Construction materials affected by black crusts (BCs) can be subjected to restoration, demolition, recycling or even to their management as waste products, thus determining their chemical features should be considered a crucial step before to undertake any action. In this work, we present the development of an analytical methodology useful to be implemented as a routine screening tool to detect recent and past atmospheric emissions of heavy metals, nowadays superficially deposited or even encapsulated in BCs. For its development, BCs together with their corresponding construction materials were sampled from the historical construction Punta Begoña Galleries (Getxo, Basque Country, North of Spain). To detect the superficial (recent depositions) and internal (past accumulations) metallic accumulations in the BCs quickly and in a cost-effective way, BCs thin sections were analysed by elemental spectroscopic imaging techniques (SEM-EDS and µ-ED-XRF). Additionally, Raman imaging studies allowed to perform the molecular speciation study of lead, the main metal accumulated inner in the BCs and coming from past atmospheric deposition events. To propose the reactivity pathway, which leads to the formation of the lead compounds, chemical equilibrium modelling was used. Finally, ICP-MS technique allowed determining the concentration of main metals accumulated in the total mass of the BCs, and through lead isotopic ratio analysis the possible source of metallic particles emission was also approached.
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