1.   Automakers dispute this, however, saying that the naturally occurring gas cannot be specifically pinned on car emissions.

2.   --- Home buyers are usually warned about the dangers of radon, a naturally occurring radioactive gas that can build up inside a tightly sealed home.

3.   Radon, a naturally occurring radioactive gas that has no odor or color, is linked to increased risks of lung cancer.

4.   Radon, a naturally occurring gas and suspected carcinogen, is another spoiler of ground water.

5.   Radon is a naturally occurring radioactive gas that escapes from underground rocks and soils.