Bioaccumulation of Heavy Metals in Tilapia Fish (Oreochromis niloticus)

Abstract

Fish are widely used to evaluate the health of any aquatic ecosystem because their biological responses serve as biomarkers of an environmental contaminant. Besides their ecological value, Nile tilapia contributes immensely to a healthy diet. However, consumption of fish is contaminated by heavy metals lead to various diseases. The aim of this study was to determine the bioaccumulation levels of seven heavy metals (Cr, Zn, Cu, Fe, Pb, Hg, and Cd) in Nile Tilapia fish (Oreochromis Niloticus) collected from Almorada fish market (Omdurman locality). The samples of fresh fish were randomly collected from the local fishermen during the month of October 2019 and packed in an ice box before being transported to the laboratory. The fish samples were tagged into A, B, C and D for easier identification, with length of 8, 9.5,11, and 13 cm and weight of 0.195, 0.206, 0.472 and 0.551 kilograms/wet, respectively. Aqua regia solution (prepared by HNO3: HCl at the ratio of 1:3, respectively) was used for the samples digestion. The samples were subsequently assayed using inductive couple plasma atomic emission spectroscopy. Different organs of the fishes accumulated varying quantities of heavy metals. In Oreochromis Niloticus, the level of heavy metals varied significantly among fish size and organs. The highest level of heavy metals was found in gill followed by the head and finally the muscle. However, the accumulation of potassium and sodium followed the sequence Head > Gill > Muscle and Head > Muscle > Gill, respectively. There were statistically significant for the level of Lead (p= 0.03), Chromium (p= 0.041) and potassium (p= 0.044) in the tilapia fish tissues rendering them above the threshold limit set by WHO/FAO 2003 as a result become toxic to human consumption. This suggests that the fish samples could be used to monitor Lead and Chromium pollution levels in the River Nile.