Magnetic and chemical biomonitoring with lichens and trees leaves for the conservation of cultural heritage

GRIFONI, L.; WINKLER, A.; BOLDRIGHINI, F.; CHAPARRO, M.A.E.; DI LELLA, L.A.; MARTE, F.; PENSABENE BUEMI, L.; RUSSO, A.; SGAMELLOTTI, A.; SPAGNUOLO, L.; STRANO, G.; TASCON, M.; LOPPI, S.

Pisa

Congreso; 118th Congress of the Italian Botanical Society (IX INTERNATIONAL PLANT SCIENCE CONFERENCE); 2023

Italian Botanical Society

Biomonitoring of air pollution applied to cultural heritage is an innovative strategy of preventive conservation from damage caused by air pollutants. The main objective of this study is to evaluate the presence of pollutants, e.g. particulate matter and potentially toxic elements (PTEs), characterizing their distribution and peculiarities using air biomonitoring techniques. Lichens and leaves were used for this purpose: lichens were firstly collected in remote areas and exposed in the sites of interest for three months, the leaves, when available, were collected on site. The biomonitors were characterized by magnetic analysis, providing information on the abundance, composition, and grain-size of their ferromagnetic burden, which is often linked to the presence of PTEs. The main magnetic parameters investigated were the magnetic susceptibility, a sensitive indicator of the magnetic minerals’ concentration, and the hysteresis properties that define the characteristics of magnetic particles. Afterward, chemical analysis using multi-element techniques such as ICP-MS was used to determine the content of PTEs. The first application of these techniques, in the light of the work in Villa Farnesina in Rome (1), and out of the usual urban context, was fine at the Peggy Guggenheim Collection of Venice (Fig. 1), where the main source of PM in urban areas, i.e. vehicle traffic, is missing. Both indoor and outdoor areas were investigated, along a transect from Canal Grande to the inner garden of the museum. The magnetic contribution differed significantly between indoor and outdoor transplants. Moreover, out of a total of ten elements (Fe, Al, Ba, Cr, Zn, Cu, Sb, N, V, S) analyzed, Sb stood out on the outside and Zn on the inside of the museum. The results from the Guggenheim Collection highlighted unusual sources of pollution, likely related to the industrial activities in Venice, i.e. the artistic glass factories. Moreover, it revealed the role of indoor sources in influencing airborne zinc’s diffusion, possibly related to mural painting and the use of filters containing zinc for the conservation of the masterpieces. Another study case is the Palatino Hill of Parco Archeologico del Colosseo, the main archeological site of Rome. Here the buffering effect of trees and shrubs along the areas facing a busy road (Via dei Cerchi) was tested, along with an ongoing biomonitoring study with lichen transplants, that are still exposed outdoors and indoors to the Schola Praeconum (Fig. 2). The deposition of magnetic particles on Quercus Ilex leaves was particularly high and mainly linked to street dust close to the road, while it was significantly lower on the shrub leaves of the Palatine hill, mostly influenced by geogenic dust. These results highlight the role of trees in the characterization and mitigation of airborne pollution from vehicular traffic. The ongoing work focuses on other study cases: the Museo Nacional de Bellas Artes and the Museo Histórico Nacional of Buenos Aires, Argentina, for comparing two lichen species.