Analysis of Pharmaceutical Effluent Discharge and Its Impact on Receiving Stream Water Quality in Ogun State

The pharmaceutical manufacturing cluster in Sagamu, Ogun State, South West Nigeria, is one of the most concentrated industrial zones in sub-Saharan Africa, and its effluent discharge practices have received insufficient scientific scrutiny. This study analyses the physicochemical and microbiological quality of effluent discharged from three pharmaceutical manufacturing facilities in Sagamu and evaluates its impact on the quality of the receiving Ogun River tributary at upstream, discharge, and downstream points. Effluent and river water samples were collected monthly over six months and analysed for pH, biochemical oxygen demand, chemical oxygen demand, total suspended solids, dissolved oxygen, conductivity, ammonia-nitrogen, phosphate, coliforms, and selected active pharmaceutical ingredients using liquid chromatography-mass spectrometry. All three facilities discharged effluent with biochemical and chemical oxygen demand values exceeding NESREA effluent discharge standards. Dissolved oxygen in the receiving stream declined from 7.4 mg/L at the upstream reference point to 2.3 mg/L at 200 metres downstream of the discharge point. Amoxicillin and metronidazole were detected at downstream sampling stations at trace concentrations. The study provides documented evidence of pharmaceutical pollution in a surface water body serving downstream agricultural communities and recommends mandatory tertiary treatment and real-time effluent monitoring for pharmaceutical facilities in Ogun State. Keywords: pharmaceutical effluent, active pharmaceutical ingredients, Ogun State, dissolved oxygen, water quality