Assessment of radioactive substance transfer and its ecological and health impacts on the Nasser Lake ecosystem.

This study investigates the distribution, transfer, and potential ecological risks of naturally occurring radioactive materials, including radon-222 ((222)Rn), radium-226 ((226)Ra), thorium-232 ((232)Th), and potassium-40 ((40)K), in the aquatic ecosystem of Nasser Lake, Egypt. As Egypt's largest freshwater reservoir and a critical source of drinking water and fish, Nasser Lake plays a key role in environmental stability and public health. A total of 40 environmental samples-sediment, water, aquatic plants, and fish-were collected from 10 strategically selected sites around the lake. Gamma spectroscopy using sodium iodide activated with thallium [NaI(Tl)] detectors and AlphaGUARD radon monitoring systems was employed to measure radionuclide activity concentrations. Spatial distribution patterns were analyzed using Geographic Information System (GIS) techniques to identify zones of elevated radioactivity. The highest concentrations of (226)Ra, (232)Th and (40)K were recorded in sediment samples near the High Dam, reaching 10.99 ± 0.42 Bq kg(-1), 23.94 ± 1.91 Bq kg(-1), and 277.38 ± 23.86 Bq kg(-1), respectively. A strong positive correlation (Pearson's r = 0.913) was observed between (226)Ra and (222)Rn exhalation rates, confirming that sediment accumulation significantly contributes to local radiological emissions. Bioaccumulation studies showed progressive uptake of radionuclides along the aquatic food chain, with fish exhibiting a bioaccumulation factor (BAF) of 0.74 for (226)Ra. Estimated annual radiation doses from fish consumption reached up to 6.435 microsieverts per year (µSv y(-1)), remaining below international reference levels established by the World Health Organization (WHO). However, the combination of localized contamination near the High Dam and high fish consumption in nearby communities may present long-term radiological exposure risks. These findings highlight the importance of continuous monitoring of radioactive contaminants in sediment, water, and aquatic organisms in Nasser Lake. The study also provides a transferable framework for assessing the behavior of technologically enhanced naturally occurring radioactive materials (TENORM) in freshwater environments and supports the goals of the United Nations Sustainable Development Goals (SDGs) for clean water and good health.