Comparative Analysis of Heavy Metal Concentrations in the African River Prawn (Macrobrachium Vollenhovenii) from the River-Nun and Opume River, Niger Delta, Nigeria

Selected heavy metals in the fresh water prawn Macrobrachium vollenhovenii from River-Nun and Opume river was investigated. This was done in order to gauge the amount of heavy metals accumulated in the prawn in order to address safety concerns about the consumption of prawn from those two river systems and establish the health status of the river bodies. Triplicate sub surface water samples were collected from three (3) sampling points from each of the water bodies once monthly for twelve (12) months. Also, prawn samples were collected monthly from three (3) fish landing points in each of the river’s catchment area for 12 months. Prawn samples were identified using standard keys. Water and Prawn samples were analyzed for the heavy metals lead (Pb), Cadmium (Cd), Mercury (Hg), Chromium (Cr) and Zinc (Zn) using standard techniques. Means and standard deviations for all metal characteristics in water and prawn were calculated. Student T-test was also employed to check for variability between river systems in the measured parameters. This was done at the 95% confidence limit (P=0.05). This was aided by the use of the SPSS® statistical tool kit. The Bioaccumulation Factors (BAFs) was determined by dividing the concentration of each heavy metal in the water by the concentration of heavy metals accumulated in the prawn. Result of the heavy metal characteristics of both rivers indicate that River-Nun values are consistently higher than values obtained in Opume river. Except for the metal Hg and Zn, all the heavy metal values obtained for the two water bodies are higher than the recommended permissible value for heavy metals in water. Bioaccumulation factor (BAF) was higher that the threshold value (BAF>1) for all metals. BAF in River-Nun was higher than that that obtained in Opume river. This imply a greater level of pollution in River-Nun. Based on the findings, the study concludes that the consumption of the studied prawn species is contaminated with elevated levels of toxic metals which is associated with higher degree of potential health risks.