goa? = BNL 11999 Late Effects of Radioactive Fallout on the Thyroid Gland e in a Marshallese Population During the past four years cases of thyreid abnormalities have developed in a Marshallese population who were accidentally exposed to radioactive fallout in 1954. Before discussing this development, I would like to briefly review the background of the accident and some of the other effects noted in this population which are believed to have been associated with their radlation exposure. The accident occurred on March lst, 1954 when a thermonuclear device was detonated at Bikini in the Pacifie proving grounds. The yield was larger than expected and since the fireball touched the ground, large amounts of incinerated coral and debris were mixed with the radioactive cloud. An unpredicted shift in winds occurred high aloft and instead of the cloud going in a northerly direction over the open sea, it veered to the east dropping radioactive fallout on several inhabited islands. The first slide shows the fallout pattern and location of the exposed islands as related to Bikini. The 64 Marshallese on Rongelap atoll received the heaviest exposure and it is this group that has shown the major radiation effects. The island groups with their exposure status are shown in the following table. Summary of Fallout Effects Group* Rongelap Ailingnae Rongerik Utirik Composition 64 Marshallese 18 Marshallese 28 Americans 157 Marshallese Fallout observed Estimated gamma dose (rads) Heavy (snowlike) 175 Moderate (mistlike) 69 Moderate (mistilike} 78 None 14 Skin Lesions Numerous Less Numerous Slight No skin lesions ; or entiation *Also exposed were 23 Japanese fishermen aboard their vessel a fo gps _ who received a sublethal dose. al