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Higher moisture content is associated with greater emissions of DEHP from PVC wallpaper
Environmental Research 152 (2017) 1–6
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Higher moisture content is associated with greater emissions of DEHP from PVC wallpaper Nai-Yun Hsua, Yu-Chun Liua, Chia-Wei Leeb,⁎⁎, Ching-Chang Leea, Huey-Jen Sua, a b
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Department of Environmental and Occupational Health, College of Medicine, National Cheng Kung University, Tainan, Taiwan Department of Safety, Health and Environment Engineering, National Kaohsiung First University of Science and Technology, Kaohsiung, Taiwan
A R T I C L E I N F O
A BS T RAC T
Keywords: Di-(2ethylhexyl) phthalate Indoor Building materials Dampness Flood
Water damage and moisture in buildings may become more prevalent due to the increasing frequency of extreme precipitation and flooding events resulting from climate change. However, the effects of moisture levels on phthalate emissions from building materials are still underreported. This study aims to evaluate the effect of moisture content (MC) on the level of di-(2ethylhexyl) phthalate (DEHP) emitted from plastic wallpaper (0.22 wt% DEHP) within 15 days in a closed chamber. A scenario of short-term exposure to DEHP in buildings suffering from water damage was simulated. Experiments, controlled at 100% relative humidity (RH) of air and 28 °C, were conducted under the following three conditions: (I) without wallpaper (control chamber), (II) dry wallpaper (MC at 3.57%) and (III) damp wallpaper (MC at 52.31%). Air and dust samples were collected at the elapsed time of 2, 4, 6, 8, 10, 13 and 15 days, and the wipe sample was collected on the last day. Higher DEHP concentrations were found to be emitted into the air and adsorbed on the dust for wallpapers with higher MC%. DEHP levels in the air exhibited an increasing trend with the length of the experiment. Overall, it was found that approximately 35.31% more total DEHP mass was released into the air, dust and wipe samples from damp wallpapers compared to dry wallpapers. It is concluded that DEHP emissions from plastic materials are affected by the inner moisture percentage.
1. Introduction Floods have been one of the most common types of natural disasters throughout the world in the past few decades (CRED, 2013), and the resulting water damage to buildings is unavoidable. Dampness and moisture problems in buildings are associated with the deterioration of indoor air quality and adverse health effects (IOM, 2004; WHO 2009), and the increasing exposure levels to indoor bioaerosols are thought to be the main cause of this association (Bloom et al., 2009; Emerson et al., 2015; He et al., 2014; Hsu et al., 2011; Rando et al., 2013). Additionally, the positive relationship between indoor dampness and exposure to phthalates could be another consideration (Jaakkola and Knight, 2008). Phthalates are widely adopted as plasticizers, fixing agents and dispersants in building materials and consumer products (Schettler, 2006; TERA, 2015). Bornehag et al. (2005) have indicated that higher concentrations of n-butyl benzyl phthalate (BBzP) were found in Swedish homes with self-reported water leakage. In China, levels of BBzP, di-2-ethylhexyl phthalate (DEHP), dioctyl phthalate (DOP) and total phthalates were higher in houses where condensation or dampness was common than ⁎
in those without (Zhang et al., 2013). Ait Bamai et al. (2014) have shown that increased levels of di-n-butyl phthalate (DnBP) and DEHP were associated with signs of higher dampness in Japanese residences. In our earlier findings, increased DEHP levels in households of Taiwan were found to be associated with self-reported floods or water leakages in the past year, and higher DnBP and DEHP levels were found in cases where larger diameters of damp stain/visible mold growth on the walls were recorded by field investigators (Hsu et al., 2012a). Exposure to indoor phthalates emerges as an important issue, owing to their various hazards to human health (Braun et al., 2013; Kay et al., 2014, 2013; North et al., 2014). It is suggested that phthalates could be released due to the degradation of materials, caused by water and moisture (Bornehag et al., 2005). However, it is still unclear whether the levels of phthalates emitted from materials are affected by the inner moisture content (MC), defined as the moisture-holding properties of materials. To understand the short-term profile for exposure to phthalates after indoor water damage, this study aims to evaluate the effect of MC on the level of phthalates emitted from plastic wallpaper within 15 days in a closed chamber. DEHP (CASRN 117-817), the highest level of which has been detected in house dust in Taiwan
Correspondence to: Department of Environmental and Occupational Health, College of Medicine, National Cheng Kung University, 138 Sheng-Li Road, Tainan 70403, Taiwan. Corresponding author. E-mail addresses: [email protected] (C.-W. Lee), [email protected] (H.-J. Su).
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http://dx.doi.org/10.1016/j.envres.2016.09.027 Received 24 June 2016; Received in revised form 23 September 2016; Accepted 30 September 2016 0013-9351/ © 2016 Elsevier Inc. All rights reserved.
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were less than 2% and 6%, respectively.
(Hsu et al., 2012b) and other countries (Ait Bamai et al., 2014; Bekö et al., 2015; Blanchard et al., 2014; Bornehag et al., 2005; Kubwabo et al., 2013; Zhang et al., 2016), was selected as the examined target for the short-term emission profile. DEHP has been classified as a group 2B agent, considered to be possibly carcinogenic to humans by the IARC Monographs (IARC, 2013).
2.3. Sample collection A total of 7 air samples were collected from every chamber at the elapsed times of 2, 4, 6, 8, 10, 13 and 15 days. The mass of DEHP in the air was sampled by Tenax® Sorbent (SKC 226-56) at the flow rate of 1 L/min (Gillian GilAir-5) for 60 min. Due to the relatively small volume of the chamber, an inlet of air to the chamber was necessary for the purpose of pumping a sufficient volume of air. While air sampling was being conducted, the chamber was purged with a total of 60 L air, approximately 25 times the chamber volume, to ensure that the DEHP mass inside the chamber was collected completely. The fresh-air inlet was equipped with an active carbon filter to remove ambient levels of DEHP. Air outside the chamber was also collected to avoid background contamination. All the pumps were calibrated before and after the experiment. The DEHP mass was measured as the object of this sampling method, and the result was then converted and presented in units of volume concentration (µg/m3). A total of 7 dust samples were also collected from every chamber at the elapsed times of 2, 4, 6, 8, 10, 13 and 15 days. Seven customized trays (15 × 1 × 1 cm3), made of stainless steel and containing 1 g of the ASHRAE 52–76 standard dust, were placed on the first stage of the shelf inside each chamber (Fig. 1a). The standard dust was composed of 72% Arizona road dust (approximately 80 µm), 23% carbon black and 5% fibers. It was shaken ultrasonically with methanol for 30 min and blow-dried with nitrogen gas prior to the test to avoid background contamination. During the experiment, one tray was taken out from the chamber on the above-mentioned days. It was then covered with a Teflon lid and parafilm and stored at −20 °C until sample analysis. Only one wipe sample was collected from every chamber on the last
2. Materials and methods 2.1. Test material and chamber design The five most purchased polyvinyl chloride (PVC)-coated wallpapers in the market were analyzed for DEHP concentration, and the one with the highest level (2160.67 µg/g; 0.22%) was selected as the test material in the current study. The DEHP was coated only on a single side. A total of five chambers with three experimental conditions, varied by the MC levels of wallpapers, were examined. A 2.4 L glass desiccator was adopted as the study chamber, and a magnetic stirrer was set up at the bottom to mix air during the elapsed time of the experiment (Fig. 1a). The chambers were airtight and without ventilation except for the hour during which air sampling was conducted. Details of the air sample collection are described in Section 2.3. A two-stage shelf (with an area of 17 × 10 cm, and 5 cm height for each stage) made of stainless steel was placed at the center of the chamber (Fig. 1a). Seven trays with dust samples were placed on the upper stage, while one piece of the wallpaper was placed on the second stage. Every chamber contained four pieces of wallpaper, including three rectangles (12.5 × 60 cm, 5 × 44.5 cm, and 9.5 × 15.5 cm) and one circle (diameter 13.8 cm). The rectangles were placed around the circumference of the inner surface as well as on the second stage of the shelf, and the circle was placed at the bottom of the chamber. The total area of wallpapers used in each chamber was 1269.6 cm2, and the weight was 35.7 g, containing approximately 77,135.92 ng mass of DEHP (0.22% of 35.7 g). 2.2. Experimental conditions Moisture content (MC) is defined as the amount of water present in a substance in relation to its oven-dry weight (kg/kg) and is expressed as the percentage moisture content (%) at the oven temperature of 217°F (103 °C) (Reeb and Milota, 1999). A total of five chambers with three conditions, varied by MC levels of the wallpapers, were examined: (I) control chamber without wallpaper. (II) chamber with dry wallpaper (MC at 3.57 ± 0.22%). (III) chamber with damp wallpaper (MC at 52.31 ± 2.45%). The (I) control chamber was set to confirm whether any background contamination existed during this experimental period. MC was approximately 3.57 ± 0.22% in the original state of the test wallpaper and was approximately 52.31 ± 2.45% in the state saturated with water content for this test material, where pre-treatment by soaking in 500 ml RO water for at least 30 min was needed before placing the sample into the chamber. Duplicates were conducted for both the second (II) and third conditions (III). The time allowed to elapse for the experiment was 15 days. The air temperature in the airtight chamber was 28°C. To simulate an indoor scenario of flood and water damage, the relative humidity (RH) of air was set to 100%, a common environmental condition during days with heavy rain. 100% RH was also useful for stabilizing the MC levels of wallpapers in the chamber. Both the in-air RH and MC of wallpapers in the chamber during 15 days were maintained by adding 1 ml RO water at the elapsed times of 2, 4, 6, 8, 10, 13 and 15 days (Fig. 1b). To determine the changes of the MC levels, a fixed-size piece (1 × 2 cm) was cut out of a wallpaper in each chamber on the above-mentioned days and measured by an Infrared Moisture Balance (FD-610, Kett). The CV (coefficients of variation) for RH and MC during the 15 days
Fig. 1. (a) Chamber illustration and (b) RO water injected into the chamber.
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Whitney U test. The statistical analysis was carried out in SPSS 17.0 (Chicago, IL, USA), and a p-value of 0.05 was considered significant.
day of the experiment. For each chamber, a standard size of sterile gauze (2 × 2 cm2) soaked with acetone and methanol was used to wipe the inner surface of the chambers. To avoid contamination, all equipment used in the experiment, including stainless steel trays, glass bottles/tubes, and tweezers, was rinsed in advance with acetone and methanol (1:1 mixture).
3. Results In control chamber (I), without wallpapers, the average level of the 7 air samples was lower than the LOD (0.0082 μg/ml), and the average level of the 7 dust samples was below the lowest level of the calibration curve (0.01 μg/ml). It was therefore concluded that there was no background contamination in the chambers during the elapsed time of the experiment. The 15-day average concentrations of DEHP in the air of chambers (II) (dry, MC=3.57%) and (III) (damp, MC=52.31%) were 1.16 and 1.83 µg/m3, respectively, while the levels in the dust were 0.51 and 0.68 µg/g, respectively (Table 1). Higher levels were detected in the chamber set up with the damp wallpaper, but no statistically significant difference was found between the two conditions in both air and dust samples. Increasing concentrations of DEHP were emitted into the air and adsorbed on dust as the length of the experiment was increased, with maximum levels observed in the chamber with the damp wallpaper at 15 days (Fig. 2). Higher average levels were found for the air samples on each sampling day in the chamber with damp wallpapers compared to those with dry ones (Fig. 2a). Although there was a larger variation in the air concentration between duplicate chambers with damp wallpapers (3.94 and 8.04 μg/m3) on the final day, the detected levels were still higher than those detected with dry wallpapers (2.10 and 2.63 μg/m3). The DEHP levels in the settled dust samples showed a fluctuating pattern. Even so, greater averages were detected in the chamber with the damp wallpapers, considering the last 5 sampling spots (Fig. 2b).. The average of total mass measured in the (II), dry, and (III), damp, conditions was 4144.93 ± 271.77 and 5608.71 ± 71.87 ng, respectively, with approximately 5.37% and 7.27%, respectively, of the total DEHP mass transferred from the wallpapers. The mass adsorbed on dust was the major component, constituting approximately 86.78% and 84.76%, respectively (Fig. 3a). Overall, approximately 35.31% more total DEHP mass was released into air, dust and wipe samples from the damp wallpapers compared to those from the dry wallpapers. After the 4th day of the experiment, the emitted masses of DEHP began to rise (Fig. 3b). The increasing trend for damp wallpaper was steeper than that for dry wallpaper.
2.4. DEHP analysis The analytical procedure for air samples was implemented according to OSHA 104. The Tenax and glass-fiber filters were ultrasonically extracted by 4 ml toluene for 30 min; of this, 1 ml was then extracted and added to 10 ml of an internal standard (benzyl benzoate, ChemService). Each of the dust samples was fully mixed before removing 50 mg for extraction and analysis. The latter was extracted with 2 ml of dichloromethane/acetone (1:1) and then shaken ultrasonically for 30 min; this was repeated twice (Hsu et al., 2012b). All the extracts were combined and dried by nitrogen gas and reconstituted with 1 ml of dichloromethane. The analytical method for the wipe sample was the same as that for the dust sample. The concentrations of DEHP in all collected samples were analyzed by gas chromatography-mass spectrophotometry (GC/MS). The column used was a DB-5MS (60 m × 0.25 mm × 0.25 µm; Agilent, Folsom, CA, USA) column, with an initial injection temperature of 290 °C; the initial column temperature was set at 50 °C for 1 min and then increased at 15 °C/min to a final temperature of 310 °C, which was maintained for 16 min The R2 of the five-point calibration curve from 0.01 to 0.3 μg/ml was 0.996. The limit of detection (LOD) was 0.0082 μg/ml. One blank, one quality check (QC) with a mixture of the phthalate standard and one spiked sample (0.04 μg/ml for DEHP) were included in each batch of analyzed samples. The mean recoveries of air, dust and gauze from the QC samples were 88.9 ± 3.7%, 88.6 ± 2.8% and 102.9 ± 14.1%, respectively; the mean recoveries from the spiked sample were 87.3 ± 3.9%, 88.6 ± 2.8% and 87.3 ± 5.0%, respectively. The average desorption efficiencies for the air and wipe samples were 101% and 96%, respectively. 2.5. Data analysis The average and standard deviation of the DEHP concentrations, measured in duplicate for each condition, are presented. The mass concentrations of air and wipe samples were calculated by multiplying the detected concentration in the sampling tube (µg/ml) by the volume of extraction solvent (4 ml and 2 ml for the air and wipe samples, respectively). For the dust mass levels, the concentrations (µg/g) were multiplied by 1 g of dust. The ‘total mass’ was the sum of mass in air, dust, and wipe samples. However, all of the wipe samples collected on the final day exhibited lower levels than the LOD (0.0082 μg/ml). Their mass levels were derived through extrapolation, since adopting half the value of the LOD would lead to an overestimation of one order of magnitude at most. The difference of DEHP levels between the samples collected from dry and damp wallpaper conditions was examined by the Mann-
4. Discussion Increased DEHP emissions were observed from damp wallpaper compared to dry wallpaper in the current study, even when pieces containing very low levels of DEHP (0.22 wt% DEHP) were tested. Therefore, it is suggested that the material should be removed within four days once it has been damaged by water. 4.1. Indoor dampness and chemistry Increasing frequency or intensity of heavy precipitation has been
Table 1 DEHP levels in the air, dust and wipe samples for three experimental conditions. Experimental conditions (sample size)
Air sample (µg/m3)
II: dry wallpaper (14) III: damp wallpaper (14)
Dust sample (µg/g)
Detection rate , %
mean ± s.d.
p-value
Detection ratea, %
mean ± s.d.
p-value
100.00 100.00
1.16 ± 0.69 1.83 ± 2.03
0.34
100.00 100.00
0.51 ± 0.20 0.68 ± 0.26
0.11
a
*p-value for the difference between II (dry) and III (damp) wallpapers, examined by Mann-Whitney U test. a Percentage of detected concentrations higher than the lowest level of the calibration curve (0.01 μg/ml).
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observed in most mid-latitude continents under the impact of climate change (Hartmann et al., 2013). Water damage to buildings may become more prevalent due to the resulting flooding events. Moisture typically increases the decay of building materials. When materials stay wet for sufficiently long periods, problems can occur, including microbial growth, physical deterioration, or chemical reactions. Carll et al. (2007) reported that seasonal moisture accumulation in the sheathing of a wood-frame house was observed to cause the cracking of stucco cladding. Measurements of wood water content have been used as indicators of the level of material degradation (Previati et al., 2012). Bio-deterioration is one of the critical factors determining the durability and natural aging of building materials (Viitanen et al., 2010). Apart from microbial contaminants, moisture sometimes contributes to the release of chemicals into indoor air. It has been known that the rate of release of volatile organic compounds (VOCs), such as formaldehyde, from building materials increases with the humidity of the surrounding air (Markowicz and Larsson, 2014; van Netten et al., 1989; Wolkoff, 1998). This happens as a consequence of the hydrolysis reaction of urea-formaldehyde (Uhde and Salthammer, 2007) or due to competition between water vapor molecules for surface sites, which displaces the VOCs (Markowicz and Larsson, 2014). However, with regard to semi-volatile organic compounds (sVOCs), no association was found between air RH levels and the specific emission rate of DEHP from PVC flooring (containing 17 wt% DEHP) in a 1-year chamber study (Clausen et al., 2007). The authors suggested that DEHP is more strongly attached to stainless-steel surfaces than water vapor and that displacement by water vapor is insignificant (Clausen et al., 2004, 2007). Ekelund et al. (2008) also reported that there was no significant influence of relative humidity on the evaporation of DEHP from pristine DEHP and plasticized PVC cables (containing 23 wt% DEHP). Fig. 2. DEHP concentrations in (a) air and (b) dust samples during the experimental period.
4.2. Impact of MC on the emission of DEHP Instead of the humidity of air, the current study examined the effects of MC levels, defined as the amount of moisture held in the material, on DEHP emissions from test pieces, and another mechanism triggering the higher emission levels is suggested. According to the sVOC emission model proposed by Xu and Little (2006), the migration of DEHP from polymeric materials to air can be categorized into two stages: diffusion of DEHP within the PVC polymer (material-phase) and transport from the polymer surface to the surrounding air (gasphase). It is suggested that the moisture in materials is more likely to accelerate the material-phase reaction from the interior to the boundary (surface) based on the two theories below. The behavior of DEHP migration inside the PVC polymer could be described by the “classical Fick’s law of diffusion”, which states that the rate of diffusion is positively associated with the area and concentration difference but inversely associated with the distance (Colombani et al., 2009; Ekelund et al., 2008; Kim et al., 2003; Wang et al., 2015). Moisture migration in building materials has a great effect on the durability and degradation of the structures (De Freitas et al., 1996; Miniotaite, 2014). It is speculated that the diffusion distances were decreased and the diffusion areas were increased for interior DEHP due to the cracking of the PVC coating film as a result of the moisture, and higher emissions of DEHP were therefore detected. On the other hand, when the DEHP concentration on the material surface decreases as a result of the hydrolysis reaction, the concentration gradient is thought to be the driving force behind the diffusion of DEHP from the interior to the boundary of the material. Weschler (2004) has mentioned in his review article that the hydrolysis reaction of indoor organic esters with carboxylic acids and alcohols can be catalyzed by moist and alkaline conditions. This was further supported by Yokota et al. (2013), who found in their chamber experiment that higher MC levels in 10 wt% DEHP flooring materials were associated with increased emission rates of 2-ethyl-1-hexanol (2E1H), a hydrolysis product of DEHP. Yokota et al. (2013) proved that the hydrolysis
Fig. 3. (a) Total mass of DEHP for the three conditions; (b) profile of released mass of DEHP over 15 days.
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rather low percentage compared to those used in previous research. Second, the distance to the emission source is a critical factor related to the exposure level. Schripp et al. (2010) revealed in a 14-day study that a concentration up to 9.8 times higher (2080 vs. 213 µg/g) was found in dust brought into direct contact with the source of 17 wt% DEHP compared to when it was separated. In another 14-day emission test, an average of 384–481 µg/g was detected when the dust samples were directly placed on the test materials (Jeon et al., 2016). In our chamber setting, there was no direct contact between the dust samples and wallpapers. Finally, we consider the effects of saturated humidity on the adsorption capacity of settled dust. It is known that the sorption capacities of organic compounds on soil dust are extremely suppressed by water vapor, resulting in about a 100-fold reduction in watersaturated soil (Chiou and Shoup, 1985). High RH leads to thick surface coverage of the water film, which competes with organic chemicals for sorption sites. Dissolution of chemicals into the water phase and subsequent adsorption onto the soil surface is especially difficult for DEHP due to its nonpolar characteristics (Goss, 1993; Hippelein and McLachlan, 2000; Unger et al., 1996). In the current study, a saturated-air environment with 100% RH was set, not only to simulate a rainy-day scenario but also to stabilize the MC levels of the test wallpapers in the chamber during the elapsed time. It is therefore thought that the relatively low levels quantified in the settled dust and wipe samples in the current experiment were partly due to the effect of saturated humidity on the adsorption capacity of the particles and chamber surface.
reaction of DEHP, in terms of the emission rate of 2E1H, was accelerated by the MC. Yet, it is still unclear whether the emission of DEHP can be elevated by the MC conditions. Our study also demonstrates that higher MC in materials can lead to greater DEHP emission, and the concentration gradient is speculated to be the driving force behind this phenomenon. More DEHP migrates to the boundary, where the DEHP level drops due to the increasing rate of the hydrolysis reaction. 4.3. DEHP in air Increasing DEHP levels were found in the air emitted from the damp wallpaper over 15 days. Although the concentrations in the chambers with damp wallpaper were not great enough to be statistically significant compared to those in chambers with dry wallpaper, the averages in the duplicates with damp wallpaper were consistently higher than those with dry wallpaper throughout the elapsed time. There was a bigger variation on the fifteenth day in the chamber with damp wallpaper. The difference of air concentrations in the duplicate chambers might be due to the divergent degradation between two damp wallpapers, for instance, the divergence of coating-cracking and DEHP hydrolysis. In contrast with the results of earlier emission studies, this study obtained greater levels of DEHP in air, with a maximum of 8.04 µg/m3. Afshari et al. (2004) conducted a 150-day chamber study to examine the DEHP emissions from PVC wallpaper (18 wt% DEHP), and the maximum level was detected to be less than 0.40 µg/m3. Another wallcovering study by Uhde et al. (2001) reported that the highest DEHP concentration was 0.94 µg/m3 at the sampling point of 6 h.
5. Conclusions The present study demonstrates that the emission of phthalates from plastic materials may be strongly affected by the interior moisture percentage. This is the first study to evaluate the effects of material moisture on the emission of phthalates in indoor environments. Buildings shelter occupants from deteriorating outdoor environments caused by the impact of extreme weather events. Preventing problems of dampness or improving the moisture resistance of building materials is critical for controlling not only the microbial burden but also the exposure to chemical substances such as phthalates emitted in indoor environments.
4.4. DEHP in settled dust Unlike the steadily rising trend of DEHP levels in air, the settled dust showed a fluctuating concentration profile, particularly in the initial four days. It is believed that the air sampling conducted every 2 or 3 days greatly disturbed the distribution of DEHP concentrations in different media. The 2.4 L chamber was purged with 60 L of clean air each time. Therefore, the influence of air sampling on the kinetics of DEHP uptake into dust and desorption (re-emission) to the air cannot be neglected. It is also thought that the absorption and desorption of DEHP on dust takes time to equilibrate, which could be the reason why the concentration variation between duplicates in dust samples was initially large but became smaller as more time elapsed during the experiment. On the other hand, Weschler and Nazaroff (2010) have suggested that when sVOCs have a higher Koa value, such as DEHP, their mass fraction in dust may not have sufficient time to equilibrate with the gas phase concentration. The fraction of organic matter in settled dust is associated with its capacity to adsorb sVOCs (Weschler and Nazaroff, 2010). The test dust adopted in the current study consists of approximately 23% carbon black, which is considered to be an acceptable range when compared to other studies, such as the range of approximately 18% in Schripp et al. (2010) and 30% in Jeon et al. (2016). A recent study conducted in a field environment revealed that substances with higher octanol-air partition coefficients (Koa), such as DEHP, are more likely to be found in dust than in air (Sukiene et al., 2016). Indeed, more than 80% of the DEHP mass in this study was found in the settled dust, albeit at relatively low detected concentrations compared to those reported previously, ranging from 0.07 to 0.99 µg/g. Three justifications are suggested. First of all, the detected level was associated with the initial concentration in the test material. DEHP concentrations of 4 and 17 wt% in the test materials resulted in DEHP levels of 408 and 2080 µg/g, respectively, in dust over a 14-day chamber study (Schripp et al., 2010). In our study, DEHP constitutes only approximately 0.22% of the weight of the tested wallpaper, a
Acknowledgement The authors would like to thank laboratory technician Hung-Miao Lai for her professional contributions on DEHP analysis. The authors are also grateful for comments and recommendations from Dr. ChienCheng Jung and Dr. Nai-Tzu Chen during the execution of this chamber experiment, and Dr. Wei-Hsiang Chang during the preparation of this manuscript. This study was partly supported by the Ministry of Science and Technology of Taiwan (MOST 101–2221-E006–158-MY3). References Afshari, A., et al., 2004. Emission of phthalates from PVC and other materials. Indoor Air 14, 120–128. Ait Bamai, Y., et al., 2014. Associations of phthalate concentrations in floor dust and multi-surface dust with the interior materials in Japanese dwellings. Sci. Total Environ. 468–469, 147–157. Bekö, G., et al., 2015. Phthalate exposure through different pathways and allergic sensitization in preschool children with asthma, allergic rhinoconjunctivitis and atopic dermatitis. Environ. Res. 137, 432–439. Blanchard, O., et al., 2014. Semivolatile organic compounds in indoor air and settled dust in 30 french dwellings. Environ. Sci. Technol. 48, 3959–3969. Bloom, E., et al., 2009. Molds and mycotoxins in dust from water-damaged homes in New Orleans after hurricane Katrina. Indoor Air 19, 153–158. Bornehag, C.G., et al., 2005. Phthalates in indoor dust and their association with building characteristics. Environ. Health Perspect. 113, 1399–1404. Braun, J.M., et al., 2013. Phthalate exposure and children’s health. Curr. Opin. Pedia. 25,
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Kim, J.-H., et al., 2003. DEHP migration behavior from excessively plasticized PVC sheets. Bull. Korean Chem. Soc. 24, 345–349. Kubwabo, C., et al., 2013. Analysis of selected phthalates in Canadian indoor dust collected using household vacuum and standardized sampling techniques. Indoor Air. Markowicz, P., Larsson, L., 2014. Influence of relative humidity on VOC concentrations in indoor air. Environ. Sci. Pollut. Res 22, 5772–5779. Miniotaite, R., 2014. The impact of climate parameters on the surface of buildings' walls. In: Chantawarangul, K. (Ed.), Sustainable Solutions in Structural Engineering and Construction.. ISEC Press, Bangkok, Thailand. North, M.L., et al., 2014. Effects of phthalates on the development and expression of allergic disease and asthma. Ann. Allergy Asthma Immunol. 112, 496–502. Previati, M., et al., 2012. Evaluation of wood degradation for timber check dams using time domain reflectometry water content measurements. Ecol. Eng. 44, 259–268. Rando, R.J., et al., 2013. Exposures to thoracic particulate matter, endotoxin, and glucan during post-hurricane katrina restoration work, New Orleans 2005–2012. J. Occup. Environ. Hyg. 11, 9–18. Reeb, J.E., Milota, M.R., 1999. Moisture content by the oven-dry method for industrial testing, In: 50th Western Dry Kiln Association Meeting. Western Dry Kiln Association (WDKA), Portland, Oregon. Schettler, T., 2006. Human exposure to phthalates via consumer products. Int J. Androl. 29, 134–139. Schripp, T., et al., 2010. Chamber studies on mass-transfer of di(2-ethylhexyl)phthalate (DEHP) and di-n-butylphthalate (DnBP) from emission sources into house dust. Atmos. Environ. 44, 2840–2845. Sukiene, V., et al., 2016. Tracking SVOCs' transfer from products to indoor air and settled dust with deuterium-labeled substances. Environ. Sci. Technol. 50, 4296–4303. TERA (Toxicology Excellence for Risk Assessment), 2015. Exposure Assessment: Composition, Production, and Use of Phthalates. U.S. Consumer Product Safety Commission (CPSC). Uhde, E., et al., 2001. Phthalic esters in the indoor environment – test chamber studies on PVC-coated wallcoverings. Indoor Air 11, 150–155. Uhde, E., Salthammer, T., 2007. Impact of reaction products from building materials and furnishings on indoor air quality – a review of recent advances in indoor chemistry. Atmos. Environ. 41, 3111–3128. Unger, D.R., et al., 1996. Predicting the effect of moisture on vapor-phase sorption of volatile organic compounds to soils. Environ. Sci. Technol. 30, 1081–1091. van Netten, C., et al., 1989. Temperature and humidity dependence of formaldehyde release from selected building materials. Bull. Environ. Contam Toxicol. 42, 558–565. Viitanen, H., et al., 2010. Moisture and bio-deterioration risk of building materials and structures. J. Build. Phys. 33, 201–224. Wang, C., et al., 2015. Diffusion of di (2-ethylhexyl) phthalate in PVC quantified by ATRIR spectroscopy. Polymer 76, 70–79. Weschler, C.J., 2004. Chemical reactions among indoor pollutants: what we’ve learned in the new millennium. Indoor Air 14, 184–194. Weschler, C.J., Nazaroff, W.W., 2010. SVOC partitioning between the gas phase and settled dust indoors. Atmos. Environ. 44, 3609–3620. WHO (World Health Organisation), 2009. WHO Guidelines for Indoor air Quality: Dampness and Mould. WHO Regional Office for Europe, Copenhagen. Wolkoff, P., 1998. Impact of air velocity, temperature, humidity, and air on long-term voc emissions from building products. Atmos. Environ. 32, 2659–2668. Xu, Y., Little, J.C., 2006. Predicting emissions of SVOCs from polymeric materials and their interaction with airborne particles. Environ Sci Technol. 40, 456–461. Yokota, T., et al., 2013. Influence of water content in sub-flooring materials using adhesive on chemical compounds emission. J. Adhes. Sci. Technol. 27, 648–658. Zhang, H., et al., 2016. Thermal and environmental conditions in Shanghai households: risk factors for childhood health. Build. Environ. 104, 35–46. Zhang, Q., et al., 2013. Levels of phthalate esters in settled house dust from urban dwellings with young children in Nanjing, China. Atmos. Environ. 69, 258–264.
247–254. Carll, C., et al., 2007. Moisture performance of a contemporary wood-frame house operated at design indoor humidity levels. Buildings X Conference, December 2-7. American Society for Heating, Refrigerating, and Air-Conditioning Engineers, Atlanta, Ga, p. 14. Chiou, C.T., Shoup, T.D., 1985. Soil sorption of organic vapors and effects of humidity on sorptive mechanism and capacity. Environ. Sci. Technol. 19, 1196–1200. Clausen, P.A., et al., 2004. Emission of di-2-ethylhexyl phthalate from PVC flooring into air and uptake in dust: emission and sorption experiments in FLEC and CLIMPAQ. Environ. Sci. Technol. 38, 2531–2537. Clausen, P.A., et al., 2007. The influence of humidity on the emission of di-(2-ethylhexyl) phthalate (DEHP) from vinyl flooring in the emission cell “FLEC”. Atmos. Environ. 41, 3217–3224. Colombani, J., et al., 2009. Leaching of plasticized PVC: effect of irradiation. J. Appl. Polym. Sci. 112, 1372–1377. CRED (Centre for Research on the Epidemiology of Disasters), 2013. Floods: the most frequent natural disasters 1993-2012. Cred Crunch, 32. De Freitas, V.P., et al., 1996. Moisture migration in building walls—Analysis of the interface phenomena. Build. Environ. 31, 99–108. Ekelund, M., et al., 2008. Long-term performance of poly(vinyl chloride) cables, Part 2: migration of plasticizer. Polym. Degrad. Stab. 93, 1704–1710. Emerson, J.B., et al., 2015. Impacts of flood damage on airborne bacteria and fungi in homes after the 2013 Colorado front range flood. Environ. Sci. Technol. 49, 2675–2684. Goss, K.U., 1993. Effects of temperature and relative humidity on the sorption of organic vapors on clay minerals. Environ. Sci. Technol. 27, 2127–2132. Hartmann, D.L., et al., 2013. Observations: atmosphere and Surface. (Climate Change) In: Stocker, T.F. (Ed.), The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2013. He, C., et al., 2014. The impact of flood and post-flood cleaning on airborne microbiological and particle contamination in residential houses. Environ. Int 69, 9–17. Hippelein, M., McLachlan, M.S., 2000. Soil/air partitioning of semivolatile organic compounds. 2. Influence of temperature and relative humidity. Environ. Sci. Technol. 34, 3521–3526. Hsu, N.Y., et al., 2011. Changes in profiles of airborne fungi in flooded homes in southern Taiwan after Typhoon Morakot. Sci. Total Environ. 409, 1677–1682. Hsu, N.Y., et al., 2012a. Relationship between indoor phthalate concentrations and dampness or visible mold, In: Proceedings of the 10th International Healthy Buildings Conference 2012, Vol. 2, Brisbane, Australia, pp. 1575–1576. Hsu, N.Y., et al., 2012b. Predicted risk of childhood allergy, asthma and reported symptoms using measured phthalate exposure in dust and urine. Indoor Air 22, 186–199. International Agency for Research on Cancer (IARC), 2013. Some Chemicals Present in Industrial and Consumer Products, Food and Drinking-water. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans 101. World Health Organization (WHO), Geneva, Switzerland. IOM (Institute of Medicine), 2004. Damp Indoor Spaces and Health. The National Academies Press, Washington, DC. Jaakkola, J.J.K., Knight, T.L., 2008. The role of exposure to phthalates from polyvinyl chloride products in the development of asthma and allergies: a systematic review and meta-analysis. Environ. Health Perspect. 116, 845–853. Jeon, S., et al., 2016. Migration of DEHP and DINP into dust from PVC flooring products at different surface temperature. Sci. Total Environ. 547, 441–446. Kay, V.R., et al., 2013. Reproductive and developmental effects of phthalate diesters in females. Crit. Rev. Toxicol. 43, 200–219. Kay, V.R., et al., 2014. Reproductive and developmental effects of phthalate diesters in males. Crit. Rev. Toxicol. 44, 467–498.
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Higher moisture content is associated with greater emissions of DEHP from PVC wallpaper Nai-Yun Hsua, Yu-Chun Liua, Chia-Wei Leeb,⁎⁎, Ching-Chang Leea, Huey-Jen Sua, a b
⁎
Department of Environmental and Occupational Health, College of Medicine, National Cheng Kung University, Tainan, Taiwan Department of Safety, Health and Environment Engineering, National Kaohsiung First University of Science and Technology, Kaohsiung, Taiwan
A R T I C L E I N F O
A BS T RAC T
Keywords: Di-(2ethylhexyl) phthalate Indoor Building materials Dampness Flood
Water damage and moisture in buildings may become more prevalent due to the increasing frequency of extreme precipitation and flooding events resulting from climate change. However, the effects of moisture levels on phthalate emissions from building materials are still underreported. This study aims to evaluate the effect of moisture content (MC) on the level of di-(2ethylhexyl) phthalate (DEHP) emitted from plastic wallpaper (0.22 wt% DEHP) within 15 days in a closed chamber. A scenario of short-term exposure to DEHP in buildings suffering from water damage was simulated. Experiments, controlled at 100% relative humidity (RH) of air and 28 °C, were conducted under the following three conditions: (I) without wallpaper (control chamber), (II) dry wallpaper (MC at 3.57%) and (III) damp wallpaper (MC at 52.31%). Air and dust samples were collected at the elapsed time of 2, 4, 6, 8, 10, 13 and 15 days, and the wipe sample was collected on the last day. Higher DEHP concentrations were found to be emitted into the air and adsorbed on the dust for wallpapers with higher MC%. DEHP levels in the air exhibited an increasing trend with the length of the experiment. Overall, it was found that approximately 35.31% more total DEHP mass was released into the air, dust and wipe samples from damp wallpapers compared to dry wallpapers. It is concluded that DEHP emissions from plastic materials are affected by the inner moisture percentage.
1. Introduction Floods have been one of the most common types of natural disasters throughout the world in the past few decades (CRED, 2013), and the resulting water damage to buildings is unavoidable. Dampness and moisture problems in buildings are associated with the deterioration of indoor air quality and adverse health effects (IOM, 2004; WHO 2009), and the increasing exposure levels to indoor bioaerosols are thought to be the main cause of this association (Bloom et al., 2009; Emerson et al., 2015; He et al., 2014; Hsu et al., 2011; Rando et al., 2013). Additionally, the positive relationship between indoor dampness and exposure to phthalates could be another consideration (Jaakkola and Knight, 2008). Phthalates are widely adopted as plasticizers, fixing agents and dispersants in building materials and consumer products (Schettler, 2006; TERA, 2015). Bornehag et al. (2005) have indicated that higher concentrations of n-butyl benzyl phthalate (BBzP) were found in Swedish homes with self-reported water leakage. In China, levels of BBzP, di-2-ethylhexyl phthalate (DEHP), dioctyl phthalate (DOP) and total phthalates were higher in houses where condensation or dampness was common than ⁎
in those without (Zhang et al., 2013). Ait Bamai et al. (2014) have shown that increased levels of di-n-butyl phthalate (DnBP) and DEHP were associated with signs of higher dampness in Japanese residences. In our earlier findings, increased DEHP levels in households of Taiwan were found to be associated with self-reported floods or water leakages in the past year, and higher DnBP and DEHP levels were found in cases where larger diameters of damp stain/visible mold growth on the walls were recorded by field investigators (Hsu et al., 2012a). Exposure to indoor phthalates emerges as an important issue, owing to their various hazards to human health (Braun et al., 2013; Kay et al., 2014, 2013; North et al., 2014). It is suggested that phthalates could be released due to the degradation of materials, caused by water and moisture (Bornehag et al., 2005). However, it is still unclear whether the levels of phthalates emitted from materials are affected by the inner moisture content (MC), defined as the moisture-holding properties of materials. To understand the short-term profile for exposure to phthalates after indoor water damage, this study aims to evaluate the effect of MC on the level of phthalates emitted from plastic wallpaper within 15 days in a closed chamber. DEHP (CASRN 117-817), the highest level of which has been detected in house dust in Taiwan
Correspondence to: Department of Environmental and Occupational Health, College of Medicine, National Cheng Kung University, 138 Sheng-Li Road, Tainan 70403, Taiwan. Corresponding author. E-mail addresses: [email protected] (C.-W. Lee), [email protected] (H.-J. Su).
⁎⁎
http://dx.doi.org/10.1016/j.envres.2016.09.027 Received 24 June 2016; Received in revised form 23 September 2016; Accepted 30 September 2016 0013-9351/ © 2016 Elsevier Inc. All rights reserved.
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were less than 2% and 6%, respectively.
(Hsu et al., 2012b) and other countries (Ait Bamai et al., 2014; Bekö et al., 2015; Blanchard et al., 2014; Bornehag et al., 2005; Kubwabo et al., 2013; Zhang et al., 2016), was selected as the examined target for the short-term emission profile. DEHP has been classified as a group 2B agent, considered to be possibly carcinogenic to humans by the IARC Monographs (IARC, 2013).
2.3. Sample collection A total of 7 air samples were collected from every chamber at the elapsed times of 2, 4, 6, 8, 10, 13 and 15 days. The mass of DEHP in the air was sampled by Tenax® Sorbent (SKC 226-56) at the flow rate of 1 L/min (Gillian GilAir-5) for 60 min. Due to the relatively small volume of the chamber, an inlet of air to the chamber was necessary for the purpose of pumping a sufficient volume of air. While air sampling was being conducted, the chamber was purged with a total of 60 L air, approximately 25 times the chamber volume, to ensure that the DEHP mass inside the chamber was collected completely. The fresh-air inlet was equipped with an active carbon filter to remove ambient levels of DEHP. Air outside the chamber was also collected to avoid background contamination. All the pumps were calibrated before and after the experiment. The DEHP mass was measured as the object of this sampling method, and the result was then converted and presented in units of volume concentration (µg/m3). A total of 7 dust samples were also collected from every chamber at the elapsed times of 2, 4, 6, 8, 10, 13 and 15 days. Seven customized trays (15 × 1 × 1 cm3), made of stainless steel and containing 1 g of the ASHRAE 52–76 standard dust, were placed on the first stage of the shelf inside each chamber (Fig. 1a). The standard dust was composed of 72% Arizona road dust (approximately 80 µm), 23% carbon black and 5% fibers. It was shaken ultrasonically with methanol for 30 min and blow-dried with nitrogen gas prior to the test to avoid background contamination. During the experiment, one tray was taken out from the chamber on the above-mentioned days. It was then covered with a Teflon lid and parafilm and stored at −20 °C until sample analysis. Only one wipe sample was collected from every chamber on the last
2. Materials and methods 2.1. Test material and chamber design The five most purchased polyvinyl chloride (PVC)-coated wallpapers in the market were analyzed for DEHP concentration, and the one with the highest level (2160.67 µg/g; 0.22%) was selected as the test material in the current study. The DEHP was coated only on a single side. A total of five chambers with three experimental conditions, varied by the MC levels of wallpapers, were examined. A 2.4 L glass desiccator was adopted as the study chamber, and a magnetic stirrer was set up at the bottom to mix air during the elapsed time of the experiment (Fig. 1a). The chambers were airtight and without ventilation except for the hour during which air sampling was conducted. Details of the air sample collection are described in Section 2.3. A two-stage shelf (with an area of 17 × 10 cm, and 5 cm height for each stage) made of stainless steel was placed at the center of the chamber (Fig. 1a). Seven trays with dust samples were placed on the upper stage, while one piece of the wallpaper was placed on the second stage. Every chamber contained four pieces of wallpaper, including three rectangles (12.5 × 60 cm, 5 × 44.5 cm, and 9.5 × 15.5 cm) and one circle (diameter 13.8 cm). The rectangles were placed around the circumference of the inner surface as well as on the second stage of the shelf, and the circle was placed at the bottom of the chamber. The total area of wallpapers used in each chamber was 1269.6 cm2, and the weight was 35.7 g, containing approximately 77,135.92 ng mass of DEHP (0.22% of 35.7 g). 2.2. Experimental conditions Moisture content (MC) is defined as the amount of water present in a substance in relation to its oven-dry weight (kg/kg) and is expressed as the percentage moisture content (%) at the oven temperature of 217°F (103 °C) (Reeb and Milota, 1999). A total of five chambers with three conditions, varied by MC levels of the wallpapers, were examined: (I) control chamber without wallpaper. (II) chamber with dry wallpaper (MC at 3.57 ± 0.22%). (III) chamber with damp wallpaper (MC at 52.31 ± 2.45%). The (I) control chamber was set to confirm whether any background contamination existed during this experimental period. MC was approximately 3.57 ± 0.22% in the original state of the test wallpaper and was approximately 52.31 ± 2.45% in the state saturated with water content for this test material, where pre-treatment by soaking in 500 ml RO water for at least 30 min was needed before placing the sample into the chamber. Duplicates were conducted for both the second (II) and third conditions (III). The time allowed to elapse for the experiment was 15 days. The air temperature in the airtight chamber was 28°C. To simulate an indoor scenario of flood and water damage, the relative humidity (RH) of air was set to 100%, a common environmental condition during days with heavy rain. 100% RH was also useful for stabilizing the MC levels of wallpapers in the chamber. Both the in-air RH and MC of wallpapers in the chamber during 15 days were maintained by adding 1 ml RO water at the elapsed times of 2, 4, 6, 8, 10, 13 and 15 days (Fig. 1b). To determine the changes of the MC levels, a fixed-size piece (1 × 2 cm) was cut out of a wallpaper in each chamber on the above-mentioned days and measured by an Infrared Moisture Balance (FD-610, Kett). The CV (coefficients of variation) for RH and MC during the 15 days
Fig. 1. (a) Chamber illustration and (b) RO water injected into the chamber.
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Whitney U test. The statistical analysis was carried out in SPSS 17.0 (Chicago, IL, USA), and a p-value of 0.05 was considered significant.
day of the experiment. For each chamber, a standard size of sterile gauze (2 × 2 cm2) soaked with acetone and methanol was used to wipe the inner surface of the chambers. To avoid contamination, all equipment used in the experiment, including stainless steel trays, glass bottles/tubes, and tweezers, was rinsed in advance with acetone and methanol (1:1 mixture).
3. Results In control chamber (I), without wallpapers, the average level of the 7 air samples was lower than the LOD (0.0082 μg/ml), and the average level of the 7 dust samples was below the lowest level of the calibration curve (0.01 μg/ml). It was therefore concluded that there was no background contamination in the chambers during the elapsed time of the experiment. The 15-day average concentrations of DEHP in the air of chambers (II) (dry, MC=3.57%) and (III) (damp, MC=52.31%) were 1.16 and 1.83 µg/m3, respectively, while the levels in the dust were 0.51 and 0.68 µg/g, respectively (Table 1). Higher levels were detected in the chamber set up with the damp wallpaper, but no statistically significant difference was found between the two conditions in both air and dust samples. Increasing concentrations of DEHP were emitted into the air and adsorbed on dust as the length of the experiment was increased, with maximum levels observed in the chamber with the damp wallpaper at 15 days (Fig. 2). Higher average levels were found for the air samples on each sampling day in the chamber with damp wallpapers compared to those with dry ones (Fig. 2a). Although there was a larger variation in the air concentration between duplicate chambers with damp wallpapers (3.94 and 8.04 μg/m3) on the final day, the detected levels were still higher than those detected with dry wallpapers (2.10 and 2.63 μg/m3). The DEHP levels in the settled dust samples showed a fluctuating pattern. Even so, greater averages were detected in the chamber with the damp wallpapers, considering the last 5 sampling spots (Fig. 2b).. The average of total mass measured in the (II), dry, and (III), damp, conditions was 4144.93 ± 271.77 and 5608.71 ± 71.87 ng, respectively, with approximately 5.37% and 7.27%, respectively, of the total DEHP mass transferred from the wallpapers. The mass adsorbed on dust was the major component, constituting approximately 86.78% and 84.76%, respectively (Fig. 3a). Overall, approximately 35.31% more total DEHP mass was released into air, dust and wipe samples from the damp wallpapers compared to those from the dry wallpapers. After the 4th day of the experiment, the emitted masses of DEHP began to rise (Fig. 3b). The increasing trend for damp wallpaper was steeper than that for dry wallpaper.
2.4. DEHP analysis The analytical procedure for air samples was implemented according to OSHA 104. The Tenax and glass-fiber filters were ultrasonically extracted by 4 ml toluene for 30 min; of this, 1 ml was then extracted and added to 10 ml of an internal standard (benzyl benzoate, ChemService). Each of the dust samples was fully mixed before removing 50 mg for extraction and analysis. The latter was extracted with 2 ml of dichloromethane/acetone (1:1) and then shaken ultrasonically for 30 min; this was repeated twice (Hsu et al., 2012b). All the extracts were combined and dried by nitrogen gas and reconstituted with 1 ml of dichloromethane. The analytical method for the wipe sample was the same as that for the dust sample. The concentrations of DEHP in all collected samples were analyzed by gas chromatography-mass spectrophotometry (GC/MS). The column used was a DB-5MS (60 m × 0.25 mm × 0.25 µm; Agilent, Folsom, CA, USA) column, with an initial injection temperature of 290 °C; the initial column temperature was set at 50 °C for 1 min and then increased at 15 °C/min to a final temperature of 310 °C, which was maintained for 16 min The R2 of the five-point calibration curve from 0.01 to 0.3 μg/ml was 0.996. The limit of detection (LOD) was 0.0082 μg/ml. One blank, one quality check (QC) with a mixture of the phthalate standard and one spiked sample (0.04 μg/ml for DEHP) were included in each batch of analyzed samples. The mean recoveries of air, dust and gauze from the QC samples were 88.9 ± 3.7%, 88.6 ± 2.8% and 102.9 ± 14.1%, respectively; the mean recoveries from the spiked sample were 87.3 ± 3.9%, 88.6 ± 2.8% and 87.3 ± 5.0%, respectively. The average desorption efficiencies for the air and wipe samples were 101% and 96%, respectively. 2.5. Data analysis The average and standard deviation of the DEHP concentrations, measured in duplicate for each condition, are presented. The mass concentrations of air and wipe samples were calculated by multiplying the detected concentration in the sampling tube (µg/ml) by the volume of extraction solvent (4 ml and 2 ml for the air and wipe samples, respectively). For the dust mass levels, the concentrations (µg/g) were multiplied by 1 g of dust. The ‘total mass’ was the sum of mass in air, dust, and wipe samples. However, all of the wipe samples collected on the final day exhibited lower levels than the LOD (0.0082 μg/ml). Their mass levels were derived through extrapolation, since adopting half the value of the LOD would lead to an overestimation of one order of magnitude at most. The difference of DEHP levels between the samples collected from dry and damp wallpaper conditions was examined by the Mann-
4. Discussion Increased DEHP emissions were observed from damp wallpaper compared to dry wallpaper in the current study, even when pieces containing very low levels of DEHP (0.22 wt% DEHP) were tested. Therefore, it is suggested that the material should be removed within four days once it has been damaged by water. 4.1. Indoor dampness and chemistry Increasing frequency or intensity of heavy precipitation has been
Table 1 DEHP levels in the air, dust and wipe samples for three experimental conditions. Experimental conditions (sample size)
Air sample (µg/m3)
II: dry wallpaper (14) III: damp wallpaper (14)
Dust sample (µg/g)
Detection rate , %
mean ± s.d.
p-value
Detection ratea, %
mean ± s.d.
p-value
100.00 100.00
1.16 ± 0.69 1.83 ± 2.03
0.34
100.00 100.00
0.51 ± 0.20 0.68 ± 0.26
0.11
a
*p-value for the difference between II (dry) and III (damp) wallpapers, examined by Mann-Whitney U test. a Percentage of detected concentrations higher than the lowest level of the calibration curve (0.01 μg/ml).
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observed in most mid-latitude continents under the impact of climate change (Hartmann et al., 2013). Water damage to buildings may become more prevalent due to the resulting flooding events. Moisture typically increases the decay of building materials. When materials stay wet for sufficiently long periods, problems can occur, including microbial growth, physical deterioration, or chemical reactions. Carll et al. (2007) reported that seasonal moisture accumulation in the sheathing of a wood-frame house was observed to cause the cracking of stucco cladding. Measurements of wood water content have been used as indicators of the level of material degradation (Previati et al., 2012). Bio-deterioration is one of the critical factors determining the durability and natural aging of building materials (Viitanen et al., 2010). Apart from microbial contaminants, moisture sometimes contributes to the release of chemicals into indoor air. It has been known that the rate of release of volatile organic compounds (VOCs), such as formaldehyde, from building materials increases with the humidity of the surrounding air (Markowicz and Larsson, 2014; van Netten et al., 1989; Wolkoff, 1998). This happens as a consequence of the hydrolysis reaction of urea-formaldehyde (Uhde and Salthammer, 2007) or due to competition between water vapor molecules for surface sites, which displaces the VOCs (Markowicz and Larsson, 2014). However, with regard to semi-volatile organic compounds (sVOCs), no association was found between air RH levels and the specific emission rate of DEHP from PVC flooring (containing 17 wt% DEHP) in a 1-year chamber study (Clausen et al., 2007). The authors suggested that DEHP is more strongly attached to stainless-steel surfaces than water vapor and that displacement by water vapor is insignificant (Clausen et al., 2004, 2007). Ekelund et al. (2008) also reported that there was no significant influence of relative humidity on the evaporation of DEHP from pristine DEHP and plasticized PVC cables (containing 23 wt% DEHP). Fig. 2. DEHP concentrations in (a) air and (b) dust samples during the experimental period.
4.2. Impact of MC on the emission of DEHP Instead of the humidity of air, the current study examined the effects of MC levels, defined as the amount of moisture held in the material, on DEHP emissions from test pieces, and another mechanism triggering the higher emission levels is suggested. According to the sVOC emission model proposed by Xu and Little (2006), the migration of DEHP from polymeric materials to air can be categorized into two stages: diffusion of DEHP within the PVC polymer (material-phase) and transport from the polymer surface to the surrounding air (gasphase). It is suggested that the moisture in materials is more likely to accelerate the material-phase reaction from the interior to the boundary (surface) based on the two theories below. The behavior of DEHP migration inside the PVC polymer could be described by the “classical Fick’s law of diffusion”, which states that the rate of diffusion is positively associated with the area and concentration difference but inversely associated with the distance (Colombani et al., 2009; Ekelund et al., 2008; Kim et al., 2003; Wang et al., 2015). Moisture migration in building materials has a great effect on the durability and degradation of the structures (De Freitas et al., 1996; Miniotaite, 2014). It is speculated that the diffusion distances were decreased and the diffusion areas were increased for interior DEHP due to the cracking of the PVC coating film as a result of the moisture, and higher emissions of DEHP were therefore detected. On the other hand, when the DEHP concentration on the material surface decreases as a result of the hydrolysis reaction, the concentration gradient is thought to be the driving force behind the diffusion of DEHP from the interior to the boundary of the material. Weschler (2004) has mentioned in his review article that the hydrolysis reaction of indoor organic esters with carboxylic acids and alcohols can be catalyzed by moist and alkaline conditions. This was further supported by Yokota et al. (2013), who found in their chamber experiment that higher MC levels in 10 wt% DEHP flooring materials were associated with increased emission rates of 2-ethyl-1-hexanol (2E1H), a hydrolysis product of DEHP. Yokota et al. (2013) proved that the hydrolysis
Fig. 3. (a) Total mass of DEHP for the three conditions; (b) profile of released mass of DEHP over 15 days.
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rather low percentage compared to those used in previous research. Second, the distance to the emission source is a critical factor related to the exposure level. Schripp et al. (2010) revealed in a 14-day study that a concentration up to 9.8 times higher (2080 vs. 213 µg/g) was found in dust brought into direct contact with the source of 17 wt% DEHP compared to when it was separated. In another 14-day emission test, an average of 384–481 µg/g was detected when the dust samples were directly placed on the test materials (Jeon et al., 2016). In our chamber setting, there was no direct contact between the dust samples and wallpapers. Finally, we consider the effects of saturated humidity on the adsorption capacity of settled dust. It is known that the sorption capacities of organic compounds on soil dust are extremely suppressed by water vapor, resulting in about a 100-fold reduction in watersaturated soil (Chiou and Shoup, 1985). High RH leads to thick surface coverage of the water film, which competes with organic chemicals for sorption sites. Dissolution of chemicals into the water phase and subsequent adsorption onto the soil surface is especially difficult for DEHP due to its nonpolar characteristics (Goss, 1993; Hippelein and McLachlan, 2000; Unger et al., 1996). In the current study, a saturated-air environment with 100% RH was set, not only to simulate a rainy-day scenario but also to stabilize the MC levels of the test wallpapers in the chamber during the elapsed time. It is therefore thought that the relatively low levels quantified in the settled dust and wipe samples in the current experiment were partly due to the effect of saturated humidity on the adsorption capacity of the particles and chamber surface.
reaction of DEHP, in terms of the emission rate of 2E1H, was accelerated by the MC. Yet, it is still unclear whether the emission of DEHP can be elevated by the MC conditions. Our study also demonstrates that higher MC in materials can lead to greater DEHP emission, and the concentration gradient is speculated to be the driving force behind this phenomenon. More DEHP migrates to the boundary, where the DEHP level drops due to the increasing rate of the hydrolysis reaction. 4.3. DEHP in air Increasing DEHP levels were found in the air emitted from the damp wallpaper over 15 days. Although the concentrations in the chambers with damp wallpaper were not great enough to be statistically significant compared to those in chambers with dry wallpaper, the averages in the duplicates with damp wallpaper were consistently higher than those with dry wallpaper throughout the elapsed time. There was a bigger variation on the fifteenth day in the chamber with damp wallpaper. The difference of air concentrations in the duplicate chambers might be due to the divergent degradation between two damp wallpapers, for instance, the divergence of coating-cracking and DEHP hydrolysis. In contrast with the results of earlier emission studies, this study obtained greater levels of DEHP in air, with a maximum of 8.04 µg/m3. Afshari et al. (2004) conducted a 150-day chamber study to examine the DEHP emissions from PVC wallpaper (18 wt% DEHP), and the maximum level was detected to be less than 0.40 µg/m3. Another wallcovering study by Uhde et al. (2001) reported that the highest DEHP concentration was 0.94 µg/m3 at the sampling point of 6 h.
5. Conclusions The present study demonstrates that the emission of phthalates from plastic materials may be strongly affected by the interior moisture percentage. This is the first study to evaluate the effects of material moisture on the emission of phthalates in indoor environments. Buildings shelter occupants from deteriorating outdoor environments caused by the impact of extreme weather events. Preventing problems of dampness or improving the moisture resistance of building materials is critical for controlling not only the microbial burden but also the exposure to chemical substances such as phthalates emitted in indoor environments.
4.4. DEHP in settled dust Unlike the steadily rising trend of DEHP levels in air, the settled dust showed a fluctuating concentration profile, particularly in the initial four days. It is believed that the air sampling conducted every 2 or 3 days greatly disturbed the distribution of DEHP concentrations in different media. The 2.4 L chamber was purged with 60 L of clean air each time. Therefore, the influence of air sampling on the kinetics of DEHP uptake into dust and desorption (re-emission) to the air cannot be neglected. It is also thought that the absorption and desorption of DEHP on dust takes time to equilibrate, which could be the reason why the concentration variation between duplicates in dust samples was initially large but became smaller as more time elapsed during the experiment. On the other hand, Weschler and Nazaroff (2010) have suggested that when sVOCs have a higher Koa value, such as DEHP, their mass fraction in dust may not have sufficient time to equilibrate with the gas phase concentration. The fraction of organic matter in settled dust is associated with its capacity to adsorb sVOCs (Weschler and Nazaroff, 2010). The test dust adopted in the current study consists of approximately 23% carbon black, which is considered to be an acceptable range when compared to other studies, such as the range of approximately 18% in Schripp et al. (2010) and 30% in Jeon et al. (2016). A recent study conducted in a field environment revealed that substances with higher octanol-air partition coefficients (Koa), such as DEHP, are more likely to be found in dust than in air (Sukiene et al., 2016). Indeed, more than 80% of the DEHP mass in this study was found in the settled dust, albeit at relatively low detected concentrations compared to those reported previously, ranging from 0.07 to 0.99 µg/g. Three justifications are suggested. First of all, the detected level was associated with the initial concentration in the test material. DEHP concentrations of 4 and 17 wt% in the test materials resulted in DEHP levels of 408 and 2080 µg/g, respectively, in dust over a 14-day chamber study (Schripp et al., 2010). In our study, DEHP constitutes only approximately 0.22% of the weight of the tested wallpaper, a
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