Leaf washing as an assessment tool to characterize dry atmospheric deposition

The aim of this work was to characterize dry atmospheric deposition after the washing of broad leaves and conifer foliage. To assess this method different sites chosen on the basis of different exposure to both point (e.g. waste incinerator plant (WIP), local crafts) and widespread (e.g. roads, agricultural practices) sources of anthropogenic pollution. The principal components analysis (PCA), performed on the major and trace elements identified after leaf washing, extracted four factors. F2 was lithogenic while the other three were anthropogenic. The enrichment factor (EF) highlights that Cd, Cu and Zn had a purely anthropogenic origin. The sites were grouped according to the predominant source of exposure and the synthetic index of enrichment (SIE) showed a decrease as follows: downwind from WIP > max exposure to WIP > min exposure to WIP > road > craft > rural zone. The leaf area allows to calculate the annual flow of elements and the deposition flux in the study area varied for Cd from 0.07 to 0.55 mg m-2, for Co from 0.1 to 0.48 mg m-2, for Cr from 0.63 to 3.7 mg m-2, for Cu from 14.5 to 32.27 mg m-2. The Cd flux in the Bologna area was lower than in some industrial zones of the World and the lowest values were found in the rural zones and under a minimum exposure to the incinerator plant, while the highest values were near the roads and under maximum exposure to the incinerator. The direct analysis of the leaf-washing water allows to discriminate the anthropogenic or geogenic metals deposited on the leaves using multivariate statistical analysis. It is also possible to predict the flow of metals in different areas of investigation.