TOKYO (AP) ? Researchers say 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.

Many Japanese, especially those who lived close to the Fukushima Dai-Ichi power plant, are concerned over the potential health risks from radiation emitted due to catastrophic meltdowns in three reactors after it was damaged by the 9.0-magnitude earthquake and tsunami on March 11, 2011.

Japanese researchers say they have found mutated butterflies with stunted wings because of the radiation, though the threat to humans ? a much larger and longer-lived species ? remains unclear.

A separate study, also released this week, found very low levels of radioactivity in people who were living near the Fukushima plant when it suffered the meltdowns.