Chemical and geochemical characterization of plant bioindicators

This study has been aimed at evaluating by means of plant bioindicators pollution resulting from atmospheric deposition of potentially toxic elements (PTE) in the urban and suburban areas of Ravenna. Therefore, three different areas were taken into account: an area of natural interest, a public green area and a cultivated area, chosen for their particular locations relative to anthropogenic impact. The research has determined 22 macro- and micro-elements, both in the leaves of vascular plants and native mosses, and the isotopic compositions of strontium (Sr: 87Sr/86Sr) and neodymium (Nd: 143Nd/144Nd) in mosses. The chemical characterization of evergreen and deciduous trees over one year time and their temporal trends indicate a seasonal pattern which depends on the plant species and the element investigated, although accumulation of PTE has been especially observed in the fall. Unlike concentrations measured in the leaves, mosses provide estimates of possible enrichment occurred over the years. For several metals, especially Cd, Cu, Sn and Zn, their enrichment factors in mosses show that the contamination threshold ranges from severe to extreme in several stations of the investigated areas. A correlation exists between the plants exposed to high vehicular traffic and the release of Pt, although the amount of Pt intercepted and retained by leaf blades results not to be absorbed, supporting the low bioavailability of this element. The use of mosses as bioindicators to define the natural and anthropogenic sources of the atmospheric particulate has shown that the joint application of Sr and Nd isotopes can provide important information on the air pollution processes.