UV-C Irradiation as a Tool to Reduce Biofilm Growth on Pompeii Wall Paintings

This study focuses on the experimentation of a method based on the use of UV-C irradiation to eliminate the biofilms present in a tomb located in the necropolis of Porta Nocera, in Pompeii. For this study, the autotrophic component of the biofilm was isolated in the laboratory, while, contemporarily, the characterization of the composition of the pigments of the frescoes took place on original fragments, which had already detached from the tomb and were examined in situ. These preliminary analyses were necessary for the recreation of test samples in the laboratory, which closely matched the original surfaces. Artificial biofilms were used for experimental exposure to UV-C radiation. The exposure to UV-C radiation was carried out at different distances for a fixed time interval. The effectiveness of the biocidal action was assessed by employing optical microscopy techniques, through a careful visual assessment of the area occupied by the biofilm on the different test samples, using a photographic survey, as well as by means of colorimetric measurements using spectrometric techniques. In order to obtain an additional parameter to evaluate the death rate of microorganism cultures exposed to the UV-C radiation, the concentrations of the photosynthetic pigments were also measured by spectrophotometry. Results showed that biofilms were completely eradicated by radiation, and no change in pigment color was observed.