TRANS URANIC RADIONUCLIDES IN ENEWETAK LAGOON 599 



sections (Noshkin et al., 1975; Noshkin et al., 1978a), Bikini and Enewetak lagoon water 

 along with dissolved species are estimated to be exchanged approximately twice per year. 

 At this rate of exchange under steady-state conditions, shghtly more than 250 yr will be 

 required to reduce the plutonium inventory in the sediment by 50%. The rates of the 

 mobilization and migration processes of plutonium away from the Atoll to the equatorial 

 Pacific waters are much faster than the rate of radioactive decay. These figures and results 

 should be considered when the consequences of disposal methods for transuranic wastes 

 to the oceans are discussed. 



Some massive corals collected from the atolls contain well-defined growth bands 

 dating from the collection time to the early 1950s. Each yearly growth concentrates 

 plutonium in proportion to the levels in the environment (Noshkin et al., 1975; Noshkin 

 et al., 1978a). Concentrations of 239+240p^ associated with grov^h increments dated 

 since 1965 in three Enewetak corals from different locations in the lagoon and one Bikini 

 lagoon sample are given in Table 7. The average amount of plutonium concentrated by 

 the coral from 1965 until the year of collection has been computed and is shown in 

 Table 7. 



The average absolute concentrations in the corals are different, as expected, and 

 reflect the local environmental concentrations in the region. In only a few growth 

 sections are the ^^^ ^'^^Pu concentrations different from the mean by more than a 

 factor of 2, and only corals 1 and 2 show this magnitude of variation. Corals 1 and 2 were 

 obtained in the water on the lagoon side of the eastern reef. The patterns of current in 



TABLE 7 Concentrations of ^ ^ ^ ^ ^ ^ ^ Pu in Yearly Growth Sections of 



Enewetak and Bikini Coral 



♦Values in parentheses are Ict counting errors expressed as the percent of the value listed. 



