582 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



Transuranic Elements Identified at the Pacific Test Site Atolls Since 1972 



Neptunium 



Concentrations of ^^''Np in several 1972 samples of unfiltered lagoon and crater water 

 from Enewetak were determined by mass spectrometry (Noshkin et al., 1974). The 

 average concentration in six samples from the lagoon was 0.058 ± 0.013 fCi/liter. Water 

 samples from Mike and Koa craters averaged 0.45 ± 0.22 fCi/liter. Outside the lagoon and 

 to the east of the Atoll, concentrations in water samples from the open ocean surface 

 averaged 0.013 ±0.003 fCi/liter. Tliis comparison shows, as do results for all other 

 transuranics, that Atoll sources contribute the major fraction of the transuranic inventory 

 in the water column of the lagoon. The ^^'^Np concentrations in the lagoon and crater 

 water samples were less than 0.2% of the measured ^^^ ^''^Pu concentrations in those 

 samples. 



Plutonium 



Many types of samples from the Atoll contain ^^^Pu, ^^^Pu, ^'^"Pu, and ^"^'Pu. Most 

 reported values are the sum of ^^^Pu and ^"^^Pu activities determined by alpha 

 spectrometry. These radionuclides are distributed widely throughout the Atoll and have 

 been detected in nearly every type of marine and terrestrial sample analyzed to date. 

 Atoll water samples, sedimentary components (including fine unidentifiable carbonate 

 sands, coral fragments, Halimeda debris, foraminifera, and moUusk shells), living algae, 

 benthic invertebrate tissues, planktonic species, and marine vertebrate tissue all contain 



239+240p^ 



The distribution of ^ ^^Pu is as wide among components in the marine environment as 

 is 239+240p^ ^^^ ^^ \o\Nex Concentrations. The ^^^Pu/^^^'^^'^^Pu ratio determined in a 

 variety of aquatic samples from different regions of the lagoon ranges from less than 0.04 

 to greater than 0.50. 



A few activity ratios of ^'*°Pu/^'^^Pu were determined by mass spectrometry. The 

 ratios in two water samples collected from the lagoon during 1972 were 0.432 and 0.289 

 (Noshkin et al., 1974). Samples of mackeral bone and of viscera collected in 1972 near 

 the island of Glenn had ^'^^Pu/'^'^Pu activity ratios of 1.15 ±0.25 and 1.27 ±0.26, 

 respectively; goatfish viscera and tridacna tissue from nearby David had ratios of 

 0.68 + 0.07 and 0.66 ± 0.19 (Gatrousis, 1975), respectively. The activity ratios in 56 soil 

 samples from seven islands ranged from 0.066 to 1.42 and averaged 0.84 ± 0.37 

 (Gatrousis, 1975), and the average ratio in seven marine water and biota samples was 

 0.66 ± 0.40. Neither average value determined in the environmental samples differed 

 greatly from the average of 0.65 ± 0.05 for global fallout debris (Krey et al., 1976). The 

 similar isotopic ratio in mackeral tissue shows no obvious discrimination in uptake of 

 isotopes by tissues of organisms in the Atoll if feeding and living are restricted to specific 

 regions of the Atoll. 



The average ^'^^Pu/'^^^Pu ratio in the yearly growth sections of a live sample of 

 Favites virens coral collected from the western basin in Bikini lagoon was 0.77 + 0.07 

 (Noshkin et al., 1975). This value is similar to the isotopic ratio in Enewetak samples. 

 However, the mean isotopic concentration ratio in soil and vegetation of Bikini and Eneu 

 islands is 1.15 (Mount et al., 1976), which is somewhat higher than the average in the 

 Bikini coral sample. 



Since the ^'*°Pu/'^^^Pu activity ratio in some environmental samples exceeds 1, it 

 seems inappropriate to use the shorthand notation, ■^^^Pu, when referring to the sum of 



