Impact of Industrial Effluents on River Owo, South West Nigeria

Characterisation of the industrial effluents from Agbara Industrial Estate showed the effluents to be varied and complex. Most analysed effluent parameters were above the permissible level of national effluent discharge in Nigeria. Twenty six macroinvertebrate families were identified from River Owo, none of which were found at the effluent outfall.The four families found at the effluent outfall were Tubifex tubifex, Nepa, Erisstalis and Chironomous species. They were the major exploiters of the Industrial Effluents and thus serve as possible pollution indicator organisms. The macroinvertebrate fauna in River Owo were dominated by insects(74.57%), and they were more abundant in the Rainy season compared with the Dry season. All the heavy metals found in the effluents were also found in the River and sediment. Under laboratory exposures,Tilapia zilli accumulated in its tissues 10 times the level in the medium of exposure. Growth of the fish was also retarded by effluents. Growth retardation and metal accumulation were found to be a function of the period of exposure and concentration in the media.