Heavy Metal Concentrations in Tissues of Manila Clams (Venerupis philippinarum) from the Cross River Basin in Itu Local Government Area, Akwa Ibom State, Nigeria

Abstract

Heavy metal contamination of aquatic environments is an important concern because metals can persist, accumulate in aquatic organisms and enter the human diet through seafood consumption. This study assessed the concentrations of cadmium (Cd), iron (Fe), copper (Cu), nickel (Ni), lead (Pb), arsenic (As) and mercury (Hg) in tissues of the Manila clam, Venerupis philippinarum, collected from the Cross River Basin in Itu Local Government Area, Akwa Ibom State, Nigeria. Clam samples were collected from five stations during ebb tide, prepared by drying and grinding the tissue, and analysed using Flame Atomic Absorption Spectrophotometry after wet digestion. The mean concentrations recorded in clam tissues were Cd (0.009 ± 0.002 mg/kg), Fe (1.317 ± 0.069 mg/kg), Cu (0.180 ± 0.018 mg/kg), Ni (0.002 ± 0.003 mg/kg) and Pb (0.001 ± 0.002 mg/kg), while As and Hg were below detectable limits across the sampled stations. The observed concentration pattern was Fe > Cu > Cd > Ni > Pb, with Fe being the most abundant metal and Pb the least abundant. Comparisons with the guideline values presented in the manuscript indicated that Cd, Cu, Ni and Pb were generally below the stated permissible limits, whereas the elevated Fe concentration requires continued attention. The absence of detectable As and Hg, together with the low concentrations of Cd, Ni and Pb, suggests limited heavy metal accumulation in V. philippinarum from the study area at the time of sampling. The findings indicate that Manila clams from the Cross River Basin may be suitable for consumption with respect to most metals assessed, although periodic monitoring remains necessary, particularly for Fe and for possible seasonal changes.