Sediment core profile of heavy metals in Lake Amponsah in the mining district of Bibiani, Ghana
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Date
2015-11-18
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Abstract
The many years of gold mining in Ghana has generated huge environmental legacy issues, such as land degradation and environmental contaminations from heavy metals. The present study evaluated the contamination from arsenic (As), cadmium (Cd), copper (Cu), mercury (Hg) and lead (Pb) 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 core was sampled to the depth of 30 cm applying a PVC corer and sliced into 5 cm segments. The concentration of As was analysed applying the Palintest (Wagtech) method, while Cd, Pb, Cu and Hg were determined applying the Anodic Stripping Voltammetry (ASV) method. The concentrations of the various metals in the sediment core ranged as follows – As: 21 – 97 mg/kg, Hg: 0.01 – 0.04 mg/kg, Cd: 0.09 – 0.74 mg/kg, Pb: 0.05 – 3.40 mg/kg, and Cu: 0.98 – 4.92 mg/kg. Generally, the concentrations of the metals were mostly greater in the upper portions of the sediment core relative to the bottom portions. This suggests greater impacts from anthropogenic activities in recent times in the Lake Amponsah watershed. Arsenic correlated strongly with Hg at the bottom half (15 – 30 cm) of the sediment core (r = 0.88). The two metals however did not correlate in the upper half (0 – 15 cm) of the sediment core. It presupposes a historically relevant association between these two metals in the older bottom sediments, culminating from largely a single source factor. It provides evidence of historical application of Hg in gold extraction in the Lake Amponsah watershed, with As as a byproduct from the arsenopyrite ore. The absence of correlation between the two metals in the upper portions of the sediment core suggests that recent contaminations from these two metals originated from quite varied source factors, which may include activities related to small scale mining, farming and leachates from waste dumps. Finally, it was established that Lake Amponsah was undergoing sedimentation at a rate of 1.76 cm/year.
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A thesis submitted to the Department of Theoretical and Applied Biology,
Kwame Nkrumah University of Science and Technology
in partial fulfillment of the requirements
Master of Science degree in Environmental Science.