Assessment of natural radioactivity levels in estuaries and coastal mangrove forests: A case study from the coastal area of Soc Trang, Vietnam

Estuarine and coastal regions globally, including those in Vietnam, act as natural sinks for sediments transported from upstream catchments. This study aims to evaluate the levels of natural radioactivity, specifically ²²⁶Ra, ²³²Th, ⁴⁰K, and ¹³⁷Cs, in estuarine and mangrove sediments along the coastal area of Soc Trang Province, Vietnam. A total of 32 surface sediment samples were collected from various locations within estuarine and mangrove environments. The activity concentrations of the radionuclides were measured using high-resolution gamma spectrometry. The results showed that the concentration ranged from of 21.3 ± 1.1 Bq/kg to 52.6 ± 2.6 Bq/kg for ²²⁶Ra, 24.5 ± 1.2 Bq/kg to 57.3 ± 2.9 Bq/kg for ²³²Th, and 349 ± 18 Bq/kg to 654 ± 33 Bq/kg for ⁴⁰K. Radiological risk indices including the absorbed gamma dose rate (D = 72 nGy h⁻¹), annual effective dose equivalent (AEDE = 88 μSv y⁻¹), Radium equivalent level (Ra_eq = 151), External hazard indices (H_ex = 0.39) and excess lifetime cancer risk (ELCR = 0.35) were subsequently calculated to assess potential health and environmental risks. These values exceed global average levels reported by international organizations such as UNSCEAR. The study results provide baseline data essential for long-term radiological monitoring and environmental risk assessment in mangrove-dominated coastal ecosystems subjected to increasing anthropogenic stress.