Potential for Mitigation of Cave Lampenflora Using Benzalkonium Chloride or UV-C

Artificial illumination in caves visited by tourists (“show caves”) gives rise to growth of photosynthetic biofilms, termed “lampenflora.” Besides being unsightly, these biofilms can damage speleothems, and thus finding a safe and effective means of controlling lampenflora is an important consideration in cave management. A variety of different physical and chemical means of biofilm mitigation have been proposed and tested. Here we tested benzalkonium chloride (BAC), a quaternary ammonium cationic detergent commonly used in pharmaceuticals and cosmetics, and germicidal UV light (UV-C) for lampenflora control. Algae and cyanobacteria derived from Carlsbad Cavern, USA, were cultivated in the lab and inoculated onto smooth calcium carbonate (CaCO 3 ) tiles and incubated under fluorescent lighting to simulate lampenflora; these were then treated with BAC or UV-C in various concentrations and intensities, respectively. A 1–10% BAC solution prevented biofilm growth, and repeated treatments with a 1% solution bleached preformed photosynthetic pigments. Germicidal UV-C (≥ 3200 mJ cm −2 ) also bleached preformed biofilms. BAC may be especially useful for bleaching thick localized growths, since high concentrations are required and toxicity to non-toxic organisms could be an issue; whereas UV-C could more easily be applied to broader areas, e.g., the tens of square meter areas in the immediate vicinity of the lamps at Carlsbad Cavern and other show caves.