Assessment of the lead and zinc contents in natural soils and tailing ponds from the Cartagena-La Unión mining district, SE Spain

Seven tailing ponds and two natural areas (soils developed on ferruginous limestone and soils developed on laminated limestone) from a Pb/Zn mining district from southeast Spain were sampled and geochemically characterized. The objectives of this study were to: 1) evaluate the degree of pollution of the area using the enrichment factor, the geo-accumulation index and a combined pollution index; 2) determine the origin of Pb and Zn in the natural areas using sequential extraction procedures, since wind erosion may have transferred metals from bare tailing ponds to the natural soils; and 3) assess the potential environmental risk of the area. Results showed that the natural soils are highly polluted by Pb and Zn. Soils developed on ferruginous limestone are more polluted (mean 4737mgPbkg^-1 and 4518mgZnkg^-1) than soils formed from laminated limestone (mean 2347mgPbkg^-1 and 1731mgZnkg^-1), and the surface samples show more enrichment of metals than subsurface samples. Considering mineralogy, statistical analysis, concentration of heavy metals in the soil profiles and sequential extraction analysis of Pb and Zn we can conclude that the high levels of Pb and Zn in soils developed on laminated and ferruginous limestones may be both due to geogenic and anthropogenic origins. Due to the high concentrations of water-soluble Zn (e.g. 1463mgZnkg^-1 in tailing pond 3) and available Pb and Zn in most of the tailing ponds (e.g. 2449mgZnkg^-1 in tailing pond 3 and 5298mgPbkg^-1 in tailing pond 4), it is recommended to carry out reclamation in order to reduce the Zn mobility and decrease the availability of Pb and Zn.