Spatial variability of metal pollution in sands and sandy soils of playgrounds and parks in the Barcelona metropolitan area: assessing the impact of urban and industrial activities

This study investigates the geochemical composition of sands and sandy soils collected from 10 playgrounds and 13 parks across the Barcelona Metropolitan Area (BMA), a region characterised by high population density, extensive industrial activity, and heavy traffic. By examining the variability in metal loads and the deposition of contaminants, the research sheds light on the impact of urban pollution sources on the spatial distribution of harmful elements. The findings reveal that playgrounds tend to exhibit coarser sand textures compared to parks, likely reflecting both the progressive milling of sand and the accumulation of deposited particulate matter (DPM) over time. Several parks exhibited significant enrichment factors (EF) (5 ≤ EF ≤ 20) for a variety of elements, which can be attributed to vehicle wear, while others showed even higher enrichments, particularly related to braking systems. Distinct anomalies in metal concentrations were found in several parks, indicating a diversity of pollution sources, including industrial emissions and port activities. Particularly noteworthy are the elevated Ce/La ratios (1.79–2.95) found in some parks, which point to vehicular catalytic emissions. Additionally, exceptional anomalies in Pb (EF: 62.3–84.1) and Sb (EF: 26.8–44.4) concentrations were identified, most likely due to industrial and port activities near certain parks. Another significant finding of this study is the higher concentrations of traffic-related metals found beneath tree canopies compared to open spaces. This suggests that the presence of vegetation, particularly trees, plays a crucial role in modifying the deposition and distribution of PM in urban green spaces. This research provides critical insights into urban pollution dynamics, particularly the distribution of metals in relation to sand composition, environmental interactions, and the role of urban greenery in mitigating the negative effects of airborne pollutants. By examining both the geochemical impacts of pollution and the physical processes that contribute to contamination in urban environments, this study underscores the importance of thoughtful urban green infrastructure in reducing the environmental and health risks associated with urban pollution.