| dc.description.abstract | Mining of precious metals started many years ago, for instance, gold (Au) and the offshoot
uranium (U) mining in South Africa's Witwatersrand Basin. Consequently, mining activities
contaminate the environment with potentially toxic elements, which could be useful but
dangerous as well. The presence of U in the atmosphere, biosphere, lithosphere, and
hydrosphere has a negative impact on the exposed population. The main aim of this research
is to investigate the dynamics of fluvial transportation of U in the Rietspruit river system
located in the Gauteng Province of South Africa.
In this study, the concentrations of U in the Rietspruit fluvial system were quantified using an
inductively coupled plasma mass spectrometry (ICP-MS) machine at the Eco-Analytical
Laboratory of the North-West University, August 2020. The river is an important stream
because it is utilized for various purposes which include domestic, farming, and spiritual
purposes. However, the main source of the water stems from the Peter Wright dam which is on
the premises of a Au and U mine.
Within the mining impacted source area, elevated concentration of U was logged. Uranium
concentration of about 781 μg/L was logged in the furrow taking water to the Peter Wright
dam. In the slimes dam and sand dump, a concentration of 72.7 mg/kg and 1043 mg/kg were
recorded, respectively. The highest concentrations of U were however recorded about 6 km
and 24 km downstream of the mining area in a marshland, with concentration above 1200
mg/kg recorded at both sites. This shows that dams and wetland are sinks for U leading to the
immobilization of U in the dam’s and wetland’s sediments. Other toxic elements such as
arsenic, cadmium, mercury and lead were also recorded in the Rietspruit water and sediment
at a concentration exceeding the acceptable limits.
In regions where human contact was observed, the amount of U in the collected water sample
was over the acceptable limit of U in drinking water 30 μg/L. Due to this, both carcinogenic
and non-carcinogenic health risk assessment was done based on the recorded concentration of
U in the water. The result showed that the observed human exposure is more at risk of chemical
toxicology than radiological toxicology.
To study the mobility of U in the water-sediment system, a large amount of sediment was
collected from a U polluted dam downstream of the Rietspruit. After drying under normal
atmospheric conditions, the sediment was rewetted with rainwater. Uranium concentration of
1211 μg/L was logged in the water sample collected instantly after rewetting. This was mainly
due to the dissolution of the salt crust rich in the U. This was the highest concentration of
dissolved U recorded after rewetting the sediment. It was observed that the release of U into
the water column was not linear due to the different phases that U was adsorbed into, for
example, iron oxide, manganese oxide, sulphates and carbonates which all have different
dissolving rates in water.
In conclusion, the Rietspruit is polluted by the U because of the Au mining operations that took
place around the Rietspruit headwater. About 24 km downstream of the Rietspruit, the water
is not suitable for domestic, agricultural, and religious activities. Residents of Lawley,
farmers, and worshippers, observed using the Rietspruit water, should be sensitized about the
dangers involved in the continuous usage of the Rietspruit water. Further study that will
quantify the concentrations of U and other toxic alloys in agricultural products – crops and
animals within this environment should be done. | en_US |
