SYNTHESIS OF THE RESEARCH LITERATURE 21 



discharges from nuclear processing plants into coastal zones. The study areas and 

 characteristics of the sources are given in Table 9. 



Plutonium has been measured in samples of ocean waters collected since 1963, 

 shortly after the peak of activity in testing weapons. The concentration has decreased 

 from 2 to 3 fCi/hter in samples of water from the northeastern Pacific in 1964 (Pillai, 

 Smith, and Folsom, 1964) to about 0.2 to 0.9 fCi/liter in samples collected between 1968 

 and 1973 (Miyake and Sugimura, 1976). The major point in studying plutonium in the 

 water column of oceans is to use variations in the concentration of this element to 

 explain movements of water and pollutants. To this end, comparisons have been made of 

 the movement of plutonium relative to ^"Sr and ^^ ^Cs in the Pacific Ocean and Atlantic 

 Ocean (Bowen, Wong, and Noshkin, 1971; Miyake and Sugimura, 1976). The Pu/^"Sr 

 and Pu/^'^^Cs ratios in surface seawater are far lower tlian those found on land, which 

 indicates that the residence time of plutonium in the water column is less than tliat of 

 ^^ ''Cs and ^°Sr. As early as 1968, from 10 to 20% of the total plutonium deposited over 

 the ocean was in deep-sea sediments at water depths of about 4000 m. The depletion of 

 plutonium from surface waters may be modeled in terms of settling rates of particulate 

 matter in the water column. The observed distribution of total plutonium in the water 

 column to 5000 m is explained in terms of a distribution of particles with the majority 

 settling at an average velocity of 195 m/yr (Bowen, Wong, and Noshkin, 1971). 



Another series of water samples was collected from the Pacific Ocean in 1973 as a 

 part of the Geosecs Program. Analyses of these samples showed that there is a maximum 

 in the concentration of plutonium at a depth of 300 to 700 m across the Pacific Ocean 

 and that the concentration of ^^^Pu in this stratum has not changed by more than 20% 

 over a period of 5 yr (Bowen, 1977). This behavior can be explained by assuming a rapid 

 transfer of plutonium to about 400 m by biogenic debris (e.g., fecal pellets) (Beasley and 

 Cross, this volume) where the plutonium returns to a soluble species that can migrate 

 upward or downward by diffusion. Experiments in the Irish Sea have shown that 

 plutonium is in solution predominantly as Pu(VI) and on particles as Pu(IIl) + Pu(IV) 

 (Nelson and Lovett, 1978). The rapid movement of plutonium to 700 m may be 

 associated with particles that sink to that depth where they dissolve and the plutonium 

 reoxidizes to Pu(VI). The higher ^ '^ ^ Am/^ 3 9 ,2 4 op^ ^^^^^ ^^^^ ^ qqq ^ j-glative to that in 

 surface waters supports this hypothesis. Since the Kd for Pu(VI) is about 1000 times 

 lower than that for Pu(IIl), Pu(IV), or by inference Am(III), any ^^^ Am that is released 

 would be preferentially taken up by any remaining particles. 



Plutonium in oceans occurs in solution over a wide range of concentrations 

 (Table 10). A more surprising result is that distribution coefficients between water and 

 suspended sediments are very similar to those in the Great Lakes and elsewhere. 



The distribution of ^^^'^"^^Pu and ^^^Pu in waters and sediments of Enewetak Atoll 

 has been studied in detail (Noshkin, tliis volume). In 1976 the total inventory of 

 2 3 9,240p^ in water and sediments was 1.24 and 249 Ci, respectively. The Kq for 

 plutonium in these sediments has been independently measured in the laboratory as 

 1.8 X 10^. A simple model can be constructed to predict the average concentration of 

 plutonium in the lagoon by assuming this equilibrium constant. This model predicts the 

 concentration of plutonium to be 32 fCi/liter. The average concentration measured in 

 1976 was 16 fCi/Uter. Furthermore, there is no indication of preferential dissolution of 

 ^^^Pu in this lagoon because the isotopic ratios of ^•^^'^'*^Pu and ^^^Pu are identical in 

 water and sediments. Similar Kq values for sediments from the Irish Sea and Enewetak 

 Atoll suggest that similar chemical reactions are occurring in all oceans. These results are 



