RADIONUCLIDES AND TRACE METALS LEVEL IN SOME BENTHOS: A CASE STUDY OF THE BONNY/NEW CALABAR RIVER ESTUARY.

Abstract

 Representative samples of Oyster (Crassostrea gasar); Mullet (Mugil cephalus); and Crabs (Callinectes amnicola) from the Bonny/New Calabar River Estuary were collected and analyzed for radionuclides and trace metal content using gamma-ray spectrometer and Atomic Absorption spectroscopy respectively. The gamma absorbed dose rates for Crassostrea gasar (oyster) ranged 0.024 to 0.024 nGy/h, Mugil cephalus (mullet) is 0.035 nGy/h and Callinectes amnicola (crab) between 0.061 and 0.062 nGy/h during the wet and dry seasons respectively. The values recorded in the benthos were below the generic screening value (10µGy/h) stipulated by Radiation Protection of the Environment (PROTECT). Results of chemical analysis shows that the concentrations of the metals varied and the ranges were Ca(31.21­ 37.53 mg/kg), Mg(51.11 ­ 55.89 mg/kg), K(28.56­34.37 mg/kg), Zn(0.24­1.28 mg/kg), Pb(0.23­ 0.30 mg/kg), Cd(0.05­ 0.09 mg/kg), Co(0.20­ 0.28 mg/kg), Cr(1.17 ­ 2.62 mg/kg), Cu(0.45­ 4.89 mg/kg), Fe(23.50 ­ 35.75 mg/kg), Ni(0.06­0.25 mg/kg) and Na(5.67­ 76.09 mg/kg). The rank profile of the trace metals in the benthos investigated according to their mean values were Mg>Ca>K>Fe>Na>Cu>Cr>Zn>Pb>Co>Ni>Cd. The observed concentrations of the trace metals in the benthos were considered to be within WHO permissible limit, environmental surveillance of the Estuary is recommended to achieve a contaminant- free benthos.