Bioaccumulation of 137Cs in lichens: Insight into the patterns of extracellular and intracellular uptake of isotope in thalli

Abstract

This study specifies the patterns of ¹³⁷Cs bioaccumulation in three widespread lichens, i.e. Cetraria islandica, Cladonia arbuscula and Ramalina siliquosa. The EDTA washing procedure was involved to determine the loads of ¹³⁷Cs incorporated intracellularly. Additionally, water-holding capacity, which largely depends on the structural properties of the thalli, was assessed. The results reveal that C. islandica tends to efficiently accumulate ¹³⁷Cs and demonstrates the capacity for its intracellular binding, making the species a suitable bioindicator for monitoring of long-term ¹³⁷Cs contamination. In turn, C. arbuscula and R. siliquosa show a lower capacity to ¹³⁷Cs accumulation with simultaneous higher EDTA extractability, suggesting that these species possibly may be useful only in the monitoring of more recent contamination. It can be assumed that the characteristics of ¹³⁷Cs accumulation in lichens largely result from the structural specificity of their thalli. In the case of C. islandica, water is largely stored intracellularly and is more difficult to drain from the thallus, therefore ¹³⁷Cs is more likely to penetrate into the cells. Whereas, upon rehydration of the thalli of C. arbuscula and R. siliquosa, a large part of the water remains in the intercellular spaces, which reduces the chance of intracellular absorption of the radionuclide and at the same time facilitates its removal from the interior of the thallus. Furthermore, no significant relationship was observed between the activity concentration of ¹³⁷Cs in the thalli of epigeic lichens and its activity concentration in the host substrate, which excludes soil as the main source of isotope recorded in the thalli.