Table 6. Size (pm) resuspendible size fractions. These fractions are shown in Table 6. The only significant change is noted in the Rocky Flats sample which showed 91% of the total activity in the resuspendible size fraction. Plutonium Index Derived From the Pulmonary Deposition and Resuspendible Fraction Soil Activity Factor © Lung Depositional Factor Modified Soil Activity Factor 0.40 0.12 0.03 0. 30 0.16 0.07 Resuspendible] Activity Factor Soil Plutonium Index 0.99 0.52 Nevada Test Site - Area 13 <2 2-5 5 - 125 0.75 1.33 2.19 4,27 0.53 Rocky Flats <2 2-5 5 - 125 2.33 3.50 1.44 0.40 0.12 0.03 0.93 0.42 0.04 7.27 1.39 0.91 1.26 1.00 1.18 Mound Laboratory <2 2-5 5 - 125 2.42 1.56 0.56 0.40 0.12 0.03 0.97 0.19 0.02 4.54 0.18 1.38 0.90 0.86 The choice of pretreatment to segregate the soil particles and to determine the plutonium size association should be given sertous consideration. The technique applied should not only consider the actual state of association but should be relatively simple without exposing the experimenter to undue hazard. Potential Application of the Soil Plutonium Index, The soil indices derived in Table 6 represent the relative potential hazard of the soil in the inhalation pathway. To show how to apply the values, one can consider the standard reported for the state of Colorado (Johnson ef al., 1976) of 2 dpm/g of soil. The value for Rocky Flats in Table 6 is 1.26. The value for NTS is 0.52, which means that the soil at NTS potentially provides less lung activity than the soil at Rocky Flats. Thus, to conform to the 2 dpm/g for Colorado, the soil in NTS could have 5 dpm/g (1.26/0.52 x 2 = 5). Similar calculations for Mound Laboratory and ORNL give 2 and 3 dpm/g, respectively. Healy (1974) suggested 500 dpm/g for bare soil without reference to particular site. If one uses the value as a general guide, the allowable concentration for NTS is 960 dpm/g (1/0.52 x 500 = 960). Oak Ridge National Laboratory <2 2-5 5 - 125 Although most of the activity in these samples were found in the resuspendible size ranges, it should be noted that the size and activity distributions were determined using water as a suspending agent (i.e., wet sieving and water sedimentation). The resuspension of particles using air forces and media may be different from the water media used here. As noted earlier, Little et at. (1973) reported only 3.7 and 11.2% of the particles to be less than 100 ym in two soils from Rocky Flats and 11 and 37% of the activity in these fractions, respectively. He used mechanical sieving without water, In the sample reported for Rocky Flats in this paper, 91% of the activity was in the less than 125 pm sizes. The segregation not only used water but the sample (as with all others) was ultrasonified for five minutes. Without ultrasonic treatment, 82% of the activity was in less than 125 wm size fractions of Rocky Flats (Table 4). Similarly for RF, ML, and ORNL, the values are 395, 425, and 615 dpm/g, respectively. 0.40 0.12 0.03 0.55 0.11 0,03 3.14 0.69 110 1.00 0.69 The soil plutonium index derived is not a soil activity standard. It is primarily aimed at evaluating the inhalation hazard of the contamination as it exists in the soil, The attraction of setting a soil level standard is the ease of obtaining samples and performing analyses. Any standard must consider the pathways to man and biota. Although the soil plutonium index considered the inhalation pathway, similar considerations must be given to factors involved in uptake by plants and eventually ingestion by man and biota. The intent of this derivation is to provide a basis for arriving at an assessment of the contamination in soil. It should be obvious that the data presented are limited; the final soil factors should consider data from many more samples, providing appropriate statistical significance to the soil factors. 111