Ecological risks and bio‐tolerance of Oreochromis niloticus to selected heavy metals in a tropical reservoir.

The concentration of nine heavy metals in Oreochromis niloticus inhabiting Agodi reservoir, Nigeria, was investigated. Samples were collected at the inlet, centre and outlet of the reservoir. The concentration of the metals was determined with Atomic Absorption Spectrophotometer. Ecological Risk Quotient (ERQ) was used to numerically quantify the ecological risks associated with the mineral, while Box Plot was used to evaluate the tolerance of the fish to heavy metals. The ERQ, which was in the order of Mn > Fe > Zn > Cu > Cd > Pb > Cr > Co > Ni, showed that Ni, Co, Cr and Pb had values of less than one, implying that they did not constitute an ecological threat to the environment, while Mn, Fe, Zn, Cu and Cd were of ecological risk. Results revealed that the concentration of Cd, Co and Ni exceeded the bio‐tolerance of the fish at the inlet, while Cd, Pb, Cu and Ni were beyond the tolerability of the fish at the centre. Similarly, the concentration of Co, Cu, Cr, Pb, Zn and Ni was above the tolerance limit of the fish. This showed that Fe and Mn were within the tolerance range of the fish and that the tolerability of the fish in relation to the location was inlet < Centre < Outlet. [ABSTRACT FROM AUTHOR]