Yes, radon gas can build up in mines and unventilated basements, making those particularly dangerous places to live and work. This does not alter the fact that radon gas is 100% natural, and was responsible for deaths from cancer long before we even knew it existed. There are, as JayUtah has pointed out, other natural sources of ionizing radiation for which the same is true.
Are you now ready to concede that there are natural causes of cancer?
These angles shold be justified for stamping anything natural: 1. Exactly as it exist in nature 2. Exactly, its natural exposure 3. Exactly in natural environment 4. Exactly natural people. I think, indoor and mine expisure and even we may not be exactly natural. I do not know about its its toxic exposure is exactly on its natural form.