542 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



population from plutonium will come from power-reactor waste products and/or 

 accidents. 



In the marine environment the distribution of transuranium elements occurs through 

 biogeochemical processes, which effect a transfer of materials between the sediments, 

 waters, and biota of the ecosystem. Surprisingly few data have been published on the 

 redistribution of radioactivity between the sediments and waters of the lagoon in the 

 contaminated environment of Bikini Atoll. This has been partly due to the secondary 

 importance placed on sediment studies compared with studies of the uptake of 

 radioactivity by flora and fauna and with studies of the radiation exposure to inhabitants 

 of the Atolls. The sediment environment at Bikini has been disturbed significantly at the 

 sites of the 23 nuclear detonations, and a significant time period may have been required 

 to achieve quasi-steady-state concentrations of sediments and radionuclides. Recent 

 studies on the concentrations of long-lived radionuclides remaining in the lagoon 

 environment have indicated that nearly steady-state processes may now exist (Noshkin 

 et al., 1974). Although the problems of data interpretation presented by the complex 

 sources of the introduction of radioactivity into the lagoon still remain, the present 

 situation at Bikini offers unique opportunities and advantages for the study of the 

 physical and biogeochemical processes, which have governed and will continue to govern 

 the fate of radionuchdes in this marine ecosystem. The data and interpretations at Bikini 

 will help in assessing the general hazards of plutonium in the marine environment. The 

 objective of this chapter, then, is to review the current status of studies on the processes 

 and mechanisms that control the distribution of transuranic elements in the Bikini lagoon 

 ecosystem. 



Sources in the Bikini Ecosystem 



The formation of transuranic elements at Bikini resulted from the detonation of fission 

 and fusion devices of different sizes using different fissile materials (■^"'^U, ^"^^Pu, and 

 ^^^U). The largest test was the Bravo event of the Castle series (1954) — 15 Mt 

 equivalent TNT. This device consisted of the fission-fusion— fission process [^^^U 

 (^^^Pu)— LiD(T)— ■^^^U] . The transuranic elements now present in the lagoon environ- 

 ment are from unburned fissile material, energetic particle-induced activation products, 

 and decay products which were incorporated in or on coral material. Recently, 

 information has been obtained that •^'*^Cm was used as a fallout tracer of the transuranic 

 elements in several nuclear devices. Significant amounts of ■^^^Pu would now be present 

 in debris from the alpha-particle decay of ■^'*'^Cm (ti^, 162 days). The formation of the 

 coral fallout particles resulted from interaction of vaporized device and soil materials in 

 the fireball with the environmental materials that were swept into the expanding fireball 

 and cloud at later times (Adams, Farlow, and Schell, 1960). 



The locations of the 23 detonations reported at Bikini are shown in Fig. 1 , and the 

 detonation parameters are given in Table 1 . The yields of the largest detonations reported 

 were: Bravo, 15 Mt in 1954 at location B;Zuni, 3.53 Mt in 1956 at location C;and Tewa, 

 5.01 Mt in 1956 at location G. There was also a "several megaton" airburst detonation in 

 1956 wliich probably resulted in relatively minor contamination of lagoon sediments. 

 Typically, two types of sites were used for testing nuclear devices at Bikini, and each 

 probably gave rise to fallout particles of distinctly different compositions and structures. 



The first was for devices exploded over water deep enough to prevent the 

 incorporation of large quantities of soil in the ensuing fireball and cloud (sites A, F, D, 



