Radiation effects from the Fukushima Daiichi nuclear disaster PBq of caesium-137. In May 2012, TEPCO reported that at least 900 PBq had been released "into the atmosphere in March last year [2011] alone" up from previous estimates of 360-370 PBq total. The primary releases of radioactive nuclides have been iodine and caesium; strontium and plutonium have also been found. These elements have been released into the air via steam; and into the water leaking into groundwater or the ocean. The expert who prepared a frequently cited Austrian Meteorological Service report asserted that the "Chernobyl accident emitted much more radioactivity and a wider diversity of radioactive elements than Fukushima
Caesium-137 limits, but some areas that are currently less than 5 mSv/year may be decontaminated, allowing 22,000 residents to return. Caesium-137 in the environment is substantially anthropogenic (human-made). Caesium-137 is produced from the nuclear fission of plutonium and uranium, and decays into barium-137. Before the construction of the first artificial nuclear reactor in late 1942 (the Chicago Pile-1), caesium-137 had not occurred on Earth in significant amounts for about 1.7 billion years. By observing the characteristic gamma rays emitted by this isotope, one can determine whether the contents of a given sealed container were made before or after the first atomic