UPTAKE BY AQUATIC ORGANISMS 619 



TABLE 6 Distribution Coefficients (R^) for 

 Plutonium Isotopes in Aquatic Systems 



Kj* Isotope Environmentf Reference 



L,F Trabalka and Eyman (1976) 



L,M Duursma and Parsi (1974) 



L,F Trabalka and Frank (1976) 



M Pillai and Mathew (1976) 



F Bowen (1974) 



F Wahlgrenetal. (1975) 



M Hetherington et al. ( 1976) 



^„ Concentration on solid phase (grams per gram) 



Concentration in liquid phase (grams per milliliter)" 

 tF, freshwater; M, marine; L, laboratory. 



content of the cast shell was approximately twice that of the shell of the intermoult 

 lobster. Whether the differences reported are due to the chemical species of plutonium 

 the organisms were exposed to at the various sites or to interspecific physiological 

 differences is open to question at this time. 



Some authors (Emery et al., 1975; Bair et al., 1974; Hakonson and Johnson, 1973; 

 Morin, Nenot, and LaFuma, 1972) have suggested that plutonium isotopes can behave 

 differently in biological systems. In environmental studies the discrepancies in behavior 

 can be explained by different physic ochemical forms of the isotopes in the original source 

 or by different sources of uptake. In laboratory experiments differences in metabolic 

 behavior can be attributed to differences in concentrations of the isotopes tested. 

 However, Fowler, Heyraud, and Beasley (1975) found that, if the different plutonium 

 isotopes (^^^Pu, ^^"^Pu, ^^^Pu, and ^^^'^"^^Pu) were present in the same physico- 

 chemical form, aquatic organisms were unable to discriminate between tliem in either 

 accumulation or excretion studies. They also concluded that the suggestion of Moghissi 

 and Carter (1975), reinforced by the work of Eyman, Trabalka, and Case (1976), is 

 correct, "that in environmental studies, ^^ ''Pu is most likely the best tracer for measuring 

 plutonium kinetics in biological systems." 



Discussion 



This chapter is not intended to be definitive, but, rather, we have attempted to evaluate 

 the most pertinent data sets. Although there appears to be a commonality (i.e., no 

 biomagnification, highest concentrations in benthic organisms and phytoplankton) among 

 all environmental data sets, whether marine or freshwater, there are also significant 

 discrepancies. The most interesting common factor we were able to extract from a wide 

 range of studies, both laboratory and field, is the similarity in the observed distribution 

 coefficient for plutonium in sediment (Table 6). Inconsistencies involve differences in CR 

 values for freshwater algae and some fissue distributions observed in both freshwater and 

 marine studies. These discrepancies are probably explainable on the basis of differences in 

 physicochemical form to which organisms were exposed at different sites. 



From a review of the data available for both freshwater and marine environments, 

 there appear to be relatively few significant differences in the patterns of accumulafion or 

 in the observed CR's. 



