UNRAVEL THE COMPLEXITIES OF URBAN SOIL CONTAMINATION: REGULATED AND EMERGING METALS CONTAMINANTS IN A POST-INDUSTRIAL CITY

Soil pollution is a pressing global issue, particularly in urban environments, where contaminants such as potentially toxic elements (PTEs) and rare earth elements (REEs) arise from human activities like improper waste disposal, industrial operations, and transportation. These pollutants often accumulate in fine soil particles (<10 µm), which have high surface areas and contain sorbents like clay minerals, Fe-Mn (oxyhydr)oxides, and organic matter. Fine particles can be easily resuspended, spreading contamination to adjacent environmental compartments such as road dust and atmospheric particulate matter (PM), thereby increasing exposure risks for humans and ecosystems. While regulations exist for PTEs like Cd, Cr, Cu, Pb, Ni, Zn, V, and Sb, these focus on total concentrations in bulk soils, overlooking the enhanced mobility and bioavailability of PTEs in fine fractions. Our study examined the behavior of PTEs in fine soil particles and their interconnections with urban matrices. Chemometric analyses and Pb isotopic studies revealed overlapping contamination sources among soils, road dust, and PM, with historical emissions, such as leaded gasoline, contributing to Pb ubiquity. The results underscore the interconnectedness of urban contamination sources, highlighting fine particles as key contributors to urban pollution in industrial and high-traffic areas. Additionally, this research addressed the emerging issue of REEs, which are increasingly prevalent due to their growing industrial use and improper disposal. Despite their unique magnetic, optical, and catalytic properties, REEs pose ecological and health risks, including kidney damage and toxicological effects. REEs remain unregulated, and their environmental mobility and availability are poorly understood. To address this gap, we optimized a microwave-assisted acid digestion method for REE quantification using ICP-MS. Analysis of 50 soil samples from Turin revealed Ce, Nd, La, and Y as the most abundant REEs in urban soils, particularly in park samples due to atmospheric deposition from industrial activities. Agricultural soils showed higher concentrations of Y, Sc, Er, and Yb, likely linked to P-containing fertilizers, while industrial sites exhibited atypical enrichments in Eu and Tb. Our study also investigated the impact of flooding on contaminant release, a scenario increasingly relevant due to climate change. Simulated flooding experiments using an automated biogeochemical microcosm system indicated that soil redox potential (Eh) and pH changes significantly affect PTE and REE mobility. Under reducing conditions, contaminants were released via the reductive dissolution of Fe-Mn (oxyhydr)oxides. REEs exhibited positive correlations with Fe and Mn, suggesting their binding to these oxides. Conversely, oxidizing and alkaline conditions promoted immobilization through adsorption or co-precipitation. This research advances our understanding of urban soil contamination by exploring fine soil particle dynamics, REE behavior, and flooding-induced contaminant release. It emphasizes the need for improved soil quality monitoring and targeted mitigation strategies addressing both regulated and emerging contaminants. These findings are essential for sustainable urban pollution management and mitigating risks to human and ecosystem health in a changing climate.