Selenium behavioral effect

Neurotoxicity. Data from an epidemiological study of humans and from studies in livestock indicate that the central nervous system is an end point of concern following oral exposure to selenium compounds (Baker et al. 1989 Boylan et al. 1990 Cukierski et al. 1989 Harrison et al. 1983 Panter et al. 1996 Rosenfeld and Beath 1964 Stowe et al. 1992 Tsunoda et al. 2000 Yang et al. 1983). Chronic oral exposure studies of laboratory animals that focus on behavioral effects and histopathological changes in the central nervous system might provide useful dose-response information on central nervous system effects. 

Thus, the ion radical salt of BTDM-TTF (ET) with TCNQ has a high conductivity of 1.3 X 102 fl-1cm-1 at room temperature with metallic behavior down to 26 K (Rovira et al. 1994). (The unit of conductance is denoted as H-1, or ohm-1, or even mho, but mostly as S, i.e., siemens 1 S = 1 Ti1). The striking observation was made that the nature and molecular size of donor or acceptor have no substantial effect on the molecular distance within a stack (from 0.32 to 0.35 nm). Meanwhile, increasing the volume of a heteroatom leads to improving intermolecular interactions within given stacks. The enhanced inter-molecular interactions were indeed observed with the substitution of selenium for sulfur. The aforementioned orbital dispersion is more pronounced in the selenium-containing representatives. This arises from the more extensive overlap properties of selenium (Beer et al. 2001). 

Figure 92 Typical transient current pulses for holes in amorphous selenium (see Ref. 422a), illustrating the effect of temperature on the degree of the dispersion in carrier transport. Left linear current (i) and time (t) axes right normalized values in logarithmic axes log(i/io) vs. log(t/t0). The arrows indicate the position of the knee dividing the two regimes of logarithmic dependence. Similar behavior can be observed in organic solids (see e.g. Ref. 422b).

It may be concluded, therefore, that attempts to provide too detailed a comparison of the coordination behavior of the chalcogeno-cyanate ions are not useful until a better understanding is obtained of the differing effects of the cyano group on the atom X in NCX . Such an interaction may, and probably does, modify the comparative chemistry that might be expected for the oxygen, sulfur, or selenium... 

Many of the health and environmental problems caused by arsenic and selenium were not predicted until recently because the distribution and behavior of arsenic and selenium in the environment were not sufficiently well known. Recent improvements have been aided by cost-effective analytical techniques and more powerful data-processing techniques, which have made it easier to prepare high-resolution geochemical maps. Also, modem digital data sets of geochemical and hydrochemical data are used increasingly in studies designed to estimate element speciation, bioavailability, and risk. 

More recently, Peraniemi et al. [229] advocated the use of zirconium-loaded activated charcoal as an effective adsorbent for mercury (and especially for arsenic and selenium), the rationale being that the presence of active metal on an impregnated charcoal surface can greatly affect the adsorption affinity. They compared the pH effects on the uptakes by both a loaded and an unloaded commercial charcoal powder and concluded that the adsorption mechanism of mercury differs from that of the anionic arsenic and selenium species. They also noted the highly complicated behavior of mercury in aqueous solutions and did not attempt to explain the apparent absence of pH dependence of the uptakes. 

Sher L. Role of thyroid hormones in the effects of selenium on mood, behavior, and cognitive function. Med Hypotheses 2001 57 480-3. 

Allylic functionalization of 187 could not be effected under a variety of conditions (e.g., A-bromosuccinimide, lead tetraacetate, selenium dioxide), nor could an additional double bond be introduced under dehydrogenation conditions (e.g., chloranil). Osmium tetroxide was ineffective in hydroxylation of 187 however, potassium permanganate treatment gave the diol 189 although in only 5.5% yield [originally reported as 33% (67)]. Compound 189 could be converted into 190 again in low yield (4.5%). The latter was shown to be identical with yet another degradation product (68, Scheme 11) of securinine by comparison of IR spectra and GLC behavior. 

Fig. 5. Isobaric volume v versus T, illustrating volume hysteresis effect. The equilibrium curve in the liquid well above Tg is unique. At a constant cooling rate g, the V falls out of equilibrium below Tg. When the sample is then annealed at constant T, the volume becomes densified and may reach a relaxed glass state, depending on the temperature. The lower portion of the solid curve represents the behavior after heating at constant q. Note c remains under its liquid value to T> Tg. This plot is similar to that found for amorphous Selenium in Ref. 71 and for a polymeric system in Ref. 79.

Once the ability of the IC-ICP-MS system to repeatedly separate the three selenium species was confirmed, efforts focused on investigating process variables which would influence the concentration of various selenium species, specifically selenocyanate (SeCN) in the SSW. One such process variable studied was pH. The study of the pH effects on the conversion of the SeCN to other selenium species, such as selenate and selenite, was undertaken to define the pH boundaries fiir any pre-treatment or treatment conditions for the SSW. Knowledge of tbrs behavior would influence the design of any systems, e.g., iron co-precipitation, built to remedate the Se in the SSW streams. 

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