Depleted uranium (DU) is a waste product of the process used to enrich natural uranium ore for use in nuclear reactors and nuclear weapons. Compared to natural uranium which has a U-235 isotopic content of 0.7%, the isotopic content of U-235 in DU is partially depleted to about a third of its original content (0.2%).DU is extremely dense and therefore used in the tips of bullets designed to pierce armour plating. It may also be used in cruise missile nose cones and has been used in the armour of tanks. In addition to its density, DU is also used in military applications because of its relatively low price (e.g. in comparison with tungsten alternatives) and the fact that it is available in huge quantities. Due to the pyrophoric nature of uranium metal and the extreme flash temperatures generated on impact, particles of uranium oxides are formed. Studies have shown that a high percentage of these particles may be of 'respirable' size, i.e. particles that can be inhaled into the deep areas of the lungs. Concerns about the human health implications of exposure to DU are related to both its radiological and chemical properties. During and after the Kosovo conflict, there were regular media reports that DU had been used in military operations by NATO. Consequently, there are concerns amongst the people of Serbia and Kosovo regarding the possible post-conflict risks to human health and the environment. These concerns are also relevant for assessing the security of field staff from the UN and other international agencies. A U.S. Department of Defense news briefing on 3 May 1999 (see bibliography no:15), appeared to confirm that depleted uranium weapons had been used by U.S. forces in the Balkans. It was reported that DU shells had been fired from A-10 aircraft. However, it is not known whether U.S. forces fired cruise missiles that contained DU. It is also not known whether other NATO forces used DU weapons in the Balkans. The present state of knowledge regarding DU use in Kosovo and possibly in Serbia is that neither the quantity of DU weapons used, nor the locations of any targets hit by DU weapons, are known. At the time of writing, the BTF has not received any official document confirming whether or not DU was used during the conflict.