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Selenium Geochemistry and Health

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Abstract

Selenium (Se) is a naturally occurring metalloid element, which is essential to human and other animal health in trace amounts but is harmful in excess. Of all the elements, Se has one of the narrowest ranges between dietary deficiency ( 400 µg day-1) (1) making it necessary to carefully control intakes by humans and other animals hence the importance of understanding the relationships between environmental exposure and health. Geology exerts a fundamental control on the concentrations of Se in the soils on which we grow the crops and animals that form the human food chain. The Se status of populations, animals and crops vary markedly around the world as a result of different geological conditions. Since diet is the most important source of Se in humans, understanding the biogeochemical controls on the distribution and mobility of environmental Se is key to the assessment of Se-related health risks.

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... Although its distribution is very heterogeneous, it has been estimated that, on average, the lithosphere contains about 0.05 ppm of Se. Some extremely polluted soils in USA, Ireland, and India reach 100 mg of selenium per kg, but concentrations over 0.1 mg per kg are uncommon [1][2][3]. In general, high concentration of selenium is associated with mining, ore treatment, or industrial activities [4]. ...
... Se(IV) and Se(VI) ions form soluble oxyanions that are frequently found in surface waters under reducing and oxidizing ambient [11]. Selenate (SeO 4 2− ) is found in more oxidizing ambient, and its capacity for adsorption and precipitation on mineral surfaces is low compared with selenite (SeO 3 2− ), which is also very soluble under less oxidizing conditions [12], and whose mobility is influenced by pH-dependent sorption/desorption phenomena [13]. Selenium is an essential bio-element that is involved in different biological processes. ...
... The study of this mobility requires knowledge of the different species of selenium at different pH and redox conditions and therefore their interaction with the different mineral species present on the Earth's crust. In carbonate media, it is important to know the influence of carbonate species CO 3 2− , HCO 3 − , H 2 CO 3 0 , and cations such as Ca 2+ and Mg 2+ , as possible factors affecting selenium mobility. ...
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Selenium is an essential bio-element, but because of its bioaccumulation potential, it can become toxic and is an important pollutant. The ubiquitous mineral calcite (CaCO3) has the ability to immobilize anions as SeO32− by different sorption or coprecipitation processes. Experimental studies have found that SeO32− can incorporate in the crystal structure of calcite by substituting CO32−. The presence of foreign ions in aqueous solution strongly affects CaCO3 precipitation, helping stabilize less stable polymorphs such as vaterite and aragonite or hydrated phases. In this work, we studied the aging process of calcium carbonates precipitated from aqueous solutions highly supersaturated with respect to CaCO3 and slightly supersaturated with respect to CaSeO3·H2O under ambient conditions, for times up to 30 days in which solids were kept in the remaining aqueous solution. Under these conditions, CaCO3 precipitated mainly as low crystallinity vaterite aggregates that hosted up to 16% atomic ratio Se:C. Vaterite purified and increased its crystallinity with aging time, but the vaterite–calcite transformation was strongly inhibited. The incorporation of Se(IV) in vaterite did not significantly affect the cell parameters or the external morphology of the aggregates. The precipitation of selenite as CaSeO3·H2O was conditioned by the availability of free Ca2+ and SeO32− that was not previously incorporated into precipitated carbonates.
... It exists in inorganic forms as selenate (SeO4 2-), selenite (SeO3 2-), selenide (Se 2-) and elemental Se (Se 0 ), and in organic forms such as selenocysteine (SeCys) and selenomethionine (SeMet). Due to this complex chemical behavior, Se is found in all natural materials on earth: soil, rocks, waters, air, plants and animals (Fordyce, 2007). During a long period, Se has been identified as a dangerous substance because of its toxicity (Fordyce et al., 2000). ...
... Rocks are the primary source of Se, which comprise approximately 40% of the total Se form in the Earth's crust (Wang & Gao, 2001). A greater Se concentration (0.06 mg/kg) is usually found in shales compared to that in limestones and sandstones (Fordyce, 2007). Coals and other organic-rich deposits can be rich in Se (typically from 1 to 20 mg/kg). ...
... Very high concentrations of Se have also been reported in some phosphatic rocks (≤ 300 mg/kg) and some black shales (300 mg/kg). Selenium is also often found as a minor component of sulfide mineral deposits (Fernández-Martínez & Charlet, 2009;Fordyce, 2007;Fordyce, 2013). ...
... It exists in inorganic forms as selenate (SeO4 2-), selenite (SeO3 2-), selenide (Se 2-) and elemental Se (Se 0 ), and in organic forms such as selenocysteine (SeCys) and selenomethionine (SeMet). Due to this complex chemical behavior, Se is found in all natural materials on earth: soil, rocks, waters, air, plants and animals (Fordyce, 2007). During a long period, Se has been identified as a dangerous substance because of its toxicity (Fordyce et al., 2000). ...
... Rocks are the primary source of Se, which comprise approximately 40% of the total Se form in the Earth's crust (Wang & Gao, 2001). A greater Se concentration (0.06 mg/kg) is usually found in shales compared to that in limestones and sandstones (Fordyce, 2007). Coals and other organic-rich deposits can be rich in Se (typically from 1 to 20 mg/kg). ...
... Very high concentrations of Se have also been reported in some phosphatic rocks (≤ 300 mg/kg) and some black shales (300 mg/kg). Selenium is also often found as a minor component of sulfide mineral deposits (Fernández-Martínez & Charlet, 2009;Fordyce, 2007;Fordyce, 2013). ...
... Selenium exists in inorganic forms as selenate (SeO 2− 4 ), selenite (SeO 2− 3 ), selenide (Se 2− ), elemental Se (Se 0 ), and in organic forms such as selenocysteine (SeCys) and selenomethionine (SeMet). Due to this diversity in form of occurrence, Se is found in all natural materials on Earth: soil, rocks, waters, air, plants and animals (Fordyce, 2007). For a long time, Se has been identified as a dangerous substance because of its toxicity (Fordyce, 2007). ...
... Due to this diversity in form of occurrence, Se is found in all natural materials on Earth: soil, rocks, waters, air, plants and animals (Fordyce, 2007). For a long time, Se has been identified as a dangerous substance because of its toxicity (Fordyce, 2007). More recently, it has also been recognized as an essential trace element due to its crucial role in the functioning of enzymes of humans and animals (Fordyce, 2013;Rayman, 2000). ...
... It has been demonstrated that Se deficiency can cause Keshan disease and Kashin-Beck disease (endemic disease) with low Se supplies in the food system, that is, weakening of the heart and also atrophy and necrosis of cartilage tissue in the joints, which has been reported in the middle of China (Stone, 2009), Saudi Arabia, the Czech Republic, Burundi, New Guinea, Nepal, Croatia, and Egypt (Wu et al., 2015). Low Se status has also been associated with a significantly increased risk of cancer incidence and mortality, cardiovascular risk, poor immune function, male infertility and lower reproduction (Fordyce, 2007;Haug et al., 2007). In addition, Se deficiency may also be a factor in some other diseases. ...
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Selenium contamination of air, aquatic environments, soils and sediments is a serious environmental concern of increasing importance. Selenium has a paradoxical feature in bringing about health benefits under the prescribed level, but only a few fold increase in its concentration causes deleterious effects to flora and fauna, humans and the environment. This book Environmental Technologies to Treat Selenium Pollution: Principles and Engineering: presents the fundamentals of the biogeochemical selenium cycle and which imbalances in this cycle result in pollution.overviews chemical and biological technologies for successful treatment of selenium contaminated water, air, soils and sediments.explores the recovery of value-added products from selenium laden waste streams, including biofortication and selenium-based nanoparticles and quantum dots. This book may serve both as an advanced textbook for undergraduate and graduate students majoring in environmental sciences, technology or engineering as well as as a handbook for tertiary educators, researchers, professionals and policy makers who conduct research and practices in selenium related fields. It is essential reading for consulting companies when dealing with selenium related environmental (bio)technologies. ISBN: 9781789061048 (Paperback) ISBN: 9781789061055 (eBook)
... Wang et al., (1994) reported that the Se concentrations in river waters of several European countries, Japan and USA are largely \ 1 lg L -1 . Selenium concentrations in fresh water generally fall within the range 0.1-100 lg L -1 with most of the values below 3 lg L -1 (Fordyce, 2007(Fordyce, , 2013. Watts and Mitchell (2009) reported an average concentration of 1.84 lg L -1 Se in surface water from a similar hilly area in Argentina. ...
... The geology of the study area is dominated by metamorphic and igneous rocks, which usually contain less Se compared to sedimentary rocks (Alexander, 2015;Fordyce et al., 2010Fordyce et al., , 2013Koljonen, 1973). Underlying rock type has a major role in Se concentration in most soils (Fordyce, 2007(Fordyce, , 2013Fordyce et al., 2009). Principal components analysis revealed that a sandy soil texture was found to be negatively correlated with Se T concentration (Fig. 2). ...
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Deficiencies of the micronutrients iodine and selenium are particularly prevalent where populations consume local agricultural produce grown on soils with low iodine and selenium availability. This study focussed on such an area, Gilgit-Baltistan in Pakistan, through a geochemical survey of iodine and selenium fractionation and speciation in irrigation water and arable soil. Iodine and selenium concentrations in water ranged from 0.01–1.79 µg L⁻¹ to 0.016–2.09 µg L⁻¹, respectively, which are smaller than levels reported in similar mountainous areas in other parts of the world. Iodate and selenate were the dominant inorganic species in all water samples. Average concentrations of iodine and selenium in soil were 685 µg kg⁻¹ and 209 µg kg⁻¹, respectively, much lower than global averages of 2600 and 400 µg kg⁻¹, respectively. The ‘reactive’ fractions (‘soluble’ and ‘adsorbed’) of iodine and selenium accounted for < 7% and < 5% of their total concentrations in soil. More than 90% of reactive iodine was organic; iodide was the main inorganic species. By contrast, 66.9 and 39.7% of ‘soluble’ and ‘adsorbed’ selenium, respectively, were present as organic species; inorganic selenium was mainly selenite. Very low distribution coefficients (kd = adsorbed/soluble; L kg⁻¹) for iodine (1.07) and selenium (1.27) suggested minimal buffering of available iodine and selenium against leaching losses and plant uptake. These geochemical characteristics suggest low availability of iodine and selenium in Gilgit-Baltistan, which may be reflected in locally grown crops. However, further investigation is required to ascertain the status of iodine and selenium in the Gilgit-Baltistan food supply and population.
... Se concentrations in rocks are generally low, and the average crustal abundance is 0.05 mg/kg [21]. Se can be enriched in phosphate rocks (up to 300 mg/kg), coal (1-20 mg/kg), and black shales (up to 600 mg/kg) [21,26]. In natural water, Se mainly occurs as selenite (Se(IV)) and selenate (Se(VI)) [21]. ...
Article
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Responsible use and effective treatment of mine water are prerequisites of sustainable mining. The behavior of contaminants in mine water evolves in relation to the metastable characteristics of some species, changes related to the mine life cycle, and mixing processes at various scales. In cold climates, water treatment requires adaptation to site-specific conditions, including high flow rates, salinity, low temperatures, remoteness, and sensitivity of receiving waterbodies. Contaminants of emerging concern (CECs) represent a newer issue in mine water treatment. This paper reviews recent research on the challenges and opportunities related to CECs in mine water treatment, with a focus on advanced oxidation and membrane-based processes on mine sites operating in cold climates. Finally, the paper identifies research needs in mine water treatment.
... The average content of Se in the Earth's crust is ∼50 μg/kg. Se is distributed extremely heterogeneously in the soil, and its concentration in different geographic regions varies from 10 to 2000 μg/kg, averaging at ∼400 μg/kg [3,4]. The content of Se in the soil depends mainly on the parent material, climate, and use of fertil izers. ...
Article
As an essential trace element, selenium (Se) plays a tremendous role in the functioning of the human organism being used for the biosynthesis of selenoproteins (proteins containing one or several selenocysteine residues). The functions of human selenoproteins in vivo are extremely diverse. Many selenoproteins have an antioxidant activity and, hence, play a key role in cell antioxidant defense and maintenance of redox homeostasis, which accounts for their involvement in diverse biological processes, such as signal transduction, proliferation, cell transformation and aging, ferroptosis, immune system functioning, etc. One of the critical functions of selenoenzymes is participation in the synthesis of thyroid hormones regulating basal metabolism in all body tissues. Over the last decades, optimization of population Se intake for prevention of diseases related to Se deficiency or excess has been recognized as a pressing issue in modern healthcare worldwide.
... broccoli (6 ng Se/g) or cabbage (9-14 ng Se/g) (Dumont, Vanhaecke, & Cornelis, 2006). Brazil nuts are high in protein and are known for their high selenium content of up to 7 μg/g (Fordyce, 2007). In products of animal origin, this element varies depending on the feed used and the species of animal (Kieliszek, 2019). ...
Chapter
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Selenium (Se) is an element commonly found in the environment at different levels. Its compounds are found in soil, water, and air. This element is also present in raw materials of plant and animal origin, so it can be introduced into human organisms through food. Selenium is a cofactor of enzymes responsible for the antioxidant protection of the body and plays an important role in regulating inflammatory processes in the body. A deficiency in selenium is associated with a number of viral diseases, including COVID-19. This element, taken in excess, may have a toxic effect in the form of joint diseases and diseases of the blood system. Persistent selenium deficiency in the body may also impact infertility, and in such cases supplementation is needed.
... In the present study, the total Se in the natural soil (45 μg kg -1 ) was larger than the Se fertiliser added as a treatment (12.5 μg kg -1 ), although it is still a very small soil Se concentration, since soils with less than 1000 μg kg -1 are considered Se deficient [39]. Indeed, in soil with Se concentration 13 of 183 μg kg -1 the application of Se increased the availability of the element to maize plants [40]. ...
Article
Backgorund Cowpea is a crop widely used in developing countries due its rusticity. Besides its rich genotypic variability, most breeding programs do not explore its potential to improve elements uptake. Selenium (Se) is a scarce element in most soils, resulting in its deficiency being common in human diets. This study aimed to evaluate the interaction between biofortification with Se and genotypic variation in cowpea, on the concentrations of Se in roots, leaves + stem and grains. Methods Twenty-nine cowpea genotypes were grown in a greenhouse in the absence (control) and presence of Se (12.5 µg Se kg⁻¹ soil) as sodium selenate, in fully randomized scheme. The plants were cultivated until grains harvest. The following variables were determined: roots dry weight (g), leaves + stems dry weight (g), grains dry weight (g), Se concentration (mg kg⁻¹) in roots, leaves + stems and grains, and Se partitioning to shoots and grains. Results Selenium application increased the Se concentration in roots, leaves + stems and grains in all genotypes. At least twofold variation in grain Se concentration was observed among genotypes. Selenium application did not impair biomass accumulation, including grain dry weight. Genotype “BRS Guariba” had the largest Se concentration in grains and leaves + stems. Genotype MNC04-795 F-158 had the largest partitioning of Se to shoots and grain, due to elevated dry weights of leaves + stems and grain, and high Se concentrations in these tissues. Conclusion This information might be valuable in future breeding programs to select for genotypes with better abilities to accumulate Se in grain to reduce widespread human Se undernutrition.
... Soil fertilization is one of the major agronomic practices for Se biofortification and plays an essential role in agriculture (Wu et al., 2020). Se deficiency has been considered a global health issue that causes endemic diseases, e.g., Kashin-Beck disease in Eastern Siberia, Northern China and North Korea (Fordyce, 2007;Nesterov, 1964). A survey showed that half to one billion people are Se-deficient around the world (Combs, 2001). ...
Article
Selenium (Se) is an essential element with application in manufacturing from food to medical industries. Water contamination by Se is of concern due to anthropogenic activities. Recently, Se remediation has received increasing attention. Hence, different types of remediation techniques are listed in this work, and their potential for Se recovery is evaluated. Sorption, co-precipitation, coagulation and precipitation are effective for low-cost Se removal. In photocatalytic, zero-valent iron and electrochemical systems, the above mechanisms occur with reduction as an immobilization and detoxification process. In combination with magnetic separation, the above techniques are promising for Se recovery. Biological Se oxyanions reduction has been widely recognized as a cost-effective method for Se remediation, simultaneously generating biosynthetic Se nanoparticles (BioSeNPs). Increasing the extracellular production of BioSeNPs and controlling their morphology will benefit its recovery. However, the mechanism of the microbial production of BioSeNPs is not well understood. Se containing products from both microbial reduction and abiotic methods need to be refined to obtain pure Se. Eco-friendly and cost-effective Se refinery methods need to be developed. Overall, this review offers insight into the necessity of shifting attention from Se remediation to Se recovery.
... In natural soil conditions, selenate (SeO 4 2− ; the most toxic form of Se) and selenite (SeO 3 2− ) are the soluble oxyanions that can be transformed into elemental Se(0) where organic matter and microbial species participate in this process. Selenate (SeO 4 2− ) is most soluble form of Se, with low adsorption and precipitation capacity, which predominates in alkaline and high redox potential soil conditions (Fordyce 2007). On the other hand, selenite (SeO 3 2− ) occurs in neutral and acidic soil conditions (Kabata-Pendias 2011) with moderate redox potential range (Milne 1998). ...
Chapter
Selenium (Se) occurs naturally as a trace element and is distributed in geologic formations at low concentration. It is categorized as a metalloid, having −2, 0, +4, and +6 primary oxidation states. Selenium is essential for plants and animals as a micronutrient (<40 μg), but higher concentration (>400 μg) may cause health hazard to living beings. Owing to its varied oxidation states it forms different types of compounds with sulfur (selenium sulfide [Se2S2] and polysulfides), oxygen (selenate, SeO4 ⁻⁻ and selenite SeO3 ⁻⁻), hydrogen selenide (H2Se) and some organometalic compounds with methyl such as dimethylselenide ((CH3)2Se), dimethyl selenone ((CH3)2SeO2) and dimethyl diselenide ((CH3)2Se2) which are widely distributed in biogeologic forms. On substitution of sulfur it forms selenocysteine, selenocystine, and selenomethionine with amino acids. The soluble forms of selenium compounds are mobile and their speciation in soil and water is highly dependent on conditions of specific location, however SeO4 ⁻ has been reported as a major species in oxygenated agriculture water. In past few decades the elevated concentration of selenium in soil and water has been reported as a serious issue of concern, therefore it is essential to know the speciation of selenium species in soil and water for remediation.
... Selenium is a microelement that rarely occurs in its elemental form in nature; instead, organic and inorganic mineral forms of selenium, such as selenide, selenate, and selenite, have been detected in soil [118][119][120]. Previous studies have shown that humans can absorb organic compounds better than inorganic compounds [121][122][123]. ...
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Osteoporosis, characterized by low bone mass and a disruption of bone microarchitecture, is traditionally treated using drugs or lifestyle modifications. Recently, several preclinical and clinical studies have investigated the effects of selenium on bone health, although the results are controversial. Selenium, an important trace element, is required for selenoprotein synthesis and acts crucially for proper growth and skeletal development. However, the intake of an optimum amount of selenium is critical, as both selenium deficiency and toxicity are hazardous for health. In this review, we have systematically analyzed the existing literature in this field to determine whether dietary or serum selenium concentrations are associated with bone health. In addition, the mode of administration of selenium as a supplement for treating bone disease is important. We have also highlighted the importance of using green-synthesized selenium nanoparticles as therapeutics for bone disease. Novel nanobiotechnology will be a bridgehead for clinical applications of trace elements and natural products.
... Its content in soils is, therefore, being studied by many scientists around the world [Kushwaha et al. 2021]. They find geographical regions where very high Se deficiency is recorded in soils below the value of less than 0.01 mg/kg soil [Fordyce 2007]. Symptoms of deficiency in animals and humans are observed there. ...
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In order to function properly, every living organism must have favourable conditions for its operation, i.e. it must be systematically supplied with the necessary nutrients. On the example of selenium (Se), it can be seen how important is the right balance between providing the right amount of it, without exceeding the level above which it is toxic. The amount of Se in soil is closely correlated with its content in the parent rock; therefore, it differs depending on the soil type and may change even in a small area. Considerable dispersion of the element in the soils of Poland is related to their formation, mainly from dump materials of various glaciations. The problem of maintaining the balance between deficiency and excess of Se in the diet of humans and animals is related primarily to the uneven distribution of this element in nature. In this paper, on the basis of scientific literature, the current issues related to the deficiency and excess of Se in the soil and its possible sources are presented. The relationship between the content in the soil and the supply of Se in plants, animals and humans was also shown. The aim of this study was to summarise the state of knowledge on the complexity of Se occurrence in the environment and its importance in the soil-plant-animals-human system.
... The Se concentration in most soils is low (world mean 0.4 mg kg -1 ), but high concentrations of Se (up to 1200 mg kg -1 ) have been reported in some seleniferous areas (Fordyce, 2007). However, in a review of the concentrations of micronutrients in soils and rocks, Reid and Horvath (1980) revealed that soil parent materials are highly variable in composition, and soil-forming processes vary substantially from one climate regime to another, such that, in some cases, the parent materials of soils can have weak relationship with the concentrations of micronutrients in the deriving soils. ...
... Selenate species are predominant in waters, sediments and soils. Noteworthy, selenate has high solubility, low precipitation and adsorption capacities, and the aqueous chemistry of selenate and sulfate are quite similar (Fordyce 2007). ...
... The low inherent soil Se content and lack of Se fertilization are the most reported reasons of low Se content in edible crops. Worldwide, the background level of Se in soils ranges from 0.01 to 2.0 mg kg −1 with average value of < 0.5 mg kg −1 soil (Fordyce, 2007). In Pakistan, Se concentration in soils is very low and reported values range between 0.032 and 0.372 mg kg −1 soil (Ahmad et al. 2009;Khan et al. 2006;Zou et al. 2019). ...
Article
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This study assessed the interactive effect of selenium (Se) and farmyard manure (FYM) on soil microbial activities, growth, yield, and Se accumulation by wheat grains. Preliminarily, the effect of Se (0–250 µg kg−1 soil) and FYM (0–12.5 g kg−1 soil) was assessed on soil microflora. Selenium exhibited an adverse impact on soil microflora; respiration was decreased at ≥ 10 µg kg−1 soil while dehydrogenase and urease activities were decreased at ≥ 125 µg kg−1 soil. At 250 µg Se kg−1 soil, respiration, dehydrogenase and urease activities were decreased by 81, 40 and 35%, respectively, on unamended soil, and by 9, 47 and 22%, respectively, on FYM-amended soil. The subsequent plant experiments were conducted with same Se and FYM rates; one was harvested 42 days after sowing and other at crop maturity. The application of 125 µg Se kg−1 and 12.5 g FYM kg−1 soil improved seedling biomass by 12.6 and 22%, respectively, while their combined use lacked synergistic effect. Similarly, at maturity Se and FYM increased grain yield while their combined effect was not synergistic. The Se-induced suppression in microbial activities was not related to yield which was improved (11% at the highest rate in unamended soil) by Se application. Selenium application increased grain Se content in a rate-dependent manner, it increased from 0 to 1025 µg kg−1 by applying 250 µg Se kg−1 soil. Moreover, FYM application decreased Se accumulation in grains. It is concluded that FYM application increased soil microbial activities and yield but reduced grain Se accumulation in wheat on Se-applied soil.
... -1 are considered deficient and above 319.75µg.day -1 can cause toxicity [46]; [47]. ...
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Nutritional biofortification of foods is a promising alternative to reduce Selenium deficiency in the diet of populations. This study evaluated the biofortification capacity of jambu with Se. The experiment was completely randomized with six treatments and five repetitions, in hydroponics. Five doses of Se in the form of sodium selenate (1, 2, 3, 4 and 5 mg.L-1) and the control dose were used. Biometric, macro and micronutrient analyzes were performed, as well as the Se content in the plant parts. The indices of translocation (TrI), tolerance (tI) and Nutrient Use Efficiency (Nue) were estimated. The results were submitted to ANOVA and principal components analysis for the construction of multivariate indicators, in order to specify the regression models. The plant obtained higher agronomic performance when submitted to a dose of 3mg.L-1, with Se translocation above 70%. The tI and Nue indices indicated that jambu reached optimal growth with the dose of 3 mg.L-1 of Se. The results obtained from the regression equation of the multivariate indicators of growth, mass and nutrition indicated that the ideal concentrations of Se varied between 2.77 and 3.36 mg.L-1. The general indicator that captured the entire plant behavior showed that the optimal concentration for biofortification is 2.98 mg.L-1 of Se. The daily consumption of 100 g of biofortified jambu at the indicated dose provides a daily content of 50.13µg of Se for the population, a sufficient amount of Se for a balanced diet.
... The global Se concentration in soil ranges from 0.01 to 2.0 mg kg −1 with an average of 0.40 mg kg −1 . However, it can be as high as 1200 mg/kg in seleniferous soils (Fiona 2007). The soil Se levels were generally divided into five grades based on the concentration range, including Se-deficient (< 0.125 mg/kg), Se-marginal (0.125-0.175 mg/kg), Se-sufficient (0.175-0.40 mg/kg), Se-rich (0.40-3.0 mg/kg), and Se-excessive (> 3.0 mg/kg) (Tan et al. 2002;Dinh et al. 2018). ...
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Selenium (Se) is an essential trace element for humans and animals. The human body mainly acquires Se from plant foods, especially cereal grains. Rice is the staple food for more than half of the world's population. Increasing the Se concentration of rice grains can increase the average human dietary Se intake. This review summarizes recent progresses on the molecular mechanisms of Se uptake, transport, subcellular distribution, organic Se retranslocation, and Se volatilization. The strategies for improving Se accumulation in rice grains by increasing Se accumulation, reducing Se volatilization and optimizing Se forms were also proposed, which provide a new insight into Se biofortification in rice by improving the utilization efficiency of Se.
... Selenium (Se) is a well known photovoltaic material, with its first studies dating back to the late 1800's. 1,2 Commonly found in metal sulfide ores, 3 Se is an earth-abundant material with a low melting point of ∼ 220 o C, a relatively simple and stable crystalline structure, and a large direct band-gap. 4 There are a few allotropes of Se, among them thermodynamically the most stable is triagonal Se (t-Se) 1 , which is a layered van der Waals solid. ...
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Selenium is an important earth-abundant and non-toxic semiconductor with numerous applications across the semiconductor industries. Selenium has drawn attention from scientific communities for photovoltaics and imaging devices. Its usage as a photosensitive material largely involves the synthesis of the amorphous phase (a-Se) via various experimental techniques. However, the ground state crystalline phase of this material, the trigonal selenium (t-Se), a layered van der Waals solid, has not been extensively studied for its optimum electronic and optical properties. In this work, we present systematic studies based on density functional theory (DFT) for ultra-thin 1 (1010) surface slabs of t-Se. We report the surface energy as well as work function, electronic and optical properties as a function of number of layers for (1010) surface slabs to access its suitability for applications as a photosensitive material and compare these calculations to historical data.
... Se holds a narrow threshold between beneficial and harmful effects on the body, with both inadequate and excessive intake of Se affecting one's health, which happens at the appropriate dose interval. If the intake is less than 40 µg/day, the human body is in a state of Se deficiency, but if it is more than 400 µg/day, it can lead to safety risks and even symptoms of Se toxicity (Fordyce 2007;Winkel et al. 2012). Therefore, deciding to have Se as a supplement needs strict control of its amount and time intervals according to the human serum levels. ...
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Aims Most crops are supplemented with selenium (Se) through the exogenous addition of inorganic Se fertilizer. There is a lack of in-depth research on organic Se fertilizers. Meanwhile, the dosage range between human Se deficiency and Se toxicity is narrow, so the Se content of agricultural products needs to be controlled within a reasonable interval. Methods Se accumulation and speciation in rice were analyzed and compared during three different growth stages (late tillering stage, initiate heading stage, and full heading stage) using three Se fertilizers: selenite, fermented Se, and potassium selenocyanoacetate (Se-AAF) via the foliar application. Results The Se content in rice sprayed with organic Se fertilizer was controlled in the relatively safe range and met the human Se supplement requirement compared to the sprayed sodium selenite, which was too high of a dose. The percentage of organic Se and protein Se in brown rice was found to be similar in all three Se fertilizers. The highest organic Se content of 91.57% was found in the grain of rice at the full heading stage by spraying Se-AAF. The main Se species in the grain was selenomethionine (SeMet), which reached 80% of the total Se. Se-methyl selenocysteine(SeMeCys) was found only in Se-AAF. The grain quality showed that all three Se fertilizers increased the consistency of gelatinization. Conclusions Appropriately delaying the spraying time and selecting organic Se fertilizer as the Se source can help to produce green and safe selenium-rich rice.
... Typically ranges of total Se concentration in most natural waters are <0.1-100 μg L − 1 (Fordyce, 2007). No data are available for the concentrations of SeNPs in the aquatic environment. ...
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Selenium nanoparticles (SeNPs) have been applied in the biomedical and biocidal domain which may have potential environmental risks for aquatic systems. However, the knowledge of its toxicity and the role of functionalization on aquatic invertebrates are scarce. Thus, the present study aimed to analyze the embryotoxicity of two types of SeNPs coated with Sodium carboxymethyl cellulose (CMC-SeNPs) and Chitosan (CS-SeNPs) to the freshwater snail Lymnaea stagnalis in lake water, focusing on embryonic development. The influence of surface coatings and ions release, on the embryonic development of SeNPs to freshwater snail L. stagnalis was investigated. For this end, the snails were exposed to different concentrations of SeNPs and Se ions (0.05–1 mg L⁻¹) during 7 days and multiple endpoints were analyzed, including developmental stage frequency, morphological alterations, embryos mortality and hatching success. The results showed that both Se forms promoted the developmental delay, mortality, morphological changes, and hatching inhibition in snail embryos in a concentration-dependent manner. CMC-SeNPs are 2.6 times more embryotoxic compared to CS-SeNPs indicating the importance of surface coating on the embryotoxicity. Moreover, the results revealed that although both forms of Se inhibited the embryo development and reduced the hatching of L. stagnalis, the mode of action on the embryogenesis was different. SeNPs had a higher toxicity to snails’ embryos compared to their dissolved counterparts. Despite significant dissolution, by comparing the SeNPs with their dissolved fraction, the results suggest SeNPs inhibition effect on the snail development could be caused by both SeNPs and Se⁴⁺, and SeNPs might be the major development retardation driver rather than Se ions. The present study evidenced by the first time the toxicity effects of SeNPs on the snail embryogenesis, and highlighted how SeNPs intrinsic properties influence their transformation and toxicity in environmental relevant scenarios.
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The world population has been stated to increase tremendously to 9 billion in the year 2050. Therefore, there is a need to explore significant numerous mineral elements that have not be explored before. The earth crust is blessed with numerous essential minerals which could play an essential function in the growth of sustainable agriculture and increase food production as well as the maintenance of a cleaner environment. Therefore, this chapter explores the significance of geochemistry in the identification of useful mineral element that could boost agricultural production and their significant role in the decontamination of heavily polluted soil and water. Special highlights were made on various classifications of geochemistry, chemical composition, as well as their benefits most especially in the area of sustainable agriculture. Detailed information was provided on the significance of geochemical effects of heavy metals on crops health.
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Geochemistry is the branch of science that uses the tools and philosophies of chemistry to give detail of the mechanisms regulating the working past and present of the earth. Geochemistry has an application in livestock like geochemistry in animal health and geochemistry and the nutrition of agriculture livestock. Geochemistry has been identified with several benefits most especially in animal health which involves dealing with the pathological and metabolic effects of different elements on animal health as well as in the nutrition of agriculture livestock which deals with the amount of ingested elements by the grazing animals. Therefore, this chapter intends to highlight the benefits of geochemistry in livestock most especially in the adequate maintenance of animal health and animal nutrition. Special highlights were also made on the significance of numerous minerals that have several roles in effective production of livestock.
Chapter
Contamination of soil with selenium (Se) has become an urgent problem globally due to the toxicity Se poses to human, plants, animals, and the environment at high concentrations. Selenium occurs naturally in soils, with the primary source originating from weathering of Se‐containing rocks. While Se is essential for humans and animals at low concentrations, agricultural and industrial processes have created soil Se pollution at toxic levels. The general non‐toxic concentration of Se for adults is approximately <300 μg Se/d, whereas grazing animals can tolerate up to 5000 μg Se/kg before exhibiting symptoms of selenosis. Soil‐derived Se may be consumed by humans indirectly through contaminated crops or drinking water; however, the chemical speciation of Se greatly influences its toxicity. Solubility of Se is generally low, with the greater potential for ingestion of toxic levels from plants or animal meat contaminated through soils. This chapter will discuss the biogeochemistry, essential nutrient status, Se sources, forms, and concentrations of Se in different environments, toxicity, human health concerns, environmental pollution risks, and cycling of selenium within the soil environment. We will examine the Se soil contamination and discuss the current body of soil remediation techniques. Conventional soil remediation techniques include phytoremediation, immobilization of Se in the soil through iron or microbial mechanisms, or loss of Se through volatile pathways (microbial or through phytoextraction), and electrokinetics to concentrate Se at one electrode. Recent innovative remediation strategies for Se soil contamination include the use of more reactive iron nanomaterials, soil washing to extract Se for reuse, or combined methodologies using two or more innovative and conventional approaches. Our discussion will also include advantages or disadvantages of each remediation method.
Chapter
Potable and usable water is one of the major environmental issues for the sustainable development of the. Water has been contaminated by various sources, including industrial, agriculture, domestic, and other sources. Selenium is one of the contaminants that significantly affects life on Earth. Selenium is found as a contaminant in water in various forms including selenate and selenites. It also has promising applications in various sectors including as a catalyst. The removal of selenium down to permissible limits is challenging and conventional methods have been suffering with certain limitations including its cost‐intensive nature. Process intensification has been widely considered for the development of wastewater treatment equipments and methods and same can be considered for treatment of selenium. This chapter provides an overview of selenium and wastewater, the basics of process intensification and its application in wastewater treatment, conventional methods with intensified approaches and scope for intensification, intensified methods and equipments, and an overall discussion and conclusion have been elaborated to understand the process intensification for selenium recovery and treatment from wastewater.
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After major pollution by nitrates and pesticides, soils and groundwater in some parts of the world are now facing the emergence of a third major issue of selenium (Se) contamination. Selenium occurrence in ecosystems results naturally from weathering of Se-containing rocks, and is further aggravated by human activities. Selenium is ubiquitous in the environment, and the two main sources of human exposure by Se are food and water. Se, a metalloid, is an important micronutrient due to Se antioxidant, anti-inflammatory and chemo-preventative properties. At normal dietary doses, selenium is an essential diet element that has nutritional properties and is necessary to maintain good health in humans and animals. Nonetheless, exposure to high concentrations of selenium is harmful to living beings. In terms of contamination, selenium as an emerging hazardous substance is receiving particular attention in developing countries, where research is focussing on water treatment. Actual remediation techniques are limited because removing Se from complex mixtures of substances is very challenging. Yet, techniques of water decontamination are developing rapidly. Here, we review selenium occurrence, pollution, properties and remediation. Advanced remediation include technologies based on zero-valent iron, iron-oxy-hydroxides, supported materials, nanofiltration, reverse osmosis, enhanced ultrafiltration, electrodialysis, and activated granular sludge.
Article
For the first time in laboratory, the diffusion behavior of Se(IV) in Tamusu clayrock core was studied by means of through-diffusion method. The effects of pH, ionic strength and humic acid on the diffusion behavior of Se(IV) in clayrock were studied. The effective diffusion coefficient, distribution coefficient and rock capacity factor value were obtained. The diffusion mechanism of radionuclide in Tamusu clayrock is discussed, which can provide experimental data support and theoretical references for the pre-selection of clayrock sites and safety assessment in China’s high-level radioactive waste deep geological repository.
Article
Carbothermal reduction is a convenient and cost-effective method to produce biochar (BC) supported iron-based nano-particles (INP) for oxyanion contaminants removal. However, considering the possible desorption of the target oxyanion during change of the surrounding environment, the detailed removal mechanisms remain unclear and the long-term efficiency of different INPs cannot be predicted. In this study, different BC/Fe composites were synthesized by controlling the pyrolysis temperatures (500 °C to 800 °C). BC/Fe3O4 composite synthesized at 500 °C (BC/Fe500) possessed the strongest surface acidity thus with the best SeO4²⁻ removal performance, and BC/Fe⁰/Fe3O4 composite synthesized at 650 °C (BC/Fe650) possessed the best reducing ability toward SeO4²⁻. Through the co-removal experiments (SeO4²⁻ and common competing oxyanions co-existed) and the investigation of Se stability loaded on BC/Fe composites, the removal of SeO4²⁻ by BC/Fe500 through highly reversible adsorption could not achieve long-term immobilization of Se, making it an appropriate adsorbent for pre-treatment only, while the efficient reduction of SeO4²⁻ to Se⁰ by BC/Fe650 could largely improve its long-term stability. This study supplies a possible strategy for Se immobilization against common competing oxyanions.
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Adsorption is one of the method that is in use for remediation of contaminated water. The experimental factors affecting the batch mode of adsorption of various metals and inorganic anions are discussed in this book. The elemental contaminants have been categorized into four major categories i.e. major toxic elements; essential elements having toxicity on excessive exposure; miscellaneous elements having undetermined effects; non-toxic elements having trivial or unidentified significance. In addition, anions like nitrate, perchlorate and sulphate as water contaminants are considered. This unique volume fills a niche in the area of water treatment. Key Features: Provides practitioners with the background they need to understand and apply batch adsorption processes to the purification of water Describes the actions of adsorption capacity or percentage removal with respect to factors affecting the adsorption process Excellent source of information for those working in the industry for remediation of metals and anions Discusses the current era of Anthropocene which is highly dependent on the anthropogenic mineral sources for its sustenance
Chapter
Globally, mankind is suffering from numerous diseases and nutritional deficiencies. The rapid increase in the population of the whole world has aggravated this scenario. The population of mankind has been stipulated to increase tremendously to 9 billion in the year 2050. Some of the challenges currently experience by majority of the global population includes suffering from several diseases, nutritional deficiencies, tropical diseases, etc. Therefore, there is a need to harness all the various natural resources available in the soil and rocks, which are present in every part of the world. Proper understanding of the benefits and demerits of these essential elements might be a proper way in establishing the role in alleviating several health challenges, nutritional disorderliness, and their application in the management of human diseases. Therefore, this chapter intends to report detailed information on the application of these essential minerals for the treatment of human diseases, like dental problem, cancer, hypertension, cardiovascular diseases (CVDs), goiter, and many more. Special attention was also laid on the application of these essential elements for the management of animal and plant diseases. Also, special highlights were made on some factor like temperature, rainfall, and hardness of water that affect the geochemical nature.
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Background: Selenium is a trace element that has been reported to be effective in regulating glucose and lipid metabolism. However, there is conflicting evidence from different clinical trials of selenium supplementation in treating cardiometabolic diseases (CMDs). Objective: This meta-analysis aimed to identify the effects of selenium supplementation on insulin resistance, glucose homeostasis, and lipid profiles in patients with CMDs. Methods: Randomized controlled trials (RCTs) of selenium supplementation for treating CMDs were screened in five electronic databases. Insulin levels, homeostatic model assessment of insulin resistance (HOMA-IR), fasting plasma glucose (FPG), and glycosylated hemoglobin A1C (HbA1c) were defined as the primary outcome markers, and lipid profiles were considered the secondary outcome markers. Results: Ten studies involving 526 participants were included in the meta-analysis. The results suggested that selenium supplementation significantly reduced serum insulin levels (standardized men difference [SMD]: -0.53; 95% confidence interval [CI] [-0.84, -0.21], p = 0.001, I2 = 68%) and HOMA-IR (SMD: -0.50, 95% CI [-0.86, -0.14], p = 0.006, I2 = 75%) and increased high-density lipoprotein cholesterol (HDL-C) levels (SMD: 0.97; 95% CI [0.26, 1.68], p = 0.007, I2 = 92%), but had no significant effect on FPG, total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), and very low-density lipoprotein cholesterol (VLDL-C). Conclusion: Current evidence supports the beneficial effects of selenium supplementation on reducing insulin levels, HOMA-IR, and increasing HDL-C levels. Selenium supplementation may be an effective strategy for reducing insulin resistance in patients with CMDs. However, more high-quality clinical studies are needed to improve the certainty of our estimates.
Article
Selenium (Se) is essential for animals and humans, and studies assessing the influence of sulfur (S) and phosphorus (P) on Se availability and biofortification in tropical soils are required. This study evaluated the adsorption of selenate (SeVI) and selenite (SeIV) in two oxidic soils with contrasting soil texture and assessed effects of phosphate and sulfate as competitive anions on Se desorption. The study also examined Se biofortification of Panicum maximum cv. Mombaça grown in Se-treated clayey soil under increasing rates of P fertilisation. In the laboratory, different Se concentrations were added to soils for adsorption studies (0, 1, 2, 4 mg L-1 for SeVI and 0, 4, 8, 16 mg L-1 for SeIV), with Se desorption performed by adding different concentrations of P (0, 2.18, 4.36, 10.90, 21.90 mg L-1) or S (0, 3.75, 7.5, 15, 30 mg L-1). Mombaça grass was grown in pots for 43 days in the clayey soil fertilised with SeVI and increasing P rates. Selenium adsorption varied depending on Se speciation, Se rate and soil texture, with SeIV showing greater adsorption than SeVI. In general, amounts of SeVI desorbed increased with increasing addition of P and (mainly) S. However, only P had a positive effect for releasing SeIV from soils. At all SeVI rates added in the clayey soil, Se contents in the shoot dry matter of Mombaça grass increased with increasing P fertilisation rate, agreeing with the desorption results. Further studies combining desorption with biofortification data are recommended for assessing the influence of P in sandy clay loam tropical soils.
Article
The distribution, speciation, and bioavailability of selenium (Se) - an essential micronutrient for human beings - in agricultural soils influence the resource recovery of agricultural benefits and the sustainable use of Se in agroecosystems. Quantitative understanding in this regard however remains limited in the world's mollisol agroecosystems, despite their critical importance in securing global food supply. Herein, a systematic investigation of Se in the river sediment-irrigation water-mollisols-rhizosphere-rice seeds continuum, at the core zone of the northern mollisol regions, was conducted to elucidate the hydrological-hydrogeochemical processes and mechanisms responsible for the distribution and bioavailability of Se. The content of total Se in the mollisols ranged between 0.12 and 0.54 mg/kg with an average of 0.31 mg/kg. At the riverside flood plains, humic-acid bound Se accounted on average for 39 % of total Se. This pool of Se can be transformed to water-soluble and ion-exchangeable Se(VI), supporting a higher potential of Se bioavailability at riparian agricultural mollisols. For mollisol lands far from the river channels, the topography affects the speciation and partitioning of Se presumably through regulating water retention and organic matter transport. Moreover, altering pH and redox conditions in response to irrigation with the river water may boost Se bioavailability in weakly acidic and high Eh mollisols. It can be in part ascribed to the transformation of organic-bound Se along with infiltrated oxygenated water that leads to the increase of water-soluble and ion-exchangeable Se. These findings reinforce that hydrological-hydrogeochemical perturbations due to irrigation with surface water need to be assessed carefully in the management of Se resources in the mollisol agroecosystems.
Chapter
Selenium (Se) is a crucial element with high metabolic activity for human health. The primary source of Se for animals and humans is diet. Dietary intakes of Se depend on geographical conditions, levels of the element in the soil, agricultural practices, type of diet, whether meat-eating or vegetarian, rich in seafood or not, and, most of all, the economic conditions of consumers. The distribution, absorption, and excretion of Se in the body after ingestion depend on many factors, especially the chemical form and total amount of the element in the diet. The kidney, liver, skeletal muscle, pancreas, and heart have the highest Se concentration. Se level is generally measured in plasma, serum, whole blood, or erythrocytes. Urinary Se is a safe marker for the latest Se uptake rather than a vital identification for Se status. It has a narrow range of doses that are essential for humans and associated with side effects. The recommended amount of dietary Se per day varies by gender and age. Se deficiency can cause health disorders such as mental retardation, goiter, muscular dystrophy, immune system, or bone diseases, although excess Se can cause death due to toxicity. Optimum selenoprotein expression and adequate level of Se intake protect from free-radical oxidation. Se is identified as an agent to prevent cardiovascular diseases, muscle disorders, some forms of cancer, and Alzheimer’s disease, as an inhibitor of viral expression, and as a delaying factor in the progression of AIDS and the aging process in HIV-positive patients.KeywordsSeleniumHumanAnimalHealthDisease
Article
Composite materials of porous MIL-100(Fe) and bulk iron oxides, including MIL-100(Fe)@Aka and MIL-100(Fe)@Hem, were prepared through in-situ growth of iron oxides and MIL-100(Fe) using hydrothermal method. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric (TG) and pore analysis revealed two phases of crystal MIL-100(Fe) and akaganeite/hematite in the composite materials. Iron oxides were not only cemented with the surface of MIL-100(Fe) but also integrated into the pores of MIL-100(Fe). Especially, the hematite was likely to get more favor to in-situ grow with MIL-100(Fe) and form the well-crystallized composite. Compared with MIL-100(Fe), MIL-100(Fe)@Aka exhibited more stable surface charge in the pH range of 3.0–8.0, and MIL-100(Fe)@Hem displayed a higher density of active sites. Both MIL-100(Fe)@Aka and MIL-100(Fe)@Hem showed spontaneous and exothermal adsorption for Se(IV), which could be well described by the linear driven forces model. MIL-100(Fe)@Aka and MIL-100(Fe)@Hem had an obvious synergistic effect on Se(IV) adsorption. The introduction of akaganeite and hematite into MIL-100(Fe) could enhance its adsorption capacity for Se(IV) by a maximum of 154% and 153% respectively, and the saturated adsorption capacity of MIL-100(Fe)@Hem0.1 was up to 301.93 mg/g as fitted by Sips model. The X-ray photoelectron spectrum (XPS) of external-electron revealed that the oxidation state of Fe atoms decreased after adsorbing Se(IV). The findings in this study are expected to reveal the synergistic effect of porous MIL-100(Fe) and bulk iron oxides for greatly improving the adsorption capacity towards pollutants, and provide some guidance for the development of effective adsorbents to be used in environmental remediation.
Chapter
Selenium (Se) is a trace element and when present in minute quantities, it becomes an essential component of biotic and abiotic ecosystem. But if present in excess, causes metal toxicity. It is released in the environment by natural and anthropogenic activities and exist in various oxidation states and inorganic and organic forms. Selenium bioavailability in soil is usually measured in terms of water-soluble Se fraction which can be uptaken by plants and enter into other biotic components through food chain/food web. Various remediation techniques are available to detoxify the adverse effects of heavy metal(Se) pollution in soil, phytoremediation being the most effective one as it re-establishes the natural conditions of soil.
Article
Oxidative damage induced by ethanol and its metabolites is one of the factors that fuels the development of alcoholic liver disease (ALD). Selenium (Se) is an effective cofactor for glutathione peroxidase (GPx), and has antioxidant effects that improve ALD. In patients with ALD, ethanol-induced oxidative damage inhibits the synthesis of related Se-containing proteins such as: selenoprotein P (Sepp1), albumin (ALB), and GPx in the liver, thus decreasing the overall Se level in patients. Both Se deficiency and excess can affect the expression of GPx, resulting in damage to the antioxidant defense system. This damage enhances oxidative stress by increasing the levels of reactive oxygen species (ROS) in the body, which aggravates the inflammatory response, lipid metabolism disorder, and lipid peroxidation and worsens ALD symptoms. A cascade of oxidative damages caused by ALD will deplete selenium deposition in the body, stimulate the expression of Gpx1, Sepp1, and Gpx4, and thus mobilize systemic selenoproteins, which can restore GPx activity in the hepatocytes of ALD patients, reduce the levels of reactive oxygen species and alleviate oxidative stress, the inflammatory response, lipid metabolism disorder, and lipid peroxidation, thus helping to mitigate ALD. This review provides a reference for future ALD studies that evaluate the regulation of Se levels and contributes to studies on the potential pathological mechanisms of Se imbalance in ALD.
Article
The atmosphere is a temporal reservoir of selenium (Se). Understanding the chemical reactions and speciation of Se in primary emissions is crucial because atmospheric deposition is an important source of both Se contamination and micronutrients for terrestrial (agricultural) systems. In this study, the concentrations of selenite and selenate in acid cloud water (pH 4.3 average), including non-precipitating and precipitating clouds, were analyzed at a site near the summit of Mt. Norikura (2770 m a.s.l.), central Japan. The soluble Se in cloud water has a positive correlation with that of non-sea-salt sulfate, implying that the Se was incorporated in ammonium sulfate. The ammonium sulfate was generated from fossil fuel combustions in industrial and urban areas of southwest Japan and China. The concentrations of selenite and selenate in cloud water gradually decreased with a rise in acidity (pH) in approximately the same proportion. The coexistence of selenite and selenate perhaps indicates an oxidation-reduction equilibrium for the HSeO3⁻–SeO4²⁻ couple. For the precipitating cloud water, the selenite was the dominant species in all cloud events. This may be attributed to scavenging of local coal-combustion aerosols from southwest Japan by the rain droplets (washout). The selenite/selenate ratios of clouds as well as precipitating clouds were not correlated with gaseous O3 concentrations and remained stable throughout both day and night. In addition, laboratory experiments with Se–hydrogen peroxide (H2O2) solutions mimicking the cloud water conditions indicated that selenious acids (HSeO3⁻) cannot be oxidized with H2O2. The observational and experimental results suggest that the Se oxidation states in acid clouds are not caused by oxidation by the possible oxidants for SO2 such as H2O2 and O3.
Article
The synthesis of organoselenium compounds through C–Se bond-forming has attracted immense attention due to their biological values and extensive pharmaceutical applications. As a result, diverse selenating reagents have been developed over the past few decades for this purpose. In particular, elemental selenium (Se), with the advantages of being non-toxic, odorless and chemically stable, has gained numerous interests as it showed great potentials for the formation of variously valuable organoseleniums via direct incorporation of Se atom into target molecules in a simple way. Moreover, direct C–H bond selenation with elemental Se has been considered as a highly atom-economic method to C–Se bond formation because it avoided substrate pre-activation. In view of the importance of organoselenium compounds, this review highlights the recent advances in organic synthesis involving elemental Se since 2002, which would be useful for researchers in the learning of Se for organic reactions.
Article
The mechanisms of abiotic sequestration of Se(VI) and Se(IV) on a sample of coal waste rock collected from the Elk Valley, Canada and on three pure mineral species (i.e., siderite, pyrite, and sphalerite) present in coal waste rock were assessed using sterile batch testing under water-saturated, anoxic conditions. Only siderite removed measurable Se(VI) from the test solutions with ~90% removal after 100 d attributed to initial adsorption to the siderite surface as Se(VI) and subsequent reduction to Se(VI) and Se(0). In contrast to Se(VI), all samples removed Se(IV) from the aqueous solutions. The rate of Se(IV) removal was pyrite > siderite > waste rock > sphalerite. The waste rock sample removed Se(IV) from solution in two stages: up to ~40% of the aqueous Se(IV) was rapidly removed (by day 1) followed by slower removal of Se(IV) with up to ~97% removal after 99 d. Se(IV) removal is attributed to the adsorption of Se(IV) and subsequent reduction to Se(0) onto the siderite and pyrite phases of the waste rock. The initial (1 d) removal of Se(IV) by waste rock was characterized using a distribution coefficient (Kd) of 15.5 L/kg. Longer-term Se(IV) removal was fitted with zero and first order removal rates. The removal of Se(IV) by sphalerite was minor and deemed to have a minimal effect on Se sequestration in the waste rock. Desorption tests on waste rock showed that the fraction of sequestered Se susceptible to desorption decreased with time as adsorbed Se(IV) was reduced to insoluble Se(0). These findings show that abiotic Se sequestration can occur in saturated, anoxic zones in coal waste rock dumps.
Article
Selenium is an essential micronutrient for the human body, given its various health benefits. However, Se deficiency is widespread globally, and dietary adjustment is a feasible way to supplement people's Se daily intake. The Multi-purpose Regional Geochemical Survey (NMPRGS) conducted in Hainan Island found an abundance of Se-rich soil. These Se resources have been utilized to grow naturally Se-rich produce. However, insufficient research has been conducted into the spatial distribution and enrichment of soil Se in Hainan Island. This paper analysed the effect of the environmental impact factors (parent rock, precipitation, etc.) on soil Se, using data from the NMPRGS database. The results showed that, in comparison to the baseline value of Chinese soil, the enrichment degree of Se in the topsoil of Hainan Island was higher, but its distribution was uneven. The parent rock, precipitation, soil type, and soil characteristics all affect the concentration and spatial distribution of regional soil Se. Geographically weighted regression showed that Iodine, pH, SOC, and TFe2O3 have a non-stationarity spatial relationship with Se. There was a significant correlation between soil Se and Chemical alteration index (CIA) in granite areas, while CIA was also related to mean annual precipitation (MAP). The concentration enrichment factor values of Se show that the external input of Se in high MAP areas is significantly higher than that in low MAP areas. Based on these results, three important environmental impact factors on soil Se enrichment at the regional scale in Hainan Island were defined: 1) Se-rich rocks; 2) precipitation; 3) SOC. These results can provide guidance for the planning and layout of Se-rich agriculture.
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Biochar–soil microbiota interactions may occur within a short or long period of time after application, and the behaviour of biochar could determine their impacts on soil. In comparison, modifications in soil microbiota function, structure, biomass and/or ecosystemic function following biochar application could translate to changes in soil fertility leading to positive and/or negative impacts. Amendment of soil with biochar has been evaluated globally as a means of improving soil health, fertility and increase soil microbial biomass. However, little is known about the mechanisms through which biochar modulates soil microbial activity or implications of these interactions. This review unravels possible interactions that may occur during soil–biochar contact time and the impacts on soil microbial function. Furthermore, the paper discusses interactions between biochar and microbial groups (such as bacteria, fungi, nematode, archaea, enzymatic activities), and elucidates possible factors that may influence biochar–microbiota behaviour in the soil environment. It also considers the implications for the associated biota and feasibility of applying biochar in weathered soils and/or contaminated land remediation. Finally, the review highlights knowledge gaps and future research directions.
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Understanding the algal toxicity of selenium nanoparticles (SeNPs) in aquatic systems by considering SeNPs physicochemical properties and environmental media characteristics is a concern of high importance for the evaluation and prediction of risk assessment. In this study, chitosan (CS) and sodium carboxymethyl cellulose (CMC) coated SeNPs are considered using Lake Geneva water and a Waris-H cell culture medium to investigate the effect of SeNPs on the toxicity of algae Poterioochromonas malhamensis, a widespread mixotrophic flagellate. The influence of surface coating, z-average diameters, ζ-potentials, aggregation behavior, ions release, and medium properties on the toxicity of SeNPs to algae P. malhamensi was investigated. It is found that SeNPs are 5–10 times more toxic in Lake Geneva water compared to the culture medium, suggesting that the traditional algal tests in Waris-H culture medium currently underestimate the toxicity of NPs in a natural water environment. Despite significant dissolution, it is also found that SeNPs themselves are the toxicity driver, and dissolved ions have only a marginal influence on toxicity. SeNPs diameter is found a minor factor in toxicity. Based on a principal component analysis (PCA) it is found that in Lake Geneva water, the nature of the surface coating (CMC versus CS) is the most influential factor controlling the toxicity of SeNPs. In the culture medium, surface coating, ζ-potential, and aggregation are found to contribute at the same level. These results highlight the importance of considering in details both NPs intrinsic and media properties in the evaluation of NPs biological effects.
Article
Application of selenium nanoparticle (SeNP)-based fertilizers results in the release of SeNPs to aquatic systems, where SeNPs may transform into inorganic selenite (Se(IV)) and selenate (Se(VI)) with higher toxicity. However, methods for the speciation analysis of different Se species are lacking, hindering the accurate assessment of the risks of SeNPs. Herein, for the first time, a Triton X-45 (TX-45)-based dual-cloud point extraction (CPE) method was established for the selective determination of SeNPs, Se(IV), and Se(VI) in water. TX-45 can adsorb on the surface of SeNPs and facilitate the extraction of SeNPs into the lower TX-45-rich phase in the first CPE, while Se(VI) and Se(IV) retain in the upper aqueous phase. In the second CPE, Se(IV) can selectively associate with diethyldithiocarbamate and be concentrated in the TX-45-rich phase, whereas Se(VI) remains in the upper phase. Different Se species can be isolated and then quantified by ICP-MS. The presence of coexisting ions and dissolved organic matter (0-30 mg C/L) did not interfere with extraction and separation. The feasibility of the presented method was confirmed by the analysis of natural water samples, with a detection limit of 0.03 μg/L and recoveries in the ranges of 61.1-104, 65.5-113, and 80.3-131% for SeNPs, Se(IV), and Se(VI), respectively. This study aims to provide an effective method to track the fate and transformation of SeNPs in aquatic systems and further contribute to estimating the potential risks of SeNPs to environmental organisms and human bodies.
Chapter
Algae can absorb and accumulate exogenous selenium (Se) from their environment through physicochemical and biological mechanisms. Nutritional essentiality to Se, the dose and Se speciation influence its uptake in different algal taxa and represent crucial factors in their cellular response. This chapter summarises previous studies and key concepts regarding Se utilisation, transport and accumulation in algae, its protective and regulatory role as well as interference of Se with sulphur metabolism and its toxicity. It highlights the importance of the algal Se detoxification strategy, especially the role of selenoenzymes and other selenoproteins with antioxidant function. The ecological aspect of Se resources, the role of algae in its biotransformation and cycling in aquatic environments is also addressed. In addition, the potential of algae as Se bioindicators and accumulators, and their applications are presented.
Article
The biogeochemical behavior of selenium (Se) has been extensively studied in Se-enriched or Se contaminated soils at low and middle latitudes. However, the Se distribution patterns have not been studied in tundra ecosystems of remote Antarctica. Here, the soils/sediments were collected from penguin and seal colonies, their adjacent tundra and lakes, tundra marsh, human-activity areas, normal tundra and the periglacial in maritime Antarctica, and total Se and seven operationally defined Se fractions were analyzed. Overall the regional distribution of Se levels showed high spatial heterogeneity (coefficient of variation, CV = 114%) in tundra soils, with the highest levels in penguin (mean 6.12 ± 2.66 μg g⁻¹) and seal (mean 2.29 ± 1.43 μg g⁻¹) colony soils, and the lowest in normal tundra soils and periglacial sediments (<0.5 μg g⁻¹). The contribution rates of penguins and seals to tundra soil Se levels amounted to 91.7% and 78.0%. The lake sediment Se levels (mean 2.15 ± 0.87 μg g⁻¹) close to penguin colonies were one order of magnitude higher than those (mean 0.49 ± 0.87 μg g⁻¹) around normal tundra. Strong positive correlations (p < 0.01) of Se concentrations between lake sediments and adjacent tundra soils, and lower Se: P (<0.001) and S: P (<1) ratios in the lake sediments close to penguin colonies, indicated the infiltration or leaching of penguin guano as the predominant Se source in lake sediment. The Se species in penguin and seal guano were dominated by SeCys2 (76.6%) and SeMet (73.5%), respectively. The evidence from the predominant proportions of total organic matter-bound Se (Seom, 67%–70% of total Se) in penguin or seal colony soils further supported penguin or seal guano had a great influence on the distribution patterns of Se fractions in the tundra. This study confirmed that sea animal activities transported substantial amount Se from ocean to land, and significantly altered the biogeochemical cycle of Se in maritime Antarctica.
Chapter
Biochar–soil microbiota interactions may occur within a short or long period of time after application, and the behaviour of biochar could determine their impacts on soil. In comparison, modifications in soil microbiota function, structure, biomass and/or ecosystemic function following biochar application could translate to changes in soil fertility leading to positive and/or negative impacts. Amendment of soil with biochar has been evaluated globally as a means of improving soil health, fertility and increase soil microbial biomass. However, little is known about the mechanisms through which biochar modulates soil microbial activity or implications of these interactions. This review unravels possible interactions that may occur during soil–biochar contact time and the impacts on soil microbial function. Furthermore, the paper discusses interactions between biochar and microbial groups (such as bacteria, fungi, nematode, archaea, enzymatic activities), and elucidates possible factors that may influence biochar–microbiota behaviour in the soil environment. It also considers the implications for the associated biota and feasibility of applying biochar in weathered soils and/or contaminated land remediation. Finally, the review highlights knowledge gaps and future research directions.
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a2 University Department of Clinical Biochemistry, The Royal Infirmary, Edinburgh EH3 9YW
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Se is an unusual trace element in having its own codon in mRNA that specifies its insertion into selenoproteins as selenocysteine (SeCys), by means of a mechanism requiring a large SeCys-insertion complex. This exacting insertion machinery for selenoprotein production has implications for the Se requirements for cancer prevention. If Se may protect against cancer, an adequate intake of Se is desirable. However, the level of intake in Europe and some parts of the world is not adequate for full expression of protective selenoproteins. The evidence for Se as a cancer preventive agent includes that from geographic, animal, prospective and intervention studies. Newly-published prospective studies on oesophageal, gastric-cardia and lung cancer have reinforced previous evidence, which is particularly strong for prostate cancer. Interventions with Se have shown benefit in reducing the risk of cancer incidence and mortality in all cancers combined, and specifically in liver, prostate, colo-rectal and lung cancers. The effect seems to be strongest in those individuals with the lowest Se status. As the level of Se that appears to be required for optimal effect is higher than that previously understood to be required to maximise the activity of selenoenzymes, the question has been raised as to whether selenoproteins are involved in the anti-cancer process. However, recent evidence showing an association between Se, reduction of DNA damage and oxidative stress together with data showing an effect of selenoprotein genotype on cancer risk implies that selenoproteins are indeed implicated. The likelihood of simultaneous and consecutive effects at different cancer stages still allows an important role for anti-cancer Se metabolites such as methyl selenol formed from gamma-glutamyl-selenomethyl-SeCys and selenomethyl-SeCys, components identified in certain plants and Se-enriched yeast that have anti-cancer effects. There is some evidence that Se may affect not only cancer risk but also progression and metastasis. Current primary and secondary prevention trials of Se are underway in the USA, including the Selenium and Vitamin E Cancer Prevention Trial (SELECT) relating to prostate cancer, although a large European trial is still desirable given the likelihood of a stronger effect in populations of lower Se status.
Article
An endemic disease was discovered in 1961 in parts of the population of Enshi County, Hubei Province of the People's Republic of China. During the years of the highest prevalence, from 1961 to 1964, the morbidity was almost 50% in the 248 inhabitants of the five most heavily affected villages; its cause was determined to be selenium intoxication. The most common sign of the poisoning was loss of hair and nails. In areas of high incidence, lesions of the skin, nervous system, and possibly teeth may have been involved. A case is reported of a middle-aged, female hemiplegic, whose illness and death apparently were related to selenosis. Daily dietary intakes of selenium, estimated after the peak prevalence had subsided, averaged 4.99 (range 3.20 to 6.69) mg and hair and blood selenium levels averaged 32.2 and 3.2 µg/ml, respectively. Up to l000× differences occurred when selenium contents of vegetables, cereals, scalp hair, blood, and urine from the selenosis areas were compared with those from Keshan disease (selenium deficiency) areas. The ultimate environmental source of selenium was a stony coal of very high selenium content (average more than 300 µg/g; one sample exceeded 80,000 µg/g). Selenium from the coal entered the soil by weathering and was available for uptake by crops because of the traditional use of lime as fertilizer in that region. This particular outbreak of human selenosis was due to a drought that caused failure of the rice crop, forcing the villagers to eat more high-selenium vegetables and maize and fewer protein foods.
Article
Selenium deficiency was suspected to be a factor in the aetiology of esophageal cancer in the Linxian and Cixian regions of the People’s Republic of China and vitamin trials in the Linxian area indicated that combined supplementation with β-carotene, vitamin E and Se reduced the mortality rate. In order to further evaluate the role of Se, the distribution of total Se in cultivated topsoils, grain, human hair and drinking water was studied in 15 villages in the Cixian area, People’s Republic of China, which in the 1980–1990s had one of the highest mortality rates from esophageal cancer in the world. This study demonstrated that total Se concentrations in drinking water, soil, grain and hair increase from the low esophageal cancer area to the high cancer area, contrary to the expected trend. This suggests that Se deficiency does not play a major role in the aetiology of esophageal cancer in the study area. Nitrate in drinking water is much higher in the area with high esophageal cancer mortality rate than in the low mortality rate area, and this may be a significant factor. Mycotoxins (especially fumonisin), nitrosamine and nitrosamine precursors in grain, in drinking water, and dietary β-carotene and Vitamin E remain as potential factors which need to be evaluated further.
Article
The distribution of Se in cultivated topsoils, grains, human hair and drinking water has been studied in 15 villages from a Keshan disease area of the People's Republic of China, villages being classified into 3 groups according to the Keshan disease incidence in the local population. In grain, hair and water the total Se follows expected trends; i.e. the highest concentrations are found in the villages where there is no incidence of Keshan disease. However, the soils from the high-incidence Keshan disease villages have the highest total Se content, an apparent contradiction, as Keshan disease is a response to a Se deficient environment. Soil analyses suggest that the organic content of the soils is a major factor in controlling the availability of Se and it is the high-incidence Keshan disease villages that have the most organic-rich soils. Although higher in total Se, the organic-rich soils have little bioavailable Se resulting in a Se deficient food chain. Soil pH is also seen to be a related factor in restricting the availability of Se and all the grain samples collected on soils with a pH <7.6 had a total Se content of less than 10% of the total soil Se. In an environment that can be classified as Se deficient small changes in the soil organic content and pH can have a critical affect on the Keshan disease status of a village.
Article
An endemic disease was discovered in 1961 in parts of the population of Enshi County, Hubei Province of the People's Republic of China. During the years of the highest prevalence, from 1961 to 1964, the morbidity was almost 50% in the 248 inhabitants of the five most heavily affected villages; its cause was determined to be selenium intoxication. The most common sign of the poisoning was loss of hair and nails. In areas of high incidence, lesions of the skin, nervous system, and possibly teeth may have been involved. A case is reported of a middle-aged, female hemiplegic, whose illness and death apparently were related to selenosis. Daily dietary intakes of selenium, estimated after the peak prevalence had subsided, averaged 4.99 (range 3.20 to 6.69) mg and hair and blood selenium levels averaged 32.2 and 3.2 micrograms/ml, respectively. Up to 1000x differences occurred when selenium contents of vegetables, cereals, scalp hair, blood, and urine from the selenosis areas were compared with those from Keshan disease (selenium deficiency) areas. The ultimate environmental source of selenium was a stony coal of very high selenium content (average more than 300 micrograms/g; one sample exceeded 80,000 micrograms/g). Selenium from the coal entered the soil by weathering and was available for uptake by crops because of the traditional use of lime as fertilizer in that region. This particular outbreak of human selenosis was due to a drought that caused failure of the rice crop, forcing the villagers to eat more high-selenium vegetables and maize and fewer protein foods.
Article
The human dietary selenium requirement in China has been estimated by various methods. The minimum dietary selenium requirement for the prevention of Keshan disease (KD) was found to be around 17 micrograms/d. On the other hand, an intake of 40 micrograms/d is required to maintain the plasma glutathione peroxidase (GPx) activity at plateau. Hence 40 micrograms/d is considered as the adequate dietary selenium requirement. Studies conducted in a chronic selenosis area indicate that the toxic dietary selenium intake (adverse effect level), which would maintain the characteristic fingernail changes, was approximately 1600 micrograms/d. The mean value of dietary selenium intakes, which enabled the five patients to recover from fingernail lesions, was found to be 819 +/- 126 micrograms/d. At a 95% confidence limit, the lower limit is around 600 micrograms/d. Therefore, 600 and 400 micrograms/d were suggested as the individual daily maximum safe selenium intake and the safe dietary selenium intake, respectively. The results were used in the prevention of Se-related endemic KD and Kashin-Beck disease (KBD).
Article
To determine whether a nutritional supplement of selenium will decrease the incidence of cancer. A multicenter, double-blind, randomized, placebo-controlled cancer prevention trial. Seven dermatology clinics in the eastern United States. A total of 1312 patients (mean age, 63 years; range, 18-80 years) with a history of basal cell or squamous cell carcinomas of the skin were randomized from 1983 through 1991. Patients were treated for a mean (SD) of 4.5 (2.8) years and had a total follow-up of 6.4 (2.0) years. Oral administration of 200 microg of selenium per day or placebo. The primary end points for the trial were the incidences of basal and squamous cell carcinomas of the skin. The secondary end points, established in 1990, were all-cause mortality and total cancer mortality, total cancer incidence, and the incidences of lung, prostate, and colorectal cancers. After a total follow-up of 8271 person-years, selenium treatment did not significantly affect the incidence of basal cell or squamous cell skin cancer. There were 377 new cases of basal cell skin cancer among patients in the selenium group and 350 cases among the control group (relative risk [RR], 1.10; 95% confidence interval [CI], 0.95-1.28), and 218 new squamous cell skin cancers in the selenium group and 190 cases among the controls (RR, 1.14; 95% CI, 0.93-1.39). Analysis of secondary end points revealed that, compared with controls, patients treated with selenium had a nonsignificant reduction in all-cause mortality (108 deaths in the selenium group and 129 deaths in the control group [RR; 0.83; 95% CI, 0.63-1.08]) and significant reductions in total cancer mortality (29 deaths in the selenium treatment group and 57 deaths in controls [RR, 0.50; 95% CI, 0.31-0.80]), total cancer incidence (77 cancers in the selenium group and 119 in controls [RR, 0.63; 95% CI, 0.47-0.85]), and incidences of lung, colorectal, and prostate cancers. Primarily because of the apparent reductions in total cancer mortality and total cancer incidence in the selenium group, the blinded phase of the trial was stopped early. No cases of selenium toxicity occurred. Selenium treatment did not protect against development of basal or squamous cell carcinomas of the skin. However, results from secondary end-point analyses support the hypothesis that supplemental selenium may reduce the incidence of, and mortality from, carcinomas of several sites. These effects of selenium require confirmation in an independent trial of appropriate design before new public health recommendations regarding selenium supplementation can be made
Article
Apart from the essential trace element iodine, which is the central constituent of thyroid hormones, a second essential trace element, selenium, is required for appropriate thyroid hormone synthesis, activation and metabolism. The human thyroid gland has the highest selenium content per gram of tissue among all organs. Several selenocysteine-containing proteins respectively enzymes are functionally expressed in the thyroid, mainly in thyrocytes themselves: three forms of glutathione peroxidases (cGPx, pGPx, and PH-GPx), the type I 5-deiodinase, thioredoxin reductase and selenoprotein P. The thyroidal expression of type II 5-deiodinase still is controversial. As thyrocytes produce H2O2 continuously throughout life an effective cell defense system against H2O2 and reactive oxygen intermediates derived thereof is essential for maintenance of normal thyroid function and protection of the gland. In experimental animal models long-term and strong selenium deficiency leads to necrosis and fibrosis after high iodide loads. Combined iodide and selenium deficiency such as in central Zaire is thought to cause the myxedematous form of endemic cretinism. Inadequate selenium supply and prediagnostically low serum selenium levels are significantly correlated with the development of thyroid carcinoma and other tumors. Though selenium supply controls expression and translation of selenocysteine-containing proteins no direct correlation is found between selenium tissue content and expression of various thyroidal selenoproteins, indicating that other regulatory factors contribute to or override selenium-dependent expression control, e.g., in thyroid adenoma, carcinoma or autoimmune disease. As both trace elements, iodine and selenium, were washed out from the upper layers of the soil during and after the ice ages in many regions of the world adequate supply with these essential compounds needs to be provided either by a balanced diet or supplementation.
Article
The association between viral disease and nutrition has long been thought to be due to effects on the host immune system. This theory suggests that when a host is malnourished, the immune system is compromised, and thus increased susceptibility to viral infection will occur. However, the virus itself may also be affected by the nutritional status of the host. We have demonstrated that a normally-benign strain of coxsackievirus B3 (CVB3/0) becomes virulent in either Se-deficient or vitamin E-deficient mice. Although the deficient animals are immunosuppressed, the virus itself is also altered. Six nucleotide changes were found in the virus that replicated in the deficient mice, and once these mutations occurred, even mice with normal nutrition became susceptible to disease. Thus, the nutritional status of the host was able to transform an avirulent virus into a virulent one due to genomic changes in the virus. We believe that a common mechanism of oxidative stress is the underlying cause of the genetic changes. Both vitamin E and Se act as antioxidants, and benign virus inoculated into GSH peroxidase (EC 1.11.1.9)-knockout mice will also convert to virulence due to genomic changes. Our work points to the importance of host nutrition during a viral disease, not only from the perspective of the host, but from the perspective of the viral pathogen as well.
Article
The relation between the trace element selenium and the etiology of cancer in humans remains elusive and intriguing, despite the number of epidemiologic studies published on the topic. We address some methodologic issues, such as misclassification of exposure, particularly to single selenium compounds, effect modification, confounding, and other sources of bias, which may explain the inconsistencies in the literature. We also review the results of cohort studies, which have yielded either inverse or null or direct associations between selenium exposure and subsequent cancer risk. To date, no beneficial effect on cancer incidence at major sites, including prostate cancer, has emerged from the Finnish program begun in 1984 to increase the average selenium intake in its population. Populations exposed to unusually high or low levels of environmental selenium might offer unique opportunities to investigate if selenium exposure is related to the etiology of human cancer.
Article
Endemic goitre has been reported in the climatic wet zone of south-west Sri Lanka for the past 50 years, but rarely occurs in the northern dry zone. Despite government-sponsored iodised salt programmes, endemic goitre is still prevalent. In recent years, it has been suggested that Se deficiency may be an important factor in the onset of goitre and other iodine deficiency disorders (IDD). Prior to the present study, environmental concentrations of Se in Sri Lanka and the possible relationships between Se deficiency and endemic goitre had not been investigated. During the present study, chemical differences in the environment (measured in soil, rice and drinking water) and the Se-status of the human population (demonstrated by hair samples from women) were determined for 15 villages. The villages were characterised by low (< 10%), moderate (10-25%) and high (> 25%) goitre incidence (NIDD, MIDD and HIDD, respectively). Results show that concentrations of soil total Se and iodine are highest in the HIDD villages, however, the soil clay and organic matter content appear to inhibit the bioavailability of these elements. Concentrations of iodine in rice are low (< or = 58 ng/g) and rice does not provide a significant source of iodine in the Sri Lankan diet. High concentrations of iodine (up to 84 microg/l) in drinking water in the dry zone may, in part, explain why goitre is uncommon in this area. This study has shown for the first time that significant proportions of the Sri Lankan female population may be Se deficient (24, 24 and 40% in the NIDD, MIDD and HIDD villages, respectively). Although Se deficiency is not restricted to areas where goitre is prevalent, a combination of iodine and Se deficiency could be involved in the pathogenesis of goitre in Sri Lanka. The distribution of red rice cultivation in Sri Lanka is coincident with the HIDD villages. Varieties of red rice grown in other countries contain anthocyanins and procyanidins, compounds which in other foodstuffs are known goitrogens. The potential goitrogenic properties of red rice in Sri Lanka are presently unknown and require further investigation. It is likely that the incidence of goitre in Sri Lanka is multi-factorial, involving trace element deficiencies and other factors such as poor nutrition and goitrogens in foodstuffs.
Article
The discovery that the juvenile cardiomyopathy known as Keshan disease likely has a dual etiology that involves both a nutritional deficiency of the essential trace mineral selenium (Se) as well as an infection with an enterovirus provided the impetus for additional studies of relationships between nutrition and viral infection. An amyocarditic strain of coxsackievirus B3, CVB3/0, converted to virulence when it was inoculated into Se-deficient mice. This conversion was accompanied by changes in the genetic structure of the virus so that its genome closely resembled that of other known virulent CVB3 strains. Similar alterations in virulence and genomic composition of CVB3/0 could be observed in mice fed normal diets but genetically deprived of the antioxidant selenoenzyme glutathione peroxidase (knockout mice). More recent research has shown that a mild strain of influenza virus, influenza A/Bangkok/1/79, also exhibits increased virulence when given to Se-deficient mice. This increased virulence is accompanied by multiple changes in the viral genome in a segment previously thought to be relatively stable. Epidemic neuropathy in Cuba has features that suggest a combined nutritional/viral etiology. Further research, both basic and applied, is needed to assess properly the possible role of malnutrition in contributing to the emergence of novel viral diseases.
Article
Selenium deficiency has been implicated in accelerated disease progression and poorer survival among populations infected with HIV in developed countries, yet these associations remain unexamined in developing countries. Among 949 HIV-1-infected Tanzanian women who were pregnant, we prospectively examined the association between plasma selenium levels and survival and CD4 counts over time. Over the 5.7-y median follow-up time, 306 of 949 women died. In a Cox multivariate model, lower plasma selenium levels were significantly associated with an increased risk of mortality (P-value, test for trend = 0.01). Each 0.1 micromol/L increase in plasma selenium levels was related to a 5% (95% CI = 0%-9%) decreased risk of mortality. Plasma selenium levels were not associated with time to progression to CD4 cell count < 200 cells/mm(3) but were weakly and positively related to CD4 cell count in the first years of follow up. Selenium status may be important for clinical outcomes related to HIV disease in sub-Saharan Africa.
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