Comparative assessment of some heavy metals in some inland fresh water fish species from River Niger and River Osara in North Central Nigeria

Abstract

The concentration levels of Cadmium(Cd), Manganese(Mn), Chromium(Cr), Nickel(Ni), Copper(Cu), Zinc(Zn) and Lead(Pb) were determined in fish fillets of some inland fresh water fish harvested from River Niger at Ajaokuta and River Osara at Itakpe North Central Nigeria. Eighty samples each of Tilapia zillii, Oreochromis niloticus, Sarotherodon galileaus and Clarias anguillaris were collected from both rivers and digested using standard methods. The metals were determined using Unicam 969 Flame Atomic Absorption Spectrophotometer fitted with deuterium lamp. The levels of heavy metals detected in the fish fillets of the different species varies with mean concentrations (mg/kg) in the range: Mn, 3.14±1.12- 5.77±0.95 in Sarotherodon galileaus-5.30±1.48-10.48±2.57 in Tilapia zillii; Zn, 1.06±0.84- 5.67±1.42 in Oreochromis niloticus-2.08±1.13-4.21±1.80 in Clarias anguillaris; Cu, 1.54±0.65-3.30±0.79 in Tilapia zillii-3.00±1.07-6.23±1.79 in Sarotherodon galileaus; Cr, 1.49±0.71-3.16±0.65 in Tilapia zillii-2.44±0.61-4.60±2.24 in Clarias anguillaris; Ni, 0.76±0.13-1.56±0.52 in Tilapia zillii-1.74±0.95-3.25±1.19 in Clarias anguillaris; Pb, 0.02±0.03-0.02±0.01 in Tilapia zillii-0.51±0.09-0.83±0.09 in Oreochromis niloticus, and Cd, 0.02±0.01-0.04±0.01 in Tilapia zillii-0.14±0.04-0.18±0.04 in Oreochromis niloticus. The differences in heavy metal levels in the different fish species examined were not significant (p>0.05), except for Mn in Tilapia zillii which was significantly higher (p<0.05) than in other species. This is probably because each fish species concentrated the heavy metals differently. Clarias anguillaris fillets appeared to hold the metals more except for Zn, followed by Oreochromis niloticus, Sarotherodon galileaus, and Tilapia zillii in that order. The detected levels were however below the WHO/FAO guideline limit in food substances, fish and fishery products. The study showed that there were differences in concentrations of Cd, Mn, Cr, Ni, Cu, Zn and Pb in fillets of Tilapia zillii, Oreochromis niloticus, Sarotherodon galilaeus and Clarias anguillaris, implying that the fishes concentrated the heavy metals differently. The levels of heavy metals detected in all the fish species were within the natural background levels.