|Splitting more than hairs|
Uranium comes in two natural isotopes: 235U and 238U. 99.3% of natural uranium is uranium-238, and this is the most stable isotope with a half-life measured in billions of years. The isotope making up the remaining 0.7%, uranium-235, has a half-life measured in hundreds of millions of years and is a lot more reactive and hence more useful if you want a self-sustained fission reaction. When you remove most of the 235U from raw uranium, what's left is called depleted uranium (DU).
Uses and hazards
Depleted uranium is weakly radioactive. It is not considered a significant radiological hazard — instead, it is recognized as a chemical hazard primarily to the kidneys, similar to lead. The most useful characteristics of DU are its very high density (19.1 g/cm3 — very close to gold and almost twice the density of lead), fracture modes that lead to a self-sharpening effect when used as a kinetic penetrator, pyrophoric properties, and a large already mined stockpile being present as a byproduct of uranium enrichment. The high density makes it a very useful material for radiation shielding — only half the thickness of lead is required (though the required mass remains roughly the same). That's right: uranium-238 is useful for shielding people and objects against nuclear radiation.
DU is an alpha emitter and as such is only dangerous when ingested or inhaled. It is a potential source of nuclear fuel: Its reaction with fast neutrons in a breeder reactor yields plutonium-239, a fissile isotope of plutonium; and certain nuclear reactor designs, intended to use natural uranium as fuel, can also use depleted uranium salted with small quantities of other fissile materials.
Some of the depleted uranium comes from spent fuel re-processing, and is contaminated with varying levels of trans-uranic actinides. While no sample of munition has been identified to have more than a trace of trans-uranic actinides, there exists a risk of accidental mix-up and use of the contaminated depleted uranium.
DU munitions are used in anti-tank shells and aircraft guns. Firing of DU munitions produces uranium oxide smoke due to pulverization and oxidation of depleted uranium metal. The smoke is toxic when inhaled. Because of the high density of uranium compounds, the smoke quickly settles, so it is a transient hazard. If you are close enough to breathe uranium oxide smoke, you should probably be more worried about the risk of immediate death from impalement. Uranium compounds from the used projectile can contaminate the soil and pass into the water supply, but they are poorly soluble in water, so this risk is limited.
Beyond the obvious effect of destroying tanks and killing people, depleted uranium munitions are not expected to raise cancer rates or cause chronic uranium poisoning in the long term, mainly due to low solubility in water of uranium compounds formed on impact. The only exception is for people who were in a vehicle hit by a DU penetrator, or those who have DU shrapnel embedded in their bodies. Although data from rodents suggests that DU may be carcinogenic, studies on humans actually exposed to it failed to detect any effect.
The 1992 Bijlmermeer, Netherlands plane crash, in which depleted uranium used as counterweight in a Boeing 747 escaped on impact, led to long-lasting health problems for survivors of the crash, but these health effects were probably not due to the effect of DU.
Depleted uranium has uses in applications of weight and leverage because of its very high density (approximately 1.7 times that of lead). At least one yacht, the Pen Duick VI, had a keel made largely of depleted uranium.
Depleted uranium scare
There is an on-and-off fear campaign about depleted uranium. The people behind it come mainly from the anti-nuclear movement and those opposed to the Iraq War. It is claimed that the weak radiation emitted by depleted uranium is capable of causing birth defects in the offspring of people exposed to it (while usually ignoring the more relevant heavy metal toxicity aspect), that it causes the "Gulf War syndrome", or that it is responsible for the increase in infant mortality in Iraq after the start of the Iraq War. This is usually accompanied by dramatically sounding statements calling DU a "weapon of mass destruction" or a "nuclear weapon", and the use of DU "radioactive warfare", and photos of children with various horrible birth defects, most of which are not recognized as caused by radiation or heavy metal poisoning.
Depleted uranium is obviously toxic, but the campaign does not focus on this or other legitimate arguments that could be made against DU munitions or the war in Iraq in general. Instead, it attempts to exploit the widespread fear of radiation. The photos used are mostly of laboratory specimens of natural birth defects from former Soviet bloc countries and first appeared in Chernobyl-related anti-nuclear propaganda. If the material cites some actual research to support the anti-DU message, the argument is often a form of guilt by association:
- People who fought in the Gulf War suffer health problems.
- Depleted uranium was used in the Gulf War.
- Therefore, those health problems are caused by depleted uranium.
This is wrong, because there are many more things which go on during a war which might affect one's health (like extreme stress, exposure to other nasty things used in weapons, being shot at, etc.) Studies usually cited in support of DU toxicity or teratogenicity do not actually investigate the effect of DU exposure, but are epidemiological studies on the effect of the Gulf War in general.
Another category of arguments is using evidence that is irrelevant, for example, studying uranium miners instead of soldiers. Uranium miners are exposed to much more than uranium, including radon gas and other decay products. Those decay products are not present in DU — the projectiles are purified from them, and the uranium decays so slowly that almost no decay products are formed during the service life of a projectile.
Example studies used to support the scare
|||Examines a group which is self-selected (people who were worried by their possible exposure to depleted uranium). Very small sample size, inappropriate control group (people from the lab performing the study). Studies chromosomal abnormality rather than health outcomes.|
|||This study refers to people who have depleted uranium shrapnel embedded in their bodies. The observed effects are entirely due to chemical toxicity. Obviously having a chunk of a toxic heavy metal in your body is not healthy.|
|||Does not investigate DU exposure. Very large confidence intervals, some of which include unity (e.g. there's too much uncertainty to determine whether the effect is real or just statistical noise).|
|||Does not investigate DU exposure. No excess birth defects observed. The rate of spontaneous abortions and ectopic pregnancies is higher, which might be a psychosomatic effect.|
|||Does not investigate DU exposure. Only an increased risk of miscarriage and poorly defined malformations was found, but this might be due to recall bias rather than any real effect.|
|||Irrelevant — investigates miners who worked at poorly ventilated mines in the 1950s. They were exposed to much more than uranium, primarily radon gas.|
|||The article explicitly says that harlequin-type ichtyosis has been identified as a heritable disorder and has nothing to do with radiation exposure or uranium toxicity.|
|||Review focuses on chemical toxicity, not radiotoxicity. It was written by someone from a psychology department. Furthermore, it says: "But, all of this data is only suggestive until it can be tied to meaningful human research. We do not even have a reasonable idea of the typical DU intake of people living in regions where DU munitions have been used."|
|||Review of chemical toxicity. Does not investigate human data.|
|||This review uses quote mining. In addition to medical literature, it heavily cites anti-nuclear sources, such as the Depleted Uranium Education Project and Helen Caldicott, as well as newspapers — which is very strange for a scholarly review.|
Birth defects in Basra and Fallujah
Many anti-depleted uranium sites mention the rise of birth defects in Fallujah and Basra as the ultimate proof that depleted uranium munitions are dangerous. However, there are several problems with this association:
- Depleted uranium was most likely not used in Fallujah, because there were no enemy tanks to use them against. The U.S. tanks used mainly HEAT (explosive) ammunition.
- While depleted uranium was used at Basra, the birth defects there started rising sharply in 1998, which was 7 years after the first Gulf War and 5 years before the second. No explanation is offered for this very large time lag.
Showing that wingnuts will use every available venue to sensationalize their cause, Stephen Lendman wrote an article on the Libya conflict titled NATO Using Nuclear Weapons in Libya. There, Lendman states that each depleted uranium round is a miniature "dirty bomb" used as an indiscriminate weapon of mass destruction. For this he also quotes Dr. Doug Rokke a number of times, a well known crank on the subject of depleted uranium.
Alternatives to depleted uranium
Due to the scare described above, depleted uranium has a bad reputation, to the point where people will petition their governments to avoid or stop using it. The problem is that there are few substances suitable for use as kinetic penetrators, and the main alternatives are various tungsten alloys, which are in fact more toxic and carcinogenic than depleted uranium. It has been shown that 100% of rats implanted with pellets of these tungsten alloys develop extremely aggressive cancers within 4-5 months.
- Health Physics Society fact sheet on DU
- Risk analysis of depleted uranium following an aircraft crash
- Blogs / Stephen Lendman's blog / NATO Using Nuclear Weapons in Libya
- Embedded weapons-grade tungsten alloy shrapnel rapidly induces metastatic high-grade rhabdomyosarcomas in F344 rats