Evaluation of ten plant-derived biocides for the inhibition of photosynthetic organisms on the karst surfaces of heritage buildings

Biodeterioration is a significant problem in the conservation of stone heritage buildings. In this study, 10 plant essential oils were assessed for their effectiveness in biofilm inhibition on stone heritage building surfaces under laboratory and in situ conditions, and were compared with traditional biocides such as benzalkonium chloride. The plant extracts were tested against algae and mosses. The effect on algae removal was evaluated by measuring the color of the surface before treatment, after 24 h and after 1 month of treatment. The effect on mosses was assessed by measuring the photosynthetic pigment content of mosses after 24 h of treatment. The results showed that the different plant extracts exhibited different levels of antibiotic activity. Benzalkonium chloride, S. aromaticum and C. cassia extracts showed strong antibiotic activity against all algae and mosses tested. T. mongolicus extracts showed antibiotic activity against only some of the algae and mosses, while the application of P. cablin extracts increased chlorophyll b content in the mosses. The other plant extracts were less effective at inhibiting the growth of algae and mosses. GC–MS compositional analysis further indicated that the higher antibiotic activity of S. aromaticum and C. cassia extracts was related to the high content of eugenol and cinnamaldehyde.