Assessment of the Bioaccumulation and the Excretion Rate of Cd, Zn and Pb in Blood, Kidney and Liver of an African Catfish Juvenile in an Artificial Fish Pond

The bio-accumulation and the rate of excretion of Cd, Zn and Pb of a ten weeks old catfish juvenile placed in an artificially polluted aquatic medium for 96 hours and then transferred to an unpolluted medium were examined. The nitrate form of lead, Pb (NO3) 2, the chloride form of cadmium, (CdCl2) and the sulphate form of zinc (ZnSO4.7H20) was chosen because of its moderate toxicity. The Arithmetic method was used to determine the 96 LC50, three different concentrations of the test solution of (10 ppm, 5 ppm and 2 ppm of lead, 8 ppm, 5 ppm and 2 ppm of cadmium and 8 ppm, 5 ppm and 2 ppm of zinc) of heavy metals were prepared. The highest concentration in each case was 20 below the LC50, previously determined. This sub lethal concentration was used to ensure the survival of more than 50 of the fish. Each concentration as well as the control was prepared in triplicate. The Cappon, (1987) method was used for digesting fish organs and thus, metal concentration in the various organs and tissues were determined using Atomic Absorption Spectrophotometer. Results from analysis reveal that Catfish fish samples exposed to different concentrations of the metal solution in their artificial habitat to assess the level of bioaccumulation witnessed the death of the species and it was observed that the mortality rate do not only depend on the concentration of the toxicant, but also depend on the type of the toxicant and period of exposure. The study further reveals that the different toxicants were differentially bio-accumulated in species organs. Pb was more bio-accumulated than cadmium and zinc. Also, some bio-accumulated toxicants were excreted over a period of time. Lead had a higher rate of excretion than the other two heavy metals investigated, namely cadmium and zinc. While the initial rate of excretion is proportional to the concentration of the toxicant, rate of excretion gradually became insignificant after an appreciable period of time. It can thus be concluded that the determination of bioaccumulation can be used to monitor the health of aquatic environment as the degree of contamination was observed to be directly proportional to bioaccumulation. Results obtained from this work also indicated that if fish exposed to contaminated environment are able to migrate to safe unpolluted environment, they can, over a period of time naturally eliminate significant amount of ingested toxicants such as heavy metals. Though, the significance of this study lies in the fact that there is need to protect the environment so that sensitive aquatic organisms, such as catfish juvenile, can be protected from danger. Fish juvenile is obviously more sensitive to toxic environment than adult fish. Protection of the environment will not only safeguard the health of man as continuous consumption of contaminated fish is detrimental to human health, but will increase the quantity of fish available for consumption. It is thus, recommended that further studies or investigation could be carried out using fingerlings and adult catfish. Other heavy metals could be also considered in such investigation.