Health effects of nuclear weapons testing.

Nuclear weapons were virtually unknown to the world before Aug 6, 1945, when the first atomic bomb was used against Japan in Hiroshima and the second 3 days later in Nagasaki. The 70th anniversary of this event is marked in the Lancet Series From Hiroshima and Nagasaki to Fukushima. 2, 3 The legacy of the atomic bomb extended far beyond Japan with atomic weapons testing programmes conducted worldwide for the next three and a half decades. Just 3 weeks before the atomic bomb attacks on Japan, the first nuclear explosion in history had taken place in secrecy in the desert of New Mexico, USA, when scientists working for the Manhattan Project tested the experimental nuclear bomb codenamed Trinity. That test ushered in an era of atmospheric nuclear testing by the USA, the USSR, the UK, China, and France that continued at sites around the world until 1980 (figure). During those years, more than 500 atomic weapons were tested in the atmosphere with a total explosive force equal to about 20 000 Hiroshima bombs. A detailed picture of the late effects of exposure to ionising radiation, namely increased risk of cancer, would not become well understood until years after the start of atmospheric nuclear weapons testing.