Size-dependent distribution of radiocesium in riverbed sediments and its relevance to the migration of radiocesium in river systems after the Fukushima Daiichi Nuclear Power Plant accident

We investigated the particle size distribution of radiocesium in riverbed sediments after the Fukushima Daiichi Nuclear Power Plant accident. Riverbed sediments were collected in the Abukuma River system in Fukushima and Miyagi Prefectures. The collected sediments were separated into 11 fractions, ranging from granular size (>2000 mu m) to clay size (<2 mu m) fractions. Cesium-137 concentrations were higher in the smaller particle size fractions, possibly reflecting specific surface areas and the mineralogy, in particular the clay mineral content A gap in Cs-137 concentration was observed between the silt size and sand size fractions of riverbed sediments at downstream sites, whereas riverbed sediments at an upstream site did not show such a concentration gap. It is likely that selective transport of small particles in suspended state from upstream areas resulted in an accumulation of radiocesium in downstream areas. (C) 2014 Elsevier Ltd. All rights reserved.