Category Archives: Peer Reviewed

Authors Lower Fukushima Cesium in North Pacific By Order of Magnitude

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.

Advertisements

Fukushima Radionuclides in Pacific Albacore Tuna Off the US Coast

Tuna and gamma spectra. (Neville et al. 2014)
Tuna and gamma spectra. (Neville et al. 2014)

By Jay T. Cullen

Introduction

As part of an ongoing series documenting the impacts of the Fukushima disaster on the North Pacific and west coast, this post summarizes a recently published study by Delvan Neville and colleagues in the peer-reviewed journal Environmental Science and Technology. The paper reports measurements of Cesium-134 and Cesium-137 in 26 albacore tuna caught off the west coast of North America between 2008 and summer 2012. Because of its relatively short half-life (~2 years) 134-Cs is an unambiguous tracer of radionuclides released from the Fukushima Dai-ichi disaster which began in March 2011. Fish collected in 2011 and 2012 had higher 134-Cs and 137-Cs that was due to Fukushima sourced cesium in the Pacific. Fish collected in 2008-2009 had lower 137-Cs activities that largely reflected historic releases of the isotope from atmospheric nuclear weapons testing in the 20th century. The authors conclude that given the highest levels of Cs isotopes measured in albacore tuna, human consumption of the fish would not not represent a significant increase in annual radiation dose. The corresponding radiological health risk due to Fukushima derived radiocesium in these tuna is, therefore, very small. Continue reading Fukushima Radionuclides in Pacific Albacore Tuna Off the US Coast

Plutonium in the Pacific Ocean From Fukushima

By Jay T. Cullen

Introduction

This post is part of an ongoing series that represents an effort to communicate peer-reviewed scientific studies of the impact of the Fukushima nuclear disaster on the North Pacific Ocean and residents of the west coast of North America. A frequently asked question of those involved in monitoring the health of the North Pacific is why more measurements of the long lived, alpha-emitting isotopes of plutonium (239-Pu half-life 24,100 years; 240-Pu 6,570 years) are not being made given the potential for these isotopes to pose radiological health risks. Measurements of air, soil and water indicate that Pu was released and broadcast into the environment as a result of the triple reactor meltdowns with estimates of the source on the order of 2.3×10^9 Bq of 239,240-Pu or 580 milligrams of the isotopes. Measurements of isotope composition and activity of Pu in seawater and sediments off the coast of Japan indicate that there was no detectable change resulting from the nuclear disaster (behind pay wall). Given that the Fukushima signal is not detectable in the ocean off Japan relative to legacy sources from atmospheric weapons testing in the 20th century there is likely little information in making the same measurements in the eastern Pacific off of North America.


Members of the public are concerned about the presence of the alpha-emitting isotopes of Pu and have been asking why measuring for these elements in seawater and marine biota is not a priority of the InFORM network. The purpose of this diary is to explain why such measurements are less likely to provide information about the plume and its impacts.

A recently published paper by Bu and colleagues in the peer-reviewed Journal of Chromotography A reports the development of a new method to determine Pu isotopes in small (20 – 60 liters) samples of seawater and measurements made of these isotopes off the coast of Japan from July 2011 to January 2013 until the present. Locations where samples were collected are shown in the figure below:

Map showing seawater collection stations from the western North Pacific and Tokyo Bay since the FDNPP accident.

For all the seawater samples analyzed by Bu and colleagues, the 239-,240-Pu activities and 240-Pu/239-Pu atom ratios where found to be 0.00043 to 0.0056 Bq m^-3 and from 0.227 to 0.284, respectively. The results are summarized in Table 4 of the paper and are shown below:

 

Before the Fukushima accident in March 2011, Pu isotopes were being monitored off the coast of Japan to assess the radiological impact of the nuclear plants on the marine environment. The 239-,240-Pu activities before the meltdowns were below 0.0083 Bq m^−3 and 0.022 Bq m^−3 respectively, with 240-Pu/239-Pu atom ratios between 0.173 and 0.322. These ratios represent the influence of the Pacific Proving Ground nuclear weapon test site, which was characterized by a high 240-Pu/239-Pu atom ratio (0.30–0.36). Results after the Fukushima disaster were typically in the background data range, suggesting no detectable Pu contamination from the accident in the marine environment ~30 km offshore of the Fukushima Dai-ichi reactor complex. This conclusion is consistent with findings from previous studies of Pu isotopes in marine sediments in the western North Pacific after the Fukushima accident.

Given the absence of isotopic and concentration anomalies thus far in the western Pacific resulting from the Fukushima meltdowns there is not very much information to be gained about the evolution of the contaminated seawater plume in time and space. Similarly, the impact of the Fukushima disaster on the health of marine ecosystem with respect to Pu isotopes will be difficult to quantify relative to weapons testing background levels that persist in the environment.

On the Methodology Used to Make the Measurements (If You are Interested, IYI)
The approach used by Bu and colleagues to measure Pu isotopes at such low concentrations and activities involves applying sector field high resolution inductively coupled mass spectrometry. The instrument is able to separate chemical species by their respective mass to charge ratios using a strong electromagnetic field downstream of the plasma ionization source. Great pains were taken maximize the instruments sensitivity to measure the isotopes of interest 238-U, 239-Pu, 240-Pu, and 242-Pu. To remove the seawater matrix (cations and anions that would reduce instrument sensitivity) and elements with mass to charge ratios that would interfere with Pu detection like 238-U the seawater samples were purified using ion selective resins held in columns by passing them through successive loading and elution steps. This process is summarized in the following flow diagram from the paper:

Flow chart of the analytical procedure for the determination of Pu isotopes in seawater by anion-exchange chromatography and SF-ICP-MS.

The preconcentration and sensitivity of SF-ICP-MS allows for the very low detection limits required to quantify Pu in relatively small (20 – 60 L) volumes of seawater.

 

More Measurements of Southward Transport of the Fukushima Contaminant Plume in the Western Pacific

by Jay T. Cullen

This post is part of an ongoing series that endeavors to report measurements of Fukushima derived radionuclides in the environment to help determine the likely impact on ecosystem and public health in western North America. One of the goals of the InFORM project is to provide quality measurements of Fukushima derived radionuclides in the North Pacific to help verify model predictions of ecosystem and public health impacts of the disaster. The purpose of this post is to summarize results of a recent peer reviewed study by Kaeriyama and colleagues published in Environmental Science & Technology who measured radioactive isotopes of cesium (137-Cs half life ~30 yr and 134-Cs half life ~ 2 yr) in the western North Pacific Ocean to help track the location and movement of the Fukushima contaminated seawater plume.

Continue reading More Measurements of Southward Transport of the Fukushima Contaminant Plume in the Western Pacific

Initial Survey of Fukushima Children Finds No Detectable Internal 137-Cesium

by Jay T. Cullen

Introduction

The purpose of this blog is to bring to the attention of interested readers a recent peer-reviewed, open-access study published in the Journal or Radiological Protection . The investigators describe the design and manufacture of a whole body sensor whose purpose is the detection of 137-Cs (half-life ~30 years) in children who were proximate to radionuclide releases after the triple meltdowns at the Fukushima-Daiichi nuclear power plant which began in March 2011. Health impacts of the disaster are likely to be most acute in Japan given that levels of radionuclides in air, soil and water resulting from the disaster were higher compared to levels measured and expected on the west coast of North America. The detector in question (called BABYSCAN) is demonstrated to have a detection limit of better than 50 Bq/body and has been installed in a hospital in Fukushima. Because children are most vulnerable to the impacts of ionizing radiation, 100 Fukushima children were scanned for the presence of 137-Cs and none were found to have detectable levels of the isotope in their bodies. Larger scale measurements of the population will be reported as the long term impacts of low levels of ionizing radiation present owing to the Fukushima disaster warrant further study.


As a result of the radionuclides released to the atmosphere after the meltdowns in March 2011 at the Fukushima-Daiichi nuclear power plant, Fukushima Prefecture was contaminated with radioactive cesium (134-Cs and 137-Cs) and other isotopes, which pose radiological health risks to the resident population.  As would be expected for parents around the world, parents of small children in Fukushima Prefecture have great concern about the internal exposure experienced by their offspring.
The paper by Hayano and colleagues describes the design and manufacture of a whole body scanner designed specifically for the purpose of detecting gamma-emitting isotopes that have been internalized by children. The instrument was first installed at the Hirata Central Hospital in Fukushima Prefecture in December 2013. The design principles, implementation and the initial operating experience are reported in the paper.

 

The age distribution of the first 100 children who were selected for isotope counting are given in the figure below:

Age distribution of the subjects.
Radioactive 134-Cs and 137-Cs was not detected in any of the 100 subjects. Naturally occurring radioactive 40-Potassium (40-K) was detected in all subjects. Typical gamma-ray energy spectra are are shown in the figure below with black dots indicating data collected with a subject in the instrument (4 min of counting), and those shown in grey dots were taken without subject (blank measurement taken over 5 hours and normalized to 4 min).

 

Typical gamma-ray energy spectra measured with the BABYSCAN. Left: 8-month-old girl, right: 8-year-old boy. The spectra shown in black dots were taken with subjects (4 min), and those in grey dots were taken without subject (measured for 5 h, normalized to 4 min). The background-subtracted spectra are shown in open circles.

Given the experimental conditions the minimum detectable activity (MDA) for 137-Cs (Bq/body), was calculated for each subject and plotted against weight for each child as shown below.

The minimum detectable activity (MDA) for 137-Cs (Bq/body) versus subjects’ weight.

The detection limit of BABYSCAN for 137-Cs, one of the most significant isotopes with respect to radiological health risks released from Fukushima, is better than 50 Bq/body. Despite this low detection limit, 137-Cs was not detected in any of the first 100 children scanned from the most contaminated areas of Japan in Fukushima Prefecture. Ongoing analyses will be carried out on a larger-scale with BABYSCAN and reported in publications by the investigators in the future. I will report on data as it becomes available.