of a purified form of a radionuclide in conjunction with metabolism trial results to predict tissue retention of another form of this radionuclide. In this case a comparison is made between the predicted liver and bone retention of plutonium-238 dioxide, calculated from its in vitro solubility and relationship to the tn vitro solubility and actual tissue retention of plutonium-238 citrate, and the actual tissue retention of plutonium-238 dioxide determined by a metabolism trial. The actual tissue retention data are from Stanley et al. (1975). The in vitro solubility during the duodenal phase was used to predict plutonium tissue retention since this phase is presently believed to be the most important aspect of plutonium absorption. The values for pH 4 and pH 5 were combined and averaged for both plutonium-238 citrate and plutonium-238 dioxide, Then, a ratio of the average solubtlity of plutonium-238 citrate to plutonium-238 dioxide was calculated (plutonium-238 citrate/plutonium-238 dioxide = 6,39). The predicted liver retention of plutonium-238 from plutonium-238 dioxide was calculated by dividing the actual retention of plutonium~238 from plutontum-238 citrate by the in vitro solubility ratio (3.5 x 1079%/ 6.39 = 5.5 x 107"2). The plutonium-238 citrate qnd pluconium-238 dioxide metabolism trials were not done in an tdentical manner. In the case of plutonium-238 citrate the cows were sacrificed 93 days following a single dose, while in the case of plutonium-238 dioxide the cows were sacrificed 73 days following the last multiple dose (Stanley et al., 1975). However, the predicted retention values of plutontum-238, from plutonium-238 dioxide, by liver and bone are in reasonable agreement with the actual retention values. This prediction procedure is based on the assumption that once the plutonium becomes soluble in ruminants, the absorption of soluble plutonium by the animal and subsequent deposition and retention by tissues will be similar from both forms of plutonium administered. Table 2 illustrates this. The portion of the dose administered which is actually soluble in the duodenum and therefore available for absorption, as calculated from tn vittro solubility, is referred to as the “effective dose." The percentages + ' oO cm as geez TABLE lL. °o eC 4 * wo o Ow -c 0 oO wo ” 38m eu 4o - 7° Se 32 Ln wn oo ” ma 4 a . 3 3H y~ a ur qa ow 5 cox - Oo por co a ) 3k i oS — x oo = x an * * ww a eo ok vary cr eo 23 on — » pee Ce es C- *K ~~ x ww a6 + on 30 ow wa ure ceo ai 3 ui uv _ a » > ad a c Qo a a) re) — — _ a 2 — o WY P 422 ™ ‘ °o C- ee * =2 eo » = “ Ee= Nd |é -] —- & a Exsls 2 — 3 |S a+/3 0 — — a oma **Stanley et al, (1975) An example is shown in Table 1 of the application of the tn vitro solubility oO o cs oo — in text The sharp rise in soluble plutonium observed for all forms following the addition of bile and enzymes and adjustment of the pH to 6 was found to be due to the presence of bile rather than to enzymes or change tn pH. * * wo vo ee oe #5 xplained When plutonium was administered as plutonium dioxide spheres having a count median diameter of 0.06 um, 5.2% became soluble shortly after administration, 1.5% was soluble following the artificial rumen incubation period, 2.3% following the abomasal pertod, and 3.5% and 3.9% when held at pH 4 and 5, respectively, in the duodenal phase. This increased to 7.4% following the addition of bile and enzymes and the adjustment of the pH to 6. ORAL DOSE OF PLUTONIUM-238 DIOXIDE PREDICTED BOVINE TISSUE RETENTION COMPARED TO ACTUAL RETENTION OF AN 13.1% following the abomasal period, and 22.5% and 24.8% when held at pH 4 and § respectively, in the duodenal phase. This increased to 59.6% following the addition of bile and enzymes and adjustment of the pH to 64.