EFFECT OF CADMIUM, LEAD AND ZINC ON MICROBIAL BIOMASS CARBON, NITROGEN, AND PHOSPHORUS IN RED SOIL

Laboratory incubation experiments were conducted to evaluate the toxicity of cadmium, lead, and zinc in the forms of acetates and chlorides to microbial biomass carbon, biomass nitrogen, and biomass phosphorus in a red soil. The critical levels of Cd, Pb,and Zn causing significant inhibition of microbial biomass carbon were 30,450,and 200mg/kg soil, respectively, when the metals were applied in the forms of chloride salts. The addition of Cd,Pb,and Zn in the form of acetate salts demonstrated a considerably greater biocidal effect on soil microbial biomass, because of higher solubility of acetate salts. The relative toxicity of the applied Cd, Pb, and Zn varied in the order: CdZnPb, irrespective of their forms of compounds.