Duncan Graham-Rowe, with Rob Edwards (New Scientist, 15 April 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."
Read "Before the dust settles", the New Scientist editorial on this story here.
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.
More crucially, she has recently found that DU radiation increases gene activity in cultured cells at doses of DU not known to cause chemical toxicity (Molecular and Cellular Biochemistry, in press). The possible consequences are made all the more uncertain because no one knows if genes switched on by DU radiation enhance the damage caused by genes switched on by DU's toxic effects, or vice versa. "I think that we assumed that we knew everything that we needed to know about uranium," says Miller. "This is something we have to consider now when we think about risk estimates."
Britain's Royal Society briefly referred to these synergistic effects in its report last year on the health effects of DU munitions. "There is a possibility of damage to DNA due to the chemical effects being enhanced by the effects of the alpha-particle irradiation." But it makes no recommendations for future research to evaluate the risks.
The bystander effect
Miller points to another reason to be concerned about DU: the so-called "bystander effect". There is a growing consensus among scientists that radiation damages more than just the cells it directly hits. In tests using equipment that allows single cells to be irradiated by individual alpha particles, gene expression increases both in irradiated cells, and in neighbouring cells that have not been exposed. "At high doses, 'bystander' is not an issue because you are killing so many cells. But at low doses that's not really true," says Miller. There is a danger that experiments not specifically looking for this effect could miss an important source of damage.
A body of research has also emerged over the past decade showing that the effects of radiation may not appear immediately. Damage to genes may be amplified as cells divide, so the full consequences may only appear many generations after the event that caused it.
And while the chemical toxicity of DU itself is more clear-cut, the possibility remains that there may still be some unforeseen synergistic effects at a genetic level. Other heavy metals, such as tungsten, nickel and cobalt are similarly genotoxic. When Miller and her team exposed human cells to a mixture of these metals, significantly more genes became activated than when the cells were exposed to the equivalent amount of each metal separately (Molecular and Cellular Biochemistry, in press).
Miller and Mothersill say that recommended safe radiation limits are often based on the idea that only irradiated cells will be affected, and ignore both the bystander effect and the possible amplification over the generations. "Nothing should be written in stone when it comes to risk assessment," agrees Michael Clark at Britain's National Radiological Protection Board. But even if there were a case for re-evaluating the dosimetry for low-dose radiation, he says we should be cautious of the significance of Miller's lab-based research. "An in vitro effect is not a health effect."
Also, says Clark, everyone has traces of natural uranium in their bodies. "If there was some sort of subtle low-dose effect I think we would have seen it," he says. Because none has shown up in epidemiological studies, it seems unlikely there are any health effects associated with DU, which is less radioactive. But Miller is not convinced. While most people have small amounts of uranium in their bodies, she says no studies have been done to see whether this contributes to cases of cancer in society at large.
The military tends to dismiss such hazards as being of only theoretical significance, at least when it comes to civilians. According to the Pentagon, the only risk of exposure is during combat, when DU shells hit hard targets and the metal ignites. This creates clouds of uranium oxide dust that can be breathed in. But heavy oxide particles quickly settle, it says, limiting the risk of exposure. "A small dust particle is still very heavy," says Michael Kilpatrick of the US Deployment Health Support Directorate. "It stays on the ground."
That sounds reassuring until you read UNEP's latest report on DU left over from conflicts in former Yugoslavia in the mid-1990s. Last month, a team of experts collaborating with the International Atomic Energy Agency, WHO and NATO concluded that DU poses little risk in Bosnia although it can still be detected at many sites. Just 11 tonnes was fired in that conflict.
But evidence that DU may be moving through the ground and could contaminate local water supplies should be investigated further, UNEP says. And on rare occasions, wind or human activity may raise DU-laden dust that local people could inhale. The Royal Society admits that localised areas of DU contamination pose a risk, particularly to young children, and should be cleared up as a priority. They also recommend the environmental sampling of affected areas (see Royal Society Reports on DU, 2002", below).
Such evidence is partly why UNEP is keen to study DU fired during the present conflict in Iraq. Assessments in former Yugoslavia were made up to seven years after DU weapons were used, UNEP admits, and a more immediate study in Iraq would give us a much better understanding of how DU behaves in the environment. Any hazards such a study identifies could be dealt with immediately, says UNEP. And even now, an investigation in Iraq could reveal risks remaining from DU fired during the Gulf war in 1991.
Veterans show ill effects
Cracks are also appearing in the argument that DU munitions have not proven harmful even to troops. In the 1991 war, more than 100 coalition troops were exposed to DU after being accidentally fired on by their own forces. The majority inhaled uranium oxide, while the rest suffered shrapnel injuries. Some still have DU in their bodies. Britain and America point out that none has developed cancers or kidney problems, as might have been expected if DU posed a long-term danger.
But researchers at the Bremen Institute for Prevention Research, Social Medicine and Epidemiology in Germany have found that all is not well with the veterans. Last month they published results from tests in which they took blood samples from 16 of the soldiers, and counted the number of chromosomes in which broken strands of DNA had been incorrectly repaired. In veterans, these abnormalities occurred at five times the rate as in a control group of 40 healthy volunteers (Radiation Protection Dosimetry, vol 103, p 211). "Increased chromosomal aberrations are associated with an increased incidence of cancers," says team member Heike Schröder. The damage occurred, they say, because the soldiers inhaled DU particles in battle.
The NRPB is unconvinced. "It is possible that exposure to significant amounts of DU could cause excess chromosome aberrations, but this study has technical flaws," says Clark. "There are no proper controls to compare results with soldiers who were not exposed to DU. And some of the reported excess aberrations are well known to be linked to chemicals rather than radiation."
Tough decision to make
Deciding whether DU is to blame will be tough. Independent research may confirm that rates of cancer have increased in the Iraqi population. But the Iraqi government has used chemical weapons on its own people that can produce the same outcome, and it is impossible to know for sure who may have been exposed. Soldiers may similarly have been exposed to chemicals in 1991. The only way to resolve the issue is more research, says Dudley Goodhead, director of Britain's Medical Research Council's Radiation and Genome Stability Unit at Harwell, near Oxford. "It's something important that needs to be explained."
Miller admits it is entirely possible that DU contamination is safe. But many of the scientific investigations into DU have only just begun, and their results will be long coming. "None of this has been looked at or even thought about it until the last few years," she says. As the dust begins to settle in Iraq, it remains to be seen when the ravages of war will end.
Royal Society reports on DU, 2002 - Conclusions
" Most soldiers have a negligible risk of dying of cancer caused by radiation from battlefield DU. It will be undetectable above the risk of dying from cancer over a normal lifetime. Soldiers should not suffer adverse effects on the kidney or other organs.
" A few soldiers, for instance those who clean up vehicles struck by DU, may have an excess risk of lung cancer and may develop short-term kidney damage.
" People living in areas where DU was deployed have a negligible risk of developing cancers as a result of inhaling DU resuspended in the air. But it is uncertain how much DU is inhaled in years following a conflict. Most people should not suffer any effects on kidney function from inhaled DU.
" Ingestion of DU from contaminated water and food, and from soil, will be highly variable and may be significant in some cases: for example, children playing in areas where DU shells have impacted.
Royal Society reports on DU, 2002 - Recommendations
" Long-term epidemiological studies of soldiers exposed to DU, and environmental sampling, particularly of water and milk, should be undertaken. Information about DU levels should be given to local populations, and contaminated areas cleaned up.
" British veterans exposed to high levels of DU should be identified and independently evaluated. An independent study of anecdotal reports of death and illness in US veterans linked to DU is required.
" In any future conflict using DU munitions, tests of kidney function should be completed on soldiers as soon after exposure as practical.
" Better estimates of DU levels in the air around tanks, and models of DU oxide behaviour during impact, are required. More information is needed on the bioavailability of DU and titanium products from munitions, and whether these concentrate in plants and animals.
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