Aggregated transfer factors of fresh Cs and Sr pollution to various vegetables from six common European soils - mesocosm experiment.

Aggregated transfer factors (Tag) were identified for three common vegetables grown in six common European soils freshly contaminated by 134Cs and 85Sr. The experiment was carried out as a mesocosm experiment in pots with an average soil weight of 15.8 kg per pot. The vegetables were grown one after the other during one vegetation season, in the order lettuce, onion, and radish (the order usually applied in private gardens and small farms). Despite the fact that lettuce was grown in the most contaminated soil, it had the lowest Tag (in m2/kg) of both radionuclides (3.6E-4 for Cs, 2.0E-2 for Sr), while onion had 6.4E-3 for Cs and 3.2E-2 for Sr and radish had 1.9E-3 for Cs and 8.1E-2 for Sr. Potassium supply did not show any statistically significant effect on Cs Tag; there was a significant impact of K on the decrease in Sr Tag. The experiments indicated that Tag is more affected by plant species than by soil type; therefore, selection of plants with a lower capacity to uptake radionuclides may be an important measure to reduce food contamination and thus minimize the committed effective dose.

Uptake of 133Cs and 134Cs by Ceratophyllum demersum L. under field and greenhouse conditions.

The phytoremediation abilities of Hornwort (Ceratophyllum demersum L.) were tested under greenhouse and field conditions. Plants were exposed for 8, 16, and 24 days (greenhouse with stable isotope 133Cs), 8 days (field with 133Cs), and 8 days (climabox with radioactive isotope 134Cs). The plants were exposed to different concentration of stable Cs provided as CsCl (0.008, 0.033, 0.133, 0.267, 0.533, 0.800, 1.067, and 1.333 mM) and different activities of 134Cs (4.46, 4.46, 4.74, 4.64, 2.23 and 2.26 kBq). The results of the experiment revealed a significant effect (p < 0.001) of exposure time on Cs uptake. The results showed highest average 133Cs removal rates of 11%, 17% and 19% for 8, 16, and 24 days, respectively, in the greenhouse, 10% for the 134Cs experiment, and 27% for the field experiment with 133Cs. The results indicated that increasing the length of exposure lowered the uptake ability, hence indicating that the plant has limited capacity for Cs removal. The accumulated amount of Cs by plants is significantly dependent (p < 0.001) on the concentration of treatment and complies to a sigmoid curve. Comparison of experiments revealed the greenhouse experiment with 133Cs and the experiment with 134Cs did not differ significantly in their removal rate. However, the field experiment was significantly different from the previous two (p < 0.001), providing a higher removal rate. C. demersum was also able to resist phytotoxic effects of Cs in the greenhouse experiment for 16 days without significant effects (p > 0.05) on health. Even after 24 days of exposure, the plant resisted up to 0.267 mM treatment concentration with no significant tissue lesion (p > 0.05). These results indicate that C. demersum has potential for remediating aquatic habitats, especially in the case of acute events, where a short duration of phytoremediation may take place.

Stable cesium (133Cs) uptake by Calla palustris from different substrates.

The uptake of stable cesium (133Cs) by Calla palustris was evaluated from four different substrates: water, soil, keramzit (a clay granule) and water with the addition of a potassium compound, after an eight days exposure to a solution of 0.5mM cesium chloride. Stable cesium was used because it is commonly supposed that its uptake by plants is the same of that of radiocesium (137Cs). The plants were differentiated in their parts (roots, healthy leaves, dead leaves and flowers) and analyzed with ICP-MS. The lowest average concentration of absorbed Cs was found in plants exposed in soil (0.7mg/kg, S.D.=96.8), while the highest in plants exposed in water (147mg/kg, S.D.=51.7). During the experiment the water planted plants removed 31.6% of provided Cs while those planted in soil removed only 0.06%. The addition of potassium to water was tested because of the competition effect that arises between these two elements: this effect was confirmed with the result that the average uptake in the presence of potassium was lower (41mg/kg in exposed plants, S.D.=76.1). The uptake was also lower in the solid-based substrates (soil and keramzit), because of the known tendency of Cs to bind with soil particles, thus becoming less available to plants. There was no evidence that the different parts of the plant showed different uptake effectiveness, or that the health of the plant (evaluated with a qualitative method) had any effect on the uptake of Cs.