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.