Occurrence and radiological risk assessment of 11 target γ-emitting radionuclides in seafood from the Ningbo coastal area, China during 2022–2025

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Background Dietary ingestion is a major exposure pathway for environmental radionuclides, and the radiological safety of seafood, an important component of the global diet, has attracted increasing public concern. As a Chinese coastal city where seafood is a traditional part of local residents’ daily diet, Ningbo lacks systematic baseline data on radionuclide levels in locally common edible seafood and associated dietary radiological risks for local residents. Methods Five categories of locally common edible seafood (fish, shrimp, crabs, mollusks and algae) were collected from the southern coastal area of Ningbo during 2022–2025. Specific activities of 11 target γ-emitting radionuclides were quantified via high-purity germanium γ spectrometry in accordance with GB/T 16145–2022, and annual effective ingestion dose (AED) was estimated using local per capita seafood consumption data and ingestion dose conversion coefficients recommended in ICRP Publication 119. Results Natural radionuclides dominated across all five seafood categories, with 40 K detected in 100% of samples. Algae had the highest detection rates of 238 U (77.8%) and 210 Pb (55.6%), crabs had the highest 228 Ra detection rate (100%), and 226 Ra was detected at the highest rate in both crabs and algae (77.8%). For specific activities, algae exhibited the highest specific activities of 238 U (median 0.78, maximum 12.80 Bq/kg), 40 K (284.10, 931.00 Bq/kg) and 210 Pb (0.41, 7.96 Bq/kg); crabs had the highest 226 Ra (0.54, 13.09 Bq/kg); shrimp had the highest median 228 Ra activity (1.26 Bq/kg) while algae had the highest maximum activity (7.90 Bq/kg). Mollusks had the lowest median specific activities overall, but a higher 238 U detection rate than fish, shrimp and crabs. Only trace 137 Cs was detected in one fish (0.05 Bq/kg) and one mollusk (0.02 Bq/kg) sample from 2025. The median total AED was 30.43 μSv/y, with a conservative constructed upper-bound maximum of 133.64 μSv/y. Conclusion For the measured γ-emitting radionuclides only, natural radionuclides dominate in seafood from the study area, and all regulated radionuclides meeting China’s food radiological safety requirements. Artificial radionuclides were negligible with no significant anthropogenic perturbation, and the dietary dose for local adults in the study area remains below the ICRP-recommended public dose limit.