Contamination Of Water, Soil And Plants By Contaminants From Gold Mine Tailings In Matjhabeng Local Municipality, South Africa

Abstract

Mining of gold in Matjhabeng Local Municipality area (MLM), Free State, South Africa has produced numerous gold mine tailings, which contain a variety of contaminants. This study, investigated the extent of pollution of water bodies and soil by contaminants from gold mine tailings in the MLM area. The uptake of contaminants by plants, such as medicinal plant species, sweet thorn, as well as food crop species, maize, was also investigated. Surface water and soil were assessed at 15 sampling sites, and within five demarcated zones in uncultivated lands in terms of six physical properties, as well as 12 potential harmful elements (PHEs), while contamination in sweet thorn plants was assessed for the PHEs. The contamination of cultivated soil and maize seeds were studied from 12 sampling sites, and within four demarcated zones in cultivated lands in terms of the physical properties and the PHEs. Groundwater contamination was assessed from eight of the 12 sampling sites, and within three of the four zones, in terms of the physical water quality properties, the PHEs, as well as microbiological properties, since groundwater in the area is also used for drinking. Several environmental pollution risk indices, as well as health risk indices were quantified to determine the potential risk of the contamination of surface water and uncultivated soils by PHEs, as well as the health risk of ingesting the different PHEs in sweet thorn leaves samples, which is used for medicinal purposes. The results of this study revealed that the water, soil and plants in the MLM area have been severely contaminated by the contaminants from the gold mine tailings and of much concern is the contamination by the PHEs. The concentrations of As, Co, Cu, Fe, and Zn, were higher than the surface water quality limits, while Fe, Pb, Ca and Mg measured in groundwater exceeded the drinking water quality limits, with Pb and Fe found to be at toxic levels. The overall contamination of groundwater, revealed that majority of the groundwater in the study area is unsuitable for drinking, as confirmed by high Drinking Water Quality Indexes. On the other hand, the concentration of Cr, Cu, Zn and Fe also exceeded the limits and the background concentrations for uncultivated soils in South Africa, while the concentrations of Cu and Zn exceeded the permissible limits for cultivated soil, as well as the background concentrations in South Africa. Concentrations of Pb and Fe measured in leaves of sweet thorn exceeded the limits while the accumulation of Pb and Se in sweet thorn leaves were found in close to 20% of the sampling sites. However, with maize samples, only arsenic exceeded the limit as stipulated by the Australian Standards for Food Safety, at four sampling sites. The high level of contamination of water, soil and plants in the MLM area was also affirmed by the Geo-accumulation Index results for surface water. The Single Factor Pollution Index results indicated a high contamination by As, and exceptionally high contamination by Se for majority of the surface water samples. On the other hand, human health risk indices results indicated severe non-carcinogenic health risk of As, Pb, Co, Cu, Fe and Pb, from the ingestion of sweet thorn leaves for medicinal purposes with Hazard Index (HI) values > 1. The carcinogenic risk for As at 20% of the sampling sites, and at 40% of the sampling sites for Pb exceeded the 1×10-4 value as stipulated by the USEPA, which suggested a significant cancer risk to the local people in the MLM area. To ascertain the total pollution risk in the MLM area, a Combined Risk Index (CRI) was developed. The results of the CRI revealed that majority of the sampling sites in the MLM area have been contaminated by PHEs and therefore poses risk to the environment and human health. The general trend was that the level of contamination decreased away from Zone 1, in the downstream direction in relation to the prevailing wind in the area, with the least level of contamination registered at the control Zone 5, which was in the upstream wind direction. The overall environmental and health risks classification results for each of the 15 sampling sites for the uncultivated lands revealed three sites, S2, S7 and S9, as high risk areas in the MLM area. Additionally, five sites, S4, S5, S10, S11 and S15 were within the low risk category, while the remainder of the sites have been classified moderate risk areas. The findings from this study indicated that gold mine tailings, as well as mining activities are the major source of PHEs contamination in the MLM area. The results from this study provides scientific facts and evidences that can be used as a baseline for further research on remediation and measures to mitigate the level of contamination by PHEs in the MLM area.