Application of Biological Research Methods for Diagnosis of the Ecological Status of Urban Soils Contaminated with Heavy Metals and Petroleum Hydrocarbons in St. Petersburg

The aim of this study is to conduct a comprehensive assessment of soils in the Vasileostrovskii District of Saint Petersburg. The following parameters have been determined in 16 samples of Urbic Technosol taken from four functional zones (transport (TZ), park-recreational (PRZ), industrial (IZ), and residential (RZ) ones): the content of mobile forms of heavy metals (Cd, Cu, Pb, Ni, and Zn), the total content of petroleum hydrocarbons, agrochemical properties (pH, available P, available K, total C, and total N), phytotoxicity (using Avena sativa as a test object), and parameters of microbiological activity (basal respiration, microbial biomass, metabolic quotient qCO2, and microbial quotient QR). The Cu and Pb content in most samples exceeds their maximal permissible concentrations (MPC). The petroleum hydrocarbon content at two sampling sites (2 and 4) exceeds the approximate permissible concentration (APC) by a factor of 1.1–1.4. The assessment of the biological status of soils has revealed a strong inhibition in microbiological activity and a stressed status of microbial communities. A reduction in seed germination (to 51% of the control), suppression of basal respiration by 40–70%, a significant decrease in microbial biomass, and an increase in the metabolic quotient qCO2 (3.4–6.4 μg C/(mg Cmic h)) are detected in most contaminated samples. It has been established that the content of petroleum hydrocarbons is a key stress factor, suppressing soil microbiological activity and plant seed germination, whereas the growth of plant vegetative organs is inhibited by elevated pH values. Assessment of the biological and ecological indicator of the studied urban soils indicates deterioration in the status of urban ecosystems in the following order: PRZ > RZ > IZ > TZ.