ASSESSMENT OF PLUTONIUM EXPOSURES IN RONGELAP AND UTIRIK POPULATIONS BY FISSION-TRACK ANALYSIS OF URINE

A nuclear device, code-named Brave, detonated at Bikini Atoll at 6:45 a.m. on 1 March 1954, unexpectedly released a large amount of radioact ivity. Over 40 years after this incident, the study of its impact on t he radiological health and environmental safety of the residents of Ro ngelap and Utirik Atolls continues. In 1987, researchers at Brookhaven National Laboratory established a fission track analysis (FTA) method for low-level Pu-239 urinalysis. Two years later, a new shipboard pro tocol was developed for collecting 24-h radiologically clean urine sam ples. The purpose of this paper is to update information on the FTA me thod for measuring low-levels of plutonium, and to summarize results o n the distribution of Pu-239 in the populations of Rongelap and Utirik between 1981-1991. Plutonium detection levels (99% confidence level) in these samples were 2-3 mu Bq, which is equivalent to 0.2-0.3 mSv ef fective dose equivalent (EDE) to age 70 for Marshallese. The latest 19 91 FTA data Indicate average EDE of 0.62 mSv and 1.6 mSv for the peopl e of Rongelap and Utirik, respectively, which both are the highest val ues since 1988.