Radiocesium sorption in relation to clay mineralogy of paddy soils in Fukushima, Japan

Abstract

Relationships between Radiocesium Interception Potential (RIP) and mineralogical characteristics of the clay fraction isolated from 97 paddy soils (Hama-dori, n=25; Naka-dori, n=36; Aizu, n=36) in Fukushima Prefecture, Japan were investigated to clarify the mineralogical factors controlling the 137Cs retention ability of soils (half-life 30.1y). Of all the fission products released by the Fukushima accident, 137Cs is the most important long-term contributor to the environmental contamination. The RIP, a quantitative index of the 137Cs retention ability, was determined for the soil clays. The composition of clay minerals in the soil clays was estimated from peak areas obtained using X-ray diffraction (XRD) analyses. The predominant clay mineral was smectite in soils from Hama-dori and Aizu, while this was variable for those from Naka-dori. Native K content of the soil clays was found to be an indicator of the amount of micaceous minerals. The average RIP for the 97 soil clays was 7.8molkg−1, and ranged from 2.4molkg−1 to 19.4molkg−1. The RIP was significantly and positively correlated with native K content for each of the geographical regions, Hama-dori (r=0.76, p<0.001), Naka-dori (r=0.43, p<0.05), and Aizu (r=0.76, P<0.001), while it was not related to the relative abundance of smectite. The linear relationship between RIP and native K content not only indicate a large contribution of micaceous minerals to the 137Cs retention ability of the soil clays, but also could be used to predict the 137Cs retention ability of soil clays for other paddy fields in Fukushima and other areas.