Abstract
The use of epiphytic lichens as quantitative monitors of airborne heavy metals needs a standardization of collection, analytical procedures and of data elaboration. Evidence is given of a patterned metal accumulation in lichens and for the foliose species, the analysis of the outermost edge of the thallus is suggested. Moreover, the raw concentrations of metals must be normalized to the earth's crustal abundance, as lichens entrap atmospheric particulates which are mostly constituted by soil and rock dust suspended by wind.