Soil Contamination in Dumps on the Karstic Areas from the Plateaus (Southeast of Madrid, Spain)

After over 10 years of accumulation of residues in the studied dumps near Madrid, it has been registered low or moderate heavy metals concentrations on the surrounding area. Only occasionally, some rubbish dumps contain significant quantities of Cu, Ni, Zn and Pb. The concentration levels of Pb, Ni, Zn and Cu are safe when they are compared with the surrounding areas levels of heavy metals. The aim of this paper is the analysis of pollutants existing around in the dumps located at the sides of the plateaus of the central valley of the Tajo River (provinces of Madrid and Toledo, Spain). The high karstification rate of the upper layer of these tablelands and the existence of numerous dumps on them (even on their slopes) make these areas vulnerable to heavy metal pollution. However, after several years of use, the concentration of pollutants only reaches moderate values in the studied areas. Dumping materials were collected at four rubbish dumps. The mineralogical composition of the materials were analysed by XRD. Sequential extraction procedure was applied for speciation of the metal forms in the collected samples. Concentrations of Zn, Pb, Ni, Cu, Cr and Cd in extracts were determined by AAS. The studied samples showed high carbonate concentration. Contamination processes are combined there with weathering processes. Heavy metals concentration in control samples (gypsum, limestones, red soils and colluviums) were compared with samples of the studied dump in order to evaluate the pollution level. Concentrations of Zn, Pb, Ni and Cu were variable. The contamination was elevated for samples in depth in relation with weathering process of heavy metals.