EVALUATION OF THE EFFECTS OF HEAVY METALS IN ANAMBRA RIVER
The distribution and occurrence of heavy metals in water column of the Anambra River were investigated in the dry season adopting standard chemical methods. Following the establishment of the presence and appreciable concentration of heavy metals in various stations (P<0.05) in the water column, biological effects of two heavy metals (copper and zinc) were investigated in laboratory bioassays against prevalent fish species of the river (Oreochromis niloticus and Clarias gariepinus) based on the toxicity scale of 96hLC50 to evaluate possible risk effect of the metals on the aquatic species and human population depending on the river. Toxicity ranking for zinc and copper in the water revealed copper to be consistently more toxic to the test species with Oreochromis niloticus being more sensitive. The binary mixtures in predetermined ratios (1:1 and 1:2) of zinc and copper acting against the test animals showed significant departures when compared to levels of toxicity attained by the individual constituent metals when acting alone against the same species. In a majority of cases, the resultant interactions (Zn-Cu against fish species) were in conformity to the model of synergism while fewer instances portrayed antagonism and additive action. There is high risk of heavy metal poisoning among the human population depending on the river and heavy metal related public health effects observed in a survey are circumstantial evidence. The work recommends setting more realistic and effective safe limits and standards to minimize and properly manage heavy metal polluted water bodies.