Potentially toxic elements in urban soils across functional zones: risk assessment, sources, and spatial distribution (Ufa City, Russia).

The pervasive contamination of urban soils, varying across city zones, demands urgent remediation strategies tailored to specific local conditions. In this study, we examined the concentrations of seven potentially toxic elements (PTEs) within urban functional zones. For these purposes, we collected a 250 topsoil samples from six major urban functional zones: (1) public (business), (2) recreational, (3) residential, (4) industrial, (5) gardening, and (6) transport zones. Statistical and geostatistical (variogram analyses and ordinary kriging) techniques were employed to study and evaluate the spatial distribution of PTEs. Results showed that the average PTE concentrations were higher than corresponding background levels and below the maximum and approximate permissible limits (MPC, APC), although some samples exceeded these limits. Exceedance of normative levels was most prevalent for Cu, Ni, and Zn, specifically in public (for Cu and Zn), recreational (for Ni and Zn), residential (for Cu and Zn), and industrial areas (for Zn). According to several pollution indices, the overall levels of pollution were low and not dangerous. We found a positive correlation between Pb and Zn (r = 0.51). PTEs demonstrated strong (Ni), moderate (Pb, Cu, Zn), and weak (Cd, As, Hg) spatial correlation, while maps showed elevated concentrations for most PTEs in industrial zones. These findings suggest that PTEs are impacted by both natural sources and multiple external contamination factors. Our study revealed that some PTEs varied across urban zones, prompting us to take this information into account in future studies.