Health consequences of the accident of Fukushima

The radioactive substances (radionuclides) released into the atmosphere as a result of the reactor accident in Fukushima on 11.03.2011 were dispersed locally, regionally and globally by the wind and subsequently deposited onto the Earth's surface. Internal radiation exposure to humans occurred through radioactive substances inhaled from the air and further on through ingestion with food. External exposure occurred through radioactive substances in the air and through radionuclides deposited on the ground.

Which radioactive substances were significant in the vicinity of the nuclear power plant of Fukushima Daiichi?

Initially two radioactive substances were of major significance for the radiation exposure of the population in the immediate and distant vicinity of the wrecked reactors in Fukushima.

• Among them were the radioactive isotopes of iodine (in particular iodine-131 and iodine-133). These radionuclides were major determining factors contributing to the radiation exposure in the first days and weeks following the accident. They have a relatively short half-life (the time it takes for a substance to lose half its radioactivity by radioactive decay) of up to 8 days.
  Individuals at risk can alleviate the effects of the radionuclides by the timely intake of high-dose non-radioactive iodine (iodine tablets), as the uptake and accumulation of radioactive iodine inhaled or possibly ingested through food by the thyroid is prevented in this way. Iodine accumulates only in the thyroid.

• The radioactive substances which are decisive for the radiation exposure in the longer term are the radionuclides of the element caesium (especially caesium-134 and caesium-137). These have a half-life of up to 30 years. In this case it is not possible to alleviate radiation exposure by administering medication or taking other measures.
  In the body, caesium enters the cells where it is involved in processes between the interior of the cell and the cellular environment which basically take place in all somatic cells but particularly in muscle and nerve cells. The body eliminates half of the absorbed caesium within about 3 months.

What levels of radiation exposure has the Japanese population in the vicinity of the reactor Fukushima Daiichi received?

In the summer of 2012, the World Health Organization WHO estimated the additional radiation exposures of the Japanese population following the accident in Fukushima. To this end, the WHO considered the additional radiation exposure due to

• the passing radioactive cloud (external radiation exposure),
• inhalation during the passage of the radioactive cloud (internal radiation exposure),
• surface contamination (external radiation exposure),
• inhalation of deposited radioactive particles (internal radiation exposure),
• consumption of contaminated food (internal radiation exposure)

for the age groups

• infants,
• children
• adults

in the following regions:

• the most affected areas of Fukushima prefecture,
• the rest of Fukushima prefecture,
• neighbouring prefectures,
• the rest of Japan,
• neighbouring countries
• the rest of the world.

The WHO estimated the radiation exposure in dose bands (see tables) in order to demonstrate that these estimates do not represent exact values. The dose estimates from their 2012 report were generally confirmed in 2015 in a re-evaluation by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR).

In the Fukushima Health Management Survey (description below) the external radiation doses of 460,000 individuals from Fukushima prefecture were estimated during the first four month following the accident. Depending on their whereabouts during and after the accident, the following doses were calculated:

• 66.3 % of individuals received external doses less than 1 mSv
• 94.9 % received doses less than 2 mSv
• 99.7 % received doses less than 5 mSv.

The maximum external dose was 25 mSv. Measurements of the internal doses of 184,205 residents of Fukushima prefecture found that 99.986 % received additional internal doses of less than 1 mSv by the accident. The maximum internal dose was 3 mSv.

Current information on the radiation (the so-called ambient gamma dose rate, in microsieverts per hour) outside the evacuation zone is available on the website of the Japanese Nuclear Regulation Authority or on the detailed Japan Radiation Map.

Radiation exposures to Japan's neighbouring countries and the rest of the world

The radiation exposures estimated for Japan's neighbouring countries and the rest of the world are significantly lower than the estimated radiation exposures for Japan. In both cases the dose estimates of the WHO are based on, among other things, measurements conducted in Japan.

Estimation of potential health hazards and risks

With the help of independent international experts, the World Health Organization WHO performed first health risk assessments (published on 28 February 2013). The report was based on the WHO's estimation of additional radiation exposures from summer 2012. Staff members of the Federal Office for Radiation Protection, which is a WHO collaborating centre in the field of radiation protection and health, were part of these international expert groups.

This report on health risks draws the following conclusions:

1. For the Japanese population, no deterministic effects (for example tissue reactions) and no increase in infant mortality or the occurrence of miscarriages, congenital malformations, developmental disorders or cognitive impairments are to be expected, as the radiation doses are too low for this to happen;
2. In the most affected regions in Fukushima prefecture, increased risks for certain types of cancer are to be expected mathematically for certain age groups and genders due to the increased radiation exposure that has occurred there;
3. Food and the environment will also have to be monitored in future.
4. Outside Japan no increase in health risks owing to the disaster of Fukushima is to be expected.

For the regions with the highest dose , the excess lifetime risk for leukaemia, breast cancer, thyroid cancer and all malignant tumours combined, shows the highest increase in the following populations:

• For boys who were one year old at the time of the accident, the lifetime risk of leukaemia is increased by up to 7 per cent compared with the spontaneous cancer rate;
• For girls who were one year old at the time of the accident, the lifetime risk of breast cancer is increased by up to 6 per cent compared with the spontaneous cancer rate.
• The lifetime risk of thyroid cancer for girls who were one year old at the time of the accident is increased by up to 70 per cent compared with the spontaneous cancer rate.
• For all solid tumours combined, the lifetime risk for girls who were one year old at the time of the accident is increased by up to 4 per cent compared with the spontaneous cancer rate.

Outside the most affected regions of Fukushima prefecture, that is, for the rest of Japan and for the rest of the world, no observable increases above the natural variations of the spontaneous rates are expected.

For the emergency workers of Fukushima Daiichi nuclear power plant, the risks for leukaemia, thyroid cancer and solid tumours are increased compared with the spontaneous rates.

The relationship between risk of cancer and radiation exposure is complex and depends on factors such as cancer type, gender and the age at which individuals are exposed to radiation. Radiation exposure during infancy or childhood generally leads to a greater increase in risk than exposure during adulthood. The gender-specific lifetime risks for all malignant tumours combined, as well as for leukaemia, thyroid cancer and, additionally for women, the increased risk of breast cancer, were calculated. In the process, three different age groups were considered (1, 10 or 20 years old at the time of the accident). Furthermore, the health risks for emergency workers of the nuclear power plant who were 20, 40 or 60 years old at the time of the accident were calculated.

The health risk data presented in the WHO report do not represent precise predictions, but rather inferences of the magnitude of the expected health risks, since they are grounded on preliminary dose estimates which in turn are based on data available until September 2011.

Fukushima Health Management Survey

In order to investigate the actual health effects of the radiation exposure following the reactor accident, the health authority of Fukushima prefecture has been conducting the Fukushima Health Management Survey since September 2011. It covers

• all residents of the prefecture as well as
• those who had been living in the prefecture at the time of the accident but moved away afterwards and
• the individuals who moved there after the accident.

The population of the survey consists of 2,057,053 individuals of all ages who are to be investigated in a long-term cohort study with regard to their health development. The first step was questioning the individuals about their behaviour shortly after the accident and performing a whole body measurement. On this basis, it was attempted to estimate the actual radiation exposure individually in the best possible way. The health condition of one part of the cohort is then recorded in detail at regular intervals. To this end, the thyroids of 370,000 individuals who were not more than 18 years old at the time of the accident are investigated.

The latest results were published in a report in 2016 that summarises the health effects of the disaster:

• The few cases of thyroid cancer in children that occurred so far in Fukushima Prefecture are probably not caused by the radiation exposure from the accident.
• The portion of individuals with obesity, impaired glucose tolerance, hepatic dysfunction and hypertension in Fukushima prefecture increased.
• Compared with the national average, there are three times as many adolescents and adults with signs of mood disorders, anxiety or post-traumatic disorders.
• While the birth rate decreased temporarily after the disaster, the number of preterm deliveries, low birth-weight babies and congenital anomalies in Fukushima prefecture are comparable to the nationwide trends.

These health effects are not induced by the radiation exposure but rather a result of the psychosocial strain caused by the disaster.

In summary, it can be said that the additional radiation exposure of the population in Japan was altogether and - with exceptions - also in the region of Fukushima relatively low following the Fukushima accident due to favourable winds and evacuation measures. Health effects in the region of Fukushima cannot be excluded. Based on the estimates of the radiation exposures, however, they should be relatively low and limited to the most affected areas. Owing to the scope of the Fukushima Health Management Survey even relatively low increases in risk might possibly be proven.