SECTION 8 HEALTH EFFECTS OF IONIZING RADIATION AND MEDICAL FOLLOWUP STUDIES OF VETERANS This chapter outlines what is known about the health effects of ionizing radiation. It then summarizes the studies conducted by several agencies to ascertain if such effects exist among veterans who participated in U.S. atmospheric nuclear weapons tests and in the postwar occupation of Hiroshima and Nagasaki, Japan. 8.1 HEALTH EFFECTS OF IONIZING RADIATION. The biological effects resulting from exposure to ionizing radiation can be grouped into two general categories, acute (quickly observed) and delayed. Examples of acute effects are erythemia or reddening of the skin, blood changes, vomiting, loss of hair (epilation), and even death in the extreme case. Before such effects can be observed, a certain minimum radiation dose, or threshold, must be exceeded. The magnitude of the effect and normally the speed at which it occurs increase with the size of the radiation dose. in fatal cases, most acute effects are not permanent. Except For example, blood will return to normal, hair will grow back, and skin burns will heal, although some scarring and pigmentation loss may occur. Acute effects and their threshold doses are well known. The table on the next page indicates the acute effects of whole-body exposure to various levels of ionizing radiation (1). Observable acute effects do not occur at radiation doses below approximately 25 rem, as noted in the table. Better than 99 percent of all doses received by nuclear test participants were well below this threshold; therefore, such effects were not evident. 178