Lichens as biomonitors for radiocaesium following the Chernobyl accident

Caesium-137 resulting from the Chernobyl accident was monitored in lichens in The Netherlands. Caesium-137 activity in Parmelia sulcata ranged from 550 to 6100 (average 2500) Bq kg-1 dry weight. The similarity between the lichen data (geographical 137Cs activity gradients and radioactivity values) and data of wet and dry deposition, indicate the validity of lichen monitoring of atmospheric 137Cs. The ratio between the 137Cs activity per unit lichen dry weight (kg) of Parmelia sulcata and the 137Cs activity deposited per unit surface area (m2) was approximately one. Measurements of 137Cs accumulation in Xanthoria parietina show that the activity concentration could be expressed both on a dry weight and on a contour surface area basis. The determination of the biological half-life of 137Cs in lichens was shown to be subject to sources of error such as growth and non-atmospheric/indirect 137Cs influxes. (Author)