592 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



TABLE 3 Plutonium Concentrations Associated with 

 Sediment Components [pCi/g (dry weight)] 



Plutonium concentration of ^^'^^""Pu [pCi/g(dry weight)] and 

 ratio of * Pu/^ ' ^ +^ " ° Pu at Enewetak Atoll (surface 2.5-cm layer) 



MoUusk shells 



Dead Halimeda fragments 



Coral fragments 



Fines «0.5 mm) 



Foraminifera 



Station 3D 



Station 40C 



2 3 9+240 



Pu 



0.64 ± 0.06 

 4.8 + 0.5 

 1.3 ±0.1 



6.85 ± 0.05 

 1.1 ± 0.1 



'Pll/^ 3 9+240 



0.09 ± 0.03 

 0.08 ±0.01 

 0.08 ± 0.03 

 0.07 ± 0.01 

 0.07 ± 0.03 



Pu 



2 3 9+240 



Pu 



Pu/ 



2 3 9+240 



Pu 



Absent in sample 



6.0 + 0.4 0.08 ± 0^01 



10 ±5 0.13 + 0.07 



23.5 ± 0.2 0.10 ±0.01 



2.7 ±0.2 0.10 ±0.02 



Plutonium concentrations at Bikini core Station B3, 

 pCi/g(dry weight) 



The possibility that subsurface remains labeled during testing were buried later in the 

 sediment column by large-scale turbulence can be discounted. Coral or Halimeda 

 fragments directly subject to a nuclear explosion probably would not retain their 

 identity. In recent yearly growth increments of a living sample of Favites virens coral 

 from station B3, the ^^^'''^'^^Pu concentrations averaged 104 ±12 pCi/kg (Noshkin 

 etal., 1975). Tliis value agrees well wdth the 239+240pjj concentrations in dead coral 

 remains in surface layers at station 33. hi no yearly growth increment from this coral 

 since 1954 was the 2 39+240py concentration below 104 ± 12 pCi/kg. Lower concentra- 

 tions are associated with coral remains deeper in the sediment column. From the 

 radiological record retained in the skeletal matrix of the Favites virens, coral labeled 

 during 1954 and 1958, for example, should have ^^^"""^"^^Pu concentrations of 39 x 10-^ 

 and 4.5 x 10^ pCi/kg, respectively (Noshkin et al., 1975). These concentrations are 

 orders of magnitude larger than those in any subsurface coral remains. These data, 

 therefore, do not support the translocation of labeled coral material deeper into the 

 sediment column by physical processes during or after testing. Burrowing organisms could 

 redistribute some fraction of labeled sedimentary components to depths in the sediment 

 column. However, when the 2 3 9-t-240pjj activities associated with each component at 

 various depths are compared to the activity in the corresponding component at the 

 surface, the 239-i-240py activities differ. For example, between 5 and 10cm, the 

 2 39+240p^ concentrations associated with the coral, Halimeda, foraminifera, and shells 

 are, respectively, 1.29, 0.83, 0.43, and 0.34 times the concentrations associated with 

 those components in the surface layer. Burrowing and mixing processes by organisms are 

 not likely to move specific components selectively down through the sediment column. 



