Mercury and cadmium budgets of the Pra estuary in the Western Region of Ghana

Abstract

Instrumental Neutron Activation Analysis was employed for the determination of mercury and cadmium in soil, water and fish samples from eight different sites of the Pra and Ayensu estuaries in Ghana. Mercury and cadmium was identified in ug/g levels and values correlated with the pH's of water column and soil samples. Substrates like the Blue tilapia and the European Green Crab were used as bioaccumulation indicators for the mercury levels in the various samples. A summary of the mean, minimum and maximum soil I water mercury and cadmium concentrations detected for the eight (8) sites, with IOkm geographical distribution; river bank at Beposo showed a maximum of 3.9511g/g of mercury, which is below the Environmental Protection Agency's permissible limit of O.134mg/g(l34.011g/g). Insignificantly low levels of mercury concentrations was analyzed in shoulder soils and water samples over the period of the study. A significantly high levels of concentrations of mercury existed in the riverbed sediments compared to that for the riverbank sediments, water and the shoulder soils. The degree of concentrations of mercury showed that, mercury and cadmium concentrations decreased significantly and gradually as one moved from Beposo to the Shama Beach through Bosomdo and Krobo. The study showed a maximum mercury and Cadmium residue of both the European green Crab and the Blue tilapia. While the maximum mercury and cadmium residue reported for the Tilapia were not consistently as high as those for the Crab. The maximum residue in the European Green Crab in three (3) reporting sites did not exceed the EPA action level (0.134 mg/g). The Crab had a higher body burden of mercury because it is a bottom-dwelling/feeding and predatory species.