Levels, source determination and health implications of trace metals in groundwater within the Lower Pra Basin, Ghana

Abstract

Two hundred and fifty samples were collected from fifty-five (No) boreholes on quarterly basis between March 2011 and October 2012 covering the wet and dry seasons within the Lower Pra Basin for water quality assessment. The analytical results show that groundwater being used by some communities within the basin is contaminated, with Al (19.2 % of boreholes), Se (18.4 % of boreholes), Cd (18 % of boreholes), As (11.6 % of boreholes), Pb (39.6 % of boreholes), Mn (5.6 % of boreholes), Hg (42 % of boreholes) and Fe (21.6 % of boreholes) at levels exceeding the WHO (Guidelines for drinking water quality. Revision of the 1993 guidelines, 2004) guideline limits for drinking water. The stability of iron species for the groundwater system under the prevailing pE/pH condition shows that amorphous Fe(OH)3 significantly controls the concentration of iron in groundwater within the basin. The results also show that pyrite and arsenopyrite oxidation processes in groundwater within the basin are not exclusively responsible for the concentration of iron in the boreholes. Calculated saturation indices (SI) of the iron and manganese species using PHREEQC for Windows show that the groundwaters are generally undersaturated with respect to melanterite (FeSO4·7H2O), siderite (FeCO3), hausmannite (Mn3O4), pyrolusite (MnO2), rhodochrosite (MnCO3), manganite (MnOOH) and pyrochroite [Mn(OH2)], and supersaturated with respect to goethite (FeOOH) and haematite (Fe2O3). Human health risks assessment show that, for both adults and children via ingestion route, the mean HQing levels were found in the order of Zn > Fe = Cu > Pb > Cd >Mn. Results further show that the HQ/HI is the same for both adults and children for all trace metals and are less than 1. Thus, the trace metals considered in this study are not of concern for potential human health risk caused by exposure to non-carcinogenic elements.