Preliminary assessment of heavy metal pollution of Opa reservoir, Ile- Ife, southwest Nigeria using Mormyrus rume and Tilapia zillii

Abstract

In this study, the concentrations of five selected heavy metals: Lead (Pb), Nickel (Ni), Mercury (Hg), Cadmium (Cd) and Selenium(Se) were determined in water and tissues of two fish species from Opa reservoir in Obafemi Awolowo University (OAU), Ile-Ife, Nigeria, with a view to assessing its pollution level. Water samples from the reservoir, and the liver, gills and fillet of six specimens of Tilapia zillii (Gervais, 1848) and six specimens of Momyrus rume (Curvier and Valenciennes, 1846) were analyzed using Flame Atomic Absorption Spectrophotometer (FAAS) for the selected metals. The mass order of the metals in the samples was:
Pb>Ni>Se³Cd>Hg for water and Ni>Pb>Se>Cd³ Hg for the fillet of both T. zillii and M. rume fillet. Ni concentration ranges in T. zillii fillet and M. rume fillet were as follows 2.60-3.00 μg/g and 2.20-2.80 μg/g, with the mean concentrations of 2.77±0.151 μg/g and 2.57±0.23. Se ranged in T. zillii fillet between 0.80 and 1.20 μg/g with mean concentration of 0.97±0.061 μg/g and in M. rume fillet, it ranged between 0.60 and 0.80 μg/g with mean concentration of 0.73±0.103 μg/g respectively. The two metals (Ni and Se) were higher in T. zillii fillet at 95% confidence interval than M. rume. Nickel and Cadmium were significantly higher at 95% level in T. zillii gill than M.rume gill. Ni in T. zillii gill ranged from 2.28-3.20 μg/g with mean concentration of 3.20±0.360 μg/g while Cd ranged from 0.60-0.80 μg/g with mean concentration of 0.73±0.103 μg/g. The concentrations of Pb, Ni and Hg in Opa reservoir water were higher than the permissible  levels for EPA, 2002; WHO, 1983; WPCL, 2004 and SON, 2007 while nickel was much higher in the fillet than the FAO, 1976 and FAO 1983 recommended limits of heavy metals in fish food. The study concluded that the Opa reservoir was heavy metal polluted.

Keywords: Opa Reservoir, Heavy Metals, Mormyrus rume and Tilapia zillii