Abstract
Heavy metals pollution in aquatic environments is mostly caused by human activities such as urbanization, industrialization, mining and agriculture. The current investigation assessed the levels of seven metals, including iron (Fe), manganese (Mn), cupper (Cu), zinc (Zn), chromium (Cr), lead (Pb) and cadmium (Cd) in water and muscle, liver, and gills of Nile tilapia (Oreochromis niloticus) collected from a set of water bodies in Menofia province derived from branches of the Nile River and some drains in some centers in Menofia Governorate. The detected metals were within limits in the Nile River water and fish collected from the Nile branches but exceeded the permissible limits in drains. Moreover, Oreochromis niloticus collected from drains showed significant irreversible tissue damage in liver, muscle, and gills compared to mild changes in those caught from the Nile. Organ-specific analysis showed that the liver contained the highest concentrations of Fe (77.811 mg/kg), Cu (15.905 mg/kg), Zn (33.134 mg/kg), Cr (1.294 mg/kg), and Cd (0.914 mg/kg), while the gills had the highest levels of Mn (4.254 mg/kg) and Pb (1.903 mg/kg). On the contrary, muscles exhibited the lowest metal concentrations compared to the liver and gills. Regarding human health, in the Nile studied locations, HI results showed insignificant non cancer risk (HI<1) but CR values for Cr and Cd indicated tolerable exposure (10-6 -10-4), and for Pb indicated insignificant exposure (CR< 10-6). On the other hand, HI results for drains exhibited potential non-carcinogenic risk (HI>1). Furthermore, CR values for Cr, Cd and Pb in fish for drains water declared significant exposure (CR>10-4). This study serves as warning signal for the concerned authorities and consumers, particularly those depend mainly on fish as a daily source of protein.

Key words: Heavy metals, Nile tilapia, Histopathology, Oreochromis niloticus, Health risk assessment, Hazard index (HI), Cancer Risk (CR), Egypt