True or False: There is a known threshold concentration below which radon exposure is considered risk-free.

The statement is false because there is no established threshold concentration of radon exposure deemed entirely risk-free. Research indicates that even low levels of radon can pose a risk for lung cancer, and risk increases with cumulative exposure over time. Regulatory bodies typically emphasize that any level of radon in indoor air is a potential health risk and advocate for mitigation strategies to reduce radon levels, especially in residential and occupational settings where long-term exposure can occur. This understanding aligns with the principle that risk can never be entirely eliminated, especially with substances like radon, which have documented long-term health effects.