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Health Risk from Fukushima Radiation

The Science of Medicine

Steven Novella

Skeptical Inquirer Volume 38.3, May/June 2014

Fear is a powerful emotion with clear protective functions. However, fear is not always adaptive. An emotion that evolved to protect our ancestors (chiefly from threats such as large predators) now is pressed into service in a complex technological civilization. The number of things we are told to be frightened of on a daily basis—by the news media, social and ecological activists, and others—is overwhelming.

Fortunately we have other tools to help us navigate the dangers we face, such as logic and evidence. These can help us put our fears into a proper perspective. These are all the more necessary, as the Internet has become a primary fear-spreading machine. Fearmongering memes are the new predators in our virtual environment, and they are always ready to pounce.

Information regarding the Fuku­shima Daiichi nuclear power plant disaster, for example, remains widespread on the Internet. It is certainly reasonable to consider whether or not radiation from the reactors pose any health risks, but what does the evidence tell us?

A fishmonger checks large bluefin tunaA fishmonger checks large bluefin tuna before the first trading of the new year at Tokyo’s Tsukiji fish market in this January 5, 2012, file photo. Bluefin tuna caught off the U.S. coast have been found to contain radioactive material from Japan’s quake-struck Fukushima nuclear plant. Researchers said the elevated radioactivity posed no risk to public health as the observed levels were more than an order of magnitude lower than the Japanese safety limit and were lower than other naturally present isotopes. (AFP PHOTO / Yoshikazu TSUNOYOSHIKAZU TSUNO/AFP/GettyImages.)

On March 11, 2011, a tsunami hit northeast Japan. The flooding overwhelmed the safety measures at the Fukushima Daiichi nuclear power plant, causing several reactors to experience meltdown and resulting in the leaking of radioactive contaminated water into the local environment (Marshall 2013). This has resulted in restrictions on fishing in the vicinity of Fukushima. Recent evidence also indicates that radioactive material continues to leak into the ocean near Fukushima, although in amounts much smaller than the original leak resulting from the tsunami.

The question remained, however: How far did radioactive elements from Fukushima spread, and do they represent a health risk to anyone outside of the local vicinity? In 2012, researchers reported detecting radioactive elements (cesium-134 and cesium-137) that could clearly be traced to Fukushima in Pacific bluefin tuna (Madigan et al. 2012). These tuna spawn off the coast of Japan and migrate across the Pacific all the way to the California coast, where some are caught and eaten. These fish were able to carry radioactive contamination all the way from Fukushima to dinner plates in California. This created fear that contamination from Fukushima might have been far worse than the authorities were telling us, and perhaps could be affecting environments all over the world. This fear was also spread through conspiracy-theorist bloggers who claimed that the Japanese and American governments were engaging in a sinister collaboration to hide the truth from American fish consumers.

Toxicity, however, is all about dose, even with something as seemingly dangerous as radiation. A follow-up study published in the Proceedings of the National Academy of Sciences (Fisher et al. 2013) found that the levels of radioactive contaminants found in Pacific bluefin tuna were negligible:

“The additional dose from Fuku­shima radionuclides to humans consuming tainted PBFT in the United States 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.” The advantage of communicating the relative risk of radiation exposure is that there is a certain background “natural” exposure that is unavoidable. When levels of exposure are less than this background, it is easy to make the point that any risk is insignificant.

The World Health Organization (WHO) has also reviewed the data concerning the radiation leaked, in all forms, from the Fukushima disaster. Most of the radiation was leaked in the week following the accident, but there have been continued leaks since then, mostly through ground water. The WHO review concluded: “A breakdown of data, based on age, gender and proximity to the nuclear plant, does show a higher cancer risk for those located in the most contaminated parts. Outside these parts—even in locations inside Fukushima Prefecture—no observable increases in cancer incidence are expected” (World Health Organization 2013). An independent 2013 review also found little evidence of any significant radiation outside the immediate area of the accident: “It is important to note that all of the radiation levels detected outside of Japan have been very low and are well below any level of public and environmental hazard” (Thakur et al. 2013).

Recent estimates are that water contaminated with radioactive elements is leaking from Fukushima into the nearby ocean at a rate of 300 tons per day (Kimura and Kawada 2013). This sounds like a lot, but the Pacific Ocean contains 714 million cubic kilometers of water. Simple dilution is reducing the concentration of radioactive contaminants below the level where there is any health risk, to sea life or to those consuming seafood. There does remain concern for the immediate vicinity, of course. For this reason Japan has banned fishing along the coast near Fukushima.


The Fukushima Daiichi disaster resulted in serious environmental contamination with radioactive contaminants. However, the contamination is mostly limited to the vicinity of Fukushima. Monitoring of contaminants in the Pacific, North America, and around the world reveal that they are at very low levels, below that which would cause any health concern or even peak above background radiation exposure. Even bluefin tuna spawning off the coast of Japan have negligible levels of contaminants and pose no risk to human health. This is all good news, but the environmental and health effects of Fukushima, which is an ongoing disaster, will need to be monitored for some time. There continue to be reports of new leaks from Fukushima, so this story is not yet over (Saito 2014). Hopefully, carefully collected evidence will dominate policy and public perception.


Nicholas S. Fisher, Karine Beaugelin-Seiller, Thomas G. Hinton, et al. 2013. Evaluation of radiation doses and associated risk from the Fukushima nuclear accident to marine biota and human consumers of seafood. Proceedings of the National Academy of Sciences (April 18).

Kimura, Shunsuke, and Toshio Kawada. 2013. Fukushima: Radioactive water flowing into Pacific Ocean despite Japanese government claim. Global Research (October 11). Available at

Daniel J. Madigan, Zofia Baumann, Nicholas S. Fisher. 2012. Pacific bluefin tuna transport Fukushima-derived radionuclides from Japan to California. Proceedings of the National Academy of Sciences (April 25). Available at

Marshall, Michael. Fukushima leaks will keep fisheries closed. 2013. The New Scientist (August 6). Available at

Saito, Mari. 2014. New highly radioactive leak at Japan’s Fukushima plant. Reuters (February 19). Available at

Thakur, P., S. Ballard, R. Nelson. 2013. An overview of Fukushima radionuclides measured in the northern hemisphere. Science of the Total Environment (Aug 1: 458–460; 577–613. doi: 10.1016/j.scitotenv.2013.03.105. Epub May 22, 2013.

World Health Organization. 2013. Global report on Fukushima nuclear accident details health risks. (February 28). Available at

Steven Novella

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Steven Novella, MD, is an assistant professor of neurology at Yale University School of Medicine. He is the host of the Skeptics’ Guide to the Universe podcast, author of the NeuroLogica blog, executive editor of the Science-Based Medicine blog, and president of The New England Skeptical Society.