At a glance
Terrestrial radiation includes radioactive materials naturally found in the earth, including rocks, soil and more. Radiation can enter the body through eating, or breathing it in. Radiation can also enter the body from direct exposure.
The basics
Radioactive materials are all around us. These materials can be naturally found in the earth and cause direct exposure or terrestrial radiation. We are also exposed to radioactive materials in the earth through breathing and eating (internal radiation). Some types of radioactive materials can also be absorbed through the skin.
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.
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.
Terrestrial external radiation
Every day we are exposed through our skin to external radiation from the earth. Terrestrial external radiation is due to the decay of radioactive materials in the earth itself.
Terrestrial external radiation is created by the process of the natural breakdown—or radioactive decay—of radioisotopes in natural materials such as rocks, soil, vegetation, and groundwater. Radioactive decay is a natural process and has taken place since the beginning of time.
Radioactive materials in the earth expose us directly to radiation in a manner similar to the exposure from a medical x-ray. This is what we call terrestrial (or direct) external radiation.
Common Questions
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.
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.
The overall levels of terrestrial external radiation are low. The average annual dose due to terrestrial external radiation exposure is 0.21 mSv (21 mrem) or 7% of a person's yearly exposure due to all natural sources. 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%
Overall levels of terrestrial external radiation are low and are unlikely to affect human health.