5 Gold Mining Effects on Water Quality in Domenase and Nkotumso along River Offin, Upper Denkyira West District

Abstract

Artisanal gold mining (ASM) has been an important source of primary livelihood activity for poor populations in Ghana. The sector now functions as a vital social safety-net and in some cases, provides the only source of income in employment-constrained economies and helping copious poor households survive during increasingly uncertain times. However, artisanal mining is linked to the release of heavy metals into the mainstream environment causing water pollution. In this study, heavy metals namely mercury (Hg), arsenic (As), manganese (Mn), lead (Pb) and iron, (Fe) were quantitatively analysed using PinAAcle 900T Perkin Elmer Atomic Absorption Spectrophotometer. The samples were taken from the core water source area of Domenase and Nkontomisa on the Offin River in the Upper Denkyira West District of the Central region of Ghana. The decreasing trend of metals was observed in water as Hg > Pb > As > Mn >Fe, whiles the average distribution of these heavy metals in water was 0.11, 0.02, 0.02, 0.122, 0.184 mg/L respectively for Nkotumso. In Domenase, the decreasing trend of metals was observed in water as Pb > Hg > As > Fe >Mn, and their averages were 0.028, 0.09, 0.018, 0,188, 0.090 mg/L, respectively. The concentration of Hg, As, and Pb in the water samples were above the WHO (2011) permissible limits except Mn and Fe which were below the guideline limit. The pH range of 6.24-6.53 was noted for Nkotumso and 5.24-5.83 (strongly to moderately acidic) for Domenase. The pH of water samples collected from Nkotumso was within WHO (2011) guideline values whereas the values of Domenase were not. The results indicate that the water is not suitable for drinking and other domestic purpose such as cooking since heavy metals such as Hg, As, and Pb which are known to be carcinogenic were high. The study recommends that continuous monitoring of Hg, As and Pb in the water and other aquatic biota of Nkotumso and Domenase along the River Offin should be assessed to ensure the safety of the ecology in the vicinity of the river.