El biodeterioro en edificios del patrimonio culturalMetodología de evaluación de tratamientos biocidas

Abstract

This research focuses on the study of biodeterioration experienced/suffered by materials that are part of cultural assets and how to evaluate the behaviour of the treatments that are used to control it. For this purpose, several buildings of Cultural Heritage in Andalusia have been studied: the church cover of the Santa Paula convent in Seville; the ataurique decoration in the Salon Rico in Medina Azahara in Córdoba; the Paintings in the Hall of the Kings of the Alhambra in Granada and the Macsura of the Mosque in Cordoba. These buildings are made up of both inorganic materials (brick, stone, wall paint) and organic materials (wood, leather) which can undergo biodeterioration processes that cause changes in their physical, chemical and aesthetic properties. The general objective is to formulate a methodology to study the biodeterioration of the constituent materials and to establish an intervention proposal from the biological point of view, by selecting effective biocide treatments that are compatible with these materials. For this purpose, a characterization of the original materials of the works under study was perfomed in order to determine how susceptibe they were to biodeterioration and to the different biocidal treatments. On the other hand, the biological species that are deteriorating these materials, are determined with microbiological and botanical studies. In addition, the effectiveness of different biocidal products is evaluated, as well as their compatibility with the different original materials of the works under study and with other conservation treatments (consolidants). Different analysis techniques were used, such as: stereoscopic microscopy, optics and scanning electronics with elemental microanalysis using X-ray dispersive energy (SEM-EDX); X-ray diffraction (XRD); Fourier transform infrared spectroscopy (FTIR) and gas chromatography (GC); culture techniques and molecular biology techniques; UV-visible spectroscopy; and determination of physical and mechanical properties: colorimetry, porosity, speed of ultrasound transmission and surface hardness. The different biocidal products to be used were selected based on the organisms detected in the different materials that made up the buildings. Thus, in the case of stone and ceramic materials, algaecides / lichenicides were used: quaternary ammonium salts (Preventol Ri80, New Des 50, Biotin T and Biotin R). While for organic materials and paints, fungicides were mainly used: voriconazole, thiabendazole, copper oxide nanoparticles, zinc oxide nanoparticles and titanium dioxide nanoparticles. Two fundemental parameters were used to evaluate these treatments: the comparative study of the efficacy of the biocides and the study of the how the biocide interacts with, or how compatible it is with the material in each of the cases under study. In order to verify how effective the biocides are in the case of geomaterials, we studied the vitality of phototrophic microorganisms under an optical microscope, the interface of lichen structures with the substrate by SEM and the estimation of photosynthetic biomass by ultraviolet-visible spectrophotometry. Likewise, in the case of wood, fungal growth was observed in specimens after applying the biocides. On the other hand, a series of tests were carried out to analyze how the biocidal products interact or interfere with the main constituent material of each monument. To this end, replicas or specimens of the different materials under study were prepared and, after applying the biocides, these materials were observed at SEM-EDX, and elemental microanalyses were carried out using X-ray dispersive energy in order to detect possible changes in the chemical compositions, as well as morphology at microscopic level. Also in some cases, when it was possible, tests were also carried out to quantify possible variations suffered in the different physical properties of the materials (colorimetry, open porosity, surface hardness, atmospheric moisture absorption, ultrasound speed, etc.). The Biotin R has proved to be the most suitable in eliminating biodeterioration in the stone of the atauriques in the Rico Salon in Medina Azahara, as much for its effectiveness as for its low level of/scarce interaction with the constituent material, however, in the case of the ceramic materials in Santa Paula, the most sutable turned out to be Preventol Ri80. In turn, it was determined that Biotin T is completely unsuitable or eliminatomg biodeteriogens from the atauriques, due to a level of high disintegration of the material detected when it was applied by immersion. In general, all these biocidal products increase, albeit very slightly, the porosity of the geomaterials analyzed. With respect to the paintings on leather in the Hall of the Kings in the Alhambra and the wood and wall paintings of the Macsura of the Mosque of Córdoba, all the biocides tested proved effective in reducing the proliferation of fungal species. The treatment with CuO nanoparticles, although it is the most effective, caused a very significant color change in all the materials it was tested on, ie wood and pictorial materials, by darkening them, so their use is not indicated in historical heritage. The pigments that were the most altered after the applying the biocides are red and blue. Thiabendazole is the fungicide that causes the least chromatic change in all cases. The study carried out by SEM-EDX, shows that there are no significant chemical or morphological changes in the surface of the samples after being treated with the products. The combination of all these studies has made it possible to determine which biocidal product is the most suitable for each case, eliminating the biological agents responsible for the deterioration of the constituent materials. Likewise, it has become clear that it is always necessary to perform preliminary characterization studies on the materials, to determine biological species and to evaluate the treatments, both with regard to how effective they are and how compatibile they are with the materials that are part of the cultural assets in study, since the effects that these treatments produce on them vary depending on their nature.