Assessment of physico-chemical properties and heavy metal contents from the Middelburg Dam in Steve Tshwete Municipality, Mpumalanga

Abstract

Poor water quality is a global concern as water contaminated with high levels of both physico-chemical parameters and heavy metals has serious effects on both human health and the environment. Surface water quality is mainly affected by changes in physico-chemical parameters and heavy metals which mostly find their way into the water bodies through anthropogenic activities causing deterioration of the quality of water in the receiving water bodies. The consumption of polluted surface water with poor quality contributes to many waterborne related illnesses and also shows detrimental effects on aquatic life. The study aimed at utilising historical data in analysing physico-chemical properties of water quality and determining the presence and concentrations of heavy metals in water in the Middelburg dam, before and after treatment. A total of ten (10) sampling points were selected between raw water from the dam and water that is consumed after treatment, where both physico-chemical parameters as well as heavy metals were assessed. The results suggested that the mean values and mean concentrations of physico-chemical parameters such as pH, turbidity, electrical conductivity, true colour, free chloride, nitrate, nitrite, fluoride, chloride, sodium, and total dissolved solids (except for sulfate) for all ten sites were within the acceptable limits of South African Standard for drinking water (SANS 241:2015). The mean concentrations of sulfate at all sampling points were above 250 mg/l, associated with aesthetic risk, while a mean concentration above 500 mg/l was in the raw water from the Middelburg Dam. Calcium, magnesium, and potassium mean concentrations for all the sampling points were also within the acceptable limits. The mean concentrations for alkalinity were very low (less than 150 mg/L) for all sampling points, which indicated that the water was corrosive, and this is related to acidity while the mean concentrations for total hardness were high (greater than 200 mg/L) indicating hard water. Aluminium and iron mean concentrations for all the sampling points were within the acceptable limits. The mean concentrations of manganese were higher at the water treatment plant and the reservoirs and slightly higher at most sampling points (above the limit of ≤ 0.1 mg/L), associated with aesthetic risk. The high levels of sulfate suggest pollution of water by activities such as coal mining. The levels of manganese suggest a considerable pollution of water with steel production and mining activities. The findings of the study can be used in Steve Tshwete Local Municipality and in any other area with the same environmental conditions by national authorities and policy makers in designing suitable strategies and approaches for water quality management. Moreover, the study recommends an in-depth analysis of the impacts of mining and other anthropogenic activities on the Middelburg dam and Klein-Olifants River catchment. All the studied physicochemical parameters and metal concentrations were within the permissible limits, so this was an indication that the current water treatment processes used by the municipality were effective.