Speciation of methylmercury and Hg(II) using baker's yeast biomass (Saccharomyces cerevisiae). Determination by continuous flow mercury cold vapor generation atomic absorption spectrometry.

Baker's yeast cells (Saccharomyces cerevisiae) were successfully used to selectively separate methylmercury and Hg(II). Several parameters affecting the degree of biosorption and the binding kinetics of methylmercury and Hg(II) were evaluated: solution pH, temperature, incubation time, amount of biomass and analyte, and presence of foreign ions. Methylmercury is immediately bound to the yeast cells over a wide pH and temperature range. The fraction of methylmercury bound was in all cases 100% and was unaffected by the parameters mentioned above. Hg(II) has less affinity for yeast cells and remains in solution, although the percentage of Hg(II) bound to the cell does increase at high incubation time (3 h) and biomass. Of the foreign ions tested, chloride at high concentrations strongly increases the Hg(II) binding efficiency. Methylmercury and Hg(II) are quantitatively separated under optimum conditions, i.e., 30 min incubation time at pH 7.0 and 37 degrees C. The results were compared with those obtained using a purified S. cerevisiae isolate, and no significant differences were observed. Our work suggests that the cell rapidly reduces CH3Hg+ to more volatile species, such as Hg(I) or Hg0, whereas Hg2+ is slowly bound and reduced, perhaps because of the different toxicities of the two species. The method was applied to the selective determination of CH3Hg+ and Hg(II) in spiked water samples. In all cases good recoveries were obtained.