Heavy Metal Concentration of Surface Water, Sediment and Fishes Impacted by Crude Oil Pollution in Bodo/Bonny River, Nigeria

Abstract

Heavy metals can be released into the aquatic environment through storm-water run-off and wastewater discharges and reprocessing from various industrial and anthropogenic activities. They have the potential to be toxic to biota above certain threshold concentrations while sediments in the marine ecosystems act as long-term sinks for many anthropogenic contaminants such as these organic pollutants. This study was therefore aimed at determining the heavy metal contents in the surface water, sediments and fishes from the Bodo/Bonny river. Sampling was done according to standard protocols. Surface water, sediment and fish samples were collected from 5 stations (BBW1, BBW2, BBW3, BBW4 and LFPW5) with LFPW5 serving as control.  Sediment was collected from 0-15 and 15-30 cm. The fish gills, liver, kidney etc. were excised from the rib for heavy metals (Pb, Fe, Zn, Cr, Cd etc) analysis using sterile scalpel. The results of heavy metal in surface water samples show that Zinc had a range of 173.1±10.21 to 179.3±11.01 mg/kg in all sampling locations above the permissible limit of DPR limit of 5 mg/kg for Brackish/ Saline water.  The sediment samples were loamy. The concentrations of trace metals in sediments revealed that Pb had the highest concentration of 48.61mg/kg at 0-15cm depth while Chromium had highest concentration of 41.54mg/kg at 15-30cm depth. Chromium, Cadmium and Copper increased with increase in depth at 15-30cm while Lead, Zinc and Iron took the reverse trend at 0-15cm depth. Heavy metal content of fish samples from the  river water show that the mean concentration values in the fresh fish was in the increasing order of Copper < Cadmium < Nickel < Lead <Iron< Zinc. The data generated from this study showed that there were actually heavy metals accumulations in fish tissues that were above the WHO permissible limits. The increased heavy metals concentration from all sites suggest that fishes that inhabit polluted areas risk bioaccumulation, which go on to affect the overall health of the human population that depend on such rivers for fishing, drinking or irrigation.