Impact of Abattoir and Saw-Mill Effluents on Water Quality of Upper Ogun River (Abeokuta)

Problem statement: The unregulated discharge of contaminants from point sources into inland freshwater aquatic systems and the resultant deterioration of water quality are largely undocumented in developing countries like Nigeria especially with respect to the role of seasonal factors on the recovery capacity of aquatic systems. Approach: The aim of this study was to assess the impact of abattoir and saw-mill industry effluents on the physicochemical properties of Upper Ogun River (Abeokuta) Nigeria. Bi-monthly sampling was carried out using three sampling points upstream and downstream of the point source of discharge over a period of six months (wet and dry season). Water samples were analyzed using standard procedures. The parameters determined were: Temperature, pH, Electrical Conductivity (EC), Total Solids (TS), Total Suspended Solids (TSS), Total Dissolved Solids, Phosphate (PO₄^3-), Nitrate (NO₃^-), Chloride (Cl^-), Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). Results: The mean values of Temperature, BOD, COD, TS, TDS, TSS, PO₄^3-, NO₃^-, Cl^- were significantly higher (p<0.05) during the dry season compared to the wet season. It was also observed that the DO values were higher during the wet season compared to the dry season. Recovery studies as a measure of the self-purification capacity of Upper Ogun River to the abattoir and saw-mill effluents being received showed that Chloride recorded the highest recovery value downstream from the point discharge. All the parameters studied except Temperature, pH and Chloride exceeded the water quality standards for fisheries and aquatic life specified by the National Environmental Standards and Regulations Enforcement Agency (NESREA) and the World Health Organization (WHO) maximum permissible standards for drinking water. Conclusion/Recommendations: The recovery capacity of river Ogun shows a strong dependence on seasonal changes. The elevated values of the physicochemical parameters are of concern with regards to the possible effects on sustainable fisheries in this river, if such pollution trends remain unchanged. It is therefore imperative that compliance of industries to standards and regulations on the use of the environment should be enforced.