Influence of discharged effluent on the quality of surface water utilized for agricultural purposes

This article reports on the level of toxic trace metals (Cd, Pb, Mn, Zn, Cu and Ni) in surface water and sediment along the Blaauwbankspruit in the West Rand District of South Africa. This spruit serves as receiving channel of wastewaters from sewage treatment plant and a gold mine. Some physical and chemical influences of released wastewater on the quality of the surface water, which is utilized for agricultural purposes was studied. Total trace metals in water and sediment samples were digested using mineral acid and then analyzed by Inductively Coupled Plasma-Atomic Emission Spectrometry. The mean concentrations of analyzed trace metals in water samples ranged from trace - 0.05, trace - 0.11, 4.35 - 942.2, 0.10 - 0.41, 0.08 - 0.88 and 0.15 - 0.42 mg/l for Cd, Pb, Mn, Zn, Ni and Cu, respectively. The mean levels of trace metals in sediment samples also ranged between trace - 0.12, trace - 0.38, 12.3 - 2957.2, 0.13 - 2.57, 0.39 - 1.96 and 0.18 - 2.84 mg/g, respectively, in the above metallic order. Higher metallic load in sediments, compared to those in water samples were obtained. Safety limits, specified by the Department of Water Affairs and Forestry for the use of water for domestic and irrigational purposes were exceeded in many samples. This further highlights the serious concern regarding the use of contaminated surface water. In addition, higher values of determinants obtained from sampling points close to the wastewater treatment plant and the mine exit channels strongly revealed their influence on the general quality of the stream. Detection of metals such as cadmium and lead above acceptable limits has dire consequences across the food chain.