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Field experiments in a contaminated farmland in Nihonmatsu city, Fukushima were conducted to assess the effectiveness of the plant-microbe interaction on removal of radiocesium. Before plowing, 93.3% of radiocesium was found in the top 5 cm layer (5,718 Bq kg DW(-1)). After plowing, Cs radioactivity in the 0-15 cm layer ranged from 2,037 to 3,277 Bq kg DW(-1). Based on sequential extraction, the percentage of available radiocesium (water soluble + exchangeable) was fewer than 10% of the total radioactive Cs. The transfer of (137)Cs was investigated in three agricultural crops; komatsuna (four cultivars), Indian mustard and buckwheat, inoculated with a Bacillus or an Azospirillum strains. Except for komatsuna Nikko and Indian mustard, inoculation with both strains resulted in an increase of biomass production by the tested plants. The highest (137)Cs radioactivity concentration in above-ground parts was found in Bacillus-inoculated komatsuna Nikko (121 Bq kg DW(-1)), accompanied with the highest (137)Cs TF (0.092). Furthermore, komatsuna Nikko-Bacillus and Indian mustard-Azospirillum associations gave the highest (137)Cs removal, 131.5 and 113.8 Bq m(-2), respectively. Despite the beneficial effect of inoculation, concentrations of (137)Cs and its transfer to the tested plants were not very high; consequently, removal of (137)Cs from soil would be very slow.

Radioactive cesium (137Cs) in distinct soil fractions provides key information to its bioavailability, and therefore determining the effect of soil characteristics and land use types on existing fractions of 137Cs in soils is important for predicting future 137Cs mobility in Fukushima. Thus, the objective of this study was to investigate the influence of soil characteristics and land use types on sequentially extracted fractions of 137Cs in Fukushima. In this study, five coniferous forest soils, eight arable soils, and eight paddy rice soils were sampled in 2012 and 2013. The 137Cs in the soils were separated into four fractions; water-soluble, exchangeable, organic matter-bound and residual fractions. More than 90% of the soil 137Cs fraction for arable and paddy rice soils was found in the residual fraction, implying significantly reduced bioavailable 137Cs with higher fixation. In contrast, forest soils measured higher exchangeable and organic matter-bound fractions of 5%–33% and 9%–44%, respectively, implying future 137Cs mobility in the forest ecosystem. Correlation analysis showed a significant negative correlation (p < 0.05) between the organic matter fraction and residual fraction in both arable and paddy rice soils. There was a significant positive correlation (p < 0.05) for both exchangeable and residual fractions with cation exchange capacity (CEC), total carbon (TC) and total nitrogen (TN) values in arable soils. Organic matter content influenced both exchangeable and residual fractions. It was not clear whether organic matter played a direct role in 137Cs fixation or mobility in the agricultural soils. In paddy rice soils, the organic matter fraction showed a significant negative correlation with TC and TN values. Soil pH was significantly negatively correlated (p < 0.05) with both water-soluble and residual fractions in forest soils but positively (p < 0.1) with the organically bound 137Cs fraction.