Radiolead (210Pb) and stable lead in the lichen Cladonia alpestris
Lichens of the genus Cladonia, mainly C. alpestris, collected during 1882-1972 were analyzed for stable lead and 210Pb. The specific activity of 210Pb (210Pb/Pb ratio) indicates a constant value of about 2 mCi/kg up to 1940, and then decreased to 0.6 mCi/kg during 1950-1960. As the average annual 210Pb deposition is relatively constant, the decrease in the 210Pb/Pb ratio after 1940 indicates an in