WIKIMEDIA COMMONS, PETR ADAMEK
Japanese officials underestimated the amount of radiation released from the Fukushima Daiichi power plant after March's devastating earthquake and tsunami, according to a recently-published report analyzing data from a global array of sensors and detectors. In June, the Japanese government released a report stating that 1.5×1016 bequerels (Bq) of caesium-137—a harmful radioisotope that was released in large amounts from the Chernobyl disaster in 1986—and 1.1×1019 Bq of xenon-133, which does not pose a serious health risk as it's not absorbed by the body or the environment, had spewed from the crippled power plant. But the new report, submitted and available for open peer review in Atmospheric Chemistry and Physics, revises those totals to almost twice the official estimate, calculating a release of 3.5×1016 Bq caesium-137 and 1.7×1019 Bq of xenon-133.
The new findings are based on reading from dozens of sensors positioned within Japan and around the globe. Andreas Stohl, an atmospheric scientist with the Norwegian Institute for Air Research in Kjeller and first author on the paper, told Nature that the larger data set his team used to generate their estimates is likely the reason that they're higher than the official Japanese numbers. For example, the Japanese government's calculations did not take into account clouds of radioactive particles that blew out over the Pacific Ocean in the aftermath of the accident.
For detailed coverage of the nuclear disaster and its effects on people, wildlife, and the environment, see our Fallout at Fukushima series.