Cultural heritage represents a defining feature of our societies, its history and customs, thus, its preservation is of utmost importance for future generations to inherit.
With that in mind, we began our research in the causes of marble degradation and restoration techniques that address these issues in the field today.
Our interest grew in biodeterioration as we found out that chemical biocides are used by conservators, often with little or no effectiveness.
Our next goal was to set our values.
For that to happen, we knew that we had to start a flow of conversation with people who address this issue every day, and who will, eventually, become our direct stakeholders.
Kostas Vasiliadis is a conservator of ancient sculptures at the Museum of Acropolis and coordinator of the sculpture conservation lab. We contacted Mr. Vasiliadis to learn more about the difficulties restorers are facing when they come up against biodeterioration and how our project would help relieve this issue.
We began our conversation with the biotic stresses on historic monuments. During our discussion, we quickly learned that microbial deterioration is a complex matter and many factors, such as the microclimate on the stone, humidity and even the orientation of the monument, play a critical role in bacterial growth. He, also, made mention of other biotic stresses such as plants which develop their root system into the stone causing irreversible damage. When asked how conservators address these issues, he said that the first thing every restorer needs to have in mind is the integrity of the monument. There are many protocols that conservators follow, according to the severity of the damage and the level of “cleanliness” the professional want, or sometimes can achieve. Every step of the procedure is taken with caution, and the restorer is always assured that no loss of material has occurred. Mr. Vasiliadis highlighted that conservators often avoid using biocides due to their harmful effects on the stone and the user. He explained that chemical biocides induce surface alterations on the monuments something that aligned with our literature research. [1] He continued that biocides are often applied in the summertime when the rainfalls are rare and the possibility of it washing off is low. However, in this period, a large number of people from all over the world visit the sites of cultural heritage. Many biocidal substances are carcinogenic and pose a direct threat to human health and welfare.
Apart from the negative impact on the human factor, chemical biocides have a huge ecological footprint. In Greece, there are 18 World Heritage Sites and many more not listed in UNESCO and most of them are in rural areas surrounded by natural landscapes. These chemical compounds are not biodegradable causing long lasting pollution in soil and, by extension, in the aquatic system. In continuation of our discussion, we wondered why conservators believe that biocides are not effective. Mr. Vasiliadis emphasized that chemical biocides often lead to the survival of microorganisms and contribute to the development of resistant strains. Because biocides are used in large volumes and discharged with wastewater, they are present at low concentration throughout the environment, extending the problem. Outdoor monuments are in constant expose to the environmental factors, making their conservation more difficult than the one that is needed for sculptures and other artifacts where the conditions are highly regulated. This issue makes the reapplication of biocides on regular intervals, necessary, enlarging resistance and degradation of the environment. For the above reasons, many restorers choose biocides to be used only as a last resort.
This interview with Mr. Vasiliadis inspired us and demonstrated some of the values our product should follow. We decided that our biocide should not put in danger the user or any person that encounters, and that it should have zero ecological footprint. Furthermore, we concluded that our active substance should be something that does not generate microbial resistance. This last value encouraged us to search for novel organic compounds and led us to the utilization of antimicrobial peptides as a biological biocide.
Then, we communicated with Maria Mertzani, the director of ancient and modern monuments conservation directorate of the Hellenic Mistry of Culture and Sports. Our discussion with Mrs. Mertzani helped us consider the additional principles that guide our project as well as the importance of maintaining the marble craftsmanship by emphasizing to us that it is inscribed on the National Inventory of Intangible Cultural Heritage in 2013 and on the Representative List of Intangible Cultural Heritage of Humanity (UNESCO, 2003) in 2015.
Our conversation started by discussing about the impact of marble in art and culture. We discussed that the art of marble that emerges through heritage monuments is a source of knowledge and admiration as they connect the present with the past. They are part of the history of each place but also unique art pieces as they are carved and decorated in detail. Protecting and preserving them from factors such as biodeterioration is therefore imperative. Mrs. Mertzani allowed us to understand that the cause of biodeterioration is difficult to deal with as it is related to external environmental factors. Changes in temperature, mechanical stresses due to the plant root system, earthquakes, as well as the abundance of inorganic pollutants in the atmospheric air, which is responsible of granular disaggregation of marble crystals, can create fractures, cracks, and delamination in the marble substructures of the monuments, thus facilitating the colonization of microorganisms and exacerbating biodeterioration. She also mentioned the characteristics of the marble substrate itself as a contributing element to biodeterioration. In particular, she highlighted to us that one of the most sensitive points of Pentelic marble is aluminosilicate mineral veins. These veins are colonized by endo- and chasmolithic microorganisms, which cause them to become areas of increased water retention due to the relative properties of both the aluminosilicate minerals and the microbial consortium. Their volume is increased, and exfoliation and material loss result in the marble. Therefore, the conservators aim to deal with the results of biodeterioration with the use of both biocides and with H2O2 for cleaning so that there is no room for the growth of bacterial spores in the marble but also to keep its surface clean and solid.
When we asked her what characteristics a biocide should have, she replied that conservators usually examine the duration of the application. She explained to us that the application of biocides must be repeated at regular intervals as the corrosive microorganisms after a period of time recolonize the marble as they become resistant to the active substances of the biocide. Therefore, it would be desirable for its action to be long-lasting. She continued that they examine how many times and in what time period the microorganisms will return after the application of the biocide on the marble surface. The respawn time will determine the reapply time. In addition, the technical requirements that the biocide has during application, if there are any by-products that corrode the marble and are toxic to humans and the environment, and also how the excess quantity that will not be used will be disposed of are factors that she told us that they should be considered. Specifically, focusing on technical requirements, Mrs. Mertzani emphasized to us that when conservators handle biocides in the field, extreme caution must be taken, and the proper protective equipment and clothing must be worn.
Therefore, according to the above and in combination with our visit to the Acropolis Museum, we concluded to synthesize a biological biocide that must be governed by the following values:
• Be environmentally friendly.
• Nontoxic to human health.
• Αffordable across maintenance services
• Easy application.
• Its long-term non-corrosive behavior
• Its chemical composition and action should not be affected by external environmental factors such as extreme heat or cold, water, and ice.
As we decided to synthesize a biological biocide in order to protect both the environment and the health of its users from the chemical toxic and corrosive compounds that are contained in chemical biocides such us isothiazolinones, we were faced with the following question.
Which form should our biological biocide have?
Our team initially assumed that a biocide in the form of spray would be easier to use as it would cover a bigger surface with each application. However, Mrs. Mertzani, at the end of the interview, pointed out that a spray can also be harmful to human health, due to the molecules' dispersion into the atmosphere and the risk of inhalation.
Moreover, she told us that the conservators in reapplication of biocide want to spread it more targeted. So, a biocide in spray form is not as effective as most microorganisms are endolithic, which colonize inside the marble pores.
Thus, following this advice we did not proceed with our initial idea of a biocide in the form of spray and, instead, focused on a liquid one.
Our initial idea to replicate the effect of chemical biocides into a more environmentally – friendly product was inspired by a paper called “Biodeterioration control for the Athens Acropolis monuments: Strategy and constraints” written by Amalia D. Karagouni and her colleagues, so we initiated an online meeting with her.
Amalia D. Karagouni – Kyrtsou is Professor of Microbiology in National and Kapodistrian University of Athens, Faculty of Biology.
She has participated in 35 international and national research projects as project leader. Her scientific publications include 3 books and 61 publications in international scientific journals.
She has also presentations in 168 conferences and has undertaken the organizing committee as chairman of 4 congresses.
In the past, she was Advisor for the Hellenic Republic Ministry of Environment, Energy and Climate Change, the Ministry of Education and Religious Affairs and the Ministry of Rural Development and Food.
With the feedback of Paris Laskaris, they explained to us that the physiochemical properties, such as the climate and pressure, are of the highest importance on what kind of microorganisms colonize the marble.
Despite the diversity mentioned above, we were advised to focus our project on combating cyanobacteria and the chemolithotrophs, because they constitute the main source of marble bioerosion in the Mediterranean countries.
As far as the experiment is concerned, they proposed a quite simple, yet effective way of testing our final product’s success, that of picking a biodeteriorated piece of rock from the ground and compare its first and final form.
It was of high importance for us to communicate with the preservers of marble-based historical monuments, in order to get a better understanding of their demands and Sophia Papida provided us with a great source of information.
Sophia Papida trained as a conservator of antiquities and works of art at the Technological Institute of Athens.
. She has an MA in museum studies and has conducted postgraduate research on stone biodeterioration.
. She has worked at various archaeological sites in Greece and since 2000 has been employed as a stone conservator at the Propylaea by the Acropolis Restoration Service (YSMA).
She emphasized that our product should keep the plaster intact, because it could be later proved to contain findings of great historical value, such as inscriptions. In fact, we were surprised to find out that the preservers’ main concern is that.
She also told us that preservers always compare a biocide’s effectiveness to the application of water on the biodeteriorated area of the monument, meaning that they seek the most aesthetically pleasing result (combined with the minimum loss of mass) and if water can achieve this, then it is considered a success. This happens to avoid the over usage of biocides that may corrode the marble, pollute the ecosystems, hinder the tourists’ health and parodically make the microbes resistant to the biocides.
As far as the product’s final form is concerned, she proposed common compresses in order to avoid the evaporation of the biocide, something that occurs with sprays. Prior to this, the area should be cleaned with Perhydrol (H2O2, 5-10%) applied with toothbrush.
