associated with the coarse silt (20-53 pm) fraction. Ten per t less usually ts associated with the soil fraction less than 5 om °r diameter. Highest activities also are assocfated with heav rn fractions (> 2,9 g/cm}, Sugge 1 sting the presence of oxid es. manera Fallout particles intercepte d by plant f smaller than 44 pm diameter (Romney et ar. ines the fovl are ot sizes vegetation at NTS selectivel y traps these small-sized particles in che matted hairs and crevi ces and on resinous giands of the leaf neon cee re capacity for retaining fallout particles largely depends pete wee anical-trapping characteristics of Plant surfa ces, We canpied foot these aged piac e emium contamination now found on vegetation n allout areas at NTS is super ficial contamination from particulat e Material, This mecha nism o a foot crently the most impor tant roure through which pluto niugereenet ion superficial grazing animals. However, the relative importance of eure ai contamination compared to the root uptake route may dimin ish th passing time for reasons to be discussed Shortly. Fortunately weette the suspendable surfa ce material was removed by wind and water os On ages ago. Resuspension problems now arise Particularly when e stabilized soil surface etust fs mechanically disturbed. That Toseut Ping these aged fallout areas (Wallace and Romney 1975; Rhoads t eee The purpose for this caution is evident from the data in able 2, which summarizes value s for the estimated inventory of Table 2. - Summary of Estimated Inventory of 239-240py for Vegetation in Aged Fallout Areas (Romney et al. 1976) a Fallout Area NTS Area ; 5 NTS Area 11A NTs Area 1B ea NTS Area 11D NTS Area 13 TTR OT TTR C81 re cs? | tnventory + §,E.4 (millicuries) 143 36 “a 56 141 4B ' 53 | 63 i Al : 86 -098 2.4 4.3 7.3 26.4 62 67 4.3 4.6 + an 114 | + .045 + 32 + 7B 4 79 4 3.5 + ,19 + (34 4 .63 + 1,2 a Vegetation invent. Soil inventory * 5-F- 00034 0028 .00039 .00048 -00039 -00060 -00012 -00013 00015 -00016 + + + + + + + + + + .000046 “0017 900058 .0 “po008. .000076 .000036 .000078 .900030 000037 ‘Time Plutonium was dispersed b y chemical ex explosive: NTS TSA: Area 5a 19541955; NTS Area 11, 1956; NTS Area 13, 1957; TTR Areas, 1963. " See note c Table 1. a plutonium for vegetation in these fallout areas. Only small amounts of the total quantity of plutonium originally deposited presently appear to move to the standing vegetation from fenced-in fallout contaminated soils which are now undisturbed, except for natural wind conditions. Advantage can be gained from keeping these sites as little disturbed as possible. This includes surface erosion by water (Hakonson etal. 1976; Hakonson and Nyhan 1976). RECYCLING OF PLUTONIUM TO VEGETATION Most of the standing biomass of vegetation in the aged fallout areas at NTS is contributed by deciduous shrubs (2,000 to 6,000 kg/hectare) which normally yield about 10 percent of their total weight as new annual foliage. The production of grasses, forbs and annual plant species is spasmodic from year to year, depending upon rainfall and climatic conditions. Seldom, however, does the productivity of these annual species exceed 1 percent of the standing shrub biomass. As the result, only from 200 to 600 kg/hectare of new plant foliage is potentially avatlable to undergo the processes of litter fall, decomposition and mineralization. Most of the fallen litter is moved about by wind action to lodge underneath sheltering shrub clumps where much of the initial breakdown is carried out by consumer organisms. Very Little is known about the impact of soil arthropods and microorganisms on plutonium in these areas at NTS, but deductions from well known effects of such organisms on inorganic nutrient elements during mineralization processes would indicate that they should help increase the biological availability (solubility) of plutonium with passing time. The relationships of microbial processes to the fate of transuranic elements in soil is discussed by Wildung et al. (1977, this volume). First glance at the data in Table 2 gives the impression of an insignificant amount of plutonium in vegetation of the fallout area. However, when one considers that this contaminated plant foliage goes through annual cycles of litter fall and decomposition and mineralization tn concentrated areas underneath shrubs, and that the plutonium will persist for tens of thousands of years, one must recognize the possibility of an increasing significance this cycling process wili have on increasing root uptake with passing time. The significance of this concentration process should be seen first with 24lam because of its greater biological availability (Romney et al. 1976b). Studies on the difference in edaphic properties underneath shrub clumps and in adjacent bare soil areas at NTS show that highly significant concentration processes have been at work increasing the levels of plant nutrients and organic matter in the root zone underneath shrubs (Romney et al. 1973a, 1973b}). Hanson (1975) recently discussed what appears ta be differential biological availability and concentration between 238py and 239py in soils, vegetation and animal components of the Trinity Site - ecosystem. He cited the data of Hakenson and Johnson (1973) showing that 238py/239py ratios increased from 0.05 (soils) to 0.10 (plants) to 1.0 (mammals), respectively. 293