Abstract
In this study, the concentrations of selected heavy metals including Cr, Co, Cu, Cd, and Pb were determined in gills, livers, and muscles of two fish species: Orochromis niloticus and Labeoberbus infermedius. The fish samples were collected from Gilgel Gibe I hydroelectric dam reservoir in may 2017. Prior to their quantitative determinations by flame atomic absorption spectroscopy, tissue samples were digested by a microwave digestion. Except, Cr (in gills) and Cd (in muscles), the target metals were detected in the gills, livers and muscles of both fish species and showed varied distributions among the tissues. But, the two species were nearly exhibited similar accumulation orders for the studied heavy metals. The order of concentrations of the metals in gill, liver and muscle of Labeoberbus infermedius were: Cu > Pb > Co > Cd; Cr > Cu > Pb > Co > Cd; and Cr > Pb > Cu > Co, respectively and while, in gill, liver and muscle of Orochromis niloticus were: Cu > Co > Pb > Cd; Cr > Cu > Co > Pb > Cd; and Cr > Pb > Cu > Co, respectively. The highest concentrations of Cr and Co were determined in livers; Cd was detected in the gills of both species; Cu was obtained in the liver of Labeoberbus infermedius and in the gill of Orochromis niloticus. Significant differences were observed among the mean concentrations of the metals in the fish tissues (p < 0.05). The concentrations Cr, Co, and Pb were higher than the maximum permissible limits recommended by FAO/WHO and EU. The concentration of Cu was below the maximum permissible limit of FAO/WHO, but above that of EU.Keywords: Gilgel Gibe I hydroelectric Dam; Orochromis niloticusor; Labeoberbus infermedius; Heavy metals
Highlights
Contamination of aquatic systems with heavy metals is the pressing worldwide problem, because of their toxicity, persistency and ability of bioaccumulation (Zeitoun and Mehana, 2014)
Two fish species are known in the dam: Nile Tilapia (Orochromis niloticusor) and
Except Cr and Cd, all the target heavy metals were detected in the gills, livers and muscles of L. infermedius and O. niloticus
Summary
Contamination of aquatic systems with heavy metals is the pressing worldwide problem, because of their toxicity, persistency and ability of bioaccumulation (Zeitoun and Mehana, 2014). Heavy metals are naturally trace components of aquatic systems, their concentration levels may be raised due to natural processes like geological weathering of rocks and soils and/or anthropogenic activities such as chemical damping, application of agrochemicals (fertilizers and certain pesticides), traffic, mining, burning of fossil fuels and industrial activities (Tüzen, 2003; Ali et al, 2011) Once they entered the water system heavy metals may precipitate, adsorbed onto the solid surfaces, remain soluble, suspended in water or may be taken up by fauna (e.g., fish) and eventually accumulate in aquatic organisms that are consumed by human beings (Lopz et al, 2003; Botson et al, 2004). The dam reservoir is surrounded by intensified small scale agricultural farm lands and receives domestic effluent wastes from the two nearby towns: Asandabo and Deneba
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