Almentary tract absorpbon @ SA Tarauim er aL using various leaching solvents (in vitro) It should be also noted that the gastromtestinal absorption of radionuchdes mcorporated im terrestrial and aquatic foodstuffs (ingested durmg chromic mtakes) are not necessarily correlated with the properties of the same radionuchdes mmediately after deposition (ingested durmg acute mtakes) Selection of f, values In this report, the literature information on alimen- tary tract absorption (f,) for key fallout radionuchdes was carefully examined Althoughf, values assigned by ICRP for workers or members of the public are conve- mient to use m dose assessments for radiation protection purposes, radionuchde absorption in man may be profoundly modified by such factors as (a) the physical and chemical characteristics of fallout particles, (b) absorb- ability of the chemical compounds formed im the alrmentary tract, and (c) the transit ome of fallout material through the human digestive system (LeRoy et al 1966) 237 In this paper, we present specific f, values for deriving acute mtakes occurrmg immediately after fallout under different test conditions (coral vs contimental tests) and for various distances from ground zero (close-in vs distant locations, that 1s, for local fallout vs regional fallout), as well as for chronic intakes occurrmg months to years after fallout resultmg from mgestion of fallout nuclides mcorporated in foodstuffs or mgested by mmadvertent mtake of soil The local fallout area, which corresponds to close-in locations, 1s defmed here as the area whereall particles with diameters greater than 50 yin are deposited For Ingh-yield tests conducted im the Marshall Islands, the local fallout area roughly extended to about 300 km downwind from ground zero Regional or tropospheric fallout consists of particles with diameters smaller than 50 ym, which are more soluble than local fallout particles In the regional fallout area, the degree of fractionation (R/V) 1s assumed to be constant and equal to 05 In this paper, regional fallout 1s considered to extend to a distance of about 3,000 km The ICRP (1986) stated that where specific mformation for a given material 1s available, this should be used to (representing the size of the terntory of the Marshall circumstances the radioactive cloud, which circles the Earth for the first derive separate f, values for specific compounds or Thus, the approach used m the following sections was to evaluate the available mformation m order to arrive at the most realistic f, values for fallout radionuchdes from various nucleartests, with particular focus on local and regional fallout tests conducted at the Marshall Islands for use m mternal dose assessments (Simon et al 2010) Furthermore, f, values for Cs and Sr derived from urme bioassay data of the Rongelap residents following the Bravo test (presented next) were given considerable weight 1m the analysis presented here for these radionuchdes Our approachrepresents what may be considered a “best estrmate,” since the f, value(s) 1s selected to represent the average feature of a given nuclide metabolic behavior and not an exceptionally high or low value of the parameter During the process of evaluation and selection of f, values for the particular situation, adequate amounts of objective mformation were not always available and some judgment, based on our experience were applied In somecases,selected f, values presented im this document were similar to the values adopted by the ICRP In other cases, our proposed values were different after considermg the specifics of the nuclear tests, the nature and radiochemical properties of fallout particles, expected solubility, distance from ground zero, and other considerations Sometimes, more than one f, value was recommendedfor the different exposure circumstances This approach was taken when sufficient information was available to justify any changes from the ICRP recommendations Islands), although, technically, 1t covers the entire world as it 1s due to fallout occurring mm the tropospheric part of time m about 2 to 3 wk Because ofthe very small size of Jandarea at the detonation sites of the Pacific Proving Ground (Bikim and Enewetak), the relative fractions of coral soil and sea water mcorporated into fallout debris were likely to be stmilar for most ground and water (sub and surface) tests Therefore, no distinction was made to our selection for f, between land and water tests There is indirect and limited evidence from some ammal studies that fastmg conditions prior to ingestion could increase the absorption of certam radionuchdes through the alimentary tract Therefore, fasting f, values were proposed here for some nuchdes when such imformation was available m the Iiterature In terms of age-specific f, values, we suggest complymg with the recommendations given m recent ICRP documents (ICRP 1993, 1996) Uptake of fallout radionuclides ingested by the Marshallese Pooled urme samples from adults were collected from residents of Rongelap within three weeks after intake of fallout from the test Bravo and imthe several months followmg for radiochemical analysis to determine the degree of mternal contammation (Harris etal 2010) The earhest samples of urme m which “I and other nuchdes were measured were obtamed by Haris of Los Alamos Scientific Laboratory (Harris 1954, Harris et al 2010) We exammed these data sets, referred to here as the (1) Walter Reed data (Woodward et al 1959), (2)