Lead is toxic because it aggressively replaces essential metals in the human body. In biochemical reactions, lead takes the place of substances such as zinc, calcium and iron in molecules and protein enzymes. This changes the shape of important molecules and obstructs their normal function.
Lead interference with calcium inhibits neurological function because it takes calcium's place in the electrical impulses of the brain. This blocks memory and can cause a permanent reduction in IQ. When lead binds with certain proteins in a child's body, the resulting chemical reactions cause growth and developmental delays. In adults, lead invasion in the body's protein molecules leads to conditions such as anemia, muscle malfunction, high blood pressure and infertility.