Metal distribution and fractionation in surface sediments of coastal Tema Harbour (Ghana) and its ecological implications

Abstract

This study investigated the distribution and fractionation of metals (Mn, Ni, Pb, Cr, Cu, Zn, As, Cd, Hg and Sn) in surface sediments of Tema Harbour (Greater Accra, Ghana) as well as its ecological implications. Significant differences in sediment concentrations of Mn, Ni, Cr, Cu, Zn, As and Sn were observed across the Tema Harbour. Geochemical indices indicate that Cd, Hg, Pb, Cu, Zn, As and Sn in the Tema Harbour sediments derived mainly from anthropogenic sources, while Mn, Ni and Cr were mainly of lithogenic origin. Metal fractionation revealed a predominance of Al, Mn, Ni, Pb, Cr, Cu, As and Sn in the residual phase. In contrast, Cd and Hg were mainly present in the exchangeable phase, while Zn was mainly associated with the reducible phase. Based on the metal fractionation in the Tema Harbour sediments, the potential risks of metal bioavailability were high for Cd and Hg, low–medium for Mn, Ni, Zn, As and Sn and low for Pb, Cr and Cu. A screening-level ecotoxicological assessment revealed high potential toxicity of Hg and moderate potential toxicities of Pb, Cu, Zn, As and Cd in the Tema Harbour sediments. The potential influence of the buffer intensity, silt–clay, total organic carbon and carbonate content on the metal distribution in the Tema Harbour sediments was also inferred from their correlations. Comparison with previous studies did not reveal a progressive increase in metal contamination at the Tema Harbour since the year 2000.