Contamination from mercury and other heavy metals in a mining district in Ghana: discerning recent trends from sediment core analysis

Abstract

Many years of gold mining in Ghana has generated huge environmental legacy issues, particularly contamination from heavy metals and metalloids. The present study evaluated the contamination from arsenic (As), cadmium (Cd), copper (Cu), mercury (Hg) and lead (Pb) in sediment cores at Bibiani, a historical gold mining town in Ghana. The study took a retrospective look at these contaminations by conducting sediment core analysis of heavy metals in sediments collected from Lake Amponsah in the Bibiani district. Sediment cores were sampled to a depth of 30 cm. The Lake was found to be undergoing sedimentation at an average rate of 1.76 cm/y. There was marginal decline in Hg concentrations over the past two decades (from the 1990s to 2010s), while the other metals showed relatively increasing trends. The Hg policy restricting Hg usage in Ghana since 1989 has contributed to the recent marginal decline of Hg in the sediment. It was found that small-scale miners illicitly applied Hg but used crude retrofits to recover some of the Hg during the gold amalgamation process. This perhaps contributed to the marginal decline being observed in the sediment compartment with depth. Nevertheless, there was concern of potential risk of exposure to gaseous Hg during the amalgamation process. Based on findings of this study, Hg legislation in Ghana should be enforced to the latter as it has shown good sign of reducing environmental contamination from this metal.