How vulnerable are species -- including humans -- to radiation?

This is a crucial question facing people around the crippled Fukushima Daiichi nuclear plant, who have to live with low-level radiation the government says is insignificant but whose long-term health consequences are still unknown.

At least one species - the pale grass blue butterfly - has been found to be vulnerable to such radiation exposure, with high rates of deformities detected among offspring, according to a research paper published in Scientific Reports last week.

This begs another question: Does that mean there will be an increase in deformities and mortality rates among humans also?

A team of Japanese scientists found a marked increase in mutations among the offspring of pale grass blue butterflies that were collected in Fukushima prefecture two months after the March 11 nuclear disaster last year.

The abnormalities included underdeveloped palpi and leg tarsus, dented eyes, rumpled or underdeveloped wings.

The incidence of deformities was even higher among butterflies collected four months after the first sample, pointing to a possibility of "mutation accumulation caused by continuous low-dose exposure through generations," such as through the ingestion of contaminated leaves, the researchers said.

Such deformities can be recreated in the lab by applying relatively strong radiation -- 55 millisieverts during the butterflies' one-month life span, according to lead researcher, Prof. Joji Otaki of the University of the Ryukyus. "It is most likely that the abnormal phenotypes observed are produced by random mutations caused by the exposure to radiation," the paper concludes.

No significant increase in genetic mutations was detected among samples taken in other prefectures such as Tokyo, Prof. Otaki said.

So what does this mean for humans? Not much, apparently.

Different species have different degrees of resistance to radiation. Even among insects, some species such as silk moths and melon flies are known to be highly resistant to radiation. "We just don't know (about the likely impact on humans). Radiation sensitivity varies among species," Prof. Otaki said.

Prof. Shinzo Kimura of Dokkyo Medical University, one of Japan's best known radiation experts, agrees. "It is very inappropriate to apply the conclusion of this study to humans," he said. "That doesn't mean we can ignore the safety risks of low level radiation, however."

Many Fukushima residents are unable to move away from the area for financial reasons and continue to stay in the parts of the prefecture that are not off-limits.

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