Category Archives: Seawater

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.

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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

Citizen Scientists Sampling for Fukushima Contamination in Port Renfrew BC (August 2016)

by Jay T. Cullen

Last evening I spoke at the monthly meeting of Surfrider Vancouver Island, one of InFORM’s non-governmental organization partners, to provide them with an update on our most recent results and progress.  Surfrider VI helps to coordinate our citizen science volunteers who sample coastal seawater every month to monitor for Fukushima derived contamination along our beaches from Victoria in the south to Lax Kw’alaams in the north of BC.  Surfrider VI is primarily responsible for sampling in Port Renfrew BC which is on the southwest coast of Vancouver Island.

I was pleasantly surprised by Lynn Wharram (Volunteer Coordinator and Combing the Coast BCU team lead) who had produced a short video chronicling her family collecting InFORM’s August 2016 seawater sample from the dock near the Port Renfrew Hotel.  You can watch the video below.

You can read more about our citizen science program methods here, our NGO partners here , and our citizen science volunteers here. Thanks again to our volunteers and to Surfrider VI for all the work they do. Go and check them out if you are interested in ocean health (and surfing).

 

Open Access Review of Fukushima Radionuclide Source Term, Fate and Impact in Pacific

Fig1Buesseleretal2017.png
Schematic of Fukushima Daiichi sources of 137-Cs from Buesseler et al. (in press). Atmospheric fallout (1) and direct ocean discharges (2) represent total petabecquerels (PBq = 10^15 Bq) released in the first month of the meltdowns. Groundwater fluxes (3) and river runoff (4) are approximate ranges for the first year in terabecquerels (TBq = 10^12 Bq), a unit 1,000 times smaller than the PBq used for fallout and direct discharge. Details on source term estimates can be found in the paper (http://www.annualreviews.org/doi/abs/10.1146/annurev-marine-010816-060733). (Buesseler et al. 2017)

by Jay T Cullen

The purpose of this post is to bring to the attention of readers here a review of the available measurements and science based investigations of the Fukushima Daiichi Nuclear Power Plant (FDNPP) and its impact on the Pacific Ocean ecosystem and public health. This post is part of an ongoing effort to summarize scientifically rigorous information about the disaster for interested readers. The new paper is a product of a working group on radioactivity in the ocean convened by the Scientific Committee on Ocean Research (SCOR) an international non-governmental non-profit organization. I highly recommend this paper for anyone who wishes to better understand what the international scientific community has found about the marine release, fate and impact of FDNPP-derived radionuclides in the marine environment.  The working group was made up of 10 experts from 9 different countries, including Japan, and published the open access paper in Annual Reviews.  The main findings of the review were as follows:

  • The amount of 137Cs released from the plant was ~50-fold less than the fall out from nuclear weapons testing in the 20th century and ~5-fold lower than that released from Chernobyl in 1986. Total releases from Fukushima are similar to the discharges of 137Cs from the nuclear fuel reprocessing plant Sellafield in the UK
  • Initial releases in the weeks to months after the disaster which began on March 11, 2011 dwarf those from aggregated ongoing releases from the plant site
  • The majority of radionuclide releases ended up in the Pacific Ocean with most deposition and input occurring close to the FDNPP
  • Current range of estimates of the total 137Cs ocean source term are 15-25 PBq (PBq = 1015 Becquerel where a Bq is one nuclear decay event per second). While many other radionuclides were released from FDNPP, the most likely isotopes to represent a health risk to the marine ecosystem and public are those of Cs given their longer half-lives for radioactive decay (134Cs = ~2 yrs; 137Cs = ~30 yrs) and higher relative abundance compared to other isotopes of concern in the FDNPP source term
  • Because Cs is very soluble it rapidly dispersed in the ocean after the disaster given mixing, transport and dilution by ocean currents.  Peak levels of 137Cs occurred close to the plant in 2011 where activity concentrations near FDNPP was tens of millions of times higher than before the accident. By 2014 137Cs concentrations in the central North Pacific was about six times the remaining weapons testing fallout and about 2-3 times higher than prior fallout levels in the northeast Pacific near to North America. Most of the fallout remains concentrated in the top few hundred meters of the ocean. Measurements being made by the Fukushima InFORM project indicate that maximum 137Cs levels off the North American coast are likely to occur this year before declining to levels associated with background nuclear weapon testing before the accident by about the end of this decade
  • There are unlikely to be measurable effects on marine life with the exception of coastal areas very close to FDNPP immediately after the disaster. Monitoring of fish species in Fukushima Prefecture show that about 50% of samples in coastal waters had radiocesium levels above the Japanese 100 Bq kg-1 limit, but that by 2015 this had dropped to less than 1% measuring over the limit. High levels continue to be found in fish around and in the FDNPP port
  • Given levels in seawater and marine organisms measurable impacts to human health through contact with the ocean and the consumption of seafoods are very unlikely

There are many informative graphics and moderately technical summaries of available studies found in the new paper.  The authors highlight the difficulty of monitoring radionuclides in the ocean  given the dynamic nature of the sea and logistical challenges presented by the temporal and spatial scales and low levels of FDNPP derived contamination going forward.  In addition to providing ongoing assessments of risk to the environment from the disaster it is likely that useful information about ocean circulation will be obtained through continued monitoring efforts.

Fukushima Radionuclides in Pacific: Doses to Japanese and World Public Unlikely to Cause Health Damage

By Jay T. Cullen

The purpose of this post is to summarize a the most recent, peer reviewed scientific study to examine the likely impact of Fukushima contamination of the North Pacific on human health. The blog is part of a continuing series that seeks to communicate the results of scientific studies aimed at determining the impact of the triple meltdowns at the Fukushima Dai-ichi nuclear power plant (FDNPP) on ecosystem and public health. Povinec and Hirose’s recent paper in Scientific Reports examined the variation in Fukushima derived 90-Strontium (90Sr half life 28.8 years), 134-Cesium (134Cs half life ~2 years) and 137-Cesium (137Cs half life ~30 years) in seawater and biota offshore of the FDNPP and in the northwest Pacific. These isotopes are most likely to represent radiologically health risks to consumers of Pacific seafood given their propensity to concentrate in organisms and, in the case of 90Sr and 137Cs, their longevity in the environment. Doses to the Japanese and world population were estimated and compared to doses attributable to naturally occurring isotopes present in food. Doses from food caught in coastal waters right next to the FDNPP to 20 km offshore were similar to doses from naturally occurring isotopes (primarily 210Po) while doses from the consumption off fish caught in the open northwest Pacific were much lower than natural doses. In each case the individual doses are well below levels where any negative health effects would be measurable in Japan or elsewhere. Continue reading Fukushima Radionuclides in Pacific: Doses to Japanese and World Public Unlikely to Cause Health Damage