EFFECTS OF SEWAGE SLUDGE ON THE ACCUMULATION OF HEAVY METALS IN URBAN SOILS

The aim of this study was to evaluate the accumulation of heavy metals in soil fertilized with municipal sewage sludge from the Municipal Wastewater Treatment Plant in Sokolka. The study was conducted on four specially prepared test areas along main streets of Bialystok. The experimental plots were sown with two lawn grass mixtures: Eko and Roadside, and three doses of sewage sludge 0.0 (control), 7.5 kg/m(2) and 15.0 kg/m(2) were used. The study included the determination of dry matter and content of Pb, Cu, Zn, Ni and Cd in soil. The heavy metal content in soil was in the acceptable level for soils of urban areas defined in the regulation of the Ministry of the Environment on the standards of the quality of soil. The general content of Zn in soil was significantly correlated with the concentrations of Pb (r = 0.4), Cu (r = 0.9) Mn (r = 0.5) and Ni (r = 0.4), while the concentrations of Ni with the level of Cd and Cu (respectively, r = 0.4 and 0.5). There was also a correlation between the content of Cd and Ni indeed (r = 0.4), Cu and Pb (r = 0.6) and Cu and Mn (r = 0.7) at alpha = 0.05. The biomass of grass mixtures obtained depended on the applied sludge dose and the location. Moreover, biomass was correlated with the content and composition of soil organic carbon and granulometric composition, respectively (r = 0.6, and r = 0.5). Soil properties, arising from its particle size, were indeed correlated with the content of metals in the soil. The content of sand was negatively correlated with the concentrations of Zn (r = -0.8), Pb (r = -0.5), Cu (r = -0.9), Mn (r = -0.5) and Ni (r = -0.6), and the concentrations of silt and clay were positively correlated with the level of Zn, respectively, (r = 0.8 and r = 0.6), Cu (r = 0.9 and r = 0.7) and Ni (r = 0.6 and r = 0.7) at alpha = 0.05. The pH values measured in water and 1 M KCl for all soil samples ranged from 6.94 to 8.02, which means that in every measure point studied heavy metals concentrations in the soil are not a threat to the environment.