Pu from the processing plant at Savannah River is 58, compared with an a % The a % 238pu of environments shows enrichment in ?3®py relative to global fallout, the effect is greatest for fresh deposition and the suspendible fraction on the soil surface. In the Savannah River case, the 23 Pu/?35pu activity ratio can serve as a useful identifier of the source of Pu and its movement in the terrestrial environment. This technique is not applicable at Oak Ridge because there are no reported differences between the a % 735pu of global fallout, local sources, and indigenous deposits. low value 30.5 m from edge. PLUTONIUM CONTAMINATION OF TERRESTRIAL VEGETATION BY THE AERIAL PATHWAY Vegetation in the Savannah River study area was contaminated by direct deposition on foliage by a small quantity of Pu chronically released from processing stacks to the atmosphere, For example, within the 3 mCi km7* dsopleth, 99% of the airborne Pu originates from stack effluents, and Pu in vegetation is attributed to direct deposition on foliage because the 738pu/total Pu activity ratio in vegetation (average of 62, Table 2?) is closer to the ratio of airborne Pu (58) than to the ratio of soil Pu (14). Suspendible particles on the soil surface having a ratio of 43 may also contribute to surface contamination of vegetation. Since the leaves were not cleaned prior to processing, surface contamination was not eliminated as a possible cause of Pu in vegetation. Results of Table 2 provide evidence that direct deposition, a physical phenomenon, is responsible for the Pu in the vegetation of the Savannah River environs. For a metabolic pathway, root uptake, to be responsible for the observed isotopic ratios in vegetation, plants would have to assimilate more 27%pu than 239py from soil. There is no evidence that plants can distinguish between Pu isotopes and selectively assimilate them nor are there even scientific bases or hypotheses of differential metabolism provided the chemical compounds of the isotopes are similar. igh value determined 7.6 m from edge of field Imeasurements for airborne Pu at ORNL floodplain were made at 1 m from ed ge of garden ploc; Pu values in samples collected 10 cm from soil surface were 0.14 and 26.3 fCi m7? during ambient and cultivation conditions respectively. Not detectable in 346 m? air sample; minimum detectable level is 0.1 pCi per sample. i Avalues determined for breathing zone using high-volume air samplers (1-2 m? min7!), TABLE 1 {Continued} 238py of 4 for Pu from global fallout (Hardy et al., 1973). Pu in environmental materials collected from the 3 mCi km-2 isopleth confirms that the Pu comes from the processing plant. While all Pu in Savannah River The concentration ratio (CR = [Pu]lveg/[Pu]soil) is Frequently used to express plant-incorporated Pu relative to sot] concentration, and a common application of the CR is to compare results obtained from diverse experiments or field observations. Observed CRs for the Savannah River environment range from 0.075 to 1.5 (Table 2). These CR values are several orders of magnitude greater than values determined in the absence of contamination of vegetation by the aerial pathway (Schulz et al., 1976; Dahlman et al., 1976). Whenever soil is not the primary source of plant-incorporated Pu, there will be limitations in the conventional use of the concentration ratio. It would be advisable to consider a different expression relating to Pu in vegetation to Pu ina source when soil is not the main contributor. 308 309