Integrated biomonitoring of airborne pollutants over space and time using tree rings, bark, leaves and epiphytic lichens

The integrated use of tree rings and outer tissues, and lichens, was tested for monitoring how pollutant concentrations vary spatially over time nearby an incinerator in industrial area in Central Italy. Trace elements in thalli of lichen Xanthoria parietina and in leaves, bark, wood of Quercus pubescens, as well as carbon, oxygen and nitrogen isotope ratios in tree rings were analyzed. The trace elements in leaves, bark, lichens and tree rings were below the thresholds found in analogous studies. Some trace elements in the leaves differed significantly between the plots, though this was not the case in lichens and bark. The values of δ13C and δ18O showed the same trend in all plots, while the values of δ15N were higher in the distal plot. The changes in trace element contents during the whole period of activity of the incineration plant were recorded in through the tree rings, but did not differ significantly in the three different periods of activity. The results indicated that trace elements were intercepted and collected by tree bark and leaves, as well as lichens, at low concentrations, and that they hardly entered into tree xylem tissues during the growing season to be stored into the woody tissues. Indeed, the study did not highlight marked changes over time and space, in accumulation of airborne pollutants in the selected biomonitors, most probably due to the low levels of industrial development. Nevertheless, the analysis of tree ring cores in combination with bark and leaves, and lichens might potentially contribute to depict historic impacts of airborne pollutants at pronounced concentrations.