Scientists in groundbreaking study on effects of radiation in Fukushima

October 04, 2012


Researchers trying to assess the impact of radiation on ecosystems due to the Fukushima nuclear disaster have come up with some surprising results: But they're not entirely sure what the findings mean.

However, they say the data from Fukushima Prefecture could be useful in determining when evacuated residents might eventually be allowed to return to their homes.

The field work is facing methodological difficulties as not all abnormalities detected are necessarily a direct result of radioactive substances that spewed from the nuclear power plant following reactor meltdowns caused by the Great East Japan Earthquake and tsunami.

In April last year, researchers from Nippon Veterinary and Life Science University (NVLU), along with other institutions, began sampling muscle tissue of wild Japanese macaques caught in the provincial capital, Fukushima, for radioactive cesium content.

The concentrations ranged between 10,000 and 25,000 becquerels per kilogram immediately after the nuclear crisis began to unfurl the month before.

The readings fell to 500-1,500 becquerels per kg in June, but rose again to more than 2,000 becquerels per kg from last winter to spring.

The seasonal variations presumably occurred because the macaques ate leaf buds, which are said to absorb radioactive cesium in high concentrations, the scientists said.

Shin-ichi Hayama, a professor of wild animal control at NVLU, said the results were the first ever taken for wild primates.

"This presents an opportunity to study the impact of low-dose radiation on primates, which are so close to humans, over a more than 20-year period," Hayama said. "That could help forecast the impact on humans as well."

A separate team led by Shin-ichi Akimoto, a professor of entomology at Hokkaido University, is investigating deformities in a species of plant lice in Kawamata, Fukushima Prefecture. Akimoto said he hopes to verify any impact of radiation by comparing them with plant lice found outside the prefecture.

The Environment Ministry started sampling flora and fauna in Fukushima Prefecture last November because past research focused solely on the impact on humans. This was due to a general assumption that humans and other mammals are more susceptible to the effects of radiation.

The ministry, noting rising public interest in environmental conservation and the fact that human existence is intertwined with ecosystems, decided to widen the scope of the investigation.

The International Commission on Radiological Protection designated 12 species--including frogs, trout, bees, crabs, earthworms, pine trees and wild grass--as "reference animals and plants" for surveys.

The Environment Ministry used that table as a basis to draw up its own list of animal and plant species. A key consideration was the feasibility of long-term surveys based on sampling in the target region.

"We want to continue the studies on a modest but sustained scale," a ministry official said.

The studies of wild animals are facing difficulties of their own.

Unlike in laboratory experiments, scientists cannot ascertain what the animals ate and where they wandered. Different species have varying degrees of resistance to radiation.

In addition, it is difficult to gauge whether a given abnormality is due to radiation, or to other factors.

A team of researchers at the University of the Ryukyus investigated the impact of radiation on pale grass blue butterflies in Fukushima Prefecture.

They crossbred butterflies caught in the region and discovered eye abnormalities and aberrant wing color patterns in the next generation. Those morphological irregularities may be due to radiation, the scientists said.

The research results were published in early August in Scientific Reports, an online journal affiliated with Britain's Nature magazine.

In late August, however, a U.S. scientist pointed out that it was impossible to assess whether any abnormalities were induced because essential data on wing sizes was not presented.

That comment was followed by a heated online controversy.

"The report is noteworthy for pointing out the possibility of induced morphological abnormalities," said Takahisa Miyatake, a professor of evolutionary ecology at Okayama University.

But he cautiously pointed to the lack of a comparison between the frequency of morphological abnormalities before and after the nuclear disaster and the scant number of the butterflies sampled.

"This paper alone falls short of providing conclusive data on the effects of radiation," Miyatake said. "Further surveys are needed."

Satoshi Yoshida, who studies environmental radiation effects at the National Institute of Radiological Sciences, said researchers were stymied in part by a lack of consensus on what constitutes the impact of radiation and a difficulty in determining radiation doses in wild animals.

Yoshida said the overall paucity of knowledge in this area had to be addressed.

"There is a need to accumulate objective data," Yoshida said. "That would allow decisions to be made on future community planning for municipalities that are now evacuated. We need to do the work now, although we do not know whether we will arrive at an answer sooner rather than later."

(This article was written by Shunsuke Kimura and Akira Hatano.)

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