Category Archives: NE Pacific

Cesium, Fukushima, Japan, N Pacific, NE Pacific, NW Pacific, Peer Reviewed, Seawater

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

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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.

Algae, Biota, Cesium, Monitoring, NE Pacific

KelpWatch 2015 Monitoring: No Fukushima derived contamination May – June ’15

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Bull Kelp, or Nereocystis luetkeana
Bull Kelp (Nereocystis luetkeana)

By Jay T. Cullen

The purpose of this diary is to report the most recent results of Kelp Watch 2015, a program dedicated to monitoring for Fukushima derived contamination along the Pacific Coast of North America.  New results from the fourth sampling period (May 4 through June 10 2015)  were released on Dec. 8, 2015 and can be found here. As with previously reported results here, here, here and here no radioactive isotopes from Fukushima were detected in kelp growing at sampling sites along our Pacific coast.  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 scientific community expects that levels of contamination rise in coastal waters as predicted by measurements and models in the coming year Kelp Watch 2015 will help to track the arrival of the plume in time and space. Continue reading KelpWatch 2015 Monitoring: No Fukushima derived contamination May – June ’15 →

British Columbia, Cesium, Monitoring, NE Pacific, Oceanic, Peer Reviewed, Seawater

Observing the Arrival of the Fukushima Contamination Plume in North American Coastal Waters

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By Jay T. Cullen

@JayTCullen and @FukushimaInFORM

This short blog summarizes an open access paper published today reporting results from a Canadian monitoring program tasked with documenting the arrival of ocean borne Fukushima contamination along the North American Pacific coast. This diary is part of an ongoing effort to communicate the best science available on the impacts of the Fukushima Dai-ichi meltdowns on the environment. High quality measurements to look for Fukushima derived radiocesium were made in seawater in the North Pacific and Arctic Oceans from 2011 to early 2014. The authors concluded that:

  1. Fukushima derived radiocesium was first detected 1500 km west of British Columbia Canada in June 2012
  2. Contamination was detected on the continental shelf (near coastal waters) in June 2013
  3. By February 2014 Fukushima radiocesium was present at levels similar to preexisting weapons testing derived 137-Cs
  4. The timing of the arrival and levels of radiocesium in the contaminated plume are in reasonable agreement with existing ocean circulation model predictions
  5. These same models predict that total radiocesium levels from weapons testing fallout and Fukushima will likely reach maximum values of ~3-5 Becquerel per cubic meter (Bq m-3 of seawater in 2015-2016 and then decline to fallout background level of ~1 Bq m-3 by 2021
  6. Fukushima will increase northeastern Pacific water to levels last seen in the 1980’s but does not represent a threat to environmental or human health

Continue reading Observing the Arrival of the Fukushima Contamination Plume in North American Coastal Waters →

British Columbia, Marine Life, NE Pacific, Peer Reviewed

Study Identifies Pathogen Responsible For Sea Star Mass Die Offs Along Pacific Coast

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By Jay T. Cullen

Sea star with Sea Star Wasting Disease photographed by the author at Botanical Beach near Port Renfrew BC in July 2014.

This diary summarizes a newly published paper by Hewson and colleagues in Proceedings of the National Academy of Sciences of the USA which investigated the cause of sea star die offs along the west coast of North America. This diary is part of series dedicated to summarizing scientific research on the impact of the triple meltdowns at the Fukushima Dai-ichii nuclear power plant on the North Pacific Ocean and the health of residents of North America. Northeast Pacific sea stars have experienced a mass die off recently and have disappeared from certain coastal ecosystems as a result. The Hewson et al. paper presents evidence that the cause of the wasting disease can be transmitted between affected to healthy individuals. The disease-carrying agent is virus sized and likely sea star-associated densovirus (SSaDV) which is found in greater numbers in diseased versus healthy sea stars. They also detected SSaDV in museum specimens of sea star dating from 1942 indicating that the virus has had a long term presence along the North American west coast.

There have been many speculative news items which have linked the release of radionuclides from Fukushima to the North Pacific Ocean to the most recent outbreak of sea star wasting which is occurring in west coast intertidal habitats. This is despite the fact that, for example, Fukushima derived radionuclides have still yet to be detected in coastal seawater collected up and down the North American Pacific coast.

Beginning in June 2013 massive numbers of sea stars have succumbed to sea-star wasting disease (SSWD) whereby they rapidly deteriorate, losing limbs, and turn into piles of slime. SSWD is an old term used to describe similar outbreaks of wasting that have occurred since at least 1979. The geographic extent and number of species impacted by the current SSWD outbreak is unprecedented. Affected individuals present with behavioural changes, lethargy, deflation, limb curling and loss, lesions and death. Very few individuals with symptoms are observed to recover.

Photographs of SSWD-affected stars (A) asymptomatic P. helianthoides, (B) symptomatic P. helianthoides, and (C) symptomatic P. ochraceus. Disease symptoms are consistent with loss of turgor, loss of rays, formation of lesions, and animal decomposition. (D) Map showing occurrence of SSWD based on first reported observation. (E) Transmission electron micrograph of negatively stained (uranyl acetate) viruses extracted from an affected wild E. troschelii from Vancouver . The sample contained 20–25-nm diameter nonenveloped icosohedral viral particles on a background of cellular debris (primarily ribosomal subunits) and degraded viral particles of similar morphology.

Hewson and colleagues examined affected and asymptomatic sea stars to demonstrate that an infective agent was responsible for SSWD. To do this they took homogenized SSWD affected sea stars and administered an inoculate or a heat killed inoculate of virus size containing filtrate to tanks containing healthy individuals. Results of these experiments indicate that heat killed inoculates did not lead healthy individuals to develop SSWD while inoculates with potentially live viral particles lead to SSWD symptoms in the previously healthy population. Previously healthy sea stars had very low loads of a virus callled Sea Star-Associated Densovirus (SSaDV) while after developing symptoms much higher amounts of SSaDV were found in the sea stars.

(A) Proportion of stars remaining asymptomatic after inoculation with control (heat-killed) or virus-sized fraction (VSF) of asteroid homogenates in first (Expt 1) and second (Expt 2) challenge. (B) Change in SSaDV load between initiation of viral challenge and termination of experiment (i.e., animal expiry in live challenge or euthanasia of control animals). Note difference in scale.
The authors then looked for the virus in asymptomatic and SSWD affected individuals in the wild finding that affected individuals were about 3 times more likely to be virus carrying than asymptomatic individuals. The virus was also found in plankton, sediments and other echinoderms. The presence of the virus in plankton and in filtration media of public aquaria affected by SSWD is consistent with observations that the disease could spread through ocean currents between infected and uninfected areas of the coast.

The authors conclude by pointing out that the spread of SSWD along our coast is most consistent with an infectious agent. Based on their observations and laboratory experiments this agent is most likely SSaDV which has been present along the coast for at least 72 years. Fukushima in not mentioned once in the article as there is no scientific evidence to relate SSWD to the trace concentrations of Fukushima derived radionuclides present offshore.

The authors identify outstanding questions as follows:

How exactly (by what mechanism) does SSaDV kill sea stars?
Are there other microbial agents involved in the wasting/death process?
What triggers outbreaks of SSWD?
How will the absence of important predators like sea stars affect the marine ecosystem along our coast?

The study highlights the increasingly recognized importance of marine viruses in helping to shape community structure and ecosystem dynamics in the ocean.

Cesium, Model, N Pacific, NE Pacific, NW Pacific, Peer Reviewed

Authors Lower Fukushima Cesium in North Pacific By Order of Magnitude

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By Jay T. Cullen

Introduction

One of the goals of the InFORM project is to make measurements of radionuclides in the North Pacific Ocean to determine maximum activities that will determine impacts on the marine ecosystem and residents of the west coast. The purpose of this post is to bring to the attention of readers a recently published correction to a prominent model that predicts the activity of Fukushima derived Cesium-137 (137-Cs, half life ~30 years) in seawater of the North Pacific. The diary is part of an ongoing series aimed at discussing research addressing the impact of the Fukushima nuclear disaster on the health of the North Pacific Ocean and inhabitants of North America’s west coast. Predictions of a model by Rossi and colleagues published in Deep-Sea Research in 2013 of the evolution of the plume of seawater contaminated by the Fukushima triple meltdowns are an order of magnitude too high. Rather than a range of ~1-30 Bq/m^3 reported previously maximum activities off the west coast of North America are likely to be ~3 Bq/m^3 or about more than 25 times lower than maximum activities measured in the Pacific in the mid-20th century resulting from atmospheric weapons tests. These activities are not likely to represent significant radiological health risks to the North Pacific ecosystem or residents of the North American west coast.

A paper by Rossi et al. (2013) used a Lagrangian model to predict the temporal and spatial evolution of the seawater plume contaminated by the Fukushima nuclear disaster beginning in March 2011. The model predicted a range of 10-30 Bq/m^3 137-Cs in waters off the coast of North America at 49 degrees North latitude as demonstrated in the figure shown below:

Activities of 137-Cs predicted by the Rossi et al. (2013) model on the continental shelves of North America at two latitudes and off Hawaii over time.

This model predicted higher maximum 137-Cs activities in seawater in the North Pacific compared with a similar model published by Behrens et al. (2012) that had maximum activities off of North America reaching only ~1-2 Bq/m^3.

Recently, after comments from Professor Michio Aoyama of Japan, Rossi and colleagues recognized an error in their model and have published a correction to their 2013 study here. The error resulted in a factor of 10 overestimation of maximum activities of 137-Cs in the Pacific such that maximum 137-Cs off N. America will likely be between 1 and 3 Bq/m^3. The corrections to the model do not affect the conclusions of the study and results from the 2013 study are easy scaled to the more accurate values given the Langrangian approach used by the authors in the original work.

The figure below shows the time evolution of the plume at various latitudes along the international date line and compares the model output with measurements made by Aoyama et al. (2013) along the international dateline at about 40 degrees N in 2012.

Activities of 137-Cs predicted by the Rossi et al. model along the international dateline in the N. Pacific over time at various latitudes.

The factor of 10 lower activity correction better agrees with the Behrens et al. (2012) modeling study and measurements of 137-Cs in seawater made by Japanese and North American scientists.

Maximum activities of ~1-3 Bq/m^3 as the heart of the contaminated plume reaches the North American coast in the coming 2 year period are roughly 25-fold lower than 137-Cs activities in the North Pacific circa 1960 resulting from atmospheric weapons testing. Therefore, it is unlikely that 137-Cs activities of 3 Bq/m^3 or associated radionuclides released at lower total activities from Fukushima will represent significant health risks to the North Pacific ecosystem.

Ongoing monitoring of radionuclide activities in the North Pacific is required to ground-truth models of Pacific Ocean circulation and plume evolution and to provide the best information to determine likely impact to residents of North America.