RELATIVE RADIOLOGICAL HAZARDS IN CONTAMINATED ENVIRONMENTS TABLE 6 CALCULATED TOTAL BODY AND BONE DOSES FROM INGESTION OF PLUTONIUM ASSOCIATED WITH PLANTS GROWING IN CONTAMINATED ENVERONMENTS Observations from dry, windy environments suggest that surface contamination of plant leaves accounts for much of the Pu of vegetation from Pu-contaminated areas (Romney et al., 1976; Hakonson and Bostick, 1976; Little, 1976). Likewise, deposition of airborne Pu released from nuclear facilities can be a major mechanism for Pu entry into vegetation (McLendon et al., 1976). Frequent ly under such conditions, the Pu content of vegetation is considered an artifact Mode of Contamination cant. Deposition of of surface contamination and Pu uptake by the root pathway is deemed insignifi- However, both root and aerial pathways can control entry of Pu into vegetation according to the results of Tables 2 and 4. The aerial pathway controls Pu levels of plants when foliage is exposed to airborne Pu; whereas the root pathway is important over long time intervals after cessation of emissions to the atmosphere and after Pu is incorporated in the soil matrix. Vegetation contaminated by airborne Pu exhibits an incipfent concentration 1 to 3 orders of magnitude greater than observed from assimilation by the root pathway. For a typical Pu concentration of 0.3 pCi g7! in vegetables, total body and bone doses were calculated assuming that an individual obtains a dietary intake of 250 g day ' from the contaminated environment, and that assimilation of Pu from the GI tract is 3 x 1073% (ICRP, 1959). From chronic ingestion of the surface contaminated vegetation, the SQ0-year dose commitment would be 20 and 0.5 mrem for bone and total body (Table 6). When Pu is incorpotated into vegetation by the root pathway, calculated doses are substantially less, simply because of the lower Pu content of ingested material. Although radiologic impact on humans depends on source characteristics and mode of exposure, potential and comparative hazards can be evaluated for contaminated environments represented by the Savannah River and Oak Ridge examples. It should be recalled that Pu in air at the Savannah River site is approximately 2 orders of magnitude greater than at Oak Ridge, while Pu of the floodplain soil is about 2 orders of magnitude greater at the Oak Ridge site than at Savannah River (Table 1). Furthermore, dose from ingestion of foods containing surface contaminated Pu can be reduced by normal food processing procedures. For example, by threshing wheat grain from contaminated chaff, the Pu content was lowered by 98%. Accordingly, the 20 and 0.5 mrem bone and whole body doses would be reduced to 0.4 and 0.01 mrem respectively. Although the reference environments at Savannah River and Oak Ridge presently are excluded from public access, the calculated doses would not necessarily prohibit human occupancy of both areas if ingestion is the critical pathway. The 50-yéar dose commitments are less than the 100 mrem yr~! average that individuals receive from natural sources of radiation (NAS/NRC, 1972), and the doses do not exceed the 25 mrem Limit proposed for a uranium fuel cycle (USEPA, 1975). Of course, population doses would also depend on exposures from other components of the fuel cycle. On the assumption that people lived in an environment where measurable airborne Pu deposited on vegetation, the resultant hazard from ingestion would be less than direct human exposure by inhalation, particularly if surface contamination of edible foods can be removed by routine Airborne Pu on Plants Uptake of Pu by Plants Pu in Soil and Vegetables (pCi _g-!) Soil Vegetable Dose™ (mrem yr) Total Body Bone 0.1-1.0 3 49 19.9 25-150 06° wl 4.2 Aanose calculations based on ingestion of 250 day —, 365 day yt}; conversion factors of 7.87 x 107! and 1.91 x 10°2 give 2a, dose (rem pCi~! ingested) for bone and total body respectively; San, dose conversion factors were 6.85 x 10°! and 1.72 x 1072 for bone and total body respectively (Killough and McKay, 1976). bIgotopic composition is 60% 738Ppy, 40% 239Ppu. values given in Tables 2 and 3, Concentration is an average of “tgotopic composition is 15% 238pu, 95% 239pu. Concentration ig average of values in Table 4.