Many of those who argue that depleted uranium (DU) cannot be a serious health risk say radiation takes a long time to produce cancers.

They say the reports from veterans of the wars in Bosnia and Kosovo, complaining of leukaemia and other cancers, are inconsistent with what we know of the time it takes for radiation to cause damage.

And they believe that even the reports from Gulf veterans and Iraqi civilians of cancers which have developed since the 1991 war suggest an improbably rapid development of the disease.

But two senior scientists have told BBC News Online they believe it may be a serious mistake to rule DU out of the equation.

Both remain open-minded on whether DU actually does damage health, but both believe its effects are poorly understood. Neither was prepared to be named.

Chernobyl's surprise

One, a professor in a university physics department, said: "We're in uncharted territory, because we have no experience of human exposure to DU.

"What we do know, though, is that thyroid cancer appeared far sooner than expected after the Chernobyl accident in 1986. That was a real surprise.

"It's true that DU is not very radioactive. But when you inhale it, it does go to the lymph nodes surrounding the lungs, and that means it could irradiate all the blood cells which pass through the nodes.

"Many experts say DU is more of a chemical threat than a radioactive one, and I think the chemical toxicity is an issue. The uranium atoms are chemically toxic, and they will visit every cell in the body where they may have an effect.

"And it would not be hard to absorb a serious dose of DU quite quickly. When it vaporises, it forms a very fine powder which can blow a long way.

Limit reached quickly

"The permitted body burden of uranium is 80 milligrams. We have calculated that if you had 10,000 particles of DU per cubic centimetre, each up to 200 nanometres in size, then it would take about a month and a half to reach that limit.

"It's not overly likely. But it's not too unlikely, either."

The other scientist is a leading expert on the effects of ionising radiation.

He told BBC News Online: "What Nato and the UK Ministry of Defence are missing is the fact that a single alpha emitter can be carcinogenic.

"We don't know how low the risk of DU is. But the uranium has the potential to cause DNA damage because of its chemical properties, and that can trigger cancer.

"That would be an unconvincing argument about Kosovo, though a possibility for the Gulf. A two-year development period for cancers caused this way is a valid hypothesis.

"The warning from Chernobyl is to remind us that the Japanese atomic bomb survivors are not typical of all types of radiation.

"We shouldn't say too lightly that two years is not long enough for radiation to cause cancer."