Stable isotopes and radionuclides in selected marine species in Red River estuaries, Vietnam.

Abstract

This study investigates radionuclide accumulation, trophic structure, and associated radiological risks in marine organisms from the Red River estuaries, a dynamic sediment-rich coastal system in northern Vietnam. Stable isotopes (δ13C and δ15N) were integrated with measurements of natural and anthropogenic radionuclides (226Ra, 232Th, 40K, 238U, 137Cs, 234Th, 228Ra, and 210Pb) in two clam species and five fish species to elucidate ecological controls on radionuclide transfer. δ13C (− 22.31 to − 16.22‰) and δ15N (9.22 to 14.84‰) values revealed clear trophic differentiation between primary consumers (clams) and higher trophic-level fish. Among radionuclides, 40K dominated in all organisms, whereas other radionuclides occurred at relatively low levels. Radiological indices, including annual effective dose (AED), internal hazard index (Hin), and radium equivalent activity (Raeq), were below international safety thresholds, indicating low immediate health risk. Excess lifetime cancer risk (ELCR) slightly exceeds the ICRP of 10− 4 but is still considered low risk; hence, long-term monitoring is recommended. Multivariate analyses demonstrate that radionuclide accumulation is primarily controlled by trophic transfer and dietary pathways, with additional contributions from sediment and water interactions. This study provides new evidence linking trophic structure to radiological risk in a river-dominated estuary with high sediment input. The findings highlight the importance of integrating ecological and geochemical processes in radiological risk assessment and offer a scientific basis for long-term monitoring and sustainable coastal management.