Around 12 percent of pale grass blue butterflies that were exposed to nuclear fallout as larvae immediately after the tsunami-sparked disaster had abnormalities, including smaller wings and damaged eyes, researchers said.
The insects were bred in a laboratory outside the fallout zone and 18 percent of their offspring displayed similar problems, said Joji Otaki, associate professor at Ryukyu University in Okinawa, southwestern Japan.
The figure rose to 34 percent in the third generation of butterflies, he said, even though one parent from each coupling was from an unaffected population.
The researchers also collected another 240 butterflies in Fukushima in September last year, six months after the disaster. Abnormalities were recorded in 52 percent, which was “a dominantly high ratio”, Otaki told AFP.
The results of the study were published in Scientific Reports, an online research journal from the publishers of Nature.
Otaki later carried out a comparison test in Okinawa exposing unaffected butterflies to low levels of radiation, with the results showing similar rates of abnormality, he said.
“We have reached the firm conclusion that radiation released from the Fukushima Daiichi plant damaged the genes of the butterflies,” Otaki said.
The quake-sparked tsunami of March 2011 knocked out cooling systems at the Fukushima Daiichi nuclear power plant, causing three reactors to go into meltdown in the world’s worst atomic disaster for 25 years.
The findings will raise fears over the long-term effects of the leaks on people who were exposed in the days and weeks after the accident, as radiation spread over a large area and forced thousands to evacuate.
There are claims that nuclear exposure effects on successive generations have been observed among people living in Hiroshima and Nagasaki, where the US dropped atomic bombs in the final days of World War II.
But Otaki warned it was too soon to jump to conclusions, saying his team’s results on the Fukushima butterflies could not be directly applied to other species, including humans.
He added he and his colleagues would conduct follow-up studies including similar tests on other animals.
No one is officially recorded as having died as a direct result of the Fukushima disaster, but many who fled the area and those who remain, including workers decommissioning the crippled plant, worry about the long-term effects.
Scientists have warned it could be decades before it is safe for some people to return to their homes.
