Seasonal Variations Of Heavy Metal Concentrations In The African River Prawn (Macrobrachium Vollenhovenii) From The River-Nun, Niger Delta, Nigeria

Seasonal variations of selected heavy metals in the fresh water prawn Macrobrachium vollenhovenii from River-Nun 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 this river system and establish the health status of the river body. Triplicate sub surface water samples were collected from three (3) sampling points from the water body once monthly for twelve (12) months. Also, prawn samples were collected monthly from three (3) fish landing points in the river 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. Analysis of Variance (ANOVA) was employed to measure for similarities and variability in heavy metal characteristics in prawn and water for the river system. Turkey HSD Post HOC test was employed to separate means where variability occurred. This was done at the 95% confidence limit (P=0.05). Student T-test was also employed to check for variability between seasons in the measured parameters. This was aided by the use of the SPSS® statistical tool kit. Result of the study indicate that wet season values of the heavy metals in water were greater than values obtain in the dry season. Except for the metals Hg and Zn, all heavy metal characteristics of the river are consistently 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. 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.