Assessment of some heavy metals in the tissues(gills,liver and muscle)of Clarias gariepinus from Calabar River,Cross River State,South-eastern Nigeria

Objective:To assess the pollution status of Calabar River in relation to the levels of heavy metal in the tissue of the African catfish[Clarias gariepinus(C.gariepinus)].Methods:A total of 45 samples of C.gariepinus were purchased from fishermen on landing at Nsidung beach along Calabar River within three months(15 samples monthly)from June to August,2014.The samples were then put into a cold box containing ice blocks immediately after buying from the fishermen.The fish samples were transported immediately to the Chemistry Laboratory,University of Calabar for digestion and heavy metal analysis.Portions of the muscle,gills and liver were removed from the fresh samples and oven dried at temperature of 120°C to constant weight and digested using standard methods.The digested tissue portions were analyzed for lead,iron,manganese,cobalt,chromium and cadmium concentrations using atomic absorption spectrophotometer.Results:Mercury was not detected at all in the muscle,liver and gills of C.gariepinus.The mean±SD of metals in liver of C.gariepinus were:(0.080±0.014),(0.110±0.014),(6.480±1.279)and(0.295±0.021)mg/kg for Cd,Cr,Fe and Mn,respectively.In the gills,heavy metals values were:(0.065±0.021),(0.115±0.035),(5.843±0.558),and(0.345±0.007)mg/kg for Cd,Cr,Fe and Mn,respectively.In the muscles,heavy metals values were(0.045±0.021),(0.115±0.353),(5.150±1.075),and(0.187±0.045)mg/kg for Cd,Cr,Fe and Mn,respectively.The general trend of metals accumulation in tissues of C.gariepinus showed a decreasing trend of Fe>Mn>Cr>Cd.Also,the metal accumulation in the three tissues showed a decreasing trend of liver>gills>muscle.Conclusions:The metal concentrations in the muscle,gills and liver of C.gariepinus were all below the World Health Organization acceptable range,and as such fishery resources from Calabar River are safe for consumption.