NUKLEONIKA 2005, 50(Supplement 1):S39-S44

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.