Heavy metals load in tilapia species: a case study of Jakara river and Kusalla dam, Kano state, Nigeria

Abstract

Between August and September 2009, twenty four (24) Tilapia species, twelve (12) from each site were sampled from Jakara River and Kusalla dam in Kano, Nigeria with the view to determine the level of some heavy metals in the muscles of the fishes so as to assess their safety or otherwise for human consumption. The weight of each of the samples was determined using Gallenkamp weighing balance and recorded to the nearest grams. The fishes were dissected to separate the muscles from head, viscera and bones. Five grams of the muscle from each sample was digested using concentrated nitric acid and hydrogen peroxide solutions prepared in the ratio of 1:1. The digested samples were aspirated using 210 VGP Atomic Absorption Spectrophotometer from which copper, zinc and lead were determined. The fish samples analysed from Jakara River had the mean copper, zinc and lead concentrations of 0.46+0.14mg/kg, 15.83+5.05 mg/kg and 0.57+0.20mg/kg and those from Kusalla dam had the means of 0.38+0.31mg/kg, 12.04+2.99 mg/kg and 0.54+0.29mg/kg respectively. Comparison of the above means with FAO standards for Cu (30mg/kg), Zn (30mg/kg) and Pb (0.50mg/kg) revealed that the mean concentrations of copper and zinc are safe for human consumption. However, the mean lead concentration exceeded the limit prescribed for human consumption. This suggests the possible adverse health effect such as damage to the gastrointestinal tract and chronic damage to the Central Nervous System among others that the people consuming Tilapia species from both study sites could be exposed to. It was recommended that considerable attention be paid to the lead content in fresh water fish at both sites by appropriate authorities due to its possible health implication on the consumers. Furthermore, continuous monitoring of heavy metals load in fish will be needed in Jakara River and Kusalla dam. Similarly, measures should be put in place to control the inflow of raw effluent into the river as they are largely the possible sources of these metals.