Contamination from Local Fallout Plants The uptake of the fission products from soil by plants is the next step in the chain by which these radioisotopes reach man. It was found that, during the first 6 weeks, only a verv small amount of the fission products is available to plants growing on contaminated soil. The fallout material appcared initially to be associated with particulate matter and to be uniformly distributed on earth, grass and food plants. Levels of beta activity of the order of 1 ye per plant and fissile material (1 > 10-4 yg) were present on the external surtaces of plants at one month (Rinehart et al, 19553. Only verv lowlevels of beta activity and no alpha activity were detected in the edible portions of the plants. The one exception was the presence of high levels of beta activity in the sap of the coconut tree (1 yc “liter}. The isotopic composition of this tree sap was very similar to that of the ground water. suggesting uptake of these pyaon pruducts by the root svstem. The predominant fission product found m the tree sap at this time was Sr§*_ presumably as a function of its abundance and relatn ely high solubibts At the ume cf the ]-vear resurvey of the island, extensive incorporation of radionuclides into plants had occurred. The gross beta activity in plants on Rongelap Island at 2 vears after the detonation 1s shown in table 3. The leve! of internal contansnaien in the plants correspond. roughh to the Jad of activity in the sou and the gamma dose rate cn the islands However. wide vanations occur in the levels of beta activity in the plants on any onc island. The availability of the fission products to the pliant 1s undoubted]y a funcron of the age of the plant. the stage of development of the fruit, the type and depth of“sorl and the phvysical-chemical] properties and distribution of the fallout material. Since the fallout from the March 1, 1954 detonation consisted of hssion products associated with large particles of CaO, Ca(OH),, CaCO, and NaCl particles, it was very soluble in the soil and could readily be absorbed through the root system of the plant. Moreover, it could be absorbed directly through the leaves. The plant portulaca was found to have by far the highest level of activity of anyof the plants analvzed. Leafy structures of plants were, in general, more radioactive than their fruit. The leaves of the plants contained primarihthe rare earth elements together with small amounts of Ru!®* and Sr, By contrast ° (table 4), the primary fission product in coconuts, papaya fruit and arrowrodt tuber was Cs!87. Very small amounts of activity were contribated to these plants” by the rare carths, Ru’ or Sr, The concentrating capacity of coconuts foe Cs'87 was especially marked when compared to the low levels of Cs¥* in the’! soil, particularly in the area of the root system of the plant. The high Cst# concentration mayreflect foliar absorption and/or a potassium deficiencyin the plants with the substitution of cesium for potassium. The Sr® concentration was uniformly lowin the edible portions of the above samples of plants. es ox mo [a CFI 311