BIOAVAILABILITY AND EFFECTS OF HEAVY-METALS ON SOIL MICROBIAL BIOMASSSURVIVAL DURING LABORATORY INCUBATION

In this work we studied the influence of Pb, Zn, and TI on microbial b iomass survival and activity during a laboratory incubation of soil. I n comparison to uncontaminated soil, the microbial biomass C decreased sharply in soil contaminated with Zn and Tl, whereas the addition of Pb did not have any significant inhibitory effect on the level of micr obial biomass C. Zn displayed the greatest biocidal effect, confirmed by the measurement of the death rate quotient (qD). The microbial acti vity, measured as CO2 evolution, increased significantly in contaminat ed soils, emphasizing the need of living organisms to expend more ener gy to survive. The greater demand for energy by microorganisms in orde r to cope with the toxicity of pollutants was also confirmed by measur ement of the metabolic quotient (qCO(2)). In order to determine whethe r soil microorganisms affect the bioavailability of these metals throu gh their mobilization and release, we studied the relationships betwee n available Pb, Zn, and Ti, and microbial biomass C. The water-soluble fraction of Tl, available Tl, and Zn, and microbial biomass C were re lated significantly, but not Pb.