Relationship between indoor and outdoor airborne ... - Springer Link

Aerobiologia (2006) 22:227–236 DOI 10.1007/s10453-006-9034-y

ORIGINAL PAPER

Relationship between indoor and outdoor airborne fungal spores, pollen, and (1fi3)-b-D-glucan in homes without visible mold growth Taekhee Lee Æ Sergey A. Grinshpun Æ Ki Youn Kim Æ Yulia Iossifova Æ Atin Adhikari Æ Tiina Reponen

Received: 11 May 2006 / Accepted: 19 June 2006 / Published online: 1 September 2006 Springer Science+Business Media B.V. 2006

Abstract In this exploratory study, indoor and outdoor airborne fungal spores, pollen, and (1fi3)-b-D-glucan levels were determined through long-term sampling (24-h) using a Button Personal Inhalable Aerosol Sampler. The air samples were collected in five Cincinnati area homes that had no visible mold growth. The total count of fungal spores and pollen in the collected samples was conducted under the microscope and Limulus Amebocyte Lysate (LAL) chromogenic assay method was utilized for the determination of the (1fi3)-b-D-glucan concentration. For the combined number concentration of fungal spores and pollen, the indoor and outdoor geometric mean values were 573 and 6,435 m–3, respectively, with a geometric mean of the Indoor/Outdoor (I/O) ratio of .09. The geometric means of indoor and outdoor (1fi3)-b-D-glucan concentrations were .92 and 6.44 ng m–3, respectively, with a geometric mean of the I/O ratio equal to .14. The

T. Lee Æ S. A. Grinshpun Æ K. Y. Kim Æ Y. Iossifova Æ A. Adhikari Æ T. Reponen Center for Health-Related Aerosol Studies, Department of Environmental Health, University of Cincinnati, Cincinnati OH 45267-0056, USA S. A. Grinshpun (&) 3223 Eden Avenue, P.O. Box 670056, Cincinnati, OH 45267-0056, USA e-mail: [email protected]

I/O ratio of (1fi3)-b-D-glucan concentration was found to be marginally greater than that calculated based on the combined number concentration of fungal spores and pollen. This suggests that (1fi3)-b-D-glucan data are affected not only by intact spores and pollen grains but also by the airborne fragments of fungi, pollen, and plant material, which are ignored by traditional enumeration methodologies. Since the (1fi3)-b-Dglucan level may elucidate the total exposure to fungal spores, pollen, and fungal fragments, its I/O ratio may be used as a risk marker for mold and pollen exposure in indoor environments. Keywords (1fi3)-b-D-Glucan Æ Aerobiology Æ Aeromycology Æ Aeropalynology Æ Fungal spores Æ Indoor Æ Outdoor Æ Pollen

1 Introduction The interest to indoor air quality, in particular to human exposure to biological aerosols, has increased recently as many investigations have linked adverse health effects to bioaerosols (Burge & Roger, 2000; Lierl & Hornung, 2003; Portnoy, Kwak, Dowling, VanOsdol, & Barnes, 2005). A review by Bornehag (2001) reported that dampness in buildings that promoted mold growth increased the risk for respiratory health effects including cough, wheeze, and asthma. In order to

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quantify the level of airborne fungi and pollen, mostly culture-based and microscopic enumeration methods have been employed in the previous studies. However, both culture-based and microscopic enumeration may underestimate the human exposure to airborne biological particles. Furthermore, fragments released from fungi and pollen are not culturable and may not be easily identifiable by microscopy. Go´rny et al. (2002) reported that fungal fragments were released together with spores from contaminated surfaces and the fragments concentration was much higher than the intact spore concentration (up to 320-fold). Fungal fragments have been shown to contain fungal antigens (Go´rny et al., 2003) and mycotoxins in certain species (Brasel, Douglas, Wilson, & Straus, 2005). Similarly, pollen allergens may exist in smaller particles than intact pollen grains (Taylor, Flagan, Valenta, & Glovsky, 2002; Taylor, Flagan, Miguel, Valenta, & Glovsky, 2004). This suggests that fragments of biological particles may potentially contribute to the adverse health effects. (1fi3)-b-D-glucan was suggested as a potential contributor for indoor air related health effects primarily associated with airway inflammation (Douwes, 2005; Rylander, 1997a). (1fi3)-b-Dglucan, a polyglucose molecule comprising up to 60% of the cell wall of most fungi, pollen, some bacteria, and most of higher and lower plants, has been used as an indicator of mold biomass (Rylander, 1999; Rylander, Fogelmark, McWilliam, & Currie, 1999). (1fi3)-b-D-glucan concentration may be linked not only to fungal spores and pollen but also to their fragments. (1–3)-b-D-glucan retains its biological activity after the death of the organism and has been used in several studies as a surrogate measure of mold exposure (Fogelmark, Thorn, & Rylander, 2001; Schram-Bijkerk et al., 2005). The functions of (1fi3)-b-D-glucan are not fully understood but one of them is to maintain the rigidity and integrity of the fungal cell wall (Ruizherrera, 1991; Williams, 1997). (1fi3)-b-Dglucan has been linked to adverse health effects in several studies. Rylander, Norrhall, Engdahl, Tunsater, and Holt (1998) investigated (1fi3)-bD-glucan concentrations in a mold problem and a control school and found that the symptoms of dry cough, cough with phlegm, and hoarseness were higher in the problem school. Thorn and Rylander

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(1998) measured the indoor level of (1fi3)-b-Dglucan in 75 rowhouses that had previous water problems. An association between exposure to (1fi3)-b-D-glucan and increased prevalence of atopy, slightly increased amount of myeloperoxidase in serum, and decreased FEVP1 were found. Wan and Li (1999) reported a strong association between (1fi3)-b-D-glucan and lethargy/fatigue but a weak association with airway inflammation. Beijer, Thorn, and Rylander (2003) investigated inflammatory markers in blood between subjects with high and low (1fi3)-b-D-glucan exposure and found that (1fi3)-b-D-glucan had an association with inflammatory and immunological systems changes including increase of TNF-a secretion in the highly exposure group. Airborne (1fi3)-b-D-glucan concentrations may potentially represent exposure to fungal spores, pollen and their fragments, and considerable portion of the exposure may originate from outdoors. However, most previous studies were conducted in indoor environments and the relationship between airborne indoor and outdoor (1fi3)-b-D-glucan levels remains to be characterized. It is particularly important to determine how the indoor air quality is affected by changes in outdoor concentrations. This will help assessing exposures and developing exposure control strategies. This exploratory study conducted using a longterm sampling in single family homes without visible mold growth is a first attempt to characterize the relationship between indoor and outdoor levels of (1fi3)-b-D-glucan. Indoor-to-oudoor (I/O) ratios for (1fi3)-b-D-glucan were compared to the fungal spore and pollen concentrations to provide valuable information on the origin of (1fi3)-b-Dglucan in the indoor environment.

2 Material and methods 2.1 Selection of sampling sites Field sampling of indoor and outdoor bioaerosols was performed in September–October 2005 in five typical single-family homes located in the Cincinnati metropolitan area (southwestern part of the Ohio State, USA). The regional climate is primarily continental with an average annual


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to the wind direction, high filter collection uniformity, and the ability to screen out large particles (Grinshpun, Aizenberg, Willeke, Smith, & Baron, 1998). Adhikari et al. (2003) reported that the sampler is efficient for collecting outdoor pollen and fungal spores. In addition, the Button Sampler has also been used for stationary measurement of fungal spores (Osborne et al., 2006) as well as for personal and ambient measurement of fungal spores and bacteria (Toivola, Nevalainen, & Alm, 2004). The Button Sampler was washed prior to each 24-hour measurement with 5% bleach and 70% ethanol solution and sterilized at 220C for 2 h. After that, polycarbonate and MCE filters were loaded into the sampler inside of a Class II Biosafety cabinet (Baker, Stanford, ME, USA). The sampler was covered with a clean cap, and carried in a dust-free box to the sampling sites. Each sampling device operated at a sampling flow rate of 4 l min–1, which was maintained by a small pump (BGI Inc., Waltham, MA, USA) and verified with Drycalr DC-Lite Calibrator (Bios International Corporation, Butler, NJ, USA) before and after each 24-h measurement. Due to the pressure drop of the polycarbonate filter, the support pad in the Button Sampler was replaced by metal screen with a sparse mesh that is autoclavable. The outdoor sampler was fixed on a tripod with a rain shield and operated at a height of 1.5 m in front of the house. The indoor air sampling set-up was placed in the living room. The

ambient temperature of 11.8C. The monthly average temperatures in September and October are approximately 16–18C. The homes were selected from a large walkthrough database collected prior to this study to meet the following criteria: no visible mold growth and no smell of mold. The selected homes differed from each other by age, window type, building material, and the efficiency of indoor air filtration, see Table 1. The age of houses ranged from 6 to 103 years, the finished area ranged from 153 m2 to 435 m2. 2.2 Measurement of indoor and outdoor (1fi3)-b-D-glucan, fungal spores, and pollen Button Personal Inhalable Aerosol Samplers (SKC Inc., Eighty Four, PA, USA) loaded with 25 mm polycarbonate filters (.4 lm pore size, GE Osmonics Inc., Minnetonka, MN, USA) were utilized to collect (1fi3)-b-D-glucan in indoor and outdoor environments and mixed cellulose ester (MCE) filters (1.2 lm pore size, 25 mm, GE Osmonics Inc.) were used for collecting fungal spores and pollen. The inlet efficiency of this device fits the inhalable convention of the American Conference of Governmental Industrial Hygienists (ACGIH)/Comite´ Europeén de Normalisation (CEN)/International Standards Organization (ISO) reasonably well. The sampler design has several advantages such as providing low sensitivity of the performance characteristics Table 1 Summary of characteristics of the selected homes House characteristics

House 1

House 2

House 3

House 4

House 5

Age (years) Total surface area (m2) House material

103 435

7 153

27 208

37 153

18 231

Wood frame with brick

Wood frame with brick and vinyl siding

Wood frame with brick and aluminum siding Double pane, vinyl



Single pane, aluminum

Double pane, wood

Window type

Double pane, wood and aluminum Moldy smell No Visible mold No HVAC system No central and filter type HVAC system

Double pane, vinyl

No No No No No No No No Central, HEPA filter Central, electrostatic Central, pleated Central, HEPA filter filter fiberglass

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pump of the indoor sampler was placed inside noise-insulated enclosures to reduce the residents’ noise exposure. Both indoor and outdoor samplers were oriented vertically relative to the ground. The residents performed their normal activities during the measurements and stayed at home in houses #1 and #4. Houses # 2, #3, and #5, however, were mostly not occupied during the daytime as the residents were at work or at school. The sampling sessions were conducted for five consecutive 24-h periods—from Monday morning to Saturday morning—at each site (overall, five pairs of samples were taken for each home). the sampling campaign was carried out in the fall (September–October) when the ambient fungal spore concentration reaches the highest annual level in Cincinnati (Adhikari, Reponen, Grinshpun, Martuzevicius, & LeMasters, 2006). The meteorological information, including the air temperature and relative humidity indoors and outdoors, as well as the outdoor precipitation level and wind speed, were recorded in parallel to the bioaerosol measurements using a Vantage Pro meteorological station (Davis Instruments, Hayward, CA, USA). 2.3 (1fi3)-b-D-glucan analysis The (1fi3)-b-D-glucan concentrations in indoor and outdoor samples were analyzed using the kinetic chromogenic Limulus Amebocyte Lysate (LAL) chromogenic assay (GLUCATELL, Associates of Cape Cod, East Falmouth, MA, USA). The lysate is processed to remove Factor C (activated by endotoxins) while the Factor G, the enzyme specific for glucans, is preserved. Thus, the lysate is specific to the glucan pathway and any false-positive results are avoided (Odabasi et al., 2004). The polycarbonate filters were unloaded from the Button Samplers and transferred to pyrogenfree tubes containing reagent water (Associates of CapeCod, East Falmouth, MA, USA). The collected particles were extracted from the filters using a touch mixer (Model 231, Fisher Scientific, Pittsburgh, PA, USA) for 2 min and ultrasonic bath (FS20, Fisher Scientific) agitation for 10 min as described by Wang, Reponen, Grinshpun, Go´rny, and Willeke (2001). After the filter

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extraction, .6 M NaOH was added and the suspension was shaken for 1 h (Wrist Action shaker, Burrell Scientific, Pittsburgh, PA, USA) at room temperature (20C) in order to extract the (1fi3)b-D-glucan from fungal spores and pollen by unwinding its triple-helix structure and making it water-soluble. Aliquots of 25 ll of the extracted samples were transferred to 96 microwell plates, and 50 ll of specific (1fi3)-b-D-glucan lysate (Associates of CapeCod, East Falmouth, MA, USA) was added. The plate was incubated in an absorbance Microplate Reader (ELx808TM, Bio-Tek Instruments, Inc. Winooski, VT, USA), and the kinetics of the ensuring color reaction was read at 405 nm. The (1fi3)-b-D-glucan concentration of blank filters ranged from .09 ng ml–1 to .22 ng ml–1, which was found to be negligible when compared with real indoor and outdoor samples. 2.4 Analysis of fungal spores and pollen The MCE filters were cleared using a modified acetone vaporizing unit (Model: Quixfix, Environmental Monitoring System, Charleston, SC, USA). Each filter was stained with glycerin jelly (gelatin 20 g, phenol crystals 2.4 g, glycerol 60 ml, water 70 ml) mixed with Calberla’s stain for light microscopic analysis (Adhikari et al., 2003). The total number of pollen grains was counted under the 100· or 400· magnification high-resolution light microscope (Labophot 2, Nikon Corp., Japan). For fungal spores, 400· or 1000· magnification was used. At least 40 randomly selected microscopic fields were examined. The identification of fungal spores and pollen grains was conducted up to the genus, family, or class level based on their morphological characteristics. Reference slides (Aerobiology Instruction and Research, Brookline, MA, USA) and illustrated identification manual by Smith (1990) were used for microbial identification. In order to perform statistical analysis and report the data, the indoor and outdoor counts of fungal spores and pollen were combined together. 2.5 Data analysis According to the normality test by the Shapiro– Wilk and Kolmogorov–Smirnov statistics, the in-


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door and outdoor concentrations of (1fi3)-b-Dglucan, the number concentrations of fungal spores and pollen, as well as their I/O ratios were all log-normal. Therefore, a log-transformation was conducted on the entire dataset. The paired t test was applied to compare the difference of indoor and outdoor concentration for (1fi3)-b-Dglucan, fungal spores, and pollen as well as their I/O ratios. To study the correlation between indoor and outdoor concentrations, Pearson Correlation coefficients were determined. The Pearson correlation analysis was also used to study the relationship between fungal concentrations and the simultaneously measured meteorological factors. All statistical analyses were performed with SAS/ Stat 9.1 (SAS Institute Inc., Cary, NC, USA). A P-value of .05 was used as the level of significance.

3 Results and discussion 3.1 Indoor and outdoor (1fi3)-b-D-glucan The single sample (1fi3)-b-D-glucan analysis (24-h measurement) revealed indoor levels from .31 to 9.35 ng m–3 and outdoor levels from 1.62 to 34.37 ng m–3. The geometric mean (GM) and geometric standard deviation (GSD) of indoor and outdoor (1fi3)-b-D-glucan concentrations determined over five consecutive days in each home are shown in Fig. 1. The outdoor concen-

3)-β-D-Glucan Concentration (ng m-3)

40

Indoor Outdoor 30

20

10

↑

(1

Fig. 1 Indoor and outdoor (1fi3)-b-Dglucan geometric mean concentrations and geometric standard deviations determined over five consecutive days in each home

trations of (1fi3)-b-D-glucan were significantly greater than indoor concentrations (P < .0001). The lowest and highest GM of the indoor concentration of (1fi3)-b-D-glucan (integrated over 5 days) were found in house #3 (.47 ng m–3) and in house #4 (1.76 ng m–3), respectively, with GSD of 2.44 and 2.05, respectively. The integrated outdoor (1fi3)-b-D-glucan concentration ranged from 3.26 ng m–3 (GSD = 2.50) (house #5) to 15.96 ng m–3 (GSD = 2.04) (house #2). The GM and GSD of the entire data set collected in five homes (indoors) were .92 ng m–3 and 2.45, respectively. For outdoor measurements, the (1fi3)-b-D-glucan concentration integrated over the entire data set was characterized by GM = 6.44 ng m–3 and GSD = 2.24. The indoor concentrations of (1fi3)-b-D-glucan obtained in this study were generally consistent with other investigations, representing clean environments or those with low level of mold contamination. For instance, (1fi3)-b-D-glucan levels reported by Rylander et al. (1998) ranged from 2.9 ng m–3 in a control school to 15.3 ng m–3 in a mold problem school. Thorn and Rylander (1998) investigated (1fi3)-b-D-glucan in 75 water damaged houses and found the levels between 0 and 19 ng m–3 with 20 houses showing 6 ng m–3. Rylander (1997b) studied the (1fi3)-b-D-glucan concentration in a water damaged day-care center that had been renovated and found that the concentration

0

House 1

House 2

House 3

House 4

House 5

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significantly decreased as a result of renovation: from 11.4 to 1.2 ng m–3. In human exposure studies conducted by Beijer et al. (2003, 2006), the low and high level of (1fi3)-b-D-glucan levels were defined as 4.0 ng m–3, respectively. The Pearson correlation analysis was applied to determine the correlation between (1fi3)-b-Dglucan, fungal spores, pollen, and meteorological factors in indoor and outdoor environment. The results are shown in Table 2. The indoor (1fi3)-b-D-glucan concentration had a positive borderline significant correlation with outdoor (1fi3)-b-D-glucan concentration. It should be noted that the low correlation is mainly due to houses #2 and #3 which are relatively new houses with tight structure and efficient (HEPA or electrostatic) filters in the heating, ventilation and air-conditioning (HVAC) system. Residents’ activities such as keeping windows closed also contributed to the low outdoor-to-indoor transport of (1fi3)-b-D-glucan. House #5 is also a relatively new house with an HEPA filter. Minor house remodeling activity, however, was performed during the measurement, which probably contributed to higher air exchange rates in this house due to the opening of windows and entrance doors. The correlation coefficient calculated without houses #2 and #3 was significant and strong (r = .654, P = .008), which means that the indoor (1fi3)-b-D-glucan concentration generally follows the outdoor concentration of (1fi3)-b-D-glucan. The indoor (1fi3)-b-D-glucan concentrations had a strong and significant correlation with the combined total number concentration of indoor fungal spores and pollen as well as indoor and

outdoor temperature. The outdoor (1fi3)-b-Dglucan concentrations, however, showed nonsignificant correlation with the combined number concentration of outdoor fungal spores and pollen. This weak correlation may be attributed to the diversity of sources of (1fi3)-b-D-glucan, which is anticipated in outdoor environment, including vegetation and some soil bacteria. Outdoor (1fi3)-b-D-glucan concentration had a significant positive correlation with outdoor temperature, which may be caused by more favorable growth conditions offered for fungi and plants by increased temperature. Chew et al. (2001) found a positive association between the level of (1fi3)b-D-glucan and culturable fungi in house dust samples, however, no relationship between the airborne fungal spores and pollen and (1fi3)-b-Dglucan has yet been reported in the literature. 3.2 Indoor and outdoor fungal spores and pollen The 24-h measured indoor concentrations of fungal spores specifically ranged from 105 to 4,961 spores m–3 with the GM (GSD) of the entire data set equal to 572 (3.1) spores m–3 while the outdoor concentration ranged from 2,456 and 28,700 spores m–3 with the GM (GSD) of the entire data set equal to 6,429 (1.7) spores m–3. The outdoor fungal spore concentrations were significantly greater than those measured indoors (P < .0001). The indoor predominant fungal types were Aspergillus/Penicillium, Cladosporium, Ascospores, Basidiospores, and Smut spores. The outdoor prevalent fungal types were Aspergillus/Penicillium, Ascospores, Basidiospores, Ganoderma,

Table 2 Spearman correlation coefficients* between the concentrations of airborne (1fi3)-b-D-glucan, total fungal spores, pollen, and simultaneously measured meteorological factors Variables

Outdoor glucan

Indoor fungal spores and pollen

Outdoor fungal spores and pollen

Indoor temperature

Outdoor temperature

Indoor relative humidity

Outdoor relative humidity

Indoor glucan Outdoor glucan Indoor fungal spores and pollen Outdoor fungal spores and pollen

.393 (.051) – –

.533 (.006) – –

.243 (.242) .326 (.112) .266 (.199)

.502 (.020) – .389 (.082)

.447 (.042) .505 (.019) .373 (.096)

– .202 (.381) – .033 (.887)

.124 (.593) – .161 (.483) .081 (.726)

–

–

–

–

.655 (.001)

–

– .158 (.495)

*P values are indicated in parentheses; Significant correlations are marked bold

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Fig. 2 Indoor and outdoor geometric mean concentrations of total fungal spores plus pollen and geometric standard deviations determined over five consecutive days in each home

Fungal spore concentration (spores m -3)

Smut spores, Cladosporium. Interestingly, relatively large fungal spores such as Alternaria and Epicoccum were detected frequently in the outdoor air environment but barely detected in indoor environments. It can be attributed to the small penetration from outdoors to indoors due to the larger size of these fungal spores as described in our previous investigation (Lee et al., 2006). The concentrations of the indoor and outdoor pollen were lower than those of fungal spores. The indoor pollen concentration ranged from 0 to 2 pollen grains m–3 and the outdoor pollen was between 1 and 44 pollen grains m–3. The outdoor pollen level was significantly greater than the indoor pollen level (P = .0008). The lower concentration of pollen observed in our study may be due to the pollination season of weed rather than trees or grass. The most prevalent genus of pollen was Ambrosia followed by Poaceae. The GM and GSD of the combined total fungal spores and pollen counts conducted from the samples collected indoors and outdoors, respectively, in each house (integrated over five consecutive days) are presented in Fig. 2. The indoor combined number concentration of fungal spores and pollen ranged from 166 m–3 (GSD = 1.75) (house #3) to 1,963 m–3 (GSD = 1.99) (house #4) and outdoor concentration ranged from 3,832 m–3 (GSD = 1.40) (house #5) to 8,365 m–3 (GSD = 1.42) (house #2). The indoor and outdoor GM (GSD) of the entire data set were 573 (3.14) and 6,435 (1.74) m–3 for the

combined number concentration of total fungal spore and pollen. The correlation between indoor and outdoor concentrations of fungal spores and pollen was neither significant nor strong (Table 2), which is inconsistent with our previous investigation (Lee et al., 2006). This can be attributed to the tight structure of the houses tested in this study and efficient filters used in their HVAC systems. Similarly to the results obtained for (1fi3)-b-Dglucan, the correlation coefficient between indoor and outdoor fungal spore and pollen concentrations determined without houses #2 and #3 was significant and strong (r = .740, P = .008). 3.3 I/O ratio of (1fi3)-b-D-glucan, fungal spores, and pollen, and its correlation The I/O ratio of (1fi3)-b-D-glucan obtained from the 24-h samples was between .02 and .66, with GM = .14, GSD = 2.56, and the median = .14 (for the entire data set). The I/O ratio of the combined concentration of fungal spores and pollen from the 24-h samples ranged from .006 to .50 with GM = .09, GSD = 3.09, and the median = .11 (for the entire data set). These findings are consistent with our previous study in which the I/O ratio measured for fungal spores in the fall ranged from .01 to .69 (Lee et al., 2006). The 5th to 95th percentile box plot of I/O ratios of (1fi3)-b-D-glucan and the total number concentration of fungi and pollen are shown in Fig. 3.

15000

Indoor Outdoor

10000

5000

0

House1

House 2

House 3

House 4

House 5

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The scatter plot of individual I/O ratios based on the (1fi3)-b-D-glucan analysis and the microscopic counted combined number concentration of fungal spores and pollen is shown in Fig. 4. Most of the I/O ratios fall above of the diagonal line, which

The GM and median I/O ratios of (1fi3)-b-Dglucan were slightly higher than the I/O ratios determined based on the microscopic count of fungal spores and pollen. Paired t test reveals marginally significant difference (P = .053). 1.0

I/O ratio

Fig. 3 The box plot of I/O ratios of (1fi3)-b-Dglucan and total concentrations of fungal spores plus pollen. The horizontal lines in the box plot from bottom to top indicate 10th, 25th, 50th (median), 75th, and 90th percentiles. The circles indicate the 5th (lower circle) and 95th (upper circle) percentiles. n is the number of samples

0.5

0.0

Fig. 4 The I/O ratio scatter plot of (1fi3)-b-Dglucan concentration vs. combined fungal spores and pollen concentration in five homes

n=25

n=25

(1→3) β D-Glucan

Fungal spore and pollen concentration

1.0 House 1 House 2 House 3 House 4 House 5

I/O ratio of (1 3) β D-Glucan

0.8

0.6

0.4

0.2

0.0 0.0

0.2

0.4

0.6

0.8

Combined I/O ratio of fungal spore and pollen

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10


demonstrates that the I/O ratios of (1fi3)-b-Dglucan are mostly greater than those of fungal spores and pollen. This suggests that airborne (1fi3)-b-D-glucan can also be carried on fragments. These small bioaerosol particles may be underestimated by traditional air sampling and analysis methods, while they have a greater chance of being inhaled deep into the human respiratory system due to their small size (