PLUTONIUM CONTENTS OF FIELD CROPS 399 



^^^Pu/^^^Pu in soils, vegetation, and animal components were obtained (Hanson, 1975). 

 Although the ^■^^Pu data in the various ecosystem components were not conclusive, 

 earlier studies by McLendon et al. (1976) at SRP support evidence presented in other 

 studies that there was an apparent increase in the bioavailability of ^^^Pu relative to that 

 of ^^^Pu in tlie environment. Hanson (1975) has already discussed the possible 

 mechanisms causing this difference. 



In general, plutonium concentrations in vegetative parts of agricultural plants at SRP, 

 where tlie primary mode of contamination was external in nature, were similar to those in 

 the forage and vegetable foliage cultured at ORNL floodplain ecosystem, where 

 contamination was caused primarily by root assimilation. However, the CR values of 

 vegetative parts of crops from SRP were about one order of magnitude higher than those 

 from ORNL. 



Plutonium data on the edible portions of root crops are almost nonexistent. Potatoes 

 grown on soils receiving only global fallout plutonium which had been peeled had a CR of 

 3 X 10"^ (Bennett, 1976). This is similar to the ORNL data, which indicate that peeling 

 subterranean crops removed most of the plutonium, as high as 99.5% in the case of beets. 

 Whether plutonium in these vegetative tissues occurred as a free ion is still unknown. 



Data on plutonium in a variety of species from the ORNL floodplain suggest that CR 

 values in the range of 10""'* to 10~^ are related to plutonium assimilation by the root 

 pathway. The order of CR values was 2.4 x 10~^ (foliage av.) > 1 .7 x 10""* (fruit 

 av.)>0.9 X lO""* (peeled root). The results for foliage compare favorably with CR values 

 for plants grown in the glasshouse at SRP where aboveground tissues were protected from 

 airborne sources of plutonium. Comparative results described in tliis chapter and 

 elsewhere (Dahlman, Bondietti, and Eyman, 1976; Dahlman and McLeod, 1977) clearly 

 ascribe high plutonium CR values (10~^ to 10*^) to contamination of foliage surfaces. 

 Assimilation of plutonium by the root pathway was responsible for CR values in foliage 

 of 10~^ or less. There was no evidence that assimilation of plutonium by the root 

 pathway had been especially enhanced as a result of weathering, complexation, or other 

 soil processes in the 30-yr period since the site was contaminated in 1944. 



Summary 



Agricultural crop experiments conducted adjacent to a reprocessing facility at SRP, which 

 releases low chronic levels of plutonium per year through an emission stack, and at the 

 woe floodplain at Oak Ridge, where plutonium was deposited in 1944 from the 

 Manhattan Project weapon development, revealed the following: 



I.Plutonium concentrations and isotopic compositions in winter wheat grown in 

 1975 at SRP were affected by distance from the stack, plant heiglit, and method of 

 processing the grain. In general, vegetative materials closer to the stack (South Field) had 

 plutonium concentrations a factor of 2 higlier than samples farther away (North Field). 

 The wheat straw had approximately two orders of magnitude higher plutonium content 

 than the straw from the control site. Grain harvested by a combine had an order of 

 magnitude higher plutonium content than laboratory-thrashed grain. When the plants 

 were short, as in March, the sources of contamination were stack emission and 

 resuspendible and soil materials, as indicated by an average 38 a % ^^^Pu. Later in the 



