Effects of Child Care Center Ventilation Strategies on Volatile Organic

Feb 19, 2008 - Preschool children can be at risk from harmful volatile organic compounds (VOCs) exposures in child care centers (CCCs). However, the ...
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Environ. Sci. Technol. 2008, 42, 2054–2059

Effects of Child Care Center Ventilation Strategies on Volatile Organic Compounds of Indoor and Outdoor Origins MOHAMED S. ZURAIMI* AND KWOK W. THAM Department of Building, School of Design and Environment, National University of Singapore, 4 Architecture Drive, SDE2, Singapore 117566

Received June 12, 2007. Revised manuscript received November 29, 2007. Accepted December 22, 2007.

Preschool children can be at risk from harmful volatile organic compounds (VOCs) exposures in child care centers (CCCs). However, the effectiveness of ventilation for mitigating indoor VOCs exposures from myriad sources in CCCs is unclear. We investigated relationships between indoor exposures and risks of VOCs from indoor and outdoor sources under different ventilation strategies in 104 tropical CCCs. Factor analyses identified five dominant source groups of which four were associated with indoor sources, and one was associated with both indoor and outdoor sources. Indoor VOCs exposures and risks associated with indoor sources were lower in naturally (NV) and hybrid ventilated (HB) CCCs compared to airconditioned CCCs (ACMV and AC). This is attributed to enhanced dilution via higher ventilation in NV and HB CCCs compared to ACMV and AC CCCs. Conversely, there were no discernible differences in VOCs exposures and risk associated with both indoor and outdoor sources across different ventilation strategies. The observations made in this study have implications of ventilation strategies used in other settings. To mitigate VOCs exposures and risk, it is important to identify their major indoor and outdoor sources first.

Introduction Exposure to volatile organic compounds (VOCs) has been associated to a variety of health effects (1–5). Among the different age groups, children are uniquely at risk from indoor VOCs exposures because they generally breathe more rapidly and are often more susceptible because their immune systems and developing organs are still immature (6, 7). While many investigations on children’s VOCs exposures indoors have evaluated levels in the homes and used them as the relevant measure of exposure (8, 9), a significant proportion of children attend some form of child care (10, 11). Currently, limited data exists on VOCs exposures in child care centers (CCCs). Indoor exposures to VOCs in CCCs are determined mainly by building ventilation and their numerous sources. Numerous investigations have documented higher VOC levels indoors than outdoors attributed to emissions from building materials, equipment and appliances, cleaning products and activities, smoking, cooking, recent painting, and renovations * Corresponding author phone: 65-65163449; fax: 65-67755502; e-mail: [email protected]. 2054

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(2, 8, 9, 13–20). Under these circumstances, ventilation can be employed to mitigate VOCs exposure. Concomitantly, proximity to outdoor sources, such as traffic emissions, has been shown to increase indoor exposures to several VOCs (2, 12). Further, some VOCs are known to have both indoor and outdoor sources (2, 12, 14, 19). Here, source identification and removal policies can be difficult and increased ventilation will not necessarily lead to lower indoor exposures. Singapore is a tropical city, where the ventilation strategies adopted by the CCCs can be classified as naturally ventilated (NV), hybrid (combination of natural ventilation and airconditioning) ventilated (HB), air-conditioned and mechanically ventilated (ACMV), and air-conditioned but without ventilation (AC). In this article, we present the exposures and risk of indoor VOCs, their sources, and the impact of ventilation strategies in a nationwide study involving 104 representative CCCs in Singapore. This investigation is part of a larger epidemiological study intended to provide decision-makers with information relating different CCC exposures with asthma, allergies, and respiratory symptoms among children attending CCCs in Singapore (21).

Experimental Section Study Design and CCCs. A cross-sectional design was adopted for this study. From the ministry’s database of 687 CCCs, 120 (18%) were randomly selected, of which, 104 (86.7%) agreed to participate. For each CCC, an indoor (main classroom) and an outdoor sampling point were randomly selected for simultaneous air sampling. Indoor samplings were performed in the middle of the classroom near the breathing zone of children (approximately 0.5–0.7 m). Designed to evaluate the “typical” levels of VOCs to which the preschool children in each CCC are exposed, samplings were conducted in the middle of the week and during the day from 8 am to 5 pm (sampling interval of 9 h). In this study, ACMV CCCs (N ) 5) are defined as those with a dedicated or shared air handling unit, filtration and fresh air provision (typically about 10% of total air change), HB CCCs (N ) 21), those that incorporate air conditioning for a portion of the day (typically 2 h) and relying on natural ventilation at other times, NV CCCs (N ) 59), those that rely on open windows only for ventilation and AC CCCs (N ) 19), those that incorporate split unit air-conditioners without any provision of fresh air. During inspections, it was found that there were rooms in some NV CCCs which were airconditioned. For these CCCs (N ) 19), an indoor air location in the NV room and another in the AC room were measured simultaneously making it a total of 123 samples. Supporting Information (SI) Table S1 provides a descriptive summary of the CCCs characteristics. VOCs Selection, Sampling, and Measurements. 31 target VOCs were selected (see SI Table S2) for sampling and analysis according to the following criteria: (a) interest because of their health and comfort significance (1, 23–29), (b) representative of the major chemical classes of compounds that occur in indoor air (30), (c) utility of one or group of few compounds as markers of pollution sources (2, 9, 12–20), and (d) ability in attaining quality assurance and control (QA/QC) in analyses. For noncarbonyls, VOCs were actively sampled using a sampling pump (AP Buck Inc.) onto preconditioned Tenax TA sorbent tubes. Duplicate flow rates were set at 5 and 10 mL min-1. For carbonyls, duplicate air samples were pumped through DNPH cartridges (Supelco) using another sampling pump at flow rates of 0.5 and 1 L min-1. Flow rates were 10.1021/es0714033 CCC: $40.75

 2008 American Chemical Society

Published on Web 02/19/2008

measured before and after sampling using the mini Buck airflow calibrator (AP Buck Inc.). The sampled VOCs on Tenax tubes were desorbed using an automated thermal desorber (Perkin-Elmer), separated using a gas chromatograph (Agilent) and analyzed using a mass selective detector (Agilent). For carbonyls, the analytes were eluted using acetonitrile and analyzed using a high performance liquid chromatography equipped with a diode array detector (Agilent). For every CCC, a field and laboratory blank is employed. VOCs with measured values lower than their method detection limit (MDL) were assigned to a value half of the MDL. Details of the sample collection, analysis and QA/QC can be found in the Supporting Information. Environmental Parameters. Carbon dioxide (CO2) concentrations were measured continuously indoors and outdoors using Tel-Aire monitors. Using the measured CO2 as a tracer gas, CCCs air exchange rates (AER) was analyzed using the TGD software (LESO-PB, EPFL, Switzerland) validated elsewhere (31). Health, Comfort, and Risk Calculation. The indoor concentrations were compared to health and comfort guidelines and risk of developing cancer. We assessed cancer risks using conventional approaches (23–26). The inhalation unit risk factors representing the probability that an individual will develop cancer as a result of exposure to 1 µg/m3 of the compound over a lifetime was used. Unit risk values were either taken from the Integrated Risk Information System (25) or the California Office of Environmental Health and Hazard Assessment (OEHHA) (26). Risks were expressed as excess cancers per 1 million population based on exposures over a 70 year lifetime. We assessed noncancer health threshold by the inhalation reference concentrations (RfCs). An inhalation RfC was defined as an estimate of a continuous inhalation exposure to the human population that is likely to be without appreciable risk of deleterious noncancer health effects during a lifetime (25). These toxicity data were obtained from various sources (23–26). VOCs odor thresholds were obtained from Devos et al. (27), and their irritation thresholds were obtained from from Cometto-Mun ˇ iz et al. and Ruth (28, 29). Following the method by Woodruff et al. (24), hazard ratios (HR) were computed by dividing each indoor VOC concentration by the VOC threshold concentrations for noncancer health (HRRfC), odor (HROT), and irritation (HRIT) thresholds. Hazard ratios greater than 1 indicate that the indoor concentration exceeds the threshold concentration. Data Analysis. Data analysis was conducted using SPSS version 14.0 (SPSS Inc., Chicago, IL). Due to the skewed distributions of VOCs and AERs, natural log transformed values were used in statistical analyses. Comparisons of means were performed using analysis of variance (ANOVA). Factor analysis was performed to investigate the dominant source type underlying the observed indoor VOCs concentrations (32). Compounds that were detected in more than 90% of the samples (24 compounds) were subjected to this analysis. Principal component analysis (PCA) and maximumlikelihood solution were used together to evaluate consistencies of estimated factor loadings (32). Orthogonal (Varimax)rotationswereperformedforbothextractionprocedures. As recommended, the original data was randomly divided into two subsets and their factor scores evaluated to confirm the factor structure (32). To account for correlation among the extracted factors or sources, an additional procedure of extraction utilizing principal axis factor with oblique (Promax) rotation was also performed.

Results and Discussion Factor Analysis. SI Table S3 summarizes the results of the factor analysis. The first factor was loaded with VOCs mainly associated with building materials (BM) found indoors such as floorings, their adhesives and finish, furniture coatings,

and laminates (16–18). The second factor represents the emissions of air fresheners and cleaning products usage (AF/ CP). Terpenes such as limonene and R-pinene are used in air fresheners and as an odorant and active ingredient in cleaning products (2, 12, 20). 2-ethyl-1-hexanol can be produced by hydrolysis of 2-diethylhexyl phthalate in PVC floorings during wet cleaning. The third factor was loaded with compounds dominantly associated with traffic emissions (TE). Results were consistent with the findings of PC analysis of VOC concentrations elsewhere (2, 14) documenting high loadings of aromatics, in particular benzene. When analysis included AER, it was significantly loaded into this factor suggesting that it is associated with a strong outdoor contribution. However, these compounds are not exclusively of outdoor origin and can also be emitted from more than 200 indoor sources and human related activities (19, 34–36). Hence, this factor has both dominant indoor and outdoor sources and correspondingly designated as TE/IN. The fourth factor is indicative of dominant water based paint (WBP) sources. When compounds with less than 90% detects were included in the factor analysis, 2-butoxy ethanol, isopropanol, and 1,1,1-trichloroethane also loaded into this factor. This result was consistent with the principal components analysis of VOC concentrations in the California study (2, 12) showing high correlations between isopropanol and 2-butoxy ethanol. 1,4-dichlorobenzene has been reported to be found in water based paints (33). Formaldehyde and acetaldehyde were highly loaded onto the fifth factor where pressed-wood materials (PWM) have been reported to be major sources of their release (13, 15). Possible sources of PWM in CCCs are the shelves, tables, and wooden floor, walls, and ceiling panels. AERs of CCCs. SI Figure S1 shows the boxplots of CCC AERs. ANOVA tests showed significant differences in AERs (P < 0.05) between CCCs with low ventilation rates (ACMV and AC CCCs where mean ((SD) values (0.6 ( 1.6 and 0.7 ( 1.2 h-1, respectively)) and those with high ventilation rates (NV and HB CCCs (4.7 ( 7.7 and 4.2 ( 6.6 h-1, respectively)). Bonferroni test revealed that there were no significant differences in AERs between NV and HB CCCs, and between ACMV and AC CCCs. The facilitation of outdoor air ingress through open windows presumably resulted in larger AERs in NV and HB CCCs compared to those in ACMV and AC CCCs where outdoor air provided for ventilation is limited typically to only 10% due to energy conservation (21). In a summer study of 47 homes in State College, Pennsylvania (22), the authors documented median AERs about 6 times higher for non-air-conditioned homes compared to airconditioned homes. Indoor and Outdoor VOC Concentrations. Summary statistics of the indoor and outdoor VOCs concentrations is given in SI Table S4. Concentrations of compounds found to be significantly higher indoors than outdoors include 1-butanol, naphthalene, formaldehyde, 2-propanone, limonene, and nonanal, whereas outdoor concentrations of 1,1,1-trichloroethane, tri- and tetra-chloroethene, benzene, styrene, n-decane, benzaldehyde, and acetophenone were significantly higher than indoors. Significant correlations (ranging from 0.188 to 0.658) were found between indoor and outdoor concentrations for most VOCs with 90% detects. Our data on indoor VOCs composition and concentrations were generally consistent with the literature reported for Singapore office buildings (19, 34). However, there were some differences such as the lower concentrations of chlorinated hydrocarbons in the CCCs. This could be due to the lesser use of environmentally harmful and toxic halocarbons in CCCs compared to office buildings. Also, contrary to our findings, it has been reported that in many studies of residences (8, 35) and office buildings (34), benzene is almost always higher indoors, even in some heavy traffic areas. This VOL. 42, NO. 6, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 1. Factor scores by ventilation strategies. From bottom to top, each box presents the 5th, 25th, 50th (i.e., median), 75th, and 95th percentiles. may, in part, reflect the lower ventilation rates in residences (mean: 0.5 h-1 (41)) and office buildings (mean: 0.9 h-1 (34)) when compared to the CCCs (range: 0.6–4.7 h-1; mean: 2.9 h-1). Although many published studies have reported total volatile organic compounds (TVOC) concentrations, very few reported speciated VOCs exposures. Further, TVOC values could not highlight the potential risk, health and comfort effects of some compounds (30). However, related CCC works have reported formaldehyde concentrations close to 6.1 µg/ m3 in Italian nurseries and kindergartens (37), 429 µg/m3 in Danish mobile buildings as opposed to 7.9 µg/m3 in permanent buildings (38), and 15 µg/m3 for 30 Finnish CCCs (39). In another Finnish study (40), researchers reported formaldehyde value of 10 µg/m3 in a CCC with mold problem. Formaldehyde levels in Singapore CCCs are thus comparable to those in Italy and Denmark but lower than those in Finland. Effects of Ventilation Strategies. Figure 1 illustrates the effect of different ventilation strategies on the factor scores derived from the PCA analyses. Statistically significant differences were found for sources associated with BM and AF/CP (P < 0.05). High responses for these two groups of sources appear to be from ACMV and AC CCCs whereas low responses were observed for NV and HB CCCs. For VOCs sources associated with WBP and PWM, the responses were similarly lower than 0 for both NV and HB CCCs. Scores associated with WBP and PWM were higher in ACMV and AC CCCs. However, no statistically significant difference was found for factor scores associated with WBP and PWM. This is attributed to some negative factor loadings in WBP and PWM, thus the effects of high response due to important compounds may be masked by the low response from compounds with negative loadings. No statistically significant difference was observed for TE/IN factor. This is due to the presence of co-occurring dominant indoor and outdoor sources associated with these VOCs. Table 1 provides the geometric mean, standard deviation and median VOCs concentrations measured indoors and outdoors of the CCCs arranged according to their identified sources. There were no statistical differences in outdoor VOCs concentrations between the four ventilation strategies (P > 0.10). However, indoor levels of most VOCs from the BM, AF/CP, WBP, and PWM source group were significantly different (P < 0.05) for the four ventilation strategies. For these compounds, the levels were higher in air-conditioned CCCs (ACMV or AC) when compared to NV and HB CCCs. No statistically significant differences (P > 0.10) were noted for all compounds from the TE/IN source group. Indoor and outdoor correlations were not altered when the data was stratified with respect to ventilation strategies (Table 1). The 2056

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nonsignificant correlations for compounds measured in ACMV CCCs were due to the low sample size (N ) 5). The I/O ratios of VOCs which offers an indication of the extent to which the compounds found indoors are dominated by indoor generation and/or influenced by ventilation effects were also computed (SI Figure S2). I/O ratios lesser than or equal to 1 indicate the absence of indoor sources or high dilution effects of indoor sources while ratios greater than unity indicate the presence of strong indoor sources or poor ventilation (34). For sources relating AF/CP, WBP, and PWM, the I/O ratios of most compounds in NV and HB CCCs were generally lower than 1, with some compounds exhibiting median I/O ratios as low as 0.4. Their corresponding I/O levels in ACMV and AC CCCs were generally higher, although statistical significance can be found only for 1,4-dichlorobenzene, 2-propanol, acetaldehyde, and formaldehyde. The significantly lower AERs in air-conditioned centers contributed to the built up of indoor generated VOCs from BM, AF/CP, WBP, and PWM in AC and ACMV CCCs. This highlights the ventilation inadequacies in diluting the dominant indoor sources of VOCs. On the other hand, the high AERs in NV CCCs lowered the concentrations of VOCs of indoor origin such as those from BM, AF/CP, and PWM associated compounds. For compounds dominantly associated with TE/IN source, a balance in the contribution of increased built-up due to emissions of indoor sources associated with these VOCs and their reduced ingress from outdoor sources in AC and ACMV CCCs was observed. In NV and HB CCCs on the other hand, the high dilution of indoor source contributions countered the higher ingress of outdoor TE/IN. This results in no significant difference (P > 0.10) in indoor exposures, I/O ratios and factor scores for most compounds associated with TE/IN source under different ventilation strategies. Risk Assessment. Summary statistics of the hazard ratios for odor, irritation, potential noncancer health risks, and estimated lifetime excess cancer risks based on indoor exposures to different VOCs under various CCC ventilation strategies are presented in detail in the Supporting Information. For the four VOCs with the highest cancer risk estimates, the highest risk (median) is benzene (229), followed by formaldehyde (79), naphthalene (69), and finally 1,4-dicholorobenzene (20). This ranking is slightly different to that modeled in the U.S.-wide study (42). The researchers had reported that formaldehyde had the highest cancer risk estimate followed by benzene, 1,3-butadiene, acetaldehyde, 1,4-dichlorobenzene, and naphthalene. For all the VOCs, neither the HROT nor HRIT exceeded 1. Benzene, acetaldehyde, naphthalene, and o-xylene presented the highest median HRRfC values where only the first three VOCs had values greater than 1. The median HROT, HRIT, and HRRfC of VOCs associated with BM, AF/CP, WBP, and PWM sources were generally higher in ACMV and AC CCCs. No discernible differences in corresponding HROT HRIT, and HRRfC values for TE/IN related VOCs such as benzene were found between different CCC ventilation strategies (SI Table S5–S7). Cancer risk estimates per one million displayed a similar trend across different ventilation strategies (SI Table S8). Median cancer risk estimates per one million were higher in ACMV and AC CCCs for indoor associated VOCs whereas risk estimates for TE/IN related benzene were indistinguishable between ventilation strategies. Uncertainties and Confounding. Because regulatory decisions are based on risk evaluations, it is important to know how CCC ventilation strategies give rise to differing risks estimates of VOC exposures. However, given the large uncertainties in risk calculations, it is difficult to ascertain significant differences between estimated cancer risks. Assumptions used by the U.S. Environmental Protection Agency

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0.1 0.1 0.6 0.6 0.1

0.2 (0.2)b 0.2 (0.1) 0.7 (0.3) 0.7 (0.3) 0.1 (0.1)

methylisobutylketone isoprene trichloroethene tetrachloroethene β-pinenea

mean (SD)

HB

b

0.1 0.1 0.6 0.6 0.1

3.5 5.2

0.3 0.4 1.3 0.1 0.3

30.5 1.1 1.8 0.3 0.4

0.1 0.6 0.2 3.3 0.4 0.9 0.6 0.3

4.8 2.9 13.7 0.6 1.2 0.2

med

0.4 (0.6) 0.1 (0.1) 0.8 (0.4) 1.0 (0.6) 0.1 (0.1)

10.8 (12.2) 14.4 (11.9)b

0.6 (0.3) 1.1 (2.3) 17.6 (2.9) 0.1 (0.1) 0.5 (0.3)

24.2 (30.1) 2.5 (1.4) 4.5 (2.6) 0.6 (0.3) 0.5 (0.3)

0.2 (0.2) 1.8 (2.6) 1.1 (0.5) 25.5 (16.2) 3.0 (5.4) 2.2 (1..3) 0.8 (0.3) 1.0 (0.9)

10.5 (19.6) 9.2 (10.5) 54.8 (50.9) 1.5 (1.1) 2.7 (1.7) 0.5 (0.6)

mean (SD)

ACMV

0.2 0.1 0.6 1.1 0.1

5.6 16.6

0.6 0.4 17.7 0.1 0.6

28.4 2.7 5.2 0.7 0.5

0.2 1.3 1.1 21 1.9 2.8 0.8 1.2

16.8 10.4 37.2 1.2 3.3 0.5

med BM 13.2 (12.3)b 8.2 (7.7)b 26.9 (27.0)b 1.1 (0.9)b 3.0 (3.3)b 0.4 (0.4)b AF/CP 0.3 (0.4) 1.5 (2.2) 1.2 (1.5) 9.4 (12.7)b 1.5 (2.1)b 2.3 (2.1)b 1.0 (0.8) 0.8 (0.7)b TE/IN 17.9 (15.0)b 1.7 (1.6)b 2.7 (3.2)b 0.6 (0.4)b 0.8 (0.5)b WBP 0.5 (0.3)b 1.6 (2.4) 8.0 (13.5) 0.1 (0.1) 0.5 (0.3)b PWM 11.5 (13.6)b 6.9 (6.2) others 0.5 (0.9)b 0.2 (0.1) 0.8 (0.4)b 0.8 (0.4) 0.1 (0.1)b

mean (SD)

AC

0.3 0.1 0.6 0.6 0.1

9.8 6.4

0.5 1.1 5.6 0.1 0.3

21.2 1.7 3.3 0.7 0.6

0.2 1.4 1.1 14.4 4.5 2.3 1.2 0.7

13.7 8.5 29.8 1.2 2.9 0.2

med

0.2 (0.2) 0.2 (0.2) 1.1 (1.1) 1.1 (0.8) 0.1 (0.1)

2.3 (3.0) 6.9 (6.8)

0.5 (0.4) 1.0 (0.8) 4.2 (5.5) 0.2 (0.1) 0.5 (0.3)

36.5 (42.3) 2.5 (2.1) 4.4 (6.2) 0.8 (0.7) 0.3 (0.3)

0.1 (0.1) 0.5 (0.4) 0.5 (0.4) 2.9 (3.9) 0.3 (0.3) 1.7 (1.3) 0.5 (0.4) 0.6 (0.4)

9.0 (10.2) 5.5 (6.3) 18.4 (17.7) 0.8 (0.8) 0.9 (0.9) 0.4 (0.3)

mean (SD)

NV

0.2 0.1 0.6 0.6 0.1

0.8 5.8

0.5 0.9 3.9 0.1 0.3

42.8 2.7 4.2 0.8 0.4

0.1 0.6 0.2 3.6 0.3 1.8 0.6 0.3

9.2 5.7 22.1 0.9 1.0 0.2

med

0.1 (0.1) 0.1 (0.1) 1.0 (0.7) 0.9 (0.5) 0.1 (0.1)

1.8 (2.2) 7.5 (8.3)

0.5 (0.3) 0.8 (0.6) 2.1 (2.8) 0.1 (0.0) 0.4 (0.2)

24.6 (19.0) 1.9 (1.1) 3.1 (2.9) 0.9 (0.5) 0.3 (0.3)

0.1 (0.1) 0.5 (0.4) 0.5 (0.3) 1.9 (2.0) 0.3 (0.2) 1.6 (1.1) 0.5 (0.4) 0.5 (0.4)

5.9 (5.1) 3.7 (3.1) 12.8 (11.3) 0.7 (0.5) 0.7 (0.5) 0.3 (0.2)

mean (SD)

HB

0.1 0.1 0.6 0.6 0.1

0.8 7.8

0.5 0.9 3.4 0.1 0.3

25.1 1.8 3.0 0.9 0.3

0.1 0.6 0.4 1.8 0.3 0.9 0.6 0.3

7.0 4.2 16.7 0.8 0.7 0.2

med

0.2 (0.3) 0.1 (0.1) 0.9 (0.8) 1.3 (1.1) 0.1 (0.1)

2.0 (2.5) 6.2 (7.3)

0.5 (0.6) 1.0 (1.0) 3.1 (3.6) 0.3 (0.6) 0.5 (0.4)

43.0 (23.5) 3.4 (2.7) 5.4 (5.4) 1.0 (1.0) 0.4 (0.5)

0.1 (0.1) 0.4 (0.3) 0.5 (0.4) 7.0 (3.9) 0.6 (0.6) 1.3 (1.1) 0.4 (0.3) 0.6 (0.5)

17.2 (22.1) 10.6 (13.7) 40.7 (36.7) 1.3 (1.7) 1.0 (1.5) 0.4 (0.3)

mean (SD)

ACMV

outdoor concentrationc (µg/m3)

c

0.2 (0.3) 0.2 (0.1) 1.1 (0.8) 1.0 (0.8) 0.1 (0.1)

1.6 (1.6) 8.5 (9.0)

0.5 (0.5) 1.0 (1.1) 5.2 (7.6) 0.2 (0.1) 0.5 (0.4)

31.9 (37.5) 2.2 (2.3) 4.0 (5.1) 0.8 (0.6) 0.4 (0.3)

0.1 (0.1) 0.5 (0.6) 0.5 (0.5) 3.3 (5.1) 0.4 (0.4) 1.6 (1.3) 0.5 (0.4) 0.6 (0.5)

8.0 (8.3) 4.9 (5.2) 16.7 (17.6) 0.9 (0.8) 1.0 (1.2) 0.4 (0.3)

mean (SD)

AC

0.2 0.1 0.6 0.6 0.1

0.8 8.9

0.6 1.0 5.8 0.1 0.3

40.8 2.5 4.6 0.8 0.4

0.1 0.6 0.4 3.8 0.4 0.9 0.2 0.5

9.1 5.6 18.6 0.9 0.8 0.2

med

Mean and standard

0.1 0.1 0.6 1.4 0.1

0.8 5.5

0.3 1.3 3.5 0.1 0.3

42.5 3.5 6.8 0.9 0.6

0.1 0.4 0.4 6.9 0.4 0.9 0.4 0.6

14 8.7 36.4 1.4 0.8 0.4

med

Significant correlations between indoor and outdoor concentrations for the type of ventilation strategy.

0.2 (0.3)b 0.2 (0.1) 0.8 (0.4) 0.8 (0.8) 0.1 (0.1)

3.0 (3.9)b 6.0 (5.0)b

0.3 (0.2)b 0.9 (1.0) 1.8 (2.5) 0.1 (0.1) 0.4 (0.2)

17.5 (22.3) 1.1 (0.9) 2.1 (2.1) 0.5 (0.3) 0.3 (0.2)

0.1 (0.1) 0.7 (0.6) 0.4 (0.2) 3.6 (4.3)b 0.3 (0.2)b 1.5 (1.2)b 0.6 (0.5) 0.4 (0.2)

5.2 (4.9)b 3.1 (2.6)b 12.7 (9.0)b 0.5 (0.4)b 1.0 (0.8)b 0.4 (0.3)b

a Significant difference in indoor concentrations. deviation (SD) are geometric. Med: median.

6.0 6.4

5.2 (6.5)b 5.7 (5.5)b

formaldehydea acetaldehydea

0.3 0.4 2.2 0.1 0.3

32.7 2.0 3.3 0.6 0.4

25.4 (23.7)b 1.8 (1.3)b 2.5 (2.9)b 0.6 (0.5) 0.3 (0.2)b

0.4 (0.3)b 1.0 (1.4) 2.2 (2.7) 0.1 (0.1) 0.4 (0.2)

0.1 0.4 0.2 3.2 0.4 0.9 0.6 0.3

8.1 5.0 18.1 0.7 0.9 0.2

med

0.1 (0.1) 0.4 (0.4) 0.4 (0.3) 2.4 (2.5)b 0.4 (0.4)b 1.4 (1.0)b 0.5 (0.4) 0.4 (0.2)

8.4 (7.3)b 5.2 (4.6)b 17.4 (13.9)b 0.6 (0.5)b 1.0 (1.0)b 0.3 (0.2)b

mean (SD)

NV

n-decanea ethylbenzene 2-propanol 1,1,1-trichloroethane 2-butoxyethanol

benzene benzaldehyde styrene acetophenone n-hexadecane

R-pinenea limonenea 2-ethyl 1-hexanola 2-propanonea 1-butanola 1,4-dichlorobenzenea nonanala n-heptanea

o-xylenea m/p-xylenea toluenea 1,3,5-trimethylbenzenea naphthalenea butyl acetate

compounds

b

indoor concentrationc (µg/m3)

TABLE 1. Concentrations of VOCs and Carbonyls in CCCs with Different Ventilation Strategies

and the Office of Environmental Health Hazard Assessment such as standard body weight and average breathing rate may not reflect the variability of the population at large and specific differences between adults and children and between Caucasians and Asians. Also, toxicity information obtained from studies using animals have uncertainty related to extrapolations from high doses for animals to low human exposures. Indeed, information providing confidence intervals for cancer potency estimates are still not available. Despite these assumptions which may bias the estimates, the median values provide a good indication of the relative risk levels among attending children in CCCs with different ventilation strategies. Also, analyses of risk assessment used in this study can provide insight not only about the high-risk VOCs, but also about the dominant sources of their exposures, which can allow proper mitigation strategies for more effective means of exposure reduction. It can be argued that since different settings of the CCCs were not identical (SI Table S1), VOCs sources could be another major influencing factor on the indoor concentration in addition to the ventilation strategies. The prevalence of wood products, carpet, and PVC flooring in ACMV CCC were generally higher than the others which might explain corresponding higher values of factor scores and VOCs exposures from sources associated with BM and PWM (Figure 1, Table 1). Similarly, the higher numbers of children in ACMV and AC CCCs could explain the elevated levels of VOCs associated with AF/CP emissions. We believe that these effects could be minor in comparison to the ventilation strategies. Comparisons of VOCs exposure and factor scores revealed that only toluene was significantly higher for CCC with carpet flooring when stratified according to ventilation strategies (SI Table S9). When the factor scores and VOC exposures related to AF/CP source were regressed against the CCC number of children, only limonene and 2-ethyl 1-hexanol were significantly associated (SI Table S10). For these compounds, their sources could be another major influencing factor in addition to the CCC ventilation strategies. Practical Implications. This study showed that ventilation strategies of CCCs created differences in indoor VOC exposures and their health risks. VOCs exposures and risks were higher in ACMV and AC CCCs attributable to their lower AERs. However, these differences are only observed for VOCs of dominant indoor sources. There were no statistical differences in concentrations and risks associated with VOC from both outdoor and indoor sources (TE/IN) for different ventilation strategies. Taken together, this study suggests that measures to mitigate VOCs exposures and risks in CCCs necessitate identification of major indoor and outdoor sources instead of just relying on ventilation. The dominant indoor sources of VOCs in CCCs identified in this study implies that source removal policies should focus on VOCs of indoor origin, at least for the high risk VOCs.

Acknowledgments This work is supported by the National University of Singapore research grant R-296-000-088-112. We thank the teachers and principals of the participating child care centers and the sampling team comprising of Adeline Phang, Khairulizwan, Loh Ting Tuan, and Tan Su Shan.

Supporting Information Available Additional details; Figures S1 and S2 and Tables S1, S2, S3, S4, S5, S6, S7, S8, S9, and S10. This material is available free of charge via the Internet at http://pubs.acs.org.

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