Radiation from the Earth (Terrestrial Radiation)

What is internal radiation?

Once inside the human body, the decay of radioactive materials results in a radiation dose, and this is referred to as internal radiation

Radioactive materials from the earth can enter into the human body by being inhaled (breathed in) or ingested (eaten).

Inhalation

The naturally occurring radioactive element uranium can break down and change into an odorless, colorless gas known as radon. Radon can be found in rocks, soil, groundwater (well water) and building materials all around us. When radon is released into the environment, we can breathe it in.

For more information on radon, click here

Ingestion

Naturally occurring radioactive elements such as carbon, potassium, uranium, thorium, and radium can be found in the soil and find their way into our food and drinking water and can be ingested.

You can also ingest radon through the water supply. However, ingesting radon poses less of a threat than inhaling it. Radon in groundwater can also contribute to radon levels in indoor air.

How much internal radiation am I exposed to?

Inhalation

On average, a person in the United States inhales enough radioactive materials to cause a radiation dose of 2.28 mSv (228 mrem) per year. About 73% of a person’s yearly exposure to natural sources of radioactive material comes from inhalation. This is mostly in the form of radon, which is the largest source of natural radiation exposure. This yearly amount of radiation is similar to the amount of radiation from twenty chest x-rays.

Ingestion

The overall levels of ingested radioactive materials are low for most people. On average, a person in the United States ingested enough natural sources of radiation to cause a small dose of about 0.29 mSv (29 mrem) per year. About 9% of a person’s yearly exposure to natural sources of radioactive material comes from ingestion. This yearly amount of radiation is similar to the amount of radiation from two chest x-rays.

Average Annual Dose for Natural Sources of Radiation

Source	Average Annual Dose	Percent of Average Annual Dose
Internal (by Inhalation)	2.28 mSv (228 mrem)	73%
External (from Cosmic Exposure)	0.33 mSv (33 mrem)	11%
Internal (by Ingestion)	0.29 mSv (29 mrem)	9%
External (from Terrestrial Exposure)	0.21 mSv (21 mrem)	7%

Reference: National Council on Radiation Protection and Measurements. NCRP Report No. 160, Ionizing Radiation Exposure of the Population of the United States. http://ncrponline.org/publications/reports/ncrp-report-160/

What is the risk from internal radiation we get from the earth?

Unless food products are contaminated as the result of a radiation emergency, levels of ingested radioactive material in the environment are low and are unlikely to affect human health.  Inhaled radioactive material in the form of radon could affect health, and radon levels in buildings should be tested and fixed if they are elevated.

The amounts of radon you are exposed to may differ depending on where you live. Having your home tested is the only effective way to determine whether you or your family is at risk of radon exposure.

 For more information on radon, click here.