Selenium Se

Another contaminant of concern for the Delta is Se. Selenium occurs in high concentrations in the soils of the western San Joaquin Valley associated with salts that have accumulated in this region [10]. Selenium is recycled through agricultural retom flows to the river and transported to the Delta and San Francisco Bay. The Se is transformed into a more bioavailable form by microbial communities and aquatic plants. The Se is passed through the foodweb with particular concern for bottomfeeding migratory waterfowl and predatory fishes. The hydrodynamics of water from the San Joaquin River is an important consideration in the intensity and distribution of Se contamination within the Delta. 

Figure 20-3. Role of the pentose phosphate pathway in the glutathione peroxidase reaction of erythrocytes. (G-S-S-G, oxidized glutathione G-SH, reduced glutathione Se, selenium cofactor.)...

Figure 45-6. Interaction and synergism between antioxidant systems operating in the lipid phase (membranes) of the cell and the aqueous phase (cytosol). (R-,free radical PUFA-00-, peroxyl free radical of polyunsaturated fatty acid in membrane phospholipid PUFA-OOH, hydroperoxy polyunsaturated fatty acid in membrane phospholipid released as hydroperoxy free fatty acid into cytosol by the action of phospholipase Aj PUFA-OH, hydroxy polyunsaturated fatty acid TocOH, vitamin E (a-tocopherol) TocO, free radical of a-tocopherol Se, selenium GSH, reduced glutathione GS-SG, oxidized glutathione, which is returned to the reduced state after reaction with NADPH catalyzed by glutathione reductase PUFA-H, polyunsaturated fatty acid.)...

Solid substances considered Se (selenium, gray, trigonal). 

Mg = magnesium S = sulfur Ca = calcium Mn = manganese Ni = nickel Se = selenium... 

Selenate is the most mobile form of Se. Selenium becomes biologically unavailable by reduction to elemental Se or by formation of metal selenides or Se-sulfides. Inorganic Se compounds can be converted to volatile organic Se such as dimethyl selenide or dimethyl diselenide by... 

Se Selenium added lo improve machinability 420 Carbon increased for higher hardness Cr, 12-14% Ni. 0.5%... 

AlkylSe and alkylTe groups can be introduced by reaction with diselenides and ditellurides, but the desired products can be prepared in a more practical and economical way, by successive addition of the elements and the alkyl halide. The insertion of the elements proceeds most easily in liquid ammonia, provided that grey Te powder and red Se powder is used (black Te powder, obtained by precipitation is unreactive, probably because of the presence of an oxide coating, while the black modification of Se,"selenium nigrum" is also less reactive). In Et20 or THF, temperatures in the range 0-20 C are necessary for the dissolution of the elements. 

PS polystyrotene PCV chlorure de polyvinyle PAV acetate de polyvinyle PXB poly isobutylene PMM polym thacrylate de mdthyle Se selenium amorplie. 

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