POLLUTION LOAD AND ECOLOGICAL RISK OF HEAVY METALS IN ABATTOIR WASTEWATER AND THE RECEIVING STREAM

ABSTRACT Abattoir wastewater contains numerous hazardous pollutants that may have severe effect on human health. Heavy metal is a term used to describe the metallic element with high atomic elements greater than 5g/cm3. They are often found in wastewaters especially those that uses petroleum products such as abattoir. Discharge of wastewater containing pollutant such as heavy metal will affect receiving water body and render it unfit for specific use; this research is therefore aimed to assess level of heavy metal contamination in Ogbomosho entral battoir and its receiving stream. Wastewater samples were collected from the abattoir waste discharge path in plastic bottles; other samples were collected at upstream, downstream and at the point of entering into the river. Collected samples were prepared and analyzed for physicochemical parameters including; total dissolved solid, dissolved oxygen, biochemical oxygen demand, total hardness, and electrical conductivity following standard procedures. Raw water samples were digested using concentrated nitric acid and the levels of the heavy metals were analyzed using inductively coupled plasma optical emission spectroscopy (ICP-OES). Physicochemical parameters of wastewater gave mean values of 6.6, 0.01 ms/cm, 129 mg/L, 143 mg/L, 1.63 mg/L, 440 mg/L and 2100 mg/L for pH, EC, BOD, total hardness, DO, Alkalinity and TDS respectively. The surface water had range of 6.5-7.3, 0.01- 0.02, 106-119, 101-122, 1.84-8.7, 1.9-20 and 1800-1950 for pH, EC, BOD, total hardness, DO, Alkalinity and TDS respectively, this values indicate high strength of the wastewater in polluting the adjoining streams. Heavy metal was present in all water samples; wastewater contained highest heavy metals with mean values of 0.138, 0.005, 0.038, 0.507, 4.00, 0.886, 0.312, and 0.155mg/L for Pb, Cd, As, Zn, Fe Mn, U and Cu respectively. Concentrations at the discharge point are 0.0548, 0.283, 1.009, 0.175, 0.103, and 0.097mg/L for Pb, Zn, Fe, Mn, U and Cu respectively while others are below detection limit. The mean concentrations of upstream are, 0.065, 0.213, 1.098, 0.099, 0.063, and 0.147mg/L respectively for Pb, Zn, Fe, Mn, U and Cu while others are below detection. The mean concentrations of downstream are, 0.009, 0.239, 1.683, 0.179, 0.089, and 0.194mg/L respectively for Pb, Zn, Fe, Mn, U and Cu while others are below detection limits. The research concluded that the new Ogbomoso Abattoir wastewater is polluted with heavy metals and it has effects on the receiving stream as the wastewater and receiving stream had overall poor quality, it is hence recommended that alternatives be sought in meat processing and wastewater should be treated before discharge into the environm