exponentially as a the concentration factor may increase hat ee s consideration because of 1 deserve but scanty 1s tine reeevecof on cated. ladino clover (Trtfoliwn repens fe) grew (1970) al. et Romney tions. ropes greenhouse conditions and cropper under soil d aminate um-cont plutoni : (p resulting estimates of Cry = dpm/g ly over a period of 5 years, The were as follows: dry weight) per dpm/g (soil, dry weight) Year Data on the plant/soil ratio for other transuranium elements are very limited. Romney et al. (1975) measures 2*!Am concentrations of the vegetation from the areas at and near the Nevada Test Site. Grouped according to species and location, the mean plutonium/americium ratio in vegetation ranged from 2.0 to 28.3 with typical values being about 10. Similar groups of soil (Gilbert et al., 1975) ranged from 5.3 to 26 with typical values also being about 10. These analyses indicate that the long-term plant/sotl ratio for americium is not significantly different from plutonium. The data on the short-term plant/ soil ratio indicate significant differences which may be related to the solubility of the element. Price (1973b) measured the uptake of 237Np, 239py, 24lan, and 244¢m by tumbleweed and cheatgrass from various solutions applied to the soil. The americium uptake was about 2 to 30 times greater than plutonium, curium was about 2 to 40 times greater, and neptunium was about 100 to 1,000 times greater. Bennett (1976) summarized much of the short-term data and concluded that americium and curium uptakes were about 10 to 30 times greater than plutonium. 4.14 x 10-9 4.38 x 1079 7.10 x 1079 . 13.95 x 1079, the to an exponential function yields A least squares fit of these data following expression: c. , FV = 1.31 x 107? exp (0.452 t), Ete is the apparent growth wate coer where t is time in years and 0.452 ate . dl abou wou ld be expected to double in , fi.e., the data indicate that C_,, the concen tration factor wou . By extrapolation to 20 years, (808 eco reage nne pere for ations observ value within the range of field ont ed and et- a af. (1970) attribute the app misleading nonetheless. Romney being conducte was iment exper the time the root growth during ium contained in ical availability of the pluton vorES any change in the biolog the contaminated soil. Variation of Plant/Soil Ratio Data presented by Romney et qi, (1975) demonstrate that the mean concentrations of plutonium in soils and plants decreases with increasing distance from ground zero locations, while the vegetation/soil ratios within sampling strata show a tendency to increase. Tamura (1976) provides a graph of soil activity versus distance from ground zero and fits the data to a power curve of the form y = ax where y ts soil activity and x is distance from ground zero, We have no comparable curve for vegetation, but we assume it would be of the same form. Based on this assumption, the vegetation/soil ratio could be expressed as follows: ate eene att s observed under field conditions in fact, the plant/soil ratio /aotl a uptake. Rommey et al. 97 ant root by ined expla be to too high e mean inated areas at NTS. to 0.44 and were : [ro 0.004 ed samples ranged d from paire of pair nof groups nt ies samp 1 and plant which rane es soil contamination of each group ior vecly relared to the mean for 506 paire sa iP ratio mean ted weigh The From 5 ox 1075 to 0.12 uCi/g. shrubs Browne ay s in this study were desert was 0 096 + 0,004. The plant t of nucheat sare Yese resul a as nium pluto with ed areas which were contaminat nts ore ee Ratios obtained by growingpla 1964. . tests conducted from 1953 to 1 07" which indicates that n to -3 107° of order the on ere at NTS is likely es from contaminated areas sampl plant in Pu the of sane neent to be due to root uptake. and 187) ‘cor soil from Hanford (Sramson and Corley, Environmental monitoring data . a4 ae fees from o range the in ratios for Corley, 1974; Fix, 1975} indicate to 4 x 107° uCi/g. al., 1976) indicate ratios from Savannah River (McLendon et 638 Vy = aye -b Ys C. = ak -by *, (10) yvCs = (a,/ag)x(Ps-by) . ne ate If b_ 0. > b, the vegetation/soil ratio will increase with increasing distance f romground zero and decreasing soil concentration. A i x 1079 concentrations in the range of 2 The higher plant/soil ratios are In general, plant/soil ratios for ?39Pu which are based on plant and soil samples collected under field conditions range from 10° to 10-3, while ratios based on laboratory studies which preclude external contamination range from 10°3 to 1075, Considering the situation at NTS, we believe it is reasonable to assume that approximately 99 percent of the plutonium associated with the vegetation compartment is due to external contamination and that no more than 1 percent is due to root uptake. 1.91 x 10-9 2 3 5 usually found at lower soil concentrations. Cry 1 4 soil concentrations in the range of 1.3 x 1079 to 1.6 x 1077 uci/g of 239py and 2 x 107! to 4.6 x 10°8 uci/g of 238Pu, ar i chelation due to bacterial decay of soil may increase with time as a result of organic matter. 639