Natural Radionuclides in Selected Freshwater Fishes from the Red River (Vietnam): Influence of Biological...

Naturally occurring radioactive substances in freshwater ecosystems pose potential radiological risks to both aquatic organisms and humans through dietary exposure. This study quantified the activity concentrations of ²²⁸Ra, ²¹⁰Pb, ²²⁶Ra, ²¹⁰Po and ⁴⁰K in ten commonly consumed fish species from the Red River, Vietnam. The results showed significant inter-isotope variability, with ⁴⁰K dominating all samples. Mean activity concentrations were 1.22 ± 0.2 (LOD-7.61) for ²²⁸Ra, 9.1 ± 1.7 (LOD-37.1) for ²¹⁰Pb, 7.69 ± 1.04 (0.70-24.7) for ²²⁶Ra, 11.8 ± 0.9 (5.16-18.7) for ²¹⁰Po, and 101 ± 8.6 (65-169) Bq.kg^-1 for ⁴⁰K. These variations reflect the different behaviors of the isotopes in aquatic environments. Negative correlation was observed between ²²⁶Ra and body weight, suggesting morphological influences on radioactivity absorption in fish. Radiation risk assessments revealed average annual effective doses of 0.105 mSv.y^-1 (0.030-0.247 mSv.y^-1), significantly lower than the safety threshold, with lifetime cancer risks ranging from 1.4 × 10^-7 to 7.7 × 10^-7, within acceptable limits. Ecological risk assessment using the ERICA Tool revealed total dose rates ranging from 0.2 to 10.4 µGy.h^-1 (mean: 3.0 µGy.h^-1), with the Zig-zag eel exceeding the screening threshold of 10 µGy·h^-1, indicating a potential radiological risk for this species, while risks remained negligible for the remaining species. These findings enhance understanding of radionuclide dynamics in freshwater food webs and inform public health risk assessments for fish consumption in the Red River basin. The study establishes essential baseline data for regional radiation monitoring programs while contributing to biodiversity protection and food safety.