Trace Metal Concentration in Sediments of Imo River Estuary, South East Nigeria

Estuarine sediments serve as repositories for trace metals introduced through industrial, agricultural, and domestic pathways, and their geochemical analysis provides valuable information on pollution history and ecological risk. This study quantifies trace metal concentrations in surface sediments of the Imo River Estuary, spanning the boundary of Imo and Abia States, South East Nigeria, which receives runoff from farming activities, small-scale mining, and light industrial areas in the hinterland. Sediment samples are collected at twelve stations spanning the upper, middle, and lower estuary zones during both dry and wet seasons. Total concentrations of copper, zinc, lead, nickel, chromium, iron, and manganese are determined by acid digestion followed by atomic absorption spectrophotometry. Sequential extraction procedures are applied to characterise metal partitioning across geochemical fractions (exchangeable, carbonate-bound, iron-manganese oxide-bound, organic-bound, and residual). Geoaccumulation index, enrichment factor, and potential ecological risk index are computed to assess the degree of anthropogenic metal enrichment and ecological significance. Grain size and organic carbon content are analysed as controls on metal sorption. Results are expected to reveal localised enrichment of zinc and copper attributable to agricultural chemical residues and artisanal manufacturing workshops. Recommendations include regular sediment quality monitoring protocols for the Imo River Basin Development Authority. Keywords: trace metals, estuarine sediments, Imo River, geoaccumulation index, ecological risk