PECULIARITIES OF HEAVY METAL CONTAMINATION OF THE SOIL COVER IN THE CITY OF ODESA

Abstract

Among the substances that pollute the environment of urbanized areas, particularly the soil cover, a special place is occupied by heavy metals, which are usually defined as metals with an atomic mass exceeding 50 atomic mass units and a density greater than 5 g/cm³. Depending on the sources of entry into the soil cover and the properties of soils, heavy metals associated with the characteristics of parent rocks are distinguished from those entering the soil cover as a result of anthropogenic activity. Pollution with heavy metals contributes to a decrease in soil porosity and adversely affects the processes of air, water, and nutrient circulation. Unlike the more dynamic atmospheric and surface water environments, where active self-purification processes take place, the soil cover practically lacks such an ability; the processes of purification from heavy metals occur very slowly, only through leaching, plant uptake, and water erosion, which determines the long-term ecological hazard in urbanized territories. Therefore, the aim of this study is to analyze the peculiarities of heavy metal contamination in the soil cover of a city whose territory is characterized by rather diverse soil-geochemical conditions. In the process of intensive urbanization, the soil cover has been exposed to numerous anthropogenic factors, resulting in changes in its physicochemical properties and increased concentrations of heavy metals. Analysis of previously conducted studies shows that the most contaminated soils with certain heavy metals (Pb, Zn, Cu, Co) are those of industrial zones and areas adjacent to highways with heavy traffic. Among these technogenically stressed areas of urban territory, a special place is occupied by park and square areas, where the recorded concentrations of lead and zinc exceed background levels, while copper content at all sites remains below the background concentration. However, the calculated range of geoaccumulation index values for these heavy metals corresponds to soil contamination levels ranging from low to moderate, depending on the distance of the sites from sources of technogenic pollution. According to the results of experimental biosensor bioluminescent analysis of the studied soils from certain parks and squares of the city of Odesa, no pronounced inhibition of luminescence levels in microbial cells, which constitute the basis of sensor elements, was detected. This indicates the absence of substances toxic to soil microorganisms. During the analysis, a slight stimulation of microbial cell luminescence was recorded, which may be associated with the influence of an increased content of organic components in the soil samples; the analyzed soil samples were classified as having a low level of ecological toxicity, corresponding to their contamination level as indicated by the geoaccumulation index. The highest calculated values of the total ecological risk index (RI) are characteristic of the industrial (27.19) and transport (10.19) functional zones of Odesa, and these indicators correspond to a minor risk magnitude.