GEOSPATIAL DISTRIBUTION OF EMERGING ELEMENTS (Ag, Pd, Rh, Sb, Co, Pt) IN ALCALÁ DE HENARES TOPSOILS: INSIGHTS FROM GIS MAPPING

Emerging contaminants such as platinum group elements (Pt, Pd, Rh), silver (Ag), antimony (Sb), and cobalt (Co) are increasingly reported in urban soils, yet their spatial distribution and environmental behaviour remain insufficiently characterised. We applied a geographic information system (GIS)-based approach to evaluate the spatial variability of Ag, Co, Pt, Rh, Sb, and Pd (inferred, not directly measured) in 137 surface soil samples (0–3 cm) collected across urban, industrial, and garden areas of Alcalá de Henares, Spain. Spatial interpolation using inverse distance weighting (IDW; power = 2, 12 neighbours), based on commonly applied parameters in urban soil mapping, revealed distinct patterns for each element. Ag and Co showed heterogeneous distributions, with higher concentrations in garden and industrial soils (Ag: up to approx. 0.9 mg/kg; Co: up to approx. 19 mg/kg), likely influenced by biosolids application and historical industrial activity. Pt and Rh were elevated near major traffic routes, consistent with vehicular emissions as dominant sources. Sb exhibited marked urban hotspots associated with brake wear and industrial legacy inputs. Although Pd was not analysed, its likely co-occurrence was inferred from the spatial congruence of Pt–Rh and shared emission sources. Correlation analysis supported the spatial findings, highlighting an anthropogenic Rh–Sb–Mo cluster (Mo included as part of the correlation dataset) and a mixed geogenic–anthropogenic profile for Co. Overall, the integration of spatial mapping and multivariate statistics demonstrates the utility of GIS for identifying contamination hotspots, supporting source apportionment and informing soil surveillance and biomonitoring strategies. Our results emphasise the need to consider less-monitored elements in regulatory frameworks to better protect vulnerable populations in complex urban environments.