Category Archives: Marine Life

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:

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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:

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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:

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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.

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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.

Conclusion

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.

Radioactive Refuges

by Ashley Braun
Originally in Hakai Magazine
Published: 16 Jan 2017

A heavily-exploited Japanese fish found sanctuary after the 2011 Fukushima earthquake.

You won’t catch any three-eyed mutant fish off the coast of Japan these days, but in the wake of the 2011 earthquake and tsunami you also won’t have a problem finding flounder, the latest species to suddenly flourish in a nuclear disaster zone after humans have been pushed away.

link to full article here.

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

Fukushima contamination of Pacific Salmon: Lessons learned in the Atlantic Ocean

By Jay T. Cullen

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Atlantic salmon (Salmo salar)

The purpose of this post is to present measurements of artificial radionuclides in wild Atlantic salmon (Salmo salar) made in 1990’s and reported in a peer reviewed paper published in the Canadian Journal of Fisheries and Aquatic Sciences by Tucker and colleagues in 1999. This post is part of an ongoing series dedicated to communicating the results of scientific research aimed at The paper combines an understanding of bioconcentration of the artificial radionuclide 137-cesium (137Cs half life ~30 years) in marine food webs with quality measurements of the contaminant in salmon that spent their lives in the North Atlantic Ocean.  The North Atlantic at the time had a strong east to west gradient in 137Cs concentrations in seawater with >10 Bq m-3 in the east owing to spent nuclear fuel reprocessing in Europe and the recent impact of the Chernobyl disaster and <1.5 Bq m-3 in the west near to Canada.  Salmon returning to the Ste. Marguerite River in Canada had a wide range of radiocesium in their bodies which reflected the entire range of values seen in fish harvested across the Atlantic Ocean.  The results indicate that the migration routes of these salmon extended all the way across the Atlantic to the Irish and Norwegian seas.  The study is relevant to understanding the impact of the Fukushima disaster on radiocesium levels in Pacific salmon as the maximum levels of contamination of seawater we see in the central and eastern North Pacific is lower than the maximum levels studies by Tucker and colleagues.  Given this fact we would predict that levels of Fukushima derived contaminants in Pacific salmon and the health risk associated with the consumption of these fish will be correspondingly lower.  Thus far the salmon monitoring results from the Integrated Fukushima Ocean Radionuclide Monitoring (InFORM) project are in keeping with the scientific communities understanding of 137Cs bioconcentration in fish outlined in the Tucker study and references therein.


Radionuclides in Atlantic Salmon: Bioconcentration and migration routes

When I was an undergraduate student at McGill University in Montreal, Dr. Joe Rasmussen (he is now at the University of Lethbridge in Alberta) headed up a freshwater ecology group that used radionuclides to understand energy and contaminant cycling in the aquatic environment. I remember learning about gamma spectrometry and the processing of samples for radionuclide determinations through conversations with his graduate students.  Their work made an impression on me and highlighted the utility of radioisotopes for understanding rates of processes and pathways of contaminant transport in natural waters.  The paper I will summarize here roughly dates to my time at McGill and is the work of Strahan Tucker who along with Marc Trudel works for Fisheries and Oceans Canada at the Pacific Biological Station in Nanaimo BC and part of the team of scientists working on the InFORM project.  Tucker and colleagues exploited the east to west gradient in 137Cs activity in seawater in the North Atlantic to determine how much radiocesium was present in Atlantic salmon returning to the Ste. Marguerite River in Canada and by extension where they had migrated and fed during their growth and development.  The figure below shows the high levels of seawater 137Cs contamination in the Irish Sea and eastern Atlantic compared to the western Atlantic near Canada owing to release of the isotope from fuel reprocessing plants in the UK and France and deposit of Chernobyl derived contamination in 1986.

Fig1Tuckeretal1999

137Cs distribution (Bq m–3) in waters of the North Atlantic with levels >10 in marginal seas of the eastern Atlantic and 0-1.5 in waters of the west near to Canada.

Given that salmon tend to bioconcentrate radiocesium about 130 times relative to the seawater in which the live (through the prey they consume) the predicted range in 137Cs in salmon from the eastern Atlantic would be 1.3 — 4.0 Bq kg-1 while fish living in the less contaminated western Atlantic would have 0.15 — 0.65 Bq kg-1.  The range of 137Cs measured by Tucker and colleagues in salmon returning to the St. Marguerite River in Quebec, Canada, predicted ranges given seawater activities in the figure above and activities in fish harvested from different areas of the North Atlantic are summarized in the figure below.

Fig1bTuckeretal1999

Frequency distribution of 137Cs concentrations (Bq kg–1) in Atlantic salmon from the Ste. Marguerite River, Que. Tissue samples were obtained fish caught in the sport fishery during the summers of 1995 (n = 33) and 1996 (n = 28) and measured by gamma spectrometry. Dashed vertical lines denote the expected range in 137Cs concentrations in salmon based on a mean bioaccumulation factor of 130 from waters in the North Atlantic outlined in the color bar above (water 137Cs concentrations color coded as in the first figure). Horizontal lines denote the observed ranges in 137Cs concentrations in salmon and other fish (cod, whiting, haddock, hake, mackerel, and plaice) caught in those same waters.

The range of activities found in the migratory Atlantic salmon is similar to the range seen for other species of fish across the North Atlantic and suggests that almost half of the Ste. Marguerite salmon spent their lives feeding in waters near to Norway and the UK.  This is an amazing result and suggested that more fish spend more time in the eastern Atlantic than was thought at the time.  The levels seen in the salmon agree well with predictions based on seawater activities and the expected bioconcentration factor in the food web to salmon of ~130.  You can read more about bioconcentration of radionuclides and concentration factors in marine organisms in one of my earlier posts here.

What does this tell us about expected contamination from Fukushima in Pacific Salmon and health risks to consumers?

The maximum seawater concentration of 137Cs in the central and eastern North Pacific we have measured through the InFORM project is about 7 — 10 Bq m-3. Given the bioconcentration expected from previous studies of salmonid species like Tucker and colleagues above we might expect maximum contamination levels in Pacific salmon of ~ 1.3 Bq kg-1 wet weight.  The range of values we have detected in Pacific species returning to British Columbia rivers and streams since the Fukushima disaster in 2011 is ~0.20-0.60 Bq kg-1 suggesting that these fish have consumed prey and lived in waters with seawater activities <10 Bq m-3.  At present the levels of Fukushima derived contamination do not lead to ionizing radiation doses to consumers that remotely approach the dose attributable to naturally occurring radioisotopes like 40K and 210Po.  The ionizing radiation dose from the naturally occurring isotopes do not approach levels where significant risks to the health of consumers are to be expected.  Given what the scientific community understands about bioconcentration of the most radiologically significant isotopes released from Fukushima and measured and forecast levels of these isotopes in the expansive North Pacific the community has confidence that levels in Pacific salmon species will not approach levels were risk to consumers will become significant. The InFORM project will continue to monitor contamination levels in seawater and the marine biota to provide accurate information and useful, scientifically derived assessment of risk to the public.