596 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



computed mean concentration in the lagoon is contingent on the number and location of 

 samples. The mean ■^^^Pu/^^^"'"^'*°Pu ratios in the lagoon water samples in 1972, 1974, 

 and 1976 were virtually the same. Differences in sample ratios between soluble and 

 particulate phases were noted sometimes, but the average ratios associated with the two 

 phases from all stations were not significantly different. 



During 1974 and 1976, 1.5 and 0.7 Ci of 



239+240 



Pu, respectively, were found in 



solution, and 0.27 and 0.53 Ci, respectively, were associated with particulate material. 

 These latter quantities represent less than 0.2% of the plutonium inventory in the surface 

 sediment and less than 0.04% of the inventory estimated to a 16-cm depth in the 

 sediment column (Table 1). The average quantities of soluble plutonium in the water are 

 also small fractions of the sediment inventory. Therefore in recent years only small 

 fractions of the Atoll plutonium inventory are either remobilized to the solution phase or 

 resuspended to the water column. 



During 1976, zooplankton samples contained less than l%ofthe'^^^ ^"^^Pu activity 

 in the total material filtered from an equivalent volume of water (Noshkin et al., 1978b). 



TABLE 5 Plutonium Concentrations in the Water Column 



at Enewetak Atoll 



Sampling time 



December 1972 



July 1974 



April 1976 



Mean concentrations in lagoon water, 

 fCi /liter 

 Soluble (<1 jum) 

 Particulate Ol nm) 



Toti 



Mean 



'Pu/ 



2 3 'i + 2 4 



Pu 



Water-column inventory, mCi/km^ 

 Soluble 

 Particulate 



Lagoon inventory, Ci 

 Soluble 

 Particulate 



Water inventory, % of sediment inventory 

 Water inventory compared to top 2.5 cm 

 of sediment -surface inventory, % 

 Soluble 

 Particulate 



Water inventory compared to top 16 cm 

 of sediment inventory, % 

 Soluble 



Particulate 



Total 



Total 



Total 



1.70 



0.68 



1.81 



0.62 

 0.11 



0.73 



0.13 

 0.023 



1.24 



0.29 

 0.21 



0.50 



0.056 

 0.045 



Total 



0.14 



0.15 



0.10 



