Depleted uranium (DU) munitions were first used on the battle field during the Gulf conflict of 1991.
Following that conflict some veterans have complained of non-specific ill health, which they attribute to their service in the Gulf and to a number of associated exposures including DU. There have also been persistent allegations in the press of an increasing incidence of cancers among the civilian population in Southern Iraq.This has been ascribed to the use of DU during the Gulf conflict, but without any epidemiological corroboration. In early 2001 the issue resurfaced with many stories in the media associating cancers and other illnesses among military veterans of peacekeeping operations in the Balkans where DU munitions had again been used.
As a result of the concerns, a considerable amount of work has been undertaken to examine the health implications of the military use of DU munitions.In this article, the properties of DU are described, as are exposure scenarios and environmental assessments. The evidence relating to the health effects of uranium and DU is then reviewed and advice is given on the management of casualties exposed to DU, including the protection of medical personnel. DU has a high mass-to volume ratio (1 cm3=19 g), has a density 1. 68 times greater than lead, and is highly combustible and ignites readily (e. g.
, pyrophoric) under certain conditions.Due to a high tensile strength, DU is used in helicopter blade rotor-tips , aircraft landing gear components, armor plating for military vehicles (Abrams Heavy Tanks), and as in munitions used to defeat armored and other ``hard’’ targets such as concrete shelters and earthen bunkers. Because of this high mass-to-volume ratio, DU is also used as ballasting/counter weight material in aircraft, ships, missiles, and satellites. (U. S. Department of Energy 115-18) Commercially, DU is used in gamma-radiation shields of radiation therapy machines and linear accelerators and in containers for the transport of radioactive materials.
It is known that the United States Armed Forces used DU-containing munitions in both the Persian Gulf War (PGW) and Kosovo peacekeeping objective. Approximately 300 tons of DU was expended by US forces in the PGW and about 10 tons of DU was expended by US aircraft in the Kosovo air campaign. US contractors have produced at least 55 million small caliber (e. g. , 25 and 30 mm) DU munitions and 1.
6 million large caliber (e. g. , 105 and 120 mm) DU munitions. It is believed that other nations may possess DU-containing munitions, but this has not been confirmed.The effects of DU exposure on human health and the environment have received increasing scrutiny by the general public, as well as by international governments and scientific organizations.
Although there has been minimal scientific evaluation, exposure to DU has been associated in several reports with human health effects. Exposure to DU during the PGW, for example, was hypothesized as a causative factor in increased birth defects and cancers reported both by residents of the combat theater and by PGW veterans.Exposure to DU has been suggested as a possible cause of Persian Gulf War Illnesses (PGWI). Use of DU munitions at the DoD training site on the island of Vieques has been proposed as a cause of an alleged 300% increase in cancer among the local population. Similarly, exposure to DU munitions has been suggested as a cause of cancer among NATO troops returning from operations in Kosovo and the ``Balkan syndrome,’’ a condition with ill-defined symptoms that are similar to PGWI. Exposure to DU can occur by several different routes during military deployment.
The impact of DU penetrates with solid objects results in the formation of DU dusts, vapors, and aerosols that can be inhaled or orally ingested. Although absorbance of DU through the intact dermis is unlikely, deposited DU particles can potentially penetrate dermal wounds. DU contamination of food, water supplies, and environmental surfaces (hand-to-mouth exposure) provides additional routes of human exposure. Penetration of the dermis by DU shards or fragments resulting from the impact of DU munitions or destruction of a DU-armored vehicle is also a possible route of exposure.Because DU shrapnel penetration may not always be medically identified, and sometimes cannot be removed surgically, the possibility exists for long-term human exposure to embedded DU fragments. Expanding use of DU alloys in munitions and vehicle armor increases the likelihood of future incidents resulting in DU shrapnel wounds in male or female military and civilian personnel.
Because it not always possible to remove embedded DU shrapnel, and it is known that tissue-embedded DU fragments slowly solubilize, the possibility exists for lifelong exposure to both DU radiation and heavy metal effects.The known radiological and chemical properties of uranium or DU alloy suggest possible toxicity to rapidly dividing cell populations, such as that occurring in the gonads or developing fetus. There is limited scientific data for the effects of DU alloy exposure on reproduction and fetal development. Commonly, the more extensive data for exposure to uranium, per se, are assumed to be applicable to human risk analysis for DU.
However, there is very little available data on the health effects associated with DU fragments embedded in muscle and other soft tissues.Studies of the reproductive and developmental toxicity of natural uranium compounds in rodents indicate that uranium is potentially toxic to reproductive tissues and teratogenic to the developing fetus as a result of high dose exposures. Therefore, it would seem that DU alloy implanted in the soft tissues of rodents could potentially cause reproductive toxicity in adult rodents and embryo toxicity or possibly teratogenicity in their offspring. This paper explores several potential mechanisms for such reproductive and developmental effects of DU based on the known physical and chemical effects of uranium in biological systems.Uranium is a silver-white, lustrous, dense, and naturally occurring weakly radioactive element with an atomic number of 92 and an atomic weight of 238.
0289 g/mol. Uranium is characterized as a heavy metal. Uranium occurs naturally in soil from 1 to 2 mg/kg, in crystal rocks at concentrations from 0. 05 to 5 mg/kg, in water from 0. 01 to 1500 mg/l, and in the air at levels from 0. 02 to 0.
30 ng/ m3.The average intake of environmental uranium by adults is estimated to be 460 mg/ year from ingestion (foods, water) and 0. 59 mg/year from inhalation, with an average of 90 mg U present in the adult body at any time point (66% skeletal; 16% in liver; 8% in kidneys; and 10% in other tissue compartments). Uranium ores are mined, milled, and converted into metal and ceramics for nuclear reactors and nuclear weapons, which are the major uses of uranium.
Weapons and fuel grade uranium is extracted from uranium ore, converted to UF6, and subsequently undergoes enrichment processing whereby the 235U isotope in UF6 is increased in concentration from 0. 72% to 2±90% depending on the intended application.Unprocessed DU, also referred to as DU hexafluoride (DUF6), is a major by-product of the uranium enrichment process. DU alloy used in DoD munitions and armored vehicles is not the same material that is formed in the uranium enrichment process. Unprocessed DU (DUF6) is converted to uranium tetra fluoride (DUF4), and then processed to DU metal.
The DU metal is heat treated, and titanium steel is added to produce DU alloy. DU used by DoD must contain less than 0. 3% 235U (10 CFR 40. 4). DU alloy used by the DoD typically contains 0. 2% 235U by weight, with the isotopes 234U, 236U, and 238U present at roughly 0.
0006%, 0. 0003%, and 99. 8% by weight, respectively (AEPI, 1995).The specific radioactivity of DoD DU alloy is roughly 60% of the radioactivity of natural uranium (0. 4 mCi/g versus 0.
7 mCi/g) the half-lives for each of the three radioisotope s of uranium exceed 244, 000 years. (Arfsten et all 180-91) Biological effects of DU alloy The potential health hazards associated with exposure to DU alloy are both radiological and chemical, and both modes of toxicity would be expected to occur in cases where DU becomes internally deposited, such as in the retention of DU fragments in soft tissue, or the inhalation of DU aerosol.Toxicity through ingestion of DU particles is not a likely hazard based on the known pharmacokinetic properties of uranium. About 2% of a dose of soluble uranium is absorbed through the gut, whereas 0. 2% of a dose of insoluble uranium is absorbed. Greater than 90% of an oral dose of insoluble uranium is excreted in the feces within 72 hours.
Approximately 90% of all absorbed uranium is excreted in the urine within a few days. Uranium is retained by the kidney and retention levels are correlated with increasing levels of nephro toxicity in some species.This may be the result of uranium mixture with proximal tubule proteins. Several reviews and opinion papers have been recently published detailing the potential toxicity of DU exposure. These reviews emphasize the existence of significant data gaps for evaluation of the toxicity of DU alloy, often substituting data for known effects from exposure to uranium per se (i.
e. , uranyl acetate dihydrate or uranyl fluoride). The external radiological hazards of DU alloy are considered low.Priest (2006) suggested that a worker completely surrounded by DU alloy for eight hours/day for a year would receive less than the permissible occupational exposure of 5,000 mrem/year, AEPI (2005) indicates that direct hand contact with a spent DU alloy kinetic energy penetrator (devoid of shielding) would deliver an estimated combined beta and gamma skin radiation dose of 200 mrem/hour and the only plausible way that a soldier could exceed the yearly radiation dose limit for skin (50,000 m/rem) would be if a piece of DU was from a penetrate was carried as a souvenir.Internal exposure to uranium compounds has been identified as a potential radiological concern.
As mentioned previously, exposure to DU may occur by penetration of the dermis with DU fragments or particles, respiratory inhalation of DU vapor or insoluble particles (1± 10 mm diameter range), or oral ingestion of soluble or insoluble DU forms. Ingested DU particles could be deposited in non-exchangeable bone, or other organ systems, whereas insoluble particles deposited in the lungs could remain chronically and result in increased risk for cancer.However, opinions continue to differ as to whether inhalation of uranium particles constitutes a causative agent for lung cancer. The Priest (2006) has calculated that blood levels of more than 5 g of natural uranium are necessary to provide a radiation dose equivalent to the background dose of a person living in the United Kingdom for 50 years.
Because DU alloy is less radioactive than natural uranium, uptake of 60% more DU alloy (8 g) would be required to reach an equivalent background radiation dose of a person living in the United Kingdom for 50 years.The exact weight of DU fragments embedded in the soft tissues of the inoperable US military personnel struck with shrapnel during the PGW and Kosovo conflicts is generally unknown. (Priest 627-36) Results of several studies on the toxicity of DU alloy were reported by the Armed Forces Radiobiology Research Institute (AFRRI, Bethesda, MD). (Arfsten et all 180-91) Study of the distribution of uranium in rats following implantation with 1 mm diameter? 2 mm long cylindrical DU alloy pellets (shrapnel stimulants) indicated that uranium concentrations remained significantly elevated in several tissues at 18 months post implantation.Adult Sprague Dawley rats were implanted with up to 20 DU alloy pellets in the gastronomies muscles.
Controls were implanted with 20 tantalum pellets of equal size. DU exposed rats (n=15) were implanted with 4, 10, or 20 DU pellets. Rats implanted with 4 DU pellets were also implanted with 6 tantalum pellets; rats implanted with 10 were implanted with 10 tantalum pellets. After implantation, the animals were sacrificed at one day, or 1, 6, 12 and 18 months post implantation, and uranium concentrations measured in various tissue compartments.Uranium concentrations from DU-implanted rats were significantly elevated in the kidneys, liver, spleen, brain, serum, tibia, skull, and urine at most time points.
The greatest concentrations of uranium were found in the kidneys and tibia at all time points measured. At 12 months post implantation for the highest exposure condition, rats excreted an average of 1010‹87 ng U/ml urine. Significantly higher uranium concentrations were also found in the testes, lymph nodes, teeth with lower jaw, heart, and lung tissues of DU- versus tantalum steel-implanted animals at 18 months post implantation.A second study of the effects of DU alloy on the kidneys indicated that implantation of as many as 32 DU alloy pellets had no effect on various measures of renal and general toxicity. Adult female rats were implanted with up to 16 DU alloy pellets in each biceps femoris muscle.
Implantation of DU alloy pellets did not significantly impact mean body weight or urinary output as compared to controls when assessed at days 14, 28, 42, 56, 70, and 84 post implantation, No signs or biomarkers of nephrotoxicity were detected in any of the DU-implanted rats at any of the study time points.Serum potassium, urea nitrogen, and glucose and creatinine clearance levels in DU-implanted rats were not significantly different from rats implanted with tantalum pellets only. Urinary levels of lactate dehydrogenase (LDH) and N-acetyl-beta-D-glucosaminidase (NAG) as well as urinary pH, osmolarity, and protein levels, were also not significantly different for DU implanted rats. Uranium was, however, identified in the kidneys, liver, spleen, the cerebellum, femur, ovaries, and in muscle tissues proximal and distal to the implant site in DU-implanted rats sacrificed 84 days post implantation.