Evaluation of the Effects of Heavy Metals on Sediments and Rainwater Samples Due to Gas Flaring in the South Eastern Nigeria

Abstract

This study evaluates the concentrations of heavy metals in sediment and rainwater samples of Ibeno, south eastern Nigeria due to gas flaring. Surface sediment samples were collected randomly in six different sites during the dry season in the intertidal zone at extremely low tide from the flare point to a distance of about 250m away from the flare site. Rainwater samples were collected with the use of pre-clean basins at an open space in three selected communities of Ibeno and were transferred into different sterilized plastic rubbers with their labels. These samples were transported to the laboratory for analysis of heavy metals concentrations using a particle induced x-ray emission (PIXE) technique. Heavy metals such as Titanium (Ti), Chromium (Cr), Manganese (Mn), Iron (Fe), Copper (Cu), Zinc (Zn), Rubidium (Rb), Strontium (Sr), Zirconium (Zr) and Lead (Pb) were analyzed in sediments while Vanadium (V), Arsenic (As), Nickel (Ni), Lead (Pb), Iron (Fe), Copper (Cu), Zinc (Zn), Chromium (Cr), Manganese (Mn) and Cadmium (Cd) were obtained in rainwater. The concentrations of Iron (Fe) in sediments are higher at the study area than every other elements but Manganese (Mn) poses more negative effects than others. The four pollution indices such as enrichment factor (EF), geo-accumulation index (Igeo), contamination factor (CF) and pollution load index (PLI) were employed to assess the contamination status of heavy metals in sediment samples of the study area. The results revealed the elemental trend to be in descending order in each area of this study, which followed the sequence Mn> Zn> Pb> Cu> Fe> Sr> Rb> Cr> Ti >Zr, while PLI revealed the extent of pollution in each site which ranged from 1.44 to 1.94. Most of the heavy metals concentrations in sediments such as Mn, Zn, Pb, Cu and Fe were far above the permissible limits, while in rainwater samples Pb, Cd, Ni, Fe and Mn were far above the permissible limits by WHO, 2008 and NSDWQ, 2007. This revealed that the rainwater in the study area were not free from toxicity and are unfit for drinking. Analysis of multi-variant statistics such as Pearson’s correlation coefficient and cluster analysis were also applied to ascertain the relationship and sources of investigated heavy metals. Both positive and negative correlations were observed among some heavy metals at 0.01 and 0.05 levels, while the cluster analysis revealed four main clusters. The study revealed that the ecosystems in the studied areas were vulnerable to bioaccumulation of heavy metals in that soil which could be of hazard effect to the ecosystem.