Concentrations of heavy metals in two Ghanaian Lagoons

Abstract

The study was conducated in Benya and Nakwa lagoons in the Central Region of Ghana, to assess the level of heavy metal pollution of the water and its sediment, as well as in two species of fish: the black chin tilapia (Sarotherodon melanotheron) and oyster (Crassostrea tulipa) both of which constitute one of the major sources of protein for the local people of Elmina and Nakwa. It was also to find out the effect of cooking and depuration (of oysters) on the heavy metal content of the biota. The method involves collection of samples of the species with cast net, scaled and gutted. But the oyster samples were hand–picked. Each sample was divided into two, weighing 500 g. each. One portion was boiled and the other part was dried to a constant weight. The oyster sample was similarly treated. The oyster sample was divided into two, one depurated and the other half not depurated. Water and sediment samples from the lagoons were also collected for analysis at WRI of CSIR.. The results indicated that cooking significantly reduced the concentration of Pb in Crassostrea tulipa from Nakwa but increased concentration of Cd, Pb. As and Hg in S. melanotheron, significantly. Depuration significantly reduced As and Cd concentration in C. tulipa from Benya, but raised the concentration of Pb and Hg in C. tulipa from Benya.