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

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

Radiostrontium uptake by lichen Hypogymnia physodes

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

Bioaccumulation of 137Cs and 60Co by Helianthus annuus

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