Physico-chemical characteristics and pollution levels of heavy metals in the rivers in Thohoyandou, South Africa

In this study, trace metal analysis of the surface waters from river Dzindi, Madanzhe and Mvudi in Thohoyandou, South Africa, were conducted with a view to obtain a baseline data of their levels. The physico-chemical forms of the metals as a means of assessing their availability and non-availability for toxicity to aquatic organisms was also investigated. Surface water samples were collected randomly from selected sites in the rivers aforementioned. The samples were analysed for Cd, Cu, Pb and Zn using a Varian flame atomic absorption spectrometer. The concentration range of the metals were: 1.6-9.3, 2.0-3.0, 10.5-20.1 and 2.1-2.5 μg l−1 for Cd, Cu, Pb and Zn, respectively. The concentration ranges of all the metals measured were found to be below the international guidelines and acceptable concentrations for drinking water except the values for Cd and Pb. Also, when compared to the world average of trace elements for unpolluted rivers, the three rivers considered were polluted by Cd and Pb. With the speciation studies, Pb was found predominantly in the particulate fraction, while Cu and Zn were dominant in the non-labile fraction. However, Cd was found in equal distribution between the labile and non-labile fractions. The non-labile fractions of Cd, Cu and Zn were considered unavailable to cause any serious danger to aquatic organisms. However, the labile Cd was considered to be bio-available and therefore, can pose a danger to aquatic organisms.