UPTAKE BY AQUATIC ORGANISMS 613 



trenches leading to the pond indicate that most of the historic transuranic releases were 

 removed in the sediments of the trenches and thus did not reach the pond. This raises the 

 possibility that the plutonium and americium deposited years earlier may constitute a 

 supply of possibly solubilized radionuclides to the pond which could influence the 

 measured values. 



Sediment contains more than 95% of the total plutonium pool in the pond. The 

 potential availability of ^^^Pu, ^^^'^'*°Pu, and ^'^^Am from sediments was estimated 

 from a series of extractions using sodium chloride, oxalate, and ethylene- 

 diaminetetraacetic acid (EDTA). Emery et al. (Emery, Klopfer, and Weimer, 1974; 

 Emery and Farland, 1974; Emery et al., 1975; Emery et al., 1976) corrected the 

 concentration ratios for pond biota to account for the estimated available fraction from 

 the sediments or water. However, for purposes of this presentation, we have chosen to 

 present concentration ratios (CR, ratio of sample plutonium concentration to source 

 plutonium concentration) for plutonium and americium related to the total 

 concentrations reported by Emery et al. in sediments and vrater. Table 1 clearly 

 demonstrates the difference in calculated CR values for aquatic biota when different 

 sources are assumed. 



Tlie rarios of either ^"^^ Am or ^^^Pu to ^^^'^^^Pu in organisms divided by those 

 same ratios in various potential source compartments (sediment, interstitial water, and 

 overlying water) are given in Table 2. A value of 1.0 would indicate that the acceptor 

 compartment (biota) contains exactly the same isotopic ratios as the proposed source 

 compartment, i.e., that the ^"^ ^ Am/^^^'^'^^Pu ratios or ^^^Pu/^^^'^'^^Pu ratios are the 

 same in both biota and source. Therefore, if we assume that there are no significant 

 differences in metaboHsm of these isotopes by aquatic biota, the compartment that 

 exhibits ratios closest to 1.0 for both isotopes can be considered the prime source of 

 transuranic elements to the biota in this system. As shown in Table 2, interstitial water 

 from sediments most closely meets this requirement. 



Marshall, Waller, and Yaguchi (1974) provided an earUer assessment of the role of 

 organisms in tlie removal of plutonium from Great Lakes waters and the potential for 

 plutonium to reach man via the food chain. Concentration ratios for 2 3 9,2 4 0p^j ^^^ 



TABLE 1 Concentration Ratios for Plutonium and Americium 

 in Aquatic Biota from U-Pond Calculated Using Different Sources* 



*Data from Emery, Klopfer, and Weimer, 1974; Emery and Farland, 1974; Emery et al., 1975: 

 Emery et al., 1976. 



