The BEIR-IV Report addresses health effects in human populations exposed to internally deposited alpha-emitting radionuclides and their decay products. Emphasis is placed on the carcinogenic effects, and where possible, quantitative risk estimates for cancer induction are presented. The largest part of the Report concentrates on health outcomes due to exposure to radon and its progeny. The Report also addresses health effects due to exposure to polonium, radium, thorium, uranium and the transuranic elements. Radiation health effects in humans include cancer induction, genetic disease, teratogenesis and degenerative changes. The important target tissues for cancer induction and degenerative changes are the respiratory tract, bone, liver, and reticuloendothelial system. Lung cancer risk is derived from epidemiological surveys of underground miners who breathe high levels of radon-222 progeny. The risk of bone sarcomas is derived from the United States radium dial painters who ingested radium-226 and radium-288 and from German patients who received radium-224 for therapeutic purposes. The risk of head sinus carcinomas is obtained from the United States radium dial painters;the radon-222 gas and its progeny accumulated in the sinuses and mastoid air cells in workers with increased body burdens of radium-226. The human data on liver cancer risk are derived from thorotrast patients who received colloidal thorium- 232 dioxide and its progeny during medical procedures. All the epidemiological surveys are presently in progress and the person-years of follow-up are still relatively small, so that the lifetime carcinogenic risks of a'phardiation exposureremain uncertain. Sufficient human data are not available for assessing the late health effects of the transuranic elements; it has been necessary to estimate risks in humans by simplified mathematical and dosimetric models or from comparison of effects with other radionuclides, where both direct experimental observation in laboratory animals and knowledge of radiation effects in humans are available.
