Temporal Variation and Source Analysis of Radiocesium in an Urban River after the 2011 Nuclear Accident in Fukushima, Japan

Abstract

The release of radiocesium from the Fukushima Dai-ichi Nuclear Power Plant caused environmental contamination. We analyzed sources, behavior, and temporal trends of radiocesium by 1-year monitoring in an urban river, the Ohori River. The concentrations of 137 Cs in both particulate and dissolved phases decreased to ~ 16% within 1 year. The partition coefficient in dry weather was estimated to be 3.2 × 10 4 L/kg. 137 Cs concentrations in the particulate phase were higher during wet weather than during dry weather on the basis of both suspended solids (SS) weight and liquid volume. The ratios of 137 Cs concentration to deposited 137 Cs in the Ohori River (e.g., composite: 0.26 m 2 /kg-SS in June-July 2012) were higher than those in the Abukuma River, probably because of differences in land use. Source analysis by a chemical mass balance method showed that 22% of 137 Cs came from river water in dry weather, 39% from river sediments, and 39% from road dust highlighting urban surface deposits such as road dust as major sources of 137 Cs in the river water even 2 years after the accident, and that the wash-off of these deposits increased the 137 Cs concentration in the river during wet weather.