Assessing the distribution of sedimentary heavy metals in the Msunduzi River Catchment, KwaZulu-Natal, South Africa.
Heavy metal pollution of freshwater environments is a global and local crisis due to the toxic nature of metals. Elevated concentrations of heavy metals in sediments, in comparison to sediment quality guidelines (SQGs), are an indication of anthropogenic input into the environment. Concentrations of cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni) and zinc (Zn) were investigated in the water and sediments of Msunduzi River and two of its tributaries, the Bayne’s Spruit and Slangspruit, in KwaZulu-Natal, South Africa. Macro-elements, aluminium (Al), iron (Fe) and manganese (Mn) were also investigated and compared to the distribution and partitioning pattern of the trace metal concentrations. Total metal concentrations in the water samples were below the detection limit of the Inductively Coupled Plasma–Optical Emission Spectrometry (ICP-OES) for most metals. In surface sediments, total metal concentrations were >Effects Range-Low (ERL) of the SQG. The Community Bureau of Reference (BCR) sequential extraction protocol was used to determine speciation of metals in the sediments and implications for potential bioavailability and overall metal toxicity. Results indicated that potentially mobile sediment fraction concentrations were >ERL for most of the metals. Fe-Mn oxyhydroxides, organic matter content and redox potential had an effect on the geochemical partitioning and possible remobilisation or precipitation of the metals in all three rivers. Negative redox values were indicative of reducing conditions that remobilised metals from the sediments. In the sediment core, the trace metals had the same deposition pattern and were correlated to organic matter content at depth. Normalisation with Al, at 95% confidence interval indicated that the sediment in the Msunduzi River Catchment is enriched with anthropogenic heavy metal input. In terms of particle size distribution in the sediment core, the sediment was mainly made up of fine sediment (≤500 μm). The sediment is a potential source of long-term heavy metal pollution in the catchment.