SYNTHESIS OF THE RESEARCH LITERATURE 21 



Alamos showed that stream-bank soils are a repository of effluent plutonium and serve as 

 a source of the element to stream-bank biota (Hakonson et al., 1979). 



It has been estimated that rivers contribute about 150 to 500 Ci/yr of ^^^Pu to 

 oceans (Simpson, Trier, and Olsen, this volume). 



Studies of the Savannah River showed tliat about 0.005% of the total plutonium in 

 the watershed is lost to the coastal zone annually (Hayes and Horton, this volume). In 

 contrast, the annual loss for a typical midwestern river, the Miami (Muller, Sprugel, and 

 Kohn, 1978; Sprugel and Bartelt, 1978), and for the Hudson (Simpson, Trier, and Olsen, 

 this volume) is an order of magnitude greater. These results indicate a residence time of 

 between 10^ and 2 x 10"* yr. In each river the majority of the plutonium is transported 

 with suspended matter. The differences in loss rates are probably related to differences in 

 watershed morphology. A major fraction of the plutonium transported in the Savannah 

 River is probably held up in impoundments at the upper reaches. 



Biotic Activity and Mechanical Disturbance. Plutonium concentrations in animal tissues 

 demonstrate the dominance of physical processes in transporting plutonium to animals in 

 natural ecosystems. In addition to the gastrointestinal tract, highest concentrations of 

 plutonium are associated with the pelt and, to a lesser degree, lung tissue as a result of 

 interaction with plutonium on soil particles (Hakonson, 1975; Little, 1976; this volume; 

 Hakonson and Nyhan, this volume; Bradley, Moor, and Naegle, 1977). 



Work at the Nevada Test Site with cattle (Smith, 1977) shows that considerable 

 amounts of soil are routinely ingested by grazing herbivores. Cattle ingest several hundred 

 grams of soil daily under normal range conditions. Transport of plutonium occurs when 

 these animals move to other areas with subsequent deposition through defecation and/or 

 death of the animal (Arthur and Alldredge, 1979). The amount of plutonium transported 

 in this manner is considered small. Foraging by herbivores, such as cattle, deer, rodents, 

 and insects, may subject a substantial amount of the plutonium in soil to digestion 

 processes over prolonged grazing histories. Whether the chemical form of ingested 

 plutonium is altered as it passes through the gastrointestinal tracts is not known, but in 

 vitro studies indicate changes in solubility in an artificial rumen, simulated abomasal, and 

 intestinal fluid procedure (Earth, 1977). 



Mechanical disturbances, such as soil tilling and construction, can transport large 

 amounts of plutonium on a local scale. Plowing enhances mixing of plutonium with the 

 soil profile and also can cause large increases in airborne soil particles. Soil tilling activities 

 at the Savannali River Plant increased local air concentration of plutonium 100-fold 

 (Milham et al., 1976). Mechanical harvesting of agricultural crops also results in surface 

 contamination of edible grains (Adriano et al., 1975). 



Existing data pertaining to plutonium distribution in natural ecosystems suggest that 

 physical processes driven by wind will become less important as plutonium migrates into 

 the soil profile. Contemporary data from fallout areas contaminated in 1945 (Hakonson 

 and Nyhan, this volume) show tliat less than 50% of the soil column inventories of 

 plutonium occurs in the surface 2.5 cm of soil. Similar relationships have been observed 

 in a Los Alamos intermittent stream initially contaminated in 1963 (Hakonson et al., 

 1979) and in the grassland study site at Rocky Flats (Little, this volume). A change in 

 physical transport of plutonium would probably change the relative importance of 

 chemical and biological transport processes. For example, long-term cropping studies of 

 Romney and Davis (1972) and Schreckhise and Chne (this volume) suggest that migration 

 of plutonium into soil may create conditions more favorable for uptake by deeper rooted 

 plants. 



