Determination of fungal spore release from wet building materials Introduction The transport of spores and other particles from the surfaces of moldy building materials is an important determinant of the exposure of people working or living in buildings with moderate or severe water- damage. Spores and other particles released from the fungal growth may contain mycotoxins, inflammagenic and allergenic compounds and could therefore be a cause of indoor air problems (Flannigan and Miller, 1994;Murtoniemietal.,2001;Nielsenetal.,1999).The release of spores will depend on a number of factors, e.g. the building material, the fungal species, relative humidity (RH), temperature, age of the mycelia, mechanical vibrations in construction materials, and the airflow over the surface. Zoberi (1961) studied the release of spores from different fungi grown on agar as a function of air velocities from 1.7 to 10 m/s and at different RH. Increased air velocity and low RH were found to increasesporerelease.Gottwald(1983)showedthatthe releaseofsporesfrom Cladosporium carpophilum grow- ing on peach was considerably increased when the RH was below 40% and slightly increased by mechanical vibrations. Pasanen et al. (1991) studied spore release fromagarculturesasafunctionofRHandairvelocity and found release of spores from Aspergillus fumigatus and Penicillium sp. at an air velocity of 0.5 m/s, while Cladosporium spores required at least 1.0 m/s. Foarde etal.(1999)foundalargeincreaseinsporereleasefrom fiberglassductmaterialsfor A. versicolor and P. chryso- genum when increasing the air velocity from 0.5 to Abstract The release and transport of fungal spores from water-damaged building materials is a key factor for understanding the exposure to particles of fungal origin as a possible cause of adverse health effects associated to growth of fungi indoors. In this study, the release of spores from nine species of typical indoor fungi has been measured under controlled conditions. The fungi were cultivated for a period of 4–6 weeks on sterilized wet wallpapered gypsum boards at a relative humidity (RH) of approximately 97%. A specially designed smallchamber(P-FLEC)wasplacedonthegypsumboard.Thereleaseoffungal spores was induced by well-defined jets of air impacting from rotating nozzles. The spores and other particles released from the surface were transported by the airflowingfromthechamberthroughatopoutlettoaparticlecounterandsizer. For two of the fungi (Penicillium chrysogenum and Trichoderma harzianum), the number of spores produced on the gypsum board and subsequently released was quantified. Also the relationship between air velocities from 0.3 to 3 m/s over the surfaceandsporereleasehasbeenmeasured.Themethodwasfoundtogivevery reproducible results for each fungal isolate, whereas the spore release is very different for different fungi under identical conditions. Also, the relationship between air velocity and spore release depends on the fungus. For some fungi a significant number of particles smaller than the spore size were released. The method applied in the study may also be useful for field studies and for gen- eration of spores for exposure studies. J. Kildesø 1 , H. Würtz 1 , K. F. Nielsen 2,3 , P. Kruse 1 , K. Wilkins 1 , U. Thrane 3 , S. Gravesen 2 , P. A. Nielsen 2 , T. Schneider 1 1 National Institute of Occupational Health, Copenhagen, Denmark; 2 Danish Building and Urban Research, Hørsholm, Denmark; 3 BioCentrum-DTU, Technical University of Denmark, Lyngby, Denmark Key words: Fungi; Spore release; Particles; Particle size distribution; Surfaces; Water-damage. J. Kildesø National Institute of Occupational Health, Lersø ParkallØ 105 DK-2100, Copenhagen, Denmark Received for review 1 December 2001. Accepted for publication 21 May 2002. Ó Indoor Air (2003) Practical Implications It is demonstrated that different fungi will release very different quantities of spores under identical conditions of growingonawetbuildingmaterial.Sporesmayalsobereleasedatvelocitiesdownto0.3 m/s.Anewmethodthatcan be used for measuring the potential spore release both in the field and in the laboratory has been developed. The method may also be applied for purposes such as determining the possible concentration of spores released during mold remediation and for measuring the release of particles or fibers from surfaces in general. Indoor Air 2003; 13: 148–155 www.blackwellpublishing.com/ina Printed in Denmark. All rights reserved Copyright Ó Blackwell Munksgaard 2003 INDOOR AIR ISSN 0905-6947 148