Radionuclide characterization and associated dose from long-lived radionuclides in close-in fallout delivered to the marine environment at Bikini andEnewetak Atolls

Between June 1946 and October 1958, Enewetak and Bikini Atolls were used by the US as testing grounds for 66 nuclear devices. The combined explosive y ield from these tests was 107 million t (million t TNT equivalents). This t esting produced close-in fallout debris that was contaminated with quantiti es of radioactive fission and particle activated products, and unspent radi oactive nuclear fuel that entered the aquatic environment of the atolls. To day, the sediments in the lagoons are reservoirs for tens of TBq of the tra nsuranics and some long-lived fission and activation products. The larger a mounts of contamination are associated with fine and coarse sediment materi al adjacent to the locations of the high yield explosions. Radionuclides ar e also distributed vertically in the sediment column to various depths in a ll regions of the lagoons. Concentrations greater than fallout background l evels are found in filtered water sampled over several decades from all loc ations and depths in the lagoons. This is a direct indication that the radi onuclides are continuously mobilized to solution from the solid phases. Of particular importance is the fact that the long-lived radionuclides are acc umulated to different levels by indigenous aquatic plants and organisms tha t are used as food by resident people. One might anticipate finding continu ous high contamination levels in many of the edible marine organisms from t he lagoons, since the radionuclides associated with the sediments are not c ontained and are available to the different organisms in a relatively shall ow water environment. This is not the case. We estimate that the radiologic al dose from consumption of the edible parts of marine foods at Enewetak an d Bikini is presently approximately 0.05% of the total 50-year integral eff ective dose from all other exposure pathways that include ingestion of terr estrial foods and drinking water, external exposure and inhalation. The tot al radiological dose from the marine pathway is dominated by the natural ra dionuclides, (210)po and (210)pb. Man-made radionuclides presently contribu te < 0.3% of the dose from these natural radionuclides in the marine food c hain and within approximately 90 years only 0.15%. Published by Elsevier Sc ience B.V.