The tailings contain mainly decay products from the decay chain involving Uranium-238. Uranium tailings contain over a dozen radioactive nuclides, which are the primary hazard posed by the tailings. The most important of these are thorium-230, radium-226, radon-222 (radon gas) and the daughter isotopes of radon decay, including polonium-210. All of those are naturally occurring radioactive materials or "NORM".