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Natural background radiation

We are all exposed to some amount of radiation just from being on this planet. This is known as background radiation. In the United States this averages about 3 millisieverts (mSv) per year. For most people, background radiation is most of their exposure to ionizing radiation during the year. It comes from several sources.

Cosmic rays

Cosmic rays are radioactive particles that hit the earth from outer space. They come from the sun and from other stars. The earth’s atmosphere blocks a portion of these rays, but some of them reach the ground.

Because the atmosphere blocks some cosmic rays, exposure is greater at higher altitudes. For example, people who live in Denver, Colorado, which is at a high elevation, are exposed to slightly more cosmic rays than people living at sea level.

People are also exposed to higher levels of cosmic rays during airplane flights. Airline pilots and flight attendants, who spend many hours at high elevations, are exposed to more of these rays, but it is not clear if they have an increased risk of cancer because of it.

Radiation in the earth

People are also exposed to small amounts of radiation from radioactive elements that occur naturally in rocks and soil. Some of these may end up in building materials used in houses and other structures. Tiny amounts of radiation may even be found in drinking water and in some plant-based foods as a result of being in contact with the soil. For people who smoke, tobacco can account for a significant portion of the yearly radiation they receive.

Radon

The largest source of natural background radiation for most people is radon. This is an odorless, colorless gas that is formed from the breakdown of radioactive elements in the ground. Radon levels are usually higher inside buildings and homes, especially in levels closer to the ground such as basements. Radon levels can vary a great deal, depending on where you live. Some people, such as people who work in mines, are exposed to higher radon levels at work.

For more on radon and its possible health effects, see Radon and Cancer.

Non-medical sources of man-made radiation

People may also be exposed to ionizing radiation from non-medical man-made sources.

Nuclear weapons

The atomic bombs dropped on Nagasaki and Hiroshima, Japan, exposed many people to radiation from x-rays, gamma rays, and neutrons. Some people died fairly quickly as a result of burns and radiation sickness, but many survived. The survivors were exposed to different amounts of radiation, depending largely on how far they were from the explosions. Much of the information that we have about radiation and cancer risk comes from studies of these survivors.

The United States government conducted above-ground nuclear tests in the South Pacific and in the state of Nevada between 1945 and 1962. Other countries have also conducted above-ground tests. Many people in the military at the time were part of training exercises in the area and were exposed to ionizing radiation from these tests. Others were exposed to radiation while working at facilities making the bombs or at other nuclear sites.

Non-military people living near or downwind of nuclear test sites may have also been exposed to radioactive byproducts. Levels of radiation are likely to be higher near these sites, but some radioactive particles from the tests entered the atmosphere and traveled great distances, landing thousands of miles away from the original site. While exposure levels were likely to be higher at the time of testing, some radiation in the soil today is the result of these tests.

Government programs have been set up to give financial support to people who were exposed to nuclear weapons testing and developed cancer. 

Nuclear power plants

Emissions of radiation from nuclear power plants are carefully monitored and controlled. According to the US Environmental Protection Agency (EPA), nuclear power plant operations account for less than 1/100 of 1% of the average American’s total radiation exposure.

Nuclear power plant accidents: Accidents at nuclear power plants are rare, but they could possibly expose people to high levels of radiation.

In 1986, an accident at the nuclear power plant at Chernobyl (in Ukraine) exposed millions of people living in the area to radiation, either directly or from radioactive elements released into the air that ended up deposited on the ground. The emergency clean-up workers were exposed to the highest levels of radiation.

In 2011, an earthquake and tsunami struck the coast of Japan that resulted in damage to the Fukushima Daiichi Nuclear Power Plant in Fukushima Prefecture, Japan. Radiation was released into the air, contaminating soil, food, and water (both fresh and seawater). An area of more than 300 square miles around the plant was found to be contaminated with radiation, although at lower levels than within the plant. Because of high radiation levels, many areas were evacuated. The health effects of this disaster are still being studied.

Workplace exposures

Some people can be exposed to radiation at work. For example:

• People who work in nuclear power plants may be exposed to higher levels of radiation than the general public, although their exposure levels are monitored carefully.
• People who work in uranium mines are monitored because of their exposure to radiation in the form of radon.
• People who work in health or dental care, particularly those who work with x-ray (or other imaging test) equipment or who work with radioactive isotopes, may also be exposed to radiation at work. Radiation exposure may also occur at some research labs.

In the United States, people who are likely to be exposed to radiation in the workplace are monitored carefully. Exposure is limited to an effective dose of 100 mSv over 5 years, with a maximum of 50 mSv in any single year.

Consumer products

Some consumer products contain small amounts of ionizing radiation.

For example, tobacco products contain low levels of radiation, which may come from the soil it’s grown in or the fertilizer used to help it grow. Tobacco may account for a significant portion of the yearly radiation exposure for people who smoke.

Some building materials used in the home or other structures may contain low levels of naturally occurring radiation, which can be given off in the form of radon gas. The amount of radiation can vary depending on what they’re made of, but the levels are unlikely to contribute much to a person’s overall exposure to radiation, according to the EPA. To learn more, see Radon and Cancer.

Many smoke detectors contain a small amount of a very low-level radioactive material that helps detect the smoke. This material is sealed in a container and does not pose a significant risk of radiation exposure.

Food irradiation

Ionizing radiation can be used to kill bacteria and other germs on certain foods, which may make them safer to eat and help them last longer. Some people may be concerned that irradiated food may itself contain radiation.

It’s important to understand that the radiation does not stay in the food. According to the US Food and Drug Administration (FDA), irradiating food does not make it radioactive and does not change its nutritional value, nor does it noticeably change the taste, texture, or appearance of the food.