Natural radioactivity and elemental associations in coastal sediments of the Sudanese Red Sea

Background Natural radioactivity in coastal and marine sediments represents an important component of environmental radiation exposure assessment and serves as a valuable indicator of geological provenance, sediment transport processes, and ecological radiological safety. Marine sediments accumulate naturally occurring radionuclides through weathering of terrestrial rocks, fluvial transport, atmospheric deposition, biogenic accumulation, and marine geochemical redistribution. Establishing regional baseline radioactivity data is essential for environmental monitoring, radiation protection planning, and sustainable coastal resource management. Despite the ecological and economic importance of the Sudanese Red Sea coastline, comprehensive environmental radiological characterization of its marine sediments remains limited. Objective This study aimed to quantitatively assess the activity concentrations of naturally occurring radionuclides ( 226 Ra, 232 Th, and 40 K) in coastal sediments collected along the Sudanese Red Sea coast, evaluate associated radiological hazard indices, investigate geochemical relationships between radionuclides and elemental composition, and benchmark findings against regional and international environmental radioactivity data. Materials and methods A total of forty coastal sediment samples were collected from nine representative locations spanning approximately 750 km of the Sudanese Red Sea coastline. Gamma-ray spectrometric analysis was performed using a calibrated NaI(Tl) scintillation detector to determine activity concentrations of 226 Ra, 232 Th, and 40 K. Elemental characterization was conducted using X-ray fluorescence spectroscopy (XRF). Standard radiological hazard indices—including radium equivalent activity (Raeq), absorbed gamma dose rate (D), annual effective dose equivalent (AEDE), annual gonadal dose equivalent (AGDE), external hazard index (H_ex), internal hazard index (H_in), representative gamma index (Iγ), and excess lifetime cancer risk (ELCR)—were calculated according to internationally accepted methodologies. Pearson correlation analysis was used to examine interrelationships among radionuclides and elemental constituents. Results Activity concentrations ranged from 3.95 to 17.11 Bq kg −1 for 226 Ra, 6.69–28.31 Bq kg −1 for 232 Th, and 68.45–508.47 Bq kg −1 for 40 K, with location-level means calculated across the nine displayed locations (the 40 individual sample results are not tabulated) of 7.47 ± 4.40, 11.10 ± 7.07, and 190.61 ± 181.95 Bq kg −1 , respectively. These mean concentrations were substantially lower than UNSCEAR global reference values for terrestrial materials, representing reductions of approximately 78.7% for 226 Ra, 63.0% for 232 Th, and 52.3% for 40 K. The mean absorbed dose rate was 16.47 nGy h −1 , approximately 72.1% lower than the worldwide outdoor average. Mean radium equivalent activity was 35.0 Bq kg −1 , corresponding to only 9.5% of the recommended safety threshold. External and internal hazard indices were 0.095 and 0.115, respectively, both substantially below unity. The estimated annual effective dose equivalent was 20.2 μSv y −1 , markedly lower than global average natural background exposure levels. The correlation between 226 Ra and 232 Th was r = 0.964 (n = 9; exploratory), indicating covariation among the location-level observations, while selected positive associations with Fe, Ti, V, Mn, and Si were exploratory and do not establish source attribution. Conclusion At the nine sampled locations, the measured radionuclide activities and calculated indices were below the international reference or screening values applied in this study. The spatial associations are exploratory and do not establish geological source attribution or exclude anthropogenic influence. These results provide location-specific baseline information for further environmental monitoring along Sudan's Red Sea coast.