2. Human Exposure Risks Assessment of Heavy Metals in Groundwater within the Amansie and Adansi Districts in Ghana using Pollution Evaluation Indices

Abstract

Non-carcinogenic risk assessment was done using Hazard Quotient (HQing/derm) and Hazard Index (HIing/derm) following USEPA methodology for a total of 59 boreholes and 12 hand dug wells sampled between July and October 2012. The objective was to assess the potential human health risks caused by exposure to non-carcinogenic heavy metals and estimate the potential environmental risk exposure in order to ensure the health safety of consumers within the Amansie and Adansi Districts. The results shows that, the heavy metal abundance in groundwater within the districts is in the order: Fe > Mn > As > Zn > Cu = Pb > Cd > Hg, for borehole water and Fe > As > Mn > Zn > Cu > Cd > Pb > Hg, for well water. The percentage contributions are: Fe (60%), Mn (20%), As (7%), Zn (5%), Cu (4%), Pb (4%), Cd (0%) and Hg (0%). The results also show that, the potential non-carcinogenic risks of exposure (HQing/derm) posed by Fe, Mn, Cd, Cu, Zn, Pb, As and Hg within a single route of exposure via ingestion or dermal contact is 3.30 x 10-2, 1.40 x 10-1, 5.00 x 10-4, 3.70 x 10-2, 3.00 x 10-1, 3.60 x 10-2, 3.00 x 10-4 and 3.00 x 10-4 respectively for both adults and children, suggesting a decreasing order of Zn > Mn > Cu > Pb > Fe > Cd > As = Hg, for borehole water, and Zn > Mn > Cu > Fe > Cd > As = Hg, for well water. The concerns for potential human health risks caused by exposure to non-carcinogenic heavy metals for Fe, Mn, Cd, Cu,Zn, Pb, As, and Hg are: 6.0 x10-2, 2.56 x 10-1, 9.15 x 10-4, 6.77 x 10-2, 5.49 x 10-1, 6.59 x 10-2, 5.49 x 10-4, 5.49 x 10-4 for boreholes, and 6.46 x 10-2, 2.74 x 10-1, 9.79 x10-4, 7.25 x 10-2, 5.88 x 10-1, 5.88 x 10-4, 5.88 x 10-4 for well water, suggesting that there is no concern for potential human health risks caused by exposure to non- arcinogenic toxic heavy metals in groundwater within the Districts (i.e HQ/HI <1). The study further show that, the risk index factor (Ri)for heavy metals was in the order: Hg > As > Cd > Pb > Cu > Zn, for borehole water, and As > Cd > Cu > Zn for well water  suggesting that, groundwater within the Districts is potentially threatened by anthropogenic activities primarily, mining activities where, chemicals such as arsenic (As) and mercury (Hg) are used to recover gold from its amalgam. Based on the classification of environmental risk using comprehensive risk factor (CRI), borehole water within the districts could be classified as very high risk, while, well water could be classified as high risk. Generally, the main environmental heavy metals that poses pollution risk in groundwater within the Districts were Hg, As and Cd and contributed mostly to the Risk index factor (Ri.