Lichen transplants as indicators of atmospheric element concentrations: a high spatial resolution comparison with PM10 samples in a polluted area (Central Italy)

Lichen transplants Evernia prunastri (L.) Ach. and recently available low-cost PM10samplers were placed side-by-side for one year at twenty-three sites located in an urban-industrial hot-spot of Central Italy, thus enablingthe construction of an extensive and dense air quality monitoring network. Accumulation levels of the elementsin lichens afterfive months and thirteen months of exposure were compared with the means of the elementconcentrations determined in the PM10sampled during the same monitoring periods. Water-soluble and in-soluble fractions of the elements in the PM10were separately analysed. Correlations between lichen and PM10element concentrations were examined by considering Pearson coefficients and by performing principal com-ponent analysis. The study allowed us to evaluate the reliability of lichen transplants as biomonitors for theassessment of the spatial variability of atmospheric element concentrations and for the individuation of theelements tracers of PM emission sources. Lichen transplants appeared to be reliable for high spatial resolutionmeasurements of PM10elemental components emitted at high concentrations by intense local PM emissionsources such as the steel plant (Co, Cr, Fe, Mn, Mo, Nb, Ni, Ti and W) and the rail network (Cu, Sb and Sn), lessreliable for spatially-resolved analyses of elements released by vehicular traffic (Cu, Sb and Sn) and not reliablefor other elements emitted by the power plant, by industrial and domestic biomass heating and/or by other lessintense emission sources (Ba, Bi, Cd, Cs, Mg, Pb, Rb and Tl). In general, bioaccumulation of the elements ap-peared to be more correlated with the total and insoluble fractions of the analysed elements than with the water-soluble one and reflected the solubility of the chemical species emitted by the main local PM emission sources.