Temporal trends (1981–2007) of trace and rare earth elements in the lichen Cetraria islandica (L.) Ach. from Italian herbaria

Twenty-four herbarium specimens of Cetraria islandica collected in Italy from 1981 to 2007 were used for retrospective analysis. Cd, Ce, Cu, Fe, Gd, La, Mn, Ni, Pb, Sb, V, Y, and Zn concentrations were measured. Pb showed a negative temporal trend, linked to the ban of leaded fuel for vehicles. Pb showed a negative correlation with the distance of the sampling sites from a highway in the years before 1995 and no relationship after that year, corresponding to the Pb content reduction in gasoline. A significant trend towards increasing Mn concentrations over time also emerged, which deserves further investigations due to Mn toxicity. Cluster analysis showed a group of elements of anthropogenic origin, while rare earth elements formed a separated cluster of natural origin. Lichens from herbaria proved to be a valuable tool for reconstructing historical trends in trace element deposition, highlighting variations produced by human activities.