Pii AND Am IN SAVANNAH RIVER MARINE ENVIRONMENT 609 



TABLE 2 Plutonium, Americium, and Gross Alpha Activities (dry-weight basis) 

 in the Savannah River Estuary Sediments 



*Mean + standard error. 



greater than this are usually indicative of other sources of plutonium in the system. The 

 ratios for the Savannali River estuary cores are reported in Table 2, and only in the 

 freshwater core in the upper to 15 cm were ratios found to be different from those 

 from fallout. These ratios were about a factor of 2 greater than fallout ratios and 

 presumably resulted from the SRP releases to the river system. 



If americium dynamics in estuaries are different from those in freshwater or 

 seawater systems, this difference would be evidenced by tlie ^^ ' Am/'^^^''^'*^Pu ratios. 

 The average value for such ratios in shallow near-shore sediments (Livingston and Bowen, 

 1975) and in Lake Michigan sediments (Edgington et al., 1976) varies from 0.14 to 

 0.34, with an average of 0.22, and no fractionation between americium and plutonium 

 has been found in these sediments, even when the radionuclides are being lost from tlie 

 sediment following upward migration (Livingston and Bowen, 1975). Except for one 

 value of 0.62, the ^^' Am/'^'^^^'^'^^Pu ratios for two sediment cores reported in Table 2 

 are not significantly different from those quoted in the literature. The indication is that 

 tlie chemistries of americium and plutonium are similar in diis estuarine sy stein and that 

 tire ^'^ ' Am has grown in from ^'^ ' Pu. 



The transuranic alpha activity in these cores represents less than 1% of the gross alpha 

 activity from the natural radionuclides that are present. Indeed, modern civilization's 

 impact on the alpha activity of these cores is small compared with die natural 

 background. 



Seafoods 



At present plutonium levels, seafoods make a very minor contribution to the overall 

 radiation-dose comnntment to the populations in the southeast. Seafood samples that 

 represent all trophic levels consumed by people in the southeastern United States were 

 collected in and near the Savannali River estuary and analyzed for plutonium. The 

 plutonium concentrations decreased as expected from the molluscs to the fish, with die 

 oyster having the higliest concentration. 0.12pCi/kg, coinpared with 0.001 pCi/kg for 

 sliad (Table 3). The 50-yr bone-dose commitment from consuming 5.9 kg of oysters per 



