Impact Of Gold Mining Activities On The Water Quality Of The Lower Pra River

ABSTRACT

 This study was conducted to assess the extent of Mercury (THg) contamination at four locations within the Shama-Mporhor Wassa catchment area of the Lower Pra River. Water, fish and sediment samples were taken twice with the longitudinal transect method at Daboase, Beposo, Bokorkope and Shama during the minor rainy season in October and at the apex of the dry season in March. Careful investigation of the Shama-Mporhor Wassa catchment area revealed that two of the locations Daboase and Beposo had been continuously impacted by the activities of Artisanal Gold miners (AGM). From the study, Total Mercury (THg) levels were found to have persisted in River water several kilometers downstream the second Artisanal Gold mining (AGM) location at Shama estuary for both seasons. Ten trace elements Mercury (Hg), Selenium (Se), Copper (Cu), Chromium (Cr), Lead (Pb), Iron (Fe), Manganese (Mn), Nickel (Ni), Zinc (Zn) and Cadmium (Cd) were determined in water, fish and sediment samples using the Atomic Absorption Spectroscopy (AAS) equipped with both Hydride Generation (HGAAS) for Selenium (Se) and Cold Vapour (CVAAS) for Total Mercury (THg). The levels of Total Mercury (THg) were largely above the WHO and USEPA guidelines for drinking water (1µg/L) and sediments (200 µg/Kg) respectively for the four locations investigated. Total Mercury (THg) exceeded the WHO, 2011 guideline value of 0.5 mg/Kg for fish species Clarias submarginatus but was below the guideline value for Xenomystus nigri. Mean concentration of Cd and Fe exceeded the WHO, 2011 guideline values for drinking water for the wet season. The other trace elements Zn, Ni, Cu, Cr, Se, Mn, and Pb had their mean concentration below the WHO, 2011 guideline values for drinking water. Apart from the mean concentration of Cd that exceeded the Canadian Interim Sediment Quality (ISQG) guideline value of 0.6 mg/Kg for the wet season, Cr, Cu, Zn, Ni and Pb were below their respective guideline values for both seasons. Statistical parameters such as the Coefficient of Variation and the Paired Sampled T- test were used to investigate the spatial and temporal variation of trace elements, water physico-chemical parameters and nutrients. Physico-chemical parameters such as total alkalinity, pH and Biochemical Oxygen Demand (BOD) were affected by seasonal variations as evident from the Paired Sampled T- Test. Environ metrics model Principal Component Analysis (PCA) proved to be an effective tool for identifying the possible sources (natural and anthropogenic) of trace elements and their relationship with water physico-chemical parameters. The model showed that Total Suspended Solids (TSS) had a major role to play in the distribution of Total Mercury (THg) and Selenium (Se) across the four locations in the study area. Generally, the Lower Pra River was found to be polluted and of poor water quality in terms of Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD),Total Suspended Solids (TSS), Total Dissolved Solids (TDS) and microbes such as E. coli, Total Coliform (TC), Fecal Coliform (FC), and Total Heterotrophic Bacteria (THB). Microbial contamination was also found to be connected to human activities along the banks of the river.