Uranium
Uranium is not very dangerous by itself, in its natural state. However, if used properly, it can be extremely devastating. Of course, I'm sure you all already know this.
I'm just trying to make a point that you shouldn't worry about terrorists putting Uranium in the water supply or air or anything like that. For middle eastern countries, Uranium is scarce and is a precious commodity. If they were going to use it against anyone, it would be in the form of a radioactive attack. Uranium isn't really dangerous until it is blasted with neutrons. I would be more worried about something like Strontium-90 getting in the water supply than Uranium.
Personally, I am worried about every little bit of Uranium that Iraq *might* get its hands on. It doesn't take much to make a powerful weapon. If I remember correctly, I read somewhere that the nuclear attacks on Hiroshima and Nagasaki used about 0.5% of the potential power in the bombs. That was because the technology wasn't sufficiently advanced to be any more efficient. These days, I'm sure that the efficiency of nuclear weapons has gone up dramatically, so it would take far less fissile material to make a bomb with the power of the Hiroshima and Nagasaki bombs.
Just so that you know, it isn't that hard for middle eastern countries to get nuclear technology. Pakistan got it simply by lying to Canada (yes, Canada is responsible for Pakistan's nukes). And before anyone starts to rag on Canada, I am Canadian and am very ashamed of my government's mistake.