Bleaching of biofilm-forming algae induced by UV-C treatment: a preliminary study on chlorophyll degradation and its optimization for an application on cultural heritage

• Published in: Environmental science and pollution research international 2018-05, Vol.25 (14), p.14097-14105
• Main Authors: Pfendler, Stéphane, Munch, Thomas, Bousta, Faisl, Alaoui-Sosse, Laurence, Aleya, Lotfi, Alaoui-Sossé, Badr
• Format: Article
• Language: English
• Subjects: Algae; Aquatic microorganisms; Aquatic Pollution; Atmospheric Protection/Air Quality Control/Air Pollution; Biodegradation; Biofilms; Biofilms - growth & development; Biofilms - radiation effects; Bleaching; Caves; Chlorella - growth & development; Chlorella - radiation effects; Chlorophyll; Chlorophyll - metabolism; Cultural heritage; Cultural resources; Earth and Environmental Science; Ecotoxicology; Environment; Environmental Chemistry; Environmental degradation; Environmental Health; Environmental science; Environmental Sciences; France; Geologic Sediments - microbiology; Irradiation; Light; Memorials & monuments; Microalgae; Microalgae - growth & development; Microalgae - radiation effects; Photosynthesis; Photosynthesis - radiation effects; Research Article; Ultraviolet radiation; Ultraviolet Rays; Waste Water Technology; Water Management; Water Pollution Control
• ISSN: 0944-1344; 1614-7499
• DOI: 10.1007/s11356-018-1654-6

Green microalgae colonizing stone surfaces represent a major problem for the conservation of heritage monuments, since they lead to biodegradation and aesthetic issues. Previous studies in La Glacière show cave (France) have demonstrated that UV-C may have a strong effect on microalgae, thus leading to chlorophyll bleaching, which was increased when biofilms were maintained under VIS-light condition unlike to those maintained in the dark. To understand the physiological mechanisms underlying this response and in order to optimize in situ treatment, 30 kJ m −2 UV-C exposure times were applied to Chlorophyta Chlorella sp. and chlorophyll degradation kinetics were then monitored. UV-C irradiation was enough to inhibit photosynthesis and to directly kill all algal cells. Results also showed that chlorophyll a was degraded faster than chlorophyll b and that 14 h were necessary for complete degradation of all the present chlorophyll. In addition, our results highlighted the importance of visible light exposition after UV-C treatment which leading to chlorophyll bleaching. Irradiated algae cultivated in the dark were still green 5 days after treatment while cultivated samples in the light lost their green color after 14 h. An efficient UV-C treatment applicable to show caves and other heritage monuments was proposed.