..it could mean that low radiation is having subtle effects that go unnoticed because cells are not dying, says Mothersill. Miller has found one way this may happen. She has discovered the first direct evidence that radiation from DU damages chromosomes within cultured cells. The chromosomes break, and the fragments reform in a way that results in abnormal joins (Military Medicine, vol 167, p 120). Both the breaks and the joins are commonly found in tumour cells.
Depleted Uranium Casts Shadow Over Peace in Iraq](News – latest in science and technology | New Scientist) New Scientist 15 Apr 03
Wrecked tanks and vehicles litter the Iraqi countryside. Ruined buildings dominate towns and cities. Many were blown to pieces by shells tipped with depleted uranium, a material that the US and Britain say poses no long-term health or environmental risks. But many Iraqis, and a growing band of scientists, are not so sure. Last week, the UN Environment Programme (UNEP) announced it wanted to send a scientific team into Iraq as soon as possible to examine the effects of depleted uranium (DU). People’s fears that DU leaves a deadly legacy must be addressed, says UNEP. Some scientists go further. Evidence is emerging that DU affects our bodies in ways we do not fully understand, they say, and the legacy could be real.
DU is both radioactive and toxic. Past studies of DU in the environment have concluded that neither of these effects poses a significant risk. But some researchers are beginning to suspect that in combination, the two effects could do significant harm. Nobody has taken a hard look at the combined effect of both, says Alexandra Miller, a radiobiologist with the Armed Forces Radiobiology Research Institute in Bethesda, Maryland. “The bottom line is it might contribute to the risk.” She is not alone. The idea that chemical and radiological damage are reinforcing each other is very plausible and gaining momentum, says Carmel Mothersill, head of the Radiation and Environmental Science Centre at the Dublin Institute of Technology in Ireland. “The regulators don’t know how to handle it. So they sweep it under the carpet.”
A by-product of the uranium enrichment process, DU is chemically identical to natural uranium. But most of the 235 isotope has been extracted leaving mainly the non-fissionable 238 isotope. It is used to make the tips of armour-piercing shells because it is extremely dense: 1.7 times as dense as lead. Also, unlike other heavy metals that tend to flatten, or mushroom, upon impact, DU has the ability to “self-sharpen” as material spread out by the impact ignites and burns off as the munition pierces its target.
During the Gulf war in 1991, the US and Britain fired an estimated 350 tonnes of DU at Iraqi tanks, a figure likely to be matched in the course of the current conflict. In the years since then, doctors in southern Iraq have reported a marked increase in cancers and birth defects, and suspicion has grown that they were caused by DU contamination from tank battles on farmland west of Basra. As the Pentagon and the Ministry of Defence point out, this claim has not been substantiated. Iraq did not allow the World Health Organization to carry out an independent assessment. Given its low radioactivity and our current understanding of radiobiology, DU cannot trigger such health effects, the British and American governments maintain.
But what if they are wrong? Though DU is 40 per cent less radioactive than natural uranium, Miller believes that its radiological and toxic effects might combine in subtle, unforeseen ways, making it more carcinogenic than thought. It’s a controversial theory, but one for which Miller has increasing evidence. Uranium is “genotoxic”. It chemically alters DNA, switching on genes that would otherwise not be expressed. The fear is that the resulting abnormally high activity in cells could be a precursor to tumour growth.
But while the chemical toxicity of DU is reasonably well established, Mothersill points out that the radiological effects of DU are less clear. To gauge the risk from low-dose radiation, researchers extrapolate from tests using higher doses. But the relationship between dose and effect is not linear: at low doses radiation kills relatively fewer cells. And though that sounds like good news, it could mean that low radiation is having subtle effects that go unnoticed because cells are not dying, says Mothersill.
Miller has found one way this may happen. She has discovered the first direct evidence that radiation from DU damages chromosomes within cultured cells. The chromosomes break, and the fragments reform in a way that results in abnormal joins (Military Medicine, vol 167, p 120). Both the breaks and the joins are commonly found in tumour cells.
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