Evaluation of Pollution Load: Heavy Metal Contents and Physiochemical Properties of the Great Kwa River, Calabar, Cross River State, Nigeria

Background and Objectives: Human activities can increase the amount of pollutants in the environment leading to water pollution. The contamination of surface water and sediments by heavy metals can result in adverse health conditions of humans, due to the bioaccumulation of metals. This study seeks to assess the pollution load of some heavy metals and physiochemical properties in Great Kwa River.

Methods: Water samples were collected once a month from three stations within four selected months in wet and dry seasons. Samples were preserved by adding 10 ml of 6 N Nitric acid and stored at 5oC. Laboratory investigations were conducted and data analyzed statistically.

Findings: The mean pH, dissolved O2, biological O2 demand, conductivity, NO3, NH4 and temperature were 7.44±1.24, 5.58±0.92, 0.957±0.002, 32.84±2.941, 0.1030±0.1701, 0.113±0.018 and 28.2±1.48, respectively during wet season. Mean concentration of Cu, Fe, Cr, Mn, Zn, Ni are 0.225±0.003, 0.489±0.009, 0.068±0.016, 0.102±0.006, 0.794±0.003, 0.031±0.001, respectively during the wet season. Mean concentration of metals in the river during the wet season were ranked in descending order as Zn > Fe > Cu > Mn > Cr > Ni. Iron (0.489±0.009 mg/l and 0.438±0.003 mg/l), chromium (0.068±0.016 mg/l and 0.055±0.008 mg/l), nickel (0.031±0.001 mg/l and 0.025±0.002 mg/l) were higher than Nigerian standard for drinking water in both seasons. The contamination factor of heavy metals in station 3 were 2.14, 1.56, 1.09, 0.89 for Fe, Cr, Ni, Zn, respectively, indicating moderate contamination. The pollution load index in stations 1, 2, 3 were 0.262, 0.537, 0.981, respectively.

Conclusion: The present study provided base-line information on the pollution levels and physiochemical properties of the river. The river was not highly polluted by heavy metals except iron, chromium and nickel that were found above the recommended standards. However, drinking of water from the river over one’s lifetime is not advisable due to detrimental health hazards.