Biosorption of Co2+ ions by lichen Hypogymnia physodes from aqueous solutions

Cobalt is one of the possible contaminants originating from radioactive wastes or from metal mines and refineries. This paper describes sorption of cobalt by the foliose lichen Hypogymnia physodes from CoCl2 solutions spiked with Co-60(2+) in laboratory experiments. Maximum uptake was reached within 1 hour; the biosorption after 24 hours is not pH-dependent within the range of pH 4 - 7, negligible at pH 2 and is not dependent on metabolic activity. The process can be described by the Freundlich adsorption isotherm with ln k = 2.77, 1/ n = 0.22 and R-2 = 0.94. Bivalent metal ions showed a concentration-dependent competitive effect on cobalt biosorption, decreasing in the order: Cu > Ni > Ca > Mg. Monovalent ions, such as K+ and Na+, showed only very weak competitive effect. Up to 98% of Co taken up by lichen can be removed by washing with 0.1 M NiCl2 at 20 degrees C. This means that only a small fraction of the cobalt is localized intracellularly. These results can be used for elucidating the behaviour of lichens as bioindicators of cobalt pollution in water systems, including the risk of cobalt leakage from lichen probes under the influence of rain, snow and atmospheric humidity.