Fukushima’s impact on the ocean environment revealed

Many environmentalists oppose nuclear power presumably because they think it is bad for the environment. Concerns about waste, radioactive releases and so on are often cited as evidence for this. Having released a very large quantity of artificial radioactive isotopes into the marine environment, Fukushima gives us a very good opportunity to test this concern in a real-world setting. Some fascinating results are now in, courtesy of Ken Buesseler and colleagues, in a paper just published in the highly-respected journal PNAS.

The numbers are impressive, which is not particularly surprising given that perhaps a tenth as much radiation as was released by Chernobyl came from Fukushima (still a very large amount). For example, levels of the two caesium isotopes Cs-134 and Cs-137 in seawater were measured by the researchers at concentrations up to 1000 times higher than before the 11 March tsunami disaster, and were found in an area of the Pacific Ocean covering 150,000 square kilometres off Japan.

This sounds scary, but bear in mind that only 30 km offshore levels drop down by 50 times, to about 600-800 becquerels per cubic metre on average, well below Japanese regulatory limits for the ocean of 90,000 Bq/m3, and also 15 times lower than the radiation released naturally by the most common natural radionuclide in the ocean, potassium-40 (which on average causes activity of 12,000 Bq/m3).

So what are the impacts on marine biota? Once again, the numbers are important – many who worry about the impact of artificial radionuclides forget that natural radionuclides are ever-present in the environment, and that living organisms are well-accustomed through billions of years’ of evolution to dealing with their impact on DNA. Accordingly, radiation doses to marine organisms further out than 30km from Fukushima are still dominated by the naturally-occurring radionuclides polonium-210 and potassium-40. The authors point out that just to reach the levels of radiation emitted by the natural polonium, caesium-137 levels in fish would have to be 1-3 orders of magnitude (10-1000x) higher than they observed in the waters off Japan.

What if you were to swim in this slightly-more-radioactive sea? The authors calculate an external dose of less than 0.01 microsieverts per day (equalling 0.003 mSv/yr) for anyone fully immersed in the ocean there, which they point out is less than 0.3% of the average daily Japanese dose from all radiation sources which adds up to about 1.4 mSv/yr. In terms of the marine biodiversity impacts, the authors conclude that

these levels are several orders of magnitude lower than those used in one study that assumed exposure to the most heavily impacted water discharged from the Fukushima NPPs to predict marked reproductive effects and possible mortality in marine biota 

The “one study” in question is referenced as ‘Fukushima wildlife dose reconstruction signals ecological consequences’, published last year in the journal Environmental Science and Technology (early PDF here). That study bore the much more worrying conclusion that

marked reproductive effects, and even mortality for the most radiosensitive taxa are predicted for all marine wildlife groups whose life history characteristics confine them to the near-field, contaminant release area

a statement based on early assessments of doses which appear now to have been massive over-estimates – albeit with the caveat that doses can be assumed to be much higher closer than 30km in to shore, an area apparently not covered in this PNAS study.

The upshot is that Fukushima-derived radiation doses experienced by marine organisms throughout the food chain are well below levels which could cause harm to ocean biodiversity, and even in the most part below levels experienced due to naturally-occurring radionuclides.

Unfortunately, perhaps, given that fish caught offshore from Fukushima are entirely safe for human consumption (measured levels in fish are 150-fold less than the legal limit on average), there is little prospect of a no-fishing zone which might provide great marine wildlife benefit as the Chernobyl exclusion zone currently does for land-based rare species.

Context is also key – I end this piece with a shot of the likely extent of tsunami debris distributed throughout the Pacific Ocean after having been washed out of coastal areas of Japan:

Given that much of this will be non-biodegradeable plastics, the effects can be expected to be vastly more significant to marine life than the relatively trivial effects of radionuclides released from Fukushima. This is very similar to the obvious but often neglected fact that the human effects of the tsunami – 19,000 deaths – vastly overwhelm any human health effects from Fukushima-originated radiation (no deaths), something never clear from most of the overblown media coverage on 11 March 2012 one-year anniversary, which tended to focus on the nuclear accident to the exclusion of all else.

Opponents of nuclear power often make out that the consequences of a serious accident are some variant of Armageddon (sterilising large areas for generations, etc). Fukushima shows that this is absolutely not the case. The environmental effects of an accident are transient, and virtually non-existent compared to other human impacts on biodiversity.


  1. Huw Jones

    Excellent context, thank you for an excellent article.

    One thing I think this article shows is that we definitely do not need another boring and fruitless round of discussion and debate regarding the validity of the Linear-Non-Threshold (LNT) theory of radiation harm. If the radioactivity in the food chain surrounding Fukushima is dwarfed by natural radioactivity, then it is obviously safe, even by the conservative standards expected by law.

    Regardless of the actual risks to wildlife and humans from radioactive materials released from Fukushima, there is going to be a psychological stigma attached to people living in the area and carrying on their lives. Most people do not understand the risks associated with radiation on any level. I myself until relatively recently did not know my Becquerels from my milliSieverts, and when explaining to most people the various definitions and quantities the default position is to resort to panic and fear.

    On several occasions when I have tried to explain the risks of eating produce from the Fukushima region, I am asked ‘Well would you eat food from there?’ – my answer is unequivocally yes. Perhaps if we imported Fukushima produce to the UK or elsewhere and made a public demonstration of eating it we could help reduce the fear – we’d help out the stricken farmers in the region too.

  2. Es Tresidder

    Interesting article, thanks. I don’t have time to read the full paper for now, what does it have to say about the impact on marine biota less than 30km from shore?

  3. Geoff Russell

    Excellent summary and the final image is perfectly placed. The impact of the debris is a good reason why nothing except nuclear power stations should be built in tsunami prone areas 🙂 The impact of the destruction of normal infrastructure on sea life will be much greater when washed away.

  4. Robert Wilson

    If people do not have the time to read the entire paper, the key results are on page 3.

    Despite the paper not finding evidence of potentially harmful levels of radiation this may, as Mark Lynas suggests, be bad news for marine biodiversity in the area as fishing is more likely to resume. Unsustainable fisheries do much more damage to biodiversity than radiation.

    In the debate over radiation numbers count, not vague assertions, and this paper is an excellent example. The simple comparison of anthropogenic to natural radiation has the double of benefit of being clear and understandable. Sadly it appears that very few journalists have paid attention to this study, and media reports on Fukushima in the last couple of days have focused on a water leak.


    These reports should be understood in the context of the scientific studies of the risks. There is a clear need for a shift in the journalistic culture, but I believe there are signs it is happening,

    1. malcolm mcewen

      good point; wildlife as similarly demonstrated by the exclusion zone around Chernobyl, actually profit from nuclear disasters since the massive reduction in human impact out weighs the negative effects of the radiation. However that should not be a reason to call nuclear safe or good but a reason to examine why we have such an adverse impact on our environment. Similarly the long term effects, the recycling of Caesium and Strontium and its subsequent impact on marine invertebrates which don’t migrate has yet to be determined

    2. Robert Wilson


      There are clearly a number of questions remaining, as the authors of the papers say. As a zooplankton modeller, who spent an uncomfortable two weeks on board a research boat, I expect that they will not be answered quickly unless the Japanese and other governments believe there is a major risk to marine life from Fukushima radiation. My guess is that this study alone cost well over £200,000, and funding bodies may question whether future studies are good value for money.

    3. Joris van Dorp

      I’m not so sure journalism is improving. Individual journalist may improve, but news organisation in the popular press are are *not* interested in any news that appears to go against the recieved wisdom of Fukushima’s nuclear ‘holocaust’ scenario. I don’t have the link, but especially in the early days of the disaster, there were reports of journalist being forced to assume a tone of panic en hopelessness in all their reporting on Fukushima. Reporters how appeared to rationalise and put the accident in context were actually taken off the story. I have no reason to believe this is not still happening, at least in my country (the netherlands). Concerning Fukushima, after more than one year, it is still impossible to get a balanced, correct view of the disaster from the MSM. It is still necessary to go out on the internet and find your own news.

      All people who get their news from the MSM in the Netherlands still firmly equate Fukushima with massive radiation exposure and prospects of massive human suffering through cancer and genetic alterations still to come. It is still almost impossible to explain to people that this is not the case, because people tend strongly to believe the mountain of nonsens that has been imprinted on their consciousness sinds 14 months of intens anti nuclear propaganda through the MSM. I would certainly hesitate to underestimate the deep and long-term effects on public acceptance of nuclear power caused by this year long anti-nuke propaganda assault. It will take a lot of effort to correct it.

      P.S. Thanks for you work on this Mark Lynas. You are one of the strongest forces for common sense on nuclear out there, along with the likes of George Monbiot and a number of other journalists and bloggers. Thanks again.

  5. Gordon Glass

    Mark – You hold up a report that focuses on the sea more than 30km away from the release of the contamination as something positive?

    Remember we not talking contamination by air – like Chernobyl – but radioactivity released direct into the sea in the form of the contaminated water used to cool the fractured reactor.

    Isn’t this rather like reporting on the contamination caused by an oil spill at Dover by sampling the sea water at Calais (34km away)?

    Do seas not have currents that move contamination sideways? Do fish not migrate from A to B?

    The nuclear industry really is a good deal more destructive than you seem capable of accepting. The Chernobyl death cloud caused horrendous harm where Belarus meets the Ukraine where it was forced to ground.

    Quoting a specialist doctor in the affected area …”In 1985, we had four lymph cancers a year. Now we have seven times that many. We have between five and eight people a year with rare bone cancers, when we never had any. We expect more cancers, and ill health. One in three pregnancies here are malformed. We are overwhelmed.”


    And plenty more evidence here that can not be simply ignored and underplayed…


    1. Marje Hecht

      For a scientific overview on Chernobyl, see
      Dr. Zbigniew Jaworowski’s articles

      Observations on Chernobyl after 25 Years of Radiophobia

      and Belarus Repopulating Chernobyl Exclusion Zone

    2. Gordon Glass

      Pretending Chernobyl did no damage has got to be a lot less useful than turning our intelligence to preventing a repeat of it.

      Site safety also has to be radically improved. Fukishima is still in a right state… “Record radiation levels detected… workers cannot enter the site and we must use robots”… No wonder nobody is rushing to study the effects in the immediate vicinity of the damaged facilities.


      And certain aspects of our nuclear use remain just plain sick. Depleted uranium rounds from nuclear waste get blown to dust and contaminate all living things. These have got to go the same way as land mines and cluster bombs. Their “unintended consequences” (civilian cancers, deformed kids etc) are similarly damaging.

    3. Robert Wilson


      The paper, which is freely available, addresses the issue of ocean currents. Your question implies you have not read the paper. Please do so before criticising it.

      As is the case with good science the paper says their findings need further confirmation.

    4. Gordon Glass

      Researching early impacts on the ocean at a 30km distance doesn’t say much that is positive to me about the safety of Fukishima.

      Surely we’re talking about contaminated water being dumped next to a plant. Wouldn’t we expect heavier contamination to take a somewhat downwards trajectory. Thus 30km away is a heavily ‘diluted’ place to start a study.

  6. EL

    Interesting, considering that much of the ocean contamination is from cooling water passed through the core of the reactor, I’m curious why they didn’t examine refractory radionuclides in their assessment? They suggest human health effects from current levels of contamination to be “low,” but reserve judgement on future impacts should the Fukushima reactors continue to be a source of “radionuclides (5) and if, as has been reported, coastal sediments are contaminated with multiple radionuclides” (p. 5). So it appears that further research is needed to validate their assessment of “low” health impacts, as well as long term observations and sampling.

  7. Leslie Corrice

    A well-written, well-researched work. You have shown that detectable is not dangerous…unless mother nature is more dangerous than Fukushima contamination. That in-itself makes no sense, and niether does the detectable-is-dangerous crowd. Good stuff.

  8. MarkB

    Stop and think…. Hiroshima, Nagasaki – doing fine these days. And we dropped the bomb on both. They cleared out the rubble and rebuilt thriving cities. That’s what radiation does.


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