Abstract:

Heavy metals are toxic to organisms even at low concentrations. In recent times, there has been the high occurrence of cancer cases locally, traceable to heavy metal contaminations of foods consumed by man and animals. The experimental site for this study was Omambala River which serves as a source point of many fresh fishes as well as its distribution throughout the state both in dry and rainy seasons. One hundred (100) samples each of Clarias gariepinus and Heterobranchus longifilis, with the size of 17–21 cm were selected from Omambala River. Heavy metal determination was done using the digestion method. All the digested samples were analyzed three times for heavy metals using SP-V21A Vis Spectrophotometer and the instrument was calibrated with standard solutions. For Risk assessment analyses, the target hazard quotients (THQ) index was applied to assess the potential non-cancer risk associated to consumption of the different species of marine organisms sampled. While the total target hazard quotient (TTHQ) was calculated as the arithmetic sum of each THQ value. The lifetime cancer risk (TR) was calculated by multiplying the daily dose by the cancer slope factor (CSF) derived by response-dose curve for toxicant ingestion. The bioaccumulation factor (BAF) was determined by dividing the metal concentration in the tissue of the organism by the metal concentration in the environment or medium. From the correlation analysis, there was a positive correlation between the four different organs of the fish species and the selected heavy metals. The toxicity of magnesium and zinc are higher in C. gariepinus while the toxicity of iron is higher in H. longifilis. The degree of toxicity is zinc > iron > magnesium > lead > cadmium > copper > mercury > chromium. The water quality index (WQI) for all the heavy metals in four different organs of the two fish species was found to be less than 1 (WQI < 1) meaning low pollution; which further means that the consumption of C. gariepinusand H. longifilis may not pose any health risk to the people of the area. However, there are reports of lifetime cancer risk on daily consumption of Chromium, Cadmium, Lead and Mercury in fish. Chemicals when found in large quantities.