Assessment of water quality status using heavy metal pollution indices: A case from Eha-Amufu catchment area of Ebonyi River, Nigeria

Abstract

The catchment area of Ebonyi River at Eha-Amufu, Enugu State, Nigeria serves as the main source of drinking water to the immediate community. However, there is dearth of information on the pollution status of this important River. The study assessed the heavy metal enrichment of catchment area of Ebonyi River at Eha-Amufu, and its suitability for human consumption using relevant heavy metal pollution indices and heavy metal toxicity load. A total of 54 water samples were collected from three different locations during rainy and dry seasons. The physico-chemical parameters, mineral nutrients and heavy metal contents of the water samples were analyzed using the standard methods. The Pearson's correlation coefficient was applied to determine the interrelationship between physico-chemical properties and heavy metals. All water samples were slightly alkaline (7.58 to 7.90) in both seasons. Sodium was the only mineral with higher concentration in rainy season. Magnesium ranked highest in the surface water, specifically at the downstream section with concentrations of 8.41 mg l−1 and 13.31 mg l−1 in the dry and rainy seasons, respectively. The mean value of trace metals viz. Pb, Cd, As, Cu, Fe, Ni, Hg, and Mn were above their respective acceptable limits for drinking water quality, except Zn and Mg. The Pearson's correlation analysis revealed existence of associations between some physico-chemical properties and some heavy metals, except for pH, implying that pH is not the major factor controlling heavy metal distribution in the surface water. Ni, As and Mn had contamination factor above 6.0, indicating very high contamination while the ecological risk index of As, Cd and Hg were above 320, suggesting serious ecological risk. The heavy metal pollution indexes, including the heavy metal toxicity load of all sites were above the threshold, indicating deteriorated water quality that is unfit for human consumption.