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