Assessment of anthropogenic contamination in an urban territory by the example of Blagoveshchensk city

Abstract

The distribution of heavy metals (HM) was analyzed in soils of Blagoveshchensk. The main physicochemical features (pH, the content of organic substance, mobile forms of phosphorus and potassium, the exchangeable cations of calcium and magnesium, as well as the total content of Cu, Cr, Ni, Co, Pb, Mn, Cd, Zn) were studied in soil samples. The anthropogenic influence on the urban environment transforms the physicochemical properties of soils: alkalizes the soil cover, increases the organic matter content, exchangeable bases, and mobile forms of biogenic elements. The total content of studied HM in the soils of Blagoveshchensk exceeds their concentrations in soils of the Mukhinka background territory and shows the spatial heterogeneity of pollutants distribution in the upper soil layer. As proceeds from the comparison of the studied elements concentrations with their MPC/APC, the most polluted territories are confined to industrial zones. Four elements, i.e., Mn, Pb, Cd and Zn, are accumulated in urban soils. However, Cu, Ni, Co, Cr accumulation is not so important. The calculation results of total contamination index in the upper soil cover layer in Blagoveshchensk taking into account the HM toxicity coefficient prove that Blagoveshchensk soils are mainly classified as moderately hazardous and nonhazardous. The evidence on the total content of HM do not allow making conclusion about their geochemical behavior in soils and about possible transition to neighbor environment. That is why the most mobile and easily mobilized forms of heavy metals, i.e., water-soluble and specifically adsorbed forms, were extracted using the method of successive extractions. The mobility of metals was established to be higher in the urban soils as compared to the background soils. Among the studied elements, Cd, Pb and Zn proved to be the most hazardous, with their mobility being close to the average risk of being included in the nutrition chains. This may lead to the contamination of Amur cross-boundary river ecosystems with heavy metals in case the groundwater level rises in the Blagoveshchensk territory due to its waterlogging by the Zeya River water.