Category Archives: Sample type

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:

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:

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:

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.


Monitoring Fukushima Contamination in Pacific Salmon and Soil in British Columbia

Beautiful sockeye salmon photographed by Eiko Jones.

Seven years on, since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, it is useful to start to bring together information from scientific studies of the impact of the contamination on the North American environment and its people. I recently wrote to communicate the most recent results of the Integrated Fukushima Ocean Radionuclide (InFORM) project. This post summarizes a recently published, peer-reviewed paper by colleagues lead by Dr. Krzyzstof Starosta of Simon Fraser University in BC working in parallel to InFORM. The open access paper was published in the Canadian Journal of Chemistry and was recently recognized with the  “Best Paper Award” by the journal. They studied the concentrations of anthropogenic radioisotopes (134Cs half-life ~2 years, 137Cs half-life ~30 years) and naturally occurring radioisotope 40K (half-life 1.25 billion years) in Pacific salmon (sockeye, chum and chinook) and in soil and roof debris collected in southern British Columbia to determine the local impact of the FDNPP accident.  Their results were as follows:

  • 134Cs (a fingerprint of Fukushima contamination) was not detected in any of the salmon samples
  • 137Cs was not detected in sockeye or chum salmon but was detected in all chinook with an average level of ~0.2 Bq kg-1
  • Annual dose from artificial radionuclides to a human consumer of chinook salmon was estimated to be ~1/300 of the dose owing to naturally occurring isotopes in the fish and ~1/30,000 of the annual dose experienced for all other natural sources by the average Canadian
  • Most soil samples contained 134Cs and 137Cs which was delivered to the region by atmospheric transport shortly after the disaster
  • Levels of Fukushima radioisotopes in soil did not approach levels known to be harmful to living organisms

Consistent with other monitoring in the area the results of the study indicate that given the trace levels of contamination present the impact of the FDNPP accident on ecosystem and public health in North America will be insignificant. Continue reading Monitoring Fukushima Contamination in Pacific Salmon and Soil in British Columbia

IAEA Affirms Japan’s Fukushima-Related Radioactivity Monitoring

by Tim Hornyak
11 October 2017
Originally published by Eos, a periodical of the American Geophysical Union

Laboratories outside Japan have validated the results. Marine radioactivity levels from the nuclear disaster have fallen, but questions remain years after the meltdown. Continue reading IAEA Affirms Japan’s Fukushima-Related Radioactivity Monitoring

Scientists Find New Source of Radioactivity from Fukushima Disaster

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

Non-native species from Japanese tsunami aided by unlikely partner: plastics

by Mark Floyd
Originally published by Oregon State University
28 September, 2017

NEWPORT, Ore. – A new study appearing this week in Science reports the discovery of a startling new role of plastic marine debris — the transport of non-native species in the world’s oceans. Continue reading Non-native species from Japanese tsunami aided by unlikely partner: plastics