The estimation of ecological risk in connection with the heavy metals accumulation in soil of urban forests

The ecological risk associated with the continued accumulation of Cd and Pb in sandy soils of the Perm Protected Areas was investigated. Soil-forming sands of ancient alluvial origin and the soils formed on them were characterized by a lower content of V, Mn, Ni, Zn, Zr, Mo, Cd, Sn, and Pb relative to the world clarks. The gray humus horizons of sandy soils are enriched with heavy metals in comparison with the soil-forming rock, including Cd and especially Pb. Phytotesting showed that with relatively little contamination (at a rate of 0.01 of Approximatele Permissible Concentration (APC) of Cd and Pb), the soils turned into unsatisfactory ecological conditions and acquired moderate toxicity. When these metals were applied at the rate of 0.25 APC of Cd and 0.1 APC of Pb, soils became environmentally hazardous and highly toxic. In general, the sandy soils of the Perm Protected Areas were characterized by low resistance to heavy metal contamination; the critical consequences for biocenoses of urban forests due to soil toxicity are likely to be expected with the accumulation of Cd to 0.42 mg/kg, and Pb to 21.4 mg/kg.