PASSIVE MONITORING OF TRACE-ELEMENTS BY MEANS OF TREE LEAVES, EPIPHYTIC LICHENS AND BARK SUBSTRATE

Total concentrations of Al, Cu, Fe, Hg, Mn, Mo and Zn in the epiphytic lichen Parmelia caperata, substrate bark and leaves of oaks (Quercus cerris and Q. pubescens) from a background area in Tuscany (central It aly) were compared. The elemental composition of unwashed samples, esp ecially bark, was clearly affected by soil dust contamination, thereby leading to incorrect interpretations of baseline concentrations and r elationships between elements. The normalization of total element conc entrations to the surface soil composition (digested and analyzed by t he same procedures), using Al as reference element, gave more reliable baseline values and allowed comparison between different biomonitors. The suitability of lichens, leaves and barks for studying the environ mental distribution of trace elements in terrestrial ecosystems is dis cussed.