A crisis was unleashed when the devastating earthquake measuring 9.0 on the Richter scale struck.

The disaster, which killed 19,000, sent huge waves 20 metres high and wiped out cooling systems at the power plant. And experts fear radiation levels could spark a string of genetic mutations after changes were found in butterflies.

Many pale grass blue butterflies born since the disaster have suffered abnormalities, including smaller wings and damaged eyes. Scientists fear the fallout from the catastrophe could also harm other animals and people. Radiation expert Kunikazu Noguchi said: "This is just one study, we need more studies to verify the entire picture of the impact on animals. “The case of Fukushima plant workers is a different story. Some of them have already topped exposure limits. It is necessary to strictly monitor them to see if there is any impact."