TRANSURANIC ELEMENTS A T BIKINI A TOLL 569 



the earth's atmosphere and hydrosphere. Thus, on the basis of the above findings, the 

 conclusions must be that different properties of the plutonium isotopes exist when the 

 isotopes interact with various components of the marine environment at Bikini Atoll. 



The ^^^Pu appears to be more soluble than the 2 3 9,240py ^ lagoon samples, as 

 evidenced by the higher ratios found in the soluble fractions than in the particulate 

 fractions from the BLVWS collections; this preferential solubility is also illustrated by the 

 fact that the 2 3 8py^2 3 9,2 4 0py ^^^^^ j^ ^ig^gj- [^^ many "batch" samples from the water 



column than in samples from the surface sediments. A source of ^^^Pu that is different 

 from bomb plutonium is indicated; most bomb debris would have much greater 

 2 3 9,240py than ^^^Pu concentrations except for those devices which used ^"^^Cm as a 

 tracer. Since both ^^^Pu and ^'*'^Pu were measured together by alpha spectroscopy, some 

 of the differences in the 2 3 8py^2 3 9,24 0p^ ratios possibly could be ascribed to variability 

 in the ^^°Pu isotope in samples. However, an evaluation of this radionuchde would 

 require a more detailed study using mass spectrometry to measure the ^"^^Pu 

 concentrations. 



Plutonium in seawater at a pH 8.0 to 8.2 forms oxy— hydroxy— carbonatoplutonyl 

 complexes. The size of the aggregates of the plutonyl complexes would depend on the 

 number of plutonium atoms available and on the charge field surrounding the aggregates 

 or clusters (the cluster hypothesis). At Bikini Atoll the coralline particles that 

 experienced the effects of the fireball contain the plutonium isotopes. The release of 

 plutonium into the water column from these particles may depend on recoil from the 

 alpha decay of the plutonium isotopes; this decay, would break the bonds between 

 plutonium clusters and the coral matrix. The ^^^Pu clusters would have a higher 

 probability of being released from the coral particles than ^^^Pu because of the 

 differences in alpha-decay half-lives (86 yr for ^^*Pu and 24,400 yr for ^^^Pu) and 

 possibly by ^^^Pu formation from the decay of ^'^^Cm (t^ of 162.5 days); thus it is 

 reasonable to assume that ^^*Pu could be more soluble than ^^^Pu. However, the 

 magnitude of this preferential solubihty has not yet been determined. 



If the clusters containing ^^*Pu are smaller (i.e., in effect, more soluble) than those 

 containing ^^^'^^*^Pu, then the results of the measurements made at Bikini lagoon and 

 deep ocean areas could be explained. The larger clusters of ^^^ '^"^^Pu could attach to the 

 riatural particles and could be removed from the water column at a more rapid rate than 

 the more-soluble ^^^Pu clusters. The availabihty of these different physicochemical states 

 of plutonium may help decide the potential hazards of transuranic elements in the 

 aquatic food chain to man. A concentrated effort is needed to collect additional data and 

 to interpret further these prehminary findings. 



Conclusions 



The measurements of the radionucUdes in Bikini lagoon sediments show that bomb 

 craters are only one of the sources for the transuranic elements in the ecosystem. 

 Sediments in the northwest quadrant of the lagoon contribute significantly to the 

 concentrations of the radionuclides found in the water and biota. Coral particles that 

 have been altered by the bomb and the environment contain the radionuclides. These 

 particles must be transported and subsequently deposited at different locations; this is 

 indicated by the high sediment rate found at station B-2 (0.58 cm/yr) and by the changes 

 observed in the radionucUde concentrations found in the sediment-core profile. 



(Text continues on page 576.) 



