The use of DU in munitions is controversial because of concerns about potential long-term health effects. Normal functioning of the kidney, brain, liver, heart, and numerous other systems can be affected by exposure to uranium, a toxic metal. It is only weakly radioactive because of the long radioactive half-life of (4468 million years) and the low amounts of (half-life about 246,000 years) and (half-life 700 million years). The biological half-life (the average time it takes for the human body to eliminate half the amount in the body) for uranium is about 15 days.