EN
The influence of different concentrations (1-2000 ppm) of Sn, Cd, Mn, Cu, Ni, Co, Pb, Zn and Hg on the survival of heterotrophic bacteria in bottom sediments of a eutrophic lake of gyttja type was examined. Cl, NO3 and SO4 salts were used in the experiment. Co, Ni and Ag were the least toxic heavy metals for heterotrophic bacteria of the bottom sediments of the eutrophic lake, whereas Hg, Sn, Pb, Cu and Mn were more toxic and Cd and Zn were the most toxic. In the presence of the toxic metals the percent of surviving heterotrophic bacteria decreased with the increase of the concentration of metals. Death curves of these microbes were very close to the sigmoidal curve. Mathematical analysis of research results showed the existance of co-interaction of Sn, Cd, Mn, Cu, Ni and Ag concentrations and the time of experiment on the mean number of heterotrophic bacteria in the examined samples of the bottom sediments of the eutrophic lake. The time of metal contact influences the amount of heterotrophic bacteria of the bottom sediments at a lower degree than its concentration.