Final answer:
The average annual indoor radon activity in the U.S. is about 1.25 pCi/L according to the EPA. Radon is the number one cause of lung cancer in nonsmokers and the second leading cause of lung cancer overall.
Step-by-step explanation:
The average annual indoor radon activity in the U.S, according to the EPA, is about 1.25 pCi/L (picocuries per liter). This level is about three times higher than the radon levels found in outside air. Approximately one in six houses in the U.S. have radon levels high enough that remediation efforts are recommended to reduce the concentration of radon. Exposure to radon increases the risk of developing cancer, especially lung cancer. In fact, radon is the number one cause of lung cancer in nonsmokers and the second leading cause of lung cancer overall. It is estimated that radon exposure causes over 20,000 deaths in the U.S. each year.