SUBJECTS selenite

Selenium has a complex chemistry in the environment because of its multiple oxidation states and variable surface adsorption properties. Qualitatively it is analogous to sulfur occurring in the oxidation states +6 (selenate, Se04 ), +4 (selenite, SeOs "), 0 (elemental selenium) and —2 (Se, selenide) The Se anion closely resembles S (radii 0.20 and 0.185nm, respectively) and is often associated with sulfide minerals. Also, like S, Se is subject to volatilization through biological methylation. 

By the action of hydrazine hydrate on a dilute solution of selenic acid, hydrazine hydrogen selenate may be obtained as a colourless compound which is not decomposed by boiling water, but which, when dry, explodes with great readiness when subjected to heat, to shock, or to fumes of hydrogen chloride. For this reason, before hydrazine hydrate is used in the analysis of selenium compounds (see p. 307), it is essential that selenic acid and selenates should be reduced to selenites by means of hydrochloric acid.3... 

Sodium selenite, at nanomolar concentrations, improved the depressed cardiac performance of the isolated heart subjected to ischemia/reperfusion injury. As ischemia/reperfusion-mediated cardiac function has been reported to occur mainly due to the development of oxidative stress and intracellular Ca2+ overload (Bolli and Marban 1999), it is likely that selenium could protect the heart... 

Table 8.2 Effects of sodium selenite (Se) on mechanical performance of hearts under is-chemia/reperfusion (I/R), or perfused with xanthine plus xanthine oxidase (X + XO), or hydrogen peroxide (H2O2), or subjected to Ca2+ paradox model...

The hearts were exposed to 75 nM sodium selenite (Se) 10 min before ischemia (or perfusions with X + XO or H2O2 or subjected to Ca2+ paradox) and 30 min during reperfusion (or 30 min perfusion with the Ca2+-containing solution). LVDP left ventricular developed pressure LVEDP left ventricular end developed pressure. Data represent means ( SEM). p < 0.05 versus I/R. (Adapted from Turan et al. 2005.)... 

Subject to limitations discussed in section 4.1., the effects of pH on anions are similar to those observed using iron oxides. Thus, the sorption of phosphate and of selenite generally decrease with increasing pH (Fig. 12.) for the reasons discussed earlier. Similar principles apply for borate. However sorption increases with increasing pH because the pK for borate dissociation is near 9. The concentration of borate ions therefore increases 10-fold for each... 

Crystalline potassium trihydrogen selenite was prepared and subjected to chemical and X-ray analysis for confirmation of the composition and crystalline state. The compound was reacted in stoichiometric proportions with a solution of lead nitrate in an electrically calibrated calorimeter. The lead selenite formed was crystalline and the reaction was quantitative. The calorimetric data have been used to calculate the enthalpy change of the reaction KH3(Se03)2(cr) + 2Pb 2PbSe03(cr) + K + 3H in Table A-83. 

No studies have demonstrated that selenium or its compounds are teratogenic in humans. Robertson (1970) reported on the outcome of pregnancies in a laboratory in which workers handled sodium selenite. Of the five pregnancies, four ended in spontaneous abortion and one resulted in an infant with bilateral clubfoot. The urinary selenium levels in all subjects were similar to those in other individuals living in the same area. The limited number of cases, possible exposure to other toxic agents, and other confounding factors leave the relationship between sodium selenite and developmental effects inconclusive. 

Description of the model. Swanson and coworkers (Patterson et al. 1993 Swanson et al. 1991) produced a model for ingested selenomethionine in adult humans based on data from human subjects who consumed a single oral dose of 200 pg 74Se as selenomethionine and the model of the kinetics of ingested selenite described above. Four major changes (indicated by bold lines in Figure 3-9) were made to the selenite model to achieve an adequate fit to the selenomethionine data (1) the amount of label absorbed into the enterocyte was increased (the absorption of 74Se was 98% for selenomethionine compared with... 

The geographical distribution of KBD and Keshan disease is overlapping in northern China. Because there is a very strong spatial correlation between selenium deficiency and Keshan disease, some authors claim the same relationship exist between selenium deficiency and KBD (Allander, 1994 Yang et al., 1988). Selenium levels in food, and also in blood and hair samples, from subjects living in areas where KBD is endemic are systematically lower than in those from nonendemic areas (Wu and Xu, 1987). Clinical trials of oral selenite—vitamin E or sodium selenite alone have been reported as an effective cure for KBD (Yang et al., 1988), but these early studies have not been confirmed to date. 

The interaction of selenium and methylmercury in the brain appears to be very complex. Despite the clear protective effect of selenite on methylmercury toxicity, selenium increases the mercury content of brain (Prohaska and Ganther, 1977 Chen et al, 1975a). Methylmercury tends to cause a shift in the concentration of selenium from the cytosol to the mitochondrial fraction in the brain. Gel filtration of the brain cytosol, however, revealed that mercury followed a pattern more closely related to protein than to selenium (Prohaska and Ganther, 1977). Therefore, the mechanism of the protective effect of selenium against methylmercury toxicity is still a subject for speculation. 

Hawrylak-Nowak B (2009) Beneficial effects of exogenous selenium in cucumber seedlings subjected to salt stress. Biol Trace Elem Res 132 259-269 Hawrylak-Nowak B (2013) Comparative effects of selenite and selenate on growth and selenium accumulation in lettuce plants under hydroponic conditions. Plant Growth Regul 70(2) 149-157. doi 10.1007/s 10725-013-9788-5... 

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