Pollutants and Chemical Markers of Anthropogenic Pressure in Urban Areas: A Cross-Analysis of Soil and Betula pendula Roth Bark

This work investigates the correlations between the concentrations of 40 chemical elements in soil (0–5(7) cm) and in Betula pendula Roth bark. Samples have been collected in transport and recreational areas of the city of Kirov, Russia (taiga zone, temperate continental climate). Pollution indices (PIs) are calculated by comparing the element content in the upper continental crust with that in the soil samples. The following series of elements with PI > 1 are established: Ag (4.91) > Cd (3.44) > Pb (3.16) > Sb (3.38) > Zn (2.19) > Ni (2.14) > Cu (1.69) > As (1.16) for recreational areas and Ag (2.97) > Cd (2.87) > Sb (2.11) > Cu (1.34) > Zn (1.28) > Pb (1.09) for transport areas. Birch bark accumulate most of these elements (PI > 10): Zn, Cd, Ag, Cu, Sb, Pb, Ni, Hg, Mn, Mo, Sn, Bi, and Cr. Cluster analysis is applied to the data. Soil elements are divided into two groups: metals associated with anthropogenic activity and rare-earth/noble metals, which are not typical of urban environments. A strong correlation is shown between some biogenic elements and potentially toxic metals Na and Zn (r = 0.68), P and Cd (r = 0.98), P and Pb (r = 0.99), Ca and Tl, and Cu, Ni (r = 0.95 to 0.998). Thus, Ag, Cd, Pb, Sb, Zn, Cu, Ni, and As are classified as pollutants that accumulate in the soil for a long time and may migrate to plants. Indicators of recent anthropogenic pressure include Hg, Mn, Mo, Sn, Bi, and Cr. Further monitoring should focus on Sc, V, Co, Zr, Ba, Hf, Ga, Rb, Ta, Be, Tl, Nb, Li, and Cs, as their concentrations correlate with both biogenic elements and pollutants.