SYNTHESIS OF THE RESEARCH LITERATURE 31 



generally not concentrated (i.e., CR < 1) by terrestrial plants and animals. On the basis of 

 laboratory studies, neptunium may be an exception (Schreckhise and Cline, this volume; 

 Price, 1972). However, there are no data from which to judge the behavior of this 

 element under field conditions, particularly in acid soils where Fe(II) would reduce 

 Np(V). 



Tables 13 and 14 show tliat CR's based on greenliouse studies are much lower than 

 those derived from field data. The higher CR's based on field data are likely due to 

 surficial contamination of plants with small soil particles, whereas CR's based on 

 greenhouse studies generally reflect only root uptake. 



Agricultural plant species accumulate transuranic elements to about the same degree 

 as native plants. The concentrations of transuranic elements in fruits and grains are 10"^ 

 to 10~ ^ times lower than those in vegetative parts (Schulz, 1977). 



Field data from a number of study sites containing up to several hundred picocuries 

 per gram of soil show that plutonium transfer to native and domestic animals is also very 

 small (Little, 1976; this volume; Hakonson and Nyhan, tliis volume; Bradley, Moor, and 

 Naegle, 1977; Smith, 1977). Concentration ratios in internal tissues of rodents are 

 comparable to those observed in internal tissues of vegetation. Concentrations of 

 plutonium in internal tissues (i.e., liver, muscle, and bone) can seldom be measured owing 

 to the low gut availability of this element (Durbin, 1975). 



Aquatic Food Webs. Transuranic elements can enter aquatic environments at a number 

 of points in complicated food chains encompassing all trophic levels from microbes to 

 vertebrates. Summaries of trophic-level studies in freshwater and marine environments 

 (Dahlman, Bondietti, and Eyman, 1976; Hetherington at al., 1976) indicate that 

 plutonium CR's relative to water generally decrease at higher trophic levels. 



Marine benthic invertebrates and invertebrate predators feeding on them exhibit tlie 

 highest levels of plutonium in coastal fauna (Noshkin, 1972; Pillai and Mathew, 1976). 

 Although these observations generally correlated with the high fraction of the plutonium 

 inventory found in sediments, experimental studies show that marine invertebrates have 

 remarkably hi^ assimilation efficiencies relative to terrestrial mammals (Beasley and 

 Cross, 1979). 



No clear correlation between sources of transuranic elements and marine fish 

 concentrations can be made at this time because of limited data. The evidence from both 

 field and experimental studies shows variations in uptake which can be attributed to tlie 

 element under study, the chemical species, and the type of fish. Studies with ^^ ''Pu show 

 that plaice can absorb plutonium as Pu(VI) by direct uptake from seawater, but 

 absorption across the gut from labeled food or sediment is very low (Pentreath, 1978a). 

 Elasmobranch fish, such as the thornback ray, however, do appear to absorb plutonium 

 across the gut wall relatively easily (Pentreath, 1978b). Environmental observations 

 indicate that americium is relatively more available to plaice than is plutonium (Pentreath 

 and Lovett, 1978). 



Except for high CR's for plutonium in phytoplankton relative to water, which appear 

 to result from a surface-adsorption phenomenon (Beasley and Cross, tliis volume), and 

 observations of a fourfold increase in the concentrations of plutonium in starfish relative 

 to those in the mussels on which they feed (Noshkin et al., 1971), no apparent 

 biomagnification has been observed in aquatic systems (Dahlman, Bondietti, and Eyman, 

 1976). 



