Origin and spatial distribution of metals in urban soils

This study assessed soils from 36 parks and gardens (Vigo City, NW of Spain) where there are different degrees of traffic intensity and activity. The soils were characterised, and the content of Ba, Ca, Cr, Cu, Fe, Mg, Mn, Na, Ni, Pb, Si, Sr and Zn was analysed. Further assessment determined the geoaccumulation index, enrichment factor and the contamination degree by metals with adverse effects on human health and environmental quality. The results reveal the existence of a moderate degree of contamination by Ba, Pb and Cu, which contribute the most to soil contamination due to the influence of industrial areas and main transport routes. Correlation and cluster analyses suggest that the metals included in the study have three possible origins: "natural" (Na and Si), "mixed" (two groups with different source intensity: Ca and Sr and Cr, Fe, Mg, Mn and Ni) and two possible "urban" sources: traffic (Cu, Pb, Zn) and mixed (Ba). None of the soils can be classified as strongly contaminated but more than 61 % of the moderate contamination degree determined in the studied soils is explained by the Ba, Cu and Pb contents.