Water Quality Assessment of the Southwestern and Coastal River Systems of Ghana

Abstract

Investigation into physico-chemical water quality and dissolved heavy metal contents of major rivers from the Southwestern and Coastal River Systems of Ghana from 19 stations was undertaken from 2007 to 2010. The waters are used in their raw states for domestic purposes including drinking in most communities in the study area. The concentrations of the various parameters were assessed in relation to the Ghana Raw Water Quality Criteria and Guidelines for raw water, and in few instances, are compared with the WHO guidelines where the waters are known to be sources of drinking water. Turbidity, Total Suspended Solids (TSS) and Total Hardness were the physical parameters selected for the quality assessment of the waters in relation to domestic use. An Adapted Water Quality Index (WQI) was used to characterize the overall water quality status of the waters.  Turbidity and TSS were found to be above their respective Target Water Quality Range (TWQR) values for raw water, while Total Hardness concentration were within guideline values. The levels of the trace metals investigated in the waters, Fe, Mn, Zn, Pb, Cr, Ni, Cu, As, Cd, and Hg, were found to be  generally low, and do not yet pose health risks in the dissolved form. However, Fe and Mn levels were moderately high, exceeding their respective TWQR values stipulated for Ghanaian freshwaters.  An assessment of non-cancerous health risk from exposure to Fe, Mn, and Zn was performed with the Risk Integrated Software for cleanup (RISC 4.02) developed by the USEPA. Results of the risk assessment, however, revealed a hazard quotient greater than 1 in some locations, indicating that the risk of adverse health effects associated with exposure to zinc, manganese and iron is high in those locations. Efforts should therefore be made to prevent metal pollutants, mainly from mining activities, from entering our water bodies to keep them suitable for their intended uses.

Keywords: Risk assessment, Southwestern Rivers Systems, Coastal Rivers Systems, Water Quality, Water Quality Index.