Global transport of 131I and 137Cs released into the atmosphere from the Fukushima nuclear accident

An atmospheric dispersion model was used to assess the global transport and deposition of ¹³¹I and ¹³⁷Cs released into the air during the Fukushima accident in 2011. Simulations results showed that the radionuclides traveled eastward across the Pacific by the westerlies. The radioactive plume estimated to reach the U.S. West Coast approximately 5 days after the accident, Europe after about 12 days, and Mongolia and China after around 16 days. It subsequently dispersed across the entire Northern Hemisphere approximately within 17 days. The calculated concentrations of radionuclides were generally consistent with observations, including monitoring data from CTBTO and Korea. A substantial portion of the released radionuclides was deposited into the Pacific Ocean, with about 54% of ¹³¹I and 76% of ¹³⁷Cs settling on the sea surface. Further analysis confirmed that the ¹³⁷Cs detected in seawater samples from the central Pacific and U.S. West Coast in April and May 2011, originated from atmospheric deposition onto the ocean rather than direct release into the sea from the Fukushima accident.