Sediment-associated natural radionuclide and radiological risk indicators in a tropical river estuarine system

Sediments in river estuarine systems facilitate the long-term accumulation of naturally occurring radionuclides, playing a critical role in controlling their environmental distribution and potential radiological exposure pathways. This study presents a gamma-spectrometric assessment of natural radionuclides (⁴⁰K, ²³⁸U, and ²³²Th) in estuarine sediments within a tropical river system where both natural geological processes and human activities occur. The sediments were quantified using a calibrated sodium iodide gamma-ray spectrometer, and standard radiological hazard indices were evaluated to assess potential environmental and human health risks. The mean activity concentrations were 490.50  i7.66 Bq/kg (⁴⁰K), 5.67 , 0.20 Bq/kg (²³⁸U), and 4.81 ),0.26 Bq/kg (²³²Th). While ⁴⁰K actively slightly exceeded the UNSCEAR average by 16.79%, the ²³⁸U and ²³²Th concentrations were 82.82% and 89.31%, respectively, below the global thresholds. Derived radiological parameters, including radium equivalent activity (50.32 Bq/kg), dose rate (26.13 nGy/h), annual effective dose (0.03 mSv/y), and annual gonadal dose (191.64 µSv/y), were all within internationally accepted safety thresholds. The results suggest that sediment-associated radionuclides in the studied estuarine environment do not pose significant radiological risks through external exposure pathways. These findings contribute baseline data for tropical estuarine sediment systems and support comparative radiological assessments across similar depositional environments globally.