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1

Plant uptake of radiocesium from contaminated soil

100%

Pipíška M. , Lesný J. , Hornik M. , Augustín J.

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tom Vol. 49,suppl.1

9-11

EN

Phytoextraction field experiments were conducted on soil contaminated with radiocesium to determine the capacity of autochthonous grasses and weeds to accumulate 137Cs. The aim of the study was to evaluate the potential of spontaneously growing vegetation as a tool for decontamination of non-agricultural contaminated land. As a test field, the closed monitored area of the radioactive wastewater treatment plant of the Nuclear Power Plant in Jaslovské Bohunice, Slovakia was used. Contamination was irregularly distributed from the level of background to spots with maximal activity up to 900 Bq/g soil. Sequential extraction analysis of soil samples showed the following extractability of radiocesium (as percent of the total): water < 0.01%; 1 M MgCl2 = 0.3-1.1%; 1 M CH3COONa = 0.3-0.9%; 0.04 M NH4Cl (in 25% CH3COOH) = 0.9-1.4%; and 30% H2O2 - 0.02 M HNO3 = 4.5-9.0%. Specific radioactivity of the most efficiently bioaccumulating plant species did not exceed 4.0 kBq kg 1 (dry weight biomass). These correspond to the soil-to-plant transfer factor (TF) values up to 44.4 × 10 4 (Bq kg 1 crop, d.w.)/(Bq kg 1 soil, d.w.). Aggregated transfer factor (Tag) of the average sample of the whole crop harvested from defined area was 0.5 × 10 5 (Bq kg 1 d.w. crop)/(Bq m 2 soil). It can be concluded that low mobility of radiocesium in analysed soil type, confirmed by sequential extraction analyses, is the main hindrance for practical application of autochthonous plants as a phytoremediation tool for aged contaminated area of non-cultivated sites. Plant cover can efficiently serve only as a soil surface-stabilising layer, mitigating the migration of radiocesium into the surrounding environment.

2

Bioaccumulation of 137Cs and 60Co by Helianthus annuus

88%

Horník M. , Pipíška M. , Vrtoch L. , Augustín J. , Lesný J.

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2005

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tom Vol. 50,suppl.1

49-52

EN

The 60Co and 137Cs bioaccumulation by Helianthus annuus L. was measured during 9 day cultivation at 20 š 2°C in hydroponic Hoagland medium. Previous starvation for K+ and for NH4 + 2.2 and 2.7 times, respectively, enhanced 137Cs uptake rate. Previous cultivation in surplus of K+ ions 50 mmol.l 1 has no effect on 137Cs bioaccumulation rate. Both 137Cs and 60Co bioaccumulation significantly increase with dilution of basic Hoagland medium up to 1:7 for caesium and up to 1:3 for cobalt followed by mild decrease at higher dilutions. Root to shoot specific 137Cs radioactivity ratio (Bq.g 1/Bq.g 1, fresh wt.) increased with dilution from 1.46 to 9.6-9.8. The values root to shoot specific radioactivity ratio for 60Co were less dependent on the nutrient concentrations and were within the range 5.7 to 8.5. 137Cs was localized mainly in young leaves (30%) and roots (39%) and 60Co mainly in roots (67%) and leaves (20%). Obtained data showed less sensitivity of 60Co uptake by sunflower on nutrient concentration in hydroponic media.

3

Influence of time, temperature, pH and inhibitors on bioaccumulation of radiocaesium - 137Cs by lichen Hypogymnia physodes

88%

Pipíška M. , Horník M. , Kočiová M. , Augustín J. , Lesný J.

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2005

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tom Vol. 50,suppl.1

39-44

EN

Caesium bioaccumulation experiments were carried out at 4 to 60°C using natural samples of the lichen Hypogymnia physodes. Thalli were incubated in 2.5 mi mol.l 1 CsCl solutions labelled with 137CsCl for up to 24 h at pH values from 2 to 10. Bioaccumulation of Cs+ ions in the first phase of the lichen-CsCl solution interaction is rapid, neither pH, nor temperature dependent within the range 4 to 60°C and observed also with the lichen biomass thermally inactivated at 60°C or chemically by formaldehyde. The second phase of 137Cs bioaccumulation is time, temperature and pH dependent and is inhibited by formaldehyde and thermal inactivation. The process at the initial concentration C0 = 2.5 ěmol.l 1 CsCl and 20°C reached equilibrium within 12 hours. It can be described by the first order reaction kinetics equation: log [Ct] = 1.89 - 0.00153 t, R = 0.950. Maximal values of Cs-bioaccumulation were observed at 20°C with minimum at 4°C and 40°C and at pH 4 5 with minimum at pH 2 and pH 6. Low caesium efflux values from lichen thalli by water and 0.1 mol.l 1 neutral salts at 20°C and 24 h equilibrium were observed. Efflux characterized by distribution coefficients D = [Cs]solution/[Cs]biomass at biomass/solution ratio 1:25 (w/v, wet wt.), decreases in the order: Li+- 78 × 10 3 >NH4 + = K+ 15 × 10 3 > Cs+ = Na+ 11 × 10 3. Low extractability of caesium from lichen by water and salt solutions can explain long persistent times of radiocaesium contamination sorbed by lichens, observed by many authors in caesiumcontaminated forest and mountain regions. Hypothesis of the role of the lichen secondary metabolites as caesium binders is discussed.

4

Radiostrontium uptake by lichen Hypogymnia physodes

88%

Pipíška M. , Horník M. , Kočiová M. , Augustín J. , Lesný J.

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2005

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tom Vol. 50,suppl.1

39-44

EN

Radiostrontium 85Sr sorption experiments were carried out at 4°C and 20°C using natural samples of the epiphytic foliose lichen Hypogymnia physodes. Thalli were incubated in water solutions containing 10 5 to 10 1 mol.l 1 SrCl2 for up to 24 h at the initial pH 5.5. Sorption equilibrium at 4°C and 20°C was observed within 1 hour and did not change within the next 24 hours. Sorption process can be described well by Freundlich adsorption isotherm in both linearised and non-linearised form, not by Langmuir adsorption isotherm. Inactivation of lichen biomass by formaldehyde or temperature pretreatment did not cause loss of biosorption activity. 85Sr biosorption was strongly pH dependent increased from negligible values at pH 2 up to nearly 100% uptake at pH 5.5. Bivalent cations Me2+ act as competitors for 85Sr biosorption with the competition effect increasing in the order Co < Mg < Ca < Cd < Ni < Ba < Zn < Cu for Me2+ concentration 0.01 mol.l 1. A number of displacing agents have been tested for their ability to release extracellular bound 85Sr2+ ions from Hypogymnia physodes. Displacing efficiency increases in the order: water <<< EDTA (acid) < NaHCO3 < Na2EDTA < oxalic acid < BaCl2 < MgCl2 < CaCl2 < SrCl2. Efficiency of strontium biosorption by different lichen taxa will reveal their role in fixation of radiostrontium contamination in biosphere.