Natural radioactivity assessment of surface sediments in the Yangtze Estuary

The activities of the natural radionuclides (²³⁸U,²³²Th,²²⁶Ra and⁴⁰K) of the surface sediments in the Yangtze Estuary were determined and used to evaluate radiation hazards in the study area. The of activities of²³⁸U,²³²Th,²²⁶Ra and⁴⁰K ranges from 14.1 to 62.3, 26.1 to 71.9, 13.7 to 52.3, and 392 to 898 Bq kg^− 1, respectively, which were comparable to values of other regions in China. The activities of²³²Th,⁴⁰K and²²⁶Ra were clearly different from the global recommended values. The radium equivalent activity was less than the recommended limit of 370 Bq kg^− 1; therefore, the sediment in this area can be safely used for reclamation. The external hazard index values were less than one. The average absorbed gamma dose rate and annual effective dose equivalent values were slightly greater than the world average value.²²⁶Ra/²³⁸U and²³²Th/²³⁸U ratios could potentially be applied for tracing sediment source.