Disentangling sources of trace element air pollution in complex urban areas by lichen biomonitoring. A case study in Milan (Italy)

In this study we investigated the bioaccumulation of selected trace elements in lichen samples transplanted for three months in Milan, Italy, with the aim of assessing the main environmental contaminants and the overall pollution load, and of disentangling the main air pollution sources as well as of estimating fluxes of element deposition. The results highlighted Cu and Sb as important contaminants and suggested a common origin for these two elements from railways and non-exhaust sources of vehicular traffic such as brake abrasion. High or very high global air pollution emerged for all study sites. Source apportionment outlined three main factors, that found reliable correlation with distance from major roads and railways, an industrial plant, and soil resuspension. Ranges of estimated mean annual element deposition rates in the study area were similar to those reported for other cities.