30 Août 2015
August 29, 2015
Aug. 29, 2015 - Updated 01:55 UTC+2
Japan's Environment Ministry has found abnormalities in fir trees near the crippled Fukushima Daiichi nuclear power plant.
The ministry has been observing about 80 species of wild animals and trees near the plant since 2011, when Japan suffered its worst nuclear accident.
At the request of the ministry, the National Institute of Radiological Sciences analyzed fir trees in areas where radiation levels are relatively high and published the results on Friday.
The results show that Japanese fir populations in the area showed a significantly increased number of morphological defects, including deletions of leader shoots of the main branch axis.
The study shows that 98 percent of fir trees in a 3.5-kilometer area from the damaged plant have defects. The radiation dose in the area is about 34 microsieverts per hour.
The results also show that 44 percent of fir trees have defects in an 8.5-kilometer zone with 20 microsieverts of radiation, and 27 percent in a 15-kilometer zone with 7 microsieverts of radiation.
The institute says the results indicate that radioactive materials emitted after the nuclear accident may have caused such morphological abnormalities.
The results have been also posted on the website of the British science magazine, Scientific Reports.
The institute's Satoshi Yoshida says conifers such as fir trees are more susceptible to radiation.
But he said relations between such defects and radiation are still unclear and that further studies are necessary.
The Environment Ministry says no abnormality has so far been confirmed in other animals and trees.
A fir tree missing its top bud. (Photo courtesy of National Institute of Radiological Sciences)
Abnormal growth has been detected in fir trees in three areas of Fukushima Prefecture exposed to high radiation levels in the wake of the Fukushima nuclear disaster, say researchers.
Research published in the academic journal Scientific Reports on Aug. 28 showed that the top buds of many fir trees in heavily contaminated areas were missing.
Researchers examined fir trees in three areas in the Fukushima Prefecture towns of Okuma and Namie, using fir trees in the city of Kitaibaraki, Ibaraki Prefecture, as a control group. The researchers checked between 111 and 202 fir trees in each location.
In the area with the highest radiation level of 33.9 microsieverts per hour, located in Okuma, 97.6 percent of the observed fir trees did not have a top bud -- without which the trees' growth cannot continue. In two areas of Namie where radiation levels reached 19.6 microsieverts per hour and 6.85 microsievers per hour, the same abnormality was seen in 43.5 percent and 27 percent of the fir trees, respectively. In Kitaibaraki, where radiation stood at 0.13 microsieverts per hour, the abnormality was seen in 5.8 percent of the fir trees.
The researchers say that these abnormalities have increased in prevalence since 2012. The Fukushima disaster occurred in 2011. At the same time, they say that more research is needed into the causal relationship between radiation and the abnormalities, and the underlying mechanisms of how the abnormalities occur.
In wild animal and plant life surveys being conducted by the Ministry of the Environment since fiscal 2011, around 80 species have been observed, but fir trees are the only one to have shown abnormalities, the ministry says.
Conifers are known to be susceptible to the effects of radiation. Abnormalities in Scots Pines were reported after the Chernobyl nuclear disaster in the former Soviet Union in 1986. However, the underlying mechanisms behind the changes are unknown.
Atsushi Kasai, a former senior researcher at the Japan Atomic Energy Research Institute, who is knowledgeable about the Chernobyl disaster, says, "The areas in Chernobyl where tree abnormalities appeared had much higher radiation levels than those in this new research. It is necessary to carefully look into the causes, taking into effect environmental factors such as weather conditions."
August 29, 2015
THE ASAHI SHIMBUN
Radiation spewed out by the crippled Fukushima No. 1 nuclear power plant may be responsible for differences in the growth of native Japanese fir trees in the area.
Researchers primarily from the National Institute of Radiological Sciences said Aug. 28 that many fir trees near the plant, as well as other areas, had undergone “morphological defects.”
They intentionally avoided words like abnormality, but used morphological defects and change.
Their studies showed that the changes occurred more frequently in areas with higher air rates of radiation.
"But it is still unclear whether the phenomenon has been caused by radial rays,” a team member concluded, adding that exposure to higher levels of radiation is “one possible cause.”
Conducted in January, the survey covered the town of Okuma in Fukushima Prefecture, located 3.5 kilometers from the plant, where radiation levels of 33.9 microsieverts per hour were detected, and two locations in the town of Namie, also in the prefecture.
While one of the Namie investigation sites is 8.5 km from the plant and measured 19.6 microsieverts per hour, readings of 6.85 microsieverts were detected at the other spot, located 15 km from the facility.
All the sites are within the government-designated difficult-to-return zone, meaning that the residents were evacuated and are prohibited from living there.
The team also examined firs in distant Kita-Ibaraki, Ibaraki Prefecture, which had radiation levels of 0.13 microsieverts per hour, for comparison.
In each of the four sites, the scientists checked 100 to 200 fir trees.
They found that more than 90 percent of firs in the Okuma site were not growing normally. Fir tree boles normally extend upward with two or so branches arising from them horizontally each year. But this was not the case.
Similar changes in shape were found in more than 40 percent of firs and around 30 percent of the trees, respectively, in the two Namie locations. Less than 10 percent of fir trees in the Kita-Ibaraki survey site also were different.
According to the NIRS, findings of studies concerning the 1986 Chernobyl nuclear disaster and other research revealed that conifers, such as firs and pine trees, are vulnerable to the effects of radiation.
However, the scientists noted that the problems reported in their latest survey may have been caused by animals, tree sickness or cold weather, not by exposure to strong radiation.
The Environment Ministry has been examining the impact of radial rays on local ecosystems since the nuclear crisis unfolded at the Fukushima nuclear plant four years ago. The NIRS study is part of those ministry efforts.
The governmental agency has to date monitored 44 kinds of animals and plants in areas around the damaged facility, but no other significant changes or abnormalities have been reported.
'LABORATORY EXPERIMENTS ESSENTIAL'
Tomoko Nakanishi, a professor of radiation plant physiology at the University of Tokyo, said the latest findings are invaluable as researchers have difficulty doing surveys in the difficult-to-return zone due to high radiation readings.
“There had been so little data on such areas,” she said.
But Nakanishi also pointed out it will require further research to conclude the morphological changes have been caused by exposure to radial rays.
“Other factors may have affected fir trees,” Nakanishi said. “Researchers need to examine through lab experiments what will happen when firs are exposed to high levels of radiation.”