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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 the Hanford nuclear site, in Washington, and Mayak nuclear plant, in Chelyabinsk Oblast, Russia. Over a period of four decades,[1] "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."[2]
The majority of plutonium isotopes are short-lived on a geological timescale,[3] though it has been argued that traces of the long-lived 244Pu isotope still exist in nature.[4] This isotope has been found in lunar soil,[5] meteorites,[6] and in the Oklo natural reactor.[7] However, one study on plutonium in marine sediments indicates that the atomic bomb fallout accounts for 66% of the 239Pu and 59% 240Pu in the English Channel. In contrast, nuclear reprocessing contributes the majority of the 238Pu and 241Pu in the Earth's oceans, whereas nuclear weapons testing is responsible for only 6.5% and 16.5% of these isotopes, respectively.[8]
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