240 Health Physics tract absorption. It is unlikely, however, that the bound fraction of Te is significant enough to impactits absorption from coral particles. August 2010, Volume 99, Number 2 Table 5. Selected f, values for cesium and rubidium. Acute intakes Exposure conditions Cesium (Cs) Because of its relatively high fission yield and long half-life (~30 y), '°’Cs is one of the most abundant radionuclides in fallout debris. It is a highly fractionating Coral tests, all types Landtests, continental soil Direct soil ingestion Local fallout Regional fallout Chronic intakes All locations 0.40 0.40 0.80 0.80 0.80 0.80 — — 0.40 isotope in fallout due to its gaseous precursor '*’Xe and adsorbs onto particle surfaces to a large extent. It is readily mobile in the environment and tends to accumulate in biota. Cesium is a chemical analog of potassium, which is a major nutrient element. Absorbed Cs is distributed uniformly in the human body andits retention tends to increase with the intake of potassium (Leggett 1986). The absorption fraction of Cs from the alimentary tract to blood varies greatly with the physical and chemical forms, potassium ingestion rate, and animal species, among other factors. Human and animal data indicate that soluble salts (1.e., CsCl) are efficiently absorbed from the alimentary tract ICRP 1979; NCRP 2006). However, Cs can bind to certain clay minerals, where its environmental mobility may be significantly reduced. Lime wasfound to increase Csretention in soil and thus may reduce its solubility and bioavailability in the environment (NAS 1963). A sample of f, values for Cs from the literature is provided in the Appendix. Reported f, values for various ingested forms ranged from 0.2 to 1.0 in humans and animal species. While the ICRP (1979, 1989, 1996) adopted an f, value of 1.0 for both acute and chronic intakes for workers and the general public, the literature data indicate that the uptake of Cs may not always be complete. The wide range of f, values reported could be attributed to the wide range of the ingested Cs forms used in the various studies. The reported f, value of 0.9 for '’Cs from the ingestion of contaminated food items by a U.S. native (Hardyet al. 1965) is based on measurements of the urinary to fecal excretion ratio to estimate the uptake in a single individual, many years after the nuclear tests were carried out at the Marshall Islands and, therefore, uncertain. Selected f, values for cesium and rubidium. Our “best estimate” of f, values for Cs and Rb under various types of intake conditions are presented in Table 5. For acute intakes from local fallout, we chose an f, of 0.4 based on the value estimated for '°’Cs from the Marshall- ese urine bioassay data following exposure to local fallout from the Bravo test (Table 4). This estimate is also consistent with the f, value reported by LeRoyetal. (1966) on the absorption of Cs from ingested local fallout simulated particles in humans (Appendix). The same f; value (0.4) is chosen for direct intake when contaminated soil is inadvertently ingested by humans. For acute intakes from regional fallout and for chronic intakes, an f, value of 0.8 is selected based on the mid-range of literature values for Cs incorporated in various food items and the ingestion of simulated distant fallout particles (LeRoy et al. 1966). The above selected f, values reflect the relative absorption of Cs associated with different particle sizes and exposure conditions for the reasons discussed. The internationally adopted f, value for Rb is 1.0 for both occupational and environmental exposures (ICRP 1980, 1996; U.S. EPA 1988). Rb is very similar in its chemical and metabolic behavior to cesium. We, therefore, chose f, values for Rb equal to those for cesium as discussed above. Strontium (Sr) and barium (Ba) Several Sr isotopes are producedin high yield in the fission process. The short-lived *’Sr (53 d half-life) is a dominant component in fresh fallout material and the long-lived Sr (~28 y half-life) is abundant in aged fallout (Cohn et al. 1954). Both *’Sr and *Sr are fractionating “volatile” radionuclides in typical fallout. However, the term “volatile” is a characteristic of their noble gases precursors and not for strontium itself. Radiochemical analysis of urine samples from a group of Marshallese indicated that *’Sr alone contrib- uted 42% of the total beta activity at 45 d post-detonation following exposure to fallout from the Bravo test (Cohn et al. 1956). Several studies on plant and animal uptake concluded that more Sr was assimilated at distant locations than for local fallout (close-in from ground zero) due to particle size and solubility differences along the forward path of fallout (Maxwell et al. 1955). Pathways of intake of strontium by humans from fallout are through the direct ingestion of fallout parti- cles, ingestion of contaminated food and milk, and to a lesser extent, inhalation. Increased calcium intake has been shownto reduce strontium absorption and retention in man (Spenceret al. 1963). Fasting was also found to