Effects of radiation on human health and the environment


The 2011 Tohoku earthquake at 14:46 JST (05:46 UTC) on Friday, March 11, 2011 was a 9.0-magnitude earthquake, with its epicenter off the coast of northeast Japan, close to the city of Sendai.

The earthquake triggered a tsunami, with waves of up to 98 ft that struck Japan minutes after the quake. (Source: NHK World News, March 30, 2011)

Fukushima Daiichi Nuclear power plant with 6 reactor units, located in Fukushima Prefecture, Japan was crippled by the tsunami when it disabled emergency generators required to cool the reactors, leading to severe problems. The integrity of primary containment vessels was damaged by explosions from hydrogen gas, and there was evidence of a partial nuclear meltdown in some of the units. In addition, radiation is leaking from these damaged units. The main radioactive components likely to escape when a reactor's fuel rods are breached are Iodine-131 and Cesium-137.

People from around the nuclear power plant have been evacuated. Outside of Japan, the public has been concerned about the effect of this radiation as it is carried away from the power plant.

What are the implications of Japanese earthquake for Washington State?

Washington State Department of Health responds to radiation implications.

What is the risk to the West Coast of radiation fallout?

The US Environmental Protection Agency (EPA) collects information through its RadNet Air Monitoring program. The program monitors potential routes of exposure to radiation, which include milk, precipitation, and drinking water. On March 22, 2011, the EPA published the statement: "Radiation Monitors Continue to Confirm That No Radiation Levels of Concern Have Reached the United States".

For more information on EPA's Radiation Air Monitoring Program, with regard to the Japanese Nuclear Emergency.

Is it safe to eat food from Japan?

Plants can become radioactive when radioactive material enters the soil and is taken up by root systems or when radioactive particles in the air settle on edible portions of the plant. Milk and meat can become contaminated when animals eat grass and other plants that are radioactive. When humans eat radioactive plants or animals, the radioactive substances, such as iodine 131, can settle in particular organs, like the thyroid gland.  This can increase the risk of thyroid cancer. Children are more vulnerable than adults to exposure to radiation because they are still growing and can absorb more contamination. 

The Japanese government has restricted the sale of some products from the affected areas.  The Food and Drug Administration (FDA) screens all imported food at US borders, and the agency recently announced that screening for radiation contamination will be stepped up. The US imports less than 4% of its food from Japan. (Source: Food from Japan: FDA checking food for radiation. LA Times, March 17, 2011) The "FDA and the Japanese government will continue to collaborate to ensure products from the affected [areas] do not pose a health risk to U.S. consumers. FDA will continue monitoring the public health risks due to radionuclide contamination, and when appropriate will remove the Import Alert and resume routine coverage of entries." (Source: US FDA)

For more information on food safety, see the FDA website.

What is ionizing radiation?

Radioactive materials that decay spontaneously produce ionizing radiation, which has sufficient energy to strip away electrons from atoms (creating two charged ions) or to break some chemical bonds. Any living tissue in the human body can be damaged by ionizing radiation. The body attempts to repair the cellular the damage, but sometimes the damage is of a nature that cannot be repaired or it is too severe or widespread to be repaired. Also mistakes made in the natural repair process at the cellular level can lead to cancerous cells. The most common forms of ionizing radiation are alpha and beta particles, and gamma and X-rays. (Source: EPA)

What are the common forms of radiation?

Alpha particles: helium nuclei consisting of two protons and two neutrons

  • Are emitted from radioactive elements such as uranium, plutonium, and radium
  • Cannot penetrate the skin, so only are dangerous if inhaled or swallowed and radiation is emitted inside the body.

Beta particles: fast-moving electrons

  • Emitted by many radioactive elements, such as iodine 131 and cesium 137
  • More penetrating than alpha particles, but can be easily shielded
  • All beta emitters, depending on the amount present, can pose a hazard if inhaled, ingested or absorbed into the body.  In addition, energetic beta emitters are capable of presenting an external radiation hazard, especially to the skin.

Gamma rays: high-energy beams (similar to X-rays)

  • Emitted by many radioactive elements, such as uranium, iodine 131, and cesium 137
  • Are very penetrating
  • Damages or kills cells

(Source: Washington Department of Health, What is Ionizing Radiation?)

How do scientists describe radiation levels?

Radiation is measured as an element’s activity or source strength, in Curies (Ci) or Becquerels (Bq).  These are measures of the number of particles (alpha or beta) or energy (gamma) emissions per time period.  Each of these emissions is also considered a "disintegration" of the element.

Radiation can also be measured in terms of the equivalent dose that would be absorbed by the human body. This is measured in terms of Standard International (SI) units, such as Sievert (Sv). A Sv is an international unit of absorbed radiation dose in tissue.  This dose is based
on the ionizing energy deposited in tissue, and takes into account the amount of damage caused by different types of radiation.   Because doses are typically low, they are commonly described as 1/1000’s of Sieverts or millisievert (mSv). The rate of this dose is also an important factor, so can be described over a time frame (mSv/hour or mSv/year) or as instantaneous (mSv).  See the slideshow from the US Department of Energy for more information on measuring radiation dose.

To put this incident into perspective, you can estimate your dose by using the US EPA’s radiation dose calculator.

What are the possible health effects from a dose of radiation?

Dose (Sv)SymptomsOutcome
0 - 0.25None--
0.25 - 1Some people feel nausea and loss of appetiteBone marrow damage, lymph nodes and spleen damaged
1 - 3Mild to severe nausea, loss of appetite and infectionSame as above, but more severe. Recovery probable, but not assured.
3 - 6Severe nausea, loss of appetite, plus hemorrhaging, infection, diarrhea, skin peels, and sterilityDeath occurs if doses higher than 3.5 Sv are left untreated
6 - 10Above symptoms plus impairment of the central nervous systemDeath expected
Above 10IncapacitationDeath

Source: Aref L, Culligan PJ, Czerwinski KR, Nepf HM. Nuclear Energy: the Good, the Bad, and the Debatable. Massachusetts Institute of Technology.

For more information on the human health effects of exposure to ionizing radiation see the US EPA's information from its Radiation Protection Programs.

How to reduce personal exposure to radiation?

  • Reduce the time spent near the source of radiation 
  • Increase the distance from the source of radiation
  • Place shielding material between you and the source of radiation

Avoid eating radiation-contaminated foods

How do radiation levels associated with the nuclear event in Japan compare to other sources of ionizing radiation?

The following table shows approximate exposures from various events and activities.

Radiation SourceDose (mSv)Time frame
Fukushima Daiichi nuclear plant in Japan (peak near plant)400per hour
Highest radiation at plant gate, as of March 16, 2011 752per hour
Maximum radiation levels in Tokyo (March 23, 2011)0.0008per hour
Radiation levels first detected in CaliforniaSlightly above background 
Chernobyl nuclear disaster in 1986 (near core)300,000 
Maximum worker exposures at Chernobyl6,000 
Initial fallout in Poland0.01per hour
Japanese regulatory limit for worker exposures
(increased to 250 mSv/yr in March 2011)
100per year
US regulatory limit for worker exposures (whole body)50per year
Recommended exposure limit to industrial radiation exposure to non-radiation workers and public1per year
Radon in average home2per year
Diagnostic X-ray [1]0.5per year
Mammogram [1]0.3 
Chest X-ray [1]0.04 
Coast-to-coast US airplane trip [1]0.041 
Average person in US, from all sources [2]6per year

Information on current status of emergency in Japan

In response to concerns about the safety of drinking water in Japan, the World Health Organization (WHO) says that drinking tap water poses no immediate health risk, but local conditions will differ and may fluctuate. WHO has prepared general advice about drinking water quality and comparative public health risks associated with a nuclear emergency. The event is continuing to evolve and WHO will continue to assess its advice based on the changing situation.

More on the Fukushima Nuclear Accident from the International Atomic Energy Agency

Other Sources of Information

National Council on Radiation Protection and Measurements

US Environmental Protection Agency's information on radon.

US Laws and Regulations

FDA Radiation in food or products.

US Environmental Protection Agency's response to radiation emergencies

Information on nuclear reactors; radioactive waste; regulations for power plants
United States Nuclear Regulatory Commission.

American Nuclear Society: a not-for-profit, international, scientific and educational organization with the purpose to promote the awareness and understanding of the application of nuclear science and technology.

Information on US policy as it relates to ionizing radiation and nuclear power:

Centers for Disease Control & Prevention. Radiation Emergencies.

U.S. Department of Energy. Argonne National Laboratory. Situation at Japan's Nuclear Reactors.

Nuclear Energy Institute.


1. US EPA,Radiation Doses in Perspective

2. NCRP, Ionizing Radiation Exposure of the Population of the United States: (Report No. 160)