Urban land use and management drive soil pollution across urban and nearby natural ecosystems in the Iberian Peninsula

Cities concentrate most of the world's population and human activities, generating pollution that threatens ecosystem functioning and human well-being. Yet, the relative importance of different drivers shaping urban pollution and the spatial distribution of multiple contaminants across cities remain poorly understood. Here, we conducted a standardized survey in 250 plots across 51 cities in the Iberian Peninsula to quantify heavy metals, pesticides, macrolitter and microplastics. We sampled four urban greenspace types (parks, golf courses, urban farms, roundabouts) and nearby natural areas to link contaminants with soil microbiome structure and functioning. Urban parks, roundabouts and urban farms accumulated the highest metal levels, with several sites exceeding regulatory thresholds for Zn, Pb, Ni, and As, whereas golf courses showed lower contamination levels. Pesticides were detected across both urban and natural soils, with no significant differences in concentrations among land use types. In contrast, microplastic concentrations peaked in natural areas, indicating that regional transport and deposition processes can decouple their accumulation from local urban sources. Macrolitter was most abundant in parks and roundabouts, while golf courses exhibited the lowest densities, highlighting the influence of local management and access control. The level of soil contamination, as quantified by contamination indices, was correlated with microbial richness, community composition, and key soil functions. Pesticides were negatively associated with bacterial richness and redox activity, whereas macrolitter was negatively associated with phosphatase activity. Heavy metal contamination was associated with shifts in bacterial and fungal richness and with changes in soil respiration and phosphatase activity, reflecting a potential influence of heavy metals on microbial communities. This study highlights that land use and management shape soil contamination, soil biodiversity, and ecosystem functioning, emphasizing the need for mitigation actions to support the implementation of the EU Soil Strategy in cities.