WHY SHOULD I BE CONCERNED?
Photo: Colorado School of Mines
Radon has always been present in the air at low levels, but awareness of radon as a public health concern is a relatively recent development. Since the 1950's, a higher than expected occurrence of lung cancer had been noted in uranium miners in the U.S., Czechoslovakia, France, and Canada. Excess lung cancers were also observed among workers who mined other minerals underground in Newfoundland, Sweden, Britain, France, China, and the U.S.
The presence of radon at elevated levels in homes, commercial buildings, and schools was not well known until the min-1980's, in part because radon cannot be detected by sight, smell, or taste. In December 1984, radon levels in a Pennsylvania house were measured at more than 3,000 pCi/L, among the highest levels ever recorded. Since then, many homes and other buildings in various parts of the United States have been found with radon levels higher than in underground mines.
Today, the effects of radon are well known. In May 2000, for example, the results of a carefully conducted study in Iowa that examined radon risk in homes were released. After taking into account smoking, home occupancy patterns, and other factors including "normal lived-in conditions," a 50% increase in lung cancer risk was found in Iowa women after only fifteen years at an exposure of 4.0pCi/L.
Studies by the National Research Council (which included a comprehensive review of all previous studies) concluded that more than 18,260 people contract lung cancer each year in the United States from exposure to indoor radon. (NRC, BEIR VI, February, 1999).
The issue is not whether radon causes cancer, but rather, how to control the radon exposure in our homes, workplaces, and schools.
RADON DECAY PRODUCTS
Once radon enters a building, it is easily dispersed through the air. The radioactive decay process that led to the creation of radon does not stop once radon forms. Radon decays into several radioactive elements called radon decay products. These decay products are made up of different isotopes of polonium, lead, and bismuth.
Unlike radon, which is a gas, radon decay products are solid particles. The particles become suspended in the air when they are formed from the decaying radon gas. They are extremely small and cannot be seen.
Because of their size, radon decay products are easily inhaled and can attach to lung tissue. They have very short “half-lives,” which means they will decay relatively quickly after they are formed. In fact, once they are inhaled, they can decay there before the lungs have an opportunity to clean themselves.
It is the radon decay products that actually present the health risk associated with radon gas.
The average person breaths in approximately 20,000 liters of air per day, which allows a significant amount of airborne particulates to be introduced into the lungs. A person’s lungs have the ability to eject these particles through normal breathing. However, some of the particles decay very quickly and can irradiate the lungs before being exhaled.
Alpha Particles Are Strong Enough To Pit Plastic
Picture: J.F. Burkhart, Ph.D
Despite their very small size, alpha particles released by the decay of radon and its decay products can damage lung tissue.
This picture shows the damage from alpha particles that struck a piece of plastic in a radon detector during three months in a home that contained an average of of 4.0 pCi/L of radon. During this 90-day period, air in the room diffused (no air pump) through a paper filter into a small container where the piece of plastic was housed. Alpha particles released by the decay of radon and its decay products within the container struck the plastic. The resulting pits or "alpha tracks," are large enough to be seen under relatively low magnification (100 power).
Consider this: If alpha particles are forceful enough to create pits in plastic, they are certainly forceful enough to impact, penetrate, and damage soft tissue. Plus, for any given time period, the simple act of breathing brings far more radon decay products into the lungs than would have diffused (drifted) through a paper filter and into the detector that housed the piece of plastic shown above.
Radon can cause lung cancer; but being exposed to radon does not mean you will contract lung cancer.
To develop lung cancer from radon, the radiation released from its decay has to strike a lung cell, and within that lung cell, it has to strike a specific location.
If the alpha particle hits a live cell's nucleus and damages the cancer suppressant gene in the cell's DNA, an increased risk for contracting lung cancer can exist. In addition to causing direct physical damage to DNA, the alpha particle can also cause ionization of material around the DNA.
This is the way radon -- and more specifically, the radon decay products -- can lead to an increased risk of lung cancer over time.
What is the probability of this happening?
It is based on the level and duration of radon exposure.
Since the radiation is released in a random manner, the potential for lung cancer increases with exposure, whether that be exposure to a small amount of radon for a long period of time or a high amount of radon for a short period of time.
As an illustration, the probability of contracting lung cancer from radon might be compared to a blind-folded person tossing darts at a dartboard. The probability of hitting the board increases if the person throws a single dart at a time for a long time, or if the person throws a handful of darts with each throw for a short time.
Similarly, the risk of radon-induced lung cancer rises with increased radon dosage and/or increased time of exposure. It also means you have more time to respond when radon is low; but the higher the radon, the faster you should act.
Real Estate Professionals may want to avoid making statements such as, "The house tested safe," or "There is no radon in that home." There is always some amount of radon in the air, both indoors and out; and a radon level below 4.0 pCi/L does not mean there is no risk at all.