by WHOI Media Relations
Published 2 October 2017
Scientists have found a previously unsuspected place where radioactive material from the Fukushima Dai-ichi nuclear power plant disaster has accumulated—in sands and brackish groundwater beneath beaches up to 60 miles away. The sands took up and retained radioactive cesium originating from the disaster in 2011 and have been slowly releasing it back to the ocean. Continue reading Scientists Find New Source of Radioactivity from Fukushima Disaster
By Jay T. Cullen
The purpose of this post is to conduct a thought experiment to arrive at (I hope) a useful estimate of how much radioactive contamination might occur if North Korea detonates a thermonuclear weapon in the lower atmosphere over the North Pacific Ocean. There are a significant number of unknowns, not the least of which is the fundamental uncertainty as to whether the rogue nation has successfully tested a Teller-Ulam style thermonuclear weapon or not. I explain my assumptions and compare the resulting global release of radioisotopes that represent a radiological health concern from such a test to the amounts recently released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) disaster, the Chernobyl disaster and aggregate atmospheric weapons testing in the last century. I invite comments and an accounting of the approach used here and how it might be improved. Continue reading North Korean Atmospheric Thermonuclear Test: How much contamination can we expect?
The purpose of this post is to report on a recently published, peer-reviewed study that investigated the levels of Fukushima derived contamination in migratory Pacific predators. The post is part of an ongoing effort to inform interested members of the public what the scientific community is finding about the impact of the Fukushima Daiichi Nuclear Power Plant (FDNPP) disaster on the environmental and human health. Madigan and colleagues looked for radiocesium (134Cs, half life ~ 2 years; 137Cs, half life ~30 years) in a variety of large, predatory organisms in the North Pacific Ocean between 2012 and 2015. Their results were as follows:
These direct measurements of contamination levels in marine predators suggest that assuming that Pacific organisms will accumulate detectable FDNPP contamination is unwise. Similarly, anxiety and speculation about the dangers of radiocesium bioaccumulation in the face of such data seems unfounded.
Between 2012 and 2015 a total of 91 different organisms from a variety of predatory marine groups were sampled and analyzed for the presence of radiocesium contamination and naturally occurring 40K. The human made isotope 134Cs, with its relatively short ~2 year half life, serves as a fingerprint of FDNPP contamination as all other human sources are sufficiently distant in the past to have completely decayed away in the environment. Organisms sampled and their radioisotope content are reported in the following table:
With the exception of a single olive ridley sea turtle no detectable (<0.1 Bq kg-1 dry weight) trace of FDNPP 134Cs contamination was found. Levels of 137Cs found in the organisms were similar to levels measured pre-Fukushima. In addition, the 137Cs levels were less than 0.2% of US FDA levels of concern (370 Bq kg-1 wet weight) and less than 0.05% of US FDA derived intervention levels (1200 Bq kg-1 wet weight). Simply stated levels in these organisms would have to be >1600-fold higher to be designated unfit for market. The levels and ionizing radiation dose to consumers from naturally occurring 40K dwarfed those from FDNPP radiocesium. Radiocesium derived ionizing radiation doses were <1% of those from 40K. Neither the doses from 40K or cesium isotopes approached, even remotely, those known to affect the health of the organisms or consumers of these organisms.
These results are consistent with those of the Integrated Fukushima Ocean Radionuclide Monitoring (InFORM) project. Ongoing, scientifically rigorous, monitoring of the marine environment provides the best evidence with which to gauge the risk that the FDNPP meltdowns represent for marine and public health here in North America.
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:
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:
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:
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.
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:
Activity of 40K (Bq kg-1) tended be ~100 fold higher in the fish tissue than radiocesium activities.
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.
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.
Did you enjoy your trip? If you were alive during the Fukushima meltdown in 2011, you received an extra dose of radiation equal to that received on a roundtrip flight from Vancouver to Tokyo. This is the result according to research presented by Nikolaos Evangeliou of the Norwegian Institute for Air Research at the annual meeting of the European Geophysical Union earlier this year.
Continue reading The fate of atmospheric Fukushima radiation
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