LONDON Both the United Nations Environment Programme (UNEP) and the World Health Organization (WHO) are now preparing studies — due to be published in a few weeks' time — which should deepen our knowledge of the impact of depleted uranium (DU) munitions in Kosovo.

But the studies still won't answer the most important question: what is the measureable impact of DU weapons on human health? For that, far more research will be needed, unless we are to rely on theoretical estimates and extrapolations.

In preparation for that research, last week the WHO European Office in Copenhagen sent four experts, including an epidemiologist, for 10 days to Kosovo to determine how to make an in-depth study of the impact of battlefield DU — and other substances. "It's an initial fact-finding mission," a WHO spokesperson told BioMed central. The experts will propose how to collect information on exposure to DU — and other wartime toxic substances; how to verify the existing Kosovan data on cancer and leukaemia incidence, and other conditions which might be related to environmental exposure to DU and other toxic agents; and how best to identify potential health risks which may require medical monitoring and follow-up.

Simultaneously, WHO is preparing a 70-page review of existing research relevant to the health impact of DU, which should be published in February. It is expected to make proposals for further research to help improve the assessment of health risks. Present weaknesses in our knowledge, according to WHO, include the chemical and physical form, leaching and subsequent environmental cycling of DU and its oxides; and the linking of such data to knowledge of the physiological behaviour of uranium compounds. WHO says it will be important to clarify the degree of kidney damage caused by uranium exposure, and to improve understanding of the reproductive, mutagenic and carcinogenic properties of uranium and depleted uranium.

In its existing published information on DU, however, WHO already claims that "in war zones, the inhalation and ingestion of DU-contaminated dust, even under extreme conditions… has been calculated to result in a radiation exposure of less than about 10 millisieverts (mSv). This represents about half the annual dose limit for radiation workers. Such an exposure is thought to result only in a small proportional increase in the risk of leukaemia, of the order of 2% over the natural incidence." Insoluble uranium oxide dust is believed to be the main battlefield remnant of the use of DU weapons.

UNEP has also had a large team in Kosovo, taking soil and other samples at 11 sites for analysis in five laboratories around the world, which will feed into the WHO analysis by giving precise information on exposure. "At the moment it's very hard to say this or that effect will occur, as we don't know the exposure levels," said WHO. UNEP's study, which should be published in March, will feed directly into this WHO research.

UNEP, in fact, produced a lengthy theoretical 'desk study' last year of the possible impact of DU in Kosovo, concluding clearly that… "A thorough review of the effects on health of exposure to DU in the medium and long term perspective is required."

In the UK last week, the Ministry of Defence (MoD) published a mass of documents dating from 1979 — when the use of DU in anti-tank weapons was first considered — to the present, which make estimations of exposure and health risk. These documents include a now infamous report of March 1997, said by the MoD to have been written by "a newly appointed Specialist Registrar (a training grade)," which warns of increased risk of cancers from DU weapons. But the MoD goes out of its way to rubbish this report, indicating a series of technical errors in its nuclear physics and its estimation of medical risks.

What is, however, lacking in all of this material, and will still be lacking when the UNEP and WHO teams report, is any precisely relevant and systematic epidemiology on DU. The WHO report will describe the literature, but it will almost certainly contain studies of uranium miners and millers, plus observations from Hiroshima, Nagasaki and Chernobyl, which will have to be extrapolated to completely different circumstances. There are few data on exposure to DU in battlefield and post-battle conditions. As UNEP reported last year: "Most effects and the majority of results that are found in the literature are related to studies in animals, usually carried out at high dose levels. There is only limited evidence for health effects in humans related to exposure to depleted uranium."

At present, however, the theoretical risk of DU does genuinely seem to be small, which would suggest that if there do prove to significant increases in the incidence of leukaemia or other health problems among troops in Kosovo, these must be caused either by previously unknown chemical or radiological risks of DU — which would be a scientific discovery — or by other agents used in the conflict.

One matter to consider would be whether the DU used in Kosovo may not have been simple waste from uranium enrichment, a process that changes the isotopic composition of uranium (decreasing the amount of U²³⁵), but also results in material that could be contaminated with other radioactive elements and isotopes. UNEP has, indeed, already detected one such isotope (U²³⁶), but in such small proportions that it is not expected to raise the radioactivity of DU more than a couple of percent.

But if there is a health problem in Kosovo — and the Gulf — perhaps it is not due to DU at all. This was one possible conclusion from the controversy that boiled over in the British Medical Journal in 1999, after a news reporter claimed that "there is considerable evidence… to back the argument that the military use of depleted uranium during the Gulf War… has caused cancer rates and congenital diseases to increase dramatically in Iraq and among Gulf War veterans." BMJ Editor Richard Smith responded to a large postbag of criticism by raising the possibility that the real issue might not be DU but "poisons used by the Iraqi Government against the Kurds."

Meanwhile WHO, controversially, is seeking funding to send a team to Iraq at President Saddam's request, so the relevance of DU to 'Gulf War Syndrome' might be better understood. "Iraq made an official request on 15 January that we look into potential health effects of DU on the population," a WHO spokesperson told BioMed central. "WHO is eager to help on anything that would have effects on human health… We are working already with the Iraqis on many health issues, including setting up cancer registry." But extrabudgetary funds would be required to the work, she said.