This contamination is the result of the routine releases, the fires and the 903 Area spill. Before 1945, plutonium was virtually nonexistent in the human environment. Then in the 1950s and 1960s, plutonium was released into the environment during atmospheric testing of nuclear weapons. Plutonium can now be found in very small amounts in the soil throughout the Northern Hemisphere because of fallout from the atmospheric testing. Plutonium has also been found in soil near nuclear weapons production plants such as Rocky Flats due to accidents and spills.
Plutonium remains radioactive in the environment for a very long time.
Plutonium decays by releasing small amounts of energy through fast-moving alpha particles. The radioactivity level of an isotope such as plutonium is determined by its half-life, which is the time it takes for half of an original quantity to decay. Plutonium particles may be released to the air where people may inhale them, or the particles may deposit on soil, plants and water. The plutonium particles landing on soil either attach to clays or stay near the soil surface where winds can pick them up and redistribute them. Plutonium particles can deposit on plants, but are not readily absorbed by the roots into the plants.