598 TRANS URANIC ELEMENTS IN THE ENVIRONMENT 



TABLE 6 Recent Determinations of the Distribution 

 Coefficient for Plutonium 



Kd 



Sediment type 



Range 



Average* 



Reference 



Enewetak, coral soil 



and sediment (laboratory 



desorption study) 

 Enewetak, groundwater particulates 

 Trombay Harbour, suspended silt 

 Bikini Tewa crater sediment 



(laboratory desorption study, 



oxic-anoxic conditions) 

 Windscale area, 5% clay, 50% silt, 



45% sand 

 Humboldt Bay, Calif., suspended 



clay-silt particulates 

 Lake Michigan, suspended 



particulates 

 Mediterranean sediment 



(laboratory sorption study) 



4 X lO^-S X 10' 



1.4 X lO'-lO* 

 4.8 X 10''-1.3 X 10' 

 4 X 10''-4 X 10' 



0.6 X 10^-22 X 10" 



4.7 X lO^-ll.S X 10" 



1.8x10' Unpublished 



2.5x10' Noshkinetal., 1976 

 0.9 X 10' PiUai and Mathew, 1976 

 2.2x10' Moand Lowman, 1976 



0.5 X 10' Hetherington, Jefferies, 

 and Lovett, 1975 



0.8 X 10' UnpubUshed data, this 

 laboratory 



3.0x10' Wahlgrenetal., 1976 



1.3 X 10" -9.4 X 10" 0.5x10' Duursma and Parsi, 1974 



Mean 1.4 x 10' cm^/g 



*Quantity of 2 3 9+24opy ^Qund to the sediment per unit dry weight of sediment divided by the 

 amount of ^ ^ ' """^ " ° Pu in water per cubic centimeter. 



Atoll source terms. If plutonium is cycled through an intermediate host, such as the 

 Halimeda, the rate at which it is released from decaying plants must be balanced by 

 uptake in the new growth to maintain a steady state condition. Given that steady state 

 conditions exist, the mean plutonium inventory in the lagoon water and the concentra- 

 tion expected in solution computed from the basic equation relating K^ to water and 

 sediment concentrations are 1 .4 Ci and 32 fCi/liter, respectively. There is general 

 agreement between the average quantity of ^^^''"^'^"Pu predicted and that measured in 

 solution (see Table 5). In 1976, the computed value differed from the measured mean 

 soluble concentration by a factor of 2. Although this is not a large discrepancy, the 

 average concentration, as was mentioned previously, probably does not represent the real 

 mean for the lagoon at the time sampled. From the appropriate dimensions for the Bikini 

 lagoon, the sediment data in Table 1 , and the Kj for 2 39+24 Op^^ ^j^^ average inventory in 

 the water column and the concentration at Bikini are computed to be 1 .7 Ci and 

 60 fCi/hter, respectively. During December 1972, the mean soluble 239+240p^ inventory 

 and the concentration in the lagoon water were 1.2 Ci and 42 ± 21 fCi/Uter, respectively 

 (Noshkin et al., 1974), and in January 1977 the respective values were 1 .4 Ci and 49 ± 21 

 fCi/liter (Noshkin et al., 1978b). These average values also are consistent with the 

 amounts predicted. 



For many reasons it may be argued that some of this agreement is fortuitous. 

 Nevertheless, the general agreement found between computed and twice-measured 

 average concentrations in both lagoons between 1972 and 1977 demonstrates the general 

 usefulness of this simple equiUbrium model in predicting long-term average concentra- 

 tions in lagoon water. From radiological records retained in yearly growth of coral 



