The radiation effects from the Fukushima nuclear accident are the observed and predicted effects as a result of the release of radioactive isotopes from the Fukushima Daiichi Nuclear Power Plant following the 2011 Tōhoku earthquake and tsunami. The release of radioactive isotopes from reactor containment vessels was a result of venting in order to reduce gaseous pressure, and the discharge of coolant water into the sea. This resulted in Japanese authorities implementing a 30 km exclusion zone around the power plant and the continued displacement of approximately 156,000 people as of early 2013. The number of evacuees has declined to 49,492 as of March 2018. Radioactive particles from the incident, including iodine-131 and caesium-134/137, have since been detected at atmospheric radionuclide sampling stations around the world, including in California and the Pacific Ocean.
Preliminary dose-estimation reports by the World Health Organization (WHO) and the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) indicate that, outside the geographical areas most affected by radiation, even in locations within Fukushima Prefecture, the predicted risks remain low and no observable increases in cancer above natural variation in baseline rates are anticipated. In comparison, after the Chernobyl reactor accident, only 0.1% of the 110,000 cleanup workers surveyed have so far developed leukemia, although not all cases resulted from the accident. However, 167 Fukushima 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 radioactivity release from the Fukushima Daiichi nuclear plant could cause 130 deaths from cancer globally (the lower bound for the estimate being 15 and the upper bound 1100) and 199 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 "because 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."
Health effects
Preliminary dose-estimation reports by the World Health Organization and the 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 this risk may not be statistically detectable, as has happened in the case of the Chernobyl disaster. After the Chernobyl accident, only 0.1% of the 110,000 cleanup workers surveyed have so far developed leukemia, although not all cases resulted from the accident Estimated effective doses from the Fukushima accident outside 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 radioactivity 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 in Hiroshima and Nagasaki). However, people who have been evacuated have suffered from depression and other mental health effects.
While there were no deaths caused by radiation exposure, approximately 18,500 people died due to the earthquake and tsunami. Very few cancers would be expected as a result of the very low radiation doses received by the public. John Ten Hoeve and Stanford University professor Mark Z. Jacobson suggest that according to the linear no-threshold model (LNT) the accident is most likely to cause an eventual total of 130 (15–1100) cancer deaths, while noting that the validity of the LNT model at such low doses remains subject to debate. Radiation epidemiologist Roy Shore contends that estimating health effects in a population from the LNT model "is not wise because of the uncertainties". The LNT model did not accurately model casualties from Chernobyl, Hiroshima, or Nagasaki; it greatly overestimated the casualties. Evidence that the LNT model is a gross distortion of damage from radiation has existed since 1946 and was suppressed by Nobel Prize winner Hermann Müller in favour of assertions that no amount of radiation is safe.
Two years after the incident (in 2013), the World Health Organization (WHO) indicated that the residents of the area who were evacuated were exposed to little radiation and that radiation induced health impacts are likely to be below detectable levels. The health risks in the WHO assessment attributable to the Fukushima radioactivity release were calculated by largely applying the conservative Linear no-threshold model of radiation exposure, which assumes that even the smallest amount of radiation exposure has a negative health effect.
The WHO report released in 2013 predicts that for populations living around the Fukushima nuclear power plant there is a 70% higher relative risk of developing thyroid cancer for females exposed as infants, a 7% higher relative risk of leukemia in males exposed as infants, and a 6% higher relative risk of breast cancer in females exposed as infants. The WHO stresses that the percentages stated in that section of their report are relative risk increases of developing these cancers, not absolute risk increases, since the lifetime absolute baseline risk of developing thyroid cancer in females is 0.75% and the radiation-induced cancer risk is now predicted to increase that 0.75% to 1.25%, with this 0.75% to 1.25% change representing the "70% higher relative risk":
The WHO calculations determined that the most at-risk group, infants who were in the most affected area, would experience an absolute increase in the risk of cancer (of all types) during their lifetime of approximately one percent (1%) due to the accident. And the lifetime risk increase for thyroid cancer due to the accident for a female infant in the most affected radiation location was estimated to be one half of one percent (0.5%). Cancer risks for unborn children are considered to be similar to those for one-year-old infants.
The estimated risk of cancer to people who were children and adults during the Fukushima accident in the most affected area was determined to be lower than that of the most at-risk group—infants. A thyroid ultrasound screening programme was conducted in 2013 in the entire Fukushima Prefecture; this screening programme is, due to the screening effect, likely to record an increase in the incidence of thyroid disease due to early detection of non-symptomatic disease cases. About one-third of people (~30%) in industrialized nations are presently diagnosed with cancer during their lifetimes. Radiation exposure can increase cancer risk, with the cancers that arise being indistinguishable from cancers resulting from other causes.
In the general population, no increase is expected in the frequency of tissue reactions attributable to radiation exposure and no increase is expected in the incidence of congenital or developmental abnormalities, including cognitive impairment attributable to in-utero radiation exposure. No significant increase in heritable effects has been found in studies of the children of the survivors of the atomic bombings of Hiroshima and Nagasaki or in the offspring of cancer survivors treated with radiotherapy, which indicates that moderate acute radiation exposures have little impact on the overall risk of heritable effects in humans.
As of August 2013, there have been more than 40 children newly diagnosed with thyroid cancer and other cancers in Fukushima Prefecture. 18 of these were diagnosed with thyroid cancer, but these cancers are not attributed to radiation from Fukushima, as similar patterns occurred before the accident in 2006 in Japan, with 1 in 100,000 children per year developing thyroid cancer in that year, that is, this is not higher than the pre-accident rate. While controversial scientist Christopher Busby disagrees, claiming the rate of thyroid cancer in Japan was 0.0 children per 100,000 in 2005, the Japan Cancer Surveillance Research Group showed a thyroid cancer rate of 1.3 per 100,000 children in 2005 based on official cancer cases. As a point of comparison, thyroid cancer incidence rates after the Chernobyl accident of 1986 did not begin to increase above the prior baseline value of about 0.7 cases per 100,000 people per year until 1989 to 1991, 3 to 5 years after the accident in both the adolescent and children age groups. Therefore, data from Chernobyl suggests that an increase in thyroid cancer around Fukushima is not expected to begin to be seen until at least 3 to 5 years after the accident
According to the Tenth Report of the Fukushima Prefecture Health Management Survey released in February 2013, more than 40% of children screened around Fukushima Prefecture were diagnosed with thyroid nodules or cysts. Ultrasonographic detectable thyroid nodules and cysts are extremely common and can be found at a frequency of up to 67% in various studies. 186 (0.5%) of these had nodules larger than 5.1 mm and/or cysts larger than 20.1 mm and underwent further investigation. None had thyroid cancer. Fukushima Medical University gives the number of children diagnosed with thyroid cancer as of December 2013 as 33 and concluded, "[I]t is unlikely that these cancers were caused by the exposure from 131I from the nuclear power plant accident in March 2011".
A 2013 article in the Stars and Stripes asserted that a Japanese government study released in February of that year had found that more than 25 times as many people in the area had developed thyroid cancer compared with data from before the disaster.
As part of the ongoing precautionary ultrasound screening program in and around Fukushima, (36%) of children in Fukushima Prefecture in 2012 were found to have thyroid nodules or cysts, but these are not considered abnormal. This screening programme is, due to the screening effect, likely, according to the WHO, to lead to an increase in the incidence of the diagnosis of thyroid disease due to early detection of non-symptomatic disease cases. For example, the overwhelming majority of thyroid growths prior to the accident, and in other parts of the world, are overdiagnosed (that is, a benign growth that will never cause any symptoms, illness, or death for the patient, even if nothing is ever done about the growth) with autopsy studies, again done prior to the accident and in other parts of the world, on people who died from other causes showing that more than one third (33%+), of adults technically has a thyroid growth/cancer, but it is benign/never caused them any harm.