SYNTHESIS OF THE RESEARCH LITERATURE 7 



Autoradiographs of leaf tissues show that plutonium occurs primarily in discrete 

 particles of suspendible size on the surface (Romney and Wallace, 1977). Washing plant 

 materials to remove surface contamination reduces the concentration of plutonium in 

 subsequent analyses (Dahlman and McLeod, 1977). 



In some cases (e.g., inadequately cleaned vegetables) soil can be ingested by humans. 

 Knowledge of the surface contamination of plant material is certainly important in 

 determining the amount of plutonium ingested by both animals and humans. 



Analyses of animal pelts, gastrointestinal tracts, and lungs give higher concentrations 

 than those of tissues not exposed directly to surface contamination (Bradley, Moor, and 

 Naegle, 1977). Humans do not normally eat tissues exposed to direct surface 

 contamination to the extent that other carnivores do. Thus IR's calculated using 

 concentration values determined from animal samples with natural levels of surface 

 contamination may be more relevant in the assessment of potential environmental 

 problems with food chains up to, but not including, humans. 



High IR values for plant Utter (Table 3) are principally due to surface contamination 

 because smaller soil particles are impossible to remove (Romney and Wallace, 1977). The 

 same is true for northern lichen-dominated communities where most dust particles are 

 intercepted before they reach the surface of the ground (Hanson, 1966; Holm and 

 Persson, 1975). Around transuranic processing facilities, aerial deposition of transuranic- 

 bearing particles is probably the dominant form of contamination of plants (Pinder et al., 

 1979). Resuspension contributes importantly to surface deposition of contaminants and 

 increases plant concentration values even in relatively moist environments (Dahlman, 

 Garten, and Hakonson, this volume; Pinder et al., 1979). 



There are few estimates of biomass of higher carnivores relative to that of vegetation. 

 In addition, contaminated areas are generally Umited in size and frequently include only 

 parts of the ranges of a few individuals. Hence reliable IR's are not available for upper 

 trophic levels, and animals are considered here as one compartment within the ecosystem. 

 Inventory ratios may have characteristic values for certain ecosystems, and identification 

 of ecosystem attributes allowing prediction of IR's would aid in assessing hazards. 

 Knowledge of the relative biomass of ecosystem components will always be useful in 

 modeling the long-term distribution of most contaminants, including transuranic 

 elements. Future research on IR's should emphasize the establishment of predictable 

 relationships and the identification of variables affecting IR values. 



Aquatic Ecosystems 



Experimental studies in the Great Lakes (Edgington and Robbins, 1975), Buzzards Bay 

 (Livingston and Bowen, 1976), Irish Sea (Hetherington, Jefferies, and Lovett, 1975; 

 Hetherington, 1978), and Trombay Harbor (Pillai and Mathew, 1976) have shown that, in 

 comparatively shallow bodies of water, more than 96% of the total plutonium released to 

 these environments is rapidly transferred to sediments. However, Bowen, Wong, and 

 Noshkin (1971) estimated that as of 1969 10 to 20% of the total plutonium in deep 

 oceans had been deposited in the sediments and that this would increase to only 30% by 

 1980. 



In those parts of Lake Michigan and Lake Erie where sedimentation rates are greater 

 than 5 mm/yr, a detailed analysis of plutonium and '^''Cs profiles in sediment cores 

 clearly reflects the worldwide fallout maximums in 1959 and 1963 (Fig. 2). Similarly, it 

 has been shown that americium and plutonium profiles in sediments from the Irish Sea 



