An assessment of heavy metal accumulation in the Vaal River system, South Africa, using artificial mussels

Abstract

This study aims to identify metal concentrations around the Vaal River system by means of spot water sampling and the use of artificial mussels (AMs). Levels of Al, Cd, Co, Cr, Cu, Fe, Mn, Pb and Zn were determined at five locations around the dam and one site downstream of the dam. Many of the water samples contained concentrations that exceeded the Target Water Quality Ranges (TWQR) set by the Department of Water Affairs and Forestry (DWAF). Artificial mussels accumulated concentrations that indicated land cover usage as a driving factor behind many of the heavy metal concentrations. Sites surrounded by commercial farmland had the highest accumulated metals in the AMs due to the site location and exhibited major metal influxes. However, pollution point sources, mainly wastewater treatment works effluents, upstream of the dam wall played a major role in the elevated concentrations found at site downstream. These findings highlight the influence of both diffuse agricultural runoff and point-source pollution on metal contamination in the Vaal River system. Thus, it is essential that constant monitoring of the Vaal River system be implemented to ensure high levels of water quality for the future.