Hygroscopicity of fungal spores

Publisher Summary Fungal spores are particles that may cause respiratory symptoms and allergies. The assessment of respiratory exposure to these particles requires information on the concentration, composition of fungal flora, and aerodynamic diameter of the spores. If a particle is hygroscopic, its size may dramatically increase in the human airways, where the relative humidity of the air approaches 100%. Previous studies by Madelin and Johnson and Pasanen concluded that fungal spores are hygroscopic. In those studies, however, the aerodynamic diameter of spores may have been more affected by the aggregation of spores than by the hygroscopic growth. In the study presented in this chapter, the hygroscopic properties of fungal spores were investigated experimentally using nonaggregated fungal spore aerosols. The chapter studies aerodynamic size and hygroscopicity of fungal spores experimentally using nonaggregated spore aerosols of five different species. The results show that fungal spores are only slightly hygroscopic. The highest hygroscopic change in particle size was found with Cladosporium cladosporioides: Its aerodynamic diameter increased from 1.8 μm to 2.3 μm when the relative humidity increased from 30% to 100%. The numerical assessment shows that this particle size change results in 20–30% increase of respiratory deposition of spores.