Radioactive concentrations and natural radionuclide risks in Ha Long Bay and Ba Che Estuary sediments, Vietnam

Abstract Near the coast, the Ba Che Estuary and Ha Long Bay are influenced by both natural processes and man-made activities. The radioactive contents of ²²⁶Ra, ⁴⁰K, and ²³²Th and the radiation risk indices of nine sediment cores were determined to assess the impact of radiation on the environment and humans. The ⁴⁰K, ²³²Th, and ²²⁶Ra had average radioactivity concentrations of 383, 41.3, and 24.2 Bq/kg, respectively. The Radium equivalent activity (Raeq), absorbed dose rate (ADR), equivalent annual effective dose (AEDE), representative gamma index (Iγr), index active use (AUI), external hazard index (Hex), and annual gonadal equivalent dose (AGDE) were 112.7 Bq/kg, 52.1 nGy/h, 0.06 mSv/y, 0.83, 0.75, 0.30, and 367.7 µSv/y, respectively. These results showed that the ⁴⁰K and ²²⁶Ra radioactivity concentrations were within the allowable range, while the ²³²Th concentration was higher than the global average. These radionuclides receive their source from the mainland, and there are moderate to strong positive correlations between ⁴⁰K and ²³²Th and between ²³²Th and ²²⁶Ra. The nine sediment cores were split into two groups: Group 1 was close to the shore, and Group 2 was both far from and close to the shore. The higher radiation risk indices in Group 1 suggested a potential health risk for ecosystems close to the shore.