Assessment of vertical contamination of Cd, Pb and Zn in soils around a former ore smelter in Wallonia, Belgium

Concentrations of trace elements (Cd, Co, Cr, Cu, Ni, Pb and Zn) and major elements (Ca, Mg, K, Fe, Al and Mn) as well as pH(KCl) and total organic carbon (TOC) were measured on 22 profiles located in a 3 km radius of a former ore treatment plant in Wallonia (Belgium). The enrichment factor (EF), vertical impoverishment factor (VIF) and availability ratio (AR) were used as diagnostic tools of contamination and migration of Cd, Pb and Zn in profiles. The data revealed that the soil profiles are significantly contaminated. The ranges of EFs for Cd (17-3570), Pb (1-2883) and Zn (2-309) are very broad with the higher EF in the topsoil of the profiles. VIFs of subhorizons are rarely above 1. In the few cases with VIF > 1, the main factor explaining is the soil type (in particular, Colluvic Regosols, Luvisols and Cambisols with shale load). Cd, Pb and Zn ARs are strongly correlated with TOC and to a lesser extent with pH(KCl); Pb and Zn ARs are influenced by soil type, while land use only has an effect on Zn AR. The Cd availability is independent of these two factors. The contents of trace elements measured in soil profiles are very high, especially in topsoil. At present, the Cd, Pb and Zn vertical distribution shows a low migration from topsoil to deeper levels. However, we must not discount the hazard of a future potential transfer.