Selenium

About: Selenium is a research topic. Over the lifetime, 21192 publications have been published within this topic receiving 429715 citations. The topic is also known as: Se & selen.

Contaminants in Drainage Water and Avian Risk Thresholds

Abstract: The toxicity of selenium to avian embryos is one of the most restrictive constraints on options for managing agricultural drainage water. Although selenium in eggs strongly predicts embryotoxicity, waterborne selenium (on a total recoverable basis) often is an unreliable predictor of average realized selenium in eggs. For the San Joaquin Valley, however, the algebraically derived equation Log (Mean Egg Se) = 3.66 + 0.57 Log (Waterborne Se) is a good predictor of the maximum potential for selenium bioaccumulation in avian eggs. Using eared grebes (Podiceps nigricollis) as an indicator species for bioaccumulation potential, the average absolute difference between observed and predicted mean selenium in eggs was only 6 percent for test cases at waterborne concentrations of 2.8, 15, 126, 176 p/b (total recoverable) selenium. Various estimates of biologically important thresholds indicate that it would be prudent to consider drainage water with 3 to 20 p/b selenium as peripherally hazardous to aquatic birds (i.e., hazardous to some species under some environmental conditions) and drainage water with more than 20 p/b selenium as widely hazardous to aquatic birds (i.e., hazardous to most species under most environmental conditions). To prevent most avian toxicity, a reasonable goal for chemical or biological decontamination technologies would be concentrations of waterborne selenium < 10 p/b. Likewise, to minimize avian contamination, a reasonable goal of purity would be waterborne selenium < 2.3 p/b. When these water standards are technically or financially unattainable, actions to significantly reduce avian use of contaminated drainage water are necessary.

Plasma selenium in specific and non-specific forms.

Abstract: Selenium is present in plasma and tissues in specific and non-specific forms. The experiments reported here were carried out to clarify some factors that affect these forms of the element in plasma. A selenium-replete human subject was given 400 microg of selenium daily for 28 days as selenomethionine and, in a separate experiment, as selenate. The selenomethionine raised plasma and albumin selenium concentrations. Selenate did neither. The molar ratio of methionine to selenium in albumin was approximately 8000 under basal and selenate-supplemented conditions but 2800 after selenomethionine supplementation. This demonstrates that selenium from selenomethionine, but not selenium from selenate, can be incorporated into albumin, presumably as selenomethionine in the methionine pool. Selenocysteine incorporation into albumin was studied in rats using (75)Se-selenocysteine. No evidence was obtained for incorporation of (75)Se into albumin after exogenous administration or endogenous synthesis of (75)Se-selenocysteine. Thus, selenocysteine does not appear to be incorporated non-specifically into proteins as is selenomethionine. These findings are in support of selenomethionine being a non-specific form of selenium that is metabolized as a constituent of the methionine pool and is unaffected by specific selenium metabolic processes. No evidence was found for non-specific incorporation of selenium into plasma proteins when it was administered as selenate or as selenocysteine. These forms of the element appear to be metabolized by specific selenium metabolic processes.

Selenium and vitamin E inhibit radiogenic and chemically induced transformation in vitro via different mechanisms (glutathione peroxidase/catalase/glutathione/free radicals/carcinogenesis)

Abstract: Results from in vivo and in vitro studies showing that antioxidants may act as anticarcinogens support the role of active oxygen in carcinogenesis and provide impetus for exploring the functions of dietary antioxidants in cancer prevention by using in vitro models. We examined the single and combined effects of selenium, a component of glutathione peroxidase, and vitamin E, a known antioxidant, on cell transformation induced in C3H/1OT-1/2 cells by x-rays, benzo(a)pyrene, or tryptophan pyrolysate and on the levels of cellular scavenging systems and peroxide destruction. Incuba- tion of C3H/1OT-1/2 cells with 2.5 ,uM Na2SeO3 (selenium) or with 7 ,M a-tocopherol succinate (vitamin E) 24 hr prior to exposure to x-rays or the chemical carcinogens resulted in an inhibition of transformation by each of the antioxidants with an additive-inhibitory action when the two nutrients were com- bined. Celluiar pretreatment with selenium resulted in in- creased levels of cellular glutathione peroxidase, catalase, and nonprotein thiols (glutathione) and in an enhanced destruction of peroxide. Cells pretreated with vitamin E did not show these biochemical effects, and the combined pretreatment with vitamin E and selenium did not augment the effect of selenium on these parameters. The results support our earlier studies showing that free radical-mediated events play a role in radiation and chemically induced transformation. They indi- cate that selenium and vitamin E act alone and in additive fashion as radioprotecting and chemopreventing agents. The results further suggest that selenium confers protection in part by inducing or activating cellular free-radical scavenging systems and by enhancing peroxide breakdown while vitamin E appears to confer its protection by an alternate complemen- tary mechanism.