Evaluation of radioactivity concentrations from the Fukushima nuclear accident in fish products and associated risk to fish consumers

Abstract

Radioactive contamination of the Pacific Ocean following the Fukushima nuclear accident has raised public concerns about seafood safety(1, 2). Many people are wondering whether fish products from the Pacific Ocean and Japan are safe to eat 2 y after the accident. There is also some concern about seafood caught locally, outside of Japan. Based on monitoring data reported in July 2013, radioactive caesium concentrations in fish products from Fukushima and adjacent prefectures are evaluated. Resulting radiation doses from annual consumption at average contamination levels and occasional fish meals at much higher levels of caesium are calculated. To put radiation doses from caesium intake in perspective, comparisons are made to doses from naturally occurring radioactive polonium commonly found in fish. Discussion and conclusions are given subsequently. The Tokyo Electric Power Company has conducted routine radioactivity measurements (134Cs and 137Cs) of various marine fish and shellfish in the ocean area within a 20-km radius of the Fukushima Daiichi Nuclear Power Station (FDNPS). Based on their posted summary on 16 August 2013(3), a total of 100 fish samples were collected from 7 to 23 July, offshore of the FDNPS and outside of its port area. The nuclide analysis report showed that 134Cs was detected in 64 samples with concentrations varying from 3.5 to 130 Bq kg−1. 137Cs was detected in 79 samples and the concentration varied from 3.6 to 260 Bq kg−1. On average, fish and shellfish caught within 20-km offshore of the FDNPS contain 12 Bq kg−1 of 134Cs and 26 Bq kg−1 of 137Cs. The Japanese Fisheries Agency (JFA), in cooperation with the relevant prefectural governments and organisations, has conducted sampling and inspections of fishery products at the major fishing ports in Fukushima and adjacent prefectures on a weekly basis to examine the possible contamination of fishery products by radioactive materials released from the FDNPS. Based on press releases made by the JFA in July 2013(4), a total of 1952 fishery products were analysed for caesium. Among them, 134Cs was found in 485 samples (25 %) and 137Cs was detected in 776 samples (40 %). The analyses were done by various institutions and the laboratory detection limits varied from <1 Bq kg−1 to ∼10 Bq kg−1. Among those samples with concentrations above detection limits, the reported 134Cs concentrations varied from 0.1 to 338 Bq kg−1 with an average of 11 Bq kg−1. The reported 137Cs concentrations varied from 0.1 to 699 Bq kg−1 and the mean of the reported values is 18 Bq kg−1. The highest concentrations (338 Bq kg−1 for 134Cs and 699 Bq kg−1 for 137Cs) were reported on 11 July from a sample of sea bass, offshore of Hitachi city. When averaged over all 1952 samples (with zero concentration for those below the detection limit), fish products from a broad ocean area in eastern Japan contain on average 3 Bq kg−1 of 134Cs and 7 Bq kg−1 of 137Cs. Naturally occurring radionuclides exist in the environment in the air we breathe and in the water we drink. Not surprisingly, naturally occurring radionuclides can be found in varying concentrations in fishery products. A literature review conducted by Hosseini et al.(5) revealed that the mean activity concentrations of natural occurring radionuclides in generic marine fish are 83 Bq kg−1 of 40K, followed by 30 Bq kg−1 of 210Po, 19 Bq kg−1 of 14C and 1.8 Bq kg−1 of 228Ra. Potassium is ingested in many foods that we eat and is a critically important element for proper functioning of the human body. Because the potassium content of the body is under strict homeostatic control in which the amount retained is actively regulated by the body, the 40K content in the human body is constant and not influenced by variations in environmental levels. Therefore, the effect of 40K intake from fish consumption will not be considered in the following discussion. For similar reasons, the effect of 14C will also be excluded in the subsequent dose assessment.