Plutonium in the environment

Since the mid-20th century, plutonium in the environment has been primarily produced by human activity. The first plants to produce plutonium for use in cold war atomic bombs were at the Hanford nuclear site, in Washington, and Mayak nuclear plant, in Chelyabinsk Oblast, Russia. Over a period of four decades, "both released more than 200 million curies of radioactive isotopes into the surrounding environment – twice the amount expelled in the Chernobyl disaster in each instance".

The majority of plutonium isotopes are short-lived on a geological timescale, though it has been argued that traces of the long-lived ²⁴⁴Pu isotope still exist in nature. This isotope has been found in lunar soil, meteorites, and in the Oklo natural reactor. However, one paper on marine sediments for plutonium in marine sediments, atomic bomb fallout is responsible for 66% of the ²³⁹Pu and 59% ²⁴⁰Pu found in the English Channel, while nuclear reprocessing is responsible for the majority of the ²³⁸Pu and ²⁴¹Pu present in the Earth's oceans (nuclear weapons testing is only responsible for 6.5 and 16.5% of these isotopes respectively).