Linked from
The 16 pages that link to Radon, each with the reason it gives.
Alpha particleRelated: Radon decay products deliver alpha radiation to lung tissue when inhaled.
Lung cancerRelated: Radon is a major lung cancer risk, especially for people who also smoke.
UraniumRelated: Uranium-bearing rocks can generate radon, which may accumulate indoors.
RadiumRelated: Radium-226 releases radon-222, which can accumulate indoors.
Uranium miningRelated: Underground uranium workings can expose workers to elevated radon.