Uranium is widely distributed in nature and often occurs in association with other metals, usually in very low concentrations. Thus many underground mines, tunnels, or caves, have measurable amounts of the radioactive gas 222Rn, a member of the uranium family which diffuses through rock and concentrates in underground openings. The primary sources of radiation exposure to persons entering such underground areas are the short-lived daughters of radon: 218Po, 214Pb, 214Bi and 214Po. These elements diffuse rapidly and attach to the first surface encountered. Either the free atoms or the particulates to which they are attached are inspired and largely retained in the respiratory tract. The effects of exposure of miners to radon daughters have been observed for many centuries, although it is only in the last 40 yr that the relationship between exposure to radon daughters and an increased incidence of lung cancer has been suspected, and only in the last 5 yr that a cause-effect relationship has been clearly demonstrated. The documented instances have occurred in the Schneeburg mining district in Germany, the Joachimsthal district of Czechoslovakia, in fluorspar mines in Newfoundland, in American uranium mines, and probably in a group of American metal miners. In all instances, the medical and environmental data are not as complete or detailed as could be desired. © 1969 Health Physics Society.
