ABSTRACT

The toxic effects of spent automobile engine oil on sharp-tooth African catfish (Clarias gariepinus) exposed to 96 hours and sub-lethal (14 days) were carried out after range finding test was conducted. Clarias gariepinus with mean body weight of 12.50 ± 0.5 g and mean standard body length of 10.21 ± 7.25 cm were randomly allotted into plastic aquaria of 45 cm x 28 cm x 28 cm dimension and exposed to five (5) different concentrations of spent engine oil from 5 ml/1 to 20 ml/1 for the lethal concentration and 0.5 ml/1 to 5 ml/1 for the sub-lethal test. The bioassay was designed with 5 treatments and three replicates given fifteen (15) experiment tanks with (10) fish in each group and the spent engine oil was introduced in different concentrations for 96 hours (4 days) and fourteen (14) days. Observation based on lethal and sub-lethal concentrations were made. Varied adjustment pattern and survival mechanism were adopted by the exposed fish, while the fish sample in the control tank exhibited normal activities without stress or adjustment. Mortality and survival adaptations were observed in the 96 hours exposure, while morphological and histopathological changes in selected fish organs for the 14 days sub-lethal exposure. The 96 hours LC50 was estimated to be 24 ml/1, 15.75 ml/1, 9.89 ml/1 for 48 hrs, 73 hrs and 96 hrs respectively. While the LT50 was estimated at 149.4 hrs, 100.7 hrs, 79.7 hrs and 57.7 hrs for 5 ml, 10 ml, 15 ml and 20 ml respectively. The significant changes observed in the fish organs (liver, muscle and gills) showed varying proportion of lesion among the exposed fish. The concentrations of trace elements in fish organs were also investigated and the result showed the presence of Nickel, Iron and Manganese in higher concentrations in the selected fish organs using Atomic Absorption Spectrophotometer. However fish mortality across treatment tanks were attributed to dissolve oxygen depletion in the various test media excluding the control; fish rapid movement to the water surface for air gulping was observed as well as quiescence among the weak fish, suffocation and asphyxiation. Although delayed mortality was observed across tanks with lesser spent oil concentrations, loss of balance, and diverse responses were observed during the bioassay including starvation and rapid movement. Histological examination of the fish liver, muscle and gills revealed obvious damages ranging from haemorrhages, rupture of the epithelial cells and slight necrosis. The mortality and cell damage experienced by the fish exposed to different spent engine oil concentration shows that at sub lethal exposure, spent engine oil has the potential to cause significant harm to aquatic life including accumulation oftrace elements in the fish organs, which could cause significant public health challenges to man when consumed. Proper disposal of such waste is there by encouraged and public awareness is recommended to sensitize the people. Further studies were also recommended to ascertain possible bio-transformation and bio-magnification potentials ofthese trace elements in the food chain.