Abstract
Urban soils in industrial cities accumulate potentially toxic elements (PTEs) from mixed lithogenic and anthropogenic sources; yet cross-regional comparisons remain rare. This study characterized 14 PTEs in surface, mid-, and deep-layer soils in four industrial cities: Ust-Kamenogorsk and Pavlodar (Kazakhstan), Toruń (Poland), and Aarhus (Denmark). Positive Matrix Factorization (PMF) resolved source contributions in two cities in Kazakhstan, complemented by assessments of enrichment factor, geoaccumulation index, hazard index, total carcinogenic risk, and potential ecological risk index across all four cities. Contamination gradient emerged from Ust-Kamenogorsk > Toruń > Pavlodar > Aarhus along environmental risk assessment and Ust-Kamenogorsk > Pavlodar > Toruń > Aarhus along human health risk assessment. Ust-Kamenogorsk exhibited the highest overall hazard levels, with surface cadmium (mean 3.35 mg kg -1 ; maximum 19.80 mg kg -1 ) and lead persisting across depth and a previously undocumented beryllium hotspot near a tailings storage facility. PMF resolved six sources in Ust-Kamenogorsk and four in Pavlodar, with anthropogenic inputs governing roughly 84% and 68% of the PTEs load, respectively, dominated by non-ferrous metallurgical emissions, coal combustion, and lead-zinc smelting (Ust-Kamenogorsk), and by combustion and traffic (Pavlodar). Whereas the two European cities were dominated by lithogenic and diffuse urban inputs, Toruń’s risk was concentrated in a few cadmium- and lead-rich legacy industrial hotspots, while Aarhus, the least contaminated city, demonstrated that additive multi-element exposure can approach hazard thresholds even where no single element does so alone. Arsenic was the dominant contributor to the hazard index across all cities (element ranking As > Cr > Cd > Pb in Kazakhstan, As > Cd > Cr > Pb in Europe), while cadmium was the principal driver of ecological risk wherever elevated risk occurred. These findings identify chromium and cadmium as priority elements and show that source-resolved, depth-explicit assessment protocols enable meaningful cross-regional comparison of urban-soil contamination.