A team of researchers have revealed that a specific species of local butterfly in Japan have mutated since the Fukushima disaster back in March 2011. The species and the massive changes in physical and genetic development suggest that radiation levels continue to be a threat in the region, and may also serve as indicator of how slowly the breakdown of radioactive materials might be.

After over a year of research, the group published their findings in the scientific journal, Nature, and roundly concluded that, “radionuclides from the Fukushima Nuclear Power Plant caused physiological and genetic damage to this species.” Researchers had already been studying the delicate butterfly species for 10 years prior to the Fukushima incident, because the group of animals is extremely senstive to environmental changes, which could offer a way for scientists to measure environmental changes.

As Prof Otaki, one of the researchers, told the BBC:

We had reported the real-time field evolution of colour patterns of this butterfly in response to global warming before, and [because] this butterfly is found in artificial environments – such as gardens and public parks – this butterfly can monitor human environments.

The BBC notes that scientists collected 144 adult pale grass blue butterflies two months after the disaster from 10 different locations, including Fukushima. Researchers quickly discovered that the butterflies from areas with radiation developed startingly smaller wings and abnormal eye development. The study became even more surprising when scientists bred the butterflies. It was then that they discovered the genetic mutations that had occurred from exposure to radiation.

Researchers noticed that the second generation, bred away from any radioactive exposure, developed strange antannae. Those butterflies bred from the Fukushima area showed a rate of mutation double that of butterflies that were taken from areas without radiation.

The research is coupled with reports that bad practices and radiation cover-ups were central parts of the Fukushima plant operations. Workers were not told of the dangers of radiation and encouraged to work in unsafe conditions. After the plant had a meltdown in March 2011, the government failed to tell people quickly about radiation, safety and resources for the disaster. People have been concerned about the return of nuclear power to the island, after president Yoshihiko Noda decided to restart some plants during the summer months.

The study on butterflies proves that while immediate fears of powerful radiation sickness on humans and animals may not be imminent, the longer effects of nuclear power and meltdown will be felt for generations to come.