National Drinking Water Database

Radon

Radon is a colorless, odorless, tasteless and radioactive gas. Radon is formed by the normal radioactive decay of uranium and radium. Underground rock containing natural uranium continuously releases radon gas into groundwater in contact with it. As a gas, radon is readily released from surface water; consequently, groundwater has potentially much higher concentrations of radon than surface water (World Health Organization 2004a). Radon itself is an unstable element that decays into radiation and other, smaller elements that are called "radiation decay products" or "daughter species" (Agency for Toxic Substances and Disease Registry (ATSDR 2008e).

Human exposure to radon has been linked to severe respiratory disease, harmful kidney effects, sexual maturation effects, mutations, and increases in lung cancer deaths (ATSDR 2008e). Studies from 11 large cohorts of underground miners have all produced data showing increase in lung cancer risk from exposure to radon. There are also dozens of epidemiologic studies linking residential radon exposure and lung cancer (ATSDR 2008e).

The amount of radon in groundwater is highly variable and dependent on the chemical concentration of radium-226 in the surrounding soil or rock. Radium is widely present in the minerals making up the Earth's crust, so radon is present virtually everywhere on Earth but particularly in the air over land and in buildings (WHO 2004a).