Water soluble fractions of crude oil deteriorates water quality parameters and alters histopathological components of juvenile Clarias gariepinus
In this study, the water quality changes after the introduction of water soluble fractions of crude oil were monitored along-side the accompanying effects on histopathological changes in selected organs of juvenile Clarias gariepinus. After a preliminary short-term (96 hours) static toxicity tests, fish were exposed to four sub-lethal concentrations (30, 45, 60 and 75 % of the LC50 corresponding to 67, 101, 135 and 169 mg/l respectively) and a control group containing clean water using a semi-static renewal method for 90 days. Water quality parameters, heavy metals and total petroleum hydrocarbon (TPH) were determined using standard methods. After the exposure period, liver, brain and gill were harvested, labeled and prepared for photomicrography. Chloride, conductivity, salinity, magnesium, biochemical oxygen demand, chemical oxygen demand, total dissolve solids, turbidity and nitrate levels increased significantly (p<0.05) with increasing concentration of water soluble fractions (WSF) of the crude oil. Temperature readings and phosphate levels were however not affected (p>0.05). Values of TPH increased (p<0.05) with increasing concentrations of the crude oil. All analysed heavy metals followed a direct proportional trend as their values increased (p<0.05) alongside concentrations. Several histopathological alterations were found in the liver (sinusoidal congestion, atrophy of hepatocytes, hepatocellular degeneration and diffuse coagulation necrosis of hepatocytes), brain (vascular congestion and atrophy of neurons, neuronal necrosis, gliosis and loss of neurons) and gill (moderate loss of the secondary gill lamellae, moderate lamellae atrophy and moderate diffuse lamellae hyperplasia). The intensity of these lesions increased with increase in exposure dose.
Keywords: Toxicity, Petroleum, Heavy metals, Water quality, Organs, Clarias gariepinus, LC50