-18- heavy tilling, produced inhalation exposures satisfactorily monitored by HV and thus, their PDE values were close to unity. The main limitation of the PD data and the derived enhancement values (POE) is that no information is obtained about the plutonium enhancement factors expressed by Equation [3]. It should be recalled that plutonium enhancement factors (EF) of the same magnitude as these PDEwere detected by HV (Table 4). (- ,: Pulmonary deposition is the penetration and retention of respirable size particles into the deep, alveolar regions of the lung and constitutes the major vector of inhalation dose. The efficiency of pulmonary deposition varies with particle size and is conventionally estimated by the ICRP Task Group on Lung Dynamics’ deposition model (9). For example, the observed change in size distribution of plutonium activity from the stabilized soil case to the disturbed <oil case (Fig. 1), increased the calculated pulmonary respirable-fraction (RESP) from 19% to 24%. Pulmonary deposition (attocuries per hour) using an inhalation rate (IN. RATE) and previously defined terms may be estimated as follows: DEPOSITION = IN. RATE X HV DUST X SOIL ACTIVITY X EF X POE X RESP (aCi h-]) (M3 h-]) (:g m-j) vg-l) (aCi . ‘ “ . [5] - Using Equation [5], data from Tables 2, 4, and 6, and the best estimates for the enhancement factors, inhalation rate, and respirable fraction extrapolated from our measurements, we calculated pulmonary deposition of 239+240Pu for four cases on Bikini (Table 7). Under the worst case condition (during tilling in a disturbed bare field), the pulmonary deposition was 1476 aCi h-l, and in the best case (light work in a coconut grove), the pulmonary deposition was 12 aCi h-l. Intermediate values were 139 aCi h-l for heavy work in a bare field, and 78 aCi h-l for light work in around houses. (In the latter case, we had to use an enhancement factor measured in the nearby field rather than in and around the houses. ) .. U... Walking along the road with one vehicular passage per hour produced an estimated 50% chance of additional pulmonary deposition of 1.58 aCi h-l (above background) but the soil plutonium activity on the road was notably lower (4.1 pCi g-l) compared to the field (15.3pCi g-l); see Table 7. To put these estimated pulmonary deposition values in perspective, we have estimated the lung and bone doses from inhalation of 23g+2q0Pu and 241Am using we assume that the ICRP lung model (8). The scenario we adopted is arbitrary; a person is in high activity conditions (1500 aCi/h pulmonary deposition) for 5 hours per day and in a situation averaging 80 aCi/h for the other 19 hours. The daily average is therefore 376 aCi/h pulmonary deposition. If it is assumed that people are exposed to this level everyday throughout their life, then the maximum bone dose rate is 5.5 mrem/y and the maximum lung dose rate is 2.4 mrem/y; the 30 year integral doses are 36 mrem and 70 mrem for bone and lung respectively. These doses are well below the Federal Guidelines for bone and lung of 500 mrem/y and 5 rem in 30’years. It is also quite possible that the selected scenario of 5 hours at the high activity deposition rate of the annual time spent (1500 aCi/hr) is on the average a very h~gh estimate under such conditions. . $ , . c;