Water quality assessment and potential ecological risk of trace metals in sediments of some selected rivers in Vhembe district, South Africa

Abstract

The monitoring of river health systems is crucial to maintain the integrity of services derived from them. This study investigated the physicochemical and microbiological levels in some tributaries of the Luvuvhu River water and sediments in South Africa. High levels of cadmium were recorded in the sediments of most of the rivers capable of posing high risk to aquatic organisms. The severity of the other metals ranged from low to medium risk. Comparable results on the effects of trace metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) on aquatic biota were obtained using various ecological indices (such as contamination factor, degree of contamination and potential ecological risk) and sediment quality guidelines (such as threshold effect level and the probable effect level of the Canadian council of the Environment (CCME) and the effect range-low and effect range-median). High levels of faecal indicator organisms (>59,000 cfu/100 mL) were recorded in all water source that are often used for domestic and agricultural purposes. The decreasing trend of faecal indicator organisms in the selected rivers were in the order: Mvudi > Mudidaba > Dzindi > Luvuvhu > Dzondo. Hence the use of the water for domestic purposes possess a potential acute human health risk. The levels of trace metals obtained from this study were above the threshold levels of water used in aquaculture though most of them complied with the regulatory limit for domestic and irrigation water use in some of the rivers. The decreasing trend of average trace metals levels were in the order: Mvudi > Mudidaba > Dzondo > Luvuvhu > Dzindi. The water quality of some of the tributaries of the Luvuvhu river (Mvudi and Mudidaba) were found to be more contaminated than the Luvuvhu River. Hence, constant monitoring of the various tributaries is recommended, and river restoration programs should be initiated where necessary.