SENDAI – Levels of radioactive cesium in soil and on the ground of two forests in Miyagi Prefecture have risen since the 2011 Fukushima nuclear disaster started, according to results of a recent survey.
In forests about 60 km and 120 km north of the severely damaged Fukushima No. 1 power plant, cesium is believed to be accumulating in the soil as cesium-contaminated leaves fall to the ground and decompose.
The government of Miyagi Prefecture, which measured cesium density in June 2012 and a year later in the two cedar forests, is worried about the impact on forestry and related industries if the trend persists, an official said.
In a forest in the town of Marumori closer to Fukushima, the average cesium level of 10 samples of fallen quills was 26,684 becquerels per kilogram in June 2012, but rose to 42,759 becquerels a year later. And the level in soil up to 10 cm deep increased from 721 becquerels to 3,225 becquerels, according to the study.
In a forest in Ishinomaki, even farther from the damaged nuclear plant, the level climbed about 50 percent to 3,611 becquerels among fallen quills and by 2.5-fold to 620 becquerels in soil.
In these forests where all cedar tree quills are replaced about every five years, the level of cesium among fallen quills could fall over a longer period, but may also remain in the ecosystem by being absorbed from the soil by trees, the official said.
The results differ from a study the Forestry Agency conducted in 2011 and 2012 in three municipalities in Fukushima Prefecture, which found levels of cesium increasing in soil but declining in fallen foliage.