Probabilistic health risk assessment of heavy metals at wastewater discharge points within the Vaal River Basin, South Africa

Recently in South Africa, wastewater treatment plants (WWTP) have come under scrutiny because of increased reports of their ineffectiveness to treat wastewater adequately. This study focused on assessing potential health risks for humans exposed to concentrations of heavy metals in river systems that receive effluents from wastewater treatment plants in the Maluti-a-Phofung municipality. Untreated influents and treated effluents from two plants, one in the town of Phuthaditjhaba, the other in the town of Harrismith, were analysed for heavy metals. Water samples were also collected from the Elands and the Wilge Rivers, which receive effluents from the treatment plants in Phuthaditjhaba and Harrismith, respectively. All samples were analysed for heavy metals; Iron (Fe), Magnesium (Mg), Manganese (Mn), Zinc (Zn), Copper (Cu), Chromium (Cr), Nickel (Ni), Lead (Pb), Cobalt (Co), Arsenic (As), Cadmium (Cd) using Inductively Coupled Plasma Mass Spectrometry. The probabilistic human health risk was estimated using the Total Hazard quotient and Monte Carlo techniques. The results showed that there was no significant difference between treated and untreated wastewater (P > 0.05) in the concentration of heavy metals for both wastewater treatment plants using the student T-test. This indicated the inability of both treatment plants to remove metal contaminants adequately. Projections of non-cancer risk for metals in river water samples indicated a high potential for non-cancer risk for humans upon exposure via ingestion, with Arsenic being a significant contributor to overall risk. The results of this study underscore the need for improved wastewater treatment facilities in this region in order to ensure ecosystem integrity and public health safety. [Display omitted] •Heavy metals removal by WWTPs was inadequate.•Heavy metals in Elands and Wilge Rivers are mainly from WWTPs.•Arsenic in river water compromises the health safety of surrounding communities.•Monitoring of heavy metals in streams that drain WWTPs is imperative.•This is the first report on probabilistic risk assessment in the Vaal River Basin.