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

Abstract

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 (CaCO3) 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.