RADON: A CHEMICALLY INERT HEALTH RISK
Substances that are chemically unreactive are generally not thought to be dangerous to health. However, radon, a colorless, odorless, chemically inert noble gas is considered to be a health risk because it is radioactive. It is believed to be the leading cause of lung cancer among nonsmokers. It has been estimated by U.S. officials that up to 8% of the country's annual lung cancer deaths can be attributed to indoor exposure to radon-222. Radon-222 is formed during a multistep process in which naturally occurring uranium-238 decays to stable lead-206. During one step of the process, radium-226, with a half-life of 1600 years, emits alpha and gamma radiation to produce radon-222:
a + 
Rn + g
Radon-222, with a half-life of 4 days, is produced in rocks and soil that contain even minute amounts of uranium-238. Because it is a gas, radon migrates readily from the soil into the surrounding air. It seeps into houses and other buildings through openings around pipes, and through cracks in basement floors and walls.
The average level of radon in homes is lower than 1 picocurie/L of air. A picocurie (10-12 curie) is equivalent to the radioactive decay of 2 radon nuclei per minute. The EPA recommends an upper limit of 4 picocuries/L for in-door air, and it has been estimated that 99% of the homes in the United States have levels below this value. However, much higher levels have been found. The highest recorded level of radioactivity from radon in a home was 2700 picocuries/L of air. This was found in a home in Pennsylvania that was built on soil rich in uranium-238. The level of radon in home air can be minimized b sealing the entry points and providing good ventilation.
The hazards associated with breathing radon-222 come not only from the alpha radiation given off as the radon decays but also from the daughter products of that decay. None of these decay products are gases, but all are radioactive. Because they are not gases, they are not exhaled and can become lodged in the lungs, where their radiation can cause serious damage.
It is difficult to decide just how much concern people should have about radon in their homes. Some experts in the field agree with the EPA recommendations, but others question the data on which those recommendations are based. It is quite easy and relatively inexpensive to test for radon in a home, and homes built in locations where the gas has been identified as a problem should be tested.
