The deterioration of stone heritage in urban environments is mainly the product of sources of air pollution like vehicular traffic and domestic heating. The results of these phenomena usually manifest as acid rain and particulate patinas, acting on the surface of stone monuments to form the so-called “black crusts”, a typical stone degradation product, mainly composed of gypsum. The aims of this study were to investigate the extent of these phenomena on the decorative apparatus of the frontal façade of Gesù Nuovo Church, in the historical centre of Naples (Italy). Preliminary diagnostics consisted of XRD and FTIR to analyse the composition of stone materials and inquire about previous restorations. The chemical characterization of black crusts was performed, using a diverse array of techniques, to highlight how different compounds are distributed along a vertical gradient and considering the proximity of specific sources of pollution (vehicle engine ignition, incense combustion, domestic heating products). Finally, molecular biology techniques were employed to identify the organisms which typically dwell in this formation and speculate about their contribution to the degradation of stone.

This study investigates the biodeterioration of mosaic surfaces in a semi-confined archaeological environment along the Phlegraean coast (Baiae, Italy), focusing on the interaction between salt efflorescence and phototrophic biofilms. A multi-analytical approach was employed, integrating in situ observations with ex situ analyses, including SEM/EDS, FTIR spectroscopy, and metabarcoding (16S and 18S rRNA), to characterize both abiotic and biotic alteration patterns. Results highlight subtle traces of spatial differentiation: samples from the more exposed sector showed a more consistent colonization by halotolerant and halophilic taxa, particularly among Halobacteria and Rubrobacter, along with abundant sodium, chloride, and sulfate signals suggestive of active salt crystallization. Protected areas exhibit a comparable presence of salts with less diverse halophilic communities that vary along a vertical gradient of light exposure. The integration of chemical and biological data supports a model in which salt stress and biofilm development are co-dependent and synergistic in driving surface degradation. These findings emphasize the need for context-specific conservation strategies that account for the combined action of environmental salinity and microbial communities on historical materials.

The conservation of cultural heritage has long garnered significant attention within the scientific community, particularly due to the biodeterioration processes driven by microbial colonization. These processes can severely compromise the aesthetic, chemical, and physical integrity of artworks. While traditional chemical biocides are widely used, they present notable drawbacks, including toxicity, chemical instability, and the risk of inducing microbial resistance. Accordingly, efforts to expand the repertoire of molecules with biocidal activity are of utmost significance. In this study, we report the synthesis and characterization of selenium-based biocides with biocidal activity. Characterization was performed using NMR spectroscopy and gas chromatography–mass spectrometry (GC-MS). The biocidal efficacy of these compounds was evaluated via algal growth inhibition tests (OECD 201), employing Raphidocelis subcapitata as a model organism. Our results indicate that certain seleno-sugars exhibit a dose-dependent inhibition of algal growth, suggesting superior biocidal activity compared to conventional agents. Notably, one compound demonstrated an optimal balance of efficacy and chemical stability and was selected for subsequent in vivo testing.

Algal biofilms contribute to the biodeterioration of building materials (BMs), while restrictions on conventional algicides stimulate the search for sustainable protection strategies. This study evaluated the antialgal potential of selected essential oils and active compounds, with particular emphasis on lemongrass essential oil (LGC), for the control of microalgal biofilms on brick and render surfaces. Three essential oils (Lavandula angustifolia, Melaleuca alternifolia, and Cymbopogon citratus) and two active compounds, eugenol (EU) and geraniol, were screened against terrestrial microalgal strains associated with biodeterioration. Antialgal activity was assessed based on minimum inhibitory and algicidal concentrations. LGC and EU inhibited microalgal growth, reducing photosynthetic activity, chlorophyll a content, and inducing cellular alterations. Metabolomic analysis revealed a strong stress response involving membrane lipid remodeling, oxidative stress, and disruption of photosynthetic metabolism. LGC and EU caused cellular damage, with LGC inducing faster degradation and EU enabling partial adaptation. LGC effectively reduced microalgal biofilms on brick and render, decreased photosynthetic activity, and partially restored surface coloration, without causing significant changes in substrate pH or water absorptivity. Effectiveness depended on biofilm maturity and substrate characteristics. The integrated microbiological, physiological, metabolomic, and material-based approach confirmed the potential of LGC as a sustainable component of future protective coatings for mineral BMs.