Particles can also deposit on vegetables or on grass eaten by cows that may later provide milk and meat for human consumption. The alpha radiation travels only about a quarter of an inch in air and cannot penetrate the skin. Therefore, if plutonium remains outside the body, it is generally not harmful. Plutonium is very toxic if it enters into the body because the alpha radiation can damage living tissue. Human exposure occurs mainly by breathing contaminated air or ingesting contaminated food or drink.
Breathing is generally the route of most concern.
When plutonium particles are inhaled and lodge in lung tissue, they continue to give off radiation internally. They can remain in the lungs or enter the gastrointestinal tract and the bloodstream. About 80 percent of the plutonium that enters the bloodstream goes either to the liver, bone or bone marrow, where it is retained for years, damaging tissue nearby. That damage may later develop into cancer. Common forms of plutonium do not dissolve significantly in water or body fluids, so little ingested material is actually absorbed into the blood from the gastrointestinal tract.