The Concentration of Heavy Metals in the Sediments of the River Nun Estuary, Around Akassa, Niger Delta, Nigeria

Abstract

Levels of the heavy metals lead (Pb), cadmium (Cd), nickel (Ni), zinc (Zn), and manganese (Mn) were analyzed in the sediments of the River Nun estuary. This was done in order gauge the impact of anthropogenic inputs such as pesticides, fertilizers, oil spillage and other industrial and anthropogenic wastes disposal, especially at the coastal parts of the region on bottom sediments. Three sampling Stations were chosen for the purpose of this research. Station 1 (Buo-Ama Creek) was established close to the entrance of Buo-Ama creek, in the Nun River estuary. Station 2 (Erewei- Kongho) was established along one of the tributaries of the Nun River estuary around Erewei- Kongho. Station 3 was established in Ogbokiri. Sediment samples were collected with the aid of a soil auger and a galvanized metal core cylinder from the three (3) sampling stations along a transect running from the low intertidal level (LIL), through the mid intertidal level (MIL) to the high intertidal level (HIL). Sediment samples were analysed in the laboratory using the method of Atomic Absorption Spectrophotometer (AAS). Means and standard deviations were calculated for all the measured parameters. A one-way ANOVA was employed at the 95% confidence limit to test for differences across stations in the heavy metals. Turkey HSD post HOC test was also employed to separate means and identify where variability and similarities exist. This was aided by the SPSS 20.0 statistical tool kit. The result shows that Pb has the highest concentration, followed by Zn, Ni, Cd, and Mn respectively. The lowest values of all metals were observed at station 2, while the highest concentrations of metals were recorded at sampling stations 1. The results show that the value of Pb was highest in station 1(1.347±0.001), followed by Station 3 (1.24±0.001). Station 2 had the least mean value of Pb (0.884±0.001). Cd showed similar patterns across the three sampling stations 1, 2 and 3, with the values 0.068±0.002, 0.046±0.001, and 0.054±0.002 respectively. Ni also presented slight difference across the three sampling stations. Concentration of Zn were higher in station 1 and 2 (1.265±0.002 and 1.038±0.002), than in station 3 (0.725±0.001). All metal concentration was however lower than the international permissible limited. The concentrations of Mn were also observed to present a similar pattern across the sampling stations. There is a significant difference (P<0.05) in all heavy metal parameters across all stations. Heavy Metal Concentrations were found to decrease with increasing distance from the river mouth, suggesting that anthropogenic inputs, related to agricultural and domestic discharge into the river, are the major sources of heavy metals in the river sediments. Land based activities therefore have a profound effect on aquatic ecosystem stability and health.