It's not just Fukushima, though that may be enough. The northern hemisphere especially had been inundated with radioactive fallout by atmospheric nuclear weapons testing from 1950 to 1963. The Nevada testing area alone produced 1200 nuclear explosions that emitted radioactive particles across the USA.
The Chernobyl incident in 1986 affected hundreds of thousands throughout Europe, Scandinavia, and Russia. The boom in nuclear reactor power plants had already started and was constantly increasing, along with considerable radiation leaking.
A 1996 international court interpretation of international treaties opened the door for widespread use of depleted uranium (DU) that had been prohibited for use as ammunition projectiles that could pierce armor. Tons of DU ammunition has been used in Bosnia andthe Mideast since, leaving a radioactive mess that will last for life times.
The point of this lengthy introduction is to make you aware that we have been and continue to be immersed in excess radioactivity from several sources. Fukushima has added more dangerous radioactivity, but corporate-government-media officials deny its dangers.