The input of trace elements from the motor transport into urban soils of Wrocław, Poland

The pH and the EC of soil solutions display a typical character of urban soils, and the concentration of some metal content in the selected locations indicate a strong influence of the motor transport on the Wrocław's congested roads. Sampling stands were located at the busiest road junctions. Pollution of soils with Zn, Cu, Pb, Ni, Cr and Cd along the more important traffic roads of Wrocław within the borders of the city has been measured. The internal ring road (encircling the central districts of the city) and the external ring road (the Eastern Ring Road) of the city of Wrocław along with busy exit roads on the border of city were compared. Zinc concentration in soils was exceeded locally relative to standard for soils of group I, according to the Polish Ministry of Environment Regulation from September 1st, 2016. The pollution indexes compared to the geochemical background in the uncontaminated soils of Poland showed an enrichment of Wrocław's soils with trace elements in many locations. Mean values of indexes for all samples display the dominant influence of zinc, copper and nickel on the soil contamination in Wrocław. The results of the studies did not confirm the correlation between the decrease of all metals concentration with the distance from the city center. The Pearson's correlation coefficients between pairs of Zn-Cu, Zn-Pb and Cu-Pb show significantly correlated linear relationships of metals in soils. The frequency histograms of trace elements in soils reveal large deviations from the Gaussian curve due to a significant diversification of metal concentrations between different locations.