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2 Background U ranium is a radioactive element that occurs naturally in soil, rocks, sur- face and underground water, air, plants, and animals (ATSDR, 1999b). It is found at an average concentration of 0.0003% in Earthâs crust and at 3.0 Âµg/L in seawater (Bleise et al., 2003). It also occurs in trace amounts in many foods and in drinking water as a result of its presence in the environment. Uranium is the heaviest naturally occurring element. Its density is 19 times that of water and 1.65 times that of lead (Kirk, 1981; ATSDR, 1999b). The chemi- cal symbol for uranium is U, and its Chemical Abstract Services Registry Number is 7440-61-1. It exists in nature as three isotopes, or forms. Isotopes have the same number of protons in the nucleus, and therefore are the same element, but a different number of neutrons. All three naturally occurring uranium isotopes are radioactive. The most abundant is 238U (99.2745% abundance), and the second- most abundant is 235U (0.7200%) (Lide, 1999). The natural abundance of 234U is only 0.0055%. Uranium is not found in its elemental state but combined with other elements in about 150 known minerals (McDiarmid and Squibb, 2001). The primary civilian use of uranium is as fuel for nuclear power plants (Cantaluppi and Degetto, 2000; Betti, 2003). Minute amounts are also used in the production of ceramic glazes, light bulbs, and photographic chemicals (ATSDR, 1999b). A personâs daily intake of uranium is estimated to be 1-2 Âµg in food and 1.5 Âµg in each liter of water consumed (ATSDR, 1999b). The International Commission on Radiological Protection has reported that the average uranium content of the human body is 90 Âµg, including 69 Âµg in the skeleton and 7 Âµg in the kidneys (ICRP, 1975). A range of total body uranium of 2-62 Âµg has been noted in human postmortem studies (Wrenn et al., 1985). 13
14 updated literature review of depleted uranium Depleted uranium is a byproduct of the uranium enrichment process used to generate fuel for nuclear power plants. Depleted uranium is so named because it has been partially depleted of radioisotopes, the abundance of both 235U and 234U is lower than natural (it may also contain 236U). The ratio of 238U to 235U in natural uranium is 137.88; in depleted uranium, it is 314.95 (Roth et al., 2003). The chemical properties of depleted uranium are the same as those of the enriched and natural forms (ATSDR, 1999b). Uses of Depleted Uranium The need for enriched nuclear fuel has been present for decades, so depleted uranium, a byproduct of the enrichment process, is abundant and inexpensive. The chemical and physical properties of depleted uranium make it ideal for sev- eral military and commercial uses. It is 67% denser than lead (with a density of 18.9 g/cm3), has a high melting point (2070Â°F, 1132Â°C), is highly pyrophoric, has a tensile strength comparable with that of most steels, and is chemically highly reactive (Kirk, 1981). It is used in commercial products, such as radiation shielding in medical equipment, aircraft counterweights, rotors, flywheels, ship ballasts, and gyroscopes (Cantaluppi and Degetto, 2000; Betti, 2003; Sztajnkrycer and Otten, 2004). The US Army began researching the use of depleted uranium for military applications in the early 1970s (Bleise et al., 2003), and depleted uranium is now used both offensively and defensively. In the Gulf War, heavy-armor tanks had a layer of depleted-uranium armor to increase protection, and depleted uranium was used in kinetic-energy cartridges and ammunition rounds by the Army (105- and 120-mm tank ammunition), Air Force (armor-piercing munitions for the Gatling gun mounted on the A-10 aircraft), Marine Corps (Harrier aircraft and tank munitions), and Navy (rounds for the Phalanx Close-in Weapon System) (DOD, 2000). The Army used an estimated 9,500 depleted-uranium tank rounds during the Gulf War, many in training and practice (DOD, 2000). The US military has continued to use depleted-uranium weapons. Ammuni- tion containing depleted uranium was used in Bosnia-Herzegovina in 1994-1995 and in Kosovo in 1999 (Cantaluppi and Degetto, 2000; Bleise et al., 2003). According to North Atlantic Treaty Organization records, about 10,800 depleted- uranium rounds were fired in Bosnia-Herzegovina and about 30,000 in Kosovo (Bleise et al., 2003). Depleted-uraniumâcontaining weapons have been used in Operation Iraqi Freedom (OIF), which began in 2003 (Burkart et al., 2005; NRC, 2008). Exposure of Military Personnel to Depleted Uranium The Gulf War marked the first time that depleted-uranium munitions and armor were extensively used by the US military (DOD, 2000). The Iraqi forces
BACKGROUND 15 did not have such munitions. US military personnel were exposed to depleted uranium as a result of friendly-fire incidents, cleanup and salvage operations, and proximity to burning depleted-uraniumâcontaining tanks and ammunition (DOD, 2000). Depleted-uraniumâcontaining projectiles struck 21 occupied Army combat vehicles (15 Bradley fighting vehicles and 6 Abrams tanks) (AEPI, 1995). In addition, US forces used depleted-uranium rounds to destroy three unoccupied Abrams tanks to prevent them from being captured by the enemy, and five Abrams tanks became contaminated when depleted-uranium rounds were involved in onboard fires (AEPI, 1995). After the war, assess- ment teams and cleanup and recovery personnel may have had contact with depleted-uraniumâcontaminated vehicles or depleted-uranium munitions. In July 1991, a large fire occurred in Camp Doha near Kuwait City. This site housed a number of combat-ready vehicles, and the series of blasts and fires damaged or destroyed vehicles and munitions, including Abrams tanks and depleted-uranium munitions. Troops at the scene and those involved in cleanup efforts may have been exposed to depleted-uranium residue. Other troops may have been exposed through contact with vehicles or inhalation of depleted- uraniumâcontaining dust. In estimating the number of US personnel exposed to depleted uranium dur- ing the Gulf War and the extent of their exposure, the Department of Defense Office of the Special Assistant for Gulf War Illnesses categorized potential depleted-uranium exposure scenarios in three levels (DOD, 2000). The levels are described briefly below and in more depth in Chapter 5. Level I, the highest exposure level, occurred in or near combat vehicles when they were struck by depleted-uranium rounds or when soldiers entered vehicles soon after impact. An estimated 134-164 people may have experi- enced level I exposure through wounds caused by depleted-uranium fragments, inhalation of airborne depleted-uranium particles, or ingestion of or wound contamination by depleted-uranium residues. Some 74 Gulf War veterans, including those with internal depleted-uranium fragments, are participating in the Depleted Uranium Follow-up Program, a medical surveillance followup study that began in 1993 at the Baltimore Veterans Affairs Medical Center (McDiarmid et al., 2007). Level II, the intermediate exposure level, occurred when soldiers and civilian employees worked on depleted-uraniumâcontaminated vehicles or were involved in cleanup efforts from the Camp Doha fire. More than 700 people may have had level II exposure through inhalation of dust containing depleted-uranium particles and residue or through ingestion by hand-to-mouth contact or contamination of clothing. Level III, the lowest level of exposure, occurred when troops were down- wind of burning depleted-uranium ammunition or vehicles or of the Camp Doha fire or when personnel entered depleted-uraniumâcontaminated Iraqi tanks. These level III exposures could have occurred though inhalation or ingestion. Hundreds
16 updated literature review of depleted uranium of people are thought to have experienced potential level III exposure, but there is little to substantiate the estimates. The US Army conducted a study to model depleted-uranium aerosol expo- sures; the results of this study are presented in the âCapstone reportâ (USACHPPM, 2004). The exposure modeling characterized depleted-uranium aerosols as aero- sols that would be generated by perforation of an Abrams tank or a Bradley fight- ing vehicle. Models were developed for level I, II, and III exposures. In addition, an evaluation of health outcomes of exposure to the depleted-uranium aerosols was conducted for level I inhalation exposures. Depending on the exposure scenario, the median intakes of depleted uranium range from 10 mg for a 1-min exposure in a ventilated Abrams tank with depleted-uranium armor to 710 mg for a 5-min exposure in an unventilated Abrams tank with depleted-uranium armor. The Capstone report is reviewed in detail in the National Research Council report Review of Toxicologic and Radiologic Risks to Military Personnel from Exposure to Depleted Uranium During and After Combat (NRC, 2008). The Royal Society, which is the United Kingdomâs equivalent of a national academy of science, convened an independent expert working group to review the evidence on health effects of exposure to depleted uranium. The Royal Societyâs âcentral estimateâ (representative of the average person in the group of people exposed in that situation) for a level I inhalation exposure was 250 mg (Royal Society, 2001). The central estimates for level II and III exposures were 1-10 and 0.05-0.8 mg, respectively. In a report prepared for the US Department of Energy, Marshall (2005) also estimated average exposures. The estimate for ânominalâ level I inhalation expo- sure (representative of the average person in the group under study) was 250 mg, for level II exposure 40 mg, and for level III exposure 6 mg. Military personnel potentially were exposed to depleted uranium during the Bosnia-Herzegovina and Kosovo wars (WHO, 2001). Aircraft-fired depleted- uranium munitions were used by the United States during those wars. Exposure would occur from handling munitions, from being protected by depleted- u Â raniumâarmored tanks, or after depleted-uranium use on the battlefield (Bolton and Foster, 2002). Urinary analyses have not found increased concentrations of uranium in several populations working in areas that might have been con- taminated with depleted uranium: US National Guard troops deployed to Bosnia (May et al., 2004), German peacekeeping personnel serving in Kosovo (Oeh et al., 2007), and International Red Cross and Red Crescent Movement workers in Kosovo (Meddings and Haldimann, 2002). As of September 30, 2007, 2,447 US military personnel who served in OIF had undergone a depleted-uranium bioassay (DOD, 2007). Ten of those personnel had confirmed urinary depleted uranium, and all ten had embedded fragments of depleted uranium or fragment injuries. Depleted-uranium concentrations were not found to be increased in 341 UK military personnel who were deployed to Iraq in 2003 (Bland et al., 2007).
BACKGROUND 17 Radiologic and Chemical Effects of Exposure to Depleted Uranium In considering the potential toxicity of depleted uranium, it is important to distinguish between radiologic and chemical toxic mechanisms. It is also impor- tant to note that the radiologic and chemical properties of uranium could act synergistically to cause health outcomes. Radiologic Considerations As discussed above, depleted uranium and naturally occurring uranium have different abundances of the three isotopes. The most notable difference is a decrease in the abundance of 235U from 0.72% to 0.20% in depleted uranium, which reduces overall radioactivity by about 40% (Harley et al., 1999). The radioactivity of a source is based on the number of radioactive atoms undergoing radioactive decay in a given period. Radioactive decay is the attempt of any atom to rearrange or transform the constituent protons and neutrons of its nucleus in such a way that the atom ends up having lower inherent energy. Radioactive decay occurs spontaneously because energy is given off, rather than consumed, in the process. The result of radioactive decay is an atom (the daugh- ter) with less inherent energy than that which preceded it (the radioactive parent atom). Uranium isotopes decay to other radioactive elements that eventually decay to stable isotopes of lead (ATSDR, 1999b). The term radioactivity describes how many radioactive atoms are undergoing radioactive decay every second. It does not reflect what type of radiation is being emitted or the energy of that radiation. The traditional unit of radioactivity is the curie (Ci); 1 Ci equals 3.7 Ã l010 disintegrations per second (dps). A disintegration occurs when an atom undergoes radioactive decay. The International System unit of radioactivity is the Becquerel (Bq); 1 Bq is equivalent to l dps. Common units of measurement are summarized in Box 2-1. Radioactive half-life is the amount of time it takes for radioactivity to decrease by half, that is, for half the radioactive atoms to undergo radioactive decay. The half-life of 238U is 4.47 Ã 109 years, and the half-life of 235U 7.04 Ã 108 years (Bleise et al., 2003); radioactivity never reaches zero but only keeps fractionally reducing. The isotopes of uranium emit alpha particles. Alpha particles are positively charged ions composed of two protons and two neutrons. Because of their size and charge, alpha particles lose their kinetic energy quickly and have little penetrating power. The range of an alpha particle is about 4 cm in air and con- siderably less (25-80 Î¼m) in tissue (ATSDR, 1999a). As a result, uranium is a radiation hazard mainly when uranium atoms are in the body. As noted above, uranium isotopes decay to other radioactive elements that eventually decay to stable isotopes of lead. In the decay process, beta particles and gamma rays are
18 updated literature review of depleted uranium BOX 2-1 Units of Measurement Specific Activity The curie (Ci) is the traditional unit of radioactivity defined as the quantity of any radioactive nuclide in which the number of disintegrations per second is 3.700 Ã 1010. It is a concentration defined as the ratio of the amount of radioactivity divided by the mass or volume of radioactive substance. The International System unit of specific activity is the becquerel (Bq). Absorbed Dose The gray (Gy), formerly the rad, is the unit that describes the magnitude of ab- sorbed radiation in terms of energy deposited in tissue. However, the amount of energy deposited in tissue does not account for differences in the biologic effects of different radiation types. Dose Equivalent The rem (roentgen-equivalent-man) is the traditional unit of measure that in- corporates the relative biologic damage caused by different radiation types and deposition mechanisms. The International System unit for the biologically effective dose, dose equivalent, is the sievert (Sv). Biologically Specific Activity Absorbed Dose Effective Dose Units curie (Ci) gray (Gy) rem becquerel (Bq) rad (old standard sievert (Sv) unit) Conversion 1 Bq = 1 transformaÂ 1 Gy = 100 rad 1 mSv = 0.001 Sv tion or disintegration 1 Sv = 100 rem per second = 2.7 Ã 10â11 Ci SOURCE: Adapted from ATSDR, 1999a,b. emitted. Beta particles are high-energy electrons; the path length of a beta particle is up to 15 m in air and up to 1 cm in solids (ATSDR, 1999b). Gamma rays are electromagnetic ionizing radiation and constitute a radiation hazard even when present outside the body because they are highly penetrating. Isotopes of uranium all have the same chemical properties because they all have the same number of protons, 92. However, variation in the number of neutrons gives the isotopes different radiologic properties. The radioactivity of isotopes can be compared by using specific activity, a measure of the number of nuclear transformations (disintegrations) per second per unit mass (see Box 2-1). The most abundant naturally occurring uranium isotope, 238U, has the low- est specific activity (1.24 Ã 104 Bq/g) (AEPI, 1995). The high specific activity of
BACKGROUND 19 234U (2.31 Ã 108 Bq/g) contributes about half the radioactivity of natural uranium, even though by weight its percentage is extremely small. Estimates of radiation risk depend on the dose received by a person. Radia- tion dose is the amount of energy deposited per unit mass. The traditional unit of absorbed dose is the rad, which is defined as the absorption of 100 ergs/g. The International System unit of absorbed dose is the gray (Gy); 1 Gy equals 100 rad (see Box 2-1). To account for cellular and subcellular differences in energy deposition pattern by alpha particles, beta particles, and gamma rays, which affect biologic consequences, doses are often expressed as dose equivalents. The dose equivalent is the absorbed dose multiplied by a radiation weighting factor, which describes the ability of a given kind of radiation to produce a particular biologic effect relative to X-rays. Radiation weighting factors range from 1 (for X-rays) to over 20 (for some alpha particles). The traditional unit of dose equivalent is the rem. The International System unit is the sievert (Sv); l Sv equals 100 rem. In relating dose of ionizing radiation to risk, an extension of the dose equivalent is used to express dose as what would have been received if the whole body had been uniformly irradiated. The âeffective dose equivalentâ is the sum of dose equivalents to different organs or body tissues weighted in such a fashion as to provide a value proportional to radiation-induced somatic and genetic risk even when the body is not uniformly irradiated. There are a number of radiologic-protection regulations and guidelines. The US Nuclear Regulatory Commissionâs regulations for occupational dose to indi- vidual adults state an annual limit of the total effective dose equivalent of 5 rem/ year (50 mSv/year) (10 CFR 20.1201). The commissionâs regulations require that the total effective dose equivalent to individual members of the general public not exceed 0.1 rem (1 mSv) in a year exclusive of background radiation (10 CFR 20.1301). The background dose in the United States is about 0.36 rem/year. Chemical Toxicity As noted above, the enriched, natural, and depleted forms of uranium have identical chemical properties and therefore the same chemical toxicity. The chem- ical toxicity of a uranium compound depends on the nature of the compound, its solubility, and its route of exposure (inhalation, ingestion, or skin absorption). Chemical toxicity, characterized predominantly by renal dysfunction as a conse- quence of exposure to soluble uranium, and lung injury potentially caused by the ionizing radiation from uranium-decay isotopes are the best-characterized con- sequences of exposure to uranium compounds (Eidson, 1994). Relatively water- soluble compounds (uranyl nitrate hexahydrate, uranium hexafluoride, uranyl fluoride, uranium tetrachloride, and uranium pentachloride) are the most potent renal toxicants (ATSDR, 1999b). Sodium diuranate and ammonium diuranate, which are less water-soluble, are of moderate to low renal toxicity; and uranium tetrafluoride, uranium trioxide, uranium dioxide, uranium peroxide, and triura-
20 updated literature review of depleted uranium nium octaoxide, which are insoluble, have little potential to cause renal toxicity but could cause pulmonary toxicity if exposure is by inhalation (ATSDR, 1999b). Insoluble uranium compounds can remain in the pulmonary tissues, especially the pulmonary lymph nodes, for a long time and constitute a localized radiologic haz- ard. As a general rule, uranium in the intestinal tract is less readily absorbed than uranium from the respiratory tract and results in lower doses per unit intake. Dose-Response Modeling and Risk Assessment The committee was charged with evaluating the scientific literature on the effects of depleted uranium. As detailed in this report, the evaluation focused on direct experimental and observational evidence in animals and human popula- tions. The committee acknowledges that there is a broader literature on risk assessment of radiologic and chemical toxicants, including uranium. In general, population-based quantitative risk assessment is used in public health to inform intervention strategies, for example, in setting policy and regula- tions. Such risk assessment is not intended to estimate risk to any given individual in a population or to determine causality. Rather, it is intended to characterize population-attributable risk broadly to support population-level, not individual- level, decisions. The current approach to quantitative risk assessment, developed by the National Research Council, consists of four steps: hazard identification, expo- sure assessment, dose-response modeling, and risk characterization (NRC, 1983, 1994). Of the four steps, the committee emphasized two as most relevant to its charge: hazard identification (that is, Does evidence of toxicity of depleted uranium exist at any level of exposure?) and exposure assessment (that is, What actual levels of exposure were experienced by military personnel serving in the Gulf War?). The committee considered mechanisms of both radiologic and chem- ical toxicity and a variety of cancer and noncancer outcomes or end points. Elements of the risk assessment approachânotably dose-response modelingâ vary among the cancer and noncancer end points. Cancer and genetic changes are modeled as a mathematical function in which risk increases with increasing exposure or dose. Although considerable controversy remains about the shape of the dose-response curve, especially at low doses, a linear no-threshold model has traditionally been used. This approach has been used for ionizing radiation as a carcinogen; for example, the National Research Council report Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2 endorses the use of such a model for radiogenic-cancer risk estimation (NRC, 2006). A linear no-threshold dose-response model implies that cancer risk increases proportionally with increasing dose and that no âsafeâ dose exists (that is, every exposure or dose conveys some riskâlow doses have low risk and higher doses proportionally higher risk). Such a model continues to be used for population- based quantitative risk assessment in public health, in spite of substantial uncer-
BACKGROUND 21 tainties in its validity, because it is the most conservative or protective approach (that is, it yields the highest estimated risk for a given exposure or dose). In the context of the committeeâs work, a key element of the examination of the possibility of adverse health effects of depleted uranium was the presence (or absence) of direct scientific evidence relevant to Gulf War veterans that could support the adoption of a no-threshold model for depleted-uranium cancer risk. The validity of the linear no-threshold model, especially for radiogenic cancer, is of greatest uncertainty at doses below 25 rem, the very range of doses to Gulf War veterans considered here. Thus, although a no-threshold model is used to estimate risk to a population, especially at higher doses, and would imply risk related to any level of depleted-uranium exposure, the committee chose to focus on direct evidence rather than a conservative, theory-driven approach in making its final determinations even while it remained mindful of the issues described here. References AEPI (Army Environmental Policy Institute). 1995. Health and environmental consequences of depleted uranium use in the U.S. Army. Arlington, VA: U.S. Army Environmental Policy Institute. ATSDR (Agency for Toxic Substances and Disease Registry). 1999a. Toxicological profile for ionizing radiation. Atlanta, GA: Public Health Service, Centers for Disease Control and Prevention. âââ. 1999b. Toxicological profile for uranium. Atlanta, GA: Public Health Service, Centers for Disease Control and Prevention. Betti, M. 2003. Civil use of depleted uranium. Journal of Environmental Radioactivity 64(2-3):113-119. Bland, D. J., R. J. Rona, D. Coggon, J. Anderson, N. Greenberg, L. Hull, and S. Wessely. 2007. Uri- nary isotopic analysis in the UK armed forces: No evidence of depleted uranium absorption in combat and other personnel in Iraq. Occupational and Environmental Medicine 64:834-838. Bleise, A., P. R. Danesi, and W. Burkart. 2003. Properties, use and health effects of depleted uranium (DU): A general overview. Journal of Environmental Radioactivity 64(2-3):93-112. Bolton, J. P. G., and C. R. M. Foster. 2002. Battlefield use of depleted uranium and the health of veterans. Journal of the Royal Army Medical Corps 148(3):221-229. Burkart, W., P. R. Danesi, and J. H. Hendry. 2005. Properties, use and health effects of depleted uranium. International Congress Series 1276:133-136. Cantaluppi, C., and S. Degetto. 2000. Civilian and military uses of depleted uranium: Environmental and health problems. Annali di Chimica 90(11-12):665-676. DOD (Department of Defense). 2000. Environmental exposure report: Depleted uranium in the Gulf (II). Washington, DC: Department of Defense. âââ. 2007. Operation Iraqi Freedom depleted uranium bioassay resultsâsixth semiannual report and request for data submission. Washington, DC: Department of Defense. Eidson, A. F. 1994. The effect of solubility on inhaled uranium compound clearance: A review. Health Physics 67(1):1-14. Harley, N. H., E. C. Foulkes, L. H. Hilborne, A. Hudson, and C. R. Anthony. 1999. A review of the scientific literature as it pertains to Gulf War illnesses: Depleted uranium. Santa Monica, CA: RAND. ICRP (International Commission on Radiological Protection). 1975. Report of the task group on reference man. Oxford, UK: Pergamon Press.
22 updated literature review of depleted uranium Kirk, W. 1981. Depleted uranium. In Mineral facts and problems. Edited by W. Kirk. Washington, DC: Department of the Interior, Bureau of Mines. Pp. 997-1003. Lide, D. R. 1999. CRC handbook of chemistry and physics. 80th ed. Edited by D. R. Lide. Boca Raton, FL: CRC Press. Marshall, A. C. 2005. Analysis of uranium dispersal and health effects using a Gulf War case study. Government Reports Announcements and Index 23:212. May, L. M., J. Heller, V. Kalinsky, J. Ejnik, S. Cordero, K. J. Oberbroekling, T. T. Long, K. C. Meakim, D. Cruess, and A. P. Lee. 2004. Military deployment human exposure assessment: Urine total and isotopic uranium sampling results. Journal of Toxicology and Environmental Health A 67(8-10):697-714. McDiarmid, M. A., and K. S. Squibb. 2001. Uranium and thorium. In Pattyâs toxicology. 5th ed. Edited by E. Bingham, B. Cohrssen, and C. H. Powell. New York: John Wiley and Sons, Inc. Pp. 381-421. McDiarmid, M. A., S. M. Engelhardt, M. Oliver, P. Gucer, P. D. Wilson, R. Kane, A. Cernich, B. Kaup, L. Anderson, D. Hoover, L. Brown, R. Albertini, R. Gudi, D. Jacobson-Kram, and K. S. Squibb. 2007. Health surveillance of Gulf War I veterans exposed to depleted uranium: Updat- ing the cohort. Health Physics 93(1):60-73. Meddings, D. R., and M. Haldimann. 2002. Depleted uranium in Kosovo: An assessment of potential exposure for aid workers. Health Physics 82(4):467-472. NRC (National Research Council). 1983. Risk assessment in the federal government: Managing the process. Washington, DC: National Academy Press. âââ. 1994. Science and judgment in risk assessment. Washington, DC: National Academy Press. âââ. 2006. Health risks from exposure to low levels of ionizing radiation: BEIR VII phase 2. Washington, DC: The National Academies Press. âââ. 2008. Review of toxicologic and radiologic risks to military personnel from exposure to depleted uranium during and after combat. Washington, DC: The National Academies Press. Oeh, U., N. D. Priest, P. Roth, K. V. Ragnarsdottir, W. B. Li, V. Hollriegl, M. F. Thirlwall, B. Michalke, A. Giussani, P. Schramel, and H. G. Paretzke. 2007. Measurements of daily urinary uranium ex- cretion in German peacekeeping personnel and residents of the Kosovo region to assess potential intakes of depleted uranium (DU). Science of the Total Environment 381(1-3):77-87. Roth, P., V. Hollriegl, E. Werner, and P. Schramel. 2003. Assessment of exposure to depleted uranium. Radiation Protection Dosimetry 105(1-4):157-161. Royal Society. 2001. The health hazards of depleted uranium munitions: Part I. London, UK: The Royal Society Working Group on the Health Hazards of Depleted Uranium Munitions. Sztajnkrycer, M. D., and E. J. Otten. 2004. Chemical and radiological toxicity of depleted uranium. Military Medicine 169(3):212-216. USACHPPM (US Army Center for Health Promotion and Preventive Medicine). 2004. Capstone report: Depleted uranium aerosol doses and risks: Summary of U.S. Assessments. Fort Belvoir, VA: US Army Heavy Metals Office, Chemical and Biological Defense Information Analysis Center. WHO (World Health Organization). 2001. Report of the world health organization depleted uranium mission to Kosovo. Geneva, Switzerland: World Health Organization. Wrenn, M. E., P. W. Durbin, B. Howard, J. Lipsztein, J. Rundo, E. T. Still, and D. L. Willis. 1985. Metabolism of ingested U and Ra. Health Physics 48(5):601-633.