PERSISTENCE OF TRITIUM AND 4 IN THE PACIFIC PROVING GROUND DESCRIPTION OF THE STUDY Eniwetok Atoll is in the northern portion of the Marshall Islands in the §.W. Pacific Ocean (11°30’ N lat, 162°15 E long) and was a proving ground for nuclear device testing from 1948 to 1958 when the last detonations took place. The detonations occurred in various environmental Islands on the eastern edge ofthe atoll. They islands were adjacent to shot areas andreceiveg close-in fallout from barge shots in the lagoon, AomonIsland had a 49-kton towershot in 1943 A mapof Eniwetok Atoll with the island nam, and craterlocationsis given in Fig. 1. Sampling procedure MC, the crater-forming shots were considered examination of the Eniwetok environmentto determine if tritium and !C are present in most appropriate. Preliminary studies of a large cratering detonation at the Nevada Test Site have indicated that a significant fraction of the residual tritium produced becomes associated with the geological materials in and displaced by the explosion.” The detonations which produced a distinct crater at Eniwetok Atoll were few (many shots being madefrom barges within theatoll lagoon), but two areas were selected for survey on the basis of their physical and biological characteristics. Cactus Shot (1958 Hardtack Series) produced a terrestrial crater at the north end of Runit Island on the eastern edge of the atoll. The crater has a distinct lip and a throwout zone of mounded coral sand and debris. Vascular plants have become reestablished on the crater materials, and trees of Scaevola frutescens and Messerschmidia argentea with diameters up to 4 in. at the crown are growing within 15 ft of the crater lip. Mike Shot (1952 Ivy Series) created a large submarine crater adjacent to Sanildefonso Island. Thecrater is actually in the coral reef This survey is intended to be an initial biological and soil materials at times up to 12 after detonation. Because of the preliminary natureof the survey,it was desirable to collect a wide variety of materials without acquiring excessively large numbersofsamplesfor analysis. In some cases a sample series may be incom. plete because of sample number limitations o its unavailability at the time of collection. In spite of some shortcomings and the preliminary; nature of this survey, the data enable us to describe in some detail the persistence oftritium and *4C in the physical and biological materia of theatoll. The samples were collected on eight island on EniwetokAtoll during July and August 1964. This was the beginning ofthe rainy season in the northern Marshall Islands. The University of Washington, Laboratory of Radiation Biology scientific staff was conducting a resurvey of Eniwetok and Bikini Atolls at this time and assisted in collecting the biological specimens. that forms the oval platform on which the It would not have been possible to obtain the wide range of samples reported in this study partially filled with coral sand since the shot date. At Japtan, Runit and Engebi Islands, wood. green leaves, litter and a soil sample were islands of the atoll have formed. The crater has Otherislandsin the atoll not involved directly in any nuclear detonation (but which undoubtedly received close-in fajlout of large particles) were also sampled to provide information on the generaltritium backgroundofthe atoll. Igurin without their valuable assistance. collected as an ecological series from the same samplesite. A wood sample from the south end of Runit Island was compared with the sample from the north end at Cactus Crater. Wood samples were also obtained from four other sampled in this series. Engebi Island at the islands. Two plant species were often present in the habitats of the detonation sites. These were Triumfetta procumbens, a prostrate vine in the This island was adjacent to many bargeshotsites species were collected on Runit Island adjacent Island at the southern end of the atoll and Japtan Island on the eastern edge were islands farthest from the detonation sites which were northeast corner of the atoll was also sampled. ee tower shots were fired on this island. Collection were also made on Aomon, Biijiri and Aaranbin, situations within or near the atoll, but fur the purposes of surveying for residual tritium and tear in the 1958 series, and in previous serig Tiliaceae, and Lepturus repens, a short grass. These T~ concentrations, and that they are presently detectable at elevated levels in the biota. wee ee i#té