Depleted Uranium (DU) is a highly toxic and mildly radioactive substance, which is a by-product that is produced when Uranium is being turned into fuel for both nuclear power stations, and nuclear bombs. This waste material has recently been packed into bombs by Coalition and NATO forces, and dropped widely across Iraq, Afghanistan and the Balkans, contaminating the land and population for hundreds, if not millions, of years.

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 for bombs and power plants - 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: 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/secondary nuclear fission process.