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 PM10 samplers were placed sideby- side for one year at twenty-three sites located in an urban-industrial hot-spot of Central Italy, thus enabling the construction of an extensive and dense air quality monitoring network. Accumulation levels of the elements in lichens after five months and thirteen months of exposure were compared with the means of the element concentrations determined in the PM10 sampled during the same monitoring periods. Water-soluble and insoluble fractions of the elements in the PM10 were separately analysed. Correlations between lichen and PM10 element concentrations were examined by considering Pearson coefficients and by performing principal component analysis. The study allowed us to evaluate the reliability of lichen transplants as biomonitors for the assessment of the spatial variability of atmospheric element concentrations and for the individuation of the elements tracers of PM emission sources. Lichen transplants appeared to be reliable for high spatial resolution measurements of PM10 elemental components emitted at high concentrations by intense local PM emission sources such as the steel plant (Co, Cr, Fe, Mn, Mo, Nb, Ni, Ti and W) and the rail network (Cu, Sb and Sn), less reliable for spatially-resolved analyses of elements released by vehicular traffic (Cu, Sb and Sn) and not reliable for other elements emitted by the power plant, by industrial and domestic biomass heating and/or by other less intense emission sources (Ba, Bi, Cd, Cs, Mg, Pb, Rb and Tl). In general, bioaccumulation of the elements appeared to be more correlated with the total and insoluble fractions of the analysed elements than with the watersoluble one and reflected the solubility of the chemical species emitted by the main local PM emission sources.