Concentration of Selected Heavy Metals in Water and the Cummulative Effect on Selected Organs of Oreochromis Niloticus and Clarias Gariepinus from Lake Victoria, Kenya

摘要

The presence of heavy metals in aquatic ecosystems has been of great concern because of their toxicity to man when their concentrations are more than the permissible levels. These metals enter the environment through different ways such as industrial activities. The objectives of the study were; to determine the concentrations of selected heavy metals (Cu, Cd and Zn) in water samples collected from three different study sites at the shores of Lake Victoria, Kenya, to determine the concentrations of the selected heavy metals in selected organs (muscles, liver, kidney, gills and intestines) of two fish species (O. niloticus and C. gariepinus) from the shores of Lake Victoria, and to determine whether there are significant differences in the levels of heavy metals among the selected organs of fish and the water from the Lake. Water samples were collected from the three sites (Kisat sewage discharge point, Molasses factory discharge point, and Coca-Cola factory discharge point) at approximately 0.2 m below the water surface using half-litre plastic (PVC) bottles. Five replicate samples were taken from each site. Immediately after sampling the samples were acidified with concentrated nitric acid then samples were stored in a cool box and transported to the laboratory for further processing. Fish samples were collected from the three sites using an electro-fisher, washed with deionized water, sorted by species, packed in polythene bags and transported to the laboratory in a cool box for further processing. The tissues of the organs were analyzed quantitatively using Atomic Absorption Spectrophotometer. Samples of fish organs were homogenized and diluted with distilled water before analysis. Single classification and three-way factorial ANOVA were used for statistical analyses. Statistical significance was declared at a =0.05. The findings of the present study revealed that the concentrations of heavy metals in water were not significantly different (P≤0.05) among sites. Cadmium ranged from 0.029-0.045 μg/L, Copper between 0.036-0.042 μg/L while zinc ranged between 0.039-0.113 μg/L. The concentrations of heavy metals were significantly higher in fish organs than in water, similarly, concentrations of heavy metals differed significantly (P≤0.05) between species. The concentrations of heavy metals differed significantly among metal types and also among fish organs. In conclusion, all the tested organs of fish species caught in Lake Victoria were contaminated with heavy metals. The two fish species demonstrated different capacities to accumulate heavy metals. Similarly, different organs offish demonstrated different capacities to accumulate heavy metals. There was a high prevalence of metal accumulation in different organs. Consumption of fish from industrial discharge points should be discouraged as it might contain high concentrations of heavy metals.