Migration of radioactive cesium to water from grass and fallen leaves

Abstract

The TEPCO Fukushima Daiichi Nuclear Power Plant accident in March 2011 led to high amounts of emitted radioactive Cs being deposited on land by both rainwater and snowfall. In addition, a significant amount of Cs was deposited on the surface of leaves, and after the accident, both trees and grasses absorbed radioactive Cs through their roots. In order to assess the effect on water sources, it is therefore important to evaluate the amount of radioactive Cs migrating to the water from both grass and fallen leaves. A number of samples of clover, dandelion, and mugwort were collected from the Yamakiya elementary school in Kawamata-machi, Date-gun, Fukushima-ken in May 2013 and May 2014. Fallen leaves were also sampled from the wood adjoining the school. Measurement of the Cs content in water was carried out by placing the sample in water for over 400 days at 10–30 °C. The radioactive Cs content was measured using the HPGe detector. In the case of grass, the amount of migration to water was saturated after about 120 days. The saturation levels of migration rate to water varied with kinds of grass in the range of 0.2–0.8. The migration rate for fallen leaves was not larger than 0.13. In addition, after leaching from grass or fallen leaves into water, the absorption of radioactive Cs to soil was observed, and therefore, migration would be limited to a small area.