Radiation effects in the Marshall Islands

On March 1, 1954, the detonation of a thermonuclear device on Bikini in the Marshall Islands resulted in the accidental deposition of fallout on several inhabited atolls and on a Japanese fishing vessel. The accident was unusual in that the explosion, occurring near ground level, resulted in a heavy, particulate fallout on Rongelap and Ailingnae, about 160km away. Utirik, further to the east, experienced a lesser, invisible fallout. Early radiation effects were observed in many of the 64 inhabitants of Rongelap and the 18 on nearby Sifo Island. During the second and third decades after the accident, most of the Rongelap children and many adults developed thyroid nodules, some of which proved to be malignant. In addition, thyroid atrophy accounted for severe growth retardation in 2 boys. The Utirik people (167 exposed) did not show early radiation effects, but thyroid nodules and thyroid cancer began to appear late in the second decade after exposure. The-cancers in both groups were of the papillary type. There have been no deattjsfrom thyroid cancer but one fatal case of acute myelogeneous leukemia occured in a Rongelap boy. The radiation exposure resulted from both internal and external sources. Calculation of risk coefficients for thyroid nodules and cancer, adjusted for their occurrence in a comparison population, gave a mean nodule risk (all ages) of 8.3 per 106 person. rad. year. and a mean cancer risk of 1.5 per 106 person. rad. year. The latter value is similar to that resulting from purely external exposure (e,gmedical x-rays) and is compatible with an equal risk from external x-rays and internal radiation from short half-life isotopes of iodine. The Marshall Islands experience clearly identifies the risk to the thyroid gland from radioactive iodine fallout in man; however, it gives no information about the risk that can be attributed to iodine-131, the predominant iodine isotope in long-range fa’llout and in medical use. The Medical R,esear(:h ~cn~er Upton, L. L, New York II . .—. J. Robbins, W. H. Adams INTRODUCTION . .. . . ..s.. .......... . .. -An’unwWIWradiation accident occurred on March l; 1954, in the Marshall Isldnc$ of the Micronesia archipelago. A thermonuclear device detonated on a .+,.,. . . tower at the testing site on Bikfni produced a 3-fold greater than anticipated ,,.. “ yield; aboW;15 megatonnes, and an unexpected wind shear condition resulted in heavy fal,l~t outside the test area. About 160km eastward, and 4 6 h after ..the explosion, the radioactive cloud deposited particulate, ash-like material on 64 inhabitants of Rongelap, on 18 Rongelapese on $ifo Island of the nearby Ailingnae Atoll and on 23 fishermen on a Japanese vessel, Fukuryu (Lucky Dragon) Maru 5. The fallout persisted for about 5 -10 h (l). Slightly to the east, 28 American servicemen on Rongerik were exposed, and after 22h the cloud reached Utirik where :67 people were dffected by a much decreased, invisible . fallout. About 2 days later, the Marshallese were evacuated to Kwajalein where they were decontaminated. The Utirik people were able to return home soon thereafter, but it was 3 years before the radiatfon on Rongelap decayed to a safe level. The American servicemen were taken to Hawafi for examinations and then returned to duty. The fishermen on the Fukuryu, thefr exposure unbeknown to the authorities, sailed for 14 days before arriving at their home port of Yaizu and were hospitalized in Tokyo for about 2 months. ~ From the time of this unfortunate incident to the present, the exposed Marshallese have been under close medical observation and’a number of reports on their health status have been published (2-5). Since 1956, this has been the responsibility of the Brookhaven National Laboratory (8NL) and was under the direction of Or. Robert A. Conard until his retirement in 1980. An ageand sex-matched comparison group of unexposed Marshallese has also been monitored to obtain information on the baseline fncidence of disease, in order to identify unexpected consequences of radiation exposure in the Rongelap and Utirik populations. Although this unique experience has reveaJed much about radiation-induced disease, it has also become clear that it may not be a precise model for other radiation accidents. One difficulty has been a persistent uncertainty about the exact radiation exposure received by the populace. As is so often the case when an accident-is not anticipated, the observers were unprepared to make the immediate measurements that are required for complete accounting. For example, the major datum from which the thyroid burden was derived is the analysis of pooled urine iodine-131 obtained 17 days after the exposure. A thorough reevaluation of the thyroid-absorbed dose was recently completed by Lessard et al (1) of the Safety and Environmental Protection Division of BNL. It was extrapolated from the urine results and from several measured and derived quantities relating to fallout arrival and observation ttmes, size and