Emissions of Phthalates from Indoor Flat Materials in Chinese

Oct 29, 2018 - Phthalates are ubiquitous pollutants in residential environments. Indoor airborne phthalate concentrations in Chinese residences are ...
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Article Cite This: Environ. Sci. Technol. 2018, 52, 13166−13173

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Emissions of Phthalates from Indoor Flat Materials in Chinese Residences Shanshan Shi,†,§,∇ Jianping Cao,‡,∥,∇ Yinping Zhang,⊥,# and Bin Zhao*,⊥,# †

School of Architecture and Urban Planning, Nanjing University, 210093 Nanjing, China School of Environmental Science and Engineering, Sun Yat-sen University, 510006 Guangzhou, China § Nicholas School of the Environment, Duke University, 27708 Durham, North Carolina, United States ∥ Department of Civil and Environmental Engineering, Virginia Tech, 24061 Blacksburg, Virginia, United States ⊥ Department of Building Science, School of Architecture, Tsinghua University, 100084 Beijing, China # Beijing Key Laboratory of Indoor Air Quality Evaluation and Control, Tsinghua University, 100084 Beijing, China

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‡

S Supporting Information *

ABSTRACT: Phthalates are ubiquitous pollutants in residential environments. Indoor airborne phthalate concentrations in Chinese residences are comparable to, or even higher than, those of western countries. However, the major sources of phthalates in Chinese residences are not well-known. In this study, we measured the phthalates emission features of 23 flat materials used in Chinese residences in the laboratory environment, including the mass fraction (wt) and the concentration in the air adjacent to the material surface (y0). The measured wt of seven phthalates ranged from below the limit of quantitation (LOQ) to 17%, and y0 ranged from LOQ to 2 μg/m3. To evaluate the potential contributions of the studied materials to phthalates in residential air, concentrations of di-2-ethylhexyl phthalate (DEHP, a typical indoor phthalate) in air due to the emissions from selected materials in typical Chinese residential scenarios were modeled and compared with measured concentrations from the literature. The modeled gas-phase, particle-phase, and airborne concentrations of DEHP in residential air due to emissions from the selected materials were 2−65 times lower than the mean values of measured concentrations. To formulate appropriate control strategies, further efforts are needed to identify the dominant sources of phthalates in Chinese residences.

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INTRODUCTION Phthalates are common additives (as plasticizers) in consumer products that are widely used in residences. Because phthalates are usually not chemically bound to the material matrix, they can be emitted from the source materials to the indoor air, and subsequently become ubiquitous indoors.1,2 Chronic exposure to phthalates may result in detrimental health outcomes for humans, including asthma,3 endocrine disruption,4 and reproductive problems.5 Considering the fact that indoor phthalates concentrations are much higher than their ambient levels,6−8 indoor sources are the major contributors to indoor phthalates. Therefore, the emission features of phthalates from indoor materials must be studied to better understand the indoor concentration levels, human exposures, and the resulting health risks. Blanchard et al.9 and Wang et al.8 compared the indoor phthalate concentrations of different countries from previous literatures. The comparisons implied that indoor phthalate concentrations in China are comparable to, or even higher than, those in western countries. For example, the measured © 2018 American Chemical Society

median concentrations of gas-phase diethyl phthalate (DEP), diisobutyl phthalate (DiBP), and di-2-ethylhexyl phthalate (DEHP) for the studied private homes in Albany, NY, in Tran et al.’s study10 were 390, 19.6, and 17.4 ng/m3, respectively. Bu et al.11 measured the gas-phase concentrations of several phthalates in residential apartments at least one year after the latest renovation in Chongqing, China. According to their results, the median values of the measured gas-phase concentrations in bedroom air were 160, 320, and 260 ng/ m3 for DEP, DiBP, and DEHP, respectively. Regarding to the particle-phase concentrations of phthalates, the median values in 30 French residences of DEHP and DiBP in Blanchard et al.’s study9 were 41.5 and 30.2 ng/m3, respectively. In this field study, half of the selected dwellings were built before 1990 and 8 out of the 30 were retrofitted within 5 years. Meanwhile, in Received: Revised: Accepted: Published: 13166

June 29, 2018 October 22, 2018 October 29, 2018 October 29, 2018 DOI: 10.1021/acs.est.8b03580 Environ. Sci. Technol. 2018, 52, 13166−13173

Article

Environmental Science & Technology Wang et al.’s study8 in Xi’an, China, the measured median concentrations of indoor particle-phase DEHP and DiBP in buildings constructed within 5 years were 560 and 720 ng/m3, respectively. Thus, it is urgent to identify the indoor sources of phthalates in Chinese residences. The mass fraction of phthalates within the material (wt, %) determines the maximum amount of phthalates that can be emitted into indoor environments. On the other hand, previous studies demonstrated that the gas-phase mass transfer at the surface of the material limited the emissions of phthalates from polymeric materials.12 The emission rate (Ss, μg/h) can be described as follows: Ss = hmA s(y0 − Cs)

highest sale volume on a Chinese shopping website (http:// www.JD.com) or from the local housing decoration market were purchased and chosen as the selected flat materials in this study. All the material samples were newly purchased, except for one laminate flooring sample, which has been used for eight years. All the material samples were examined to determine both the wt and y0 of phthalates. It should be noted that the SPME-based method cannot quantify the y0 values for the samples of flooring materials and the supporting materials (because y0 is below the quantitation limit of the SPME-based method) even though the wt values were quantified by the extraction method for some of them. For these cases, the y0 values were predicted based on the relationship between wt and y0 from the literature (see details below). Chemicals. Seven phthalates were selected as the target pollutants; their physicochemical features are listed in Table 1.

(1)

where hm is the mass transfer coefficient at the emission surface (m/h), As is the surface area of the material (m2), y0 is the phthalate concentration in the air adjacent to the material surface (μg/m3), and Cs is the background gas-phase concentration of phthalate (μg/m3). Therefore, wt and y0 are the key parameters governing the emissions of phthalates from the source materials. In the past two decades, emissions of phthalates from polyvinyl chloride (PVC) floorings have been frequently studied,13−16 and these studies have found that y0 can be treated as constant after a sufficiently long period (e.g., after one year for DEHP according to Clausen et al.14). However, PVC flooring is more widely used in western countries than in China. In 2010, PVC flooring occupied 17.1% and 11.0% of the total flooring sales by volume in the United States and Western Europe, respectively. Meanwhile, PVC flooring only occupied 4.8% of sales in the Chinese flooring market.17 Chinese residents prefer laminate flooring and various wood floorings, including solid wood flooring and multilayer wood flooring. However, whether or not these commonly used flooring materials in China make a contribution to indoor phthalates keeps unknown. In addition, the phthalate emission features of other commonly utilized flat materials in Chinese residences have also not been studied. The objective of this study was to experimentally investigate the phthalate emission features of 23 flat materials available in the Chinese housing decoration market. We measured wt within the selected flat materials using the extraction method, and y0 of the selected materials were measured using the solidphase microextraction (SPME) sealed-chamber method recently developed by Cao et al.18 To evaluate the potential contribution of the selected flat materials to phthalates in residential air, airborne concentrations of DEHP due to the emission from the studied materials were modeled with the measured emission features.

Table 1. Physicochemical Features of the Selected Phthalates molecular weight (g/mol)

CAS no.

log Koaa

name

abbr.

chemical formula

dimethyl phthalate diethyl phthalate diisobutyl phthalate di-n-butyl phthalate butyl benzyl phthalate di(2ethylhexyl) phthalate di-n-octyl phthalate

DMP

C10H10O4

194.2

131−11−3

7.01

DEP

C12H14O4

222.2

84−66−2

7.55

DiBP

C16H22O4

278.3

84−69−5

8.54

DBP

C16H22O4

278.4

84−74−2

8.54

BBzP

C19H20O4

312.4

85−68−7

8.78

DEHP

C24H38O4

390.6

117−81−7

10.5

DOP

C24H38O4

390.6

117−84−0

10.5

Octanol/air partition coefficients (Koa) at 25 °C. Obtained from Cousins and Mackay.21

a

Among them, di-n-octyl phthalate (DOP) is the phthalate with the largest yield in China,19 and the others were frequently detected in Chinese residences in existing studies.7,8,11,20 All standards used in this study were purchased from SigmaAldrich Co. LLC. A certified reference material of DiBP was used for calibration of DiBP. A standard mixture of the other six phthalates (2000 μg/mL of each phthalate in methanol), including dimethyl phthalate (DMP), DEP, di-n-butyl phthalate (DBP), butyl benzyl phthalate (BBzP), DEHP, and DOP, was used for their calibration. Dichloromethane (CH2Cl2, MREDA Tech. Inc., HPLC grade) was used as the solvent. SPMEs (with polydimethylsiloxane as the coating material) were purchased from Sigma-Aldrich Co. LLC (Supelco Analytical, No. 57302). Extraction of Phthalates from Flat Materials. Phthalates in flat materials were extracted using a Soxhlet apparatus.22 Extractions were immediately started after the delivery of the materials. A small piece (approximately 0.2−0.4 g) from each material was cut from a random location and weighed. Samples were extracted with 60 mL of CH2Cl2 at 70 °C for 12 h (overnight). The extracts were concentrated to 10 mL using a rotary evaporator. Then, 100 μL of the concentrated extracts were transferred into 5 mL volumetric flask and diluted to 5 mL with CH2Cl2. Finally, 100 μL of the diluted extracts were transferred from the 5 mL volumetric

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MATERIALS AND METHODS Selection of Flat Materials in Chinese Residences. The emissions of phthalates from the following flat materials were analyzed: a plastic table mat, two PVC wallpapers, a PVC carpet, two PVC floorings, a toddler play mat, two dados (a kind of wall material usually installed on the lower part of the facade wall), and a window sticker. Additionally, several flooring materials together with the corresponding supporting materials, which are commonly used in Chinese residences, were also measured. The types of flooring materials included solid wood flooring, multilayer solid wood parquet flooring, and laminate flooring. The measured supporting materials were a moisture-proof mat and a poly mat. The products have the 13167

DOI: 10.1021/acs.est.8b03580 Environ. Sci. Technol. 2018, 52, 13166−13173

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Environmental Science & Technology flask into 2 mL Agilent sample vials equipped with 250 μL microvolume inserts using a 100 μL syringe. The vials were stored at −4 °C in a laboratory refrigerator and analyzed within 1 week. The wt of each material sample was measured for three times. Measurement of Phthalate Concentration in the Air Adjacent to the Material Surface Based on the SolidPhase Microextraction Method. We followed the SPME sealed-chamber method developed by Cao et al.18 to measure y0 values for phthalates emitted from flat materials. A detailed principle of the method and structure of the measurement system can be found in Cao et al.18 Experiments were immediately conducted after the delivery of the materials. Two circular samples (diameter: 22.0 cm) were cut from randomly selected locations of each material, which were then placed on the top and bottom of a circular ring made of stainless steel (thickness: 2.0 cm; inner diameter: 20.0 cm; outer diameter: 22.0 cm). Two flat plates made of stainless steel (thickness: 5 mm; diameter: 22.0 cm) were placed on the other side of each surface material. The gravity of the flat plate on the top helped to seal the airtight cavity (thickness: 2.0 cm; diameter: 20.0 cm) formed between the two flat materials and the circular ring. In addition, several small holes (diameter: 1.0 mm) were drilled in the middle of the side of the circular ring so that the SPME could be inserted into the chamber to quantify the y0 values. Gas-phase phthalates in the airtight cavity were sorbed by the coating of SPME, and the sorption amount was linearly related with y0 and the sampling time.18 According to the analysis of a previous study, the sampling time for DEP, DMP, DiBP, and DBP was set as 15 min, and it was set as 6 h for BBzP, DEHP, and DOP.23 The temperature of the whole experimental system was set as 25 °C during the measurement. For each material sample, the measurement of y0 was repeated three times. Instrumental Analysis. All samples (extracts in vials and SPME samples) were analyzed using a gas chromatography− mass spectrometry system (GC−MS, Agilent Technologies 7820A gas chromatograph (GC) system equipped with a 5975C Mass Spectrometer (MS)). A fused silica capillary column (HP-5MS, 30 m × 0.25 mm × 0.25 μm) was used for GC separation using high purity helium with a flow rate of 1.2 mL/min as the carrier gas. The GC oven temperature was maintained at 100 °C for 2 min, increased to 300 °C at 10 °C/ min, and finally maintained at 300 °C for 1 min (23 min in total). Temperatures of the GC injection port and MS ion source were set at 280 and 250 °C, respectively. For extracts in vials, the injection volume was 1.0 μL. For SPME samples, the coating of the SPME fiber was manually inserted into the GC injection port for 5 min (i.e., thermally desorbed for 5 min at 280 °C). The GC was operated in splitless mode, and the MS was operated in selected ion monitoring mode. The target compounds were quantified using the selected molecular ions, namely m/z = 163 for DMP and m/z = 149 for the other six phthalates. Quality Assurance and Control. A nine-point calibration was prepared based on 1 μL injections of mixture solutions of the seven phthalates with concentrations of 0.05, 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, 10, and 20 μg/mL. The mixture solutions were analyzed using the GC−MS system according to the procedure described in the previous section. A linear function between the GC−MS peak area and the concentration of each phthalate (for solvent extracts) or the injected amount of each phthalate

(for SPME samples) was obtained. The calibration curve was valid only when R2 of the linear fitting was larger than 0.99. For solvent extracts, the limit of quantitation (LOQ) was 0.05 μg/mL because the calibration line was no longer linear below this level. If the phthalate concentration in the extract was greater than 20 μg/mL, then the extract was diluted and reanalyzed. No phthalate was detected in the lab blanks (Soxhlet extraction but without flat materials in the extraction flask). For SPME samples, when the measured amount of phthalates was greater than 20 ng (corresponding to 20 μg/ mL × 1 μL), the sampling time of SPME samples was reduced by half; conversely, the sampling time was doubled if the measured amount was less than 0.05 ng (corresponding to 0.05 μg/mL × 1 μL). It should be noted that the sampling time should be less than tlinear according to the principle of the SPME-based method,18,23 where tlinear is the longest time that ensures the uptake rate of phthalates by SPME keeping constant (after tlinear, the uptake rate decreases as the sampling time increases). According to our measurements, tlinear was about 20 h for BBzP, DEHP, and DOP, and about 2 h for the other four phthalates. If the measured amount was still less than 0.05 ng when the sampling time reached tlinear, y0 cannot be quantified with the SPME based method, and the relationship between wt and y0 from the literature was used to estimate y0 values (see details below). Before measurements, each SPME sample was conditioned (thermally desorbed) by heating in the GC injection port at 280 °C for 5 min. After conditioning, the amount of each phthalate remaining in the SPME coating was undetected. Relationship between Mass Fraction and the Concentration in the Air Adjacent to the Material Surface. Eichler et al. studied the equilibrium relationship between the phthalates in PVC products and the corresponding y0.24 According to this analysis, the theoretical correlation between the volume fraction (φ, %) of phthalates within the source material and y0 obeys Henry’s law, which can be represented as the following equation: y0 = cφ

(2)

where c is a compound-specific constant related to the activity coefficient. In this study, c was set as 3.7 according to Eichler et al.’s study. The φ of phthalates within the source material can be derived from the wt as follows: φi =

Vph, i Vm

wt i /ρph, i

= n

wt j

∑j=1 ρ

ph, j

n

+

1 − ∑ j = 1 wt j ρm

(3)

where subscript “ph” represents phthalate, subscript “m” represents source material, V represents the volume (m3), and ρ represents the density (g/cm3). The measured density of the selected materials was utilized as ρm here, and ρph of each phthalate specie was obtained from CAMEO Chemicals (https://cameochemicals.noaa.gov). Potential Contribution of the Selected Flat Materials to Indoor Phthalates. To evaluate the potential contribution of the selected flat materials to indoor phthalates, indoor airborne concentrations of phthalate due to the emissions from the selected materials were calculated for several typical Chinese residential scenarios. Then, the calculated concentrations were compared to measured ones in Chinese residences obtained from the literatures. DEHP was selected 13168

DOI: 10.1021/acs.est.8b03580 Environ. Sci. Technol. 2018, 52, 13166−13173

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Environmental Science & Technology Table 2. Mass Fraction of the Target Phthalates within the Flat Materials (wt, %) material/compound

DMP

DEP

DiBP

DnBP

BBP

DEHP

DOP

plastic table mat wallpaper I wallpaper II carpet PVC flooring I PVC flooring II toddler play mat dado A dado B window sticker moisture proof mat poly mat solid wood flooring I solid wood flooring II solid wood flooring III solid wood flooring IV multilayer solid wood parquet flooring I multilayer solid wood parquet flooring II laminate flooring I laminate flooring II laminate flooring III laminate flooring IV laminate flooring V

/a / / / / / / / / / / / / / / / / / / / / / /

/ / / / / / / / / / / / / / LOQ-0.06 / / / / / / LOQ-0.09 /

/ / / / / / / / / / / / LOQ-0.08c / / / / / / / / / /

/ / / / 0.07 ± 0.01 / / / / / / / / / / / / / / / / / /

/ / / / / / / / / / / / / / / / / / / / / LOQ-0.1 /

17 ± 0.8b / 2 ± 0.7 3 ± 0.4 4 ± 0.6 14 ± 0.7 0.01 ± 0.002 / / 7 ± 0.3 / / LOQ-0.1 / / / / LOQ-0.1 / / / / /

/ / / 2 ± 0.2 / 0.09 ± 0.01 / / / / / / / / / LOQ-0.2 / / / / / LOQ-0.2 /

a

/ means all the wt of a material from the triplicate measurements are below the limit of quantitation. bIf all the wt of a material from the triplicate measurements are over the limit of quantitation, the measured wt is represented by mean ± standard deviation. cIf some of the wt of a material from the triplicate measurements are over the limit of quantitation, the measured wt is represented by min-max and LOQ means blow the limit of quantitation.

as the target compound for comparison as it is a ubiquitous phthalate congener in Chinese residences. We previously developed a model to predict indoor phasespecific concentrations of semivolatile organic compounds (SVOCs)25 that considers the kinetic partition process between gas-phase SVOCs and airborne particles. According to this model, the mass balance of gas- and particle-phase DEHP at the steady state can be described as follows:26,27 ij Csp yzz S zz + s V = 0 − αnCs − hmpA pNpjjjjCs − j K pC p zz { k

ij Csp yzz zz − DpCsp = 0 − αnCsp + hmpA pNpjjjjCs − j K pC p zz { k

Cs =

y A i h mpA pNp hm Vs y0 jjj K C + αn + Dpzzz { k p p

(hmpA pNp + αn + hm AV )(αn + Dp) + s

h mpA pNp K pC p

(αn + hm AV ) s

(6)

A

Csp =

hm Vs y0 hmpA pNp

(hmpA pNp + αn + hm AV )(αn + Dp) + s

h mpA pNp K pC p

(αn + hm AV ) s

(7)

A naturally ventilated apartment was set up to represent a typical residential scenario in China. αn was set as 2 h−1 to represent a long-term average scenario for the naturally ventilated apartments according to our previous studies.28,29 Kp is strongly dependent on indoor air temperature (ta, °C), which was set as 25 °C as a typical indoor scenario. The empirical equation proposed by Cao et al.18 was utilized to determine the vapor pressure of DEHP (PL, Pa) at 25 °C. Then, Kp of DEHP at 25 °C was calculated to be 0.034 m3/μg based on its relationship with PL.30,31 Indoor air speed (va, m/ s) within the residence with αn as 2 h−1 was estimated via Liu et al.’s empirical equation.32 The corresponding hm can be subsequently calculated with ta and va,33 which was 1.24 m/h for the modeled scenario. PM10 (particles with aerodynamic diameters smaller than 10 μm) was set to represent indoor airborne particles. For the modeled scenario, Cp of PM10 was set as 150 μg/m3, which is the national standard of indoor PM10 in China.34 To account for the influence of particle diameter on particle related parameters (i.e., hmp, Ap, Dp), PM10 was divided into eight diameter bins: < 0.10, 0.10−0.22, 0.22− 0.36, 0.36−0.56, 0.56−1.14, 1.14−2.26, 2.26−5.66, and 5.66− 10.0 μm. For each particle-related parameter, the value of each diameter bin was first determined and then the integrated value of PM10 was obtained by averaging the size-resolved parameter

(4)

(5)

where αn is the air exchange rate (h−1), hmp is the mass transfer coefficient at the surface of airborne particles (m/h), Ap is the surface area of an individual particle (m2), Np is the indoor particle number concentration (m−3), Csp is the indoor particle-phase DEHP concentration (μg/m3), Kp is the particle-gas partition coefficient of DEHP (m3/μg), Cp is the indoor particle mass concentration (μg/m3), V is the volume of the indoor environment (m3), and Dp is the indoor particle deposition rate (h−1). Detailed information on the model can be found in the original study.25 Because the atmospheric DEHP concentrations are much lower than the concentration levels in residences in China,6−8 the influence of atmospheric DEHP was not taken into account. The emission of DEHP from indoor flat materials can be described with eq 1. Therefore, gas- and particle-phase concentrations of DEHP can be calculated with the following equations by solving eqs 1, 4 and 5: 13169

DOI: 10.1021/acs.est.8b03580 Environ. Sci. Technol. 2018, 52, 13166−13173

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Environmental Science & Technology Table 3. Equilibrium Concentration in the Air Adjacent to the Product Surface (y0, μg/m3) material/compound

DMP

DEP

DiBP

DBP

BBzP

DEHP

DOP

plastic table mata wallpaper I wallpaper IIa carpeta PVC flooring Ia PVC flooring IIa toddler play mat dado I dado II window stickera moisture-proof mat poly mat solid wood flooring Ib Solid wood flooring II solid wood flooring III solid wood flooring IVb multilayer solid wood parquet flooring I multilayer solid wood parquet flooring IIb laminate flooring I laminate flooring II laminate flooring III laminate flooring IVb laminate flooring V (Used) vinyl flooring Ic,12 vinyl flooring IIc,16 vinyl flooring IIIc,16 vinyl flooring IVc,16 vinyl flooring Vc,16

/d / / / / / / / / / / / / / / / / / / / / / / −e − − − −

/ / / / / / / / / / / / / / / / / / / / / / / − − − − −

/ / / / / / / / / / / / / / / / / / / / / / / − − − − −

/ / / / / / / / / / / / / / / / / / / / / / / − − − − −

/ / / / / / / / / / / / / / / / / / / / / 0.05 / − − − − −

2 ± 0.07 / 0.2 ± 0.01 0.07 ± 0.06 1 ± 0.05 2 ± 0.01 / / / 2 ± 0.3 / / 0.009 / / / / 0.008 / / / / / 1.13 2.3 2.37 0.02 1.54

/ / / 0.1 ± 0.03 / / / / / / / / / / / 0.002 / / / / / 0.003 / − − − − −

a

Measured y0 according to the solid-phase microextraction sealed-chamber method bCalculated y0 from the measured mass fraction cSummarized y0 from the literature d/ means below the limit of quantitation e− means not reported

the limit of quantitation (LOQ), the relative standard deviations of wt were all less than 30%, giving confidence in the accuracy of our measurements of wt. The selected flooring materials and the supporting materials corresponded to very small wt values of the target phthalate species (i.e., LOQ0.2%). Among the selected flat materials, wallpaper I, dados I and II, moisture-proof mat, poly mat, solid wood flooring II, multilayer solid wood parquet flooring I, and laminate floorings I, II, III, and V were found to be free of the target phthalates. None of the target phthalates were detected in the used laminate flooring sample. Afshari et al.1 summarized the wt of DEHP and DBP in some indoor materials, including PVC flooring and wallpaper. In their study, the wt of DEHP within the PVC flooring materials ranged from 17% to 18.5%, while that of wallpaper was 18%. These surveyed wt values of DEHP were much larger than the majority of the measured ones in the present study. As the health hazards of phthalates have become well recognized, more governments and agencies have issued regulations to limit the amount of phthalates in consumer products.37,38 As a result, newly produced materials tested in this study may have a smaller wt of phthalates compared to those of the surveyed materials. PVC flooring I and the window sticker selected in this study are heterogeneous materials that are made up with layers of different materials. However, the wt of phthalates from the extraction method was obtained by dividing the amount of phthalates within the material by the total weight of the material. In this case, the measured wt may deviate from the actual value.

weighted by a typical mass distribution of PM10 in residential environment.35 The determinations of αn, Kp, hm, and size resolved particle related parameters are introduced in detail in Supporting Information (SI) Section S1. It is noteworthy that indoor environmental factors, including indoor air temperature (ta), air exchange rate (αn) and indoor particle concentration (Cp), affects both mass transfer and source emission of phthalates.32,33,36 Therefore, sensitivity analysis was conducted to investigate the influences of ta, αn, and Cp on the calculated indoor DEHP concentrations in air due to the emission from the selected flat materials, which are introduced in detail in SI Section S2.

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RESULTS AND DISCUSSION Mass Fraction of Phthalates within the Materials. Mass fractions of the target phthalates within the selected flat materials (wt, %) are listed in Table 2. Six of the seven targeted phthalates were found in the selected flat materials. In general, the detection rates of phthalates were not high among the selected flat materials. DEHP had the highest detection rate (39.1%), followed by DOP (17.4%), DEP (8.7%), and DiBP/ DBP/BBzP (4.3%). DMP was not detected in any of the selected flat materials. The plastic table mat had the largest wt of the target phthalate species, which was 17%. The wt of the target phthalate species in the carpet, PVC flooring B and window sticker were also larger than 5%. For the rest flat materials, the wt of the target phthalate species were smaller than 5%. For materials with all the wt of the triplicate measurements over 13170

DOI: 10.1021/acs.est.8b03580 Environ. Sci. Technol. 2018, 52, 13166−13173

Article

Environmental Science & Technology Equilibrium Concentration in the Air Directly Adjacent to the Material Surface. The measured equilibrium concentrations in the air adjacent to the material surface (y0) are listed in Table 3. For plastic table mat, wallpaper II, carpet, PVC flooring I and II, window sticker, and solid wood flooring I, y0 was represented as the average value and the standard deviation from the triplicate measurements. For solid wood flooring IV, multilayer solid wood parquet flooring II, and laminate flooring IV, y0 was calculated from the maximum measured wt from the triplicate experiments using eqs 2 and 3 to show the most unfavorable situation. For materials with all the measured wt from the triplicate experiments smaller than 0.1%, the corresponding y0 could not be quantitatively determined. For DEHP, the plastic table mat, PVC flooring II, and window sticker had the largest y0 (i.e., 2 μg/m3) and the multilayer solid wood parquet flooring II had the smallest y0 (i.e., 0.008 μg/m3). For DOP, the carpet had the largest y0 (i.e., 0.1 μg/m3) and the solid wood flooring IV had the smallest y0 (i.e., 0.002 μg/m3). For BBzP, the laminate flooring IV was found to have an y0 of 0.05 μg/m3. Previous studies have examined the y0 of DEHP within vinyl flooring materials,12,16 the results of which are also summarized in Table 3. For the selected flooring materials in this study, the determined y0 of DEHP was 0.009 and 0.008 μg/m3 for the solid wood flooring I and multilayer solid wood parquet flooring II, which were two orders smaller than most of the vinyl flooring materials measured in previous studies. Potential Contribution of the Selected Flat Materials to Indoor Phthalates. The measured materials were classified into three categories according to their emission strengths (i.e., y0) and applied surface areas. Category 1 refers to materials with small y0 but large applied surface areas, represented by wallpaper II; category 2 refers to materials with large y0 but small applied surface areas, represented by window sticker; category 3 refers to materials with large y0 and relatively large applied surface areas, represented by PVC flooring II. Then, DEHP concentrations in indoor air due to the emissions of the representative material were calculated for each category to estimate the potential contribution of the selected materials to indoor DEHP. y0 was set as the measured value of the representative material. The applied area of the source material was represented by the loading factor of the source material (i.e., As/V). As/V was set as 1.0 m2/m3 for wallpaper II as it is an experience value of inner wall surface area. For window sticker and PVC flooring II, As/V was set as 0.1 and 0.4 m2/m3, respectively.39 The calculated airborne DEHP concentrations due to the emissions from the representative materials are shown in Figure 1. Several studies have reported indoor gas- and particle-phase concentrations of DEHP in Chinese residences, as summarized in Table 4. For wallpaper II, representing materials with small emission strength but large applied area, the modeled gas-phase, particle-phase, and airborne concentrations of indoor DEHP due to its emissions were 0.017, 0.087, and 0.10 μg/m3, respectively, which are 11−65 times smaller than the average measured values from the literature. With regard to window sticker, although it has a strong emission strength, the modeled indoor gas-phase, particle-phase and airborne concentrations of DEHP, that is, 0.018, 0.095, and 0.11 μg/m3, respectively, due to its emission were also 10−61 times smaller than the average values from the field measurements. Therefore, these two categories of materials may not be the major contribution to

Figure 1. DEHP concentrations in residential air due to the emissions from the selected flat materials.

Table 4. DEHP Concentrations in the Air of Chinese Residences from the Literature references Pei et al., 20137 Wang et al., 20148 Bu et al., 201611 Tao et al., 201340 a

gas-phase (μg/ m3)a

particle-phase (μg/ m3)a

1.12 0.47

1.32 1.04

airborne (μg/ m3)a

0.38 1.19

Mean value from the reference.

indoor DEHP in Chinese residences. For PVC flooring II, it had the highest modeled concentrations of indoor gas-phase, particle-phase and airborne DEHP, which were 0.071, 0.37, and 0.44 μg/m3. These modeled concentrations were about 6− 37% of the average measured ones from the literature. Although PVC flooring has the same emission strength (i.e., y0) comparing to window sticker, the larger applied surface area of PVC flooring II make it a possible important contributor to indoor DEHP. However, it has been stated that PVC flooring materials are not commonly used as residential flooring material in China. Hence, to sum up, the flat materials selected in this study might not be the major contributors to indoor DEHP for most Chinese residences. It is noteworthy that y0 of phthalates increased significantly with increasing temperature.13 The measurements of Pei et al.7 and Tao et al.40 were conducted in normal residences in transient seasons. The indoor temperatures during the measurements by Wang et al.8 and Bu et al.11 ranged from 14.6 to 21.5 °C and 3.1 to 18.8 °C, respectively. The indoor air temperature of the modeled scenario was set as 25 °C, which was higher than the air temperatures of the majority of the measured scenarios. Because evaluated indoor temperature would increase y08, the modeled DEHP concentrations due to the selected flat materials in the measured scenarios of these literatures may be further lower than the measured results. In addition, results of sensitivity analysis (see details in SI Section S2) also support the above conclusion, that is, the materials measured in this study might not be the major contributors of indoor SVOCs for most Chinese residences. Limitations and Further Study. There were several limitations in the present study. First, the selected flat materials 13171

DOI: 10.1021/acs.est.8b03580 Environ. Sci. Technol. 2018, 52, 13166−13173

Article

Environmental Science & Technology Author Contributions

may not represent the overall source materials of phthalates in Chinese residences. Personal care products, plastic shoes, and shower curtains are also potential sources of indoor phthalates in residences,41 but they were not considered in this study. Second, the extraction method may not be suitable to measure the wt of phthalates within heterogeneous materials, which were composed of multiple layers. Third, the model utilized to estimate DEHP concentrations in indoor air due to the emissions from the selected flat materials was a simplified model based on several assumptions. The kinetic partitions between gas-phase DEHP and indoor sorption surfaces, and settled dust were not considered. The modeled residence was assumed to be well-mixed and reached a steady state. This was supported by the measured data of existing studies for the case where stable and persistent sources of phthalates (such as the flat materials measured in this study) have stayed in the room for a sufficient amount of time.14,42 Quantitative analysis of the errors caused by these assumptions is worthwhile, but may require the employment of computational fluid dynamics (CFD) modeling, which was out of the scope of this study. A previous study reported that the relative difference between SVOC phase-specific concentrations at a steady state with time-averaged input parameters and time-averaged phasespecific concentrations resulting from the nonsteady state model with periodic input parameters can be nearly 20%.26 Finally, as an assumption in eq 5, all particles were assumed to have the same residence time and particle-air partition coefficient of DEHP. However, assuming the same residence time for indoor particles may not be the real case (i.e., residence time varies among individual particles), and this assumption may result in an error of up to 30% to the modeled SVOC concentrations.43 Besides, the particle-air partition coefficient of DEHP is dependent on the particle type.44 The emissions of phthalates from more materials and consumer products containing phthalates with a large consumption volume in Chinese residences still need to be examined. Moreover, the contributions of different sources to Chinese residential phthalates need to be quantitatively studied in controlled experiments. By understanding the major sources of phthalates in Chinese residences, optimal control strategies can be subsequently formulated to reduce indoor airborne phthalates and mitigate the related health risks.

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Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This study was supported by the National Key Project of the Ministry of Science and Technology, China, on “Green Buildings and Building Industrialization” through Grant No. 2016YFC0700500, by funding from the National Natural Science Foundation of China through Grant No. 51708278 and 51521005, and by funding from the Natural Science Foundation of Jiangsu Province of China through Grant No. BK20170643.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.est.8b03580. Additional details of input parameters of the typical exposure scenarios for Chinese residences (Section S1), and sensitivity analysis for room temperature, air exchange rate, and particle concentration (Section S2, Figure S1, Tables S1 and S2) (PDF)

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Authors S.S. and J.C. contributed equally.

AUTHOR INFORMATION

Corresponding Author

*Phone: +86-10-6277-9995; fax: +86-10-62773461; e-mail: [email protected]. ORCID

Shanshan Shi: 0000-0002-8848-4219 Jianping Cao: 0000-0002-8633-388X Yinping Zhang: 0000-0001-9175-7890 Bin Zhao: 0000-0003-1325-6091 13172

DOI: 10.1021/acs.est.8b03580 Environ. Sci. Technol. 2018, 52, 13166−13173

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