Geochemical assessment of radionuclides, heavy metals and POPs in urban forest soils: hidden exposure pathways and health risks

Urban forests contribute significantly to human well-being and climate resilience, yet they may also act as reservoirs of contaminants such as radionuclides, heavy metals, and persistent organic pollutants (POPs). These pollutants accumulate in soils and can pose chronic exposure risks to surrounding communities. This study quantified radionuclides, heavy metals and POPs in soils of the protected Mount Avala forest near Belgrade, Serbia, and evaluated the associated health risks. Natural radionuclide activities exceeded the global averages, particularly for ⁴⁰K, while ¹³⁷Cs behavior appeared to be highly influenced by site-specific forest conditions and post-depositional processes. Mean radiological excess lifetime cancer risk (ELCR) was ∼60 % above the global average. Strong correlations among ²²⁶Ra, ²³²Th, Co, and Ni indicate a predominantly lithogenic origin, whereas the strong correlation between ¹³⁷Cs and DDE suggests similar dynamics of these contaminants under forest-specific conditions. The homogeneous distribution of ¹³⁷Cs and other surface-deposited contaminants indicates downward migration and redistribution over time, driven by post-depositional processes. Soils at AT6 showed extreme enrichment in As and Pb, whereas AT8 exhibited elevated PCB 52 and DDT metabolites. While radiological hazard indices remained within safety limits, certain metals and POPs exceeded non-carcinogenic and carcinogenic intervention criteria at identified hotspots. Spatial heterogeneity in pollutant concentrations reflects both geological controls and localized anthropogenic inputs. Integrating radionuclide- and contaminant-focused monitoring, hotspot-targeted remediation, and risk-informed urban planning is essential to ensure that urban green infrastructure remains safe, sustainable, and health-supportive.