Inorganic selenium

Inorganic Compounds. Inorganic selenium compounds are similar to those of sulfur and tellurium. The most important inorganic compounds are the selenides, haUdes, oxides, and oxyacids. Selenium oxidation states are —2, 0, +1, +2, +4, and +6. Detailed descriptions of the compounds, techniques, and methods of preparation, and references to original work are available (1—3,5,6—10, 51—54). Some important physical properties of inorganic selenium compounds are Hsted in Table 3. 

Table 3. Physical Properties of Inorganic Selenium Compounds ...

Other inorganic selenium compounds include sodium selenocyanate [4768-87-0], NaSeCN, which is prepared by melting together selenium and sodium cyanide selenocyanogen [27151 -67-3] (SeCN)2 sodium selenosulfate [25468-09-1], Na2SeS02, which is prepared by dissolving selenium in aqueous sodium sulfite (acidification decomposes this compound) and selenate alums, eg, Al2(Se0 2 I SeO [13530-59-1]. 

Cobo, M. G., Palacios, M. A., and Camara, C., Effect of Physicochemical Parameters on Trace Inorganic Selenium Stability, Analytica Chimica Acta, 286, 1994, 371-379. 

The only means by which inorganic wastes can be rendered nonhazardous are dilution, isolation (as in deep-well injection), in some cases changes in oxidation state, and neutralization. Acidic wastes made up one-fifth of the injected waste volume and involved one-third of the injection wells in 1983. Most of the volume was from inorganic acids (hydrochloric, sulfuric, and nitric). Acid-base characteristics and neutralization were discussed in detail earlier, so the remainder of this section will focus on heavy metals and other hazardous inorganics (selenium and cyanide). 

Matsumura, H., et al. (1991). Inhibition of sleep in rats by inorganic selenium... 

Non-volatile elemental and inorganic selenium, biologically formed in bacterial or plant samples, can be determined via atomic absorption spectrometry (AAS)... 

Bertine, K.K. and E.D. Goldberg. 1972. Trace elements in clams, mussels, and shrimp. Limnol. Ocean. 17 877-884. Besser, J.M., T.J. Canfield, and T.W. La Point. 1993. Bioaccumulation of organic and inorganic selenium in a laboratory food chain. Environ. Toxicol. Chem. 12 57-72. 

Heinz, G.H., D.J. Hoffman, and L.G. Gold. 1988. Toxicity of organic and inorganic selenium to mallard ducklings. Arch. Environ. Contamin. Toxicol. 17 561-568. 

This review is conceived as a progress report. It includes only compounds of selenium and tellurium with the element directly bonded to fluorine. The chemical literature of the last 10 years, including 1979, has been searched thoroughly, and emphasis has been placed on facts rather than on interpretation. There are some earlier reviews covering the same area "Fluorine Compounds of Selenium and Tellurium 1970 (40), "Inorganic Selenium Chemistry 1975 (48), and "Inorganic Chemistry of Tellurium 1975 (53). 

Selenium is present in meat, seafood and cereals. The former two contain the highest levels. It is present in soil as inorganic selenium that enters the food chain via plants. In plant protein, it is present as selenomethionine and in animals as selenocysteine this difference is due to the metabolism of selenomethionine in the liver as part of the normal catabolic pathway for methionine (Chapter 8). Somewhat surprisingly, selenocysteine is incorporated into protein via a specific tRNA which possesses a UCA anticodon for this amino acid. 

Inorganic selenium compound Se 3d3/2,5/2 eV q Oxidation (effective charge) number ... 

Simultaneous speciation of inorganic selenium and tellurium in water samples by ICP-MS was performed after selective solid phase extraction (SPE), as discussed by Yu et al 9 Under acidic conditions Se (IV) and (TV) complexes with ammonium pyrrolidine dithiocarbamate were formed. The detection limits for Se and species in water samples were found to be 7ngl 1 and 3 ng 1 1, respectively. 

In 1957, Schwartz and associates showed that the toxic element selenium was also a nutritional factor essential for prevention of the death of liver cells in rats.527 Liver necrosis would be prevented by as little as 0.1 ppm of selenium in the diet. Similar amounts of selenium were shown to prevent a muscular dystrophy called "white muscle disease" in cattle and sheep grazing on selenium-deficient soil. Sodium selenite and other inorganic selenium compounds were more effective than organic compounds in which Se had replaced sulfur. Keshan disease, an often fatal heart condition that is prevalent among childen in Se-deficient regions of China, can be prevented by supplementation of the diet with NaSe03.528 Even the little crustacean "water flea" Daphnia needs 0.1 part per billion of Se in its water.529... 

Although inorganic selenium does not have antioxidant properties, selenium has an important role in cellular antioxidant defenses as a necessary component of selenoproteins. Selenium is incorporated into selenoproteins as selenocysteine. The glutathione (GSH) peroxidases are the best-characterized selenoproteins, although other circulating selenoproteins also have antioxidant functions. 

In laboratory animals, parenteral administration of organic and inorganic selenium (210 to 12,000 ig/kg) has been shown to protect against cisplatin-induced nephrotoxicity. Protection occurs without apparent inhibition of the antineoplastic activity of cisplatin, although this may be attributed to the fact that selenium administration allows for higher doses of cisplatin to be used. Additionally, selenium administration reduces cisplatin-induced myelosuppression. This raises a concern similar to that with administering cisplatin with thiol compounds, i.e., that the reduction of myelosuppression may indicate that selenium can also interfere with the antitumor activity of cisplatin. Selenium, with chemical properties similar to those of sulfur, can bind with platinum and... 

Camara, C., Cobo, M.G., Palacios, M.A., Munoz, R. and Quevauviller, Ph. (1998) Feasibility study for the certification of the contents of inorganic selenium (IV) and (VI) (selenite and selenate) species and total inorganic selenium in artificial freshwater reference materials. Analyst, 123, 947. 

While total inorganic selenium in seawater increases with depth, total inorganic tellurium (Te) is highest at the surface and decreases with depth. Although the +VI oxidation state is more abundant than the +IV state for both Te and Se, in contrast to Se and SeIV, Te is thermodynamically less stable than Te (Lee and Edmond, 1985). The two coexisting oxidation states of Se occur as tetrahe-drally (Se ) and pyramidally (Se ) coordinated forms whereas Te and Te are found in octahedral and tetrahedral coordination, respectively. Te, principally in the form of Te(OH)g and TeO(OH)5, decreases to values at depth that are approximately 50% of surface concentrations, while Te as TeO(OH)3 and Te02(0H)2- is approximately constant with depth. 

Interest in selenium concentrations in the environment and in foodstuffs has been due to the dual role of selenium as an essential nutrient at low concentration levels and as a toxic substance at high levels of concentration. The narrow range between the two levels requires accurate methods for measurements of selenium concentrations. Selenium can exist in a number of different chemical forms and oxidation states. Inorganic selenium can be present in the environment as selenate (Se ), selenite (Se ), elemental selenium (Se°) and selenide (Se2-). 

A detailed review of the stabilities of inorganic selenium species, i.e. Se and Se, in water has been published (Heninger et al., 1997). No loss of either species was detected in aqueous solutions stored at — 20°C for 1 year. The concentrations studied were 10 and SOngmF1 (Cobo et al., 1994). Losses of Se occurred at higher temperatures for solutions of pH 2 and 6 stored in polyethylene containers. The maximum time for preservation was 1-2 months. In another investigation (Heninger et al., 1997), aqueous samples stored in Teflon containers at 4°C lost 29% of Se by oxidation in less than 1 month. The authors stated that catalytic oxidation of Se had occurred as a result of chlorine produced by a reaction between dissolved chloride and oxygen. 

Cheam, V. and H. Agemian. 1980. Preservation and stability of inorganic selenium compounds at ppb levels in water samples. Anal. Chim. Acta 113 237-245. 

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