Assessment of Heavy Metal Pollution and Ecological Risk In Bottom Sediments of the Qua-Iboe River Estuary, Southeast Nigeria

Abstract

The distribution, contamination status, and ecological risk of heavy metals in bottom sediments of the Qua-Iboe River Estuary, Southeast Nigeria, were investigated to evaluate the environmental quality of this tropical estuarine ecosystem. A total of 55 recent bottom sediment samples were collected from water depths ranging from 1 to 10 m and analyzed for Cu, Pb, Zn, Cd, Ni, and Fe using Atomic Absorption Spectrometry (AAS). Heavy metal concentrations ranged from 0.000–0.400 mg/kg (Cu), 0.000–0.030 mg/kg (Pb), 0.000–0.620 mg/kg (Zn), 0.000–0.171 mg/kg (Cd), 0.200–0.670 mg/kg (Ni), and 1.000–1.230 mg/kg (Fe), with mean concentrations of 0.180, 0.003, 0.341, 0.069, 0.476, and 1.090 mg/kg, respectively. The abundance of heavy metals followed the order Fe > Ni > Zn > Cu > Cd > Pb. All measured concentrations were considerably lower than the Average Shale Values and the Department of Petroleum Resources (DPR) sediment quality guidelines, indicating minimal contamination. The calculated geo-accumulation index (Igeo) values were all ≤ 0, classifying the sediments as unpolluted, while contamination factor (CF) values for all metals were < 1, indicating low contamination. The degree of contamination (DC) values ranged from 0.0049 to 0.5967, and pollution load index (PLI) values ranged from 0.0000 to 0.0048, confirming the absence of overall heavy metal pollution. Ecological risk assessment showed that ecological risk factor (Er) values for all metals were < 40, whereas the ecological risk index (RI) ranged from 0.0243 to 17.2072, indicating low ecological risk throughout the estuary. Hierarchical Cluster Analysis classified the investigated metals into two distinct groups, suggesting contributions from both natural geogenic sources and localized anthropogenic inputs. Although the sediments are presently of good environmental quality, increasing industrialization, oil-related activities, and domestic waste discharge within the Niger Delta necessitate continuous environmental monitoring to prevent future heavy metal accumulation and safeguard the ecological integrity of the Qua-Iboe River Estuary.