The sceptics' case: DU is neither very radioactive nor especially rare

Given what is known about depleted uranium (DU), it is difficult for scientists to be universally convinced about it being the cause of the cancers and other illnesses seen in soldiers and civilians caught up in the Gulf War and the Balkans conflict.

Given what is known about depleted uranium (DU), it is difficult for scientists to be universally convinced about it being the cause of the cancers and other illnesses seen in soldiers and civilians caught up in the Gulf War and the Balkans conflict.

Uranium occurs naturally in the soil in an average concentration of about 3 parts per million, the equivalent of a teaspoon of the metal in a lorry load of dirt. We naturally ingest small amounts of uranium in food and water.

More than 98 per cent of the element exists in the form uranium-238, and less than 1 per cent as the more radioactive isotope, uranium-235. Uranium processing removes most, but not all, of the more dangerous uranium-235.

DU is what is left behind after mined uranium ore has been processed during the manufacture of fuel for nuclear reactors. The processing removes about 40 per cent of the radioactivity, making DU significantly less hazardous than the ore itself.

DU is thus on a par with the natural sources of radiation that most people come into contact with at some time in their lives. However, being a heavy metal, DU is chemically toxic if ingested in high enough doses.

DU has several characteristics of interest to the military. It is cheap, widely available and extremely dense - nearly twice the density of lead - and therefore ideal for packing the necessary punch to crack open heavy armour.

Unlike tungsten, the other heavy metal used in armour-piercing weapons, DU possesses the unique characteristic of "self sharpening" during impact with a tank's armour. Whereas the tungsten shell forms a mushroom shape, the tip of the DU projectile burns away at the edges during the split second of impact, aiding its penetration through several inches of armour plating.

Research into DU weapons began in the 1970s, and DU was first used on the battlefield during the Gulf War of 1991. DU's defensive capabilities were shown in one exchange between an American M1A1 main battle tank protected with DU armour and three Iraqi T-72s. The M1A1 took three direct hits with conventional shells before dispatching the T-72s with a single DU round to each tank.

The main radiological hazard of DU is its emission of "alpha particles", which do not penetrate clothing or skin but can be dangerous if ingested or inhaled. Nevertheless, in terms of alpha emissions, DU is about a million times less toxic than plutonium.

The primary health risk of DU arises from its chemical toxicity as a heavy metal. Animal experiments show that in heavy doses DU can, like other heavy metals, build up in the body and cause potentially serious damage to kidneys.

When DU shells explode they scatter uranium powder that can readily be inhaled or ingested. The burning of uranium during an explosion also produces various oxides which can dissolve in body fluids. Once dissolved, uranium readily reacts with biological molecules to toxic effect.

However, the US Department of Defense said that it has failed to find any evidence that soldiers exposed to exploded DU have suffered any ill effects.

The DoD cites a study of 33 veterans of the Gulf War who were exposed to DU as a result of being mistakenly attacked during "friendly fire" incidents. About half of them have DU fragments still embedded in their bodies.

"For the 33 veterans in the programme, tests for kidney function have all been normal. In addition, the reproductive health of this group appears to be normal in that all babies fathered by these veterans between 1991 and 1997 had no observable birth defects," says the defense department.

Scientists have also failed to find any significant health risks, such as blood cancers, in uranium workers who have been exposed to some of the highest levels of uranium contamination on the planet.

Leo Kinlen, a cancer epidemiologist at Oxford University, said that in trying to assess the cause of the leukaemias in soldiers who took part in the Balkans conflict it is first essential to determine whether there is a genuine "excess" of cancers among all of those who took part, and not just in a selected minority.

"You've got to know whether there is a real excess. Anecdotal reports are quite another thing," Professor Kinlen said.

"I would then want to know details of exposure to depleted uranium, no matter in how crude a form this information can be gathered."

Cancer epidemiology is difficult. It is one thing for the media to note a possible link between DU and cancer. Scientific proof is another matter.