Nuclear leak linked to mutations
Radiation from the leaking Fukushima nuclear plant following last year's tsunami caused mutations in some butterflies and damaged the local environment though humans seem relatively unaffected, researchers say.
The mutations - including dented eyes and stunted wings - are the first evidence that the radiation has caused genetic changes in living organisms. They are likely to add to concerns among ordinary people about potential health risks among humans though there is no evidence of it yet. Scientists say more study is needed to link human health with the Fukushima disaster.
The catastrophic meltdowns in three reactors of the Fukushima Dai-ichi power plant after it was damaged by the 9.0-magnitude earthquake and tsunami on March 11, 2011 prompted a public backlash against nuclear power, and forced the government to reassess resource-scarce Japan's entire energy strategy.
But the most visible example of the radiation's effect was claimed by a group of Japanese researchers who found radical physical changes in successive generations of a type of butterfly, which they said was caused by radiation exposure. They also said that threat to humans - a much larger and longer-lived species - remains unclear.
"Our findings suggest that the contaminants are causing ecological damage. I do not know its implication to humans," said Joji Otaki, of the University of the Ryukyus in Okinawa, a member of the team that conducted the research.
A separate study, released this week, found very low levels of radioactivity in people who were living near the Fukushima plant when it suffered the meltdowns.
The paper, published in the Journal of the American Medical Association, measured caesium levels in 8,066 adults and 1,432 children and found average doses of less than one millisievert, which are considered safe. It was the first such study measuring internal exposures to caesium in a large number of people from the disaster.
The research shows contamination decreased over time, particularly among children, in part because more precautions were taken with their food, water and outdoor activity.
So far, the actual radiation doses inflicted just after the accident are not exactly known, though exposure is thought to be very small, said David Brenner, a radiation physicist at Columbia University, who was not part of the research.