616 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



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Fig. 1 Plutonium concentrations in various Lake Michigan compartments. (Data from 

 Wahlgren and MarshaU, 1974.) 



Edgington et al. (1976) measured the plutonium and americium concentrations in 

 Lake Michigan sediments and identified some of their characteristics. They calculated 

 that approximately 97% of the plutonium that has entered Lake Michigan now resides in 

 the sediments. Surface sediments in Lake Michigan now contain between 140 and 400 

 fCi/g of dry sediment, whereas the concentration in the water column is less than 1 

 fCi/liter. Earlier, Edgington et al. (1976) had indicated a negligible contribution to the 

 input of plutonium to Lake Michigan from runoff via tributary rivers and streams. Their 

 data suggest a significant redistribution of sedimentary material in the lake with a rapid 

 movement of the radioactivity from its site of deposition on the sediment surface to a 

 final site of deposition in the sediments. Apparently there are large areas of Lake 

 Michigan where no significant sedimentation occurs. These areas have a layer of tloc, 

 containing somewhat higher concentrations of plutonium, overlying the glacial till or 

 sand. Since no significant accumulations of sediment have occurred in these areas, it is 

 likely tliat tliese 1- to 2-cm-thick deposits are transitory and that the material is readily 

 resuspended. 



The 2 3 9,2 4 0pjj ^j^ values for shoreline plants in Lake Ontario found by Bowen 

 (1974) were similar to those reported by Marshall, Waller, and Yaguchi (1974). However, 

 the plankton CR values ranged tVom 10 to 300 (vs. 600 to 15,000 as reported by 

 Marshall, Waller, and Yaguchi, 1974). Further, Marshall, Waller, and Yaguchi reported CR 



