Assessment of physicochemical and metal characteristics of effluent in Ebonyi State, Nigeria, implications for aquatic ecosystem health and food security
Industrial and domestic effluent discharge contributes significantly to surface and groundwater pollution. Industrialisation in rapidly urbanising regions of Sub-Saharan Africa often impacts the environment, leading to severe aquatic degradation. This study presents a comprehensive physicochemical, metal, and toxicological characterisation of industrial effluents within Abakaliki metropolis, Ebonyi State, Nigeria. Twenty-nine representative samples were collected from strategic discharge points: nine from the Royal Salt processing area, which doubles as a lead-zinc mining region; four each from abattoirs, the building material market area, the Iyiudele River, and municipal drainage canals; and four from control (unpolluted reference) sites. Analysis was conducted for eighteen parameters following the 24th edition of the American Public Health Association (APHA, 2023) Standard Methods and ASTM D3370-18 sampling protocols, including heavy metal speciation by spectrophotometry and atomic absorption spectrometry. Results indicated a critical state of pollution, with several parameters significantly exceeding the World Health Organization (WHO, 2023) and Standards Organisation of Nigeria (SON) permissible limits. Notably, arsenate (As) and lead (Pb) exhibited mean concentrations of 0.07 mg/L and 0.105 mg/L, respectively, representing substantial exceedance of safety thresholds. Organic loading was equally severe, with five-day biochemical oxygen demand (BOD₅) averaging 88.5 mg/L, corresponding to a Contamination Factor (CF, the ratio of the observed mean concentration to the permissible limit) of 2.95, while dissolved oxygen (DO) fell to a hypoxic mean of 1.85 mg/L. Nutrient enrichment was extreme, with total phosphate (5.29 mg/L) exceeding the guideline value more than ten-fold, signalling a high risk of irreversible eutrophication in receiving water bodies such as the Iyiokwu River. One-way analysis of variance (ANOVA, p < 0.05) confirmed significant spatial variation in contaminant plumes, linking the Royal Salt processing zone to metal toxicity and abattoir discharge to organic hypoxia. The study concludes that uncontrolled discharge of untreated effluents poses an immediate threat to the regional “One Health” framework, necessitating urgent bio-remediation strategies such as phytoremediation and low-cost adsorption treatment, alongside stricter enforcement of National Environmental Standards and Regulations Enforcement Agency (NESREA) discharge permits. These findings provide baseline data for future longitudinal studies on the biomagnification of neurotoxic metals within the local food chain.