Final answer:
The EPA recommends reducing radon levels in homes to below 4 pCi/L to mitigate the health risks associated with radon exposure, such as lung cancer.
Step-by-step explanation:
The Environmental Protection Agency (EPA) recommends that action be taken to reduce elevated levels of radon in homes to a concentration less than 4 picocuries per liter (pCi/L). Radon is a naturally occurring radioactive gas that can seep into buildings from the soil, posing a health risk particularly in areas with low air exchange with the outside world such as basements. Exposure to radon is linked to an increased risk of lung cancer, and it is the number one cause of lung cancer among nonsmokers. The health risks associated with radon are on par with the dangers of smoking in terms of the number of lung cancer cases attributed to it annually.