Occurrence of PCDD/Fs and PCBs in Parks of the Porto Metropolitan Area

Persistent organic pollutants accumulate in urban soils, yet information on the occurrence, spatial variability and human health implications of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dl-PCBs) remains limited, particularly in Portugal. Surface soils were collected from six urban and peri-urban green spaces across the Porto Metropolitan Area, encompassing contrasting land-use histories and anthropogenic settings. Seventeen sampling locations were analysed for the 17 WHO-priority PCDD/F congeners and the 12 dioxin-like PCB congeners. The total number of 2005 toxic equivalents (TEQs) was determined, and screening-level human health risks were evaluated for adults considering incidental soil ingestion, dermal contact and inhalation of resuspended soil particles. PCDD/Fs and dl-PCBs were detected at all sampling locations, with total TEQ concentrations ranging from 1.91 to 330.9 ng TEQ kg⁻¹ dry weight. PCDD/Fs accounted for most of the overall toxicity. The majority of the samples under analysis can be considered representative of the urban background level in Porto, at 2.51 ± 0.54 ng TEQ kg⁻¹ dw. TEQ concentrations at most sites were consistent with diffuse urban background levels reported internationally, whereas one informal urban allotment constituted a distinct contamination hotspot. This spatial pattern was reflected in the risk assessment. Non-carcinogenic and carcinogenic risks remained below widely accepted screening thresholds at all locations except the hotspot, where children exhibited a hazard index (HI) of 1.50 and an incremental lifetime cancer risk (ILCR) of 1.17 × 10⁻⁵. Incidental soil ingestion was the predominant exposure pathway; dermal contact contributed modestly, and inhalation contributed negligibly. Sensitivity analysis demonstrated that these conclusions were robust to alternative assumptions about soil ingestion. These findings suggest that historical land use is a major determinant of site-specific PCDD/F and dl-PCB contamination and associated human health risks in urban green spaces. Incorporating land-use history into urban soil assessments could improve contamination hotspot identification and strengthen environmental monitoring and risk management strategies.