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

Abstract

Background: 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. Results: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. Conclusion: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.

Sedimentation and sediment core profile of heavy metals in the Owabi reservoir in Ghana

“…For the present study, which was conducted close to the city environment, the Pb in sediment cores apparently decreased from the 1990s to 2010s. Compared to earlier studies of the mining environment (Hogarh et al, 2016), Pb exhibited a gradual increase in sediment cores across this time period, presumably due to localized influences from the mining environment.…”

“…As the reservoir is located in a wildlife sanctuary, it is likely that the surrounding vegetation has helped retard erosion of sandy materials and debris into the head‐pond, consistent with the observation that vegetation cover has been found to reduce overland flow during rainstorms and has a positive impact in reducing erosion and its attendant sedimentation issues (Prosser & Williams, ). Previous studies, for example, suggest that when forest cover is removed through such events as natural fires (Prosser & Williams, ), or anthropogenic activities such as clearing of land for mining (Hogarh et al, ), such disturbances have led to increased sedimentation rates. In the mining district of Bibiani in Ghana, the sediment yield to Lake Amponsah was found to be average 1.76 cm/year, which is two orders of magnitude greater than the rate for Owabi Reservoir (Hogarh et al, ).…”

“…Previous studies, for example, suggest that when forest cover is removed through such events as natural fires (Prosser & Williams, ), or anthropogenic activities such as clearing of land for mining (Hogarh et al, ), such disturbances have led to increased sedimentation rates. In the mining district of Bibiani in Ghana, the sediment yield to Lake Amponsah was found to be average 1.76 cm/year, which is two orders of magnitude greater than the rate for Owabi Reservoir (Hogarh et al, ). Given the benefit of forest cover for reduced sedimentation and sustainable use of Owabi Reservoir, it is important the wildlife sanctuary is protected against loss of vegetation cover.…”

“…Thus, the sediments can be viewed as providing an environmental record of pollutants, as well as being useful for retrospectively establishing the pollution history of an area. Sediments accumulate gradually in a waterbody, with older sediments being locked up in deeper layers, while recent sediments accumulate in the upper layers (Hogarh, Adu-Gyamfi, Nukpezah, Akoto, & Adu-Kumi, 2016). Thus, a sediment core provides a good spectrum of pollution dynamics in a watershed over time (Spencer & MacLeod, 2002).…”

Assessing Historical Mining and Smelting Effects on Heavy Metal Pollution of River Systems over Span of Two Decades

“…River bottom sediment is commonly considered as a legacy of the past, especially where historical metal mining activity being the contamination source is concerned. Most studies regarding contamination of aquatic environment with heavy metals sourced from active or historical mining activities focus on examination of only bottom sediment (Jabłońska-Czapla et al 2016 ; Dadová et al 2016 ; Hogarh et al 2016 ). However, in order to assess other than historical sources of river contamination and to differentiate between historical and present anthropogenic pollution sources, the investigation of suspended particulate matter should also be considered.…”