6 7 8 



SALINITY (R P. T.) 



10 



12 



13 



14 



15 



Figure 5.-- Body burdens of cesium 137 in Rangia cuneata as a function of salinity. 



of Rangia was almost independent of salinity. 

 Other workers have suggested that cesium 137 

 could constitute a potential radiological hazard 

 in brackish- ■Water organisms at low salinities- - 

 because of the much higher concentration 

 factors for cesium. In Rangia , though, we 

 observed only about three times as much 

 cesium 137 in animals from fresh water as in 

 those from 15 p.p.t. We can deduce from this 

 situation that there is a gradient of cesium 137 

 in the Trent and Neuse Rivers; the concentra- 

 tions are lowest in fresh water and in- 

 crease with the salinity in a downstream 



direction. 



By manipulating the regressions relating 

 concentration factors and cesium 137 content 

 to salinity, we can solve for the cesium 137 

 content of the water as a function of salinity, 

 as follows: 



The derived relation (d) for the content of 

 cesium 137 as a function of salinity is shown in 

 figure 6. Included on this graph for comparison 

 are the four values that were obtainedby gamma 

 spectral analysis of water samples. 



The deduced relation in figure 6 is consistent 

 with the fact that cesium is very strongly 

 adsorbed on sediments and is effectively 

 desorbed by sodium and potassium. Alow con- 

 centration of cesium in fresh water would 

 therefore be expected because of adsorption on 

 bottom sediments. As the salinity increases, 

 this adsorption equilibrium shifts toward higher 

 dissolved cesium values. Concentration of 

 fallout cesium 137 in the water should in- 

 crease in a downstream direction until dilution 

 by deeper oceanic water becomes significant. 

 We would expect this phenomenon to occur 

 whenever the estuary has a salinity gradient 

 extending over several kilometers with little 



(a) Log concentration factor = 1.69 - 1.32 log salinity. 



^3' log Cs 



(b) Log concentration factor = log Cs ([>„„„;„) 

 0.48 - 0,18 log salinity. 



(c) Log Cs (Vangia) 



(d) Log Cs'37 = 1,15 log salinity - 1.22. 



137 

 (H2O)' 



16 



