plutonium uptake was about 3 orders of magnitude higher where the soil was spiked with plutonium nitrate solution prior to conducting the uptake experiments. Now, if the addition of the plutonium-nitrate solutions to non-radioactive soils resulted in 0.1 um plutonium-bearing particles in the soil, the surface areas of the particles so formed would be larger by 3 orders of magnitude. That is, if the diameter of the particle is reduced 1000 fold, from 100 um to 0.1 um, the surface area per gram would go up by a factor of 1000. From this consideration it is certain that the particle size of the transuranic present in soil will influence availability. In addition to particle size, the particle composition of the source material can be expected to have an influence on availability of the transuranic in question. Upon studying barley uptake of plutonium and americium of soil from Area 13 of the Nevada Test Site, Schulz et al. (1976b) found that americium was taken up and translocated about 8 times more readily than plutonium. Now, this is much less of a difference than the 100 to 1000 fold greater availability of americium, compared to plutonium, reported by the Plant Panel (1976). The analytical data on particles recovered from Area 13 indicate that the particles are primarily plutonium-uranium oxides. It would appear likely that availability of plutonium to planta will be related to the chemical characteristics of the plutonium-uranium particle. Americium 241 will be produced by decay of ?“!pu present in the particle and will therefore reside throughout these particles, To a large extent, then, it could be expected that the availability of americium to plants will therefore be governed by the chemical and physical characteristics of these plutonium-uranium oxide particles. It should be noted, however, in other recent work much lower americium/plutonium CR's than those reported by the Plant Panel (1976) have been reported by Schulz et al. (1976a). SOIL CHARACTERISTICS AND CHELATING AGENTS A number of investigators have studied the effect of synthetic chelating agents on plant uptake of transuranics. Wallace (1974) found that DTPA greatiy increased the uptake of *"!Am from soils under all conditions studied. Lipton and Goldin (1976) found that chelates caused increases in plant uptake of 23%py from sand cultures in the order of 103. Romney et al. (1970) found that plant uptake of 739bu from contaminated Nevada Test Site soil was enhanced by the chelating agent DTPA. In other experiments by Romney et al. (1976) chelating agents were generally effective in increasing plant uptake of either plutonium or americiun. On the basis of evidence cited, it is clearly established that synthetic chelates can enhance plant uptake of transuranics. This could well be important where chelating agents are used in nuclear fuel reprocessing and in agriculture, etc. However, the influence of natural chelates on transuranic uptake is not so clear. Studies on the effect of the role of natural soil humates in making metals more readily available to plants go 326 been established back to at least 1932, and their "carrier" effects have ion of organic for a long time. Soil humates are formed by decomposit of organic matter on matter by microorganisms. What might be the effect plant uptake of transuranics? 1974) showed that Work at Battelle Northwest Laboratories (Garland et al., in increased plant incubation of soil with carbon and hydrogen resulted it did not. uptake of plutonium in one soil and in the other soil, (Romney et al., 1970) At UCLA, a 5-year cropping experiment was carried out clover crops increased In this experiment, the concentration or CR of the the increased uptake o each year the experiment was continued. Now, was of plutonium by soil organic plutonium due to possible organic complexation tion in the conmatter, or was it simply due to increased root concentra tainers as the plants grew older, or neither? In another experiment at the form of alfalfa meal—-was UCLA (Romney _et al. 1976), organic matter--in The results from this experiment were added to contaminated NTS soil, had no statistically signifisomewhat erratic and the added organic matter In some cases the cant influence on root uptake of the radionuclides. to be reduced by the addiplant uptake of plutonium and americium appeared This is certainly a possiblity as “free or tion of organic matter. temporarily tied up in a “soluble” plutonium and americium could have been organic matter additions. large microorganism population generated by the In this same y, however. Such an event would be expected to be transitor the effect of added nitrogen series of experiments the investigators studied and again no clear-cut and sulfur on uptake of plutonium and americium effect was observed. properties such as nutrient Tt certainly is reasonable to expect some soil capacity, etc. to exert status, organic matter content, pH, cation exchange However, as just menan influence on the plant uptake of transuranics. UCLA did not show any significant tioned, the experimentation carried out at response to fertilizers or added organic matter. effect of soil pH, and in some A number of investigators have studied the in uptake from soils at lower cases there does not seem to be an increase pH's. Again, the work ig not conclusive. experiments have been carried out At Battelle Northwest Laboratories some may inhibit plant uptake of plutomatter organic soil that suggest which in o et _al., 1975). It is indeed possible that organic matter nium (Catald le. We could have a mechanism a soil could make transuranics less availab humate that is not available for where the chelating agent could be a soil be unavailable Transuranics bound by the humate would then root uptake. ratios It 19 also possible that lower concentration for plant uptake. e capacity of goil with higher could be due simply to the higher exchang organic content. 327