Comparative Acute Toxicity Assessment of Industrial Effluents from Benin City, Nigeria Using the African Catfish (Clarias gariepinus)

This study investigated effluents from three industrial facilities (alcoholic, non-alcoholic, and abattoir) located in Benin City, Nigeria, to ascertain the suitability of the discharges for aquatic life using the African catfish (Clarias gariepinus). The physicochemical properties and heavy metals assessment of the effluents were measured using standard methods, while the acute toxicity assays were done using a static bioassay with continuous aeration for 96 h under laboratory conditions. The results indicate non-conformation with the standards set by national and international regulatory bodies for most of the physicochemical parameters (78.79%), while the levels of the heavy metals were majorly (76.67%) below the permissible limits. The alcoholic industrial effluent recorded the highest mortality with a 96-h LC50 of 8.71 mg/L despite having better effluent quality. The observed mortality showed alcoholic (60%) > non-alcoholic (42.50%) > abattoir (41.25%) effluents, whereas the effluent quality assessment result showed alcoholic > non-alcoholic > abattoir effluents. The dissolved oxygen levels and the overall effect of the complex mix of pollutants in the effluents may have exerted a considerable contribution to their toxicity to the fish. Hence, toxicity assays should be carried out complementarily to physicochemical and microbiological evaluations in effluents before discharge into water bodies.