Comparative assessment of heavy metal levels in crabs, periwinkles and oysters obtained from Eyaa Creek, Upper Bonny Estuary, Onne, Nigeria

Abstract

This study examined heavy metals in some aquatic organisms [crabs (Callinectes amnicola), periwinkles (Tympanotonus fuscatus) and  oysters (Crassostrea gasar)] from Eyaa Creek, Onne, in southern Nigeria. Samples were collected from four stations monthly for three  months. Characterization of the environment was via physico-chemical properties, while heavy metal analysis was by Atomic Absorption Spectrometry. Physico-chemistry results indicated: temperature; 30.2 – 30.7^oC; pH: 6.7 – 6.8; dissolved oxygen: 6.1 – 6.3 mg/l; electrical  conductivity: 18.8 – 20. 8 mS/cm; total dissolved solids: 4698.5 – 6212.0 mg/l; salinity: 11.1 - 12.4 PSU and turbidity: 3.7 - 4.7 NTU. ANOVA  showed insignificant difference (p>0.05) between stations indicating homogeneity of the area assessed. Mean metal concentrations (mg/ kg) in the organisms were cadmium: 0.18 ± 0.09 - 0.60 ± 0.08; chromium: 0.41 ± 0.14 – 0.78 ± 0.08; iron: 12.1 ± 6.9 - 20.2 ± 7.7; lead: 0.31 ±  0.2 – 0.91 ± 0.05. Chromium and lead values were above permissible values of FAO/WHO and EU but cadmium fell within and above the  limits. Principal component analysis did not show a clear pattern with organisms’ feeding habit but discriminated based on metal  concentrations. In conclusion metal concentration in periwinkles>crabs>oysters which was related to their feeding habits in terms of  sediment and pelagic affiliations.