Uranium isotopes (234U and 238U) in Perna viridis from a titanium placer coastal zone in Vietnam: bioaccumulation patterns and radiological risk assessment

Abstract Activity concentrations of 234 U and 238 U as well as 234 U/ 238 U ratios were investigated in the muscle and digestive diverticulum organs of ten size group samples of Asian green mussel ( Perna viridis ) from Binh Thuan, Vietnam by alpha-spectrometry, and radiological risk assessment was carried out. The 234 U and 238 U activities in muscle tissues and digestive diverticulum ranged from 1.4 ± 0.1 to 53.2 ± 4.3 Bq.kg −1 , from 1.2 ± 0.2 to 57.2 ± 4.5 Bq.kg −1 , and from 3.8 ± 0.3 to 45.0 ± 7.5 Bq.kg −1 , from 3.1 ± 0.2 to 42.0 ± 6.6 Bq.kg −1 , respectively. Uranium activities showed a decreasing trend in groups with smaller shell lengths from 5 to 6.5 cm and stabilized in individuals larger than 7 cm. Bioaccumulation factors were higher in smaller mussels, demonstrating greater accumulation, indicating their suitability as sentinel organisms for further study and radioecological monitoring of uranium isotopes. The 234 U/ 238 U activity ratios in digestive diverticula were consistently higher than in muscle tissues, suggesting dual uranium uptake pathways: direct absorption from seawater and ingestion of contaminated foods. The average risk to the mussels from exposure to uranium alone is below the ERICA screening reference level of 10 µGy.h −1 , but a single sample exceeded this level indicating further investigation is necessary. Annual committed effective doses from consuming mussels containing 234 U and 238 U ranged from 2.11 to 43.60 µSv.y −1 , with a mean of 12.04 µSv.y −1 . While doses from 234 and 238 U are within UNSCEAR safety thresholds, other radionuclides (e.g., Po, Pb, and Ra isotopes) should be considered for a comprehensive assessment. Not consuming small mussels is recommended due to higher potential radionuclide accumulation.