[Source: Scientific Reports, full page: (LINK). Abstract, edited.]

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

Olivier Evrard, Caroline Chartin, Yuichi Onda, Jeremy Patin, Hugo Lepage, Irène Lefèvre, Sophie Ayrault, Catherine Ottlé & Philippe Bonté

Scientific Reports, 3, Article number: 3079 - doi:10.1038/srep03079
Received 22 July 2013 - Accepted 15 October 2013 - Published 29 October 2013


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.