Radon

Radon is one of the main causes of lung cancer in non-smokers, as it is naturally occuring in the environment and radioactive, emitting alpha particles. The decay products are also radioactive, so when radon decays, the result is alpha, beta, and gamma radiation as well as x-rays [5].

Radon is mostly mentioned in regards to inhalation, but it can also be ingested, e.g. when dissolved in water. It is a tasteless, odorless, colorless gas, and causes no obvious symptoms of exposure, and thus impossible to detect without proper equipment [5].