Mutant Butterflies Linked to Japan's Fukushima Disaster

Deformed butterflies near the Fukushima nuclear disaster — Severe genetic mutations were found in pale grass blue butterflies (*Zizeeria maha*) found near the Fukushima disaster, with so-called eclosion failure (left) in which the butterfly can't fight its way out of its cocoon, and bent wings (left). See more deformed butterfly images.

(Image credit: Hiyama et al, Scientific Reports)

One legacy of the Fukushima nuclear disaster last year has already become apparent through a study of butterflies in Japan: Their rate of genetic mutations and deformities has increased with succeeding generations.

"Nature in the Fukushima area has been damaged," said Joji Otaki, a professor at the University of the Ryukyus in Okinawa, who is the senior author of the new study.

The abnormalities, which the researchers traced to the radiation released from the nuclear power plant, include infertility, deformed wings, dented eyes, aberrant spot patterns, malformed antennas and legs, and the inability to fight their way out of their cocoons. The butterflies from the sites with the most radiation in the environment have the most physical abnormalities, the researchers found.

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The Tohoku earthquake and tsunami on March 11, 2011, cut off power to the Fukushima Daiichi plant, leading to meltdowns that released radionuclides including iodine-131 and cesium-134/137.The researchers combined laboratory and field studies to show the radionuclides caused the deformities and genetic defects. Butterflies netted six months after the release had more than twice as many abnormalities as insects plucked two months following the release, the team found. The rise in mutations means radiation from the accident is still affecting the butterflies' development, even though levels in the environment have declined, the study concluded. [See Photos of Fukushima's Deformed Butterflies]

"One very important implication of this study is that it demonstrates that harmful mutations can be passed from one generation to the next, and that these might actually accumulate and increase over time, leading to larger effects with each generation," said Timothy Mousseau, a professor of biology at the University of South Carolina who studies the impacts of radiation from Fukushima and from the 1986 Chernobyl explosion in Ukraine.

It is likely that the first generation of butterflies suffered both physical damage from radiation sickness and genetic damage from the massive exposure to radioactive isotopes after the disaster, the researchers reported. This generation passed on their genetic mutations to their offspring, who then acquired their own genetic defects from eating radioactive leaves and from exposure to low levels of radiation remaining in the environment. The cumulative effect caused successive generations to develop more serious physical abnormalities. "Note that every generation was continuously exposed," said Otaki.

The findings are consistent with previous studies in Japan and at Chernobyl, Mousseau added. "The ecological studies that we have conducted found that the entire butterfly community in Fukushima was depressed in radioactive areas, as were the birds, and that the patterns seen in Fukushima were similar to what has been observed in Chernobyl. If the plants and animals are mutating and dying, this should be cause for significant public concern."

Becky Oskin covers Earth science, climate change and space, as well as general science topics. Becky was a science reporter at Live Science and The Pasadena Star-News; she has freelanced for New Scientist and the American Institute of Physics. She earned a master's degree in geology from Caltech, a bachelor's degree from Washington State University, and a graduate certificate in science writing from the University of California, Santa Cruz.