A methodology was developed about lead preconcentration in water samples that were addeddithizone as complexing agent, previously dissolved in the nonionic surfactant Triton X-114,until the formation of the critical micelle concentration and the cloud point temperature. Thecentrifuged system gave a precipitate with high concentrations of Pb (II) that was measuredby atomic absorption spectroscopy with flame (EAAF). The method has proved feasible tobe implemented as a method of preconcentration and analysis of Pb in aqueous samples withconcentrations less than 1 ppm. Several parameters were evaluated to obtain a percentagerecovery of 89.8%.

We have studied the inhibitory effect of Se(IV) concentration on Saccharomyces cerevisiae LALVIN RC 212 in 4 replicates of cell count and optic density for a 72 hours culture. Values were adjusted to the modified Gompertz model with a confidence level of 95 % and a determination coefficient higher than 0,90. We used the YEPD liquid medium (pH=6 at the beginning) at 30 °C and 200 rpm, with added selenite 5 hours after inoculation. The analysed concentrations were 2, 4, 6, 8 y 10 mg Se(IV)/L and the control. The highest value of biomass was 6,9 x107± 4,7x106 viable cells /mL and the highest growth speed was 0,646 h-1, which correspond to the concentration of 2 mg Se/L in the experimental medium. According to ANOVA (Analysis of Variance), LSD (Least Significance Difference) and the percentage of nonviable cells, the inhibition of yeast growth appeared 24 hours after inoculation, for the c...