The Fukushima Daiichi nuclear plant in the Fukushima prefecture of Japan was hit by first a massive earthquake, then a devastating tsunami, on March 11, 2011. It was immediately recognized as one of the worst nuclear accidents in world history, alongside Chernobyl and Three Mile Island. According to a team of scientists, the radiation spewed by the crippled plant affected every person on earth. But don’t panic – you got only about a single X-ray’s worth. 
To be sure, the less radiation you have over your lifetime, the better. There is no “good” nuclear radiation. Still, considering how touch-and-go the situation has been and continues to be (fire crews finally extinguished a 12-days-long wildfire in Fukushima’s no-go zone, sparking fresh radiation fears), you and I are pretty fortunate to have gotten away with so little damage.
According to the results of a global survey of the disaster’s effects, conducted by a team of scientists from the Norwegian Institute for Air Research, the average person received about 0.5 millisieverts of radiation from the accident. Those who lived in the immediate vicinity of the Fukushima Daiichi plant received about 1 to 5 millisieverts. Radiation sickness develops at approximately 1,000 millisieverts. 
Thousands upon thousands of people died as a result of the earthquake and subsequent tsunami; but, shockingly, no one died as a direct result of the explosion in Reactor No. 1 and meltdown that occurred in a total of three of the plant’s reactors.
The main source of the radiation was the radioactive element cesium-137.
Nikolas Evangeliou, a member of the research team, said:
“More than 80 per cent of the radiation was deposited in the ocean and poles, so I think the global population got the least exposure. What I found was that we got one extra S-ray each.” 
On average, Americans get about 6.2 millisieverts per year, according to the U.S. Nuclear Regulatory Committee. The majority of that radiation comes from natural background radiation, or naturally occurring sources such as radon in the air and in cosmic rays. The rest comes from medical procedures, industrial sources, and other man-made sources. 
There is debate as to whether there has been a Fukushima-related increase in cases of thyroid cancer. It’s possible many of those cases are the result of over-diagnosis spurred by fears in the aftermath of the crisis.
It’s also possible that authorities are covering up the truth. The 3.11 Children’s Fund for Thyroid Cancer, a support group for children with thyroid cancer, discovered after auditing medical bills that a 4-year-old underwent thyroid surgery at a state-run university. The school claimed it had never treated anyone under 5 for thyroid cancer.
The damage done to plants and other animals is more visible to the naked eye, however. Evangeliou says increased levels of radiation around Fukushima have been linked to declines in bird populations there between 2011 and 2014. 
“There have also been reports of declines in other species such as insects and some mammals.” 
 Raw Story
 New Scientist