Assessment of Elemental Contamination of Selected Major Dams from Osun State, Nigeria by Multivariate and Hazard Index Analyses
Dams and their environment, interrelate with a degree of complexity that often affects the availability of potable water. In Nigeria, dams are an important source of drinking water in many communities but are vulnerable to contamination from different sources. This study assessed the possible elemental (Cd, Cr, Cu, Fe, Ni, Pb, Mn, and Zn) contamination sources of selected dams in a total of 126 samples comprising 54 surface water, and 72 sediment samples collected from six main dams in Osun State using multivariate analyses like Principal Component Analysis (PCA) and Cluster Analysis (CA). Generally, the average elemental concentration was in the decreasing order of Cr > Ni > Cd > Pb > Cu > Fe > Zn > Mn and Pb > Cr > Ni > Cd > Zn > Mn > Fe > Cu for surface water and sediment samples respectively. Furthermore, statistical analysis showed that the average concentrations of the potentially toxic elements (PTEs) did not differ significantly (p < 0.05) across the sampling sites, indicating similar PTEs profiles. The PCA and CA revealed possible sources of elemental contamination to the dam quality as weathering of bedrocks, uncontrolled farming activities, abandoned equipment, boat fueling, maintenance, and repairs. Although only 13.9% of the hazard quotients (HQ) were higher than one for all the studied heavy metals in surface water, 91.7% of the hazard index (HI) were higher than one. This suggests an unacceptable risk of non-carcinogenic effects from the direct consumption of dam water. Furthermore, the oral target cancer risk, TCRoral in children > adults and > 1 × 10−4 for cancer risk set by USEPA, however, the % contribution of Cr to ∑TCRoral in adults which is > 1 × 10−4 ranged between 98.9 to 99.5%, indicating that Cr is the most dominant carcinogens in the overall cancer risk in adults.
