Should we worry about eating fish irradiated by Fukushima?

Summary: There are many scary stories circulating about the effects of the radiation released into the Pacific by the explosions at Fukushima, contamination now flowing towards us. Today we review the evidence, so you can decide for yourself. But Fukushima still leaks, and there are good grounds to worry about a massive radiation release in the future.

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Contents

1. The radiation is coming for us
2. Excellent summaries with good news
3. Hard evidence that we need not worry
4. More research
5. For more information about Fukushima

(1) The radiation is coming for us

“Where Will the Debris from Japanʼs Tsunami Drift in the Ocean?“, press release from The University of Hawaii’s International Pacific Research Center, 5 April 2011 — Fukushima exploded 906 days ago. Their animation:

(2) Excellent summaries with good news

(a) “Radioactive Water Leaks from Fukushima: What We Know“, LiveScience, 13 August 2013 — Money paragraph:

The radioactive groundwater leaks could still become worse in the future if TEPCO does not contain the problem, U.S. scientists say. But they cautioned against drawing firm conclusions about the latest impacts on ocean life until new peer-reviewed studies come out.

… The overall contamination of ocean life by the Fukushima meltdown still remains very low compared with the effects of naturally occurring radioactivity and leftover contamination from U.S. and Soviet nuclear weapons testing in the 1960s. Fisher said he’d be “shocked” if the ongoing leaks of contaminated water had a significant impact on the ocean ecosystems.

(b) “Fukushima’s Radioactive Ocean Plume to Reach US Waters by 2014“, LiveScience, 30 August 2013 — About Rossi 2013, below. Excerpt:

Ocean simulations showed that the plume of radioactive cesium-137 released by the Fukushima disaster in 2011 could begin flowing into U.S. coastal waters starting in early 2014 and peak in 2016. Luckily, two ocean currents off the eastern coast of Japan — the Kuroshio Current and the Kuroshio Extension — would have diluted the radioactive material so that its concentration fell well below the World Health Organization’s safety levels within four months of the Fukushima incident.

(3) Hard evidence that we need not worry

Scientists have been and are closely studying the radiation released by Fukushima, as seen in the following research. So far there appears to be little reason for concern.

“Evaluation of radiation doses and associated risk from the Fukushima nuclear accident to marine biota and human consumers of seafood“, Nicholas S. Fishera et al, Proceedings of the National Academy of Sciences (PNAS), 3 June 2013 — Abstract:

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Radioactive isotopes originating from the damaged Fukushima nuclear reactor in Japan following the earthquake and tsunami in March 2011 were found in resident marine animals and in migratory Pacific bluefin tuna (PBFT). Publication of this information resulted in a worldwide response that caused public anxiety and concern, although PBFT captured off California in August 2011 contained activity concentrations below those from naturally occurring radionuclides.

To link the radioactivity to possible health impairments, we calculated doses, attributable to the Fukushima-derived and the naturally occurring radionuclides, to both the marine biota and human fish consumers.

• We showed that doses in all cases were dominated by the naturally occurring alpha-emitter 210Po and
• that Fukushima-derived doses were 3 to 4 orders of magnitude below 210Po-derived doses.
• Doses to marine biota were about 2 orders of magnitude below the lowest benchmark protection level proposed for ecosystems (10 µGy⋅h−1).
• The additional dose from Fukushima radionuclides to humans consuming tainted PBFT in the US was calculated to be 0.9 and 4.7 µSv for average consumers and subsistence fishermen, respectively.
• Such doses are comparable to, or less than, the dose all humans routinely obtain from naturally occurring radionuclides in many food items, medical treatments, air travel, or other background sources.

Although uncertainties remain regarding the assessment of cancer risk at low doses of ionizing radiation to humans, the dose received from PBFT consumption by subsistence fishermen can be estimated to result in two additional fatal cancer cases per 10,000,000 similarly exposed people.

(4) More research

(a) “Model simulations on the long-term dispersal of 137Cs released into the Pacific Ocean off Fukushima“, Erik Behrens et al, Environmental Research Letters, July 2012 — Abstract:

A sequence of global ocean circulation models, with horizontal mesh sizes of 0.5°, 0.25° and 0.1°, are used to estimate the long-term dispersion by ocean currents and mesoscale eddies of a slowly decaying tracer (half-life of 30 years, comparable to that of 137Cs) from the local waters off the Fukushima Dai-ichi Nuclear Power Plants. The tracer was continuously injected into the coastal waters over some weeks; its subsequent spreading and dilution in the Pacific Ocean was then simulated for 10 years. The simulations do not include any data assimilation, and thus, do not account for the actual state of the local ocean currents during the release of highly contaminated water from the damaged plants in March–April 2011.

An ensemble differing in initial current distributions illustrates their importance for the tracer patterns evolving during the first months, but suggests a minor relevance for the large-scale tracer distributions after 2–3 years. By then the tracer cloud has penetrated to depths of more than 400 m, spanning the western and central North Pacific between 25°N and 55°N, leading to a rapid dilution of concentrations.

… Tentatively assuming a value of 10 PBq for the net 137Cs input during the first weeks after the Fukushima incident, the simulation suggests a rapid dilution of peak radioactivity values to about 10 Bq m−3 during the first two years, followed by a gradual decline to 1–2 Bq m−3 over the next 4–7 years. The total peak radioactivity levels would then still be about twice the pre-Fukushima values.

(b) “Estimation of radioactive leakages into the Pacific Ocean due to Fukushima nuclear accident“, R. N. Nair et al, Environmental Earth Sciences, May 2013 — Abstract:

High concentrations of several radionuclides were reported in the sea near the Fukushima Daiichi Nuclear Power Station (FDNPS) in Japan due to the nuclear accident that occurred on 11 March 2011. The main source of these concentrations was leakage of highly radioactive liquid effluent from a pit in the turbine building near the intake canal of Unit-2 of FDNPS through a crack in the concrete wall. In the immediate vicinity of the plant, seawater concentrations reached 68 MBq m⁻³ for ¹³⁴Cs and ¹³⁷Cs, and exceeded 100 MBq m⁻³ for ¹³¹I in early April 2011. These concentrations began to fall as of 11 April 2011 and, at the end of April, had reached a value close to 0.1 MBq m⁻³ for ¹³⁷Cs.

… In this study, the measured concentrations of different radionuclides near the south discharge canal of the FDNPS were used to estimate their leakages into the Pacific Ocean. The method is based on estimating the release rates that reproduce the concentration of radionuclides in seawater at a chosen location using a two-dimensional advection–dispersion model in an iterative manner. The radioactive leakages were estimated as 5.68 PBq for ¹³¹I, 2.24 PBq for ¹³⁴Cs and 2.25 PBq for ¹³⁷Cs. Leakages were also estimated for ^99mTc, ¹³⁶Cs, ¹⁴⁰Ba and ¹⁴⁰La and they range between 0.02 PBq (^99mTc) and 0.53 PBq (¹⁴⁰Ba). It was estimated that about 11.28 PBq of radioactivity in total was leaked into the Pacific Ocean from the damaged FDNPS. Out of this, ¹³¹I constitutes 50.3 %; ¹³⁴Cs 20 %; ¹³⁷Cs 20 %; ¹⁴⁰Ba 4.6 %; ¹³⁶Cs 2.6 %; ¹⁴⁰La 2.3 % and ^99mTc 0.2 % of the total radioactive leakage.

Such quantitative estimates of radioactive leakages are essential prerequisites for short-term and local-scale as well as long-term and large-scale radiological impact assessment of the nuclear accident.

(c) “Input of 129I into the western Pacific Ocean resulting from the Fukushima nuclear event“, S. J. Tumey et al, Journal of Radioanalytical and Nuclear Chemistry, May 2013 — Abstract:

We present an initial characterization of the input of ¹²⁹I into the Pacific Ocean resulting from the 2011 Fukushima nuclear accident. This characterization is based primarily on ¹²⁹I measurements on samples collected from a research cruise conducted in waters off the eastern coast of Japan in June 2011. These measurements were compared with samples intended to reflect pre-Fukushima background that were collected during a May 2011 transect of the Pacific by a commercial container vessel. In surface waters, we observed peak ¹²⁹I concentrations of ~300 μBq/m³ which represents an elevation of nearly three orders of magnitude compared to pre-Fukushima backgrounds.

We coupled our ¹²⁹I results with ¹³⁷Cs measurements from the same cruise and derived an average ¹²⁹I/¹³⁷Cs activity ratio of 0.442 × 10⁻⁶ for the effluent from Fukushima. Finally, we present ¹²⁹I depth profiles from five stations from this cruise which form the basis for future studies of ocean transport and mixing process as well as estimations of the total budget of ¹²⁹I released into the Pacific.

(d) “An ensemble estimation of impact times and strength of Fukushima nuclear pollution to the east coast of China and the west coast of America”, GuiJun Han et al, Science China Earth Sciences, August 2013 — Abstract here:

Based on the statistics of all surface drifting buoys of 1978–2011 and Lagrangian tracers simulated from high quality ocean reanalysis currents, the impact times and strength of Fukushima nuclear pollution to the east coast of China and the west coast of America have been estimated. … starting from 1% at 1.5-year, of the initial level at the originating area of Fukushima nuclear pollution, the impact strength of Cesium-137 in the South China Sea continuously increases up to 3% by 4 years, while the impact strength of Cesium-137 in the west coast of America is as high as 4% due to the role of strong Kuroshio-extension currents as a major transport mechanism of nuclear pollutants for that area.

(e) “Multi-decadal projections of surface and interior pathways of the Fukushima Cesium-137 radioactive plume”, Vincent Rossi et al, Deep Sea Research Part I, October 2013 — Gated. Abstract here:

Following the March 2011 Fukushima disaster, large amounts of water contaminated with radionuclides, including Cesium-137, were released into the Pacific Ocean. With a half-life of 30.1 years, Cs-137 has the potential to travel large distances within the ocean. Using an ensemble of regional eddy-resolving simulations, this study investigates the long-term ventilation pathways of the leaked Cs-137 in the North Pacific Ocean. The simulations suggest that the contaminated plume would have been rapidly diluted below 10,000 Bq/m3 by the energetic Kuroshio Current and Kurushio Extension by July 2011.

Based on our source function of 22 Bq/m3, which sits at the upper range of the published estimates, waters with Cs-137 concentrations >10 Bq/m3 are projected to reach the northwestern American coast and the Hawaiian archipelago by early 2014. Driven by quasi-zonal oceanic jets, shelf waters north of 45°N experience Cs-137 levels of 10–30 Bq/m3 between 2014 and 2020, while the Californian coast is projected to see lower concentrations (10–20 Bq/m3) slightly later (2016–2025). This late but prolonged exposure is related to subsurface pathways of mode waters, where Cs-137 is subducted toward the subtropics before being upwelled from deeper sources along the southern Californian coast. … The sensitivity of our results to uncertainties in the source function and to inter-annual to multi-decadal variability is discussed.

(5) For more information about Fukushima

Many of the sources used here were found in these posts at Washington’s Blog, although the conclusions drawn are exactly opposite:

• “‘Absolutely Every One’ – 15 Out of 15 – Bluefin Tuna Tested In California Waters Contaminated with Fukushima Radiation“, 29 May 2012
• “Is Fukushima Radiation Contaminating Tuna, Salmon and Herring On the West Coast of North America?, 26 August 2013

Other posts about Fukushima (both have ample links to more info):

• Let’s watch the oceans die while we worry about other things!, 16 July 2013
• We fear what we’re told to fear, not what we should fear. Like Fukushima., 11 August 2013

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