Assessment of the mobile forms of zinc and copper content in soil samples from areas of different land use on example of the Krasnogvardeisky District of the St. Petersburg

The present study investigated the actual content of Zn and Cu mobile fractions (buffer extractable) in soils of different land use scenarios within the Krasnogvardeisky District of the Saint Petersburg (Russia). The data were obtained via Atomic Adsorption Spectrophotometry, analyzing ammonium acetate buffer extracts (pH 4.8) of soil samples collected. The buffer-extracted metals are considered to be the most mobile fractions at given soil pH conditions. The results have shown low concentrations of mobile Zn and Cu in soils of recreational, agricultural and even industrial areas, fluctuating relative to the local area soil background values (Zn = 1.2; Cu = 2.70 mg kg⁻¹). Substantial levels of contamination were found in the loamy sand Technosol of residential land use amended with composted municipal solid wastes and savage sludge. Calculated geo-accumulation indices (I _geo), pollution indices (PI) and contamination factors (C _f) were of the higher values, indicating moderate to extremely high pollution levels with the mobile trace metals. Median topsoil metal concentrations three times exceeded the maximal permissible concentrations for soils (Zn = 23.00; Cu = 3.00 mg kg⁻¹), reaching the maximal values of 69.58 mg kg⁻¹ for Zn and 10.17 mg kg⁻¹ for Cu, respectively.