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 theepiphytic lichen Parmelia caperata, substrate bark andleaves of oaks (Quercus cerris and Q. pubescens)from a background area in Tuscany (central Italy) werecompared. The elemental composition of unwashed samples,especially bark, was clearly affected by soil dustcontamination, thereby leading to incorrect interpretations ofbaseline concentrations and relationships between elements.The normalization of total element concentrations to thesurface soil composition (digested and analyzed by the sameprocedures), using Al as reference element, gave more reliablebaseline values and allowed comparison between differentbiomonitors. The suitability of lichens, leaves and barks forstudying the environmental distribution of trace elements interrestrial ecosystems is discussed.