The Dangers of Radon
 
 
In the atmosphere, radon is harmless because it is diluted. The average radon level outdoors is 0.2 picocuries per liter (pCi/L) of air or less. (Levels of radon are reported in one of two ways: pCi/L or Working Levels (WL) of radon). In an enclosed area, radon can build up to a dangerously high level. Extremely high radon levels-hundreds and thousands pCi/L have been detected in some homes throughout the United States.
Exposure to radon is dangerous because some of radon's decay products revert to a solid form (isotopes of polonium). These radioactive atoms can become lodged in lung tissue, damaging the DNA genetic code of cells. Such damage may lead to lung cancer, though the condition may not develop for years or even decades after exposure. Lung cancer is the only known health risk posed by radon. Radon is attributed to anywhere from 7,000 to 30,000 lung cancer deaths each year.
The higher the radon level and the longer the exposure, the higher the risk of developing radon-induced lung cancer. Breathing in tobacco smoke also increases the risk because the smoke provides another vehicle by which radon can enter the lungs of the smoker and, through secondhand smoke, the nonsmoker as well. Smokers, however, face the greater health risks. Children may be the most vulnerable to radon, possibly facing triple the health risk of adults.
Because radon risk estimates are based on studies of underground miners exposed to varying degrees of radon, scientists are considerably more certain of the risk estimates for radon than they are of risk estimates based solely on animal studies .