Cesium-137 stored on and discharged from banks of an agricultural canal in Iitate, Fukushima

Abstract

This study aimed to investigate the dynamics of ¹³⁷Cs around banks along an agricultural canal for paddy fields in Iitate, Fukushima, Japan. Five plots (2.4-12.6 m²) on the banks were monitored intermittently during six time periods from May 2018 to November 2019. We directly collected runoff water samples discharged from the banks followed by partitioning it into particulate and dissolved fractions and determining ¹³⁷Cs in them. To investigate the source of ¹³⁷Cs in the runoff water, we sequentially extracted ¹³⁷Cs in various chemical forms from litter samples collected on the banks. The results showed that the discharge rates of the dissolved ¹³⁷Cs per unit area from the plots were lower than those observed at the downstream of the agricultural canal, whereas more than 50% of the ¹³⁷Cs discharged from the plots was in the dissolved fraction. Moreover, the results indicate that ¹³⁷Cs stored in the standing plants and the litter was the primary source of the dissolved ¹³⁷Cs discharged into the agricultural canal. The concentrations of the water-soluble ¹³⁷Cs in the litter per plot area may have been retained by the sufficiently higher concentrations of ¹³⁷Cs in litter in other chemical forms and those in the standing plants, which are the source of the litter.

Keywords: Cesium-137; Fukushima Daiichi nuclear power plant; Litter; Radiocesium; Sequential extraction.