Showing papers on "Selenium published in 1990"

Transformations of selenium as affected by sediment oxidation-reduction potential and pH.

Abstract: Etude en laboratoire de l'influence du potentiel redox et du pH des sediments sur la solubilite, la speciation et la volatilisation du selenium

National contaminant biomonitoring program: Concentrations of arsenic, cadmium, copper, lead, mercury, selenium, and zinc in U.S. Freshwater Fish, 1976-1984.

Abstract: From late 1984 to early 1985, the U.S. Fish and Wildlife Service collected a total of 315 composite samples of whole fish from 109 stations nationwide, which were analyzed for arsenic, cadmium, copper, lead, mercury, selenium, and zinc. Geometric mean, maximum, and 85th percentile concentrations (μg/g wet weight) for 1984 samples were as follows: arsenic-0.14, 1.5, 0.27; cadmium-0.03, 0.22, 0.05; copper-0.65, 23.1, 1.0; mercury-0.10, 0.37, 0.17; lead-0.11, 4.88, 0.22; selenium-0.42, 2.30, 0.73; and zinc-21.7, 118.4, 34.2. The mean concentrations of selenium and lead were significantly lower than in the previous NCBP collection (1980–81). Mean concentrations of arsenic and cadmium also declined significantly between 1976, when elemental contaminants in fish were first measured in the NCBP, and 1984. Of greatest significance, lead concentrations declined steadily from 1976 to 1984, suggesting that regulatory measures have successfully reduced the influx of lead to the aquatic environment.

Activity of Methylated Forms of Selenium in Cancer Prevention

Abstract: The anticarcinogenic activity of selenium in animal models is well established. The active forms of selenium involved have not been identified to date, but conversion of selenium via hydrogen selenide (H2Se) to methylated forms such as dimethylselenide and trimethylselenonium ion is an important metabolic fate. By controlling the entry of selenium into various points within this pathway through selection of appropriate starting compounds, it is possible to pinpoint more closely the form(s) of selenium responsible for its anticarcinogenic activity. Selenobetaine in the chloride form [(CH3)2Se+CH2COOH] and its methyl ester are extensively metabolized in the rat to mono-, di-, and trimethylated selenides, largely bypassing the inorganic H2Se intermediary pool. The chemopreventive efficacy of these selenobetaines was determined at 1 and 2 ppm selenium supplemented in the diet throughout the duration of the experiment using the dimethylbenz(a)anthracene induced mammary tumor model in rats. There was a dose-dependent inhibitory response to both compounds, and they appeared to be slightly more active than selenite. These doses were without any adverse effects on the animals. Coadministration of selenobetaine with arsenite (5 ppm arsenic) enhanced the tumor-suppressive effect of selenobetaine, although arsenic by itself was totally inactive. Arsenite is known to inhibit certain steps in selenium methylation. The substantial prophylactic efficacy of methylated selenides and the enhancement by arsenite suggest that partially methylated forms of selenium may be directly involved in the anticarcinogenic action of selenium.

Measurement of in situ rates of selenate removal by dissimilatory bacterial reduction in sediments

Abstract: vertical distribution in sediments relative to other forms • A radioisotope method for measurement of bacterial of anaerobic bacterial respiration. An understanding of respiratory reduction of selenate to elemental selenium in how the process of dissimilatory selenate reduction oper­ aquatic sediments was devised. Sediments were labeled ates in these respects should ultimately aid the design of with [75Se]selenate, incubated, and washed, and 75SeO(S) treatment schemes and the rehabilitation of selenium­ was determined as counts remaining in the sediment. Core contaminated regions. In order to answer these questions profiles of selenate reduction, sulfate reduction, and den­ and to achieve these long-term goals, it was f1I'St necessary itrification were made simultaneously in the sediments of to devise a method for measuring in situ selenate reduction. an agricultural wastewater evaporation pond. Most of the In situ measures of bacterial activities have been a focus in situ selenate reduction (850/0) and all the denitrification of microbial ecology for the past 25 years. A variety of activities were confined to the upper 4-8 em of the profile, whereas sulfate reduction was greatest below 8 em (890/0 techniques employing radioisotopes, gas chromatography, of total). The integrated areal rate of selenate reduction and/or enzyme inhibitors or analogues have been exploited was 301 J,tmol m-2 day", which results in a turnover of to assess environmental rates of methanogenesis (8), den­ water column selenate in 82.4 days. itrification (9, 10), nitrogen fixation (11), and sulfate re­ duction (12). This latter process is analogous to the methods we report herein to measure selenate reduction. Introduction However, in the case of selenate reduction, our task was Oxyanions of selenium have been identified as toxic simplified because 75Se is a 'Y-emitting radioisotope (t l / 2 constituents in drainage waters from irrigated, seleniferous =120 days), which circumvents the quenching/efficiency agricultural soils (1). This environmental problem is ap­ problem associated with liquid scintillation counting of parently quite common in many regions of the western weak ~-emitters like 35S. Thus, there was no need to United States (2). Therefore, methods that address the volatilize and trap the product 75SeO(S) as there is for question of removal of selenium oxyanions from soils [35S]sulfide, but merely to wash away the added [75Se]­ and/or drainage waters by various means have received selenate. Our results with core profiles from a selenium­ considerable attention because they offer the prospect of rich agricultural wastewater evaporation pond represent restoring water or soil quality while allowing for the con­ "quasi" in situ assays because they were incubated in the tinuation of irrigated farming. With regard to possible laboratory under conditions approximating the field. microbiological methods, volatilization of selenium by However, our results indicate that selenate reduction oc­ formation of alkylated gases (e.g., dimethyl selenide) has curs in the surficial layers of these sediments, in proximity been suggested for treatment of soils (3) or impacted marsh to the region of active denitrification, yet spatially sepa­ waters, such as those of the Kesterson Wildlife Refuge (4, rated from sulfate reduction occurring deeper in the core. 5). Areal rates of selenate removal obtained from this core J Recently, we reported on a novel process by which indicate its rapid removal by reduction to SeO(s), and a anaerobic bacteria respire selenate, which in turn bio­ quick turnover of water column selenate. When combined chemically reduces this oxyanion to selenite and ultimately with previous observations with regard to inhibitors and to elemental selenium (6). This dissimilatory reduction stimulators of selenium reduction, the conceptual design was demonstrated to occur in sediments, was independent of an efficient anaerobic selenate "digester" can be dis­ of sulfate, and was inhibited by nitrate and chromate. cerned. Bacterial cultures capable of selenate respiratory growth have been isolated (6, 7). Although we were able to show Experimental Section that this process holds the potential to rapidly remove and Sites and Sampling. Surficial (upper ro.J20 em) sedi­ sequester considerable quantities (millimolar) of added ments were collected from Hunter Drain, an agricultural selenate from sediment slurries, the questions remained drain located in Stillwater, NV, where selenium contam­ as to how rapidly it proceeds in nature, and what was its ination is documented (2), as well as from the littoral zone of Big Soda Lake, an alkaline/saline environment (13)

Predictors of selenium concentration in human toenails

Abstract: To assess the validity of the selenium concentration in human toenails as a measure of selenium intake and to determine other correlates of toenail selenium level, the authors examined the predictors of toenail selenium within two subgroups of a large cohort study of US women. Mean toenail selenium was higher among 38 consumers of selenium supplements (0.904 micrograms/g, standard deviation (SD) 0.217) than among 96 nonusers (0.748 micrograms/g, SD 0.149; p less than 0.001), and a dose-response relation was observed among supplement users (Spearman's r = 0.32; p = 0.05). In a second subgroup of 677 women, selenium supplement use was also associated with higher mean toenail selenium (0.906 micrograms/g, SD 0.214, among 18 users and 0.801 micrograms/g, SD 0.148, among 659 nonusers; p = 0.02), and the dose-response relation was also significant (Spearman's r = 0.50; p = 0.03). The geographic variation in toenail selenium levels was consistent with the geographic distribution of selenium in forage crops. Toenail selenium declined with age and was significantly reduced among cigarette smokers (mean = 0.746, SD 0.124, among 146 current smokers and mean = 0.817, SD 0.159, among 311 never smokers; p less than 0.001) but was not materially affected by alcohol consumption. A dietary selenium score calculated from a food frequency questionnaire failed to predict toenail selenium level, demonstrating the suspected inability of diet questionnaires to measure individual selenium intake because of the highly variable selenium composition of different samples of the same food.(ABSTRACT TRUNCATED AT 250 WORDS)

Toxicity of organic selenium in the diet to chinook salmon

Abstract: The toxicity of two organoselenium diets was evaluated in 90- to 120-d partial life cycle tests with two life stages of chinook salmon (Oncorhynchus tshawytscha Walbaum) One of the diets contained fish meal made from high-selenium mosquitofish (Gambusia affinis Baird and Girard) collected from the selenium-laden San Luis Drain, California (here termed SLD diet) and the other contained meal made from low-selenium mosquitofish (collected from a reference site) fortified with selenomethionine A 90-d study was conducted with swim-up larvae in a water-simulating dilution of San Luis Drain water in a standardized fresh water; and a 120-d study was conducted with fingerlings 70-mm long in a water of similar quality but prepared with a standardized brackish water After 90 d of exposure in the freshwater study, survival was reduced in fish fed ≥96 μg Se/g of either diet, and growth was reduced in fish fed ≥53 μg Se/g of SLD diet or ≥182 μg Se/g of selenomethionine diet Reduced fish growth, whole-body concentrations of selenium and survival were strongly correlated to concentrations of selenium in both diets After 120 d of exposure in the brackish-water study, survival was unaffected but growth was reduced in fish fed ≥182 μg Se/g of SLD diet or 354 μg Se/g of selenomethionine diet After 120 d of dietary exposure, survival during a 10-d seawater challenge test was reduced in fish fed 354 μg Se/g of either diet In this second dietary study, concentration—response relations were observed in both dietary treatments between the dietary concentrations of selenium and all three characteristics — fish growth, whole-body concentrations of selenium and survival in seawater

Advances in Radioprotection through the Use of Combined Agent Regimens

Abstract: SummaryThe most effective radioprotective agents exhibit toxicities that can limit their usefulness. It may be possible to use combinations of agents with different radioprotective mechanisms of action at less toxic doses, or to reduce the toxicity of the major protective compound by adding another agent. With regard to the latter possibility, improved radioprotection and reduced lethal toxicity of the phosphorothioate WR-2721 was observed when it was administered in combination with metals (selenium, zinc or copper). The known mechanisms of action of potential radioprotective agents and varying effects of different doses and times of administration in relation to radiation exposure must be considered when using combined-agent regimens. A number of receptor-mediated protectors and other biological compounds, including endotoxin, eicosanoids and cytokines, have at least an additive effect when administered with thiol protectors. Eicosanoids and other bioactive lipids must be administered before radiation e...

Reduced selenium in asthmatic subjects in New Zealand.

Abstract: Selenium is an essential component of glutathione peroxidase, an enzyme that helps protect cells against oxidation damage and modulates the lipoxygenase pathway of arachidonic acid metabolism. Low selenium concentrations might therefore influence the inflammatory process in asthma by reducing the activity of glutathione peroxidase. Whole blood and plasma selenium concentrations and glutathione peroxidase activity have been measured in 56 asthmatic patients and 59 non-asthmatic control subjects in New Zealand, a country with a low dietary selenium intake and a high prevalence of asthma. When compared with control subjects the asthmatic patients had lower values for whole blood selenium concentrations (-4.9, 95% confidence interval -10.2 to 0.4 ng/ml) and glutathione peroxidase activity (-3.3, 95% CI -5.8 to -0.8 units/g Hb). There was a 1.9 and 5.8 fold increased risk of asthma in subjects with the lowest range of whole blood selenium concentration and glutathione peroxidase activity respectively (95% CI 0.6 to 5.6 and 1.6 to 21.2). Levels were lower in patients and control subjects without an atopic predisposition, but were not affected by prednisone use. Similar differences between the asthmatic and control subjects were not observed for selenium concentration or glutathione peroxidase activity measured in plasma, which reflects short term rather than long term selenium content. These findings are consistent with the hypothesis that low selenium concentrations may have a role in the pathogenesis of asthma in New Zealand.

Selenium in diet, blood, and toenails in relation to breast cancer: a case-control study

Abstract: The association between breast cancer and selenium, measured in the diet, plasma, erythrocytes, and toenails, was investigated in a case-control study in the Netherlands during 1985-1987. Dietary selenium intake was assessed by a structured dietary history technique among 133 breast cancer cases and 238 population controls. Absolute and energy-adjusted selenium intake and selenium concentrations in plasma, erythrocytes, and toenails were similar in cases and controls. The multivariate adjusted odds ratios of breast cancer for subjects in the lowest quartile compared with the highest quartile were 1.6 (95% confidence interval (CI) 0.8-3.4) for dietary selenium, 2.0 (95% CI 0.9-4.4) for plasma selenium, 0.9 (95% CI 0.4-1.9) for erythrocyte selenium, and 1.1 (95% CI 0.6-2.1) for toenail selenium. No statistically significant trend was observed in the odds ratios for any of the four indicators of selenium. These results do not suggest a substantial association between selenium and breast cancer for both short- and long-term markers of selenium status. Chemicals/CAS: selenium, 7782-49-2; Selenium, 7782-49-2

Selenium accumulation and elimination in mallards

Abstract: Selenium accumulation and loss were measured in adult mallards (Anas platyrhynchos) fed selenomethionine during two experiments. In Experiment 1, both sexes were fed a diet containing 10 ppm selenium for 6 weeks, followed by 6 weeks on untreated feed. Selenium accumulation in liver and muscle of females was described by C=A(1−e−bt). Concentrations of selenium were predicted to reach 95% of equilibrium faster in liver (7.8 days) than in muscle (81 days). The loss of selenium from liver and muscle of females was described by the exponential loss rate equation: C=Ae−bt, with half-times of 18.7 and 30.1 days, respectively. Males reached similar levels of selenium in liver and breast muscle as females and declined to similar levels once selenium treatment ended. In Experiment 2, females were fed increasing levels of selenium until some died. Survivors were switched to an untreated diet and selenium was measured in blood, liver, and breast muscle over 64 days. The same equation as in Experiment 1, C=Ae−bt, was used to describe the loss of selenium from blood and muscle. Halftimes were 9.8 and 23.9 days, respectively. For liver, the equation $$C = A_1 e^{ - b_1 t} + A_2 e^{ - b_2 t} $$ was used. Selenium initially decreased in liver by one-half in 3.3 days, with subsequent half-times of 3.9, 6.0, and 45.1 days.

Selenium and cardiovascular disease.

Abstract: For humans, ecological and epidemiological results are reported that show a relationship between the serum selenium concentration and cardiovascular disease in populations where low serum selenium concentrations are found, e.g., in Eastern Finland. From clinical studies done in Germany (FRG and GDR), Finland, and Sweden, subnormal serum selenium and partially whole blood selenium concentrations are reported in patients with acute myocardial infarction. For patients with coronary arteriosclerosis, subnormal serum selenium concentrations are reported from the USA and Germany and subnormal whole blood selenium concentrations from Germany. Subnormal serum and subnormal whole blood selenium concentrations of patients with cardiomyopathy are reported from non Keshan disease affected areas in Germany, France, and China. In selenium deficiency, an accumulation of lipid peroxides in the heart may occur, especially under ischemic conditions and if ischemic tissue is reperfused. Lipid peroxides in the heart may damage the cell membrane and may lead to an impaired calcium transport with an uncontrolled calcium accumulation in the cell. This may result in an activation of phospholipids, and, in consequence, to an enhanced formation of arachidonic acid. An increased concentration of lipid peroxides owing to selenium deficiency may shift the prostaglandin synthesis from prostacyclin to thromboxane, causing enhanced blood pressure and platelet aggregability. From animal experiments, it is known that selenium protects against cardiotoxic elements, cardiotoxic xenobiotics, and viral infections that affect the heart. Selenium deficiency may also be a secondary factor in the causation of hypertension and myocardial ischemia.

Acute toxicity of boron, molybdenum, and selenium to fry of chinook salmon and coho salmon.

Abstract: The acute toxicities of boron, molybdenum, and various forms of selenium, individually and in environmentally relevant mixtures, to swim-up and advanced fry of chinook salmon (Oncorhynchus tshawytscha) and coho salmon (O. kisutch) were determined in site-specific fresh and brackish waters. Boron and molybdenum were relatively non-toxic (96-hr LC50s greater than 100 mg/L) to both life stages of both species. Selenite was significantly more toxic than selenate to both species. Swim-up fry tested in fresh water were significantly more sensitive than advanced fry in brackish water to selenate and selenite. No mortalities occurred in any concentrations tested of seleno-DL-methionine; however, in the highest concentration (21.6 mg Se/L), at least 50% of the fish showed pronounced surfacing behavior. Coho salmon were more sensitive than chinook salmon to both selenate and selenite at either life stage; only the swim-up fry of coho salmon were more sensitive than chinook salmon to boron. In additional tests with swim-up chinook salmon, differences in the characteristics of the dilution water did not significantly modify the relative toxicities of boron, selenate, and selenite. In binary mixture studies, the joint acute toxic action of selenate and selenite, combined in various ratios, was additive to both species. Based on a comparison of the individual acute values for chinook salmon to the expected environmental concentrations, the margin of safety for boron was only 56 in fresh and 46 in brackish water. The margins of safety for selenate and selenite exceeded 275 in both fresh and brackish waters. However, the margin of safety for both selenate and selenite in the mixture test was 145 in fresh water and 220 in brackish water.

Selenium deficiency in Crustacea

Abstract: The effect of selenium deprivation onDaphnia magna was examined under controlled rearing conditions in a synthetic culture medium. After three generations, fertility was significantly reduced in deprived (Se−) animals. Growth and mortality of parent daphnids and development of parthenogenetic eggs were not affected during this period. In the fourth generation Se− daphnids rejected parts of their second antennae. At the ultrastructural level antennal muscle tissue was severely affected. Animals deprived of selenium had mitochondria and sarcoplasmic reticulum with myelin-like alterations. Giant lysosomes were present and complete lysis of muscle fibrils was observed in antennal muscle cells. These alterations are characteristic features of peroxidic damage in tissues. This interpretation is consistent with the function of selenium as a constituent of the enzyme glutathione peroxidase which protects cells from peroxidation. Selenium should be included in synthetic culture media for daphnids.

Determination of trace amounts of cadmium, cobalt, chromium, iron, molybdenum, nickel, selenium, titanium, vanadium and zinc in blood and milk by neutron activation analysis

Abstract: The concentrations of Cd, Co, Cr, Fe, Mo, Ni, Se, Ti, V and Zn in biological fluids, human blood serum and market milk were determined by neutron activation analysis, with enrichment by coprecipitation. The pre-concentration of these trace elements was accomplished by converting the dissolved trace metal ions into their pyrrolidinedithiocarbamate (1-pyrrolidinecarbodithioate) chelates, followed by coprecipitation with a metal carrier such as Ni, Pb or Bi. The coprecipitation was carried out prior to irradiation for the short-lived nuclides (V, Ti and Se) and after irradiation for the other elements. The validity of the method was checked using certified biological reference materials; the concentrations of trace elements found by the proposed method agreed well with the published certified data. The limits of detection for Cd, Co, Cr, Fe, Mo, Ni, Se (obtained through the long-lived isotope 75Se) and Zn under the present experimental conditions were found to be 5, 5, 10, 520, 5, 70, 10 and 150 ng, respectively, for 5 ml of biological liquor. The limits of detection for Ti and V obtained (through their short-lived radionuclides 51Ti and 52V, respectively) were found to be 180 and 1.4 ng, respectively, for 50 ml of market milk, or 70 and 0.7 ng for 1 ml of blood serum.

Transfer of toxic concentrations of selenium from parent to progeny in the fathead minnow (Pimephales promelas)

Abstract: Selenium, an essential trace element, may become concentrated in aquatic ecosystems to levels that are toxic to fish. Finley (1985) and Gillespie and Baumann (1986) have shown that selenium in overflow water from coal burning power plant settling basins contributed to a decline in fish populations. The leaching of selenium from the soil into water systems used for irrigation in highly seleniferous areas of the country poses another serious problem. Studies demonstrated that female bluegill sunfish transfer selenium to their progeny. The objective of the study was to determine whether the selenium levels within fathead minnow embryos in a semi-natural ecosystem resulted from direct uptake by the embryos following spawning, from female-to-progeny transferral, or from some combination of these two occurrences.

Enhanced electronic properties of GaAs surfaces chemically passivated by selenium reactions

Abstract: We describe chemical modifications of GaAs surfaces which produce robust selenium layers that significantly enhance the electronic properties of the surface. The terminating layers are produced by depositing elemental selenium on GaAs surfaces under alkaline conditions followed by conversion to selenide and selenate using sodium sulfide. These selenium phases are more stable against photo‐oxidation than their sulfide counterparts. On the chemically modified surface, photoluminescence is enhanced 400× and Raman spectroscopy indicates that surface band bending has been reduced to ∼0.1 eV. X‐ray photoelectron spectroscopy reveals significant AsSe bond formation at the surface and a complicated interfacial structure with selenium present in oxidation states varying from 2− to 4+.

The effect of selenium on sulfur uptake by barley and rice

Abstract: Because of their chemical and physical similarities, plant uptake of S and Se are closely related. Barley (Hordeum vulgare L.) and rice (Oryza sativa L.) were grown in greenhouse solution culture to examine the synergistic interactions between SO4 and Se6+ in plant uptake. In the presence of low concentrations of solution SO4, shoot and root yields were decreased with additions of Se6+. However, when SO4 was present in elevated concentrations, no Se-induced yield reduction occurred. A synergistic interaction between SO4 and Se6+ caused an increase in the shoot S concentrations with increasing concentrations of Se6+ at low SO4 solution concentrations. At elevated SO4 concentrations, no synergism was osberved. Selenium had a lesser effect on the S concentration in plant roots.

Distributional pattern of zinc, cadmium, mercury, and selenium in livers of hooded seal (Cystophora cristata).

Abstract: The liver of Hooded Seal (Cystophora cristata) consists of six lobes of unequal sizes. Extensive sampling by means of cutout samples covering the depth horizon 2–30 mm below liver surface indicates that the liver may be considered homogeneous as to concentrations of zinc, cadmium, mercury, and selenium (residuals of overall mean compatible with normality, the all-organ variance negligibly in excess of within-lobe variance). Mercury and selenium are present in equimolar concentrations. Cutout samples have mercury and selenium concentrations respectively c. 17 and 8% (dry weight basis) above those of homogenates of the same lobe. The apparent dilution of mercury and selenium is tentatively attributed to coarse blood vessels and bile ducts abundantly present in the homogenate but almost absent from the cutouts.

Automated measurement of two indicators of human selenium status, and applicability to population studies.

Abstract: We developed an automated system consisting of a centrifugal analyzer and an atomic absorption spectrophotometer with Zeeman background correction to produce a profile of the concentrations of selenium and the selenium-dependent enzyme glutathione peroxidase (EC 1.11.1.9) in serum and whole blood, for use in epidemiological surveys in Northern Ireland. No pretreatment of samples other than dilution is required, and at least 35 subjects can be screened within 24 h of venesection. For selenium in serum the between-run CV was 5.7% and 4.4% within run. For selenium in whole blood the CV was 5.9% between runs, 5.7% within run. The within-run CV for glutathione peroxidase was 0.92% for serum, 1.18% for blood; the between-run CV was 8.3% for serum. To illustrate the use of the system, we present the profile of selenium and glutathione peroxidase in serum and whole blood from 100 adults 25 to 64 years old.