Tag Archives: Fish

Radioactivity in fish and shellfish samples from the west coast of Canada after Fukushima (2011-18) 

The purpose of this post is to bring the public up to date on monitoring efforts of a research program into the impact of the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident on environmental and public health here in North America. This post is part of an ongoing series summarizing work carried out by the Integrated Fukushima Ocean Radionuclide Monitoring (InFORM) project which operated from 2014-2020. Radioactive contamination of the Pacific Ocean following the FDNPP accident raised public concern about seafood safety, particularly in coastal Indigenous communities in British Columbia where I live. To address this, InFORM along with Health Canada,  Department of Fisheries and Oceans Canada and First Nations 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. We examined the activities of cesium radioisotopes (134Cs half-life ~2 years and 137Cs half-life ~30 years) that were released in relatively large quantities from the Fukushima Dai-ichi Nuclear Power Plant (FDNNP) disaster in 2011 and would be most likely to pose radiological health concerns for human consumers of marine animals. Through careful analysis to determine the amount of radioactive isotopes in the seafood we have been able to carry out a health impact assessment. I wish to thank the following First Nations from British Columbia, Canada, for their generous donation of fish: Tr’ondëk Hwëch’in, Selkirk, Champagne and Aishihik, Taku River Tlingit, Tahltan, Nisga’a, Wet’suwet’en, Wuikinuxv, ‘Namgis, Hupacasath, Syilix, and Vuntut Gwich’in. I also thank Kayla Mohns and Brenna Collicutt of the Hakai Institute for assistance with the collection of shellfish samples. These results have recently been published in the peer-reviewed scientific literature in the Journal of Environmental Radioactivity and can be accessed here.

Highlights of the paper and key findings:

  • the vast majority of fish and shellfish did not have detectable levels of 137Cs or 134Cs where the minimum detectable level was 0.7 — 1.0 Bq kg-1 fresh weight for 6 hours of analysis by counting with a sensitive gamma emission spectrometer
  • 19 fish that had detectable levels of 137Cs were freeze dried and recounted for 336 hours and found to have an average 137Cs content of 0.29±0.02 Bq kg-1 fw
  • 2 of these 19 fish had detectable levels of 134Cs, the short-lived isotope, which showed clearly that fallout from the FDNPP was present in these particular fish. Given that the ratio of 137Cs:134Cs in the releases from the FDNPP was 1:1 we determined that the contribution of contamination in these fish from the nuclear accident was 49% and 24% respectively with the majority of caesium contamination coming from other sources like nuclear weapons testing and the Chernobyl disaster in the 20th century
  • 38 shellfish showed no contamination from FDNPP in either their shells or meat
  • 8 years of measurements showed that radioactivity in fish was dominated by naturally occurring radioisotopes and that levels of human-made radioisotopes remained small in the Pacific off North American following the FDNPP disaster
  • upper bounds for ingested doses of ionizing radiation from 137​​​​​​​Cs was determined to be ~0.26 micro-Sieverts per year and far below the annual effective dose of 2400 micro-Sieverts from exposure to other sources of radiation
  • we conclude that fish and shellfish from the Canadian west coast are not a radiological health concern despite the FDNPP accident of 2011

What we did

Samples were collected with the help of 13 First Nations, the Department of Fisheries and Oceans and the Hakai Institute in coastal waters and rivers of western Canada at sites indicated on the map below.

Figure 1 (a) Map of fish samples collected from 2014 to 2018 through the InFORM project. (b) Map of shellfish (bivalves) collected in 2016 and 2017.

For fish we removed the skin and bone to measure fillets which are typically consumed. Whole-body tissues of mussels, oysters, and clams were processed as they are generally eaten whole, but for scallops only the muscle itself was processed. In addition, we crushed up the shells of the individual shellfish to determine if radiocesium had accumulated in the shell as they are sometimes used to fertilize garden beds or adjust the hardness of rainwater used for home gardens.  We measured the radiocesium and naturally occurring radioisotopes in the samples using gamma spectrometry which you can learn about here. All samples were analyzed for 6 hours to screen samples for the presence of 137Cs and a subset of 19 were counted for a further 336 hours to determine if any 134Cs was present. This represents 10110 hours (more than 421 days) of counting time.

What we found

Results of the 6 hour counts and the extended counting samples can be found in here and here respectively. Given the extremely low levels of 137Cs present in the fish tissue (almost always below our minimum detectable concentration for individual fish) we averaged the gamma emission spectra of all fish collected in each year to determine the average 137Cs content. 137Cs content of all fish samples in each year fell between 0.18 and 0.25 Bq kg-1 fresh weight with the highest average concentration in 2017 and the lowest 2015. Data are here. The challenge of measuring and quantifying the amount of 137Cs can be understood by looking at the gamma emission spectrum and the averages for each year between 2014 and 2018 in the following figure.

Figure 2 Spectral summation of fish samples from 2014 to 2018, normalized to sample number. (a) Overlay, 150–2000 keV (b) Overlay with focus on the principal emission line for 137Cs at 661.7 keV

What the figure shows is that even after averaging the results for every fish collected in each year it was difficult for our team to detect human-made caesium isotopes. There was also no clear trend in time with 137Cs neither increasing nor decreasing with time in Pacific fish. In fact, the level of 137Cs found in the Pacific salmon was similar to levels found in Atlantic salmon (Table 4, 0.20 Bq kg-1) we collected in 2017 and analyzed from the Miramichi River on Canada’s east coast in New Brunswick. Careful analysis of 19 fish with longer counting times led us to be able to detect 2 fish with measurable levels of 134Cs which was an unmistakable sign of contamination from the FDNPP. However, given our understanding of the releases of 137Cs and 134Cs from the FDNPP following the disaster, most of the 137Cs present in the fish reflected contamination in the Pacific from nuclear weapons testing and the Chernobyl disaster rather than events following the 2011 meltdowns at FDNPP. For shellfish harvested from Canada’s west coast in 2016 and 2017, spectral summation of fresh weight samples (tissue and shell, respectively) yielded no detectable radiocesium or any other anthropogenic isotopes.

What it means

From 2011 to 2018, radioactivity measurements were made by the Fukushima InFORM project of 621 fish and shellfish samples harvested from Canada’s west coast. To investigate the impact of the oceanic contamination plume of Fukushima radioactivity to coastal waters, we used highly sensitive analyses and data reduction techniques to show that the concentration of 137Cs in the tissue of marine fish has not changed (0.18–0.25 Bq·kg−1 fw) from 2014 to 2018 while that of shellfish was undetectable. Relative to the abundance of naturally occurring isotopes like 210-Polonium in the same fish samples or to the annual dose exposure due to naturally occurring background radiation, it is abundantly clear that, by any metric, the radiocesium content of fish and shellfish from Canada’s west coast does not constitute a health risk, despite the FDNPP accident of 2011. The ecosystem and public health on the west coast of North America was never under threat from the FDNPP accident.

Measuring Fukushima Contamination in Fish Caught in Hawaii

Yellowfin tuna, Thunnus albacares leaping from the water

By Jay T. Cullen

The purpose of this post is to summarize a recently published, peer reviewed, scientific study that investigated levels of Fukushima derived contamination in fish caught in the North Pacific and sold at market in Hawai’i.  This post is part of an ongoing series dedicated to bringing quality scientifically derived information to readers so that they can form an evidence based opinion regarding the environmental impact of the Fukushima Daiichi Nuclear Power Plant meltdowns. The paper by Azouz and Dulai (both at the University of Hawai’i at Manoa) summarizes levels of human made 134-Cesium (134Cs half life ~2 years) and 137-Cesium (137Cs half life ~30 years) and naturally occurring 40-Potassium (40K half life 1.25 billion years) in 13 different fish purchased in Hawai’i in 2015.  The findings of the study were that:

  1. 3 of the 13 fish had detectable levels (above the 95% confidence interval) of 134Cs which can be linked to the Fukushima disaster
  2. Highest levels of radiocesium were found in ‘ahi tuna with 134Cs and 137Cs of 0.10 ± 0.04 Bq kg-1 and 0.62 ± 0.05 Bq kg-1 respectively
  3. Most of the fish carried no fingerprint of the Fukushima disaster
  4. Levels of radiocesium were well below intervention levels of 1,200 Bq kg-1 set by the United States Food and Drug Administration
  5. Doses to fish consumers from human made radioisotopes were 30-1,000 fold lower than the dose experienced because of naturally occurring 40K in the fish
  6. Neither the effective dose from the natural nor the human made radioisotopes represent a significant health risk to consumers of the fish given scientifically established dose-response relationships

These results agree with the results of the Integrated Fukushima Ocean Radionuclide Monitoring Project (InFORM) I head up at the University of Victoria which has been making similar measurements on North Pacific fish returning to rivers in North America.

The Azouz and Dulai paper was published recently in the journal Pacific Science and can be found here.  The authors obtained 13 different species (Ahi, Albacore Tuna, King Salmon, Cod, Dover Sole, Halibut, Mahi Mahi, Monchong, Onaga, Opah, Opakapaka, Swordfish and Yellowfin Tuna) of fish that were caught in the North Pacific (>20oN) and commonly consumed in Hawai’i at local markets.  Information about the range and size of the fish are given in Table 1:


Levels of Radiocesium in Fish From Hawai’i

Samples of the fish tissue were freeze dried and homogenized before gamma emitting radioisotopes were measured using a gamma spectrometer by counting samples for a period of 7 days. Levels of 134Cs, because of its short half life, serve as a fingerprint of Fukushima in samples as previous sources of this human made isotope (e.g. 20th century nuclear weapons testing and the Chernobyl disaster) are sufficiently far in the past that all of the isotope has decayed away and is no longer present in the environment.  Results of the analyses are summarized in the following figure:

Fig. 1 Cesium activities in fish collected in the North Pacific in 2015 and available for consumption in Hawai’i

In 3 fish statistically significant (>95% confidence interval) but trace levels of 134Cs was detected.  Given that 137Cs/134Cs ratio in vast majority of the release from the Fukushima site was ~1 the authors were able to determine the fraction of radiocesium present in these fish owing to Fukushima versus legacy sources like atmospheric weapons testing.  Maximum radiocesium levels in the fish approached 0.7-0.8 Bq kg-1 which is more than 1,500 fold lower than conservative levels thought be a health risk set by the FDA (1,200 Bq kg-1).  Most fish had radiocesium attributable to weapons testing fallout. Fukushima radiocesium accounted for ~60% of the radiocesium detected in an Ahi measured by the authors.

Levels of Naturally Occurring 40-Potassium in Fish

Naturally occurring 40K decays with a half life of 1.25 billion years and in taken up into the tissue of marine fish.  The levels of 40K in the fish measured by the authors are summarized in the table below:

Levels of artificial radiocesium and naturally occurring 40-K in fish from Hawai’i

Activity of 40K (Bq kg-1) tended be ~100 fold higher in the fish tissue than radiocesium activities.

Effective Dose of Ionizing Radiation and Health Impact to Fish Consumers

The authors determined the impact of fish consumption on the ionizing radiation dose experienced by individuals consuming an average amount of fish per year (24.1 kg per year or 53.1 pounds per year).  The table below compares the dose in nanoSieverts per year (10-9 Sv yr-1) owing to historic and Fukushima sourced radiocesium and naturally occurring 40K in seafood.

Committed effective dose to fish consumers from artificial (human made) and naturally occurring 40-K

Converting isotope activities in the fish to dose demonstrates that 40K is responsible for ~100 times higher dose than 134Cs + 137Cs. Doses to humans from consuming the fish owing to radiocesium were 0.02–0.2 µ Sv yr-1, while doses of 6–20 µ Sv yr-1 were contributed by the natural 40K present in the same fish. These levels of radioisotopes and the calculated doses to consumers are similar to those reported by the InFORM project who have looked at Pacific salmon returning to rivers and streams in North America over the last 3-4 years. It is important to note that the bulk of ionizing radiation dose to fish consumers normally results from 210-Polonium (210Po half life 138 days) naturally present in the fish but this isotope was not measured in the Azouz and Dulai study.


Fukushima derived radioisotopes 134Cs and 137Cs were detected (at 95% confidence interval) in 3 of 13 fish caught in the North Pacific and commonly consumed by people living in the Hawaiian islands.  The radiocesium in most fish reflected contamination largely present in the North Pacific Ocean owing to atmospheric weapons testing during the last century.  The levels of radiocesium in the fish were a small fraction of the levels of naturally occurring radioisotopes like 40K.  The committed effective dose of ionizing radiation to fish consumers is dominated by the naturally occurring isotopes and do not remotely approach levels known to represent a significant or measurable health risk to human beings.  The results of this study agree with previously published research and results of the InFORM project which focuses on the impact of the Fukushima disaster on the marine ecosystem and public health in North America.

Updated – No Fukushima radiation found in 2016 Alaskan fish

Alaska Department of Environmental ConservationNo Fukushima contamination was found in any of the 14 fish Alaskan fish samples that were collected between February and September 2016, according to the Alaska Department of Environmental Conservation. The results, released on the Alaksa DEC website, show that the sampled herring, cod, and pollock, halibut, and salmon did not have any detectable levels of 131I, 134Cs (the Fukushima fingerprint radionuclide with a half-life of ~2 years) or 137Cs in the tissues.  These samples were from across Alaskan waters from Southeast to Bristol Bay and the Aleutian archipelago and the Bering Sea. Results from 2016 are similar to their results from 2015 and are part of the network of institutions monitoring for Fukushima radiation in marine waters and seafoods.

The average minimum detectable concentrations for these Alaskan samples on this gamma spectrometer were 63.7 Bq kg-1, 2.1 Bq kg-1, and 1.9 Bq kg-1 respectively for 131I 137Cs,  and 134Cs. While InFORM does not analyze for 131I, those detection thresholds for cesium are 2-3 times higher than are typical for our biotic monitoring program. This may be due to either a smaller sample size or a shorter time in the gamma spectrometer for the Alaskan samples, but the result remains that levels are well below those where intervention is needed (intervention levels for 131I = 170 Bq kg-1 and 134Cs + 137Cs = 1200 Bq kg-1 according to the US Food and Drug Administration). InFORM monitoring in 2016 found 9 salmon (out of 123) from BC and Yukon rivers with detectable levels (where the minimum detectable concentrations were less than 1 Bq kg-1) of  137Cs after a six hour detector run. These nine samples are currently being freeze-dried for an extended, 2 week long, detection run. Results from this additional analysis are expected probably mid-late spring 2017.

An interesting aspect of these 2016 Alaskan samples is that this was the first time a field-deployable gamma spectrometer has been sent by the US Food and Drug Administration to a site for local analyses of samples. Data from the spectrometer were then electronically sent to FDA scientists for analysis. The thought is that this model could be used in the event of nuclear emergency to allow for more rapid analyses of environmental samples.

Alaska DEC will continue monitoring fish samples for Fukushima radiation for at least 2017 and possibly beyond.

No Fukushima radiation found in 2016 Alaskan fish

Alaska Department of Environmental ConservationNo Fukushima contamination was found in any of the 7 fish Alaskan fish samples that were collected during February and March of 2016. The results, released on the Department of Environmental Conservation website, show that the herring, cod, and pollock sampled did not have any detectable levels of 131I, 134Cs (the Fukushima fingerprint radionuclide with a half-life of ~2 years) or 137Cs in the tissues.  These samples follow on their similar results from 2015 and are part of the network of institutions monitoring for Fukushima radiation in marine waters and seafoods. Continue reading No Fukushima radiation found in 2016 Alaskan fish

Update: InFORM Monitoring Results For Pacific Salmon Collected Summer 2015

InFORM salmon 2015 river-01
Activities of artificial radiocesium in seawater (2014-2015) and fish (2015) from the northeast Pacific Ocean measured by the InFORM project.  No increase in artificial radionuclides was detected in fish compared to those harvested in 2014.  Approximate range of relevant fish species relative to the contaminated plume of seawater are shown in hashed and dotted lines.  Figure by Dr. Jonathan Kellogg.

Measurements undertaken as part of the InFORM project to look for Fukushima derived radionuclides in fish during our second of three years of monitoring are now complete on an additional 156 fish. Sockeye salmon (Oncorhynchus nerka) and Steelhead Trout (Oncorhynchus mykiss) (as well as some Chinook (Oncorhynchus tshawytscha) and Pink (Oncorhynchus gorbuscha) Salmon) were caught off the west coast of Canada in Summer 2015 as they were returning to their home streams and rivers up and down the coast of British Columbia. Samples of fish were obtained with the cooperation and collaboration of the Champagne and Aishihik, ‘Namgis, Nisga’a, Selkirk, Syilix, Tahltan, Taku River Tlingit, Tr’ondëk Hwëch’in, Wet’suwet’en and Wuikinuxv First Nations. These results add to the first ~100 fish collected and analyzed in 2014.

What we have found so far:

  1. With the exception of 7 fish discussed in point 3 below individual fish were not found to have detectable levels of either 134Cs or 137Cs so average levels were calculated for all fish harvested in a given location.
  2. Similar to 2014, none of the fish from 2015 analyzed thus far were found to contain detectable levels of 134Cs a man-made radionuclide that serves as a fingerprint of the Fukushima disaster.
  3. The average level of 137Cs seen in InFORM 2015 fish samples (0.19 Bq kg-1) is similar to the level observed in the 2014 campaign (0.21 Bq kg-1).  As with 134Cs, the Fukushima disaster resulted in the release of a large quantity of 137Cs. However, 137Cs, which has a longer half-life, was already present in the Pacific Ocean prior to the Fukushima accident because of the nuclear weapons testing fallout.
    • The 137Cs levels observed in the 2015 InFORM samples represent a fraction of the Health Canada guidelines (1000 Bq kg-1) and a fraction of the radiation exposure owing to naturally occurring radionuclides Polonium-210 (210Po) and Potassium-40 (40K) which dominate the ionizing radiation dose to fish consumers.
    • While the average 137Cs concentration remained nearly identical from 2014 to 2015, 7 individual fish (out of 156) have shown a detectable level of 137Cs (ranging from 0.27 to 0.60 Bq kg-1) while individual fish from 2014 were below detection limit. Because no 134Cs was detected in these fish it is not possible to say whether detectable 137Cs can be attributed to Fukushima contamination or simply normal variability in contamination owing to nuclear weapons testing fallout.
  4. What this means is that radioactivity from the Fukushima meltdowns has not been detected in the InFORM fish samples caught in BC waters as of summer 2015.
  5. Neither the 137Cs present in the fish nor the naturally occurring radioisotopes in fish represent a measurable health risk to consumers in Canada.

Measurements of radioactive elements in these fish and from previous years are available for download at the Government of Canada Open Data website. Continue reading Update: InFORM Monitoring Results For Pacific Salmon Collected Summer 2015