Among the most startling observations in mammalian toxicology is that a lethal dose of selenium
can be overcome by an otherwise lethal dose of arsenic. We report the molecular basis of this antagonism.
Using X-ray absorption spectroscopy we have identified a new arsenic−selenium compound in the bile of
rabbits injected with aqueous selenite and arsenite solutions. This compound contains equimolar arsenic and
selenium and exhibits X-ray absorption spectra which are essentially identical with those of a synthetic species
in solution which we have identified spectroscopically as the seleno-bis(S-glutathionyl) arsinium ion. The in
vivo detection of this compound links the mammalian metabolism of arsenite, selenite, and sulfur. It provides
a molecular basis for the antagonistic interaction between these metalloid compounds, and a potential explanation
of the association of cancer with prolonged intake of inorganic arsenic in humans.
Raman and FTIR spectroscopies are used to investigate the sorption mechanisms of benzene, toluene, and 2-and 4-picoline onto silica as models for volatile aromatic pollutant interactions with a soil constituent. Benzene and toluene vapor adsorption on silica occurs via weak π-system-hydrogen bonding with silanols on the silica surface. This weak interaction would likely result in low vadose zone retention, especially in wet conditions where water adsorption would successfully compete for surface sites. The vapor adsorption of 2-and 4-picoline (2-and 4-methylpyridine) is studied to model aza-arene environmental contaminants. These species adsorb to surface silanols by a more specific and stronger hydrogen-bonding mechanism involving the lone pair electrons on the N atom. The strength of these interactions is probably sufficient to result in their retention by dry or damp vadose zone soil, slowing their transport. This work illustrates the utility of these vibrational spectroscopic techniques in elucidating specific surface interactions of pollutants with mineral oxides and in helping to predict the fate of pollutants in the environment.
A graphite rod electrothermal vaporizer used to introduce microliter-sized samples into a direct current plasma (DCP) atomic emission spectrometer is reported in this work. Several important experimental conditions were found to be important in achieving good analytical performance from the electrothermal vaporization (ETV-DCP) system. A combination of lowered plasma electrode sleeve gas flow rates, when compared to that commonly used in the DC plasma jet, and relatively low carrier gas flow rates resulted in very good analytical performance. Relative precision for the ETV-DCP instrument using B, Cd, Cu, Fe, and Pb solutions ranged between 4% and 10%. Limits of detection (LOD) lower than 100 pg were achieved for these elements, roughly an order of magnitude better than other ETV-DCP studies that used commercial graphite boat/furnace combinations. In addition, good calibration linearity was observed, with 2 -4 orders of magnitude linearity for the elements investigated.
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