Heavy metals in soil on spoil heap of an abandoned lead ore treatment plant, SE Congo-Brazzaville

Abstract

Total concentrations of 4 heavy metals (Pb, Zn, Cu, and Mn), non-metal As and three reference elements (Ti, Fe and Al) of a soil profile on spoil heap were examined. 54 soil samples were collected in the soil profile at different depths: 15 to 45, 45 to 75, 75 to 105, 105 to 135 and 135 to 150 cm. The first 15 cm of top layer contained an accumulation of ores and was not sampled. Lead, zinc, copper, manganese and arsenic levels in the soil profile decreased from 11800 to 2000, 2400 to 1200, 270 to 90, 6700 to 750 and 1300 to 600 mg/kg, respectively. The levels of these trace elements were higher than the permissible limit level in soil according to European norms. The concentration levels of heavy metals and arsenic in the soil profile are listed in the following order: Pb > Mn > Zn > As > Cu. High positive correlations were observed between As, Cu, Zn and Al, Fe, Mn, Ti. Among the heavy metals, lead was not significantly correlated with Al, Fe and Ti. Evaluation of enrichment factor, geo-accumulation index and pollution load index values from the measured concentrations of heavy metals and continental crust values shows a very high contamination of the soil profile by the heavy metals studied and arsenic.

Key words: Heavy metals, spoil heap, contamination, enrichment factor, geo-accumulation index, pollution load index.