Dispersal Mechanisms of Trace Metal Elements in the Environment: The Case of Mineral Wastes Stored in Tshamilemba District of the City of Lubumbashi, DR Congo

Abstract

Since 2001, the Tshamilemba quarter, located in the City of Lubumbashi (DRC), has been home to copper- and cobalt-producing plants, which generate great amounts of mineral waste, the storage of which has resulted in environmental pollution. Previous studies conducted in the Tshamilemba district have identified the weathering process of stored mineral wastes as the main source of trace metal elements (TMEs) involved in the contamination of soil and well water, and have highlighted the population exposure to cobalt. This study strives to identify or establish the dispersal mechanisms of pollutants in the environment that contaminate soil, surface water and edible plants. This study measured major physicochemical parameters, determined TME concentrations in samples (soil, water and edible plants) and established, based on data from soil sample analysis mathematically processed using Matlab 7.1 software, the spatial distributions of TMEs, in both the upper and deep soil (20 cm). The soil sample analysis revealed an average pH of 7.69 and a value of 9.1 for the near-white crusts collected at some spots. In the soil, TMEs were present in upper layers (Co, Cu, Zn and Fe) and the deep layers (Co, Cu, Pb, Zn and Fe) at phytotoxic concentrations. TMEs were observed in water samples at concentrations (Cu, Co, Mn, Zn and Pb) surpassing the quality standards for drinking water. This also applies to edible plant samples of Saccharum officinarum (Co, Cd, Ni, Mg and Pb) and Musa acuminate (Cd, Co, Pb, Zn, Mn and Ni). TMEs disperse in the environment as airborne particles from aerial erosion and as dissolved species in run-off water, mixed with acidic, metal-rich waters spreading from the weathering of stored mineral waste. TMEs contaminate the surrounding soil near to the surface water and build up in edible plants. Therefore, fear among the population about the environment pollution in Tshamilemba is well justified. Understanding the dispersal mechanisms of TMEs is of paramount importance to better control and to contain mineral pollution and design strategies for minimizing the effects on human health.