Radioactivity concentration measurements in fish and shellfish samples from the west coast of Canada after the Fukushima nuclear accident (2011-2018)

Radioactive contamination of the Pacific Ocean following the Fukushima nuclear accident has raised public concern about seafood safety, particularly in coastal Indigenous communities. To address this, Health Canada and partners have collected and analyzed a total of 621 samples of commonly consumed salmon, ground fish, and shellfish from the Canadian west coast from 2011 to 2018. While the vast majority of the ¹³⁷Cs and ¹³⁴Cs levels were below the Minimum Detectable Concentration (MDC, typically 0.7-1.0 Bq kg^-1 fw for a 6 h counting), further examination of 19 fish samples revealed ¹³⁷Cs concentrations of 0.17-0.53 Bq kg^-1 fw with an average value and uncertainty (k = 1) of 0.29 ± 0.02 Bq kg^-1 fw. Of these, only two samples were found to have trace levels of ¹³⁴Cs likely derived from the Fukushima accident. The global fallout contribution from atmospheric nuclear weapons testing to the observed ¹³⁷Cs in these two samples was determined to be 0.26 ± 0.08 Bq kg^-1 fw (49 ± 14%) and 0.12 ± 0.02 Bq kg^-1 fw (24 ± 4%) for collection years 2015 and 2016, respectively. The annual average level of ¹³⁷Cs in fish and shellfish was also determined by spectral summation for collection years 2014-2018. In fish, ¹³⁷Cs levels determined through spectral summation were relatively constant (0.18-0.25 Bq kg^-1 fw) with an average value and uncertainty of 0.21 ± 0.02 Bq kg^-1 fw. By contrast, 38 shellfish samples (bivalves) were measured and revealed no radiocesium or other anomalies in either tissue or shell. In all, measurements over eight years showed that the radioactivity in fish and shellfish was dominated by natural radionuclides and that the level of anthropogenic radionuclides, as indicated by the radioactive cesium content, remained small. An upper bound for ingested dose from ¹³⁷Cs was determined to be approximately 0.26 μSv per year, far below the worldwide average annual effective dose of 2400 μSv from exposure to natural background radiation. We can therefore conclude that fish, such as salmon, ground fish, and shellfish from the Canadian west coast are of no radiological health concern despite the Fukushima Dai-ichi nuclear accident of 2011.