Japan radiation risk FAQs from the World Health Organization

Current risk of radiation-related health problems in Japan

What is the current risk of radiation-related health problems in Japan to those near the reactor at the time, and those in other parts of Japan?

* The actions proposed by the Government of Japan are in line with the existing recommendations based on public health expertise. The government is asking people living within 20 km of the Fukushima Daiichi nuclear power plant to evacuate and those between 20 km and 30 km away from the plant are asked to stay indoors in unventilated rooms. People living farther away are at lower risk than those who live nearby.

* This assessment can change if there are further incidents at these plants and WHO is following the situation closely. However, radiation-related health consequences will depend on exposure. Exposure in turn is dependent on the amount of radiation released from the reactor, weather conditions such as wind and rain at the time of the exposure, the distance someone is from the plant, and the amount of time someone is in irradiated areas.

What is ionizing radiation?

* When certain atoms disintegrate, either naturally or in man-made situations, they release a type of energy called ionizing radiation (IR). This energy can travel as either electromagnetic waves (gamma or X-rays) or as particles (neutrons, beta or alpha).

* The atoms that emit radiation are called radionuclides.

* The time required for the energy released by a radionuclide to decrease by half (i.e., the half-life) range from tiny fractions of a second to millions of years depending on the type of atoms.

Are people normally exposed to ionizing radiation?

* Human beings are exposed to natural radiation on a daily basis. The radiation comes from space (cosmic rays) as well as natural radioactive materials found in the soil, water and air. Radon gas is a naturally formed gas that is the main natural source of radiation.
* People can also be exposed to radiation from human-made sources. Today, the most common man-made source of ionizing radiation are certain medical devices such as X-ray machines.
* The radiation dose can be expressed in units of Sievert (Sv). On average, a person is exposed to approximately 3.0 mSv/year of which, 80% (2.4 mSv) is due to naturally-occurring sources (i.e., background radiation), 19.6 % (almost 0.6 mSv) is due to the medical use of radiation and the remaining 0.4% (around 0.01 mSv) is due to other sources of human-made radiation.
* In some parts of the world, levels of exposure to natural radiation differ due to differences in the local geology. People in some areas can be exposed to more than 200 times the global average.

How are people exposed to ionizing radiation?

* Ionizing radiation may result from sources outside or inside of the body (i.e. external irradiation or internal contamination).

* Internal contamination may result from breathing in or swallowing radioactive material or through contamination of wounds.

* External irradiation is produced when a person is exposed to external sources such as X-rays or when radioactive material (e.g. dust, liquid, aerosols) becomes attached to skin or clothes, resulting in external contamination.

* External contamination can often be washed off the body.

What type of radiation exposure could occur in a nuclear power plant accident?

* If a nuclear power plant does not function properly, radioactivity may be released into the surrounding area by a mixture of products generated inside the reactor (“nuclear fission products”). The main radionuclides representing health risk are radioactive caesium and radioactive iodine. Members of the public may be exposed directly to such radionuclides in the suspended air or if food and drink are contaminated by such materials.

* Rescuers, first responders and nuclear power plant (NPP) workers may be exposed to higher radiation doses due to their professional activities and direct exposure to radioactive materials inside the power plant.

What is the WHO travel advice for Japan?

At this time, WHO is not advising general restrictions on travel to Japan.

However, travellers should avoid travel to the areas most affected by the earthquake and tsunami because of disruptions to essential services, such as transport and electric power, and the ongoing disaster relief activities, including the nuclear power plant emergency response and control activities, will make travel difficult and could consume resources needed by relief worker and residents. Moreover, as indicated by the Japanese authorities, travel within the evacuation and exclusion zones surrounding the Fukushima Daiichi nuclear power plant is prohibited.

In general, travellers who do not have essential reasons to travel should give careful consideration to deferring travel to any areas where there has been considerable disruption to the normal infrastructure and where authorities are responding to urgent humanitarian needs.

What are the precautions when travelling in Japan?

Travellers should also be aware of the risk of further earthquakes across Japan. Moreover, there may be areas of power, fuel, food and water shortages.

Travellers in Japan should monitor local media, follow the advice and instructions issued by local authorities and register their travel and location details with their respective embassy or consulate. Information on the status of the nuclear facilities in Fukushima can be found on Japan’s Nuclear and Industrial Safety Agency (NISA) website and on the International Atomic Energy Agency (IAEA) website. Additional information can be found on the WHO web site.

* Japan’s Nuclear and Industrial Safety Agency (NISA)

* International Atomic Energy Agency (IAEA)

Do travellers returning from Japan represent a health risk for others?

At this time, only those involved in the emergency response near the plant remain in the area where there are higher levels of radioactivity. For their own safety, all personnel in these areas should undergo decontamination procedures when they leave the site. Travellers returning from Japan who have come from the 20 km evacuation zone surrounding the Fukushima Daiichi nuclear power plant and who have undergone proper screening and decontamination procedures, and travellers from all other areas, do not pose a radioactive health risk to others.

What are the acute health effects of radiation exposure?

* If the dose of radiation exceeds a certain threshold level, then it can produce acute effects, such as skin redness, hair loss, radiation burns, and acute radiation syndrome (ARS1).

* In a nuclear power plant accident, the general population is not likely to be exposed to doses high enough to cause such effects.

* Rescuers, first responders and nuclear power plant workers are more likely to be exposed to doses of radiation high enough to cause acute effects.

What long-term effects can be expected from radiation exposure?

* Exposure to radiation can increase the risk of cancer. Among the Japanese atomic bomb survivors, the risk of leukaemia increased a few years after radiation exposure, whereas the risks of other cancers increased more than 10 years after the exposure.

* Radioactive iodine can be released during nuclear emergencies. If breathed in or swallowed, it will concentrate in the thyroid gland and increase the risk of thyroid cancer. Among persons exposed to radioactive iodine, the risk of thyroid cancer can be lowered by taking potassium iodide pills, which helps prevent the uptake of the radioactive iodine.

* The risk of thyroid cancer following radiation exposure is higher in children and young adults.

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