UV–C irradiation as a tool to eradicate algae in caves

Algal proliferation has commonly been reported to occur on monuments, such as crypts, churches, and caves, as soon as artificial lighting is used. In this work we study the effects of UV–C irradiation on algae collected in different caves in Dordogne (southwest of France). First, the effect of UV–C irradiation was tested on algal cell suspensions during increasing exposure times. After treatment, the photosynthetic capacity was assayed using a polarometric method, and algal cell viability was then estimated using a Trypan blue test after a rest period of 15 h. UV–C irradiation was then studied on algal cells cultivated on a solid support consisting of pieces of calcareous stone. Drops of concentrated algal cells were inoculated on stone and exposed to UV–C radiation for 3, 6, or 9 h. After this irradiation, half of the samples were submitted to a high white light intensity (1400 μmol m−2 s−1 of photosynthetically active radiation, PAR) for 6 h while the other half were incubated in the culture room. Subsequently, algal macroscopic parameters such as covering rate and colonized area were measured by macro photography. Both experiments led to the conclusion that UV–C irradiation has deleterious effects on photosynthetic parameters and growth of algal cells.