Hydro-chemical Characterization and Contamination Status of Surface Water and Sediments Along the New Calabar River Basin

Abstract

This study evaluated the physicochemical characteristics, heavy metal concentrations, microbiological content, irrigation suitability, and human health risks of surface water and sediment along the Middle Reaches of the New Calabar River (Iwofe, Tombia, Bukuma, and Bakana). Utilizing a purposive sampling strategy, fifteen water samples and composite sediment cores were collected and analyzed following standard analytical protocols. The results revealed near-neutral surface water pH (6.80 to 7.32) but severe ionic enrichment, with electrical conductivity reaching 29,500 μS/cm and total dissolved solids up to 20,650 mg/L. Total hydrocarbon contents were consistently elevated across all sites, exceeding 211 mg/L in water and 3,000 mg/kg in sediment. Sediment samples exhibited acidic conditions (pH 4.89 to 5.21) and severe heavy metal accumulation, with cadmium, lead, and chromium exceeding threshold and probable effect levels , particularly at Tombia and Bakana. Microbiological analyses showed that total heterotrophic bacteria dominated water samples, reaching peak concentrations of 1.10 × 105 cfu/ml at Bukuma. The Weighted Arithmetic Water Quality Index yielded values ranging from 948 to 1,464, classifying the river water entirely as unsuitable for drinking purposes. Irrigation indices (SAR, Na%, and PI) indicated high sodium and salinity hazards, restricting agricultural utilization. Human health risk assessments demonstrated that cumulative Hazard Index values exceeded safe thresholds (HI > 1), with severe non-carcinogenic and carcinogenic risks driven primarily by localized arsenic spikes at Tombia, where adult oral Hazard Quotients reached 11,065.07. Monte Carlo simulations confirmed that pediatric cohorts face heightened susceptibility to toxic exposure. The study underscores the urgent need for stringent industrial effluent regulation, continuous environmental monitoring, and remediation strategies to safeguard aquatic ecosystems and public health in the region.

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