Cesium-137 monitoring using lichens from Macedonia, northern Greece

Cs-137 content in lichens collected from Macedonia, Greece, was measured at regular intervals during the last decade following the Chernobyl reactor accident. An increase in Cs-137 concentration was observed for about 2-3 years after the accident. Later a gradual decrease was detected which depended on the biotopes and the collected species. Higher Cs-137 amounts were observed in epilithic lichens compared with epigeic or epiphytic lichens. Furthermore, such foliose or crustose lichens as Parmelia sulcata, Xanthoria parietina, Xanthoria calcicola, and Xanthoparmelia somloensis were more contaminated than filamentose lichens at the same biotope. Among filamentose or fruticose species, those with large surface area to biomass ratio (e.g., Usnea sp.) also showed greater accumulation capacity. From the studied biotopes, Mount Vermion presented the highest values and even 10 years after the Chernobyl accident could be characterized as a "hot" biotope. The high Cs-137 activities found in lichens 10 years after Chernobyl suggest that these primitive plants are suitable and inexpensive biological detectors of the fallout pattern.