Geoenvironmental Assessments of Heavy Metals in Surface Sediments from Some Creeks of the Great Kwa River, Southeastern Nigeria

Abstract

In southeastern Nigeria, the Great Kwa River watershed which was originally covered by tropical rainforest has now become a beehive of various agricultural, extractive and industrial activities. The present study focused on the investigation of the current level and distribution of seven heavy metals (Pb, Zn, Cu, Ni, Cr, Cd, As) collected from surface sediment at 12 stations, located within Mbat-Abbiati and Oberakkai Creeks of the Great Kwa River. Results show that the measured heavy metals have an abundance trend in the order Zn>Cr>Ni>Cu>Pb>As>Cd for sediments from Mbat-Abbiati and Zn>Cr>Ni>Pb>Cu>As>Cd for sediments from Oberakkai Creek. Enhanced concentrations and significant spatial variation was recorded for heavy metals in sediments from Oberrakai Creek as against what obtains in sediments from Mbat-Abbiati Creek. The pollution status was evaluated using Enrichment Factor (EF), Index of Geoaccumulation (Igeo), Contamination Factor (Cf), Degree of Contamination (Cd) and Pollution Load Index (PLI). Indication from both the contamination factor and degree of contamination is that all the measured heavy metals, excluding Pb and Cd, exhibits low contamination status in the sediment. Based on geoaccumulation index, the sediments are generally classified as unpolluted with regards to the measured heavy metals. The computed Enrichment Factors (EF) showed that some heavy metals (Pb, Zn, Cr, Cd) have EF values of up to 1, which indicates enrichment through lithogenic and anthropogenic sources. Further screening revealed that more than 55% of the calculated EF values for the Pb, Zn, Cr and Cd are from lithogenic sources, thereby suggesting that the main sources of pollution are geogenic materials, probably sourced through mining and quarrying activities that thrive within the catchment region. Results of the Pollution Load Index conclude that sediments from both Mbat-Abbiati and Oberakkai Creeks are generally unpolluted.

Keywords: Geoenvironment, pollution, sediment, Nigeria, Great Kwa River