Bacterial Contaminants and Heavy Metal Accumulating Potentials of Fin-Fishes (Synodontis obesus and Marcusenius senegalensis) from Humic Freshwater

Abstract

The bacterial contaminants and heavy metal accumulating potentials of fin-fishes (Synodontis obesus and Marcusenius senegalensis) from the humic ecosystem of Eniong River, Akwa Ibom State were investigated. The results obtained revealed that the bacterial loads varied with the type of fin-fish and were much higher in fish intestines, when compared with the skin and gills. The heterotrophic bacterial loads obtained exceeded the 1.2 x 105cfu/g limit recommended for fresh fishes. High and unsafe fecal coliform (1.1 ± 0.1 x 103cfu/g -2.0 +0.39x 103cfu/g) loads were also obtained. Heavy metal analysis also revealed the presence of Cd, Cr, Cu, Ni and Pb in the humic sediment. Concentrations of Cd (4.71 ± 0.34 to 4.91± 0.39 mg/kg), Cr (18.06 ± 5.78 to 20.22 ± 1.11 mg/kg), Cu (35.33 ± 3.25 to 40.28 ± 2.44 mg/kg), Ni (2.16 ± 0.07 to  2.26 ± 0.18 mg/kg) and Pb (175.85 ± 7.75 to 191. 08 ± 20.11 mg/kg) were found in the order Pb>Cu>Cr>Cd>Ni. Sequential extraction method (SEM) of analysis revealed the poor bioavailability status of heavy metals in sediment. It also showed that the percentage of bio-available and non-bio-available fractions of metals in sediment varied with the type of metals. Cu with 62.04% availability rate was the most bio-available element, as against Pb with 25.22% availability rate. These correspond to their 32.4% and 65.2 % residual potency rates. The calculated Biota to Sediment Accumulating Factor values for heavy metals in the fin-fishes revealed varied levels of accumulation in fishes. Cu (3.73±1.39 mg/kg) in Synodontis obesus was the most accumulated. However, analysis of the bio-accumulation factors (BCF values) revealed generally low accumulation determined by fish type as well as the metal fractions and bio-available status. The results indicate the poor microbiological quality and poor potential of the fin-fishes as sentinel organism for metals contamination monitoring. These call for proper processing of aquatic foods  as well as routine monitoring (but with alternative sentinels) to arrest the growing influence of anthropogenic activities on the level of heavy metals in Eniong River.