Radiocesium and radioiodine in soil particles agitated by agricultural practices: field observation after the Fukushima nuclear accident.

Three weeks after the accident at the Fukushima Daiichi Nuclear Power Plant, we determined the activity concentrations of (131)I, (134)Cs and (137)Cs in atmospheric dust fugitively resuspended from soil particles due to soil surface perturbation by agricultural practices. The atmospheric concentrations of (131)I, (134)Cs and (137)Cs increased because of the agitation of soil particles by a hammer-knife mower and a rotary tiller. Coarse soil particles were primarily agitated by the perturbation of the soil surface of Andosols. For dust particles smaller than 10 μm, the resuspension factors of radiocesium during the operation of agricultural equipment were 16-times higher than those under background condition. Before tillage, most of the radionuclides accumulated within a few cm of the soil surface. Tillage diluted their concentration in the uppermost soil layer.