This post reports on a recently published peer reviewed study by Steinhauser and colleagues in the journal Science of the Total Environment (behind pay wall) comparing the Chernobyl and Fukushima nuclear accidents. The post is part of an ongoing effort to communicate the results of scientific studies into the impact of the Fukushima disaster on the environment. A majority of the radioactivity released from both Chernobyl and Fukushima can be attributed to volatile radionuclides (noble gases, iodine, cesium, tellurium). In contrast, the amounts of more refractory elements (including actinides like plutonium), released by Chernobyl was ~four orders of magnitude (10,000 fold) higher than releases from Fukushima. The most cited source term for Chernobyl is 5300 PBq (excluding noble gases) while a review of published studies of Fukushima carried out by the authors above allow an estimate for the total atmospheric source term of 520 (a range of 340–800) PBq. Monitoring of air, soil and water for radionuclides after the respective accidents indicate that the environmental impact of Chernobyl is likely to be much greater than the Fukushima accident. The post is relatively information dense as I have provided data tables for those who are interested in the estimates and the peer-reviewed studies from which they come. Apologies up front to those who find such information tedious. Continue reading Comparing the Environmental Impacts of the Chernobyl and Fukushima Disasters→
This post is part of an ongoing effort to communicate the risks to people living on the west coast of North America resulting from the ongoing release of radionuclides from the Fukushima-Daiichi nuclear power plant after the Tohoku earthquake and subsequent triple reactor meltdowns in March 2011. The purpose of this post is to explain how the concentration of radionuclides in seawater impacts the amount of radioactive elements taken up by the marine biota.
The goal is to answer questions like:
How high can we expect radioactive element concentrations to get in marine organisms?
What might be the exposure of marine organisms and human consumers of these organisms to Fukushima sourced radionuclides?
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.
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.
Distribution of soil activity concentration due to 134Cs and 137Cs within 80 km of the Fukushima Daiichi nuclear power plant. Considering radioactive decay, the activity concentrations in the graph were corrected to July 2, 2011 From Koo et al. (2014)
The purpose of this post is to address an error in a recently published review of current release estimates from the Fukushima Dai-ichi nuclear power plant disaster that began in March 2011. The post is part of an ongoing effort to communicate results of scientific studies aimed at understanding the impact of Fukushima on the health of the North Pacific and residents of the west coast of North America. In a recent review paper published in Progress in Nuclear Energy by Koo and colleagues this July, compiled estimates of atmospheric and ocean releases from Fukushima were presented. Due to an error in interpretation they suggest that direct ocean releases were a factor of 4 greater than atmospheric releases of radiologically significant isotopes like 131-I (~8 day half life) and 137-Cs (~30 year half life). This error inflates release estimates and has been reported on to suggest Fukushima releases exceed Chernobyl’s. Accurate estimates of releases from Fukushima suggest that they are about an order of magnitude less than those from Chernobyl in 1986.
The study of Koo and others (link to a ResearchGate upload) estimated atmospheric releases of 131-I, 137-Cs and the noble gas 133-Xe (half life ~ 5 days) from the Fukushima Dai-ichii nuclear power plant. Their estimates compared with previously published estimates are reported in the following table (Table 2 from paper):
Summary of source terms released into the atmosphere from units 1–3. Koo et al. (2014)
Similar to previous work, for example, they estimate the atmospheric release of 137-Cs from the plant to be 10-50 PBq or somewhere between 3 and 17 kg of the isotope. Given the core inventories of reactors 1-3 this release represents about 4% of the inventory at the time of the meltdowns in March 2011.
The authors make a significant error when they begin their estimate of direct releases from Fukushima to the ocean when they state the following in section 2.2.2. Release from the primary system into the sea:
It is reported that, of the total radioactivity released from the units 1–3 into the environment, more than 80% of it flowed into the sea (Hoeve and Jacobson, 2012 and Christoudias and Lelieveld, 2013), implying that 4 times more radioactivity was released to the sea than to the atmosphere.
Bolds are mine. In stating that 80% of the total radioisotope releases flowed into the sea they fundamentally misinterpret the studies they cite. What the study of Christoudias and Lelieveld (2013), and other studies not referenced here in the diary, actually show and establish is that (quoting from the Christoudias and Lelieveld work):
We calculated that about 80% of the radioactivity from Fukushima which was released to the atmosphere deposited into the Pacific Ocean.
This is a fundamentally different than the interpretation Koo and colleagues use in their study. By wrongly interpreting that atmospheric releases represent 20% of the total release they assume that direct ocean releases are 4 fold greater than the 4% of core inventories (10-50 PBq) or 16% of core inventories of 137-Cs in March 2011. This error greatly increases the estimated total releases from the plant (atmosphere + direct ocean).
It is very likely that this incorrect approach will lead others to conclude that total releases from Fukushima are greater than those from Chernobyl. For example a back of the envelope calculation assuming the 4% of the total core inventory of 137-Cs (760-820 PBq according to the table above) was released to the atmosphere and 16% to the ocean would lead to a total release of ~152-164 PBq. Such a calculation was done by a popular news aggregator and editorial site that has a history of misinterpreting and misinformation the public about Fukushima. This estimate, not surprisingly, is at great odds with existing estimates based on measurements and modeling.
Best estimates to date suggest that:
1. atmospheric releases of 137-Cs were 19.4 +- 3.0 PBq through the end of March 2011
2. direct ocean discharge of 137-Cs to the Pacific in addition to atmospheric deposition are in the range 2.3 to 26.9 PBq
3. About 19.5 +- 5% of releases were deposited to land while about 80% ended up in the Pacific Ocean
A report reviewing the most recent peer reviewed studies which reaches these conclusions was summarized in a post here.
Releases of isotopes that represent potential radiological health threats given their respective total activities and/or their significant half lives (e.g. 131-I and 137-Cs) were about an order of magnitude (factor of 10 times) lower than the releases from the Chernobyl disaster in 1986 (see reports here and here for example). More and more observations are being made globally by the international scientific community which will help to improve source term and release estimates. I will report on these studies as the data becomes available.
I have contacted the authors to bring their attention to this problem with their study.
This post reports on the most recent study of plutonium releases from Fukushima to the Pacific Ocean. The post contributes to an ongoing effort to report peer-reviewed studies on the impact of the triple meltdowns at the Fukushima Dai-ichii nuclear power plant on the health of the Pacific ecosystem and residents of the west coast of North America. Plutonium is an alpha-emitting isotope that carries significant radiological health risks if internalized with risk of exposure increasing with the activity of Pu isotopes in the environment. Previous work indicates that 239,240-Pu releases from Fukushima were about 100,000 and 5,000,000 times lower than releases from the Chernobyl disaster in 1986 and 20th century weapons testing respectively. Initial measurements of Pu isotopes in seawater and marine sediments off the coast from Fukushima indicated no detectable change occurred in Pu inventories in the western Pacific after the disaster. More recent and more expansive work supports earlier studies drawing the conclusion that up to two years after the accident the release of Pu isotopes by the Fukushima accident to the Pacific Ocean has been negligible.
A paper by Bu and colleagues was recently published in the peer-reviewed journal Environmental Science and Technology which investigated the activity of Pu isotopes marine sediments collected within 30 km of the Fukushima reactor sites. 239,240,241-Pu and radiocesium isotopes (134-Cs and 137-Cs) were measured. Given that Pu is a particle reactive element that would tend to be concentrated in sediments such measurements should help to determine the extent and degree of Fukushima derived Pu in the marine environment. Sample collection sites are indicated in the map below.
Map showing the locations for (a) sediment samples collected within the 30 km zone around the FDNPP site and (b) sediment samples collected outside the 30 km zone around the FDNPP site in previously published studies by Bu and colleagues.
Relatively high activities of 134-Cs and 137-Cs and a decay corrected ratio near 1 indicated that the sediments were indeed contaminated with Fukushima derived radionuclides.
137-Cs activities and 134-Cs/137-Cs activity ratios in the marine sediments (decay corrected to 15 March 2011) determined by Bu et al. 2014. The blue dashed line represents the 134Cs/137Cs activity ratio fingerprint of the radiocesium released by the Fukushima disaster.
In contrast to the clear imprint of Fukushima derived Cs on the marine sediments the activities of 239,240-Pu and 241-Pu were low compared with the background level before the accident. The Pu activity ratios (240-Pu/239-Pu and 241-Pu/239-Pu) suggested that the Pu detected was the result of global fallout and the pacific proving ground (PPG) close-in fallout resulting from atmospheric weapons testing in the 20th century. The following figure is a mixing diagram that helps to determine the relative contributions to the observed Pu contamination of marine sediments off the Japanese coast.
Mixing plot of 241-Pu/239-Pu atom ratio vs 240-Pu/239-Pu activity ratio in Fukushima sediments compared with Pu compositions of global weapons fallout, Fukushima release, and the Pacific Proving Ground weapons fallout. The closed orange circles (soil and litter samples) and closed black circles (aerosol samples) represent the Fukushima source; the closed pink circle represents the global weapons test fallout; the closed blue circles represent the surface sediment samples collected outside the 30 km zone; the open black circles represent sediment samples within 30 km of the Fukushima site; the closed violet circle represents Sagami Bay sediment samples; the closed wine colored circles represent Pacific Proving Ground source.
The mixing diagram indicates that the isotopic ratio of Pu in marine sediments is inconsistent with a significant release of Fukushima Pu to the marine environment. The isotopic composition of Pu in marine sediments is consistent with Pu deposited during atmospheric weapons testing in the last century.
While initial releases from the plant and ongoing releases due to groundwater infiltration and terrestrial runoff have been negligible thus far according the authors they rightly point out that significant inventories of Pu are insecurely stored at the Fukushima site. So far estimates suggest that about 2.3×10^9 Bq of 239,240-Pu or 580 milligrams of the isotopes have been broadcast to the environment from Fukushima. Bu et al. (2014) estimate that contained within the roughly 270,000 tons of radioactive liquid waste stored in large tanks at Fukushima there exists approximately a further 1×10^8 Bq of 239,240-Pu. Given that future earthquakes or other events could mobilize this Pu, continued monitoring of Pu isotopes in the marine environment is necessary and prudent.
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