Assessment of Metal Availability in Soils from a Pb-Zn Mine Site of South-Central Spain

Heavy metal pollution of the soils around an abandoned Pb-Zn mine site located in the Alcudia Valley (South Central Spain) have been characterized by analysis of extractable and total metal concentrations in 60 samples of arable, pasture, and mine lands. The samples showed a broad range of size-particle distribution, cation exchange capacity, and pH values as well as high levels of total metal concentrations (up to 98510 mg kg^?1 of Pb, up to 20912 mg kg^?1 of Zn, and up to 61 mg kg^?1 of Cd). In order to assess the potential availability of metals the metal partitioning in two different soil size fractions (<2 mm and <63 μm) was determined using EDTA and CaCl₂ as sequestering reagents. The average contents of Pb, Zn, and Cd in the <63 μm particle size fraction for both extractions were higher than those of the <2 mm fraction due to the high metal adsorption capacity of the fine soil particles. Concentrations of heavy metals extracted by CaCl₂ were up to three orders of magnitude lower than those extracted by EDTA, because CaCl₂ only extracts the easily mobile fraction. Metal concentrations extracted by both procedures in the two granulometric fractions increased with total metal concentrations, thus increasing the potential environmental risk associated to heavy metal pollution.