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Levels of Indoor Airborne Microbes Are Associated with Ventilation Rates in Naturally-ventilated Residences
| Content Provider | Semantic Scholar |
|---|---|
| Author | Chien, H.-P. |
| Copyright Year | 2005 |
| Abstract | Indoor microbial exposure has been implicated to various adverse health effects. This study aimed to examine the effects of ventilation efficiency on indoor/outdoor levels of airborne microbes in homes with natural ventilation, a predominant type of residential buildings in Taiwan where high microbial concentrations have been reported. Environmental investigations were conducted in 44 homes. Indoor and outdoor airborne bacteria and fungi were collected by Burkard sampler with Trypticase Soy agar and Malt Extract agar in a flow rate of 10 LPM. The air change rate (ACH) was measured by tracer gas concentration decay method. Indoor airborne bacteria and total fungi levels in most investigated houses were generally greater than 1000 CFU/m. The most frequently isolated fungal genus was Aspergillus, Penicillium, Cladosporium, Alternaria and Yeast. The higher indoor/outdoor (I/O) ratios of total fungal levels were found in those houses with higher ACH rates (p=0.09). The same phenomenon was also observed in I/O ratio of Alternaria (p=0.09), a genus commonly known of outdoor origin. However, such an association could not be identified with concentrations of indoor and outdoor airborne bacteria. Results have suggested higher air change rate in residences with natural ventilation may, in turn, elevate effectively indoor microbial levels of outdoor origin especially with absence of proper filtration. INDEX TERMS fungi, bacteria, air change rate (ACH), I/O ratio, naturally-ventilation INTRODUCTION Indoor air quality (IAQ) is a major contributor to total exposure from air pollution for people spending most of their time indoors (Spengler JD. et al., 1994). Studies have found that most fungi growing in domestic environments are associated with levels of dampness or presence of water damage at homes (Veroeff AP. et al., 1992; Pasanen AL. et al., 2000), and we have reported high levels of airborne fungi and endotoxin in homes of southern Taiwan, attributable to warm temperature and high relative humidity in the region (Su HJ. et al., 2001; Wu PC. et al., 2000a). Epidemiological evidences have demonstrated repeatedly relationships between indoor fungal exposures and adverse respiratory symptoms (Verhoeff AP. et al., 1997; Horner WE. et al., 1995), and indoor bioaerosol contaminations have therefore become a major concern for public health. The most of the indoor air fungi and fungal allergen molecules are derived from outdoor sources, in particular from regional vegetation or agriculture activities (Glushakova AM. et al., 2004). The determining factors affecting the ratios of indoor to outdoor airborne fungi levels are the type of ventilation system and/or air exchange rate. It was also investigated that different types of ventilation system in large office buildings would affect the microbial concentrations penetrated from outdoor into indoor air (Wu PC. et al., 2004). However, ventilation is expected to dilute the levels of indoor air pollutants (ASHRAE Standard 62-2001), and the performance of ventilation is considered strongly associated with reporting comfort and health outcomes, including Sick Building Syndrome (SBS) symptoms, asthma, allergy and short-term sick leave of residents in these buildings (Wargocki et al., 2002; Smedje et al.,2000; Sundell et al.,1994). This study therefore aimed to examine the effects of ventilation efficiency on indoor/outdoor levels of airborne microbes in homes with natural ventilation, a predominant type of residential buildings in Taiwan. RESEARCH METHODS Sampling sites Based on distributions of ambient air concentrations reported by Taiwan’s Environmental Protection * Corresponding author email: amb.wu@msa.hinet.net Proceedings: Indoor Air 2005 1798 Administration, the residential houses were selected from the southern and eastern of Taiwan, 2 regions with high and low air pollution, respectively. We randomly selected at least 5 villages around environmental monitoring stations. With consent, 44 homes with natural ventilation, mostly single houses and a few apartments, participated in the study. Standard protocol specified where to sample inside and outside of each home for collecting airborne fungi and bacteria while air change rate was also measured. Airborne fungi and bacteria measurement The Burkard sampler (Rickmansworth, UK) with Malt Extract Agar plates (MEA) and Tryptic Soy Agar (TSA) were used to collect the airborne fungi and bacteria at a calibrated orifice air-flow rate of 10 LPM (Macher et al., 1995; Su et al., 2001). The duplicate samples were sampled at 1.2-1.5 m from the floor, approximating the height of human respiratory tract. The sampling time was 30 seconds and concurrent measurements of temperature and relative humidity were also taken. The concentrations of airborne fungi and bacteria were expressed in colony forming unit per cubic meter (CFU/m). Air Change Rate Measurement. Air change rate was determined with tracer gas concentration decay method by releasing sulphur hexafluoride (CO2) gas into the sealed room and mixing it well with the fan. The tracer gas concentration decayed as air flowing, and the ACH rate was measured by continuous Multi-Gas monitor Type 1302e (Brüel & Kjær, Demmark) (Shaw CY. et al., 1991). The following equation is used for estimating air exchange rate. ln C(τs ) – ln C(τf ) Δt Air Change Rate (ACH)= where C(τs ): concentration at time=τs (m/m) C(τf ): concentration at time =τf (m/m) Δt: total measurement period (h) Statistics Statistics were performed on SPSS 11.0 for Windows. Descriptive statistics were calculated for ACH rate, climatic factors and microbial concentrations, and Mann-Whitney U test was used to examine these variables between two sampling area. The associations of indoor and outdoor microbial concentrations were made using Linear regression. Nonparametric tests were used to examine the associations between indoor/outdoor (I/O) ratio of microbial concentrations and ACH rate. RESULTS With most samplings conducted in summer, the range of relative humidity and temperature were 46-76% and 27-33 °C , respectively. The geometric mean from all samples collected of indoor/outdoor airborne concentrations were 2078.3/868.7 CFU/m for total culturable bacteria in air and 2022.8/2395.7 CFU/m for fungi. The most frequently isolated fungal genus were Aspergillus(especially for Aspergillus niger) , Penicillium, Cladosporium, Alternaria and Yeast (over 70%), less frequently isolated Paecilomyces, Fusarium. The geometric mean of ACH rate of naturally-ventilated residences was 2.13/h (min 0.67, max 5.4), with most of them staying in the range of 1.5-2 ACH/h, similar to previous findings, and only one lower than 0.4 ACH/h, the recommendable value of residential ventilation in U.S.A. (Uniform Building Code, 1997). There was no significance difference between the averaged ACHs from homes in eastern or southern Taiwan, a key variable in this investigation. Therefore, analysis followed was performed with all measurements together. The correlation coefficient between geometric mean of concentrations of total bacteria, total fungi and the most frequently isolated genus in either indoor or outdoor environments were shown in table 1. It was found that indoor concentrations and outdoor concentrations were significantly correlated in total fungi, Aspergillus , Penicillium, Cladosporium, Alternaria and PM10. The indoor and outdoor levels of total fungi and Cladosporium were moderately well correlated (r= 0.82 and r= 0.74, respectivitly. P<0.01) But the correlations were not observed in total bacteria and yeast. However, the ratios of indoor/outdoor bioaerosols were analyzed with levels of ACHs to understand the changed distribution between outdoor and indoor microbial concentrations through the mediation of ventilation. First, the mean of I/O ratio based on microbial concentrations was log-transformed, and the ACHs were divided by either the median, or 25 percentile (table2). Only the I/O ratio of total fungi and alternaria was lower for those homes with ACH<2.13/h, the median value, compared to those with Proceedings: Indoor Air 2005 1799 greater than 2.13, though without significant difference. Moreover, the I/O ratio of A. candidus was significantly different among 4 groups of homes with ACHs of different quartiles. A weak, but not significant, association was observed between the increasing I/O ratios of Cladosporium and Alternaria and increasing ACH rates. No similar trend could be identified with I/O ratio of airborne bacteria. Table 1. The geometric mean of concentrations and correlations between indoor and outdoor airborne microbes and PM10. (N=44) Total bacteria Total fungi Aspergillus Penicillium Cladosporium Alternaria Yeast PM10 Total bacteria 0.18 0.05 0.18 0.15 0.23 -0.19 0.25 0.15 Total fungi -0.08 0.82 0.35* 0.15 0.64 0.41 0.27 -0.24 Aspergillus <0.01 0.40 0.33* 0.21 0.30 -0.12 0.39* -0.22 Penicillium -0.15 0.09 0.023 0.63 0.63 -0.07 0.07 -0.02 Cladosporium 0.07 0.66 0.26 0.12 0.74 0.22 0.14 -0.26 Alternaria -0.13 -0.15 -0.19 -0.10 0.12 0.33* -0.27 -0.09 Yeast -0.07 -0.03 0.24 0.34* -0.10 0.06 0.28 0.22 PM10 -0.41* -0.01 0.07 0.20 -0.13 -0.52 -0.04 0.38* *: P<0.05 in Pearson Correlation # : P<0.01 in Pearson Correlation Table 2. The geometric mean of I/O ratios with microbial concentrations at different percentile of ACH rate. |
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| Alternate Webpage(s) | http://www.isiaq.org/docs/PDFs/1797.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
