Water Quality and Ecotoxicological Impacts of Surfactants and Heavy Metals in Urban Rivers of Benin City, Niger Delta, Nigeria

Abstract

Urban rivers in Nigeria are increasingly affected by detergent residues, domestic wastewater, and trace-metal inputs associated with rapid urbanisation. This study assessed the physicochemical characteristics, surfactant concentrations, and selected heavy metals in three urban rivers in Benin City, Edo State. Water samples were collected once from midstream points in each river and analysed for pH, dissolved oxygen (DO), biological oxygen demand (BOD), chemical oxygen demand (COD), turbidity, linear alkylbenzene sulfonates (LAS), sodium dodecyl sulfate (SDS), and metals (Ni, Cu, Zn, Mn, Fe) using APHA, MBAS, and AAS methods. pH ranged from 6.5 to 6.9, DO from 4.8 to 5.5 mg/L, BOD from 18 to 22 mg/L, COD from 40 to 50 mg/L, and turbidity from 10 to 15 NTU, with River B consistently exhibiting the poorest water quality. Surfactant concentrations were highest in River B, where LAS reached 0.22 mg/L and SDS 0.12 mg/L. Heavy metals followed the same spatial pattern, with River B recording the highest values of Ni (25 µg/L), Cu (17 µg/L), Zn (60 µg/L), Mn (110 µg/L), and Fe (350 µg/L), the latter exceeding WHO limits. The combined occurrence of organic enrichment, elevated surfactants, and trace metals indicates substantial anthropogenic influence and potential ecological stress, although biological impacts were not directly measured. These findings highlight the need for strengthened wastewater management, regulation of detergent-rich effluents, and routine monitoring to protect vulnerable urban freshwater ecosystems.