Distribution of heavy metals in fish organs, associated water and sediment from Ero Dam, Ekiti State, Nigeria

Abstract

An investigation into the distribution of lead, manganese, copper, zinc, mercury, iron, chromium and cadmium in the sediment, water and the organs of Oreochromis niloticus, Tilapia zillii, African catfish (Clarias gariepinus) and Citharinus citerus obtained from Ero Dam in Ikun-Ekiti, Ekiti State, Nigeria was undertaken. This was done to ascertain the presence of these metals in the three matrixes and to determine the bioaccumulation factors of these metals in the organs of these fishes. The three matrixes were differently digested and analysed for heavy metals using Atomic Absorption Spectrophotometer (Buck 200). Hg was determined via cold vapour generation. The levels of the metals in water were very much lower than their corresponding concentrations in the sediment. In the same vein, concentrations of the metals in the fish organs were higher than those recorded for the water except Cu and Mn that showed slight variations. The most concentrated metal in the organs of the four fish species was Zn which recorded concentrations (mg/kg) ranging from 7.36±0.03 in the head of Clarias gariepinus to 8.12±0.13 in that of Citharinus citerus. In Clarias gariepinus, Cr, Cd and Hg were only detected in its gills. On the contrary, all the metals were detected in the organs of Oreochromis niloticus and Tilapia zillii. Zn, Mn and Fe were the three most abundant metals in the organs of these fishes. The highly toxic metals (Pb, Cd and Hg) in this determination were either not detected or detected at low levels. It is obvious from this work that Zn was bioaccumulated most in the organs of each fish. It is certain that heavy metals are present in Ero dam but in low concentrations. This calls for constant monitoring because as industries are established in Ekiti State, Nigeria, the level of heavy metals in this dam may increase.

Keywords: Oreochromis niloticus, Tilapia zillii, Citharinus citerus