568 TRANS URANIC ELEMENTS IN THE ENVIRONMENT 



difference between this extrapolated value (soluble) and the total concentration measured 

 in bed 1 is defined as the amount present in the colloidal state. Table 5 gives the amount 

 of 2 3 9,240py present in the total sample, i.e., soluble, colloidal, and percent colloidal. 

 The average of the colloidal concentration of 2 3 9,24 0pjj ^ ^.j^g 22 lagoon samples 

 measured from Bikini Atoll was 12 ± 8% (SD). This average can be compared with the 

 tank studies at 31.6 %q salinity in which 15 ± 3% (SD) was found in the colloidal state. 

 Since only two AI2O3 beds in the BLVWS were used for the collections at Bikini 

 Atoll in 1972, no colloidal fraction could be determined, and a systematic error may have 

 been present in the total plutonium concentration data. The 1976 results have been 

 evaluated with only two beds to observe if significant systematic errors were present in 

 the 1972 data. Of the total plutonium present in 14 samples tested, 91% (range, 78 to 

 100%) would have been measured if only the first two beds had been used in the 

 calculations of total concentrations. Thus the 1972 data for individual samples measured 

 by the BLVWS technique should be reliable to within about 20%. 



Speciation of"^^ ^Pu and ^ ^ ^ '^^^Pu into Paniculate and Soluble Fractions. The isotope 

 ratios of 2 3 8pjj^2 3 9,24 0p^ ^ surface sediments and in the overlying batch water samples 

 are shown in Figs. 18 and 19, respectively. The range of ^^^Pu/^^''^'*°Pu ratios in the 

 surface sediments is 0.004 to 0.52; the average value determined from 28 measurements is 

 0.029 ± 0.027 (SD). The 2 3 8py^2 3 9,24 0py ^^^^^^ -j^ ^^ ^^^gj. samples collected at 2 m 

 above the bottom show that at several stations the 2 3 8p^^23 9,240p^ ratios in water are 

 similar to those of underlying sediments. However, the ^^^Pu/^^^'^'^^Pu ratios in water, 

 which range from <0.02 to 1.11, are considerably more variable than those in the 

 sediments. It appears that there may be enrichment in ^^^Pu/^^^'^'^^Pu ratios in the 

 overlying water compared with those in sediment. 



The 238p^^239,240py ^^^j^^ f^^ ^.j^g BLVWS collection of plutonium in surface- and 



deep-water samples with 0.3-ium Millipore filters and two AI2O3 sorption beds are shown 

 in Figs. 20 and 21, respectively. The 2 3 8p|j^23 9,240py j^^jq^ ^gre not usually constant 

 for the three fractions of the same surface- or deep-water samples. This unexpected 

 finding was at first questioned, and the analysis and counting of the samples were 

 repeated. Possible contamination by ^'^^ Am and ^^^Th, which decay by alpha particles 

 of nearly the same energy as ^^^Pu, was rechecked. The results showed that the original 

 values were real and that the particulate fraction had 2 3 8p|j^2 3 9,24 0py ratios that were 

 significantly different from the two soluble (<0.3 /im) fractions. In fact, the two soluble 

 fractions (first AI2O3 bed and second AI2O3 bed) also had different 2 3 8py/2 3 9,2 4 0p^ 

 ratios. The source of plutonium isotopes to the water column is the contaminated lagoon 

 sediments, but only a few water samples have 2 3 8py^2 3 9,24 0p^ ratios equal to those of 

 the sediment. In the surface waters of the lagoon, the ranges of ^^^Pu/^^^'^^°Pu ratios 

 were: MiUipore filters, 0.014 to 0.57; first AI2O3 bed, 0.06 to 0.64; second AI2O3 bed, 

 0.09 to 0.46. The 238p^j^239,240pjj j2Ltios in surface-water samples from the craters and 

 outside the lagoon were even more variable. In fact, the 2 3 8p^^2 3 9,24 0py ratios in a few 

 collections made outside the lagoon were greater than 1; i.e., more ^^^Pu than 



2 3 9,24 0p^^ was present in the samples where the total concentration was less than 



3 pCi/m^ . 



An external source of ^^®Pu, such as SNAP-9A, which burned up in the atmosphere 

 over the Indian Ocean in 1964 (Volchok, 1969), may contribute to the higher 

 ^^^Pu/^^^'^'*°Pu ratios in the water column at Bikini. However, the amount of this 

 material at any location would be small since 17 kCi of ^^®Pu was dispersed throughout 



