Aesthetic Alteration of Marble Surfaces Caused by Biofilm Formation: Effects of Chemical Cleaning

Abstract

Despite the massive presence of biofilms causing aesthetic alteration to the façade of the Monza Cathedral, our team in a previous work proved that the biocolonization was not a primary damaging factor if compared to chemical-physical deterioration due to the impact of air pollution. Nonetheless, the conservators tried to remove the sessile dwelling microorganisms to reduce discolouration. In this research, two nearby sculpted leaves made of Candoglia marble were selected to study the effects of a chemical treatment combining the biocides benzalkonium chloride, hydrogen peroxide and Algophase® and mechanical cleaning procedures. One leaf was cleaned with the biocides and mechanically, and the other was left untreated as control. The impact of the treatment was investigated after 1 month from the cleaning by digital microscopy, environmental scanning electron microscopy, confocal microscopy and molecular methods to determine the composition and the functional profiles of the bacterial communities. Despite the acceptable aesthetic results obtained, the overall cleaning treatment was only partially effective in removing the biofilm from the colonized surfaces and, therefore, not adequately suitable for the specific substrate. Furthermore, the cleaning process selected microorganisms potentially more resistant to biocides so that the efficacy of future re-treatment by antimicrobial agents could be negatively affected.

Calcitic-based stones protection by a low-fluorine modified methacrylic coating

“…Moreover, some centimeter-thick dark-greenish silicate layers (mainly represented by diopside and tremolite) characterize the texture of the marble. The stone porosity is less than 1% (Toniolo et al 2002a ; Villa et al 2020 ). It has been largely used in local rural constructions and historical buildings (for example Monza Cathedral in Italy), but its most famous application has been for the Milan Cathedral construction (back to fourteenth century).…”

The Control of Cultural Heritage Microbial Deterioration

“…However, biocidal treatments have a brief duration and must often be repeated frequently, creating a repeated threat to the heritage material and the environment [ 17 ]. In addition, repeated biocidal treatments can cause resistance in target biological agents, and they can modify biofilm structures favoring the growth of more harmful biodeteriogens [ 12 , 18 ]. Biocide application has indeed caused damage to non-target organisms.…”

“… Confocal laser scanning imaging of biofilm growing on a Candoglia marble after a chemical cleaning (5% benzalkonium chloride followed by hydrogen peroxide) combined with a mechanical treatment (mechanical brushing and wet brushing) as previously reported by Villa et al [ 12 ]. The green signal corresponding to Syto9 stain, which binds to DNA, appeared to be spread across the mineral surface.…”

In Living Color: Pigment-Based Microbial Ecology At the Mineral–Air Interface

“…Therefore, photosynthetic pigment fingerprints emerged as indicators of cell viability that can be exploited to search for extraterrestrial life (box 3 ). The same technique was applied by Villa and colleagues ( 2020 ) to study the healthy state of phototrophs colonizing a stone monument before and after a cleaning treatment. The pigment spectral profile of SABs exposed to a chemical treatment showed characteristic emission peaks between 540 and 590 nm, indicating the disorganization of the light-harvesting complex.…”