Extractability of trace metals in urban soils

Abstract

Urbanization and industrialization may have negative effects in urban soils functions. One of the most challenging problems is the accumulation of pollutants coming from the anthropogenic activities, such as heavy metals. It is not enough to analyse the total concentrations of this pollutants, but we need to evaluate their bioavailability and determine which concentration could enter to the food chain through plant uptake. In this study we analysed the bioavailability of five heavy metals (Pb, Cu, Zn, Ni and Cr) in 55 soils of Santiago de Compostela with different land uses (grassland, forest and agricultural) and different lithologies. Soluble metals were evaluated using an extraction with 0.01M CaCl₂, in which only soluble Zn appears in a significant amount. Bioavailability of exchangeable metals, evaluated using an EDTA extraction, followed a decreasing trend Pb > Zn > Cu > Ni > Cr. Moreover, we found that higher concentrations of Zn and Cu correspond to agricultural soils, developed most over gneiss, which explains the significant relation between Cu concentrations and gneiss lithology.