carbon (methanol) and nutrients were added to the water prior to its injection. A conservative tracer (Br-) was also added to track the migration of injected water across the SRF, identify wells with minimal dilution and used to quantify the extent of bioreduction. The evolution of the Se species through the SRF was monitored in time and space for 201 d. Selenium concentrations of <3.8 μg L-1 were attained in monitoring wells located 38 m from the injection wells after 114 to 141 d of operation. Concentrations of Se species in water samples from complementary long-term (351-498 d) column experiments using influent Se(VI) concentrations of 1.0 mg L-1 were consistent with the results of the in situ experiment. Solid samples collected at the completion of the column experiments confirmed the presence of indigenous Se-reducing bacteria and that the sequestered Se was present as insoluble Se(0), likely in Se-S ring compounds. Based on the success of this ongoing bioremediation experiment, this technology is being applied at other mine sites.

Antioxidant Response of Maternal and Fetal Rat Liver to Selenium Nanoparticle Supplementation Compared to Sodium Selenite: Sex Differences between Fetuses

To compare the effects of organic selenium nanoparticles (SeNPs, Se0) and inorganic sodium selenite (NaSe, Na2SeO3, Se4+) on the antioxidant response in maternal and fetal rat liver, pregnant females were treated with two forms of selenium (Se) at equivalent doses during gestation (0.5 mg SeNPs or 0.5 mg NaSe/kg body weight/day). Structural parameters of the liver of gravid females and their fetuses were examined in a sex-specific manner. The oxidative stress parameters superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR), glutathione S-transferase (GST), total glutathione (GSH) and sulfhydryl groups (SH) were established. In addition, the Se concentration was determined in the blood, liver, urine and feces of the gravid females and in the liver of the fetuses. The structure of the liver of gravid females remained histologically the same after supplementation with both forms of Se, while the oxidative stress in the liver was significantly lower after the use of SeNPs compared to NaSe. Immaturity of fetal antioxidant defenses and sex specificity were demonstrated. This study provides a detailed insight into the differences in the bioavailability of the nano form of Se compared to sodium selenite in the livers of pregnant females and fetuses.

Effect of Different Selenium Species on Indole-3-Acetic Acid Activity of Selenium Nanoparticles Producing Strain Bacillus altitudinis LH18

Acting as a growth regulator, Indole-3-acetic acid (IAA) is an important phytohormone that can be produced by several Bacillus species. However, few studies have been published on the comprehensive evaluation of the strains for practical applications and the effects of selenium species on their IAA-producing ability. The present study showed the selenite reduction strain Bacillus altitudinis LH18, which is capable of producing selenium nanoparticles (SeNPs) at a high yield in a cost-effective manner. Bio-SeNPs were systematically characterized by using DLS, zeta potential, SEM, and FTIR. The results showed that these bio-SeNPs were small in particle size, homogeneously dispersed, and highly stable. Significantly, the IAA-producing ability of strain was differently affected under different selenium species. The addition of SeNPs and sodium selenite resulted in IAA contents of 221.7 µg/mL and 91.01 µg/mL, respectively, which were 3.23 and 1.33 times higher than that of the control. This study is the first to examine the influence of various selenium species on the IAA-producing capacity of Bacillus spp., providing a theoretical foundation for the enhancement of the IAA-production potential of microorganisms.

The correlation between selenium intake and lung function in asthmatic people: a cross-sectional study

Objective

This study aimed to examine the correlation between selenium intake and lung function in asthmatic people.

Methods

A total of 4,541 individuals in the US National Health and Nutrition Examination Survey (NHANES) were included in this study. Multivariate linear regression, variance inflation factor, restricted cubic splines and quantile regression were used to analyze the relationship between Se intake and lung function. We divided selenium intake into four levels based on quartiles: Q1: Se ≤ 76.75 mcg/d; Q2: 76.75-105.1 mcg/d; Q3: 105.1-137.65 mcg/d; and Q4: Se ≥137.65 mcg/d.

Results

Asthma was negatively associated with the Ratio of Forced Expiratory Volume 1st Second to Forced Vital Capacity (FEV1/FVC) (β = -0.04, 95% CI: -0.06 to -0.02) and FEV1 (β = -215, 95% CI: -340 to -90). Se intake was positively associated with Forced Expiratory Volume 1st Second (FEV1) (β =3.30 95% CI: 2.60 to 4.00) and Forced Vital Capacity (FVC) (β =4.30, 95% CI: 3.50 to 5.10). In asthmatic individuals, the positive effects of Se intake on FVC were enhanced with increasing Se intake, while the positive effects of Se intake on FEV1 varied less dramatically. High Se intake (Q4 level, above 137.65 mcg/d) improved FVC (β = 353, 95% CI: 80 to 626) and FEV1 (β = 543, 95% CI: 118 to 969) in asthmatic patients compared to low Se intake (Q1 level, below 76.75 mcg/d). At the Q2 level (76.75-105.1 mcg/d) and Q4 level (Se ≥137.65 mcg/d) of Se intake, the correlation between FEV1 and asthma disappeared.

Conclusion

Our research has revealed a positive correlation between selenium intake and lung function in asthma patients and the strength of this positive correlation is related to the amount of selenium intake. We recommend that asthma patients consume 137.65 mcg to 200 mcg of selenium daily to improve pulmonary function while avoiding the adverse effects of selenium on the human body.

Bromide Ion Impurity-Induced Reaction between Selenium(IV) and Acidic Bromate: Prototype of a Cycle with Autocatalytic Behavior

The selenium(IV)-bromate reaction in an acidic medium using phosphoric acid/phosphate buffer was investigated by UV-vis spectroscopy monitoring the formation of bromine. In an excess of bromate, the absorbance-time curves measured at 450 nm display a characteristic sigmoidal shape having a fairly long induction period, while in the opposite case, when selenium(IV) species is used in excess, the measured data follow the rise and fall behavior. Depending on the excess of Se(IV) the final bromine-containing product is either an elementary bromine or bromide ion. Simultaneous evaluation of the measured kinetic traces clearly indicated that, surprisingly, no direct reaction takes place between the reactants. Instead of that, a trace amount of bromide ion impurity in the stock bromate solution is sufficient to drive the system via the oxidation of the bromide ion by bromate producing elementary bromine followed by the subsequent selenite-bromine reaction reestablishing the bromide ion to open a new cycle. As a result, the concentration of bromide ions increases in a sigmoidal fashion during the course of the reaction unless enough selenium(IV) species is present; hence, the overall synergetic effect observed is the autocatalytic rise of bromide ions. Therefore, the cycle mentioned above may be considered as a prototype of autocatalytic cycles. This observation prompted us to clarify the explicit difference between an autocatalytic cycle and an autocatalytic reaction.

Simultaneous selenite reduction and nitrogen removal using Paracoccus sp.: Reactor performance, microbial community, and mechanism

Selenium-containing wastewater has a high concentration of nitrogen compounds (ammonia nitrogen [NH4+-N]), leading to water pollution. Thus, the simultaneous reduction of selenium and removal of nitrogen compounds during wastewater treatment has become the top priority. However, the exogenous bacteria that can simultaneously reduce selenite and remove ammonia nitrogen and colonize in the wastewater treatment systems have not been reported. Additionally, the effects and the underlying mechanism of biofortification on the reduction and removal efficiency of the microorganisms remain unclear. In this study, we investigated the simultaneous selenite reduction and nitrogen removal efficiency of Paracoccus sp. (strain SSJ) isolated from selenium-contaminated soil and explored biofortification effects on the composition and structure of the microbial community. Using sequencing biofilm batch reactors (SBBRs), the structural and functional characteristics of the microbial community were systematically compared between the control (group A) and biofortified (group B) groups. Strain SSJ could simultaneously reduce 63.28% of selenite and remove 93.05% of NH4+-N within 24 h. Moreover, no accumulation of nitrate nitrogen (NO3--N) and nitrite nitrogen (NO2--N) was observed in the reaction process. The performance and stability of the SBBRs enhanced by strain SSJ were greatly improved. Illumina sequencing results showed that strain SSJ was surprisingly colonized, and Paracoccus was the predominant genus in group B (relative abundance: 13.93%). Moreover, PICRUSt2 analysis results suggested that the microbial community in group B demonstrated increased rates of ammonia nitrogen removal through ammonia assimilation and selenite reduction through sulfur metabolism and glutathione-mediated selenite reduction pathway. In summary, our findings shed light on the mechanism for simultaneous selenite reduction and nitrogen removal by biofortification and provide novel microbial resources for the treatment of selenite-containing wastewater.

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.

Integrated bioprocess for Se(VI) remediation using duckweed: Coupling selenate removal to biogas production

The use of phytoremediation as a method for wastewater treatment or removal of pollutants is garnering significant interest and duckweed (DW), a free floating macrophyte, depicts significant potential for the removal of nutrients and toxic compounds from contaminated waters. The present work aimed to develop an integrated process for remediating selenate (Se(VI)) using DW biomass and subsequent use of Se(VI) enriched DW for biogas production. The main objective is to extend the application of selenium (Se) enriched DW biomass for biogas production. Se(VI) enriched DW biomass (Se-DW) gave higher methane production (48.38 ± 3.6 mL gCOD-1) than control DW biomass (C-DW) (24.46 ± 3.6 mL gCOD-1). To further enhance methane production, three pre-treatment approaches (acid, alkali and hydrothermal) were assessed and the solid and liquid fractions obtained after pre-treatment were used as a substrate. Pre-treatments increased biogas production in both Se-DW and C-DW than untreated conditions. Liquid fractions gave higher biogas production than solid fractions. In Se-DW, highest biogas production was observed in hydrothermal pre-treated Se-DW, while in C-DW, acid pre-treatment gave higher biogas production. Methane production was shown to be enhanced up to a Se(VI) concentration of 1.7 mg L-1, whereas a concentration beyond this lowered biogas production.

Relationships between growth indicators, liver and kidney function markers, and blood concentrations of essential and potentially toxic elements in environmentally exposed young children

Environmental exposure to multiple metals and metalloids is widespread, leading to a global concern relating to the adverse health effects of mixed-metals exposure, especially in young children living around industrial areas. This study aimed to quantify the concentrations of essential and potentially toxic elements in blood and to examine the potential associations between multiple elements exposures, growth determinants, and liver and kidney function biomarkers in children living in several industrial areas in Dhaka, Bangladesh. The blood distribution of 20 trace elements As, Ag, Bi, Br, Cd, Co, Cr, Cu, I, Mn, Hg, Mo, Ni, Pb, Se, Sb, Tl, V, U, and Zn, growth determinants such as body mass index and body fats, blood pressure, liver and kidney injury biomarkers including serum alanine aminotransferase and alkaline phosphatase activities, serum calcium, and creatinine levels, blood urea nitrogen, and hemoglobin concentrations, and glomerular filtration rate were measured in 141 children, aged six to 16 years. Among these elements, blood concentrations of Ag, U, V, Cr, Cd, Sb, and Bi were measured below LOQs and excluded from subsequent statistical analysis. This comprehensive study revealed that blood concentrations of these elements in children, living in industrial areas, exceeded critical reference values to varying extents; elevated exposure to As, Pb, Br, Cu, and Se was found in children living in multiple industrial areas. A significant positive association between elevated blood Tl concentration and obesity (β = 0.300, p = 0.007) and an inverse relationship between lower As concentration and underweight (β = -0.351, p < 0.001) compared to healthy weight children indicate that chronic exposure to Tl and As may influence the metabolic burden and physical growth in children. Concentration-dependent positive associations were observed between the blood concentrations of Cu, Se, and Br and hepatic- and renal dysfunction biomarkers, an inverse association with blood Mo and I level, however, indicates an increased risk of Cu, Se, and Br-induced liver and kidney toxicity. Further in-depth studies are warranted to elucidate the underlying mechanisms of the observed associations. Regular biomonitoring of elemental exposures is also indispensable to regulate pollution in consideration of the long-term health effects of mixed-elements exposure in children.

Fabrication of bioactive nanocomposites from chitosan, cress mucilage, and selenium nanoparticles with powerful antibacterial and anticancerous actions

Natural bioactive alternatives are the utmost requests from researchers to provide biosafe and effectual health-guarding agents. The biopolymers chitosan nanoparticles (NCT), mucilage of cress seed (GCm; Lepidium sativum), and GCm-mediated selenium nanoparticles (GCm/SeNPs) were innovatively employed for fabricating novel bioactive natural nanocomposites (NCs) with elevated bioactivities as bactericidal (against Salmonella typhimurium and Staphylococcus aureus) and anticancer (against CaCo-2 and HeLa cells). The SeNPs were successfully generated with GCm, and different NCs formulations were fabricated from NCT:GCm/SeNPs amalgam ratios including T1, T2, and T3 with 2:1, 1:1, and 1:2 ratios, respectively. The infrared analysis of synthesized molecules appointed apparent physical interactions among interacted molecules. The average particles' sizes and charges of molecules/NCs were (12.7, 316.4, 252.8, and 127.3 nm) and (-6.9, +38.7, +26.2, and -25.8 mV) for SeNPs, T1, T2, and T3, respectively. The biocidal assessment of NCs indicated that T1 was the strongest antibacterial formulation, whereas T3 was the superior anticancer amalgam. These NCs formulations could exceed the biocidal potentialities of standard biocides. T1-NC could cause severe destructions/deformations in challenged S. typhimurium within 9 h, whereas T3-NCs induced apparent fluorescent apoptosis signs in treated HeLa cells. The prospective applications innovatively designed biocidal natural NCs that are recommended for controlling pathogenic bacteria and fighting cancerous cells.

Time-Resolved Examination of Fungal Selenium Redox Transformations

Selenium (Se) is both a micronutrient required for most life and an element of environmental concern due to its toxicity at high concentrations, and both bioavailability and toxicity are largely influenced by the Se oxidation state. Environmentally relevant fungi have been shown to aerobically reduce Se(IV) and Se(VI), the generally more toxic and bioavailable Se forms. The goal of this study was to shed light on fungal Se(IV) reduction pathways and biotransformation products over time and fungal growth stages. Two Ascomycete fungi were grown with moderate (0.1 mM) and high (0.5 mM) Se(IV) concentrations in batch culture over 1 month. Fungal growth was measured throughout the experiments, and aqueous and biomass-associated Se was quantified and speciated using analytical geochemistry, transmission electron microscopy (TEM), and synchrotron-based X-ray absorption spectroscopy (XAS) approaches. The results show that Se transformation products were largely Se(0) nanoparticles, with a smaller proportion of volatile, methylated Se compounds and Se-containing amino acids. Interestingly, the relative proportions of these products were consistent throughout all fungal growth stages, and the products appeared stable over time even as growth and Se(IV) concentration declined. This time-series experiment showing different biotransformation products throughout the different growth phases suggests that multiple mechanisms are responsible for Se detoxification, but some of these mechanisms might be independent of Se presence and serve other cellular functions. Knowing and predicting fungal Se transformation products has important implications for environmental and biological health as well as for biotechnology applications such as bioremediation, nanobiosensors, and chemotherapeutic agents.

Selenite reduction and biogenesis of selenium-nanoparticles by different size groups of aerobic granular sludge under aerobic conditions

Microbial transformations play a vital role in Se cycle in the environment and decrease the solubility and toxicity of Se oxyanions by converting to elemental selenium (Se⁰) nanostructures. Aerobic granular sludge (AGS) has attracted interest due to efficient reduction of selenite to biogenic Se⁰ (Bio-Se⁰) and retention in bioreactors. Here, selenite removal, biogenesis of Bio-Se⁰ and entrapment of Bio-Se⁰ by different size groups of aerobic granules were investigated to optimize biological treatment process for Se-laden wastewaters. Furthermore, a bacterial strain showing high selenite tolerance and reduction was isolated and characterized. Removal of selenite and conversion to Bio-Se⁰ were achieved by all the size groups of granules ranging from 0.12 mm to 2 mm and above. However, selenite reduction and Bio-Se⁰ formation were rapid and more efficient with large aerobic granules (≥0.5 mm). The formed Bio-Se⁰ was majorly associated with the large granules, due to better entrapment capabilities. In contrast, the Bio-Se⁰ formed by the small granules (≤0.2 mm) was distributed both in the granules and aqueous phase because of ineffective entrapment. Scanning electron microscope and energy dispersive X-ray (SEM-EDX) analysis confirmed formation of Se⁰ spheres and association with the granules. Efficient selenite reduction and entrapment of Bio-Se⁰ was related to prevalent anoxic/anaerobic zones in the large granules. A bacterial strain showing efficient SeO₃^2- reduction of up to 15 mM SeO₃^2- under aerobic conditions was identified as Microbacterium azadirachtae. SEM-EDX analysis confirmed the formation and entrapment of Se⁰ nanospheres (size: 100 ± 5 nm) in the extracellular matrix. The cells immobilized in alginate beads showed effective SeO₃^2- reduction and Bio-Se⁰ entrapment. Efficient reduction and immobilization of bio-transformed metalloids by large AGS and AGS-borne bacteria implicates prospective use in bioremediation of metal(loid) oxyanions and bio-recovery.

Selenium uptake, translocation, subcellular distribution and speciation in winter wheat in response to phosphorus application combined with three types of selenium fertilizer

BACKGROUND

Selenium (Se) deficiency causes a series of health disorders in humans, and Se concentrations in the edible parts of crops can be improved by altering exogenous Se species. However, the uptake, transport, subcellular distribution and metabolism of selenite, selenate and SeMet (selenomethionine) under the influence of phosphorus (P) has not been well characterized.

RESULTS

The results showed that increasing the P application rate enhanced photosynthesis and then increased the dry matter weight of shoots with selenite and SeMet treatment, and an appropriate amount of P combined with selenite treatment increased the dry matter weight of roots by enhancing root growth. With selenite treatment, increasing the P application rate significantly decreased the concentration and accumulation of Se in roots and shoots. P₁ decreased the Se migration coefficient, which could be attributed to the inhibited distribution of Se in the root cell wall, but increased distribution of Se in the root soluble fraction, as well as the promoted proportion of SeMet and MeSeCys (Se-methyl-selenocysteine) in roots. With selenate treatment, P_0.1 and P₁ significantly increased the Se concentration and distribution in shoots and the Se migration coefficient, which could be attributed to the enhanced proportion of Se (IV) in roots but decreased proportion of SeMet in roots. With SeMet treatment, increasing the P application rate significantly decreased the Se concentration in shoots and roots but increased the proportion of SeCys₂ (selenocystine) in roots.

CONCLUSION

Compared with selenate or SeMet treatment, treatment with an appropriate amount of P combined with selenite could promote plant growth, reduce Se uptake, alter Se subcellular distribution and speciation, and affect Se bioavailability in wheat.

Understanding the Effect of Single Atom Cationic Defect Sites in an Al2O3 (012) Surface on Altering Selenate and Sulfate Adsorption: An Ab Initio Study

Adsorption is a promising under-the-sink selenate remediation technique for distributed water systems. Recently it was shown that adsorption induced water network re-arraignment control adsorption energetics on the α - Al 2 O 3 (012) surface. Here, we aim to elucidate the relative importance of the water network effects and surface cation identity on controlling selenate and sulfate adsorption energy using density functional theory calculations. Density functional theory (DFT) calculations predicted the adsorption energies of selenate and sulfate on nine transition metal cations (Sc-Cu) and two alkali metal cations (Ga and In) in the α - Al 2 O 3 (012) surface under simulated acidic and neutral pH conditions. We find that the water network effects had larger impact on the adsorption energy than the cationic identity. However, cation identity secondarily controlled adsorption. Most cations decreased the adsorption energy weakening the overall performance, the larger Sc and In cations enabled inner-sphere adsorption in acidic conditions because they relaxed outward from the surface providing more space for adsorption. Additionally, only Ti induced Se selectivity over S by reducing the adsorbing selenate to selenite but not reducing the sulfate. Overall, this study indicates that tuning water network structure will likely have a larger impact than tuning cation-selenate interactions for increasing adsorbate effectiveness.

Use of Microbial Consortia in Bioremediation of Metalloid Polluted Environments

Metalloids are released into the environment due to the erosion of the rocks or anthropogenic activities, causing problems for human health in different world regions. Meanwhile, microorganisms with different mechanisms to tolerate and detoxify metalloid contaminants have an essential role in reducing risks. In this review, we first define metalloids and bioremediation methods and examine the ecology and biodiversity of microorganisms in areas contaminated with these metalloids. Then we studied the genes and proteins involved in the tolerance, transport, uptake, and reduction of these metalloids. Most of these studies focused on a single metalloid and co-contamination of multiple pollutants were poorly discussed in the literature. Furthermore, microbial communication within consortia was rarely explored. Finally, we summarized the microbial relationships between microorganisms in consortia and biofilms to remove one or more contaminants. Therefore, this review article contains valuable information about microbial consortia and their mechanisms in the bioremediation of metalloids.

Identification of the spatial patterns and controlling factors of Se in soil and rice in Guangxi through hot spot analysis

Selenium (Se) is essential to human health, anti-cancer, possessing antioxidant, and antiviral properties. In this study, the spatial patterns of rice Se and their varying relationship with soil Se on a regional scale were studied using hot spot analysis for the agricultural soils in Guangxi. According to the hot and cold spot maps, rice Se correlates positively with soil Se in Guangxi agricultural soils. High rice Se accompanies high soil Se in the central part of Guangxi (e.g., Liuzhou, Laibin), and low rice Se is in line with low soil Se in the western part (e.g., Baise). However, the hot spot analysis maps indicate that southwestern Guangxi exhibits a special characteristic of low rice Se with high soil Se (e.g., Chongzuo). This special pattern is strongly associated with the high concentrations of Fe₂O₃ (ferromanganese nodules) in the carbonate rock area. The hot spot analysis proves useful in revealing the spatial patterns of rice Se in Guangxi and identifying the hidden patterns.

Uptake of Selenite by Rahnella aquatilis HX2 Involves the Aquaporin AqpZ and Na+/H+ Antiporter NhaA

Microbial transformation of selenite [Se(IV)] to elemental selenium nanoparticles (SeNPs) is known to be an important process for removing toxic soluble selenium (Se) oxyanions and recovery of Se from the environment as valuable nanoparticles. However, the mechanism of selenite uptake by microorganisms, the first step through which Se exerts its cellular function, remains not well studied. In this study, the effects of selenite concentration, time, pH, metabolic inhibitors, and anionic analogues on selenite uptake in Rahnella aquatilis HX2 were investigated. Selenite uptake by R. aquatilis HX2 was concentration- and time-dependent, and its transport activity was significantly dependent on pH. In addition, selenite uptake in R. aquatilis HX2 was significantly inhibited by the aquaporin inhibitor AgNO₃ and sulfite (SO₃^2-), and partially inhibited by carbonyl cyanide m-chlorophenyl hydrazone (CCCP) and 2,4-dinitrophenol (2,4-DNP) treatments. Three mutants with in-frame deletions of aqpZ, glpF, and nhaA genes were constructed. The transport assay showed that the water channel protein AqpZ, and not GlpF, was a key channel of selenite uptake by R. aquatilis HX2, and sulfite and selenite had a common uptake pathway. In addition, the Na⁺/H⁺ antiporter NhaA is also involved in selenite uptake in R. aquatilis HX2.

Selenium speciation in soils using flow injection hydride generation atomic absorption spectrometry with on-line removal of organic matter interferences

A method based on flow injection hydride generation atomic absorption spectrometry (FI-HGAAS) with an on-line pre-reduction of Se(VI) to Se(IV) was developed and optimized to determine phosphate-extractable Se (0.1 M phosphate buffer KH₂PO₄/K₂HPO₄ at pH 7). The extracted fraction involves water-soluble Se (i.e. the most mobile Se fraction) and exchangeable Se (i.e. sorbed onto soil component surface). Kinetic discrimination mechanisms allowed the complete removal of interferences caused by organic matter due to the formation of humic substances (HS)-Se(IV) complexes observed when batch pre-reduction processes were used. Se(IV) and Se(VI) recoveries ranged 95-105% at a fortification level of 150 μg kg^-1. The pre-reduction was efficiently carried out in 20 s in a 6 M HCl medium at 100 °C. Results from phosphate-extractable fractions were comparable to those obtained by ICP-MS. Se bound to organic matter was released digesting the remaining material from the phosphate buffer extraction with 0.1 M K₂S₂O₈. Detection and quantification limits were 15 μg kg^-1 Se and 50 μg kg^-1 Se, respectively, in each fraction. The methodology was applied to 10 agricultural soils from Argentina with total Se concentration levels between 130 μg kg^-1 and 419 μg kg^-1.

Microbial community and extracellular polymeric substances analysis of anaerobic granular sludge exposed to selenate, cadmium and zinc

The microbial community and extracellular polymeric substances composition of anaerobic granular sludge exposed to selenate (~10 mg/L), cadmium (Cd) and zinc (Zn) (~2 and 5 mg/L) were investigated by high-throughput sequencing and fluorescence excitation emission matrix (FEEM) spectra, respectively. As a response to selenate, Cd and/or Zn exposure, significant fluorescence quenching of fulvic-like acids and humic-like substances was observed. With selenate, Cd and/or Zn in the influent with respective concentrations of 10, 5 and 5 mg/L, the abundance of the phyla Proteobacteria, Firmicutes, Spirochaetae, Cloacimonetes and Synergistetes increased significantly, and the dominant taxa in the anaerobic granular sludge exposed to Se, Cd and/or Zn were Halothiobacillaceae (10.2%), Pseudomonas (8.8%), Synergistaceae (7.7%), Spirochaetaceae (7.2%), Blvii28 wastewater sludge group (6.7%), Telmatospirillum (4.6%), Veillonellaceae (4.3%), Geobacter (4.0%) and Enterobacteriaceae (3.0%). Compared with the inoculum, the abundance of the archaea Methanobacterium and Methanosaeta decreased to below detection limit in the UASB reactor after 116 days exposure to Se, Cd and Zn.

Probability of cultivating Se-rich maize in Se-poor farmland based on intensive field sampling and artificial neural network modelling

Selenium (Se) is a necessary micronutrient for humans, and its supplementation from crop grains is important to address the ubiquitous Se deficiency in people worldwide. Se uptake by crops largely depend on soil bioavailable Se rather than soil total Se content, which provides possibilities to explore the Se-rich crops in Se-poor area. Here, the possibility of cultivating Se-rich maize grains in Se-poor farmland was tested based on intensive field sampling and mathematical modelling. Sampling was conducted at county scale, and a total of 7779 topsoil samples and 109 maize samples with paired rhizosphere soils samples were collected. Results showed that although the soil Se content in the study county from southwestern China was at a low level (0.01-2.75 mg kg^-1), 54.1% of the maize grain samples satisfied the standard for Se-rich products (0.02-0.30 mg kg^-1). Soil organic matter, iron oxide, and phosphorus levels were correlated negatively with Se bioconcentration factor (BCF) of maize grain. Compared with the multivariate linear regression model, the artificial neural network (ANN) model was more accurate and reliable in predicting maize Se BCF. Prediction using the ANN model showed that 22.7% of the county's farmland was suitable for cultivating naturally Se-rich maize, which increased 21.3% growing areas than that from cultivation based on simply soil total Se. This study provided a new methodological framework for natural Se-rich maize production and verified the probability of cultivating naturally Se-rich maize in Se-poor farmland.

Evidence and Mechanisms of Selenate Reduction to Extracellular Elemental Selenium Nanoparticles on the Biocathode

Intracellular selenium nanoparticles (SeNPs) production is a roadblock to the recovery of selenium from biological water treatment processes because it is energy intensive to break microbial cells and then separate SeNPs. This study provided evidence of significantly more extracellular SeNP production on the biocathode (97-99%) compared to the conventional reactors (1-90%) using transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy. The cathodic microbial community analysis showed that relative abundance of Azospira oryzae, Desulfovibrio, Stenotrophomonas, and Rhodocyclaceae was <1% in the inoculum but enriched to 10-21% for each group when the bioelectrochemical reactor reached a steady state. These four groups of microorganisms simultaneously produce intracellular and extracellular SeNPs in conventional biofilm reactors per literature review but prefer to produce extracellular SeNPs on the cathode. This observation may be explained by the cellular energetics: by producing extracellular SeNPs on the biocathode, microbes do not need to transfer selenate and the electrons from the cathode into the cells, thereby saving energy. Extracellular SeNP production on the biocathode is feasible since we found high concentrations of C-type cytochrome, which is well known for its ability to transfer electrons from electrodes to microbial cells and reduce selenate to SeNPs on the cell membrane.

The importance and status of the micronutrient selenium in South Africa: a review

Selenium (Se) is a vital micronutrient with widespread biological action but leads to toxicity when taken in excessive amounts. The biological benefits of Se are mainly derived from its presence in active sites of selenoproteins such as glutathione peroxidase (GPx). An enzyme whose role is to protect tissues against oxidative stress by catalysing the reduction of peroxidase responsible for various forms of cellular damage. The benefits of Se can be harvested when proper regulations of its intake are used. In South Africa, Se distribution in people's diets and animals are low with socio-economic factors and heterogeneous spread of Se in soil throughout the country playing a significant role. The possible causes of low Se in soils may be influenced by underlying geological material, climatic conditions, and anthropogenic activities. Sedimentary rock formations show higher Se concentrations compared to igneous and metamorphic rock formations. Higher Se concentrations in soils dominates in humid and sub-humid areas of South Africa. Furthermore, atmospheric acid deposition dramatically influences the availability of Se to plants. The studies reviewed in this article have shown that atomic absorption spectroscopy (AAS) is the most utilised analytical technique for total Se concentration determination in environmental samples and there is a lack of speciation data for Se concentrations. Shortcomings in Se studies have been identified, and the future research directions of Se in South Africa have been discussed.

Biogenic Selenium Nanoparticles and Their Anticancer Effects Pertaining to Probiotic Bacteria—A Review

Selenium nanoparticles (SeNPs) can be produced by biogenic, physical, and chemical processes. The physical and chemical processes have hazardous effects. However, biogenic synthesis (by microorganisms) is an eco-friendly and economical technique that is non-toxic to human and animal health. The mechanism for biogenic SeNPs from microorganisms is still not well understood. Over the past two decades, extensive research has been conducted on the nutritional and therapeutic applications of biogenic SeNPs. The research revealed that biogenic SeNPs are considered novel competitors in the pharmaceutical and food industries, as they have been shown to be virtually non-toxic when used in medical practice and as dietary supplements and release only trace amounts of Se ions when ingested. Various pathogenic and probiotic/nonpathogenic bacteria are used for the biogenic synthesis of SeNPs. However, in the case of biosynthesis by pathogenic bacteria, extraction and purification techniques are required for further useful applications of these biogenic SeNPs. This review focuses on the applications of SeNPs (derived from probiotic/nonpathogenic organisms) as promising anticancer agents. This review describes that SeNPs derived from probiotic/nonpathogenic organisms are considered safe for human consumption. These biogenic SeNPs reduce oxidative stress in the human body and have also been shown to be effective against breast, prostate, lung, liver, and colon cancers. This review provides helpful information on the safe use of biogenic SeNPs and their economic importance for dietary and therapeutic purposes, especially as anticancer agents.

Potential ecological risk assessment of heavy metals (trace elements) in coastal soils of southwest Iran

Heavy metal pollution has become one of the most important threats that can endanger the health of animals, the environment, and humans. The present study was performed to investigate the potential ecological risk (PER) of heavy metals [zinc (Zn), copper (Cu), cobalt (Co), molybdenum (Mo), manganese (Mn), and selenium (Se)] in the coastal soils of southwest Iran in 2019. The samples were collected from six soil sites and three depth intervals (0-15, 15-30, and 30-45 cm) among bare and vegetated coastal soils. The soil samples to study the soil properties (soil grain size, pH, EC, and soil organic carbon) and metal contamination were taken from soil (36 samples), water (6 samples), and plants (24 samples). The soil ecological risk (ER), the pollution load index (PLI), contamination degree (Cdeg), modified contamination degree (mCdeg) for heavy metal contamination in the soil, and enrichment factor (EF index) indicate the origin of metals entering the environment, and hence these parameters were investigated. The results of this study showed that the levels of Zn, Cu, Co, Mn, Se, and Mo were in the range of low-risk contaminants in this region. According to the results of the study, the risk index (RI) for metals was in the range of 1.296-3.845, which is much lower than 150, and therefore the ecological risk potential calculated in this study was in the low-risk category for toxic elements. Based on the results, it was found that agricultural, industrial, and human activities played an effective role in the accumulation of Zn, Cu, Co, Se, and Mo in the soil. In addition, the main source of Mn metal is believed to be natural due to geological activities in the region.

How sulfur species can accelerate the biological immobilization of the toxic selenium oxyanions and promote stable hexagonal Se0 formation

Toxic selenium oxyanions and sulfur species are often jointly present in contaminated waters and soils. This study investigated the effect on kinetics and resulting products for bio-reduction of selenium oxyanions in the presence of biologically produced sulfur resulting from bio-oxidation of sulfide in (bio)gas-desulfurization (bio-S⁰) and of sulfate. Selenite and selenate (~2 mmol L^-1) bio-reduction was studied in batch up to 28 days at 30 ^oC and pH 7 using lactic acid and a sulfate-reducing sludge, 'Emmtec'. Bio-S⁰ addition increased the selenite removal rate, but initially slightly decreased selenate reduction rates. Selenite reacted with biologically generated sulfide resulting in selenium-sulfur, which upon further bio-reduction creates a sulfur bio-reduction cycle. Sulfate addition increased the bio-reduction rate for both selenite and sulfate. Bio-S⁰ or sulfate promoted hexagonal selenium formation, whereas without these, mostly amorphous Se⁰ resulted. With another inoculum, 'Eerbeek', bio-S⁰ accelerated the selenite reduction rate less than for 'Emmtec' because of lower sulfur and higher selenite bio-reduction rates. Bio-S⁰ addition increased the selenate reduction rate slightly and accelerated hexagonal selenium formation. Hexagonal selenium formation is advantageous because it facilitates separation and recovery and is less mobile and toxic than amorphous Se⁰. Insights into the interaction between selenium and sulfur bio-reduction are valuable for understanding environmental pathways and considerations regarding remediation and recovery.

Succession of function, assembly, and interaction of microbial community in sequencing biofilm batch reactors under selenite stress

The mechanism of interaction between selenite, a toxic substance, and the microbial community in wastewater is still not well understood. Herein, nine sequencing biofilm batch reactors were used to systematically investigate the response of the microbial community to the continuous selenite stress. The results showed that selenite affected the reactor performance and reduced the biofilm mass. Also, it increased the proportion of the living cells, and changed the protein and polysaccharide composition of the biofilm as well as cellular secretions. Selenite facilitated the removal of NO₃-N, according to water-quality and bioinformatics analyses. As such, the selenite was converted into selenium nanoparticles. α-diversity analysis further revealed that 20 μM selenite enhanced the microbial community resilience, while 200 μM selenite had the reverse effect. Community composition analysis showed that Variovorax, Rhizobium, and Simkania had positive correlations with selenite (P < 0.05). Functional prediction suggested that selenite changed the C, N, and S cycle functions. Furthermore, determinism dominated the community assembly process, and the deterministic proportion increased with the increase of selenite concentration. Network analysis showed that selenite improved the stability and positive correlation ratio of the overall microbial network, and accelerated the communication between microorganisms. However, when compared with the 20 μM selenite, the 200 μM selenite boosted the competition and parasitism/predation among microorganisms. Low-abundance genera played a key role in the network of selenite-reducing microbial community. In addition, under selenite stress, biofilm network exhibited better stability and faster information exchange than suspended network, and the positive association between biofilm and suspended microorganisms increased. All in all, this research sheds light on the interaction between selenite and microbial community, as well as provides crucial information on selenium-containing wastewater.

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

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

Voyage of selenium from environment to life: Beneficial or toxic?

Selenium (Se), a naturally occurring metalloid, is an essential micronutrient for life as it is incorporated as selenocysteine in proteins. Although beneficial at low doses, Se is hazardous at high concentrations and poses a serious threat to various ecosystems. Due to this contrasting 'dual' nature, Se has garnered the attention of researchers wishing to unravel its puzzling properties. In this review, we describe the impact of selenium's journey from environment to diverse biological systems, with an emphasis on its chemical advantage. We describe the uneven distribution of Se and how this affects the bioavailability of this element, which, in turn, profoundly affects the habitat of a region. Once taken up, the subsequent incorporation of Se into proteins as selenocysteine and its antioxidant functions are detailed here. The causes of improved protein function due to the incorporation of redox-active Se atom (instead of S) are examined. Subsequently, the reasons for the deleterious effects of Se, which depend on its chemical form (organo-selenium or the inorganic forms) in different organisms are elaborated. Although Se is vital for the function of many antioxidant enzymes, how the pro-oxidant nature of Se can be potentially exploited in different therapies is highlighted. Furthermore, we succinctly explain how the presence of Se in biological systems offsets the toxic effects of heavy metal mercury. Finally, the different avenues of research that are fundamental to expand our understanding of selenium biology are suggested.

Effects of Selenium in Different Valences on the Community Structure and Microbial Functions of Biofilms

With the wide application of selenium (Se) in industrial production, different Se-based compounds (selenate and selenite) are produced and released into aquatic environments. The potential impacts of such Se compounds on the biofilms (a complex microbial aggregate in aquatic systems) need to be substantially explored. Herein, we investigated the responses of bacterial community diversity, composition and structure, and function of biofilms after 21 days of exposure to low concentrations (100 µg/L) and high concentrations (1 mg/L) of sodium selenate and sodium selenite, respectively. Distinct effects of selenium in different valences on the community structure and microbial functions of biofilms were observed. Compared with the controls, the addition of selenate and selenite solutions altered the richness of biofilms but not the diversity, which is dependent on the concentration and valences, with sodium selenite (1 mg/L) exhibiting a strong inhibition effect on community richness. Significant changes of community composition and structure were observed, with a significant increase in Proteobacteria (31.08–58.00%) and a significant decrease in Bacteroidetes (32.15–11.45%) after exposure to sodium selenite with high concentration. Also, different responses of gamma-Proteobacteria and alpha-Proteobacteria were observed between the sodium selenite and sodium selenate treatments. Moreover, results showed that sodium selenite could strengthen the function of the metabolism of biofilms, and the higher the concentration is, the more apparent the enhancement effect is. All these results suggested that the effects of different valence states of selenium were obvious, and sodium selenite with high concentration strongly changed the diversity, structure and function of biofilms.

Unlocking All-Solid Ion Selective Electrodes: Prospects in Crop Detection

This paper reviews the development of all-solid-state ion-selective electrodes (ASSISEs) for agricultural crop detection. Both nutrient ions and heavy metal ions inside and outside the plant have a significant influence on crop growth. This review begins with the detection principle of ASSISEs. The second section introduces the key characteristics of ASSISE and demonstrates its feasibility in crop detection based on previous research. The third section considers the development of ASSISEs in the detection of corps internally and externally (e.g., crop nutrition, heavy metal pollution, soil salinization, N enrichment, and sensor miniaturization, etc.) and discusses the interference of the test environment. The suggestions and conclusions discussed in this paper may provide the foundation for additional research into ion detection for crops.

Biotransformation of selenium in the mycelium of the fungus Phycomyces blakesleeanus

Biotransformation of toxic selenium ions to non-toxic species has been mainly focused on biofortification of microorganisms and production of selenium nanoparticles (SeNPs), while far less attention is paid to the mechanisms of transformation. In this study, we applied a combination of analytical techniques with the aim of characterizing the SeNPs themselves as well as monitoring the course of selenium transformation in the mycelium of the fungus Phycomyces blakesleeanus. Red coloration and pungent odor that appeared after only a few hours of incubation with 10 mM Se⁺⁴ indicate the formation of SeNPs and volatile methylated selenium compounds. SEM-EDS confirmed pure selenium NPs with an average diameter of 57 nm, which indicates potentially very good medical, optical, and photoelectric characteristics. XANES of mycelium revealed concentration-dependent mechanisms of reduction, where 0.5 mM Se⁺⁴ led to the predominant formation of Se-S-containing organic molecules, while 10 mM Se⁺⁴ induced production of biomethylated selenide (Se^-2) in the form of volatile dimethylselenide (DMSe) and selenium nanoparticles (SeNPs), with the SeNPs/DMSe ratio rising with incubation time. Several structural forms of elemental selenium, predominantly monoclinic Se₈ chains, together with trigonal Se polymer chain, Se₈ and Se₆ ring structures, were detected by Raman spectroscopy.

Characteristics of Se in water-soil-plant system and threshold of soil Se in seleniferous areas in Enshi, China

Se-enrichment characteristics in water-soil-plant system and dietary Se status of local residents in seleniferous areas were investigated. Results showed that Se in well water might mainly derived from Se-enriched shales and coals, and Se mobility in seleniferous soils was relatively low with less than 6.7% bioavailable forms in high-Se areas. Soil Se with irrigation, precipitation and fertilization sources contributed more to soil Se than Se-enriched shales and coals in low-Se areas, resulting in slightly higher mobility of Se in low-Se soils. Se concentration in edible parts of main crops ranged from 0.005 mg kg^-1 to 4.17 mg kg^-1, and cereal plants had a higher Se-enrichment ability than tuber plants. The probable dietary Se intake (PDI) in high-Se areas was decreased to 959.3 μg d^-1 in recent years, which might be attributed to tap water as drinking water in recent year rather than well water-dependent and changes in dietary structure, but still far above the permissible value of 400 μg d^-1. Reducing cereal-derived dietary Se intake is an important strategy to better Se nutrition status in high-Se areas. After synthesis considerations on soil Se bioavailability and PDI of Se, the soil total Se of 4 mg kg^-1 and the soil available Se content of 0.32 mg kg^-1 were proposed to be the reference threshold values of soil Se excess in high-Se areas in Enshi, respectively.

Zinc ferrite nanoparticles from industrial waste for Se (IV) elimination from wastewater

The presence of high concentrations of selenium ions in wastewater is considered an environmental problem. However, the mechanism of selenium ions (Se (IV)) removal by the adsorption process has not been investigated in-depth so far. Also, the recovery and conversion of the industrial waste materials into valuable materials is a vital issue. Therefore, in this study, zinc ferrite nanopowders are economically synthesized from steel-making wastes by co-precipitation method for investigating as adsorbents of selenium species. The produced nanopowders were annealed at 150, 300, 500, and 850 °C for 5 h to scrutinize the impact of annealing temperature on their crystallite size. The compositional, optical, and magnetic features of the nanopowders were defined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), UV-Vis. spectrophotometer along with vibrating sample magnetometer (VSM). Optical absorbance spectra were found characteristic due to the electronic structure of Fe³⁺ (3d⁵) considering the C_3v local symmetry of Fe³⁺ ions. The prepared nanopowders demonstrated good adsorption capacity toward selenium ions (43.67 mg/g at pH 2.5) from an aqueous medium. Adsorption data were found fitting to Freundlich isotherm model. Thus, ZnFe₂O₄ can be recommended to effectively eliminate selenium ions from aqueous solutions.

Hourly emission estimation of black carbon and brown carbon absorption from domestic coal burning in China

Residential coal combustion (RCC) emission demonstrates obvious daily variation, while no real-time estimation of air pollutants from RCC has been reported, as the limitation of hourly activity data and emission factors. With a dilution sampling system, a high-precision electronic balance, and an Aethalometer Model AE33, a real-time monitoring platform for RCC emission was established. Hourly emission factors (EFs) of BC and absorption emission factors (AEFs) of BrC from eleven kinds of chunk coals and nine kinds of honeycomb coals burning in China were obtained. The monthly and hourly coal consumption amounts were calculated with the activity data from literature reviews and a field survey. The first hourly BC and absorption cross section of BrC emission inventories from RCC were established in China. The historical emission trends (2003-2017) indicated that the policy has rapidly controlled the emission of BC and ACS_BrC from RCC in urban area (26.7% and 31.8% decreased, respectively in 2013). While in rural areas, their emission continually increased by 1.2% ~ 5.3% until more strict law enacted in 2017. Emissions of BC and ACS_BrC in winter seasons were 60.1 Gg and 1064.1 Gm², which accounted for 54.3% and 55.1% of the total BC and ACS_BrC emissions correspondingly. The peak values of hourly emission of BC and ACS_BrC (in 370 nm) normally appeared at 19:00-23:00, accounting for 43.0% and 41.5% of their total daily emission. The low emission periods were at cooking times including 7:00, 12:00, and 17:00 of a day and the whole emission of BC and ACS_BrC for the three periods accounted for 1.8% and 2.3% of their daily emission. This high-resolution BC and ACS_BrC emission inventories can be useful for future modeling works on the formation and evolution of a haze event, the smoke aging and transportation, as well as corresponding climate and human health effects.