Evolution of radioactive dose rates in fresh sediment deposits along coastal rivers draining Fukushima contamination plume

Evolution of radioactive dose rates in fresh sediment deposits along coastal rivers draining Fukushima contamination plume.

Measurement of radioactive dose rates in fine sediment that has recently deposited on channel bed-sand

provides a solution to address the lack of continuous river monitoring in Fukushima Prefecture after

Fukushima Dai-ichi nuclear power plant (FDNPP) accident. We show that coastal rivers of Eastern

Fukushima Prefecture were rapidly supplied with sediment contaminated by radionuclides originating

from inland mountain ranges, and that this contaminated material was partly exported by typhoons to the

coastal plains as soon as by November 2011. This export was amplified during snowmelt and typhoons in 2012. In 2013, contamination levels measured in sediment found in the upper parts of the catchments were almost systematically lower than the ones measured in nearby soils, whereas their contamination was higher in the coastal plains. We thereby suggest that storage of contaminated sediment in reservoirs and in coastal sections of the river channels now represents the most crucial issue.

The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident led to the release of large radionuclide quantities into the atmosphere1,2 and to the formation of a soil contamination plume across Fukushima Prefecture, in northeastern Japan3,4. As radionuclides are strongly sorbed by fine particles, they are likely to be redistributed within the landscape and supplied to the rivers, in association with the mobilization and transport of soil and sediment particles by erosion processes and runoff 5.

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