Concentrations of some metals in three species of terrestrial molluscs (Achatina fulica, Achatina achatina and Archachatina marginata) in bushes within University of Calabar, Calabar, Nigeria

The study on heavy metals concentrations in three species of terrestrial molluscs (land snails) in University of Calabar, Cross River State was carried out for a period of four months (August to November 2014). Three terrestrial molluscs namely: Achatina fulica, Achatina achatina and Archachatina marginata were used for the study. Snail samples were collected within University of Calabar Farm and along the shores of the Great Kwa River near University of Calabar Staff Quarters. Metals such as: Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn were analyzed after digestion using Graphite Furnace Atomic Absorption Spectrophotometer. Cd and Hg were Below Detectable Level (BDL) in the three species. Mean values of metal concentrations in Achatina fulica were: Co, 0.029±0.020mg/kg; Cr, 0.029±0.020mg/kg; Cu, 0.047±0.008mg/kg; Fe, 0.042±0.001mg/kg; Mn, 0.035±0.005mg/kg; Ni, 0.011±0.023mg/kg; Pb, 0.029±0.058mg/kg and Zn 0.047±0.005mg/kg. Mean values of metal concentrations in Achatina achatina were: Co, 0.030±0.021mg/kg; Cr, 0.028±0.019mg/kg; Cu, 0.043±0.004mg/kg; Fe, 0.043±0.002mg/kg; Mn 0.035±0.005mg/kg; Ni, 0.014±0.028mg/kg; Pb, 0.027±0.055mg/kg and Zn 0.043±0.012mg/kg. Mean metal concentrations in Archachatina marginata were: Co, 0.019±0.022mg/kg; Cr, 0.016±0.019mg/kg; Cu, 0.037±0.005mg/kg; Fe, 0.043±0.009mg/kg; Mn, 0.040±0.006mg/kg; Ni, 0.125±0.250mg/kg; Pb, 0.058±0.067mg/kg and Zn 0.046±0.012mg/kg. The concentrations of the metals did not vary statistically (p > 0.05) in the three species of molluscs, therefore were not statistically significant. Total rank score assessment showed that Archachatina marginata had the highest level of metals followed by Achatina fulica while Achatina achatina had the least concentrations, although the concentrations of metals in the three species were within the tolerance limits set out by WHO. Therefore consumption of snails picked within University of Calabar farm and along the shores of the Great Kwa River near University of Calabar Staff Quarters is recommended though continuous monitoring of these metals is necessary since metals can bio-accumulate in biological tissues over a period of time.