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Despite the availability of selenium (Se)-enriched trace mineral supplements, we have observed low Se status in cattle and sheep offered traditional inorganic Se supplements. Reasons for this may include inadequate intake or low bioavailability of inorganic Se sources. The objective of this study was to determine whether rumen microorganisms (RMO) alter the bioavailability of Se sources commonly used in Se supplements. Rumen microorganisms were isolated from ewes (n = 4) and incubated ex vivo with no Se (control), with inorganic Na selenite or Na selenate, or with organic selenomethionine (SeMet). Total Se incorporated into RMO and the amount of elemental Se formed were determined under equivalent conditions. Incorporation of Se from Na selenite, Na selenate, or SeMet into RMO was measured as fold change compared with control (no added Se). Incorporation of Se into microbial mass was greater for SeMet (13.2-fold greater than no-Se control) compared with inorganic Se supplements (P = 0.02); no differences were observed between inorganic Na selenate (3.3-fold greater than no-Se control) and Na selenite (3.5-fold greater than no-Se control; P = 0.97). Formation of non-bioavailable, elemental Se was less for RMO incubated with SeMet compared with inorganic Se sources (P = 0.01); no differences were observed between Na selenate and Na selenite (P = 0.09). The clinical importance of these results is that the oral bioavailability of organic SeMet should be greater compared with inorganic Se sources because of greater RMO incorporation of Se and decreased formation of elemental Se by RMO.

Construction and optimisation of a hyphenated analytical system for high performance liquid chromatography with hydride generation atomic absorption spectrometry detection system are described together with results of its use for investigation of food products. The use of anion-exchange chromatographic column permitted separation of inorganic selenium species Se(IV) and Se(VI) at the limit of detection of 10 ng mL−1 for both species. The analytical system was used for determination of selenium species in dietary supplements available on the Polish market. The content of inorganic selenium species was found not to exceed 50% of its total content, and in the majority of products, the dominant species was Se(IV). In the majority of products, the total contents of selenium were close to those declared by the producers.

A new method was established for the speciation of Se by hydride generation-atomic fluorescence spectrometry. Effective separation of organic and inorganic Se in Se-enriched eggs was achieved by precipitating albumen with trichloroacetic acid. The detection limit for Se was 0.07 μg L−1. The proposed method was successfully applied for the determination of organic and inorganic Se as well as total Se in Se-enriched eggs with the recovery of 90.1–112% and the relative standard deviation (n = 5) of 0.6–3.4%. Se in Se-enriched eggs presents mainly in organic forms, the content of which was three to seven times that of inorganic Se.

For studying geochemical behavior of selenium, a marine investigation was conducted in September 1998 cruise in the Bohai Sea. Horizontal and vertical distributions of inorganic selenium and selenite were studied. The inorganic selenium varied from 0.73 to 2.41 nmol/L, with an average of 1.31 nmol/L; while selenite varied from 0.18 to 0.72 nmol/L with an average of 0.47 nmol/L. The average ratio of selenite to selenate was 0.68, and selenate was the predominant species of inorganic selenium in the most study area. Concentrations of inorganic selenium and selenite decreased with distance from the coast. No apparent variations of the concentration between surface and bottom was shown. There were two water masses in the area, one from the Huanghe (Yellow) River and other from the Yellow Sea. Of the two, Huanghe River was the major source of inorganic selenium.

A method for the analysis of selenium in marine aquatic products by HG-AFS has been investigated. The method is based on the reduction of inorganic selenium to volatile SeH2 which is bubbled out by carrier gas of pure argon, and then swept to Ar-H2 flame quarts atomizer to measure its fluorescence intensity. The hydride generation, transportation, atomization and some instrumental parameters were studied by a kind of orthogonal design. The optimum conditions selected are as follows: reactive acidity, 20% HC1; the amount of NaBH4, 4.9mL; gas flow of argon, 6OO mLmin−1; atomizing temperature, 200°C, negative high voltage,−300V; light current, 100 mA; integral time, 7 s. The detection limit of the presented method is 0.072µgL−1 for selenium. The calibration curve shows a satisfactory line in the concentration range from 0.000 to l.OOOµgL−1 Se. The recovery is 95.8%–102.2% .

The toxicity and essential nature of selenium in the environment depend on its concentration and on the chemical forms in which it is present. Dissolved inorganic selenium can be found in natural waters as selenides (Se-II), colloidal elemental selenium (Se0), selenite (SeIV) as well as selenate (SeVI). Organic forms of selenium that may be found in organisms, air or in the aqueous environment are volatile methylselenides, trimethylselenonium ion and selenoamino acids. This review article intends to show some general ideas in speciation analysis of selenium and to highlight some important procedures.

Inorganic selenium species were determined in several parts of a freshwater fish of the speciesTilapia nilotica found breeding in disused tin-mining pools. The inorganic selenium species in the monazite-rich ores can enter the human food chain through the consumption of the fish. The Se(IV) and Se(VI) species were preconcentrated by solvent extraction with APCDT-CHCl3 before irradiation in a TRIGA Mk.II reactor. Total inorganic selenium species separation was done using Chelex-100 chelating resin. Quantitative interpretations of the distribution of inorganic selenium species in the fish are discussed with particular reference to the Se(IV)/Se(VI) ratio.

A selenium-dependent bacterium, Bacillus sp., failed to grow on selenium-free media. However, it is able to grow at high concentrations of sodium selenite containing media up to 3% (w/v). It accumulated extraordinary high quantities of selenium, 432 ppm/mL. The bacterium generated the transformation of inorganic selenium into volatile selenium form(s) into the atmosphere. The biological release of volatile selenium basically depended on several factors: incubation temperature, pH, incubation periods, and substrate concentration. Maximal quantity of the volatile selenium form was obtained at 30 degrees C, pH 7, and 1% (w/v) sodium selenite.

The toxicity of selenomethionine and sodium selenite to mallard ducklings (Anas platyrhynchos) was measured by feeding each form from hatching to six weeks of age at dietary concentrations of 0, 10, 20, 40, and 80 ppm selenium. At 80 ppm selenium, sodium selenite caused 97.5% mortality by six weeks and selenomethionine caused 100% mortality. At 40 ppm, these two forms of selenium caused 25 and 12.5% mortality. No mortality occurred at 10 or 20 ppm. Diets containing 20, 40, or 80 ppm selenium in both forms caused decreases in food consumption and growth. The only statistically significant effect of 10 ppm selenium was with sodium selenite, which resulted in larger livers than controls. Selenomethionine was more readily stored in the liver than sodium selenite at levels above 10 ppm selenium in the diet. Based on comparisons of residues of selenium in livers of surviving and dead ducklings, concentrations in the liver were not diagnostic of death due to selenium poisoning. Because both forms of selenium resulted in severe reductions in food consumption, selenium-induced starvation may have been related to duckling mortality. It was not clear whether either form of selenium at 10 ppm in the diet resulted in a leveling off of selenium concentrations in the liver within six weeks.

The excretion of selenium in milk was investigated in twelve ewes. Four of these were injected 12–29 days before, and four immediately after delivery, with Se(75)-sodium selenite. One month after delivery two ewes were injected with Se(75)-selenomethionine, and two with Se(75)-sodium selenite. The Se(75)-concentration was measured in the milk and its various fractions as well as in the plasma, whole blood and organs of three lambs. The excretion of Se(75) into the milk was markedly higher when Se(75)-selenomethionine was administered than when Se(75)-sodium selenite was given. The amount of Se(75) in the various milk fractions was, to a great extent, proportional to the amount of protein in the fractions; this applied to the administration of organic as well as inorganic selenium. The highest Se(75)-concentration in the milk was obtained already within 24 hours after injection. Selenium administered before delivery gave the highest concentration in samples taken less than six hours after delivery. The lambs which received Se(75) via the milk had a higher content of Se(75) than those who received it during the fetal period.

The placental transmission of selenium was investigated in thirteen ewes during late gestation. The ewes were injected either with Se75-sodium selenite, Se75(L)-selenocystine or Se75 (L)-selenomethionine. Twelve lambs and nine ewes were killed soon after delivery and the Se75-concentration was measured in the tissues of the lambs and ewes. The Se75-concentration in the tissues of the lambs was about half that of the ewes when they were injected with selenite. This indicates that the placenta constitutes to a certain extent a barrier for the passage of inorganic selenium. Se75-selenomethionine and Se75-selenocystine were more easily transferred across the placenta than Se75-sodium selenite. When the selenite dose was increased ten times the selenium uptake in milligrams per gram tissue in the lambs increased 5–8 times. Die Ubertragung des Selens auf den Fotus wurde bei dreizehn hochtrachtigen Mutterschafen untersucht. Den Mutterschafen wurde entweder Se75-Natriumselenit (zwei verschiedene Dosen: 0,48 oder 5,1 mg Se), Se75-Selencystin oder Se75-Selenmethionin subkutan injiziert. Zwolf Lammer und neun Mutterschafe wurden gleich nach dem Partus getotet und die Se75-Konzentration in den Geweben der Lammer und der Mutterschafe gemessen. Als den Mutterschafen Selenit injiziert wurde, betrug die Se75-Konzentration in den Geweben der Lammer ungefahr die Halfte der in den Geweben der Mutterschafe vorhandenen. Dies deutet darauf hin, dass die Plazenta ein gewisses Hindernis fur die Passage anorganischen Selens von der Mutter zum Fotus bildet. Se75-Selenmethionin und Se75-Selencystin passierten die Plazenta leichter als Selenit. Die Se75-Konzentration bei den Lammern war hier in den meisten Organen ebenso hoch und in gewissen Organen sogar noch hoher als bei den Mutterschafen. Wurde die Selenitdosis zehnfach erhoht, so nahm der Selenzuschuss in den Geweben der Lammer funf- bis achtmal zu, in Milligram Se pro Gramm Gewebe gerechnet. Overforingen av selen till foster un der soktes pa tretton hogdraktiga tackor. Tackorna injicerades subkutant antingen med Se75-natrium-selenit (tva olika doser: 0,48 eller 5,1 mg Se), Se75-selencystin eller Se75-selenmetionin. Tolv lamm och nio tackor avlivades strax efter forlossningen och Se75-koncentrationen mattes i lammens och tackornas vavnader. Nar tackorna injicerades med selenit var Se75-koncentrationen i lammens vavnader omkring halften av den i tackornas. Detta tyder pa att placentan utgor ett visst hinder for det oorganiska selenets passage fran moder till foster. Se75-selenmetionin och Se75-selencystin passerade placentan lattare an selenit. Se75-koncentration hos lammen var da i de fiesta organ nastan lika hog som och i vissa organ hogre an hos tackorna. Nar selenitdosen okade tio ganger okade selentillskottet i lammens vavnader fem till atta ganger raknat i milligram Se per gram vavnad.

The use of purified aminoacid mixtures in children with inborn errors of metabolism on protein restricted diets has led to a reduction of the intake of most essential micronutrients. As an integral part of glutathione peroxidase(GSH-Px), se is considered to be essential:it should thus be provided in adequate amounts as a biologically active compound as to prevent selenium deficiency.