The radiation effects from the Fukushima Daiichi nuclear disaster are the observed and predicted effects resulting from the release of radioactive isotopes from the Fukushima Daiichi Nuclear Power Plant after the 2011 Tōhoku earthquake and tsunami. Radioactive isotopes were released from reactor containment vessels as a result of venting to reduce gaseous pressure, and the discharge of coolant water into the sea. This resulted in Japanese authorities implementing a 20 km exclusion zone around the power plant, and the continued displacement of approximately 156,000 people as of early 2013. Trace quantities of radioactive particles from the incident, including iodine-131 and caesium-134/137, have since been detected around the world. As of early 2013, no physical health effects due to radiation had been observed among the public or Fukushima Daiichi Nuclear Power Plant workers.
In early 2013, The World Health Organization (WHO) released a comprehensive health risk assessment report which concluded that, for the general population inside and outside of Japan, the predicted health risks are small and that no observable increases in cancer rates above background rates are expected. The report estimates an increase in risk for specific cancers for certain subsets of the population inside the Fukushima Prefecture. For the people in the most contaminated locations within the prefecture, this includes a 4% increase for solid cancers in females exposed as infants, a 6% increase in breast cancer in females exposed as infants, and a 7% increase in leukaemia for males exposed as infants. The risk of thyroid cancer in females exposed as infants has risen from a lifetime risk of 0.75% to 1.25%.
Preliminary dose-estimation reports by WHO and the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) indicate that future health effects due to the accident may not be statistically detectable. However, 167 plant workers received radiation doses that slightly elevate their risk of developing cancer. Estimated effective doses from the accident outside of Japan are considered to be below (or far below) the dose levels regarded as very small by the international radiological protection community. The United Nations Scientific Committee on the Effects of Atomic Radiation is expected to release a final report on the effects of radiation exposure from the accident by the end of 2013.
A June 2012 Stanford University study estimated, using a linear no-threshold model, that the radiation release from the Fukushima Daiichi nuclear plant could cause 130 deaths from cancer globally (the lower bound for the estimater being 15 and the upper bound 1100) and 180 cancer cases in total (the lower bound being 24 and the upper bound 1800), most of which are estimated to occur in Japan. Radiation exposure to workers at the plant was projected to result in 2 to 12 deaths. However, a December 2012 UNSCEAR statement to the Fukushima Ministerial Conference on Nuclear Safety advised that "[b]ecause of the great uncertainties in risk estimates at very low doses, UNSCEAR does not recommend multiplying very low doses by large numbers of individuals to estimate numbers of radiation-induced health effects within a population exposed to incremental doses at levels equivalent to or lower than natural background levels
Preliminary dose-estimation reports by the World Health Organization and United Nations Scientific Committee on the Effects of Atomic Radiation indicate that 167 plant workers received radiation doses that slightly elevate their risk of developing cancer, but that it may not be statistically detectable. Estimated effective doses from the accident outside of Japan are considered to be below (or far below) the dose levels regarded as very small by the international radiological protection community.
According to the Japanese Government, 180,592 people in the general population were screened in March 2011 for radiation exposure and no case was found which affects health. Thirty workers conducting operations at the plant had exposure levels greater than 100 mSv. It is believed that the health effects of the radiation release are primarily psychological rather than physical effects. Even in the most severely affected areas, radiation doses never reached more than a quarter of the radiation dose linked to an increase in cancer risk. (25 mSv whereas 100 mSv has been linked to an increase in cancer rates among victims at Hiroshima and Nagasaki) However, people who have been evacuated have suffered from depression and other mental health effects.
The negative health effects of the Fukushima nuclear disaster include thyroid abnormalities, infertility and an increased risk of cancer. One study conducted by a research team in Fukushima, Japan found that more than a third (36%) of children in Fukushima have abnormal growths in their thyroid glands. Furthermore, a WHO report found that there is a significant increase in the risk of developing cancers for people who live near Fukushima. This includes a 70% higher risk of developing thyroid cancer for newborn babies, a 7% higher risk of leukemia in males exposed as infants, a 6% higher risk of breast cancer in females exposed as infants and a 4% higher risk of developing solid cancers for females. An increase in infertility has also been reported.
As of August 2013, there have been more than 40 children newly diagnosed with thyroid cancer and other cancers in Fukushima prefecture alone and nuclear experts warn that this pattern may also occur in other areas of Japan.
As of September 2011, six workers at the Fukushima Daiichi site have exceeded lifetime legal limits for radiation and more than 300 have received significant radiation doses. Still, there were no deaths or serious injuries due to direct radiation exposures.
According to a June 2012 Stanford University study[unreliable source], the radiation released could cause 130 deaths from cancer (the lower bound for the estimater being 15 and the upper bound 1100) and 180 cancer cases (the lower bound being 24 and the upper bound 1800), mostly in Japan[unreliable source]. Radiation exposure to workers at the plant was projected to result in 2 to 12 deaths. The radiation released was an order of magnitude lower than that released from Chernobyl, and some 80% of the radioactivity from Fukushima was deposited over the Pacific Ocean; preventive actions taken by the Japanese government may have substantially reduced the health impact of the radiation release. An additional approximately 600 deaths have been reported due to non-radiological causes such as mandatory evacuations. Evacuation procedures after the accident may have potentially reduced deaths from radiation by 3 to 245 cases, the best estimate being 28; even the upper bound projection of the lives saved from the evacuation is lower than the number of deaths already caused by the evacuation itself.
However, that estimate has been challenged, with some scientists arguing that accidents and pollution from coal or gas plants would have caused more lost years of life.
The radiation emitted in Fukushima instigated evacuations of "16,000 people", which, according to a study, has also caused mental illness and psychological effects on these people. Stress, fatigue and people even being around other seriously ill people are some of the main contributors to the mental health of many of these individuals during the evacuation. The study also identifies how children are more susceptible to the radiation "because their cells are dividing more rapidly and radiation-damaged RNA may be carried in more generations of cells." In addition, DNA damage is also common among people with prolonged exposure to the radiation through "air, ground and food."
According to the Wall Street Journal, some areas were exposed to about 2 rem of radiation and some other areas as much as 22 rems.
A report by the World Health Organization published in February 2013 anticipated that there would be small noticeable increases in cancer rates for the overall population, but somewhat elevated rates for particular sub-groups. For example infants of Namie Town and Iitate Village were estimated to have a 6% increase in female breast cancer risk and a 7% increase in male leukaemia risk. A third of emergency workers involved in the accident would have increased cancer risks.
On 24 May 2012, more than a year after the disaster, TEPCO released their estimate of radiation releases due to the Fukushima Daiichi Nuclear Disaster. An estimated 538,100 terabecquerels (TBq) of iodine-131, caesium-134 and caesium-137 was released. 520,000 TBq was released into the atmosphere between 12 to 31 March 2011 and 18,100 TBq into the ocean from 26 March to 30 September 2011. A total of 511,000 TBq of iodine-131 was released into both the atmosphere and the ocean, 13,500 TBq of caesium-134 and 13,600 TBq of caesium-137. In May 2012, TEPCO reported that at least 900 PBq had been released "into the atmosphere in March last year  alone" up from previous estimates of 360-370 PBq total.
The primary releases of radioactive nuclides have been iodine and caesium; strontium and plutonium have also been found. These elements have been released into the air via steam; and into the water leaking into groundwater or the ocean. The expert who prepared a frequently cited Austrian Meteorological Service report asserted that the "Chernobyl accident emitted much more radioactivity and a wider diversity of radioactive elements than Fukushima Daiichi has so far, but it was iodine and caesium that caused most of the health risk – especially outside the immediate area of the Chernobyl plant." Iodine-131 has a half-life of 8 days while caesium-137 has a half-life of over 30 years. The IAEA has developed a method that weighs the "radiological equivalence" for different elements. TEPCO has published estimates using a simple-sum methodology,
According to a June 2011 report of the International Atomic Energy Agency (IAEA), at that time no confirmed long-term health effects to any person had been reported as a result of radiation exposure from the nuclear accident.
In a leaked TEPCO report dated June 2011, it was revealed that plutonium-238, −239, −240, and −241 were released "to the air" from the site during the first 100 hours after the earthquake, the total amount of plutonium said to be 120 billion becquerels (120 GBq) — perhaps as much as 50 grams. The same paper mentioned a release of 7.6 trillion becquerels of neptunium-239 – about 1 milligram. As neptunium-239 decays, it becomes plutonium-239. TEPCO made this report for a press conference on 6 June, but according to Mochizuki of the Fukushima Diary website, the media knew and "kept concealing the risk for 7 months and kept people exposed".[unreliable source?]
According to one expert, the release of radioactivity is about one-tenth that from the Chernobyl disaster and the contaminated area is also about one-tenth that that of Chernobyl.
A 12 April report prepared by NISA estimated the total air release of iodine-131 and caesium-137 at between 370 PBq and 630 PBq, combining iodine and caesium with IAEA methodology. On 23 April the NSC updated its release estimates, but it did not reestimate the total release, instead indicating that 154 TBq of air release were occurring daily as of 5 April.
On 24 August 2011, the Nuclear Safety Commission (NSC) of Japan published the results of the recalculation of the total amount of radioactive materials released into the air during the incident at the Fukushima Daiichi Nuclear Power Station. The total amounts released between 11 March and 5 April were revised downwards to 130 PBq for iodine-131 (I-131) and 11 PBq for caesium-137 (Cs-137). Earlier estimations were 150 PBq and 12 PBq.
On 20 September the Japanese government and TEPCO announced the installation of new filters at reactors 1, 2 and 3 to reduce the release of radioactive materials into the air. Gases from the reactors would be decontaminated before they would be released into the air. In the first half of September 2011 the amount of radioactive substances released from the plant was about 200 million becquerels per hour, according to TEPCO, which was approximately one-four millionths of the level of the initial stages of the accident in March.
According to TEPCO the emissions immediately after the accident were around 220 billion becquerel; readings declined after that, and in November and December 2011 they dropped to 17 thousand becquerel, about one-13 millionth the initial level. But in January 2012 due to human activities at the plant, the emissions rose again up to 19 thousand becquerel. Radioactive materials around reactor 2, where the surroundings were still highly contaminated, got stirred up by the workers going in and out of the building, when they inserted an optical endoscope into the containment vessel as a first step toward decommissioning the reactor.
A widely cited Austrian Meteorological Service report estimated the total amount of I-131 radiation released into the air as of 19 March based on extrapolating data from several days of ideal observation at some of its worldwide CTBTO radionuclide measuring facilities (Freiburg, Germany; Stockholm, Sweden; Takasaki, Japan and Sacramento, USA) during the first 10 days of the accident. The report's estimates of total I-131 emissions based on these worldwide measuring stations ranged from 10 PBq to 700 PBq. This estimate was 1% to 40% of the 1760 PBq of the I-131 estimated to have been released at Chernobyl.
A later, 12 April 2011, NISA and NSC report estimated the total air release of iodine-131 at 130 PBq and 150 PBq, respectively – about 30 grams. However, on 23 April, the NSC revised its original estimates of iodine-131 released. The NSC did not estimate the total release size based upon these updated numbers, but estimated a release of 0.14 TBq per hour on 5 April.
On 22 September the results were published of a survey conducted by the Japanese Science Ministry. This survey showed that radioactive iodine was spread northwest and south of the plant. Soil samples were taken at 2,200 locations, mostly in Fukushima Prefecture, in June and July, and with this a map was created of the radioactive contamination as of 14 June. Because of the short half-life of 8 days only 400 locations were still positive. This map showed that iodine-131 spread northwest of the plant, just like caesium-137 as indicated on an earlier map. But I-131 was also found south of the plant at relatively high levels, even higher than those of caesium-137 in coastal areas south of the plant. According to the ministry, clouds moving southwards apparently caught large amounts of iodine-131 that were emitted at the time. The survey was done to determine the risks for thyroid cancer within the population.
On 31 October the Japanese ministry of Education, Culture, Sports, Science and Technology released a map showing the contamination of radioactive tellurium-129m within a 100-kilometer radius around the Fukushima No. 1 nuclear plant. The map displayed the concentrations found of tellurium-129m – a byproduct of uranium fission – in the soil at 14 June 2011. High concentrations were discovered northwest of the plant and also at 28 kilometers south near the coast, in the cities of Iwaki, Fukushima Prefecture, and Kitaibaraki, Ibaraki Prefecture. Iodine-131 was also found in the same areas, and most likely the tellurium was deposited at the same time as the iodine. The highest concentration found was 2.66 million becquerels per square meter, two kilometers from the plant in the empty town of Okuma. Tellurium-129m has a half-life of 6 days, so present levels are a very small fraction of the initial contamination. Tellurium has no biological functions, so even when drinks or food were contaminated with it, it would not accumulate in the body, like iodine in the thyroid gland.
On 24 March, the Austrian Meteorological Service report estimated the total amount of caesium-137 radiation released into the air as of 19 March based on extrapolating data from several days of ideal observation at a handful of worldwide CTBTO radionuclide measuring facilities. The agency estimated an average being 5,000 TBq daily. Over the course of the disaster, Chernobyl put out a total of 85,000 TBq of caesium-137. However, later reporting on 12 April estimated total caesium releases at 6,100 TBq to 12,000 TBq, respectively by NISA and NSC – about 2–4 kg. On 23 April, NSC updated this number to 0.14 TBq per hour of caesium-137 on 5 April, but did not recalculate the entire release estimate.
On 12 October 2011 a concentration of 195 becquerels/kilogram of Strontium-90 was found in the sediment on the roof of an apartment building in the city of Yokohama, south of Tokyo, some 250 km from the plant in Fukushima. This first find of strontium above 100 becquerels per kilogram raised serious concerns that leaked radioactivity might have spread far further than the Japanese government expected. The find was done by a private agency that conducted the test upon the request of a resident. After this find Yokohama city started an investigation of soil samples collected from areas near the building. The science ministry said that the source of the Strontium was still unclear.
On 30 September 2011, the Japanese Ministry of Education and Science published the results of a plutonium fallout survey, for which in June and July 50 soil samples were collected from a radius of slightly more than 80 km around the Fukushima Daiichi plant. Plutonium was found in all samples, which is to be expected since plutonium from the nuclear weapon tests of the 1950s and '60s is found everywhere on the planet. The highest levels found (of Pu-239 and Pu-240 combined) were 15 becquerels per square meters in Fukushima prefecture and 9.4 Bq in Ibaraki prefecture, compared to a global average of 0.4 to 3.7 bq / kg from atomic bomb tests. Earlier in June, university researchers detected smaller amounts of plutonium in soil outside the plant after they collected samples during filming by NHK.
A recent study published in Nature found up to 35 bq / kg plutonium 241 in leaf litter in 3 out of 19 sites in the most contaminated zone in Fukushima. They estimated the Pu-241 dose for a person living for 50 years in the vicinity of the most contaminated site to be 0.44 mSv. However, the Cs-137 activity at the sites where Pu-241 was found was very high (up to 4.7Mbq / kg or about 135,000 times greater than the plutonium 241 activity), which suggests that it will be the Cs-137 which prevents habitation rather than the relatively small amounts of plutonium of any isotope in these areas.
On 21 April, TEPCO estimated that 520 tons of radioactive water leaked into the sea before leaks in a pit in unit 2 were plugged, totaling 4,700 TBq of water release (calculated by simple sum, which is inconsistent with the IAEA methodology for mixed-nuclide releases) (20,000 times facility's annual limit). TEPCO's detailed estimates were 2,800 TBq of I-131, 940 TBq of Cs-134, 940 TBq of Cs-137.
Another 300,000 tons of relatively less-radioactive water had already been reported to have leaked or been purposefully pumped into the sea to free room for storage of highly radioactively contaminated water. TEPCO had attempted to contain contaminated water in the harbor near the plant by installing "curtains" to prevent outflow, but now believes this effort was unsuccessful.
According to a report published in October 2011 by the French Institute for Radiological Protection and Nuclear Safety, between 21 March and mid-July around 2.7 × 1016 Bq of caesium-137 (about 8.4 kg) entered the ocean, about 82 percent having flowed into the sea before 8 April. This emission of radioactivity into the sea represents the most important individual emission of artificial radioactivity into the sea ever observed.
However, the Fukushima coast has some of the world's strongest currents and these transported the contaminated waters far into the Pacific Ocean, thus causing great dispersion of the radioactive elements. The results of measurements of both the seawater and the coastal sediments led to the supposition that the consequences of the accident, in terms of radioactivity, would be minor for marine life as of autumn 2011 (weak concentration of radioactivity in the water and limited accumulation in sediments). On the other hand, significant pollution of sea water along the coast near the nuclear plan might persist, because of the continuing arrival of radioactive material transported towards the sea by surface water running over contaminated soil. Further, some coastal areas might have less-favorable dilution or sedimentation characteristics than those observed so far. Finally, the possible presence of other persistent radioactive substances, such as strontium-90 or plutonium, has not been sufficiently studied. Recent measurements show persistent contamination of some marine species (mostly fish) caught along the coast of Fukushima district.
Organisms that filter water and fish at the top of the food chain are, over time, the most sensitive to caesium pollution. It is thus justified to maintain surveillance of marine life that is fished in the coastal waters off Fukushima. Despite caesium isotopic concentration in the waters off of Japan being 10 to 1000 times above concentration prior to the accident, radiation risks are below what is generally considered harmful to marine animals and human consumers.
A year after the disaster, in April 2012, sea fish caught near the Fukushima power plant still contain as much radioactive 134Cs and 137Cs compared to fish caught in the days after the disaster. At the end of October 2012 TEPCO admitted that it could not exclude radiation emissions into the ocean, although the radiation levels were stabilised. Undetected leaks into the ocean from the reactors, could not be ruled out, because their basements remain flooded with cooling water, and the 2,400-foot-long steel and concrete wall between the site’s reactors and the ocean, that should reach 100 feet underground, was still under construction, and would not be finished before mid-2014. Around August 2012 two greenling were caught close to the Fukushima shore, they contained more than 25,000 becquerels a kilogram of cesium, the highest cesium levels found in fish since the disaster and 250 times the government’s safety limit.
In August 2013, a Nuclear Regulatory Authority task force reported that contaminated groundwater had breached an underground barrier, was rising toward the surface and exceeded legal limits of radioactive discharge. The underground barrier was only effective in solidifying the ground at least 1.8 meters below the surface, and water began seeping through shallow areas of earth into the sea.."