The use of Depleted Uranium (DU) Weapons in the Gulf War, and more recently in the Balkan Wars, has drawn a lot of attention.
This short review will explain what is DU, for what purpose DU weapons have been manufactured, and how many of them were used, first in the Gulf War and then later on in the Balkan Wars in Herzegovina and Kosovo.
Widespread leukemia and other ailments have been claimed in the media. They were mostly attributed to the radioactivity of DU and partially to the chemical effects of the heavy metal. A critical analysis of these claims needs a brief review of basic physics and relevant radiation regulations as well as legal limits on toxic chemicals. How is DU ammunition dispersed on impact, and how can minute particles find their way into the human body. Possible health risks will be put in perspective and compared with other risks in war and in daily life. The question is raised, if DU weapons can be called still conventional or if they fit better the definition of radiological and chemical weapons. DU weapons and their “efficiency” have to be seen also in the context of treaties on so-called weapons of mass destruction (WMDs), which are signed and even ratified, but do not yet have an implementation procedure or the political will to enact.
1. What is Depleted Uranium (DU)?
1.1 Activity of Uranium Ore Before and After Extraction
Uranium is a chemical element that is more abundant than silver, gold, mercury and cadmium and is contained by 2 to 4 millionths in the Earth’s crust. It can be found on surface and in ore mines in many countries, among them Zaire, South Africa, and Canada and also in the Czech Republic. One ton of ore contains on the average about 3 kg of uranium.
Uranium comes essentially in three isotopic forms. Isotopes are any of two or more forms of an element having the same atomic number (i.e. the same chemical property) but different atomic weights due to a different number of neutrons in the nucleus. Natural uranium contains 99.274% of 238U, 0.720% of 235U, and 0.0055% of 234U, they all have 92 protons in the nucleus, but 146, 143 and 142 neutrons, respectively. The half-life of 238U, 235U, and 234U is 4.49·109, 7.10·108, and 2.48·105 years, respectively, ranging from billion to million years. The longer the half-life the less radioactive decay products appear in a given time interval and could effect human health. When uranium is dug out of the Earth its radioactive decay products come along. However, in the chemical process of uranium extraction of the three isotopes from the ore, all radioactive daughter products in the radioactive decay series’ 238U and 235U are eliminated, with the exception of the radiogenic isotope 234U.
In short, radiation background in mines and in extraction facilities is different and so are the health risks. There is an extensive evidence of excess lung cancers in underground uranium miners caused by the decay products of the radioactive gas radon (222Rn). But uranium mill workers have not shown increased mortality or excess lung cancers despite their increased exposure to uranium dust and radon decay products. There is no obvious explanation for this difference.
1.2 Enriched and Depleted Uranium
The extraction of energy from uranium for peaceful or military purposes asks for well-defined ratios of the two isotopes. In order to sustain the chain reaction of nuclear fission, uranium has to be enriched by the fissible isotope 235U to a reactor grade of 3.2 – 3.6% or weapon grade (90%+) uranium. This process not only produces the enriched product, but also a waste stream depleted in 235U, typically to less than 0.3%, which is often called the tail. The 235U content in the depleted uranium in the U.S. are lowered to 28% of its content in natural uranium.
Depleted uranium is a byproduct of uranium enrichment process, with a relatively small contribution from reprocessing of nuclear spent fuel. In addition to the 3 natural isotopes 238U, 235U, and 234U, depleted uranium from this latter source also contains a minute quantity (0.003%) of a man-made isotope 236U. The specific activity of DU is 15,902 Bq/gram (for definitions of radioactive units see annex). Traces of 236U were found in Kosovo after the war and gave rise to – unjustifiable – concern in various press reports.
Based on the measured isotopic composition of depleted uranium, the total activity (a-particles = helium nuclei, b-particles = electrons, g-rays) can be calculated as 22% less and the a-activity as 43% less compared to natural uranium.
The gaseous diffusion process for enrichment of the fissible isotope 235U is used in the United States. This process requires uranium in the form of uranium hexafluoride (UF6), primarily because the compound can be used in the gas form for processing, in the liquid form for filling containers, and in the solid form for storage. At atmospheric pressure, UF6 is solid at temperatures below 57°C and a gas above this temperature.
Workers in metal processing plants, including those who make DU penetrators, do not exhibit increased mortality or excess cancers.
2. Application of DU
Depleted Uranium is a low cost material that is readily available, since it was produced during the separation of weapon grade uranium. The Department of Energy in the U.S., as of June 1998, is in possession of almost 3/4 of a million metric tons (725·103 tons) stockpile of depleted uranium hexafluoride. This corresponds to a total activity of 527,000 Ci and a-activity 193,000 Ci. The a-activity per mass amounts to 0.389 mCi/kg.
Depleted uranium’s high density (19.05 g/cm3, 1.7 times more than 11.35 g/cm3 for lead) and its high atomic number Z = 92 also provide useful solution for g-radiation shielding. It has been used at various occasions at particle accelerators, e.g. at CERN in the UA2 detector.
Control surfaces on wide body aircraft require heavy counterweights. Tungsten (with density 19.3 g/cm3) or DU is ideal materials for this application where volume constraints prohibit the use of less dense metals. An airplane such as Boeing 747 needs 1,500 kg of counterweight. However, DU for this purpose gets out of fashion due to a few accidents and problems with surface embrittlement.
2.1 DU Ammunition
The US Army considered high-density materials such as tungsten and DU as metal in kinetic energy penetrators and tank armor already in the early 1970’s. DU was ultimately selected due to its availability and pyrophoricity. While 50% of tungsten has to be imported, mainly from China (US$ 150/kg in 1980), DU is provided for free to arms manufacturers. Tungsten also has much higher melting point than uranium and lacks pyrophoricity. DU penetrators contain no explosives; they act only by impact and immediate ignition of the dust (500°C). Conventional ammunition does not penetrate DU armor, however DU projectiles are capable of piercing it.
2.2 Proliferation of DU Weapons
The United States is no longer the only country with DU munitions. 17 countries including Britain, France, Russia, Greece, Turkey, Israel, Saudi Arabia, Bahrain, Egypt, Kuwait, Pakistan, Thailand, South Korea, Taiwan, and other countries have acquired depleted uranium weapons. Probably NATO countries will follow soon. These weapons were extensively tested on at least 14 sites in the U.S. and also in Britain.
As of early 1994 already more than 1.6 million tank penetrators and 55 million small caliber penetrators had been manufactured in the U.S. and another 200 million rounds (some part made out of tungsten) had been ordered by 1998. The approximate cost per shell of a 120-mm tank round is US$ 3,300, implying that handling of DU and manufacturing of ammunition takes the lion’s share, whereas the material itself comes almost for free.
3. Combat and Accidents
The US military used depleted uranium ammunition on the battlefield for the first time during the Gulf War in 1991. The amount of DU munitions released in Saudi Arabia, Kuwait, and Iraq during the Operation Desert Storm totals to 860,550 rounds and corresponds to 294,500 kg DU, for a total activity of 312 Ci and a-activity of 115 Ci. In addition, 9,720 DU aircraft rounds and 660 DU tank rounds (6,430 kg of DU) burned as a result of a monstrous fire in the ammunition storage area and motor pool at the US Army base in Kuwait.
Data on the use of DU ammunition are still less well known for the war in Bosnia in 1994-1995 and in Kosovo in 1999. They are estimated to 11,000 and 31,000 rounds, corresponding to a total of 10,000 kg of DU.
4. Effects of Depleted Uranium
4.1 Effects of DU Penetrator Impact
When a depleted uranium penetrator impacts armor, 18 – 70% of the penetrator rod will burn and oxidize into dust. The DU oxide aerosol formed during the impact has 50 – 96% of respirable size particles (with diameter less than 10 mm, conditions very similar to “desirable” particle size for efficiency in chemical or biological warfare), and 17 – 48% of those particles are soluble in water. Particles generated from impact of a hard target are virtually all respirable. While the heavier non-respirable particles settle down rapidly, the respirable DU aerosol remains airborne for hours.
The solubility of the uranium particles determines the rate at which the uranium moves from the site of internalization (lungs for inhalation, gastrointestinal tract for ingestion, or the injury site for wound contamination) into the blood stream. About 70% of the soluble uranium in the blood stream are excreted in urine within 24 hours without being deposited in any organ and the remainder primarily depositing in the kidneys and bones. The kidney is the organ most sensitive to depleted uranium toxicity. When DU particles of respirable size are inhaled, roughly 25% of the particles become trapped in the lungs, where the insoluble particles can remain for years. Approximately 25% of the inhaled DU is exhaled (particle diameters between 1 and 5 mm) and the remaining 50% is subsequently swallowed.
4.2 Radiological effects
4.2.1 The Regulations
The International Commission on Radiological Protection (ICRP) recommends and the Nuclear Regulatory Commission in the US (NRC) mandates an occupational annual dose equivalent for the whole body no more than 5 rem/year and no more than 10 rem in 5 years. No short-term health effects are detectable at this dose equivalent.
The non-occupational annual dose equivalent limit for the general public is selected as 100 mrem/year, which is comparable to the average background of 363 mrem/year.
There are well-defined legal limits for inhalation and digestion of DU.
4.2.2 Calculated and measured doses
The impact of one 120-mm tank round with the 5.35 kg DU penetrator on an armored target, with 18 – 70% of the penetrator rod oxidizing into aerosol, is taken as an example. The initial contaminated area from the impact of one DU tank round inaccessible to general public (50 m radius circle) is about 0.8 hectares. If contamination spreads with weather elements up to 38 hectares become inaccessible to general public, with 0.9 nCi/m2 the allowed surface contamination for general public.
The air contamination after the impact and before the DU dust settles can be estimated to maximum of soluble uranium 16 times higher than the NRC limit for radiation workers and 3,500 times higher than the allowed air concentration for general public. The maximum air concentration of insoluble uranium is 800 times higher than the NRC limit for radiation workers and 180,000 times higher than the allowed air concentration for general public.
The residual contamination in Iraq 8 years after the end of the Golf War in the oil fields north of Kuwait was measured. It showed radiation levels 35 times above the background over parts of the battlefield and 50 times above the background over the rusting tanks hit by DU ammunition.
The accumulated dose equivalent becomes significant when spent but unexploded DU penetrators are worn by army personnel as war souvenirs in direct contact with the skin (1,800 rem/year) or when used by children as toys. The skin dose equivalent limit of 50 mrem/year for radiation workers would be reached in about 10 days.
4.3 Chemical Toxicity
4.3.1 Uranium Effects on Kidney
The RAND review on radiological and toxic effects of uranium puts the overall maximum permissible concentration, i.e. concentration of metal in the kidney associated with no significant increase in the frequency of kidney malfunction, at 3 mg/kg of kidney for uranium and calls it a de facto standard.
Soluble uranium, which is absorbed in the blood circulation within the body, is eliminated rapidly through the kidney in urine. About 67% are excreted within the first day without being deposited in any organ. Approximately 11% is initially deposited in the kidney and excreted with a 15-day half-life. Most of the remaining 22% is initially deposited in the bone (up to 20%), which is the principle storage site in the body, and the rest is distributed to other organs and tissues.
The Occupational Safety and Health Administration (OSHA) established occupational limits for inhalation of heavy metals. The values for tungsten, lead, uranium in soluble form are 1, 0.05, and 0.05 mg/m3, for insoluble form 5, 0.10, and 0.25 mg/m3, respectively. Current Environmental Protection Agency (EPA) standards set the values at 44 mg/l for groundwater and 20 mg/l for drinking water.
4.4.2 Gulf War Illness
An estimate for exposure of a veteran from the Gulf War is difficult to make and studies on the illness came not yet to a final conclusion. More than 10,000 veterans (out of a total of 695,000) reported mysterious illnesses, like muscle and joint pain, chronic fatigue, depressed immune systems, neurological disorders, memory loss, chemical sensitivities, rashes. They may have exceeded the OSHA limit for inhalation of DU by a factor of 3 and the ATSDR minimal risk level intake for general public by 17 times.
Many factors may have contributed to the ailments, such as·
- Multiple vaccinations against anthrax and botulinum toxoid
- Medical treatment with pyridostigmine bromide to counter effects of potential chemical exposure
- Petroleum from oil fire
- Pesticide and insect repellants
- Tropical parasites such as leishmaniasis
- Depleted uranium dust and shrapnel from DU ammunition and armor.
It is not clear to which extend DU contributed to the reported illnesses.
However, there is ample evidence to show that contact with DU ammunition had consequences, especially for children, among them an increase of childhood leukemia in southern Iraqi provinces by a factor of 3 between 1989 – 93, while in the Central Provinces the incidence remained normal. Local concentrations of DU may have been exceedingly high producing this high incidence of leukemia.
It appears premature to attribute reported illnesses of military personnel to effects of DU ammunition in Kosovo. In Kosovo, similar to Iraq, many parameters may have played a role in producing symptoms, that could be also attributed to the release of chemicals after bombing of factories.
A study of possible health effects has been made , assuming that 100 tons of DU were distributed uniformly over a one-kilometer-wide strip along 100 kilometers on the “Highway of Death” between Kuwait City and Basra, a city in southern Iraq . Under this assumption average dose for someone who lived in the area for a year would be about one millirem – or about 10 percent of the dose from uranium and its decay products already naturally occurring in the soil. The authors came to the conclusion that an individual’s estimated added risk of dying from cancer from such a dose would be about one in 20,000. The doses for heavy metal effects are probably also far below the exposure limits set by OSHA. However, since no exposure and urine tests had been done for two years after the war, it is now too late to draw any conclusions.
5. Comparison of DU with other risks
DU is a dangerous material when used as ammunition in war fighting. Obviously, the driver of an armored tank or vehicle, that is hit by a DU penetrator, has a high chance to die from the blast and/or the heat immediately, and he is no longer subject to the consequences of inhaling or digesting DU.
The spread of DU weighs on the environment and the population, civil or military, in the vicinity of the impact as a long-term consequence. For DU, and likewise for chemical, biological or radiological weapons, the local concentration and time constants of the dispersed material play the important role.
The legal limit for exposure to chemicals and radioactivity is set such, that values just beyond are not detrimental to human health or the environment. Only an excess value by order(s) of magnitude should give rise to serious concern.
The consequences of the use of DU ammunition pale in comparison with the other direct and indirect effects of war. As an example may serve the estimated 30,000 unexploded fragmentation bomblets lying on Kosovo’s ground, adding substantial danger to the not yet cleared land mines.
In order to put the danger from radioactive exposure into perspective the following example may be instructive.
The risks associated with radioactivity and irradiation in general are, usually, measured in Sieverts. For most people, even scientists, this unit has no real meaning. Therefore, following a suggestion , a comparison is made with the risk with similar consequence of producing cancer. Cigarette smoking is such a case. The data are based on the following dose-effect relations: 0.04 lethal cancers per Sievert, 1 lethal cancer per eighty thousand cigarette packs.
|Comparison between effects of some irradiation exposures and cigarette smoking|
|Annual dose in millisieverts||Equivalent number of annual cigarette packs|
|Natural total irradiation||
|Comparison of allowed doses of irradiation to effects of cigarette smoking|
|Maximum allowed dose in millisieverts/year||Equivalent in cigarette packs/year|
Depleted uranium produced as a by-product of uranium enrichment is classified as radioactive and toxic waste and it is subjected to numerous regulations for handling and disposal. Yet the US regulatory limits for general public exposure are exceeded – at least locally and temporarily – up to five orders of magnitude for airborne radioactive emissions and up to 3 orders of magnitude for residual radioactive contamination when DU ammunition has been used in battlefield. The use of DU ammunition, perhaps the most effective new weapon, was not publicly revealed until a year after the Gulf War. These weapons have an indiscriminate character and can have adverse health effects not only on combatants but also on the population at large. Precautions could have been taken to limit possible health effects for the combatants and the civil population, and immediate medical tests could have removed a lot of ambiguities of the effects of DU ammunition.
Cancer can be the expected long-term consequence of both the radiological and toxic effects of depleted uranium exposure, albeit with an extremely low probability.
In 1996 the UN Subcommittee on Prevention of Discrimination and Protection of Minorities passed a resolution in which they “urged all States to be guided in their national policies by the need to curb production and spread of weapons of mass destruction or with indiscriminate effect, in particular nuclear weapons, chemical weapons, fuel-air bombs, napalm, cluster bombs, biological weaponry, and weaponry containing depleted uranium”.
If nothing else, the double standard for DU in radiation protection and handling of low radioactive waste in the civilian sector on one hand and by the military on the battlefield on the other is morally and legally untenable.
The manufacturing and use of DU weapons is a new man-made problem that should be addressed by the international community on an appropriate level. However, it pales compared to major, other unsolved problems in arms control. There is not yet an implementation program for the biological weapons convention (BWC, ratified in 1972!)! The elimination of enormous stockpiles of chemical weapons may take decades, but there is at least a working implementation body of the Chemical Weapons Convention (CWC). The number of nuclear warheads does not shrink, only some of their delivery vehicles are being discarded, slowly approaching the limit set in the Strategic Arms Reduction Treaty (START II). The Anti-ballistic Missile Treaty (ABM) is in danger to be discarded, the Test-Ban Treaty (TBT) is not yet ratified by all Nuclear Weapon States (NWSs), and major possessors of land mines have not signed up to the Ottawa Treaty.
7. Some Selected References Review of Radioactivity, Military Use, and Health Effects of Depleted Uranium Compiled by Vladimir S. Zajik, July 1999 http://members.tripod.com/vzajic/  After the dust settles Steve Fetter & Frank von Hippel The Bulletin of Atomic Scientists, November/December 1999, pp. 42-45  Global warming or nuclear waste – which do we want? H. Nifenecker and E. Huffer europhysics news March/April 2001, pp. 52- 55
Some radiation units:
1 Curie = 1 [Ci] = 37·109 decays/second or = 37·109 Becquerel = 37·109 [Bq] 1 milliCurie-of-intensity-hour = 1 Sievert = 1 [Sv] 1 Sievert corresponds approximately to 8.38 Roentgen
1 rem = roentgen equivalent man
The dose equivalents for the uranium isotopes 238U, 235U, and 234U and their decay products uniformly distributed in the whole body are 1.28, 1.30, 1.32 [(mrem/year)/(pCi/kg)].