Tag Archives: Cesium

Update: Fukushima Derived Contamination in Pacific Surface Water Up Until 2017

Northeast subarctic Pacific from the deck of the Canadian Coast Guard Ship J.P. Tully in September 2

By Jay T. Cullen

The purpose of this post is to summarize a recently published, peer-reviewed study that documents levels of Fukushima derived contamination in surface waters of the Pacific Ocean. This post is part of an ongoing series aimed at communicating scientifically derived information about the impact of the disaster on marine environmental and public health. Michio Aoyama and colleagues measured the activity of Cesium-137 (137Cs, half life ~30 years) and Cesium-134 (134Cs, half life ~ 2 years) in seawater collected from the western Pacific Ocean including waters off the coast of Fukushima Prefecture from 2011-2017. They found the following:

  • Contamination decreased dramatically and rapidly in waters offshore of the Fukushima Daiichi Nuclear Power Plant (FDNPP) from maximum values of ~3000 Becquerel per cubic meter (Bq m-3) of seawater in 2011 to values  in 2015-16 of ~2-3 Bq m-3. This precipitous decline is consistent with the ongoing but relatively low rates of release of radionuclides from the site compared to the bulk of contamination that was released in March-April 2011.
  • Levels of 137Cs close to FDNPP now are similar to levels of contamination present there before the disaster occurred (1.5-2 Bq m-3) owing to atmospheric nuclear weapons testing in the middle of the 20th century.
  • Levels in the western Pacific were around 1-7 Bq m-3 in 2011-2012 but stabilized at lower values in 2017.

Levels being measured in nearshore and offshore waters in the western Pacific near to Japan do not approach levels known to represent a credible risk for ocean or public health. These results in the western Pacific are consistent with what the Integrated Fukushima Ocean Radionuclide Monitoring (InFORM) project is finding in the eastern Pacific off of North America.

Aoyama and others recently published their study in the Journal of Environmental Radioactivity. The collected and analyzed surface seawater for the presence of radiocesium isotopes between 2011 and 2017 in waters of the western Pacific in the following locations:

AoyamaetalFig1.jpg
Boundaries of areas (boxes) sampled by Aoyama et al. (2018) in the western and central Pacific Ocean.

​The activity of 137Cs and 134Cs in Bq m-3 with time that they found are summarized in the following figure:

1-s2.0-S0265931X17307750-gr2_lrg.jpg
Long term trends (2011-2017) in radiocesium activity in boxes defined in the first figure. Solid blue squares are 137Cs activity concentration and open red circles represent 134Cs.

The researchers found that in Box 2 (closest to the FDNPP) contamination in surface waters offshore were highest in early 2011 coincident with the largest releases from the site in March-April of that year when the vast majority of radionuclides were released to the atmosphere and directly to the ocean.  Values dropped dramatically so that by 2014-2016 levels were ~3 Bq m-3 and similar to levels of contamination measured before the disaster occurred owing to nuclear weapons testing that occurred in the 1950s-60s. Note that the concentrations of 134Cs diminish relative to 137Cs, and the red symbols on the figure diverge from the blue symbols, because 134Cs has an ~2 year half life and is decaying away from the environment much more rapidly. Indeed, it is becoming increasingly challenging analytically to detect Fukushima 134Cs in environmental samples.  Contamination farther offshore in Boxes 4-6 indicate that maximum levels of contamination from Fukushima approached by did not exceed 200 Bq m-3 in 2011 and are now ~2-3 Bq m-3.

Based on best estimates of how much radiocesium was released from FDNPP in March-April 2011 the authors used a model of the water circulation and mixing in the Pacific to predict the levels and movement of Fukushima 134Cs in the Pacific from April 2012 until October 2016.  The results of the modeling study are summarized in the following figure:

1-s2.0-S0265931X17307750-gr3b_lrg.jpg
Horizontal distribution of 134Cs from Fukushima for the period April 2012 to October 2016. Open circles represent observations/measurements of 134Cs while shading reflects model results.

What the model and observations indicate is that the bulk of contamination from the site went into the Pacific Ocean in 2011 and that rates of release from the site after that time are very small in comparison. Most of the Fukushima contamination is now in the eastern Pacific near to North America and that levels in behind the main body of contamination are difficult to detect.  Similarly, the lack of appreciable 134Cs and 134Cs/137Cs activity ratios close to FDNPP indicate that there is little evidence for ongoing fission in the reactors at the site as is commonly speculated by those with little scientific training.  The levels the scientific community is measuring close to FDNPP and those expected and measured in waters close to North America do not represent a significant risk to the marine ecosystem or public health.

The Fukushima InFORM project will continue its monitoring activities in the eastern Pacific until Spring 2019.

Continue reading Update: Fukushima Derived Contamination in Pacific Surface Water Up Until 2017

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How much Fukushima contamination is in migratory Pacific fish?

Proposed migration pathways of North Pacific predators.

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:

  • Fukushima derived 134Cs could not be detected in any of the organisms with the exception of a single olive ridley sea turtle with trace levels (0.1 Bq kg-1 dry weight)
  • Levels of 137Cs varied in the organisms but were generally unchanged compared with levels measured in organisms prior to the FDNPP disaster (pre-2011)
  • Levels of 137Cs were roughly 10 to 100-fold lower in the organisms than levels of naturally occurring Potassium-40 (40K)
  • Neither the levels of radiocesium or 40K approach levels known to represent a significant health risk to the animal or human consumers

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:

Table1_Madiganetal2017.png

 

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.

Update: 2016 Sampling of North American Pacific Kelp Finds No Signature of Fukushima Contamination

By Jay T. Cullen

Wikipedia image by Ed Bierman from Redwood City, USA of diver exploring a coastal kelp forest

 

The purpose of this post is to report the most recent and last results from Kelp Watch 2015, a program dedicated to monitoring for Fukushima derived contamination along the Pacific Coast of North America.  This post is the latest in a series dedicated to public outreach and dissemination of scientifically derived information about the impacts of the Fukushima Dai-ichi disaster on the health of the North Pacific Ocean ecosystem and health of North American residents. Results from the fifth sampling period (March 2 through June 3 2016)  were released on July 15, 2016 and can be found here. As with previously reported results here, here, here, here, and here no radioactive isotopes from Fukushima were detected in kelp growing at sampling sites along our Pacific coast or elsewhere in the Pacific (see sampling sites).  The absence of 134Cs in kelp suggests that ocean transport of Fukushima contamination had yet to reach persistently high enough levels in North American coastal water to bioaccumulate in kelp. The levels of Fukushima derived contamination in kelp in 2016 will not pose a significant risk to the health of the kelp or other species, including humans, which rely on them as a foodstuff.

Continue reading Update: 2016 Sampling of North American Pacific Kelp Finds No Signature of Fukushima Contamination

Most radioactive caesium fallout on Tokyo from Fukushima accident was concentrated in glass microparticles

by Goldschmidt Conference
Originally published by EurekAlert
26 June 2016

New research shows that most of the radioactive fallout which landed on downtown Tokyo a few days after the Fukushima accident was concentrated and deposited in non-soluble glass microparticles, as a type of ‘glassy soot’. This meant that most of the radioactive material was not dissolved in rain and running water, and probably stayed in the environment until removed by direct washing or physical removal. The particles also concentrated the radioactive caesium (Cs), meaning that in some cases dose effects of the fallout are still unclear. These results are announced at the Goldschmidt geochemistry conference in Yokohama, Japan. Continue reading Most radioactive caesium fallout on Tokyo from Fukushima accident was concentrated in glass microparticles