Surprisingly contrasting metal distribution and fractionation patterns in copper smelter-affected tropical soils in forested and grassland areas (Mufulira, Zambian Copperbelt)

摘要

Six soil profiles located near Mufulira (Zambian Copperbelt) were studied to evaluate and compare the extent of environmental pollution of Cu-ore mining and smelting in both forested and grassland areas. The highest metal concentrations were detected in the uppermost soil layers with the following maxima: Co 45.8 mg kg~(-1), Cu 8980 mg kg~(-1), Pb 41.6 mg kg~(-1), and Zn 97.0 mg kg~(-1). Numerous anthropogenic metal-bearing particles were detected in the most polluted soil layers. The spherical smelter-derived particles were mainly composed of covellite (CuS) and chalcocite (Cu_2S), while the angular mining-derived particles were mostly composed of chalcopyrite (CuFeS_2). Additionally, Fe-Cu oxide particles predominantly corresponding to tenorite (CuO) and delafossite (Cu~(1+)Fe~(3+)O_2), along with hydrated Fe-oxides corresponding to secondary weathering products, were detected. In contrast to smelter-affected soils in temperate climates, where forest soils are significantly more enriched in metals than tilled soils due to high canopy interception, our data indicate a higher proportion of metal-bearing anthropogenic particles and higher metal concentrations in soils from unforested sites. This phenomenon is probably related to the more frequent and intense bushfires in forested areas, leading to the mobilization of pollutants contained in the biomass-rich surface soils back into the atmosphere.