Trace Metal Contamination and Risk Assessment of an Urban River in Limpopo Province, South Africa

Ecological and human health risk assessments were undertaken in an urban river, Sand River. Suitability of river water for irrigation was also determined. Samples were taken on a monthly basis from four sites. Site 1 was upstream of a sewage treatment plant, sites 2, 3 and 4 were downstream. The mean concentrations of trace metals in Sand River water after sewage effluent discharge followed the order Fe > Mn > Pb > Cu > Zn ≥ Cd. Trace metal concentrations in the sediment, grass and fish after discharge followed the order Fe > Mn > Zn > Cu > Pb > Cd. The geo-accumulation index showed that the sediment was not contaminated with trace metals. The health risk assessment index showed that consumption of fish from the Sand River was risky because of the high lead levels. Sodium adsorption ratio and soluble sodium percentage were 2.54% and 49.7% respectively. Both these values indicate that Sand River water is suitable for irrigation after effluent discharge.