Selenate/selenite

Thousands of compounds of the actinide elements have been prepared, and the properties of some of the important binary compounds are summarized in Table 8 (13,17,18,22). The binary compounds with carbon, boron, nitrogen, siUcon, and sulfur are not included these are of interest, however, because of their stabiUty at high temperatures. A large number of ternary compounds, including numerous oxyhaUdes, and more compHcated compounds have been synthesized and characterized. These include many intermediate (nonstoichiometric) oxides, and besides the nitrates, sulfates, peroxides, and carbonates, compounds such as phosphates, arsenates, cyanides, cyanates, thiocyanates, selenocyanates, sulfites, selenates, selenites, teUurates, tellurites, selenides, and teUurides. 

Wells, J.M. and D.H.S. Richardson. 1985. Anion accumulation by the moss Hylocomium splendens uptake and competition studies involving arsenate, selenate, selenite, phosphate, sulphate and sulphite. New Phytol. 101 571-583. 

The body of research on isotopic fractionation induced by sulfate and nitrate reduction provides insight into selenate, selenite and chromate reduction. For sulfate and nitrate oxyanions, reduction is generally microbially mediated, is irreversible, and involves a fairly large but variable isotopic fractionation. As described below, Se and Cr oxyanion reduction follows suit, though abiotic reactions may have a greater role in some transformations. 

Zinc forms a wide variety of other salts, many by reaction with the adds, though some can only be obtained by fusing the oxides together. The salts include arsenates (ortho, pyro, and meta), the borate, bromate, chlorate, chlorite, various chromates, cyanide, iodate. various periodates, permanganate, phosphates (ortho, pyro, meta, various double phosphates 1. die selenate, selenites, various silicates, fluosilicate. sulfate, sulfite, and duocyanate. 

Maier, K.J. and Knight, A.W. (1993) Comparative acute toxicity and bioconcentration of selenium by the midge Chironomus decorus exposed to selenate, selenite, and seleno-DL-methionine, Archives of Environmental Contamination and Toxicology 25 (3), 365-370. 

Coordination polymers, open-framework materials, and hybrid compounds built up with various anions have been described in the literature. The most common anions employed in open-framework structures are silicates and phosphates.1-3 Metal carboxylates with a variety of structures and dimensionalities have also been described in the recent literature.4 5 In recent years, other oxyanions such as sulfate, selenate, selenite, and tellurite have also been employed to design these structures.6,7 Surprisingly, coordination polymers... 

Selenates, selenites, and tellurates. Uranyl selenates and selenites have been prepared and can be expected to have the same coordination features as the sulfates and sulfites. In addition to the selenate, U02Se04, the ternary selenite (U02)2(OH)2(Se03), has been reported to form in... 

VI 0 OH, UjO, borates and polyborates, silicate and polysilicates, borosilicates and aluminosilicates, columbates, tantalates, P04 ", As04 , antimonates, antimonites, aisenites, germanates, germanites, V04 , Cr04 , Mo04 , W04, S04 , COj , NOj", selenate, selenite, tellurate, tellurite, iodate, organic hydroxyl and carboxylate... 

Fig. 50. Uranyl selenate-selenite sheet in the structure of [C5Hi4N]4[(U02)3(Se04)4(HSe03)(H20)](H2Se03)(HSe04).

Biological Materials Selenate Selenite Percentage Distribution Other References... 

Trade names Bio-Active Selenium (Solaray) Exsel Shampoo Head Shoulders Intensive Treatment Dandruff Shampoo (Procter Gamble) Selenate Selenite selenium dioxide selenium sulfide selenocysteine SelenoMax (Source Naturals) selenomethionine Selsun Blue (Chattem) Selsun Shampoo (Chattem) Vpak5 I... 

Some epidemiological studies report data from populations exposed to selenium in the food chain in areas with high selenium levels in soil. It is likely that selenite, selenate, and the selenium found in food and in dietary supplements comprise the majority of selenium compounds to which oral, off-site selenium exposures will occur at or near hazardous waste sites. Aside from the variation in effective dose, the health effects from exposure to selenate, selenite, and dietary selenium are not expected to differ greatly. However, oral exposures to many other compounds of selenium could occur (primarily through soil or edible plant ingestion) if those compounds were deposited at the site, or if local environmental conditions greatly favor transformation to those forms. Heavy metal selenides, aluminum selenide, tungsten diselenides, and cadmium selenide are used in industry and may end up in waste sites. 

Clausen J, Nielsen SA. 1988. Comparison of whole blood selenium values and erythrocyte glutathione peroxidase activities of normal individuals on supplementation with selenate, selenite, L-selenomethionine, and high selenium yeast. Biol Trace Elem Res 15 125-138. 

Schroeder HA. 1967. Effects of selenate, selenite and tellurite on the growth and early survival of mice and rats. J Nutr 92 334-338. 

The effect of selenate, selenite and sulfate on six species of unicellular algae. J Exp Mar Biol Ecol 57 181-194. 

Figure 4 Depth profiles for concentrations of total selenium and different chemical forms of selenium (selenate, selenite, and organic selenium compounds) in filtered seawater samples from the eastern tropical North Pacific Ocean (18° N, 108° W Oct.-Nov. 1981). Data are from Cutter GA and Bruland KW (1984) The marine biogeochemistry of selenium A reevaluation. Limnology and Oceanography 29 1179-1192.

The concentrations of the mixed standard (selenate, selenite, and selenocyanate) were confirmed by measuring the total selenium concentration of the solution. The mixed standards were also carried through the digestion procedure as a quality control check of the recovery. Recoveries were generally in the range of 95-98 %. Examples of the spike information, as well as a comparison of total Se data versus the sum of the calculated species can be found in Table 4. 

Suarez et al. (36) use a combination of FTIR spectroscopy, electrophoretic mobility and pH titration data to deduce the specific nature of anionic surface species sorbed to aluminum and silicon oxide minerals. Phosphate, carbonate, borate, selenate, selenite and molybdate data are reviewed and new data on arsenate and arsenite sorption are presented. In all cases the surface species formed are inner-sphere complexes, both monodentate and bidentate. Two step kinetics is typical with monodentate species forming during the initial, rapid sorption step. Subsequent slow sorption is presumed due to the formation of a bidentate surface complex, or in some cases to diffusion controlled sorption to internal sites on poorly crystalline solids. 

Identification of the specific species of the adsorbed oxyanion as well as mode of bonding to the oxide surface is often possible using a combination of Fourier Transform Infrared (FTIR) spectroscopy, electrophoretic mobility (EM) and sorption-proton balance data. This information is required for selection of realistic surface species when using surface complexation models and prediction of oxyanion transport. Earlier, limited IR research on surface speciation was conducted under dry conditions, thus results may not correspond to those for natural systems where surface species may be hydrated. In this study we review adsorbed phosphate, carbonate, borate, selenate, selenite, and molybdate species on aluminum and iron oxides using FTIR spectroscopy in both Attenuated Total Reflectance (ATR) and Diffuse Reflectance Infrared Fourier Transform (DRIFT) modes. We present new FTIR, EM, and titration information on adsorbed arsenate and arsenite. Using these techniques we... 

The MBfR is another process variation and typically referred to a membrane biofilm reactor where hydrogen is the electron acceptor. A large number of bacteria can use hydrogen as an electron acceptor, and the delivery of hydrogen via a membrane offers an efficient and safe solution. A number of studies have been undertaken for the hydrogenotrophic reduction of pollutants such as perchlorate, chlorate, chlorite, bromate, chromate, selenate, selenite, arsenate, and dichlo-romethane. A recent review of the technology is provided by Martin and Nerenberg [67]. 

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