DISTRIBUTION OF PLUTONIUM IN ECOSYSTEMS 375 



WHITE 



OAK 



CREEK 



S30 



S60 



S90 



PPZ^ 150 pCi/g 

 ^^ 100 pCi/g 

 ^3 25 pCi/g 



[ ■ .] 10 pCi/g 



S300 



Fig. 1 Approximation of areal distribution of plutonium at the contaminated Oak 

 Ridge floodplain. Grid size is 30 by 30 m for an area of 900 m^ . Distribution is generally 

 estimated from 0- to 10-cm soil samples plus a few samples from the 10- to 20-cm depth. 



White Oak Creek, and in the upper part of the floodplain. The maximum concentration 

 of plutonium occurred where the creek is beheved to have entered the historic 

 impoundment between coordinates E60-S120 and E120-S30 (Fig. 1). Sediment-borne 

 plutonium probably settled from the water column as the stream velocity decreased on 

 entering the impoundment. Downstream from the site of initial deposition the higher 

 plutonium concentrations tended to follow the watercourse of White Oak Creek (WOC). 



Plutonium is not distributed uniformly between the loam and clay fractions of the 

 soil. The loam fraction (>0.002 mm) contains 60% of the plutonium; whereas 24% of the 

 <0.002-mm size class contains 40% of the plutonium. The high affinity of plutonium for 

 colloids may be responsible for plutonium enrichment in clay. The distribution 

 coefficient (K^), determined by desorption in 0.01MNaHCO3,is 5 X 10^ (Bondietti and 

 Tamura, this volume). 



The highest concentration of plutonium is observed in the 0- to 10-cm zone of the 

 soil profile. Occasionally a higher concentration of plutonium occurs below 10 cm. This 

 atypical distribution is attributed to deposition of sediments over the initial plutonium 

 deposit rather than to movement of the element by biogeochemical processes. 



