Elsevier

Atmospheric Environment

Volume 41, Issue 37, December 2007, Pages 8140-8149
Atmospheric Environment

Fungal fragments in moldy houses: A field study in homes in New Orleans and Southern Ohio

https://doi.org/10.1016/j.atmosenv.2007.06.027Get rights and content

Abstract

Smaller-sized fungal fragments (<1 μm) may contribute to mold-related health effects. Previous laboratory-based studies have shown that the number concentration of fungal fragments can be up to 500 times higher than that of fungal spores, but this has not yet been confirmed in a field study due to lack of suitable methodology. We have recently developed a field-compatible method for the sampling and analysis of airborne fungal fragments. The new methodology was utilized for characterizing fungal fragment exposures in mold-contaminated homes selected in New Orleans, Louisiana and Southern Ohio. Airborne fungal particles were separated into three distinct size fractions: (i) >2.25 μm (spores), (ii) 1.05–2.25 μm (mixture), and (iii) <1.0 μm (submicrometer-sized fragments). Samples were collected in five homes in summer and winter and analyzed for (1→3)-β-d-glucan.

The total (1→3)-β-d-glucan varied from 0.2 to 16.0 ng m−3. The ratio of (1→3)-β-d-glucan mass in fragment size fraction to that in spore size fraction (F/S) varied from 0.011 to 2.163. The mass ratio was higher in winter (average=1.017) than in summer (0.227) coinciding with a lower relative humidity in the winter. Assuming a mass-based F/S-ratio=1 and the spore size=3 μm, the corresponding number-based F/S-ratio (fragment number/spore number) would be 103 and 106, for the fragment sizes of 0.3 and 0.03 μm, respectively. These results indicate that the actual (field) contribution of fungal fragments to the overall exposure may be very high, even much greater than that estimated in our earlier laboratory-based studies.

Introduction

Moisture damage is common around the world and has been reported for various kinds of buildings such as homes, schools, offices, and even hospitals. If the moisture damage is not observed or remediated, it may be conductive to microbial growth. Several epidemiological studies have found an association between dampness or visible mold and respiratory illness of children and adults as summarized by the Institute of Medicine (2004). It is notable that majority of the previous epidemiological studies have relied on either self-reported mold and dampness or surveyor-assessed moisture and visible mold. However, attempts to correlate health outcomes with spore counts have not indicated strong associations. Furthermore, several field studies have shown that the concentrations of airborne fungal spores in mold problem buildings are not necessarily higher than in non-problem ones (Strachan et al., 1990; Nevalainen et al., 1991; Garrett et al., 1998; Chew et al., 2003). This indicates that spore concentrations may not be an adequate measure for fungal exposures.

The existence of larger hyphal fragments in the ambient air has been recognized for some time (Glikson et al., 1995; Li and Kendrick, 1995), but has so far been overlooked when assessing exposures in moldy buildings. Hyphal fragments have been shown to represent 6–56% of the total fungal particle counts in field samples based on microscopic sample analysis (Li and Kendrick, 1995; Foto et al., 2005; Green et al., 2005). This method is limited typically to particles >1 μm (Green et al., 2006). Recent laboratory-based studies (Górny et al., 2002, Górny et al., 2003; Cho et al., 2005) have reported that large quantities of submicrometer-sized fungal and actinomycete fragments (ranging from 30 nm to 1 μm) are released together with intact spores from contaminated surfaces. These studies demonstrated that the number of released fragments was always higher, up to 500 times, than the number of intact spores. Furthermore, the number of spores and fragments did not correlate.

Assessing exposure to smaller-sized fungal fragments may be important for several reasons. Smaller-sized fragments have longer lifetimes in the air compared to larger spores and can penetrate deeply into the alveolar region when inhaled. Fungal fragments have been shown to contain fungal antigens (Górny et al., 2002), mycotoxins (Brasel et al., 2005a, Brasel et al., 2005b), and (1→3)-β-d-glucan (Seo et al., 2007). The small size, large quantities, and biological properties of fungal fragments suggest that these particles may potentially contribute to the adverse health effects and raises the need for further characterizations of fungal fragments in moldy buildings. The quantification of fungal fragments, including those of nanoscale sizes, has previously been hindered by the lack of suitable field-compatible sampling and analysis methods.

To our knowledge, there is only one previous study assessing submicrometer-sized fungal fragments in mold-contaminated buildings (Brasel et al., 2005b). Fungal fragments were separated from spores using two filters of decreasing pore sizes placed in a series. While this method allows an efficient separation of submicrometer-sized fragments from intact spores, it is likely to underestimate the amount of submicrometer-sized fragments, as a large proportion of these particles are collected already onto the first filter due to diffusion. Cascade impactors would be an alternative that potentially offers a sharp separation of fragments from spores. Our previous study, however, showed that collection of purified fragments by impactors is challenging because of the spore bounce from upper stages to lower stages (Cho et al., 2005).

We have recently developed a field-compatible method for separation and analysis of airborne submicrometer-sized fungal fragments (Seo et al., 2007). The Fragment Sampling System utilized Sharp-Cut cyclones, which allow minimizing the spore bounce separating the airborne particles into three distinct size fractions, which are subsequently, analyzed for (1→3)-β-d-glucan. This new methodology was utilized for characterizing submicrometer-sized fungal fragments in aerosol samples collected in field conditions in moldy homes.

Section snippets

Selection of homes

The field investigation was conducted in five mold-contaminated single-family houses (Table 1). Three houses, located in New Orleans, Louisiana, were flooded during hurricane Katrina, and were severely mold-contaminated. Two other houses located in Southern Ohio; both had suffered water-damage in the basement and had either water-damage (house 4) or visible mold (house 5). Sampling was performed in all five homes during the summer of 2006 (June–September) and repeated in two homes in the winter

Results

Results on relative humidity and temperature during the environmental sampling are presented in Table 2. The highest values for indoor relative humidity (69.3–90.4%) and temperature (28.9–38.8 °C) were measured in New Orleans in the summer. The values were the lowest during the winter measurement cycle.

The total fungal spore concentrations as measured with the Button Sampler are shown in Fig. 1 and Table 3. Table 3 shows that the concentrations varied from 0.5×103 to 101.1×103 spores m−3 in

Discussion

Traditional microbiological methods, such as cultivation and microscopic counting cannot be used for the analysis of fungal fragments. In laboratory-based studies, direct-reading particle counters can be deployed for the enumeration of fragments as non-fungal particles are eliminated in the laboratory set-up. In the field situations, fungal fragments are masked by other particles, and a specific assay is needed aiming to analyze fungal components. (1→3)-β-d-glucan was selected as a surrogate of

Acknowledgements

This work was funded by the NIEHS Center for Environmental Genetics Pilot Project Program (Grant #PO30ES006096) and National Institute of Occupational Safety and Health NORA Research Program of the University of Cincinnati Education and Research Center (#T42/CCT510420).

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