Sediment Pollution Indices and Ecological Risk Evaluation in the Lanfenwa River, Southwest Nigeria

This study assessed the sediment quality of the Lanfenwa River in Abeokuta, Southwest Nigeria, by evaluating heavy metal concentrations, pollution indices, and ecological risk classifications across nine georeferenced sampling points (SP1–SP9). The river traverses zones with varying anthropogenic influence across upstream (reference), midstream (urban-impacted), and downstream (accumulation zones). Sediment samples were analyzed for physicochemical properties and heavy metals (Pb, Cd, Zn, Cu, Cr, Ni, Mn, and Fe) using Atomic Absorption Spectrophotometry (AAS) following USEPA Method 3050B. Results revealed that cadmium (Cd), copper (Cu), and lead (Pb) were the most elevated metals, particularly in midstream zones influenced by market runoff, informal industries, and vehicular activities. Physicochemical parameters such as pH (5.65–7.88), EC (125.4–372.2 µS/cm), and organic matter (3.20–6.43%) influenced metal mobility and distribution. Pollution indices, including Contamination Factor (CF), Geo-accumulation Index (Igeo), Enrichment Factor (EF), and Pollution Load Index (PLI), confirmed significant anthropogenic enrichment of Cd, Pb, and Zn. The CF values for Cd exceeded 4.0 at multiple sites, classifying it under “considerable to very high contamination.” Ecological risk was evaluated using Hazard Quotients (HQ) based on NOAA Threshold Effect Levels. Cd and Cu recorded HQ > 2.0, indicating high ecological risk, while Pb showed moderate risk. Multivariate analyses supported the clustering of metal sources and highlighted pollution gradients across zones. The study concludes that urban activities in the midstream section have significantly altered sediment quality. It recommends urgent pollution control, bioindicator-based monitoring, and improved waste management practices. These findings contribute to the broader understanding of metal pollution dynamics in Nigerian urban rivers and underscore the need for continuous biomonitoring and policy intervention.