Heavy Metal Pollution in the Receiving Environment of the University of Dar Es Salaam Waste Stabilization Ponds

Abstract

The aim of this study was to examine the availability, concentration levels and bioaccumulation of heavy metals namely; Mercury (Hg), Cadmium (Cd), Lead (Pb), Zinc (Zn) and Molybdenum (Mo) in the waste Stabilization Ponds of the University of Dar es Salaam. A total of 135 samples were analyzed, out of which 27 were samples of water, 27 of sediments and 81 samples of fish tissues. Two types of fishes were used namely; Oreochromis niloticus and Clarias gariepinus.

Heavy metal concentration varied significantly between water, sediment, fish species and tissues. Hg, Cd, Zn and Mo concentrations in water and sediment were within WHO safe limits. However, Pb in water and Cd, Pb and Zn concentrations in sediments were found to be above WHO standards (p<0.05). Concentration levels for Cd, Pb and Zn were above acceptable levels in Oreochromis niloticus while Hg was found to be within safe limits in both fish species (p<0.05). Molybdenum was found to be below the detection limits in Oreochromis niloticus. While Cd was not detected, Pb, Zn and Mo were found highly accumulated in Clarias gariepinus (p<0.05). Oreochromis niloticus accumulated metals in the increasing order from dorsal muscles < gills < liver while Clarias gariepinus accumulated metals in the decreasing order from dorsal muscle < gills < liver.

Public awareness on the dangers to which fish consumers from the site are exposed is highly suggested and purposeful mitigation measures of stopping all fishing activities in these sites is needed, also animal feeding around the ponds should be forbidden.