Assessment Of Heavy Metal Concentration In African River Prawn (Macrobrachium Vollenhovenii - Herklots, 1857) In The Lower Cross River System, Southeastern Nigeria

Abstract

The assessment of heavy metals in the tissues of prawns is essential to understand the extent of contamination and potential health risk in human and the aquatic ecosystem. The study aimed to determine the concentration levels of iron, chromium, lead and cadmium in the tissues of Macrobrachium vollenhovenii of the lower Cross River System comparing it with the permissible consumption limits of Federal Ministry of Environment (FMENV) and the World Health Organization (WHO). Samples of the prawn were collected from artisanal fishermen on landing between November, 2022 and January, 2023. Collected samples were placed on ice and transported to the laboratory for Atomic Absorption Spectrophotometry analysis. The prawn samples had a total length and weight of 18.0cm – 24.0cm and 98.42g – 248.64g, respectively. The results revealed that the toxicity levels of heavy metals in the tissues of M. vollenhovenii ranged as follows: Fe: 1.041 - 2.082mg/kg; Pb:  0.173 - 0.618mg/kg; Cd: 0.114 - 0.242mg/kg; Cr:  0.007 - 0.038mg/kg. The results from the analysis indicated that, Fe had the highest concentration, followed by Pb, Cd and least was Cr. The result revealed that, there was no statistically significant difference in the Lead levels (p=0.266) and chromium levels (p=0.882) across the months (NOV-JAN). There was statistically significant increase in the Iron levels across the months (NOV-JAN) (p=0.037). There was statistically significant decrease in the cadmium levels across the months (NOV-JAN) (p=0.022). Therefore, this study presents valuable information about heavy metals bioaccumulation in a commercially important prawn caught from the lower Cross River which is consumed by locals in the region. Also the evaluation of possible risks on health associated with contaminated prawn consumption on human is clear.  Except for Cr, the heavy metal concentrations in the prawn samples analyzed were above the prescribed limits set by various authorities (WHO/FMENV). The result of this study calls for a close monitoring of anthropogenic activities of the area for safety in seafood consumption by human.