Contribution of submicronic (PM1) and coarse (PM>1) particulate matter deposition to the heavy metal load of lichens transplanted along a busy road

The aim of this study was to estimate the contribution of submicronic (PM1) and coarse (PM > 1) particulate matter deposition to the heavy metal load of lichens exposed along a busy road, based on the assumption that the accumulation of heavy metals occurs mostly as particles. We tested the hypothesis that lichens exposed inside a nylon cover with mesh size of 1 μm accumulate less heavy metals than lichens exposed without any cover. To this purpose, thalli of the lichen Evernia prunastri were transplanted for three months along a busy road of the urban area of Siena (Central Italy), with half of the samples exposed inside a nylon cover with a mesh size of 1 μm. The content of Al, As, Cd, Cr, Cu, Fe, Ni, Pb, Sb, and Zn was measured by ICP-MS before and after the exposure. The results showed that samples exposed inside the nylon cover accumulated a lower amount of most chemical elements and that Sb, along with Cd and Cu were the main traffic-related elements in the study area. Differences in element uptake were not caused by differences in sample vitality caused by the experimental procedure. Using a conversion factor it was possible to estimate element deposition rates for PM1 and PM > 1.