One health risk assessment of heavy-metal contamination in Nile tilapia (Oreochromis niloticus) from contrasting aquaculture systems in Egypt.

In water-scarce Egypt, aquaculture relies on agricultural drainage water, raising health concerns. Water and Nile tilapia were sampled seasonally from four sites (drainage versus Nile freshwater). Lead (Pb), cadmium (Cd), chromium (Cr), and mercury (Hg) were measured in water and fish tissues by ICP-MS and FAAS. Bioaccumulation factors (BAFs) and health risks (EDI, THQ, HI) were calculated. Kitchener Drain showed severe contamination, with Pb, Cd, Cr, and Hg exceeding WHO limits 5-54-fold. Bioaccumulation followed liver > kidney > muscle, with Pb reaching 4.90 mg/kg in summer liver. Muscle remained within FAO/WHO limits. BAFs showed metal transfer even at low ambient levels. All THQ values were < 1. The HI at Kitchener Drain (0.36) was 3.6-fold higher than reference sites (HI=0.10), peaking in summer. Correlations between water, tissue, and human health risk were strong (r > 0.85, p < 0.001). Although edible muscle poses no immediate risk, narrow Pb safety margins (0.28 mg/kg vs 0.3 mg/kg) and higher cumulative risk highlight the need for monitoring and water treatment. This One Health assessment supports sustainable aquaculture management in Egypt.