24 TRANS URANIC ELEMENTS IN THE ENVIRONMENT 



in marked contrast to the data for Bikini Atoll (Schell, Lowman, and Marshall, this 

 volume) where preferential mobilization of ■^^^Pu was inferred from increased ratios of 

 ^^^Pu to ^^^'■^''Opu between nonfilterable and filterable fractions from lagoon water. 

 These findings were postulated to result from recoil damage from high-specific-activity 

 ^^^Pu, which caused increased solubility. However, such an explanation must assume 

 that 2 3 9,2 4 0p^^j ^^^ ^^^Pu are in separate particles originally. 



There is Uttle evidence to suggest that differing sources of transuranic elements affect 

 tlieir chemical properties when the elements are moderately well dispersed in aquatic 

 systems. Transuranic elements are soluble, to a limited extent, in both freshwater and 

 marine systems and are therefore available for transfer across biological membranes. 

 Plutonium apparently behaves similarly in oceans and in the Great Lakes, as shown by 

 values of Kq and chemical speciation. These systems can be considered oUgotrophic with 

 their chemical properties largely controlled by their respective carbonate cycles. Hence 

 the similarities in values of Kq and ratios of Pu(VI)/Pu(IV) are expected. 



Because tire pH of the ocean is well buffered, plutonium apparently cannot exist 

 except as Pu(III) or Pu(VI) in solution in the water column or as Pu(IV) in sediments if 

 the relationships shown in Fig. 4 hold. However, in freshwater lakes large variations in 

 composition are possible, and the pH can be relatively low (about 4). Under these 

 conditions dramatic changes in concentrations of plutonium are observed and can be 

 explained by the presence of Pu(in) or Pu(IV) as complexes. 



Environmental studies show the danger of using the results of laboratory experiments 

 with moderately concentrated solutions (\0~^M) to predict the behavior of plutonium in 

 tlie environment, where the maximum observed concentration has not exceeded 

 10"' ■^M. Somewhere within the concentration range of 10"'^ to 10" ^M, plutonium 

 ceases to exhibit the properties of simple ions, and tlie possible formation of polymeric 

 species must be considered. 



Transport 



Terrestrial 



Most environmental plutonium exists in a strongly adsorbed state on surface soils. Hence 

 most investigators have concluded that the transport of this element, at least over the last 

 30 yr, has been governed by processes regulating the distribution and transport of soil 

 (Essington et al., 1976; Hakonson, 1975; Hakonson, Nyhan, and Purtymun, 1976; 

 Hakonson and Nyhan, this volume; Hayes and Horton, this volume; Romney and Wallace, 

 1977; and Sprugel and Bartelt, 1978). In natural systems soil-erosion processes are mainly 

 driven by wind and water. 



Wind Erosion. Wind transport of plutonium in soil can be documented anywhere that 

 appropriate soil, vegetation, and climatic conditions exist. These conditions exist when 

 soil is loose, dry, and of optimum particle size; the soil surface is relatively smooth; 

 vegetation cover is sparse; and winds are sufficiently strong to initiate soil movement 

 (Beasley, 1972). 



Wind redistributes plutonium in soil, as inferred from samphng of contaminated sites 

 (Little, 1976; this volume; Markham, Puphal, and Filer, 1978; Romney and Wallace, 

 1977) and from studies focused specifically on wind transport of plutonium (Gallegos, 

 1978; Sehmel, 1978; Anspaugh, Shinn, and Wilson, 1974; Anspaugli, Shinn, and Phelps, 

 1974; 1975). These observations and field studies, primarily in arid regions, imply that 



