Plutonium Accumulation by Vegetation on Different Soils

High variability of plutonium transfer factors presented in publications makes it relevant to study the mechanisms that affect plutonium migration ability and its availability for vegetation. Varying transfer factors are explained by different properties of soils, since the redox potential and soil acidity can affect significantly the plutonium mobility. Plutonium migration in the soil-agricultural plant system was studied for different soils in a vegetation experiment. The content of Pu239+240 was analyzed by alpha spectrometry with preliminary radiochemical isolation. Plutonium migration parameters were determined using barley (Hordeum) and beans (Fabaceae) as test cultures. Plutonium transfer factors obtained in the course of vegetation experiments range within 3.1 x 10(-4)-6.8 x 10(-3) with the average value of 3.8 x 10(-3) for the aboveground part of barley; and they range within 9.2 x 10(-3)-7.6 x 10(-2) with the average value of 3.8 x 10(-2) for the root system of barley. The transfer factor range was 1.5 x 10(-3)-5.7 x 10(-3) (with the average value of 3.7 x 10(-3)) and 5.8 x 10(-2)-6.5 x 10(-2) (with the average value of 6.2 x 10(-2)) for the aboveground and root parts of beans, respectively. The mode of plutonium distribution by the vegetative organs of the considered crops was found to be nonuniform. On average, the transfer factor of plutonium is 40 times lower in the aboveground part of plants than in their roots. The accumulation of plutonium in the aboveground parts of plants growing on different soil types was found to be not the same for individual species/organs of agricultural plants. For the aboveground part of the agricultural crops under consideration, the transfer factors differ up to several orders of magnitude. In general, the accumulation of plutonium by vegetation growing on different soils forms the following sequence: soddy-podzolic (Retisol) and gray forest (Phaeozem) > low-moor peatbog (Histosol) >> typical chernozem (Chernozem). The smallest accumulation of plutonium by vegetation is observed in soils with a high content of organic matter. For the root system of plants, the dependence of plutonium transfer factors on soil properties is uncertain.