CHAPTER 3 NATURE OF THE RESIDUAL CONTAMINATION IN PLANTS, SOIL, CORAL, LAGOON-BOTTOM SILT, AND WATER Evaluation of the residual contamination from the fall-out on the atoll islands was determined by study of the long-lived fission products. These long-lived nuclides present the greatest internal radiation hazard to human inhabitants of a contaminated area, Radiochemical analyses for Sr°%, total rare earths, Zr”, Rul, and Cs}3' were performed as these fission products comprise the bulk of the activity remaining 16 months after the nuclear detonation. 3.1 RESULTS AND DISCUSSION In Table 3.1 the relative contributions of the various nuclides are shown as percentages of the total activity. . The difference in compoSition of coftamination in the edible coconut fractions and in the frond is to be noted, as are the similarity of coco- nut and pandanus contamination as well as the high Cs}*! concentrations encountered in most food plants. An additional point of interest is the agreement of the soil composition with that predicted * from an analysis of Rongelap soil during Project 4.1. Rare earths and ruthenium are somewhat higher than predicted, indicating a washout of the other nuclides. Arrowroot samples showed rather wide variation in composition which had not been expected* from consideration of the variables involved. Rare earth nuclides and Ru! make up the bulk of the activity which remains fixed to coral island soil under the influence of tropical rains. Ground water and lagoon water values were similar to those of the soil. Lagoon-bottom silt gives very nearly the same nuclide distribution as soil and it appears that solubility may be a better criteria for predicting nuclide mobility through soil than complex formation with matrix components, The high uptake of Cs!*! by the edible portions of plant foods is probably the result of potassium deficiency in the soil and the utilization of cesium to replace needed potassium. A comparison of the coconut frond and edible coconut fractions illustrates their selectivity for tt individual nuclides. et aw. aw Wee -13-