Fate Of Se Research Articles

Selenium metabolism and bioavailability.

Selenium (Se) is at once an essential and toxic nutrient that occurs in both inorganic and organic forms. The biological functions of Se are mediated through at least 13 selenoproteins that contain Se as selenocysteine (Se-cyst). The endogenous synthesis of this amino acid from inorganic Se (selenide Se-2) and serine is encoded by a stop codon UGA in mRNA and involves a unique tRNA. Selenium can also substitute for sulfur in methionine to form an analog, selenomethionine (Se-meth), which is the main form of Se found in food. Animals cannot synthesize Se-meth or distinguish it from methionine and as a result it is nonspecifically incorporated into a wide range of Se-containing proteins. The metabolic fate of Se varies according to the form ingested and the overall Se status of an individual. This paper reviews the bioavailability, including absorption, transport, metabolism, storage, and excretion, of the different forms of exogenous and endogenous Se.

Uptake, transformation and fixation of Se(VI) by a mixed selenium-tolerant ecosystem

The uptake, transformation and fate of Se, added as selenate to a mixed microbial ecosystem containing Se-tolerant bacteria and cyanobacteria, has been studied in simulated laboratory ponds. There was evidence of concerted activities of the microbial community in the system. Motile bacteria were responsible for transport into a surface mat and the combined actions of the microbial consortium provide chemical conditions under which the Se could be reduced to the elemental form and physically entrained in the mat. Strong qualitative indications of the formation of volatile alkylselenium compounds were also observed. The removal of Se from the water column was rapid and essentially quantitative. The advantages of such biological ecosystems for remediation of Se-contaminated aquatic ecosystems are discussed.

Effects of Soil Flooding on Selenium Transformations and Accumulation by Rice

AbstractThe fate of Se in flooded soil is not well known. This greenhouse study was conducted to determine the fate of Se in flooded soil and to determine the effects of Se on plant growth. Rice plants (Oryza sativa L. cv. M101) were grown in pots containing Panoche loam soil (fine‐loamy, mixed, calcareous, thermic Typic Torriorthents) to which 0, 1.5, 3, and 6 mg Se kg−1 as Na2SeO4 was added. Rice was grown in continuously flooded or nonflooded (upland) soil. The flooded treatments were amended with organic matter (OM) at concentrations of 0, 2.5, and 5 g cellulose kg−1. Soil solution samples were taken weekly from the flooded treatments and analyzed for pH, Eh, EC, and Se concentration and Se oxidation state. Plants were harvested and analyzed for Se at three plant growth stages. Selenate soil solution concentrations were reduced 95% after 6 and 10 wk following flooding for the 5.0 and 0 g OM kg−1 treatments, respectively. Selenite in solution reached a maximum concentration (340‐1920 µg Se[IV] L−1) 5 to 8 wk after flooding and then decreased to trace levels (<0.5 µg L−1). Selenium accumulated in all rice plant parts in direct proportion to the added Se. Plants grown in flooded soil with added OM had tissue Se concentrations <20% that of rice grown without added OM or in upland conditions. Selenium phytotoxicity symptoms were observed in plants grown in flooded soil without OM and in the upland soil when Se was added. Tissue Se concentrations associated with a 10% reduction in shoot dry matter were 160 and 81 mg Se kg−1 for upland and flooded rice (without added OM). No Se‐induced yield loss occurred when OM was added to flooded soil. Flooding those soils containing Se[VI] may be an effective way to reduce soluble Se concentrations in soil to nontoxic concentrations.