Spatial distributions, sources, and ecological risks of metals in soils from the largest industrial city of Ulsan, South Korea

The levels, contamination degrees, and spatial distributions of 13 metals-aluminum (Al), arsenic (As), barium (Ba), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), vanadium (V), and zinc (Zn)-were investigated in soils from suburban, urban, and industrial sites in Ulsan, the largest multi-industrial city in South Korea. At the industrial sites, the mean concentrations of As (13.4 mg/kg), Cd (1.49 mg/kg), Cu (129 mg/kg), Ni (12.8 mg/kg), Pb (122 mg/kg), and Zn (376 mg/kg) were higher than those at the urban and suburban sites. In particular, soils from the non-ferrous metal and petrochemical industrial complexes were highly contaminated with As, Cd, Cu, Pb, and Zn, as supported by spatial distributions and multiple pollution indices. Ecological risks, assessed using the potential ecological risk index (RI), were very high at six industrial sites (913-1748), while those at the suburban (214-476) and urban sites (187-518) were at moderate to considerable levels. On average, Cd and As contributed 70% and 17% of the total ecological risks, respectively. According to the principal component analysis, As, Cd, Cu, Pb, and Zn were significantly associated with industrial soils, suggesting that industrial emissions are the primary source, whereas Al, Co, Cr, Fe, Mn, Ni, and V were not significantly affected by industrial activities or vehicular emissions. The results highlight the need for remediation strategies in the industrial complexes to mitigate severe ecological risks in soils and prevent further contamination of other environmental media and ecosystems.