Acute and chronic intakes of fallout radionuclides @ S. L. SIMoNn ET AL. as a basis to estimate the chronic intakesfor the residents ofall other atolls, with the exception of Utrik. The detection of substantial levels of °Zn in the bodies of the Rongelap and Utrik evacuees poses a dosimetric estimation problem since normalized deposition factors for Zn were not reported by Hicks (1984). We assumedthat ©Zn was produced by neutron activation of weapons materials and of entrained sea water, admittedly in small amounts, and was, therefore, present in local and regional fallout. The °Zn was then apparently absorbed by phyto- plankton and zooplankton and further concentrated by fish and other aquatic animals feeding on plankton in ocean and lagoon areas close to each atoll (Donaldson 1963*; Donaldson et al. 1997). The fact that most of the activity of plankton and fish in the mid-1950’s was due to activation products (Fe, ’Co, “Co, Zn) seems to indicate the avidity of plankton and seafood for those elements (Welander 1958). On the other hand, “Sr and '°’Cs are mainly found in terrestrial foodstuffs contaminated as a result of root uptake. Because most of the atolls were not evacuated and their populations not monitored, it 1s essential to estimate the variation of the dietary intake rate with time after the test. We assumedthat the temporal variation of the dietary 165 results of the bioassay measurements conducted in 1957 among the Rongelap Island community were not only due to Bravo, but also, to some extent, to fallout at Rongelap from all other tests conducted in 1948, 1951, 1952, 1954, and 1956, in addition, to a small degree, to fallout at Kwajalein and Majuro from the tests conducted before or during the periods of residence of the evacuees at those atolls (Table 1, Simon et al. 2010). The envi- ronmental inventories of the long-lived radionuclides on Rongelap Atoll in 1957, the year when the whole-body and bioassay measurements were made, include contributions from all tests that resulted in measurable fallout on the atoll before that year. Taking ®Zn as an example, we estimated that the inventory of that radionuclide at Rongelap in 1957 was mainly due to Bravo (73%), with only minor contributions from the other 1954 tests (15%) and from the 1956 tests (12%). Therefore, the °Zn whole- body contents measured in 1957 could also have been obtained if Bravo hadledto a “theoretical” '"’Cs deposition density at Rongelap 1.4 times greater than what was estimated (100 kBq m7; Table 7 of Beck et al. 2010) and if no other test had contributed to the °Zn whole-body contents measured in 1957 among the Rongelap Island intake shown in egn (5) also holds for the initial period of community. In our calculations, we assumed that for each was not inhabited and, therefore, no measurements were made. Eqn (5) can therefore be modified as: was heavily fractionated at Rongelap, the relationship be- time of approximately three years, during which Rongelap q(Z, Bravo, Rongelap, t) = g(Z, Bravo, Rongelap, 0) x eh AZ) + KZ, Rongelap) |< 7} (6) test, the “initial” intake rate of °Zn was proportionalto the deposition density of '°’Cs. Taking into account that ®Zn tween the initial intake rate of “Zn and the theoretical deposition density of '*’Cs can be expressed as: q(®Zn, Bravo, Rongelap, 0) = a(°Zn) Using eqn (6), the radionuclide intakerates at the time of the x K(°Zn, Bravo, Rongelap) Bravo test, g(Z, Bravo, Rongelap, 0), are estimated to be 3,900 Bq d| for *Fe, 1,600 Bg d' for Co, 164,000 Bq d' for °Zn, 2.8 Bg d' for *’Sr, and 540 Bq d! for '°’Cs. Those “‘initial” intake rates are theoretical because it would have taken some time for the chronic intake pathways to becomeestablished since they involve contamination of the vegetation by root uptake and the contamination of seafood, and the populations of Rongelap and Utrik were evacuated within two days after the Bravo test before any significant chronic intake could occur. As will be evidenced later, it is essential to establish a relationship between the “initial” intake rates (which are only available for Bravo at Rongelap and Utrik) and the '"’Cs deposition densities (which are available forall tests and all atolls). The '*’Cs deposition density for Bravo at Rongelap, estimated as 100 kBq m*in Becket al. (2010), cannot be used for that purpose because the X Depinel'*’Cs°Zn), Bravo, Rongelap], (7) where g(°Zn, Bravo, Rongelap, 0) = 164,000 Bq d! a(°Zn) = the ratio of the initial dietary intake of Zn, in Bq d', andofthe deposition density of SCs, in kBq m’, for a reference level of fractionation, R/V, of 0.5; K(°Zn, Bravo, Rongelap) = 4.07 is the degree of fractionation of ®Zn relative to '’Cs for Bravo at Rongelap;** and * Donaldson LR. Evaluation of radioactivity in the marine environment of the Pacific Proving Ground. Conference on Nuclear Detonations and Marine Radioactivity, Kjeller, Norway, 16—21 September 1963. * This means that the Zn to '°’Cs activity ratio at the time of fallout from Bravo was 4.07 times greater at Rongelap than at distant atolls.