UK working party estimates small association between depleted uranium and lung cancer

LONDON The association between depleted uranium in weapons and lung cancer is very small even in people exposed to high levels, according to an estimate published by an independent working group from The Royal Society this week. But the initiative has highlighted the lack of hard data from soldiers exposed to depleted uranium during conflicts in the last decade. 'The health hazards of depleted uranium (DU) munitions Part 1' is the first of two reports being prepared by The Royal Society in an attempt to review the scientific evidence available on this highly contentious issue. The aim was to assess the amounts of DU to which soldiers could be exposed on the battlefield and to calculate the risks of radiation from what has been observed previously in epidemiological studies. A second report, to be published later this year, will address the risks from toxic poisoning and environmental effects of DU.The issue has provoked a great deal of debate about the possible health effects of DU munitions, which were deployed in the Gulf War in 1991 and in the Balkans in the late 1990s. Depleted uranium is derived from natural uranium mined from the earth's crust. Uranium is made up of three isotopes – U238, U235 and U234, which decay to other radioactive elements and ultimately to stable non-radioactive isotopes of lead. Uranium isotopes emit alpha particles during decay, with high energy but poor penetration. This means that uranium potentially poses a radiation hazard to tissues in close proximity if it is absorbed. Depleted uranium has only two-thirds (60%) of the radioactivity of natural uranium, having much of its highly radioactive isotopes — U234 and U235 — removed.The Royal Society working group estimated the potential intake of DU for different battlefield scenarios. These ranged from high exposure (Level I; for example personnel in a tank hit by a DU penetrator, affected by DU inhalation or shrapnel wounds), to medium (Level II; soldiers working in or on DU-contaminated vehicles) and low (Level III; other exposures, such as being downwind of aerosols containing DU). They then used mathematical models, based on recommendations from the International Commission on Radiological Protection (ICRP), to estimate how much DU could reach different organs and tissues and then calculated the associated risk of cancer.Once a radioactive material — such as a DU particle — reaches the inside of the human body, it will irradiate the tissues surrounding the spot where it is embedded. Chair of the working party Professor Brian Spratt commented: "We thought that the main risk of DU was associated with inhalation of particles so we concentrated on this." Inhalation of insoluble uranium dioxide dust leads to accumulation in the lungs with very slow clearance.The working group calculated that the best estimate of the additional lifetime risk of fatal lung cancer in soldiers with high-level exposure was 1.2 per thousand, representing a 2% increase. The risk fell to 2.5 per 100,000 for medium exposure and 3.7 per 10 million for low-level DU exposure. The worst estimate — calculated by assuming very high levels of DU inhalation — gave an increased risk of lung cancer of 6.5 per 100 for high-level exposure, representing a doubling of the lung cancer rates in the normal population. The risk of leukaemia and other cancers was estimated to be extremely low.The estimates are in line with previous reviews of uranium exposure and cancer risk in people working with uranium. This is hardly surprising, as they were based on the same models of occupational exposure. The US Centers for Disease Control and Prevention and the Agency for Toxic Substances and Disease Registry concluded that there was no difference in the rate of lung cancer between workers who were occupationally exposed to uranium and control populations. A review of several studies in uranium miners attributed the increase in lung cancer that was observed to radon rather than to uranium. "A second review by the US National Academy of Sciences Institutes of Medicine evaluated existing epidemiological studies more rigorously but concluded that there was limited/suggestive evidence of no association between exposure to uranium and lung cancer at cumulative internal dose levels lower than 200mSv or 25cGy," commented Melissa McDiarmid, Professor of Medicine at the University of Maryland School of Medicine, Baltimore, writing in a recent editorial in the British Medical Journal. The review concluded that there was inadequate or insufficient evidence to determine whether an association does or does not exist with uranium exposure.Based on The Royal Society findings, Professor Spratt said: "The greatest radiological risk associated with DU exposure is lung cancer, but this is very low for soldiers except for those with the highest level of exposure." No soldiers from the UK are thought to have suffered high-level exposure but some US troops were exposed to these levels. But, the report acknowledged that its findings were limited by being based only on modelling, rather than observations. The working party therefore suggested that more research is needed. In particular, it called for careful monitoring of soldiers exposed to DU weapons. The standard test for DU measures urine excretion of uranium.The Royal Society report was heavily criticised for its reliance on mathematical models derived from previous studies based on exposure of people working with uranium rather than with DU weapons. Malcolm Hooper, Chief Scientific Advisor to the Gulf War Veterans' Association, pointed out that the report failed to address other potential health effects of DU, such as on the immune system. Professor Spratt said that the report looked at cancer risk because models exist only for the carcinogenic effects of uranium, however he acknowledged the need to look at wider health effects.Hooper pointed out that veterans have never undergone urine tests for DU levels. Ten years ago, when the Gulf War occurred, there were no accurate methods to measure DU levels, but measurement techniques have become available in the last few years. He warned: "There has been no attempt to obtain direct data from troops who served in the Gulf or the Balkans – who are, essentially 'experimental animals' in which to study the effects of DU exposure." The report recommended that all UK veterans with high-level DU exposures should be identified and invited to participate in an independent evaluation programme.A spokesman for the Ministry of Defence confirmed that a detailed research programme of troops who served in the Gulf and the Balkans will begin later this year. The science of human DU exposure will then be able to progress from the realms of theoretical modelling to observational investigation.

UK working party estimates small association between depleted uranium and lung cancer

The association between depleted uranium in weapons and lung cancer is very small even in people exposed to high levels.

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