Ecotoxicological effects of downstream wastewater samples on Cloeon perkinsi larvae, Rana temporaria tadpoles and Clarias gariepinus frys and fingerlings

Abstract

Indiscriminate dumping of refuse and direct defaecation into surface water bodies alter physico-chemical qualities of the water and adversely affect the existence of certain fauna. Downstream water samples were collected from five streams (Irefin, Gege, Gbagi, Odinjo and Omi Adio) receiving domestic wastes in Ibadan and a control stream within the University of Ibadan, Oyo state, Nigeria. Physico-chemical qualities of the downstream water were analysed using standard methods.  Acute toxicity of contaminated water was investigated on some fauna. The 48-hour-LC50 of stream samples was determined for Cloeon perkinsi (mayfly) larvae (CP); while 96-hour-LC50 for Rana temporaria tadpoles, Clarias gariepinus frys (CG1) and fingerlings (CG2) were determined using Probit method. Zero dissolved oxygen values were recorded for Irefin and Gege while 1.07 mg/L was recorded for Odinjo and these were lower than permissible limit for aquatic life. The values of biochemical oxygen demand (43.34 – 160.66 mg/L), chemical oxygen demand (136 – 487.10 mg/L) and phosphate (81.63 – 1877.60 mg/L) recorded for all the samples were significantly higher (P<0.05) than the control sample and were higher than limits set by National Environmental Standards and Regulatory Enforcement Agency (NESREA). The 48-hour-LC50 of contaminated stream water to CP (Irefin, 12.67%; Gege, 8.63%), and 96-hour-LC50 to CG1 (Gege, 0.79%; Gbagi, 2.75%) and CG2 (Gege, 3.33%; Irefin, 5.64%) indicated high toxicity of the sites. High toxicity of the study sites revealed that the streams were polluted in Ibadan. Therefore, there is need for adequate management and disposal of solid wastes to prevent further environmental contamination.