The Japanese government estimated that 15,000 terabecquerels of cesium were released from the damaged Fukushima nuclear plant, reports the Telegraph, yet the new study says the real figure is more than twice that: 36,000 terabecquerels, or 42 percent of the total radiation released in the Chernobyl disaster.
Initial measurements in Japan did not factor in the radiation that was blown out to sea, the researchers say. Based on data from radiation monitoring stations across Japan, Europe and North America, they believe only around 20 percent of the total cesium emissions fell over Japanese territory.
The rest was carried over the Pacific Ocean, with around 2 percent landing in other countries. The possible health risks of the radiation are unclear. Cesium-137 is linked to cancer and can remain in the environment for 30 years.
The impact of the disaster could have been much worse, however, lead researcher Andreas Stohl told Nature News.
In the days following the accident, clouds of radiation blew back over Japan, but fortunately they passed over Tokyo and other densely populated areas without any precipitation. If it had rained over the cities, the population would have been exposed to far greater quantities of radiation, Stohl said.