Japanese scientists have looked at several generations of butterflies near the power plant and found some concerning "abnormalities."
A massive release of radioactive material is never good, but so far it's been hard to evaluate the precise effects of the collapse of the Fukushima Dai-ichi nuclear power plant on the surrounding environment. But this new study, published in Scientific Reports, is concerning. Japanese scientists have looked at several generations of pale grass blue butterfly populations in the affected area and have found physical mutations and genetic damage. In short: mutant butterflies.
From Yale e360:
...butterflies collected from the Fukushima area about two months after the 2011 accident were more likely to have leg, antennae, and wing shape mutations than those found elsewhere [and] butterflies found in areas with higher levels of radiation developed much smaller wings and eye irregularities. After breeding these butterflies in a laboratory, researchers found the next generation had numerous abnormalities not seen in the previous generation, including malformed antennae. And adult butterflies collected near Fukushima six months after the initial tests were more than twice as likely to have mutations than those found soon after the accident.\n
So in other words, the radiation caused mutations in the butterflies that were directly exposed, and the rate of mutations actually increased in their offspring.
These butterflies are especially good indicators of the effects of radiation, the study's authors explain, because they're widespread in Japan, making comparisons easy, and their wing colorations are especially sensitive to environmental changes.
Here are some "representative abnormalities" of butterflies they caught near Fukushima, including malformed wings and dented eyes.
The authors stop short of speculating what this might mean for other animals (like humans), and I'm not even sure what the worst case scenario is here. Let's call it a cause for concern.