Distribution of potentially toxic soil elements along a transect across Kazakhstan

The present study aims to investigate the distribution of selected potentially toxic elements (PTEs) in Kazakhstan's topsoils. Soil samples collected across a north-south gradient (n = 40) near main highways connecting major residential/industrial areas were characterized for their As, Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn content as well as for soil physio-chemical properties. The majority of the soils had neutral pH (no significant relationship between pH and PTE concentrations). The soil organic carbon was higher at the northern and farther southern parts of the transect (along with higher concentrations of PTEs in soils). As, Mn, and Ni concentrations in soils were elevated in comparison to relevant background concentrations. Critical concentrations of As, Cd, Co, Mn, and Ni (with respect to regulatory limits) were found at multiple locations, with As being particularly of potential concern (range: 8.7–42 mg × kg⁻¹). The distance from the nearest settlement seems to influence the soil PTE concentrations, however the relationship is not statistically significant. In total, eight locations had statistically outlier PTE concentrations for Cd, Mn, Ni, and Zn. The overall results were comparable to similar studies across the world except that the Pb content of the study soils was less elevated. Studies on site characterization and human health risk assessment covering identified hotspots and PTEs are recommended.