TABLE 2 PLUTONIUM CONCENTRATION AND CONCENTRATION RATIOS (CR) OF VEGETATION IN THE ENVIRONS OF SAVANNAH REVER Vegetation Location a Pu Concentration (pCi g7!) a % 238py b CR 0 Annual-Biennial A 1.78 62 1.5 x 10 Perennial A 0,836 63 7.2 x 10 Briar A 0.217 69 1.9 x 1074 Wheat Straw A 0.088 58 7.5 x 10 Plum B 0.084 75 2.1 x 10 Honeysuckle e Camphorweed® -1 -2 -1 -l C e.010 50 ll x 10 c 0.013 48 1.4 x 10 -1 ®concentratione of Pu in soil were 1,16 pci g-!, 0.40 pCi g-!, and 0.09 pci g7! for locations A, B, and C respectively. econcentration ratio is [Pole (Pula oan, “Data from McLendon et al., 1976. Plant habit may affect interception and retention of Pu according to data of Table 2. At site A, containing the highest soil Pu, plants exhibiting the annual-biennial habit (Solidago, Aster, and Gnaphalium) contained the most Pu followed by perennial species (briars and Grasses) and wheat, which contained the least Pu, The comparison of Pu concentration of the annual-biennia l and perennial habit at site A was confounded by the latge quaritity of dead material that was included in the perennial! samples which could have diluted the concentration, The comparison is more appropriate at site C with camphorweed (annualbiennial) and honeysuckle (perennial). At this site, the concentrations were essentially identical. The low Pu concentration and CR of wheat indicate the effect of the short time of exposure to the airborne Pu. Concentration ratios for native vegetation at site A ranged from 0.2 to 1.5. With an a % 2398py value of about 60 in the native vegetation, the Pu was attributed to deposition of airborne Pu on leaf surfaces, At sites B and C, which contained successively lower soil concentrations of Pu, CRs were about 0.1. The high ao % 738Py value suggests airborne Pu as the source, Relative contribution of airborne Pu by direct deposition vs. surface contamination by suspended particles of soilborne Pu was estimated from serial wheat samples (Table 3), Early in the season (March), when leaves are in close proximity to the soil surface, the isotopic ratio of 735pu/239pu was similar to that of the suspendible fraction (38 vs. 43). Later in the season (April, June), when leaves have extended 50 to 100 cm above the soil surface, the a 4% 238pu value of approximately 60 reflects increased deposition of airborne Pu. Plutonium concentration and CR decreased from March to April. During this period of rapid plant growth, the values decreased because of biomass accumulation occurring simultaneously with a constant Pu deposition rate. The Pu concentration and CR increased from April to June because of lower biomass The changes in the Pu content and accumulation while Pu deposition continued. a % 738py over the three-month period indicate the importance of duration of exposure of the foliage to an airborne source. INCORPORATION OF PLUTONIUM BY VEGETATION VIA THE ROOT PATHWAY Root uptake is an important route for Pu incorporation into vegetation once the element becomes part of the soil matrix. This pathway is particularly important over extended time intervals in humid and heavily vegetated environments where contamination of leaf surfaces by suspended soil particles is not a major contributor of Pu to vegetation. The contaminated floodplain site at Oak Ridge ts representative of such conditions, and experimental results from field studies describe root uptake of Pu by native species and vegetable crops (Table 4). 310