Xerophilic fungi in museum repositories challenge our perception of healthy buildings and the preservation of cultural heritage

Within the last decade, fungal infestations have emerged in Danish museum repositories challenging museum staff's health and heritage preservation. The growth is most unexpected, as most repositories are climate-controlled, according to the international guidelines for heritage collections. This pilot study aims to enlighten unexpected fungal growth in three climate-controlled repositories. The environmental conditions were assessed with measurements of relative humidity (RH), temperature, and material moisture content (MC), showing no evidence of elevated moisture. Morphological and molecular identification showed the growth of A. halophilicus, A. domesticus, A. magnivesiculatus and A. vitricola; four xerophilic fungi able to grow at low water activity. Except for the xerophilic species, none of the detected airborne species gave rise to growth. The growth of xerophilic fungi is inexplicable but may be associated with a revision in the international environmental guidelines for heritage collections expanding the RH range. The study questions if the revision adequately prevents the risk of fungal growth to ensure heritage preservation and the occupational health of the museum staff.