Naturally Occurring Radiation
Naturally occurring radiation can be found all around us. Radiation can be found in soils, in our air and water, and in us. Because it occurs in our natural environment, we encounter it every day through the food we eat, the water we drink, and the air we breathe. It is also in building materials and items we commonly use.
There are three groupings of naturally occurring radiation, mostly based on where the radiation comes from. First there is the radiation in the soils and rocks, called primordial or terrestrial. Then there is radiation that comes from space, called cosmic or cosmogenic. The third is human-made, something created by humans that wouldn’t exist otherwise or something that contains more radiation in it than normal (enhanced) because humans have done something to it.
It has been estimated that individuals in the United States receive about 0.62 rem each year from all of these sources (Table source: NCRP 160, 2009).
Annual U.S. Estimated Radiation Dose Per Person
|Source||Average annual effective dose (mrem)|
|Radon and other radionuclides we eat, drink, or breathe||
|Radiation from soils, rocks, building materials||
Most of the radiation dose we receive is from naturally occurring sources—most of this is from radon (discussed in the following part). The next largest dose is from medical radiation. The smallest dose we receive (<1 percent) is from nuclear power plant emissions and fallout from past atomic bomb detonations.
Individuals who frequently fly wonder about the extra radiation exposure they receive from flying. That depends on several things, including how long the flight lasts, how high up the plane flies and, of course, how often a person flies. Some of the approximate doses when flying at 36,000 feet are:
- New York to Los Angeles round trip = 4 mrem
- New York to Paris round trip = 6 mrem
- New York to London round trip = 6 mrem
- Los Angeles to Paris round trip = 10 mrem
- Los Angeles to Chicago round trip = 2 mrem
Radon is a colorless, odorless gas that can be found in the soil and rocks beneath homes, in well water, and in building materials. Radon is in the soil because the soil contains naturally occurring uranium that eventually decays to radon gas. Radon can get into our homes from the soil through any cracks or holes in the foundation and from the water supply. The radon concentration allowed in water supplies is highly regulated; therefore, it is the radon in air coming in to your home from the ground that can pose a danger.
Radon can pose a danger if it concentrates to high levels once it gets in the house. We build our newer homes to be very fuel efficient and well insulated, and because we do that, there is little outdoor air exchange unless we open doors or windows. This gives radon the opportunity to build up if it is able to get into the house. That is one of the factors determining radon activity in houses—can it get into the house? Another factor is how much is coming out of the ground. Certain types of soils—those high in limestone, for example—appear to have a higher concentration of radon to release.
Of course, radon is in the natural outdoor air as well, but it is diluted by all the air that is available. The Environmental Protection Agency (EPA) did a national survey in the United States and determine that the average indoor air concentration (1.3 picocuries of radon per liter of air) is about three times higher than the average outdoor air concentration (0.4 picocuries per liter). The average indoor air concentration is three times less than the recommended limit (4.0 picocuries per liter). Even though, on average, we could expect our house to have about 1.3 picocuries per liter of radon, the EPA estimates that nearly 1 out of every 15 homes in the United States has elevated radon levels.
Since radon is a gas, it is inhaled into our lungs as we breathe. Although much of the radon is then exhaled, the portion that stays in the lungs as radon (and then as the radioactive decay products that come from radon) irradiates the lungs. We are also getting radioactive materials into our lungs when we inhale radon’s radioactive decay products in the air we’re breathing. It has been estimated by the EPA that radon and its decay products may cause up to 21,000 lung cancers each year—second only to cigarette smoking.
If you have concerns and want more information, or to find out how to monitor the level of radon in your home, visit the EPA Web site ( www.epa.gov).