RESEARCH ARTICLE UV-C as an efficient means to combat biofilm formation in show caves: evidence from the La Glacière Cave (France) and laboratory experiments Stéphane Pfendler 1 & Olympe Einhorn 1 & Battle Karimi 2 & Faisl Bousta 3 & Didier Cailhol 4 & Laurence Alaoui-Sosse 1 & Badr Alaoui-Sosse 1 & Lotfi Aleya 1 Received: 27 April 2017 /Accepted: 7 September 2017 /Published online: 14 September 2017 # Springer-Verlag GmbH Germany 2017 Abstract Ultra-violet C (UV-C) treatment is commonly used in sterilization processes in industry, laboratories, and hospi- tals, showing its efficacy against microorganisms such as bac- teria, algae, or fungi. In this study, we have eradicated for the first time all proliferating biofilms present in a show cave (the La Glacière Cave, Chaux-lès-Passavant, France). Colorimetric measurements of irradiated biofilms were then monitored for 21 months. To understand the importance of exposition of algae to light just after UV radiation, similar tests were carried out in laboratory conditions. Since UV-C can be deleterious for biofilm support, especially parietal painting, we investigated their effects on prehistoric pigment. Results showed complete eradication of cave biofilms with no algae proliferation observed after 21 months. Moreover, quantum yield results showed a decrease directly after UV-C treatment, indicating inhibition of algae photosynthesis. Furthermore, no changes in pigment color nor in chemical and crystalline prop- erties has been demonstrated. The present findings demon- strate that the UV-C method can be considered environmen- tally friendly and the best alternative to chemicals. This inexpensive and easily implemented method is advantageous for cave owners and managers. Keywords Algae . Caves . Conservation . UV-C irradiation . Bleaching effect Introduction Caves are oligotrophic habitats in which temperature and rel- ative humidity are almost constant throughout the year (Borderie et al. 2015; Popović et al., 2015These ecosystems were long considered stable as they were subjected to few disturbances. In recent decades, however, they have begun to suffer from an important level of touristic activity, requiring the installation of artificial lights with high-power lamps dur- ing most of the day. Due to the increased number of visits, carbon dioxide levels in cave atmospheres have risen (Faimon et al. 2006). The changes in illumination along with increased carbon dioxide has induced algal proliferation that has led to the development of structured complex multispecies biofilms (Faimon et al. 2006; Mulec and Kosi 2009; Popović et al., 2015; Smith and Olson 2007; Piano et al. 2015; Borderie et al. 2016). This situation is of great concern to cave owners and managers who find themselves faced with a dual problem: the esthetic impact of biofilms (Adhikary et al. 2015; Ciferri 1999; Cutler et al. 2013) and the biodeterioration they induce to geological formations and historical cave paintings (Albertano 2012; Nugari et al. 2009). Indeed, many authors have used cultural methods (Vinogradova et al. 1998; Grobbelaar 2000; Cennamo et al. 2012) or genetic analysis (Cennamo et al. 2012; Hallmann et al. 2013) to describe wide diversity in metabolism and physiological pathways in interacting microorganisms in biofilms that include al- gae, bacteria, and fungi biofilms, and whose physiological Responsible editor: Philippe Garrigues * Lotfi Aleya lotfi.aleya@univ-fcomte.fr 1 Laboratoire Chrono-Environnement – UMR CNRS 6249, Université de Bourgogne Franche-Comté, Besançon, France 2 Institut National de Recherche Agronomique (INRA), UMR1347 Agroécologie, BP 86510, 21000 Dijon, France 3 Centre de Recherche sur la Conservation, Laboratoire de recherche des monuments historiques, USR 3224, Champs-Sur-Marne, Paris, France 4 Laboratoire Environnement, Dynamique et Territoires de Montagne (EDYTEM), UMRCNRS5204, Université de Savoie, Le Bourg et du Lac, 73376 Chambery, France Environ Sci Pollut Res (2017) 24:24611–24623 DOI 10.1007/s11356-017-0143-7