Indoor Air Quality - Radon
What is Radon?
Radon is a naturally occurring radioactive gas. It is colorless, odorless, tasteless, and chemically inert. Unless you test for it, there is no way of telling if it is present and how much is there.
Radon is formed by the natural radioactive decay of uranium in rock and soil. Naturally existing, low levels of uranium occur widely in the Earth's crust. Thus, it can be found in all 50 states. Uranium decays into several other elements (called "daughters"), one at a time and is collectivity known as a "decay chain". Along this decay chain, one of the elements that is produced is Radon. Radon is unique from the other Uranium decay products because it is a gas and as a gas, it is capable of migrating from its' original Uranium location into the surrounding soil gas. Once produced, radon moves through the ground into the air above. The worldwide average is about two radon atoms are emitted from every square centimeter of soil everywhere on the Earth every second of the day. Thus, virtually every house on the planet has had Radon present.
Why is Radon dangerous?
To understand Radon's danger, we have to understand what it means to be radioactive and thus the dangers from radioactive decay. Radioactive decay is the spontaneous disintegration of an unstable nucleus of a molecule and the resulting material is now referred to as the "daughter" of the original material. During each radioactive decay, energy is released from the atom. The released energy is collectively given the term "ionizing radiation" and the atom is said to exhibit "radioactivity". At least one of three types of ionizing radiation is emitted during each decay by Radon and the short lived radon daughters: alpha, beta, and gamma particles. Of these, the alpha particles are the most easily stopped and therefore present the biggest danger. Since the alpha particle is large and easily stopped, the alpha particle transfers virtually all of its energy to the material which has stopped the particle. Since Radon is airborne, the daughters of Radon also have a high probability of being airborne. If the Radon or its' daughters are breathed in and thus inside the lung when they decay, the lining of the lung wall becomes the stopping material. Since the alveolar cells of the lung wall do not have a significant protective coating, an alpha particle can collide with the live cell and impart an enormous amount of energy to the cell. This imparted energy can possibly disrupt the DNA within the cell. If the body's DNA repair mechanisms fail, the cell may encode improper information or may "dedifferentiate". In other words, it may cause Cancer. Only smoking causes more cases of lung cancer. If you smoke and are exposed to elevated radon levels, your risk of lung cancer is especially high.
What is the "acceptable" level of radon in the air?
The EPA states that any Radon exposure carries some risk; no level of Radon exposure is always safe. However, the EPA recommends homes be fixed if an occupant's long-term exposure will average 4 pico-curies per liter (pCi/L) or higher. Interestingly, New Jersey has set a limit of only 2 pCi/L.
A pCi is a measure of the rate of radioactive decay of Radon. One pCi is one trillionth of a Curie, which is 0.037 disintegrations per second or 2.22 disintegrations per minute. Therefore, at the EPA recommended action level of 4 pCi/L in a 10 foot by 10 foot room with 8 foot ceiling during a 24 hour period, there will be approximately 290 million disintegrations.
How often is indoor Radon a problem?
Nationwide, nearly one out of every 15 homes has a Radon level the EPA considers to be elevated (meaning 4 pCi/L or greater). The US average radon-in-air level in single family homes is 1.3 pCi/L. In Utah in Salt Lake County, the average radon-in-air level is 4.2 pCi/L and 1 in 3 houses exceed the EPA's action level of 4 pCi/L. Davis county's average is slightly higher at 4.7 pCi/L, Utah county's average is slightly lower at 4.1 pCi/L. Summit and Tooele counties are both higher averaging 5.0 pCi/L, but with the limited number of tests performed in these counties this number may not be an accurate average although it can still be used as good indicator that testing should be done.
How does Radon get into a building?
Most indoor Radon comes into the building from the soil or rock beneath it. Radon and other gases rise through the soil and get trapped under the building. The trapped gases build up pressure. Air pressure within homes is usually lower (due to stack effect and ventilation equipment) than the pressure in the soil. Therefore, the higher pressure under the building forces gases through the cracks and gaps, in the floor and walls, and into the building. Once inside, radon can become trapped and concentrated.
How do I know if Radon is a problem in my house?
The simple answer is to get it tested. Indoor Radon levels vary building to building. You cannot rely on Radon test results in other houses in the neighborhood - even ones next door - to estimate the Radon level in your house. The existence of even a small deposit of radium under a building will greatly influence the concentration of radon gas within the building. Micro geological formations such as local disturbances during construction, micro faults, and rock out-croppings can significantly alter the Radon concentration at the surface. Thus the soil and rock formations under your house can cause the Radon levels to vary greatly. In general, houses built closer to the mountain, over the hard rock, tend to have higher Radon levels than those built in the flat areas of the valley (i.e. lake bottom). This is most likely because the Radon has more avenues for escape with the houses built over lake bottom compared to the houses built over the hard rock.
How do I get my house tested?
First off, no one actually tests for Radon, this is too expensive. The tests that are done trap the decay products from the short lived radon daughters and the Radon level are derived from that information. There are three types of tests that can be performed: charcoal canisters, alpha-track monitors, and continuous working level monitors. There are advantages and disadvantages to each and with the exception of real estate transaction (professional only), each can be done by a professional or a homeowner.
Charcoal canisters method is the most widely used method of screening. It measures the gamma radiation from the short lived radon daughters. The test is widely available, a kit can be found at most home improvement store, and for around $30 per test is relatively inexpensive. However, the weather can have a strong influence on the results. For example, if there was a rain storm or it is cold outside, these can cause the results to be higher than if the test was done on a dry or mild temperature day.
Interesting Links
Utah' Dept of Environmental Quality - Radon info
Environmental Protection Agency - EPA's radon information