Ecological risks of PTEs pollution in soils of the Lower Don floodplain and the Taganrog Bay coast

The Lower Don basin and the adjacent coastal zone of the Azov Sea are considered one of the most economically developed and anthropogenically transformed regions within Southern Russia. This territory is characterized by a high degree of urbanization, intensive agriculture, and diverse transport infrastructure facilities. Long-term anthropogenic activities have resulted in a strong transformation of the natural environment of the Lower Don floodplain, the Don Delta and Taganrog Bay coast. One of the main consequences of human activities is related to the degradation of vegetation and soil cover of subaquatic landscapes caused by pollution of potentially toxic elements (PTEs). The main aim of this study was to assess potential environmental risks of Cr, Mn, Ni, Cu, Zn, As, Cd, and Pb in soils of the Lower Don floodplain and the Taganrog Bay coast.

The floodplain and coastal landscapes of the study area are dominated by Eutric and Calcaric Gleyic Fluvisols, Gleyic Fluvisols (Humic), Gleyic Phaeozems and Haplic Chernozems which are background soils of the region are less common. Soil samples were collected in summer 2020 from the surface soil horizon (0–20 cm deep). The total concentrations of Cr, Mn, Ni, Cu, Zn, Cd, and Pb were determined in air-dried powder samples by X-ray fluorescence analysis using a Spectroscan MAX-GV spectrometer (Spectron, Russia). Environmental risks were assessed using potential ecological risk factor (Er) and the potential ecological risk index (RI) based on the single pollution index (PI) and modified potential ecological risk factor (MEr) and the modified potential ecological risk index (MRI) based on the Müller geoaccumulation index (Igeo).

The obtained results showed that Er and MEr indicated a low ecological risk for most of the PTEs studied, with the exception of Cd, which was found to be moderate in 8% and 3.5% of the samples, respectively. The highest values of both Er and MEr for Cd were detected in the soils of the Don Delta. Integral ecological risk assessed using RI and MRI, based on the sum of all Er and MEr, respectively, was low in all samples studied. Values of RI ranged from 10.52 to 86.87 with a mean of 32.2. Similar results were observed for MRI, which ranged from 7.01 to 57.91 with a mean of 21.46. The highest values of both RI and MRI were observed in soils of the Don Delta in the vicinity of urbanized territories, which indicates an additional supply of PTEs due to more significant anthropogenic pressure. Thus, according to the results of the study, the risk of a potential negative impact of soil pollution on adjacent components of the landscapes of the Lower Don and Taganrog Bay does not cause serious concerns. Apparently, a relatively favourable land-use regime with a predominance of agriculture has developed in the region.

This work was funded by the Russian Science Foundation, grant no. 20-14-00317.