Distribution of cesium-137 in tree crop products collected from residence islands impacted by the U.S. nuclear test program in the northern Marshall Islands

The Marshall Islands Program at the Lawrence Livermore National Laboratory has completed a series of radiological surveys at Bikini, Rongelap, Utroek, and Enewetak Atolls in the Marshall Islands designed to take a representative sample of food supplies with emphasis on determining 137Cs activity concentrations in common food plants. Coconuts (Cocos nucifera L.) are the most common and abundant food plant, and provided a common sample type to characterize the level and variability of activity concentrations of 137Cs in plant foods collected from different islands and atolls. Other dominant food types included Pandanus (Pandanus spp.) and breadfruit (Actocarpus spp.). In general, the activity concentration of 137Cs in food plants was found to decrease significantly between the main residence islands on Bikini, Rongelap, Utrōk, and Enewetak Atolls. The mean activity concentration of 137Cs measured in drinking coconut meat and juice was 0.72 (95 % CI 0.68-0.77) and 0.34 (95 % CI 0.30-0.38) Bq g-1, respectively, on Bikini Island; 0.019 (95 % CI 0.017-0.021) and 0.027 (95 % CI 0.023-0.031) Bq g-1, respectively, on Rongelap Island; 0.010 (95 % CI 0.007-0.013) and 0.007 (95 % CI 0.004-0.009) Bq g-1, respectively, on Utroek Island; and 0.002 (95 % CI 0.0013-0.0024) and 0.002 (95 % CI 0.001-0.0025) Bq g-1, respectively, on Enewetak Island. High levels of variability are reported across all islands. These results will be used to improve the accuracy and reliability of predictive dose assessments, help characterize levels of uncertainty and variability in activity concentrations of fallout radionuclides in plant foods, and allow atoll communities to make informed decisions about resettlement and possible options for cleanup and rehabilitation of islands and atolls. (author)