Tracing the spatial distribution and mobility of metal/metalloid contaminants in Oxisols in the vicinity of the Nkana copper smelter, Copperbelt province, Zambia
Abstract
Topsoils in the vicinity of the Nkana copper smelter were studied in order to assess the spatial distribution of metal/metalloid contaminants (As, Co, Cu, Pb, Zn) around the smelter. The bulk concentrations of metal/metalloid contaminants were determined by ICP techniques, supplemented by the determination of the Pb isotopic composition of selected samples measured by quadrupole-based ICP-MS.
The spatial distribution of the major contaminants indicated the highest contamination NW of the smelter stack, corresponding to the prevailing wind direction in the area. Lead isotopes helped to differentiate the extent of metallic pollution and indicated the mixing of three major pollution sources: smelting activities, petrol combustion and regional background.
To assess the vertical mobility of inorganic contaminants, a 110-cm-deep profile in Oxisol in a highly polluted zone in the near vicinity of the Nkana smelter was sampled and studied by combination of bulk chemical analysis, sequential extraction procedure (SEP) and Pb isotopic tracing. The contamination was mostly located in the uppermost soil horizons enriched in organic matter.
Based on SEP, the isotopic composition and knowledge of smelter activities in the area, it was predicted that anthropogenic Pb exhibited downward migration in the soil profile with estimated penetration rate of 1.36 cm year(-1). Copper, being substantially bound in the exchangeable fraction, also showed significant mobility in the profile.
As a result, the sources of anthropogenic emissions in the Kitwe smelting area represent an important source of mobile (and potentially bioavailable) metals.