Accumulation and risk assessment of heavy metals-induced biochemical and histopathological alterations in O. niloticus from Lake Nasser, Egypt

Lake Nasser is the world's second greatest man-made lake and the main reservoir of fresh water in Egypt. There are no direct sources of heavy metal pollution in Lake Nasser. However, metals enter the lake ecosystem in many ways as erosion of the geological matrix, air deposition, anthropogenic activity, and from upstream of the Nile's basin. The current study aimed to evaluate the physiological and histopathological effect of heavy metals on different organs of the Nile tilapia (O. niloticus) and assess the possible human health risk related to consuming fish from Lake Nasser. Fish were assembled from different khors of Lake Nasser (Bekheet, Medahib, Korosko, Sukar, and Yassen). Blood serum glucose, total protein, albumin, total lipids, ALT, AST, urea, uric acid, and creatinine, in addition to heavy metals accumulation (Fe, Mn, Zn, Cu, Cd, and Pb) in muscles, gills, and liver organs were determined in the current study. Also, these selected organs were histologically examined. The higher metal index was recorded in the liver followed by gills and muscles. Both physiological and histological parameters recorded a site-dependent response. The recorded data confirmed the negative effect of heavy metals on fish health and internal organs’ function. Metals were accumulated in muscles, gills, and liver tissues according to the following order; Fe > Zn > Cu > Mn > Pb > Cd. However, the metal load in the muscles of O. niloticus was within the permissible limits for human consumption, and the hazard index recorded no adverse health effects on neither normal nor habitual consumers among all sampling sites.