BIODETERIORATION OF ROMAN HYPOGEA: THE CASE STUDIES OF THE CATACOMBS OF SS MARCELLINO AND PIETRO (ROME, ITALY)

The Catacombs of SS. Marcellino and Pietro are Christian cemeteries, excavated between the 3rd and 5th centuries CE, comprising of 18000 m2 of corridors and chambers around 16 m under ground level. As is the case for all the other Roman Catacombs, they are important religious and cultural heritage resources that are visited by thousands of tourists each year. In order to be visited these sites need to be illuminated and unfortunately, when this intervention is coupled with the environmental conditions of the catacombs there is generally a promotion of phototrophic biofilm growth on the stone surfaces. These growths can cause aesthetic damage to the sites and can also threaten their durability. There is no information available on these consortia (the site was only recently opened to the public in 2014) and so there is a need to characterise these microbial communities in order to compare them with results from other previously studied Roman Catacombs. Phototrophic microorganisms were investigated by microscopy and culture methods on samples collected with non-invasive methods from different illuminated sites along the tourist path. Innovative and non-destructive strategies involving singular and combinations of essential oils are presently being tested and developed to prevent biodeterioration of these sites. Tests are being carried to determine the effect of the oils not only on the biofilms but also on the decorated substrates (frescoed plaster) to determine any discolouration that may occur. A Lidar scanning prototype (developed By ENEA) has been used to perform both laser induced fluorescence (LIF) and reflectance measurements on the decorated stone substrate before and after the application of the essential oils. The obtained fluorescence maps of the treated surface areas in this on going study will identify any eventual colorimetric variations due to oil application which will be evaluated by the reflectance results and data from a standard contact colorimeter.