Aerosol characteristics of airborne actinomycetes and fungi
Grinshpun, S. A., Reponen, T. and Willeke, K.
1997
Journal of Aerosol Science, 28, sup.1, pp. 667-668
Grinshpun, S. A., Reponen, T. and Willeke, K., (1997), "Aerosol characteristics of airborne actinomycetes and fungi", Journal of Aerosol Science, 28, sup.1, pp. 667-668.
| Abstract: |
| INTRODUCTION Knowledge of the physical and microbiological characteristics of airborne microorganisms is essential when investigating the behavior, transport and health effects of bioaerosols in indoor and outdoor environments. Among other particles of biological origin, airborne actinomycete and fungal spores have gained special interest in the literature. Exposure to airborne fungi may cause asthma and other health problems. Actinomycetes have recently been found to be indicators of mold problems in buildings. Information on the characteristics of fungal and actinomycete spores and their size dependence on environmental factors, such as the relative humidity, has primarily been obtained through field studies. While some data on the aerodynamic sizes of fungal spores are available through the laboratory studies of Pasanen et al. (1991), Madelin and Johnson (1992), Griffiths et al. (1996), Reponen et al. (1996), there are almost no data on actinomycetes. The following aspects have been addressed through our work: (a) dynamic particle sizing of single airborne actinomycete and fungi and their chain aggregates, (b) hygroscopic growth of these spores under environmental conditions that represent the human respiratory system, and (c) survival and recovery of different actinomycetes and fungi after their collection on surfaces. These three issues have been investigated through laboratory experiments using bioaerosol generation techniques developed by this research team (Willeke et al., 1996) and several newly-developed and commercially available bioaerosol measurement methods (Juozaitis et al., 1994; Grinshpun et al., 1996).METHODSThe experimental setup, shown schematically in Fig. 1, includes an agar-tube spore disperser with entrance and exit orifices (Willeke et al., 1996), an air drying/humidification system with relative humidity controller and electrostatic neutralizer, and a test chamber in which the airborne spores are collected and analyzed using three methods in parallel: aerodynamic particle sizing, glass-slide impaction, and agar-surface impaction. In the agar-tube disperser (an improved version of the one introduced by Pasanen et al., 1991), actinomycete and fungal spores were aerosolized directly from growth on the agar surface by a HEPA-filtered air jet. The entrance orifice of the agar-tube disperser increases the air turbulence and the exit orifice deagglomerates the spore aggregates. After being diluted with desiccated or humidified air, the bioaerosol enters the test chamber and is sampled by various devices. The concentration and size distribution of airborne spores was measured with an Aerosizer (API, Inc., Hadley, MA) and in some selected tests, with the APS (TSI, Inc., St. Paul, MN) for comparison. Our recently developed glass-slide and agar-slide bioaerosol impactors (Juozaitis et al., 1994) were used in parallel. The data obtained with the glass-slide impactor allowed us to determine the degree of the spore aggregation. The microbial recovery after spore collection was determined through colony enumeration using our agar-slide impactor with a moving slide. In some selected tests, we also used an Andersen viable impactor. Three species of actinomycetes and five of fungi, selected among those most common in indoor air or known as indicators of mold problems, were used in this study. The relative humidity range in our experiments was from 30 to =<100%. The data on the aerodynamic characteristics of actinomycete and fungal spores, collected through our experiments were used in a computer-based model, LUDEP 1.0 (ICRP, 1994), which estimated the human respiratory deposition of these spores.RESULTS AND DISCUSSIONFigure.2 shows the particle size distributions of airborne Streptomyces albus (actinomycete) and Penicillum brevicompactum (fungi) measured at RH = 30%. The geometric means of the aerodynamic diameter, dg, and the standard deviations, g, indicated in Fig. 2, represent primarily single spores: e.g., the percentage of aggregates found by microscopic examination of fungal spore samples taken by the glass-slide impactor did not exceed 10-15%. However, the number of aggregates may be as much as 60% if the spores are generated without the deagglomerating orifice. Size-spectrometric measurements showed that the relative humidity effect on the aerodynamic diameter of the tested actinomycete and fungal spores is not very high when the RH changes from 30 to about 100%. The highest change of the spore diameter, from 1.8 to 2.3 m, was found for Cladosporium cladosporioides (fungi). The effect of hygroscopic growth on the respiratory deposition of the tested actinomycete and fungal spores of 0.5 - 3 m, calculated using the ICRP (1994) model, was found to be of low significance: e.g., the doubling of the spore volume results
Keywords: Bioaerosol; actinomycete; fungi; aerodynamic size; aerosolization; hygroscopicity; survival |
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