In simple terms, to make Nuclear fuel, natural Uranium must be enriched by separating the different Uranium atoms, with certain parts of the Uranium then being used as fuel for nuclear fission - the process which creates nuclear energy - and the leftovers are what we describe as 'Depleted Uranium'. When absorbed by humans and other living creatures, this Depleted Uranium is mildly radioactive, but highly toxic.

Here is a more insightful explanation about how Depleted Uranium is produced:

Natural Uranium is composed of mainly three types of Uranium atoms (also called isotopes). It is composed of approximately 99.27% Uranium-238 (U-238), 0.72% U-235 and 0.0055% U-234. For nuclear reactor fuel, and for nuclear bombs, it is necessary to have the level of U-235 in the Uranium as high as possible, and the enriched portion - which ultimately ends up as nuclear fuel - usually contains most of the U-235. The leftover portion, the Depleted Uranium, mainly consists of U-238, it has less than a third of the natural levels of both U-235 and U-234, and is about 60% as radioactive as natural Uranium, which is significantly less radioactive than the enriched Uranium.

Depleted Uranium can also be a waste product of reprocessed spent nuclear reactor fuel, and this kind can be distinguished by the presence of another Uranium atom, U-236. If reprocessed Uranium is present in DU, it may be considered much more dangerous to humans, with higher levels of radioactivity present, plus the possible inclusion of other harmful substances, which were produced/used during the original nuclear fission process.

Depleted Uranium is used by advanced military's due to it's armour piercing qualities, it's cost-effectiveness, and it's availability. The bombs which can be made from this cheap but highly dangerous substance, can get through any type of armour, or structure, and then explode outwards, thus vaporising everything in their wake. This creates the most effective of battlefield missiles, particularly against tanks and armoured vehicles, aswell as for levelling fortified or strong buildings. They have been used extensively in both Gulf War's, and in the former Yugoslavia, by Coalition and NATO forces respectively. For example, according to Time Magazine... "NATO aircraft rained more than 30,000 DU shells on Kosovo during the 11-week air campaign".

In the immediate areas where bombs have been used, there have been huge rises in cancer levels, and in the numbers of newborn children with strange deformities and conditions. Rises in related health issues usually begin to take place a few years after the bombs were let off, and contamination - and the high level of associated health problems - will remain for many generations in the affected areas, possibly even for hundreds of years. Similar levels of rises in similar cancers have been recorded amongst the returning US and UK soldiers which had been handling and firing these bombs during their time in Iraq and Kosovo, as have high levels of abnormalities and deformities in their subsequent newborn children. This collective rise in health conditions amongst ex-soldiers and their families, has been widely termed the 'Gulf War Syndrome'.

For a humans health to be affected by Uranium, it is believed that it must be absorbed through eating, drinking, or breathing it in, or through contact with the skin. The major issue with DU being dropped over Iraq, Afghanistan and the Balkans, is that when these bombs are set off over large population centres, they can contaminate large areas of land and air.

This is a list of health effects which have been associated with exposure to high levels of Uranium. Only those conditions which have been identified by testing on humans are included below, although there has been additional extensive animal testing which has identified other possible side-effects to Uranium exposure.