Researchers trying to unravel spread of cesium and its impact on ecosystem after Fukushima disaster via The Asahi Shimbun

More than 90 percent of the fir trees in forests close to the site of Japan’s 2011 nuclear disaster are showing signs of abnormality, and plant lice specimens collected in a town more than 30 kilometers from the crippled facility are missing legs or crooked.

But it remains unclear whether the mutations in plants and animals are definitively connected to the disaster at the Fukushima No. 1 nuclear power plant.


The research has major ramifications in terms of what authorities and residents living near a nuclear power plant can expect if a similar accident occurs again. It also offers valuable insight for evacuees weighing their options about rebuilding their lives near the stricken plant.

Among radioactive substances, cesium-137 is of primary concern as it has a half-life of 30 or so years. As forests were excluded from decontamination work, an undetermined amount of cesium is bound to remain in forests and lie buried in the ground for many years to come.

Mountainous forests cover 70 percent of the Fukushima Prefecture’s land space.

The government-affiliated Japan Atomic Energy Agency (JAEA) is among research organizations studying the effects of radioactivity and the way cesium spreads in forested areas.

During a recent field trip in Kawauchi, radiation levels in the air showed 1.2 to 1.3 microsieverts per hour at a survey point.

Cesium in the soil registered between 300,000 and 400,000 becquerels of radioactivity per square meter.


At the Ogaki dam, almost 20 km northwest of the nuclear plant, researchers took cesium measurements of 800,000 becquerels per kilogram at a site 20 cm below the lake bed close to where the Ukedogawa river empties out.

But a reading close to the surface of the lake bed showed below 200,000 becquerels.

The difference, researchers say, is easy to explain: Dirt containing high levels of cesium flowed into the dam in the immediate aftermath of the accident, while dirt with lower radiation levels accumulated on top of it.

Researchers are still trying to figure out whether the release of radioactive materials affected the growth of plants and animals.

Scientists have reported on mutations and abnormalities among species varying from fir trees and plant lice to Japanese monkeys, carp and frogs.

The National Institute of Radiological Sciences (NIRS), a government-affiliated entity, said in late August that the trunks of fir trees are not growing vertically.

Fir trees are among the 44 species that the Environment Ministry asked the NIRS and other research organizations to study in trying to determine the effects of radiation on living creatures.

The NIRS reported that the frequency of these mutations corresponds to a rise in natural background radiation.

More than 90 percent of fir trees in the town of Okuma, just 3.5 kilometers from the crippled plant, showed signs of abnormal growth.

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