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

•Calla palustris is a good candidate for phytoremediation.•The percentage of removed Cs varies from 31.6% in water to 0.06% in soil.•The control samples show some natural background of stable Cs.•The uptake is worse in solid-based substrates (i.e. keramzit and soil).•There is no statistically significant difference of uptake among particular parts of the plant.•There is no evidence that health condition of the plant affects the uptake.

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 0.5 mM 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 (0.7 mg/kg, S.D.=96.8), while the highest in plants exposed in water (147 mg/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 (41 mg/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.