APPENDIX 14 Chromosome Studies on Marshallese People Exposed to Fallout Radiation Hermann Lisco, M.D.* and Robert A. Conard, M.D. Chromosome aberrations in blood lymphocytes have been demonstrated in a number of population groups exposed to ionizing radiation. These have included patients during and after radio-therapy for ankylosing spondylitis (1,2) and malignant tumors (3,4,5), persons exposed in diagnostic procedures (6), and others exposed in the course of their work (7). Similar pt 4 findings have been reported in individuals involved in radiation accidents (8,9) and in survivors of the atomic bombings in Hiroshima and Nagasaki in 1945 (10,11,12). One of the more interesting and possibly significant points in all of these studies was the observation that chromosome aberrations can persist in circulating lymphocytes in variable degree for many years following exposure. It seemed of interest to determine whether residual damage of this type could be found in Marshallese people who had been exposed to fallout radiation (13). The accidental exposure of these people to radioactive fallout occurred on Rongelap Island in the Pacific Ocean in 1954, This was caused by an unpredicted shift in winds following detonation of a high yield nuclear device at Bikini 100 miles away. There were 64 people living on the island who received an estimated dose of 175 rads whole-body gamma-ray exposure. Eighteen other Rongelap people were away fishing on another island nearby and received an estimated dose of 70 rads. The exposure resulted in temporary blood cell depression, skin burns from beta radiation, and internal absorp- tion of radionuclides, the most important of which were iodine and strontium. It was estimated that the thyroid glands of the adults received 150 rads and those of the children as much as 1,000 rads from absorbed radioiodine in addition to the whole-body gamma-ray exposure. The recent development of thyroid pathology is believed to be a consequence of this exposure (14). Chromosome preparations were obtained on 51 individuals during the annual medical review of the Marshallese people in 1964. Of these, 30 had been exposed to 175 rads and 13 to 70 rads of gamma rays. Eight Marshallese who had not been exposed served as a comparison group. There were 20 males and 20 females in the exposed group and the ages ranged from an embryo in utero to 67 years at the time of exposure. Twenty-one were below and 22 above the age of 20, with males and females in about equal numbers. Of the comparison group, three were males and five females, ranging in age from 10 to71 years. Unfortunately, it was not possible to examine a larger number of unexposed individuals matched to the exposed with respect to age and sex. *New England Deaconess Hospital, Boston, Massachusetts. 137