Final answer:
The primary health risk associated with high radon levels in the home is lung cancer, especially among smokers. Radon-related lung cancer accounts for about 21,000 deaths in the US annually, making radon the second leading cause of lung cancer after smoking.
Step-by-step explanation:
When exposed to high radon levels in the home, the primary health risk is an increased chance of developing lung cancer. Radon is a radioactive gas that can be inhaled, and over time, can lead to lung cancer, particularly in those who smoke, as their lungs have already been damaged by the smoking, raising the risk even higher. In the United States, radon exposure is the second leading cause of lung cancer after smoking and the number one cause of lung cancer among non-smokers. The US Environmental Protection Agency (EPA) estimates that radon-related lung cancer deaths are around 21,000 annually. There's some debate and unclear evidence concerning the link between radon and other health conditions such as respiratory problems or heart disease, but the central concern remains the increased risk of lung cancer.