654 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



TABLE 5 Concentration Ratios (CR's) in Seston, 

 Zooplankton, and Crayfish Relative to Filtered Pond Water 



*pCi ' ^ ' '^ " °Pu/g acceptor - pCi ' ^ ' '^ " ° Pu/ml water. Mean ± 

 standard error. 



The transfer of plutonium from water to seston was extremely high (Table 5). The 

 concentration ratios (CR's) relative to filtered water were of the order of lO'* to 10^. 

 Concentration ratio is defined as 



_ picocuries per gram seston (dry weight) 

 picocuries per milliliter water (filtered) 



These CR's were higher than those previously observed in marine systems. Laboratory 

 experiments revealed that the mechanisms involved were more than simple surface 

 sorption (Johnson, Svalberg, and Paine, 1974). 



Zooplankton 



Although several species of cladocerans, copepods, and amphipods were collected, 

 sufficient biomasses for analysis were never obtained at any one sampling period. This 

 necessitated a pooling of the samples over several months. This was especially true for the 

 B-series ponds, which contained almost no zooplankton throughout the study. Zoo- 

 plankton showed CR's relative to filtered water in the IC* range (Table 5), These CR's 

 are similar to those reported in marine studies. If ingestion is the primary route of 

 transfer in these organisms, then higher concentration factors would be expected from 

 the simple phytoplankton-to-zooplankton food chain. Since an increase in trophic-level 

 concentration of plutonium did not occur, there appears to be a selective mechanism that 

 discriminates against plutonium at this level. This would result in a decreased potential 

 hazard when considering the transfer of plutonium through ingestion routes. 



