The application of LA-ICP-MS for chemical characterization of black crusts on building stones and the evaluation of the effect of environmental pollution in their genesis

Black layers, which develop on monuments due to the interaction of stones with the atmosphere, have been a serious problem since a very long time. The application of LA-ICP-MS to the study of black crusts proved to be extremely advantageous in geochemical characterization, both to determine a great number of trace elements and to carry out precise and sensitive analyses in a relatively short time. It also provided information on the state of conservation and degree of deterioration of stone, as well as on the extent of pollution in the environments where black crusts form. LA-ICP-MS analyses were carried out on samples collected from monumental buildings and churches belonging to the European Built Heritage, i.e., the Cathedral of St. Rombouts in Mechelen (Belgium), the Church of St. Eustache in Paris (France), the London Tower (England) and the Corner Palace in Venice, the Cathedral of Milan, the Cathedral of St. Maria del Fiore in Florence, the Vittoriano Monument in Rome (Italy). They were chosen for their historical significance and because they offer the possibility of analyzing polluted environments in Europe. Specifically, all examined samples revealed the migration of some heavy metals such as V, Cr, Ni, Cu Zn, As and Pb from crust to altered substrates. The high concentrations of heavy metals in black crusts on all samples (although in differing amounts) indicate that the crusts are greatly influenced by the varying degrees of anthropogenic pollution affecting the cities, such as presence of industries, vehicular traffic, domestic heating, etc. In addition, results show that the various enrichment trends in heavy metals observed in the BCs of these monuments are due also to many factors: sampling height, exposure, orientation, and the shape of the deposition surface