244 Health Physics Table 8. Selected f, values for uranium. Acute intakes Exposure conditions Coral tests, all types Landtests, continental soil Direct soil ingestion Local fallout Regional fallout Chronic intakes All locations 2x107% 2x 107 2x 107 2x 10°? 2x 107 2x 10°? — — 2x 10> August 2010, Volume 99, Number 2 metals are expected to occur as refractory oxides in fallout. Literature values for the alimentary tract absorption of these elements are summarized in the Appendix. Iron (Fe). Iron absorption from the alimentary tract is a function of several factors including: the chemical form ingested, age, gender, and the amount of reserve iron in the body. Due to the lack of fallout-relevant information for Fe, we chose an f, value of 0.1 for all ingesting U oxides (U.S. EPA 1988). For regional fallout and chronic intakes, the recent ICRP recommendation of f, = 2 X 10* seems appropriate andis representative of literature values for U in diet and drinking water. For direct soil ingestion, the lower f, value (2 X 10°) is selected, which reflects the expected low U solubility for this type of intake. For fasting conditions, the f, value is increased to 5 X 10 * corresponding with results from animalstudies. The rare earth elements (Ce, Y, La, Pr) The principal fallout elements in this group include isotopes of Ce, Y, La, and Pr. Most radionuclides of these elements are highly refractory and virtually insoluble in fallout. These elements have no essential function in biological systems and they exhibit low mobility and biological uptake through the food chain. As a group, the rare earths are very poorly absorbed from the alimentary tract. The ICRP (1980, 1981, 1996) adopted f, values of these elements are in the range of 10° to 10* based on limited literature data for various ingested forms (Appendix). Selected f, values for rare earth elements. The ICRP recommendations (1980, 1981) for f, for most of the rare earths applied to acute intakes by workers are based on very limited literature data, some using soluble chloride and nitrate forms of the elements. Due to the same limitations of the available information, most ICRP recommendations (1989, 1996) for chronic intakes ap- types of intakes as adopted by ICRP (1980, 1995). Cobalt (Co). The available data on the absorption of Co are variable and are affected by the mass and chemical form ingested (Appendix). Due to the lack of fallout-relevant data on Co absorption, the ICRP (1979) adopted f, value of 0.05 for acute intakes of the oxide and hydroxide forms are applied here for local fallout. For regional fallout and chronic intakes, an f, value of 0.10 is chosen equal to the ICRP (1993, 1996) adopted value for exposure of the public to environmental levels of Co. Zine (Zn). All ICRP reports since 1980 (1980, 1993, 1996) adopted an f, value of 0.50 for Zn for both acute and chronic intakes, although it may be an overestimation when incorporated in some foods (ICRP 1993). As discussed in Simonet al. (2010), Zn was an important contributor to chronic exposure from the ingestion of contaminated seafood. Due to the lack of fallout-relevant information, the mid-range of 0.35 for dietary Zn (Honstead and Brady 1967) wasselected ofall fallout exposure conditions. Zirconium (Zr). ”Zr is highly refractory and fairly insoluble in fallout debris, particularly when incorporated into large particles that deposit locally. It is expected to be present in the oxide form after detonation (Freiling 1961). The limited literature data presented in actinide elements. Dueto the lack of fallout-relevant data the Appendix are based on the alimentary tract absorption of soluble chemical forms of Zr in rats. No studies on the uptake of the oxide form could be found. For acute rare earths and some actinides, we chose f, values for pounds of Zr is 2 X 10*. For chronic intakes, ICRP plied to the general public are set similar to some of the and similarity of the physico-chemical properties of most intakes the adopted ICRP (1979) f, value for all com- these elements equal to those selected for Pu and other actinide elements, for all types of intakes (Table 7). recommendation (1989, 1996) increased f, to 1 X 10 * The heavy metals (Fe, Co, Zn, Zr, Ru) to the lack of fallout-relevant information, we select the dose among the heavy metals group are Fe, Co, Zn, Zr, and 1 X 10° for chronic intakes. The fallout radionuclides giving the most significant and Ru. Radionuclides *’Fe, °’Co, and ®Zn are presentin fallout from neutron activation of bomb construction material. Some Zn may also be due to activation of Zn in seawater being entrained into the fireball. Most heavy to allow for the possibility that Zr uptake might be greater for biologically incorporated forms in food. Due ICRP f, value of 2 X 10° for local and regional fallout Ruthenium (Ru). For Ru intake from local fallout, an f, value of about 1 < 10* was estimated from the Marshallese urine bioassay data (Table 4). However,this