Depth distribution of cesium-137 in paddy fields across the Fukushima pollution plume in 2013. (September 2015)

• Record Type: Journal Article
• Authors: Lepage, Hugo; Evrard, Olivier; Onda, Yuichi; Lefèvre, Irène; Laceby, J. Patrick; Ayrault, Sophie
• Is Part Of: Journal of environmental radioactivity. Volume 147(2015:Sep.)
• Page Start: 157
• Page End: 164
• Publication Date: 2015-09
• Subjects: Cesium-137 -- Soil core -- Depth distribution; Radioactivity -- Periodicals; Radiation, Background -- Periodicals; Radioecology -- Periodicals; Radioactive pollution -- Periodicals; Environmental Pollutants -- Periodicals; Radioactive Pollutants -- Periodicals; Radioactivity -- Periodicals; Radioécologie -- Périodiques; Pollution radioactive -- Périodiques; Fond de rayonnement -- Périodiques; 539.752
• DOI: 10.1016/j.jenvrad.2015.05.003
• Languages: English
• ISSNs: 0265-931X

Abstract

Abstract: Large quantities of radiocesium were deposited across a 3000 km 2 area northwest of the Fukushima Dai-ichi nuclear power plant after the March 2011 accident. Although many studies have investigated the fate of 137 Cs in soil in the months following the accident, the depth distribution of this radioactive contaminant in rice paddy fields requires further examination after the typhoons that occurred in this region. Such investigations will help minimize potential human exposure in rice paddy fields. Radionuclide activity concentrations, organic content and particle size were analysed in 10 soil cores sampled from paddy fields in November 2013, 20 km north of the Fukushima power plant. Our results demonstrate limited depth migration of 137 Cs with the majority concentrated in the uppermost layers of soils (<5 cm). More than 30 months after the accident, between 46.8 and 98.7% of the total 137 Cs inventories was found within the top 5 cm of the soil surface, despite cumulative rainfall totalling 3300 mm. Furthermore, there were no significant correlations between 137 Cs depth distribution and the other parameters. We attributed the maximum depth penetration of 137 Cs to grass cutting (73.6–98.5% of 137 Cs in the upper 5 cm) and farming operations (tillage – 46.8–51.6% of 137 Cs in the upper 5 cm). As this area is exposed to erosive events, ongoing decontamination works may increase soil erodibility. We therefore recommend the rapid removal of the uppermost – contaminated – layer of the soil after removing the vegetation to avoid erosion of contaminated material during the subsequent rainfall events. Further analysis is required to thoroughly understand the impacts of erosion on the redistribution of radiocesium throughout the Fukushima Prefecture. Highlights: Depth migration of 137 Cs were investigated in soil cores collected on contaminated paddy field. Major part of 137 Cs remain in the uppermost 5 cm even 30 months after the accident. More than 50% of contamination could remain in tilled soil after decontamination. Radiocesium migrate in the uppermost 3 cm after grass cutting.