PLUTONIUM CONTENTS OF FIELD CROPS 387 



This ratio was used to evaluate the relative importance of different pathways of 

 Plutonium movement. 



White Oak Creek Floodplain, Oak Ridge 



A successional floodplain forest characterizes the vegetation of the study site (Dalilman 

 and Van Voris, 1976). A small area was cleared of native vegetation to provide adequate 

 sunlight for growing vegetables and field crops on the contaminated site. Soil was 

 cultivated by tilling in the early spring of 1975 and 1976. Common varieties of vegetable 

 and forage seed stock were 6btained from local vendors. All plants were grown in parallel 

 rows randomly placed in each of four 5- by 5-m subplots. Each species (except potato 

 and tomato) was grown in two replicated rows per subplot. The entire 100-m^ plot 

 contained eight row replications of all species except potato and tomato. Single rows of 

 potatoes and tomatoes were grown in each subplot for a total of four rows per 100-m^ 

 plot. Analysis of variance among subplots showed no significant difference in plutonium 

 concentration for a given species among subplots where sufficient plant material was 

 collected for plutonium analysis. 



After the seedUngs emerged, black plastic mulch was placed on the soil surface to 

 prevent weed growth and resuspension of soil-borne plutonium. This method proved 

 effective because the ambient air concentration of plutonium 10 cm above the soil 

 surface did not exceed 0.14 x 10"^ pCi/m^ (Dahlman and McLeod, 1977). Air samples 

 were collected over mulched soil containing 63 ± 0.4 (standard error) pCi Pu/g. 

 Monitoring results for the Oak Ridge area showed that ambient plutonium was 

 0.016 X 10"^ pCi/m^ at a height of 1 m above ground (Oakes and Shank. 1977). It was 

 not determined if the higher value at 10 cm represented normal plutonium in ambient air 

 near the floodplain soil or if it represented radioactivity induced by air currents frorh the 

 high-volume samples (approximately 30 cfm). We suspect the latter caused it. 



Vegetative samples were cleaned before radiochemical analysis. Bush bean, soybean, 

 and tomato leaves were washed and rinsed in an ultrasonic cleaning device, where fresh 

 samples (about 5 to 10% by volume) were placed in a 14iter-capacity cleaning tray 

 containing 700 ml of distilled water. The sonifier was tuned to give an optimal frequency 

 for cleaning each sample for a 2-min period. This was determined by the maximum 

 agitation delivered to the loaded cleaning tray by the wave generator. The cleaned 

 vegetation was carefully separated from residues, which settled in the bottom of the 

 sonifier tray. After the residue had been discarded and the tray rinsed with acid, the 

 vegetation was cleaned a second time with fresh distilled water. Samples were finally 

 removed from the tray, dried, chopped, and prepared for radiochemical analysis. 



Other garden vegetables were cleaned according to kitchen food-preparation 

 techniques. Lettuce was cleaned under running tap water by gently rubbing the leaves. 

 The samples were drained, dried, chopped, and prepared for radiochemical analysis. Root 

 samples (radish, carrot, and potato) were vigorously hand scrubbed under running tap 

 water. The samples were dried, chopped, and prepared for radiochemical analysis. 



The samples were sent to LFE, Richmond, Calif, for radiochemical analysis. The 

 analytical procedure has been discussed previously by Wessman et al. (1978). 



