Lower Se Concentrations Research Articles

Selenium in surface waters of the lower Athabasca River watershed: Chemical speciation and implications for aquatic life

Selenium in the lower Athabasca River (Alberta, Canada) is of concern due to potential inputs from the weathering of shallow bitumen deposits and emissions from nearby surface mines and upgraders. Understanding the source of this Se, however, is complicated by contributions from naturally saline groundwater and organic matter-rich tributaries. As part of a two-year multi-disciplinary study to assess natural and anthropogenic inputs, Se and its chemical speciation were determined in water samples collected along a ∼125 km transect of the Athabasca River and associated tributaries. Selenium was also determined in the muscle of Trout-perch (Percopsis omiscomaycus), a non-migratory fish species, that were sampled from selected locations. Dissolved (<0.45 μm) Se in the Athabasca River was consistently low in 2014 (0.11 ± 0.02 μg L−1; n = 14) and 2015 (0.16 ± 0.02 μg L−1; n = 21), with no observable increase from upstream to downstream. Selenate was the predominant inorganic form (∼60 ng L−1) and selenite was below detection limits at most locations. The average concentration of Se in Trout-perch muscle was 2.2 ± 0.4 mg kg−1 (n = 34), and no significant difference (p > 0.05) was observed between upstream and midstream (industrial) or downstream reaches. Tributary waters contained very low concentrations of Se (typically < 0.1 μg L−1), which was most likely present in the form of dissolved organic colloids.

Selenium and drinking water quality indicators in Mongolia.

Mongolia is characterized by restricted sources of drinking water and intensive water pollution due to high rates of urbanization, mining industry development, enormous amount of livestock, and ever-growing attempts in domestic production of cereals and vegetables. Among others, Se is the least studied element in Mongolian water resources. Based on fluorimetric method of analysis, the first results on Se levels in drinking water of five aimags, Ulaanbaatar, and Erdenet were obtained. Uneven distribution of Se in Mongolia was manifested, the highest Se concentrations being typical for the southern resources (up to 18,600μg/L) and the lowest, for the Northern ones (up to 0.022μg/L). ICP-MS data of Al, As, B, Ca, Cd, Co, Cr, Cu, Fe, Hg, I, K, Li, Mg, Mn, Na, Ni, P, Pb, Si, Sn, Sr, V, and Zn contents indicate poly-microelementosis existence in the South of Mongolia (Dorno-Gobi aimag) where ground water is characterized by elevated levels of As and extremely high levels of Se, Li, Na, F, Cl, B, and nitrates ions, exceeding maximum permissible levels by 1.86; 4.3; 3.1; 3.1; 2.7; 3.4; and 1.8 times respectively. Toxic concentrations of Se in groundwater of Dorno-Gobi aimag contradict with the published low human serum Se and low content of the element in horseflesh that suggests the possible effect of the above pollutants on Se bioavailability. Revealed phenomenon and mosaic distribution of heavy metals in areas with high and low Se content in water resources indicate the need of direct search for Se and other pollutant transfer in food chain in various ecological loading conditions, creation of a map of Se distribution in water resources of other Mongolian regions, and large-scale evaluation of the human poly-elemental status.

Alteration in Prooxidant-antioxidant Balance Associated with Selenium Concentration in Patients with Congenital Hypothyroidism.

SummaryBackgroundThere is a paucity of studies regarding oxidative balance and selenium (Se) status in congenital hypothyroidism. Recently, more attention has been given to the use of Se supplementation as a new treatment for thyroid disorders. Oxidative stress increases in different thyroid disorders and causes many pathological outcomes. The present study aimed to determine the serum prooxidant-anti - oxidant balance (PAB), Se, thyroid stimulating hormone (TSH) and free thyroxine (FT4) concentration in congenital hypothyroidism (CH) patients and the association of their probable change with hematological indices.MethodsBlood samples were collected from 60 healthy and 39 CH subjects. Serum PAB values were measured and Se, TSH, FT4 and hematological indices were determined. Data were analyzed by SPSS version 16 and p value less than 0.05 was considered statistically significant.ResultsSerum TSH concentration was significantly higher in CH patients group compared to the controls (p value < 0.05); however, FT4 was in the same concentration in patients and controls. Platelet (Plt) and lymphocytes (Lym) counts markedly decreased in all patients and showed a significant direct correlation with serum TSH levels (rs = 0.307, p value = 0.004 and rs = 0.413, p value < 0.0001). Serum PAB and Se had no significant correlation with he - mato logical indices in the studied subjects.ConclusionsAlthough there was no correlation between PAB and also Se with hematologic and biochemical markers in CH patients, changes in these two factors might be considered as a potential risk factor due to the other known effects of high PAB values and low Se concentrations.

Efficient electrochemical recovery of dilute selenium by cyclone electrowinning

Efficient recovery of selenium from the dilute acidic solution is of great importance to the cleaner production of this scattered element. In order to overcome the bottlenecks of low recovery ratio and severe environment issues in conventional processes, an easy-operation electrochemical recovery process of Se was developed using low-cost stainless steel cathodes. It has been demonstrated that Se ions can be successfully electrodeposited, but the recovery ratio of Se is significantly limited by the low Se concentration. Consequently, a cylinder turbulent electrochemical reactor was employed for the extraction of metals from dilute solution (0.3 g/L Se(IV)). 97.6% selenium was successfully recovered within 90 min, nano-sized and mesoporous selenium product was also obtained due to the excellent mass transport effect. This mass transport-enhanced technique may serve as a promising alternative for metal and metalloid electrowinning.

The influence of selenium on expression levels of the rbcL gene in Chlorella vulgaris.

In this study, the effects of selenium on the microalgae Chlorella vulgaris were examined. Four groups of C. vulgaris were cultivated using Bristol medium: group I (control), no sodium selenite (Se); group II, 1µM Se; group III, 10µM Se; and group IV, 100µM Se. Algal biomass samples were collected for biochemical evaluation and gene expression studies on the 21st day of cultivation. The following parameters were investigated: chlorophyll a (Cla), chlorophyll b (Clb) and total carotene content, total protein, and total glutathione (GSH) and malondialdehyde (MDA) levels. Gene expression levels of large subunits of Rubisco (rbcL) were analyzed using real-time quantitative polymerase chain reaction. Total Cla and total carotene in C. vulgaris decreased in high concentrations of Se (100µM) (around 23 and 42%, respectively) when compared to controls while, Clb content increased by about 10%. 10µM of Se led to increased GSH levels (3.04 ± 0.02µg GSH/mg protein) and decreased MDA levels (2.02 ± 0.1µmol MDA/mg protein) when compared to control groups (1.18 ± 0.04µg GSH/mg protein and 0.94 ± 0.23µmol MDA/mg protein), while a significant decrease in GSH and an increase in MDA levels in the presence of 100µM Se showed the opposite effect. rbcL gene expression increased 1.76 ± 1.37-fold and 0.86 ± 1.33-fold in 10and 100µM selenium experiments when compared to control groups. Our results suggest both pro-oxidant and antioxidant activities of Se on C. vulgaris and upregulation of the rbcL gene for the first time. Treatment with low concentrations of Se improves the antioxidant features of the microalgae, C. vulgaris.

Selenium enhanced degradation of diesel by Erigeron annuus

Diesel leakage is a global problem and high-level contamination cannot be removed by traditional phytoremediation because rhizospheric microorganisms are inhibited at high concentrations of petroleum hydrocarbons. Hence, we look for an exogenous substance that can increase the tolerance of phytoremediation systems to high concentrations of diesel. This study assessed the effects of selenium (0.5 mg Se kg−1 soil) on Erigeron annuus exposed to various levels of diesel (0, 15, 20, 25 g kg−1) during a 60-day pot-culture experiment. Response variables included biomass, photosynthesis parameters, antioxidant enzyme activity, and the degradation rate of diesel. Concentration-dependent decreases were found in biomass, chlorophyll content, and all photosynthesis parameters exposure, except for intercellular CO2 and non-photochemical quenching, which increased. Diesel exposure induced oxidative stress, producing concentration-dependent increases in catalase (CAT) and malondialdehyde (MDA), and a decline in superoxide dismutase (SOD). Addition of Se to soil reduced the toxic response of E. annuus to diesel, attributed to Se-enhanced antioxidant activity. In addition to increasing E. annuus tolerance to diesel, Se significantly increased the removal rate; 43.7 ± 13% in Se treated soil, compared to 37 ± 10% in the control. A low concentration of Se in soil enhances the removal of diesel from soil by Erigeron annuus. This enhancement is due to increased plant tolerance toward diesel, resulting in increased E. annuus biomass and photosynthesis. Se enhances the removal of soil diesel by E. annuus and can contribute to the ongoing effort to develop an effective phytoremediation system for soils highly contaminated by diesel.

A QTL located on chromosome 3D enhances the selenium concentration of wheat grain by improving phytoavailability and root structure

Background and aimsAs an essential mineral element, selenium (Se) plays a critical role in human health. Given the low concentrations (<100 mg Se kg–1) of Se in staple crops, the identification of genetic resources with enriched Se, as well as the genes controlling Se concentration, is valuable for the marker-assisted selection of Se-rich varieties.MethodsWe determined the chromosomal quantitative trait (QTL) for Se concentration over two consecutive plant growth cycles using recombinant inbred lines (RILs) treated with two different concentrations of Se under both field-grown and hydroponic conditions.ResultsSeveral QTL for Se concentration were detected across the different treatments. Significant genotypic variation in the tissues of the RIL was found at Se-deficicencycondition. Notably, a QTL located on 3D (interval 214.00–218.00, Qse.sau-3D) affected root length and Se concentration in the leaves and grains, suggesting the existence of the same allele with distinctly different functions. However, the QTL for the agronomic traits measured (plant height, flowering time, and tillering number) and Se concentration were not found to be located on the same chromosomal regions, suggesting that marker-assisted selection for both traits is feasible. Se concentrations in the grains were primarily determined by the mineral transport efficiency of the lines, and the line with the highest Se concentration in the grains always possessed larger, more fibrous root systems. The concentrations of Se in the plant tissues were in the order of: root > stem > grain.ConclusionsThis is the first study to document a Se-rich synthetic wheat line, and root structure and Se grain concentration was strongly affected by QTL located on 3D.

Effect of Se dopping on the structural and electronic properties, charge redistribution and efficiency of the Cu2ZnSnS4 solar cells

ABSTRACTIn this study, we systematically investigated the doping effects of Se in CZTS, the crystal structure, electronic structure, and electron charge redistribution properties of Cu2ZnSn(SxSe1-x)4 with different concentrations were calculated using density functional theory. Se doping causes very gentle lattice distortion and induces crystal expansion in all concentrations. The calculated formation energies show that Cu2ZnSn(SxSe1-x)4 alloys are highly miscible with positive formation energy and it costs additional energy to replace Se with S anions to form the Cu2ZnSn(SxSe1-x)4 .The band gaps of the Cu2ZnSn(SxSe1-x)4 alloy decrease with the increase of Se content.Our results show that Solar cells based on Cu2ZnSn(SxSe1-x)4 alloys with high Se concentration can have higher efficiency than those with low Se content. The results can be helpful to determine the optimal alloy composition to achieve high efficiency Cu2ZnSn(SxSe1-x)4-based solar cells.

Selenium Deficiency as a Risk Factor for Development of Anemia

SummaryAnemia is an important public health problem worldwide. Although iron (Fe) deficiency is considered the main factor in the pathogenesis of anemia, only 40-60% of anemia cases are responsive to Fe supplementation. Considerable data exist that other micronutrient deficiencies, such as selenium (Se), could be possible causes of anemia. The issue of Se deficiency as a risk factor for the development of anemia is of particular interest to our country since the Balkan region is known by a low Se content of soils. The aim of the study was to examine the contemporary conception of the influence of Se deficiency on the development of anemia by a review of the scientific literature. Most animal studies have shown a significant relation between Se deficiency and anemia, but one study indicates that there is no impact of Se deficiency on the hematological parameters. Associations of low serum Se with anemia have been found in a number of human studies including subjects of various age groups and pathological conditions. Three possible biological mechanisms have been suggested for the involvement of Se deficiency in the development of anemia: increased oxidative stress, modulation of inflammation through induction of interleukin-6, and increased expression of heme oxygenase-1. A more categorical clarification of the relationships between Se deficiency and development of anemia is needed with respect to appropriate trace element supplementation in cases of anemia with insufficient or absent therapeutic response to Fe treatment.

Mesophyll cell ultrastructure of wheat leaves etiolated by lead and selenium

The ultrastructure of mesophyll cells was studied in leaves of the Triticum aestivum L. cv. “Trizo” seedlings after two weeks of growth on soil contaminated by Pb and/or Se. The soil treatments: control; (Pb1) 50mgkg−1; (Pb2) 100mgkg−1; (Se1) 0.4mgkg−1; (Se2) 0.8mgkg−1; (Pb1+Se1); (Pb1+Se2); (P2+Se1); and (Pb2+Se2) were used. Light and other conditions were optimal for plant growth. The (Se1)-plants showed enhanced growth and biomass production; (Pb1+Se1)-plants did not lag behind the controls, though O2 evolution decreased; chlorophyll content did not differ statistically in these treatments. Other treatments led to statistically significant growth suppression, chlorophyll content reduction, inhibition of photosynthesis, stress development tested by H2O2 and leaf etiolation at the end of 14-days experiment. The tops of etiolated leaves remained green, while the main leaf parts were visually white. Plastids in mesophyll cells of etiolated parts of leaves were mainly represented by etioplasts and an insignificant amount of degraded chloroplasts. Other cellular organelles remained intact in most mesophyll cells of the plants, except (Pb2+Se2)-plants. Ruptured tonoplast and etioplast envelope, swelled cytoplasm and mitochondria, and electron transparent matrix of gialoplasm were observed in the mesophyll cells at (Pb2+Se2)-treatment, that caused maximal inhibition of plant growth. The results indicate that Pb and Se effects on growth of wheat leaves are likely to target meristem in which the development of proplastids to chloroplasts under the light is determined by chlorophyll biosynthesis. Antagonistic effect of low concentration of Se and Pb in combination may retard etiolation process.

Selenium and salt mobilization in wetland and arid upland soils of Pariette Draw, Utah (USA)

Selenium (Se) mobilization in the soils of the Pariette Draw and subsequent accumulation into the Pariette Wetlands threaten wildlife. To gain a better understanding of the soil biogeochemistry of Se in the draw, the physical and chemical properties for two soils in the Pariette Draw located in eastern Utah were compared: one a formerly arid soil (elevation 1448m) that was flooded following the creation of the wetlands in 1975, and the other an arid soil (elevation 1467m). The soils were analyzed, and the influence of inundation by irrigation return water of Pariette Draw of Utah was assessed to obtain a better understanding of soil Se and salts in this system. It appears that Se mobility, especially in the wetlands soil, is associated with the distribution of soluble salts in the soil profile. Due to a fluctuating water table caused by a deluge of irrigation return water and high evapotranspiration rates coupled with low precipitation, capillary migration is the dominant mechanism driving the distribution and accumulation of salts and soluble Se in the upper horizons (Byz) of the wetlands soil. The distribution of soluble salts and Se in the upland soil is typical of a downward gravity-driven hydrology process. Gypsum solubility regulated sulfate levels within the Byz horizons of the wetlands soil. We surmise that soluble Se is regulated by the solubility of a sodium selenate sulfate coprecipitate. It appears that the relatively low concentration of Se in the local Pariette Wetlands soil is not the source and cause of Se responsible for adversely affecting wildlife in the wetlands.

Reduced Dietary Selenium Impairs Vascular Function by Increasing Oxidative Stress in Sprague-Dawley Rat Aortas.

This study aimed to determine whether low dietary Se content affects the function and mechanisms mediating the vascular relaxation of rat aortas, and to test the role of oxidative stress in observed differences. Male Sprague Dawley (SD) rats were maintained for 10 weeks on low Se (low-Se group; N = 20) or normal Se content (norm-Se group; N = 20) rat chow. Dose responses to acetylcholine (ACh; 10−9–10−5M) and the response to reduced pO2 were tested in noradrenaline-precontracted aortic rings in the absence/presence of the nitric oxide synthase (NOS) inhibitor nitro-l-arginine methyl ester (l-NAME), the cyclooxygenase 1 and 2 (COX-1, 2) inhibitor Indomethacin, and the antioxidative agent Tempol in tissue bath. mRNA expression of glutathione peroxidase 1 (GPx1), catalase (CAT), and Cu/Zn superoxide dismutase (SOD) was measured in rat aortas. Oxidative stress (Thiobarbituric Acid Reactive Substances; TBARS), antioxidative plasma capacity (ferric reducing ability of plasma assay; FRAP), and protein levels of GPx1 were measured in plasma and serum samples, respectively. Reduced ACh-induced relaxation (AChIR) (dominantly mediated by NO) in the low-Se group compared to the norm-Se group was restored by Tempol administration. Hypoxia-induced relaxation (HIR) (dominantly mediated by COX-1, 2), TBARS, and FRAP as well as GPx1 serum concentrations were similar between the groups. mRNA GPx1 expression in rat aortas was significantly decreased in the low-Se compared to the norm-Se group. These data suggest that low dietary Se content increases the local oxidative stress level, which subsequently affects the NO-mediated vascular response.

Use of selenium to alleviate naphthalene induced oxidative stress in Trifolium repens L

Polycyclic aromatic hydrocarbons (PAHs) are among the most dangerous of environmental contaminants, due to their toxicity, carcinogenicity and mutagenicity. This study investigated the use of selenium (Se) to protect plants from the toxic effects of naphthalene (NPH). Exposing Trifolium repens L. (white clover) to a high concentration of NPH (soil spiked to 500mgkg−1) for 60 d significantly decreased biomass, CO2 assimilation rate (Pn), stomatal conductance (Gs) and intercellular CO2 concentration (Ci), while inducing production of H2O2 and malondialdehyde (MDA). Application of Se (soil spiked to 0.5mgkg−1) to plants exposed to NPH clearly protected the plants; biomass, Pn, Gs and Ci were significantly higher and contents of MDA and H2O2 decreased. The protection provided to Trifolium repens L. by Se is attributed primarily to an increase in photosynthesis and a decrease in oxidative stress. This study demonstrates that a low concentration of Se protects plants against oxidative stress induced by NPH and can provide a means for improving phytoremediation in PAHs contaminated soils.

Broad Spectral Response of Se‐Doped SnS Nanorods Synthesized through Electrodeposition

AbstractUn‐ and Se‐doped nanostructured SnS thin films were synthesized (deposited) on FTO‐coated glass substrates using an electrodeposition method. A study of the crystallinity indicated an orthorhombic phase with a grain size of 54–75 nm. Morphological features of the films showed a well‐developed rod structure (less than 100 nm). Optical energy band gaps in the range of 1.26–1.46 eV were estimated for the deposited films. The effect of Se as a dopant on the determination of the optoelectronic and conductivity conversion from p‐ to n‐type nanostructured SnS thin films was investigated. In addition, an n‐type Se‐SnS film was obtained at lower concentrations of Se. This technique is suggested to control the electrical conductivity of deposited films to be applied in photoswitching‐based devices.

Selenium deficiency in subtropical littoral pampas: environmental and dietary aspects.

Se deficiency has a critical effect on human health. The littoral near Patos Lagoon in the south of Brazil is composed of Quaternary sandy deposits and nutrient-deficient soils, which contribute to Se deficiency in the surrounding environment. The average concentration of Se in littoral soils is six times lower than the metalloid deficiency threshold of 0.5mgkg-1 and is close to that in countries where Keshan disease is registered. The sediments in the Patos Estuary are also notably lower in Se than near-shore marine sediments. Foodstuffs produced in the littoral pampas are characterised by extremely low Se concentrations compared with the same alimentary products reported worldwide. The total daily dietary intake of Se in the region is 24μgday-1, which is half the Estimated Average Requirement for adults. Black beans in the local diet provide over 40% of daily Se intake. Prescriptive addition of Se to prevalent products seems the most effective solution to the problem of metalloid dietary deficiency in the region. Similar environmental conditions and significant concentration of the population in the littoral zone suggest that the problem of Se deficiency probably affects a large proportion of the population along the Atlantic coast of Brazil.

Geochemical characteristics of selenium and its correlation to other elements and minerals in selenium-enriched rocks in Ziyang County, Shaanxi Province, China

Ziyang County, Shaanxi Province, China is a world known selenium (Se)-enriched area, and a severe selenosis incident was reported in Naore Village during the 1990s. This study investigated the geochemical characteristics of Se and its fractions in Se-enriched rocks from Ziyang. Se distribution is uneven, ranging from 0.23 to 57.00 μg/g (17.29±15.52 μg/g). Se content is higher in slate than chert, and even lower in carbonate rocks. Cd, As and V are enriched but Pb is depleted in Se-enriched strata. Se has different correlations both with TS (total sulfur) (R2=0.59 for chert) and TC (total carbon) (R2=0.77 for slate, R2=0.87 for carbonate). Se has significant positive correlations with V (r=0.65), As (r=0.485), Cd (r=0.459) and Pb (r=0.405). The Se level correlates with mineral content, positively with pyrite, chlorite and illite, negatively with albite. Se associated with sulfide/selenide and elemental Se are the predominant fractions of total recovered Se, suggesting that a reducing environment and the formation of sulfides were significant to Se deposition during its geochemical cycle. Although low concentration of bio-available Se (average 5.62%±3.69%) may reduce the risk of Se poisoning in the target area, utilization of Se-rich rock as natural fertilizer should be restricted.

Relationships for mercury and selenium in muscle and ova of gravid freshwater fish.

At high concentrations, mercury (Hg) is toxic to vertebrates, causing neurological, behavioral, and teratological dysfunction. Selenium (Se) not only is an essential element but also has a high affinity for Hg, binding to organic methyl mercury at a molar ratio of Se/Hg of 1:1. Ratios of <1 increase risk of Hg toxicity. For gravid fish, low concentrations of Se in ova could increase potential for Hg toxicity, compromising embryonic development and fitness of fry. Mercury and selenium concentrations and ratios were investigated in the muscle and ovaries of six species from five families of fish to assess potential for risk to ecological fitness. Molar ratios of Se/Hg in muscle were typically >18 for lower trophic level species but ≤2 for piscivores. For all species combined, the concentrations of Hg in ova were significantly related to concentrations of Hg in muscle. Concentrations of Se in ova versus muscle showed a similar significant relationship that was independent of muscle Hg concentration. Mean ova molar Se/Hg ratios were high, ranging from 69 to 955 for the 6 species. However, a declining relationship between the ova Se/Hg molar ratio and the muscle concentration of Hg for all species combined suggests that development of ova and fry might be compromised for those piscivores with the highest muscle Hg concentrations because of Hg-related Se deficiency.

Effects of Selenium on Growth Parameters of Tomato and Basil under Fertigation Management

Tomato ‘Abigail’ (Solanum lycopersicum L.) and basil ‘Perry’ (Ocimum basilicum L.) were selected as model plants for selenium (Se) supplementation to evaluate a) effects of Se concentration in nutrient solution on Se content in different organs under fertigation, b) Se phytotoxicity threshold values, and c) mechanisms. Plants grown in a glasshouse were irrigated with 0, 1, 2, 5, and 10 mg Se/L in the first experiment, while with 0, 0.25, 0.5, 0.75, 1.0, and 1.5 mg Se/L in the second. Tomato plants accumulated Se linearly with rising Se concentrations, whereas accumulation in basil followed a saturation curve. Plants supplemented with 1.5 mg Se/L in the irrigation water accumulated 0.23 and 0.88 mg Se/g dry weight (DW) in tomato fruits and basil shoots, respectively. However, tomato roots, shoots and fruits DW were 56%, 36%, and 66% lower than in controls, respectively, and basil roots and shoots DW were 92% and 88% lower than in control, respectively. Calculated toxicity-threshold values were 1.27 mg Se/L for tomato and 0.44 mg Se/L for basil. Tomato crops were more tolerant than basil crops, although data suggested yield reduction at lower Se concentrations than those effecting biomass reductions. The results indicate that Se supplementation through drip irrigation may efficiently fortify tomato and basil. However, Se concentrations should be lower than 0.75 and 0.25 mg·L−1 for tomato and basil, respectively, to avoid yield reduction and possible Se phytotoxicity.

Effects of selenium on biological and physiological properties of the duckweed Landoltia punctata.

Duckweed can be used for bioremediation of selenium (Se) polluted water because of its capability of absorbing minerals from growing media. However, the presence of Se in the media may affect the growth of the duckweed. Landoltia punctata 7449 has been studied for its changes in chemical and biological properties with the presence of Se in the media. The duckweed was cultivated over a 12-day period at different initial concentrations of selenite (Na2 SeO3 ) from 0 to 80μmol·l(-1) . The growth rate, the organic and total Se contents, the activity of antioxidant enzymes, the photosynthetic pigment contents, the chlorophyll a fluorescence OJIP transient, and the ultrastructure of the duckweed were monitored during the experiment. The results have shown that Se at low concentrations of ≤20μmol·l(-1) promoted the growth of the L.punctata and inhibited lipid peroxidation. Substantial increases in duckweed growth rate and organic Se content in the duckweed were observed at low Se concentrations. The anti-oxidative effect occurred likely with the increases in guaiacol peroxidase, catalase and superoxide dismutase activities as well as the amount of photosynthetic pigments. However, negative impact to the duckweed was observed when the L.punctata was exposed to high Se concentrations (≥40μmol·l(-1) ), in which the duckweed growth was inhibited by the selenium. The results indicate that L.punctata 7449 can be used for bioremediation of selenium (Se) polluted water when the Se concentration is ≤20μmol·l(-1) .

Long-Term Selenium-Deficient Diet Induces Liver Damage by Altering Hepatocyte Ultrastructure and MMP1/3 and TIMP1/3 Expression in Growing Rats

The effects of selenium (Se)-deficient diet on the liver were evaluated by using growing rats which were fed with normal and Se-deficient diets, respectively, for 109days. The results showed that rats fed with Se-deficient diet led to a decrease in Se concentration in the liver, particularly among male rats from the low-Se group. This causes alterations to the ultrastructure of hepatocytes with condensed chromatin and swelling mitochondria observed after low Se intake. Meanwhile, pathological changes and increased fibrosis in hepatic periportal were detected by hematoxylin and eosin and Masson's trichrome staining in low-Se group. Furthermore, through immunohistochemistry (IHC) staining, higher expressions of metalloproteinases (MMP1/3) and their tissue inhibitors of metalloproteinases (TIMP1/3) were observed in the hepatic periportal of rats from the low-Se group. However, higher expressions of MMP1/3 and lower expressions of TIMP1/3 were detected in hepatic central vein and hepatic sinusoid. In addition, upregulated expressions of MMP1/3 and downregulated expressions of TIMP1/3 at the messenger RNA (mRNA) and protein levels also appeared to be relevant to low Se intake. In conclusion, Se-deficient diet could cause low Se concentration in the liver, alterations of hepatocyte ultrastructure, differential expressions of MMP1/3 and TIMP1/3 as well as fibrosis in the liver hepatic periportal.