Trace metal contamination of soil and groundwater in the Rietvlei Catchment, Cape Town

Abstract

Trace metal elements are naturally found in sediments, soils, water and plants. They occur at concentrations less than 100 mg/kg and are more commonly known as heavy metals. There are a number of anthropogenic sources where TMEs stem from mining and metal extraction, agricultural activities, oil, wood and coal burning, manufacturing, cremation and waste disposal. Once trace metal elements are introduced into the environment by a specific method, it may move to different environmental components that can be a result of the nature of interactions that occurs in this natural system. Soil possess the ability to bind with various chemicals and contaminants which tends to accumulate in this medium. The movement of TMEs in soil is controlled by soil components, how it interacts with other solid states, environmental factors and its quantities. Trace metal elements can bound or sorb by specific natural substances, which can change the mobility. Sorption specifically plays the main role in controlling transfer, non-polar organic soil compound behaviour and toxicity. All chemical processes are directly and indirectly influenced by the soil solution pH and redox potential and therefore influence TME behaviour in soil. The transport mechanisms of TMEs through soil is an important factor. Topography mainly affects metal mobility and availability in floodplains. TMEs in soil leach into groundwater and generally contains pollutants. Groundwater resources is a principle origin of water, due to good water quality. It plays a crucial part in aiding the geological environment, sustaining the ecosystem equilibrium and maintaining life. When groundwater has been polluted, it could persist that way for decades or even centuries due to the slow-going natural processes of through-flushing. Ground- and surface water bodies are linked to each other in a majority landscapes. Rietvlei is a located about 5 km on the north side of Cape Town. To establish the spatial distribution extent of TMEs, Visible and Near-Infrared Reflectance Spectroscopy have been used. This research aims to establish the TMEs found within the soils and groundwater in the Rietvlei area and the sub-catchment.