Metal concentrations in Clarias gariepinus and Labeo umbratus from the Olifants and Klein Olifants River, Mpumalanga, South Africa : zinc, copper, manganese, lead, chromium, nickel, aluminium and iron

The upper catchment of the Olifants River, from its origin near Bethal to its confluence with the Wilge River, north of Witbank, and its tributaries are being subjected to increasing afforestation, mining, power generation, irrigation, domestic and industrial activities. These activities have a profound effect on the water quality. The major point sources of pollution in the study area include mines, industries and very importantly, combined sewage purification works that are located alongside the river. In addition to oxidizable material, these sources contain detergents, nutrients and metals. It was therefore necessary to determine the extent to which these activities affect the water quality of the system. The bioaccumulation of zinc (Zn), copper(Cu), manganese (Mn), lead (Pb), chromium (Cr), nickel (Ni), aluminium (Al) and iron (Fe) in the skin, muscle, liver and gill tissues of Clarias gariepinus and Labeo umbratus from the Upper Olifants River and Klein Olifants River was investigated over the period February 1994 to May 1995. The highest concentrations of these metals were found in the gill and liver tissues of both species, with lower concentrations in the skin and muscle tissues. Bioaccumulation patterns were found to vary according to the species of the fish, mainly according to their different feeding habits and the routes of metal uptake. It also varied as a function of the different localities. Accumulation was size specific, with higher concentrations of metals found in smaller fish.