Natural and anthropogenic radionuclides in Norwegian farmed Atlantic salmon (Salmo salar)

Norway is one of the main producers of farmed fish and the world's second-largest exporter of seafood. Farmed Atlantic salmon (Salmo salar) represents the most exported species. This is the first comprehensive survey of anthropogenic (¹³⁷Cs, ⁹⁰Sr, ²³⁸Pu, ^239,240Pu and ²⁴¹Am) and natural (⁴⁰K, ²²⁶Ra, ²²⁸Ra, ²¹⁰Pb, ²¹⁰Po) radionuclides in farmed salmon and manufactured fish feed from Norway. The only anthropogenic radionuclide detected in salmon and fish feed was ¹³⁷Cs. The levels were low with arithmetic means in salmon and feed of 0.13 and 0.30 Bq/kg fresh weight (fw), respectively. The natural radionuclide ⁴⁰K exhibited the highest levels with arithmetic means in salmon and feed of 115 and 239 Bq/kg fw, respectively. The arithmetic means of ²¹⁰Po and ²¹⁰Pb in salmon were 0.013 and 0.044 Bq/kg fw, respectively, with a mean ²¹⁰Po:²¹⁰Pb activity ratio of 0.32. For fish feed, the situation was reversed: the arithmetic means of ²¹⁰Po and ²¹⁰Pb were 3.8 and 0.67 Bq/kg fw, respectively, with a mean ²¹⁰Po:²¹⁰Pb activity ratio of 5.7. The radionuclide levels found in farmed salmon in the present study are comparable to or lower than the levels found in other fish species in the North Atlantic Ocean. A highly conservative dose estimate for consumption showed that doses were no higher than 1.2 μSv/year for toddlers and 4.0 μSv/year for adults. This suggests that the risk associated with radioactivity in farmed salmon is very low even when considering individuals with high consumption and the highest radionuclide levels found in this study.