Susceptibility of fungi to commercially available traditional chemical products and to potentially alternative products for use in cultural heritage preservation

Traditional chemical biocide products are still widely used to control fungal development in the field of cultural heritage preservation, despite increasing criticism related to environmental and human health concerns. Moreover, the efficacy of biocidal products varies depending on the type of micro-organism targeted. It is therefore crucial to assess the susceptibility of fungal species to biocide compounds prior to their use. This study tests the susceptibility of 193 different fungal species to eight commercially available biocide products. Five of these products were classical biocides that target all microorganism deposits, and were composed of either quaternary ammonium salts or a combination of quaternary ammonium salts and isothiazolinone. One biocide was composed of econazole nitrate and specifically targeted fungi. The two remaining biocides were greener products designed solely for green deposits, and were assessed as potential alternatives to classical biocides. They were composed of lemongrass essential oil and pelargonic acid, respectively. The susceptibility to biocides was genus dependent for several fungal genera, while it was species dependent in other cases. The classical biocide product Biotin T™ was the most efficient in inhibiting fungal growth overall. Only weak fungal growth inhibition was obtained with the two products that were tested as alternative solutions. The fungi-specific product was very efficient in some cases but inefficient in others, thus underlining the importance of testing the products before use. These results showed that however desirable alternative solutions to traditional biocide products may be, there are actually very few commercially available alternative solutions.