Science of the Total Environment

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Occurrence of cyclic and linear siloxanes in indoor air from Albany, New York, USA, and its implications for inhalation exposure

Tri Manh Tran

^a,b

, Kurunthachalam Kannan

^a,c,

⁎

aWadsworth Center, New York State Department of Health, Department of Environmental Health Sciences, School of Public Health, State University of New York at Albany, Empire State Plaza, P.O. Box 509, Albany, NY 12201-0509, United States

bFaculty of Chemistry, Hanoi University of Science, Vietnam National University, 19 Le Thanh Tong, Hoan Kiem, Hanoi, Viet Nam

cBiochemistry Department, Faculty of Science and Experimental Biochemistry Unit, King Fahd Medical Research Center, King Abdulaziz University, Jeddah 21589, Saudi Arabia

H I G H L I G H T S

•Cyclic and linear siloxanes were determined in 60 indoor air samples.

•Concentrations of 14 siloxanes ranged from 249 to 6210 ng/m³with the highest levels in salons.

•High molecular weight siloxanes were preferably sorbed in particulate phase of indoor air.

•Inhalation exposure dose to siloxanes ranged from 0.27 to 3.18μg/kg-bw/d.

a b s t r a c t a r t i c l e i n f o

Article history:

Received 10 October 2014

Received in revised form 7 December 2014 Accepted 8 December 2014

Available online xxxx Editor: Adrian Covaci Keywords:

Siloxane Indoor air Inhalation exposure PDMS

Cyclic methylsiloxane D5

Cyclic and linear siloxanes are used in a wide variety of household and consumer products. Nevertheless, very few studies have reported the occurrence of these compounds in indoor air or inhalation exposure to these compounds.

In this study,ﬁve cyclic (D3–D7) and nine linear siloxanes (L3–L11) were determined in 60 indoor air samples collected in Albany, New York, USA. The mean concentrations of individual siloxanes in particulate and vapor phases ranged fromb12μg g⁻¹(for octamethyltrisiloxane [L3], decamethyltetrasiloxane [L4]) to 2420μg g⁻¹ (for decamethylcyclopentasiloxane [D5]) and from 1.05 ng m⁻³to 543 ng m⁻³, respectively. The mean concentrations of individual siloxanes in combined particulate and vapor phases of bulk indoor air ranged from 1.41 ng m⁻³ (for L4) to 721 ng m⁻³(for D5). Cyclic siloxanes hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), D5, dodecamethylcyclohexasiloxane (D6), and octadecamethylcycloheptasiloxane (D7) were found in all indoor air samples. The mean concentrations of total siloxanes (i.e., sum of cyclic and linear siloxanes) ranged from 249 ng m⁻³in laboratories to 6210 ng m⁻³in salons, with an overall mean concentration of 1470 ng m⁻³in bulk indoor air samples. The calculated mean daily inhalation exposure doses of total siloxanes (sum of 14 siloxanes) for infants, toddlers, children, teenagers, and adults were 3.18, 1.59, 0.76, 0.34, and 0.27μg/kg-bw/day, respectively.

1. Introduction

Siloxanes are organo-silicone compounds and consist of–(CH3)2SiO –structural units. Two major groups of siloxanes of commercial signiﬁ- cance are cyclic and linear siloxanes. Siloxanes are used in a wide variety of consumer and industrial products (Horii and Kannan, 2008; Ortega and Subrenat, 2009). Personal care products contain siloxanes at concentrations on the order of several percentages by weight (Horii and Kannan, 2008; Wang et al., 2009). Cyclic siloxanes–D4, D5, D6, and D7–were found in consumer products at mean concentrations of

9380, 81,800, 43,100, and 846 μg g⁻¹ respectively; skin lotions contained total linear siloxanes at concentrations (sum of L4 to L14) as high as 73,000μg g⁻¹ (i.e., 7.3% by weight;Horii and Kannan, 2008). The total cyclic siloxane concentrations (D6 to D25) in silicon- ized rubber products marketed for food contact use were in the range of 3310 to 14,700μg g⁻¹(Kawamura et al., 2001).

Studies have reported the occurrence of siloxanes in a wide range of environmental samples, including outdoor air, water, wastewater, indoor dust, soil, landﬁll biogas, sediment, sewage sludge, and biota, including humans (Wang et al., 2001, 2013a,2013b; Badjagbo et al., 2010; Kierkegaard and McLachlan, 2010; Sánchez-Brunete et al., 2010; Zhang et al., 2011; Bletsou et al., 2013; Blanchard et al., 2014;

Cortada et al., 2014; Lee et al., 2014). A recent review has summarized environmental occurrence of cyclic siloxanes (Wang et al., 2013a).

Science of the Total Environment 511 (2015) 138–144

⁎ Corresponding author at: Wadsworth Center, Empire State Plaza, PO Box 509, Albany, NY 12201-0509, USA.

E-mail address:[email protected](K. Kannan).

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Accumulation of D5 inﬁsh from the arctic environment has been shown (Warner et al., 2010).

Despite the use of siloxane-containing products in the indoor environment and the volatility of siloxanes, very few studies have reported the occurrence of these compounds in indoor air (Shields et al., 1996;

Latimer et al., 1998; Kaj et al., 2005; Companioni-Damas et al., 2014).

One study reported the occurrence of cyclic and linear siloxanes in indoor air samples collected from the UK and Italy, at concentrations as high as 170μg m⁻³(Pieri et al., 2013). Another study reported a median concentration of 2200 ng m⁻³for the sum of D4, D5, and D6 concentrations in indoor air samples from Chicago, Illinois, USA (Yucuis et al., 2013). A guidance value of 4000μg m⁻³and a precautionary guideline value of 400μg m⁻³were recommended for the sum of D3 to D6 in indoor air in Germany (GermanEnvironment Agency, 2011).

Studies have reported reproductive and endocrine effects of siloxanes in laboratory animals. Estrogenic and androgenic activities of D4 and/or D5 have been reported in rats (McKim et al., 2001; Quinn et al., 2007b). A recent article has reviewed the toxicity of cyclic siloxanes (Wang et al., 2013a). The potential of D4 to suppress the pre- ovulatory luteinizing hormone surge and ovulation has been shown in laboratory rodent studies (Quinn et al., 2007a).Meeks et al. (2007) showed that a single dose of D4 on the day prior to mating resulted in a signiﬁcant reduction in fertility in female rats. A dose-dependent increase in uterine weights in ovariectomized mice and an increase in uterine peroxidase activity were shown in D4-exposed mice (He et al., 2003). Inhalation exposure of rats to D5 did not alter humoral immunity and caused only minor, transient changes in hematological, clinical, and anatomical parameters (Burns-Naas et al., 1998). Several environmental risk assessment studies conducted in Canada, Sweden and the UK suggested that methylsiloxanes are persistent and can pose harmful effects on the environment (Kaj et al., 2005; Environment Canada, 2008;

Brooke et al., 2009).

Siloxanes are ubiquitous in the environment, and potential exists for contamination in laboratories and sampling devices, which imposes challenges in the collection and analysis of siloxanes in environmental samples. A few studies have reported the methods to collect siloxanes in air (Wang et al., 2001; Badjagbo et al., 2009; Kierkegaard and McLachlan, 2010; Yucuis et al., 2013; Pieri et al., 2013; Conpanioni- Damas et al., 2014). In this study, by use of a combination of quartz fiberfilters and polyurethane foam (PUF) plugs, we collected indoor air samples by a low-volume air sampler at various indoor environments including homes, offices, schools, salons and public places. The objectives of this study were to determinefive cyclic and nine linear siloxanes in both particulate and vapor phases of indoor air in Albany, New York, USA. Inhalation exposure of humans to siloxanes was also estimated.

2. Materials and methods 2.1. Standards

Hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6), with a purity ofN95%, were purchased from Tokyo Chemical Industry, Inc. (Wellesley Hills, MA, USA). Octamethyltri- siloxane (L3) (98%), decamethyltetrasiloxane (L4) (97%), and dodeca- methylpentasiloxane (L5) (97%) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Polydimethylsiloxane (PDMS) 200ﬂuid (viscosity of 5 cSt) that contained octadecamethylcycloheptasiloxane (D7), linear tetradecamethylhexasiloxane (L6), and other polydimethylsiloxanes (L7, L8, L9, L10, and L11) were purchased from Sigma-Aldrich (Table S1). Tetrakis (trimethylsiloxy)-silane (M4Q) of 97% purity was from Aldrich, and ¹³C-labeled decamethylcyclopentasiloxane- [2,4,6,8,10-¹³C5] (¹³C-D5) of 98% purity was from Bristlecone Biosci- ences, Inc. (Brea, CA, USA), and these two compounds were used as surrogate standards. All standards were dissolved in hexane. The

composition of PDMS was determined and reported in our previous study (Horii and Kannan, 2008) and the PDMS mixture was used in the determination of concentrations of linear siloxanes.

2.2. Sample collection and preparation

PUF plugs (ORBO-1000 PUF dimensions: 2.2 cm O.D × 7.6 cm length) were from Supelco (Bellefonte, PA, USA). For the analysis of background levels of siloxanes, PUF plugs were extracted twice with 100 mL mixture of dichloromethane (DCM) and hexane (3:1, v:v) and analyzed by gas chromatography–mass spectrometry (GC–MS). It was found that each of the newly purchased PUF plugs contained D3, D4, D5, D6, and D7 at 6.03 ± 4.72 ng, 19.9 ± 6.59 ng, 32.2 ± 12.5 ng, 7.44 ± 3.05 ng, and 4.18 ± 2.19 ng, respectively (n= 5). Therefore, all PUF plugs required additional cleaning prior to use. PUFs were purified by shaking with 100 mL mixture of DCM and hexane (3:1, v:v) for 30 min. This procedure was performed twice. The cleaned PUFs were wrapped in solvent rinsed aluminum foil, stored in a glass jar, and kept in an oven at 100 °C until sampling. The quartzfiberfilters (Whatman, grade QM-A, pore size: 2.2μm with a particle retention rating at 98% efficiency in liquid, 32 mm diameter) were prepared by heating at 450 °C for 20 h. The purified quartzfiberfilters were kept in an oven at 100 °C until use. The quartz fiberfilters were weighed in an analytical balance (to nearest 0.01 mg) before and after the collection of air samples for the determination of particle content.

Two PUF plugs were packed in tandem in a glass tube (ACE glass, 2.2 cm O.D × 25 cm length), and the quartzfiberfilter was held with a Teflon cartridge (Supelco, PUF filter cartridge assembly, cat. no.

21031) on top of the glass tube packed with PUF plugs. All glassware used for sampling and analysis was rinsed with acetone and hexane and heated at 450 °C immediately prior to use.

Indoor air samples were collected for 12 to 24 h by a low-volume air sampler (LP-20; A.P. Buck Inc., Orlando, FL, USA) at aflow rate of 5 L per minute. The total volume of air collected from each location ranged from 3.6 m³to 7.2 m³. Air samples (both PUFs andfilters) were kept at−18 °C until analysis. The samples were kept for no longer than 3 weeks for analysis. The samples were collected from March to May 2014 at several locations in Albany, New York, USA. The sampling locations were grouped into six categories: homes (n = 20), offices (n = 7), laboratories (n = 13), schools (n = 6), salons (n = 6, hair and nail salons), and public places (n = 8, e.g., shopping malls).

Prior to analysis, samples (both PUFs andﬁlters) were spiked with 100 ng of M4Q and¹³C-D5 as surrogate standards. PUF plugs were extracted by shaking in an orbital shaker (Eberbach Corporation, Ann Arbor, MI, USA) with DCM and hexane (3:1, v:v) for 30 min. The extraction was performed twice, with 100 mL of solvent mixture for theﬁrst extraction and 80 mL for the second. The extracts were concentrated in a rotary evaporator at 40 °C to approximately 5 mL. The solution was then transferred into a 12-mL glass tube and concentrated by a gentle stream of nitrogen to exactly 1 mL and transferred into a GC vial.

The particulate samples were extracted by shaking glassﬁberﬁlters with a mixture of DCM and hexane (3:1; 20 mL; v:v) each time for 5 min, which was performed three times. The extract was concentrated in a rotary evaporator and then by a gentle stream of nitrogen to exactly 1 mL. The extract was then transferred into a GC vial.

2.3. Instrumental analysis

Analysis was performed on an Agilent Technologies 6890 gas chro- matograph (GC) interfaced with a 5973 mass spectrometer (MS).

Separation of siloxanes was achieved by HP-5MS capillary column (Agilent, Santa Clara, CA, USA; 5% diphenyl 95% dimethylpolysiloxane, 30 m × 0.25 mm i.d. × 0.25μmﬁlm thickness). Samples were injected in the splitless mode, and the injection volume was 2μL. The oven temperature was programmed from 40 °C (held for 2 min) to 220 °C at 20 °C/min, increased to 280 °C at 5 °C/min (held for 10 min), and

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held for 5 min at 300 °C. Ion fragmentm/z207 was monitored for D3,m/z 281 for D4, D7, and L5,m/z355 for D5, andm/z341 for D6. Ion fragment m/z147 was used for conﬁrmation of L6 and L7. Ion fragmentm/z207 was monitored for conﬁrmation of L4 andm/z221 for the other siloxanes (Horii and Kannan, 2008; Badjagbo et al., 2009; Zhang et al., 2011;

Bletsou et al., 2013). Ion fragmentm/z 281 was monitored for M4Q and m/z360 for¹³C-D5.

2.4. Quality assurance and quality control

Siloxanes are present in several laboratory products, which have been examined in our previous study (Horii and Kannan, 2008). Efforts were taken to minimize background levels of siloxane contamination in our analysis. All glassware was heated for 20 h at 450 °C prior to use. Sol- vents were used directly from glass bottles, and exposure of solvent to air was kept minimal. GC vials were capped in an aluminum foil (instead of rubber septum). Procedural blanks were analyzed with every set of 8 samples. D3, D4, D5, and D6 levels in procedural blanks were 3.31 ± 0.91 ng, 4.2 ± 2.46 ng, 7.18 ± 3.52 ng, and 1.8 ± 0.36 ng, respectively.

Other siloxanes were not detected in the procedural blanks. The contamination of siloxanes in procedural blanks is from solvents, glassware, or residual levels present in PUFs (after puriﬁcation). The reported concentrations in indoor air samples were subtracted by the average values found for the procedural blanks. The calibration curve was linear over a concentration range of 1 ng/mL to 500 ng/mL for individual siloxanes (R²N0.995). Duplicate samples were collected in three locations and the relative standard deviation (RSD) of measured concentrations was b10%.

A total of 100 ng of M4Q and¹³C-D5, D3, D4, D5, D6, L3, L4, and L5 were spiked into blank PUF plugs and a glassfiberfilter and passed through the entire analytical procedure. The recoveries of target compounds spiked into PUFs andfilters are shown inTable 1. The recoveries of M4Q spiked into samples ranged from 90.8 to 116% (mean: 101%;

RSD: 8.7%) in the particle phase and from 87.5 to 120% (mean: 104%;

RSD: 10.4%) in the vapor phase. The method detection limit (MDL) and the method quantiﬁcation limit (MQL) were determined on the basis of an average volume of air collected, which was 3.6 m³; the average weight of airborne particle collected, which was 0.25 mg, and the lowest point in the calibration standard with a signal-to-noise ratio of 3 and 10, respectively. The sample concentration/dilution factors were included in the calculation of MDL and MQL. For the vapor phase, the MQL ranged from 0.22 to 2.22 ng m⁻³, and, for the particulate phase, the MQL ranged from 3.2 to 32 ng g⁻¹. The mean recoveries of four

cyclic and three linear siloxanes in gas and particulate phases were from 73.4 to 116%, with an RSD of 7.3 to 15.6% (Table 1). For values below the MQL, the concentrations were set at one-half of the MQL for statistical analysis. Statistical analysis was conducted through Microsoft Excel (Microsoft Ofﬁce 2010) and GraphPad Prism version 5.0. Statisti- cal signiﬁcance was set atpb0.05.

3. Results and discussion

3.1. Concentrations of siloxanes in particulate phase

The concentrations of individual siloxanes in the particulate phase (Table 2) were calculated based on the weight of the airborne particle collected in a glassﬁberﬁlter (that ranged from 0.15 mg to 0.45 mg).

D3, D4, D5, D6, and D7 were found in all samples, whereas L3 and L11 were detected in only 26.7% and 8.33% of the samples, respectively. L5 to L9 were found frequently in samples (75% to 95%) at high concentrations, whereas L3, L4, and L11 were rarely detected. Among various siloxanes analyzed, D5 and L8 were the most abundant compounds in the particulate phase. The concentrations of D5 in the particulate phase ranged from 29.3 to 34,300μg g⁻¹(mean: 2420) and the concentrations of L8 ranged from below MQL to 12,700μg g⁻¹(mean: 1320).

The air volume based measurements (ng m⁻³) of siloxanes in the particulate phase of indoor air are shown as the supporting information (Table S2).

Because airborne particles are a source of indoor dust after deposi- tion, concentrations of siloxanes measured in airborne particles were compared with those reported in indoor dust. The concentrations of siloxanes in airborne particles were four times higher than the concentrations reported in indoor dust from China (Lu et al., 2010). The sum of mean concentration ofﬁve cyclic and nine linear siloxanes in the particulate phase of indoor air was 6000μg g⁻¹(i.e., approximately 0.6% by weight). The highest concentrations of siloxanes were found in salons.

Personal care products are the major sources of siloxanes in the indoor environment (Horii and Kannan, 2008; Wang et al., 2009), which ex- plains the elevated concentrations found in air samples from salons.

3.2. Concentrations of siloxanes in vapor phase

The concentrations of siloxanes in the vapor phase of indoor air are shown inTable 3. The concentrations of D4, D5, and D6 were higher in the vapor phase than in the particulate phase (Fig. 1). Higher concentrations of these three siloxanes in the vapor phase than in the particulate

Table 1

The method detection limit, quantitation limit and the recoveries of siloxanes through the analytical method used in this study.

Vapor phase Particulate phase

Recoveries, % (n = 8) Recoveries, % (n = 8)

MDL (ng m⁻³) MQL (ng m⁻³) Range Mean RSD MDL (ng g⁻¹) MQL (ng g⁻¹) Range Mean RSD

D3 0.06 0.22 66.0–84.9 73.4 7.3 0.8 3.2 77.5–105 91.2 9.8

D4 0.08 0.28 85.4–121 105 13.1 1.2 4.0 86.6–119 106 11.8

D5 0.06 0.22 88.7–126 109 14.7 0.8 3.2 98.4–125 116 8.6

D6 0.06 0.22 93.9–123 109 11.9 0.8 3.2 80.7–115 99.7 12.2

D7 0.19 0.56 – – – 2.8 8.0 – – –

L3 0.14 0.83 75.5–110 93.9 10.6 2.0 12.0 79.5–112 96.9 12.0

L4 0.14 0.83 93.6–123 112 12.7 2.0 12.0 78.0–122 104 15.6

L5 0.14 0.56 82.5–116 103 11.9 2.0 8.0 96.9–120 110 8.7

L6 0.19 0.83 – – – 2.0 12.0 – – –

L7 0.19 0.83 – – – 2.0 12.0 – – –

L8 0.56 1.94 – – – 8.0 28.0 – – –

L9 0.56 1.94 – – – 8.0 28.0 – – –

L10 0.83 2.22 – – – 12.0 32.0 – – –

L11 0.83 2.22 – – – 12.0 32.0 – – –

M4Q – – 87.5–120 104 10.4 – – 90.8–116 101 8.7

13C-D5 – – 84.4–122 106 14.4 – – 83–115 97.6 11.8

Method detection limit (MDL) and method quantitation limit (MQL) were calculated on the basis of the average volume of air collected which was 3.6 m³and the average weight of airborne particle collected, which was 0.25 mg. RSD: relative standard deviation.

140 T.M. Tran, K. Kannan / Science of the Total Environment 511 (2015) 138–144

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Concentrations of individual siloxanes in the particulate phase of indoor air samples collected from various locations in Albany, New York, USA (μg g⁻¹).

D3 D4 D5 D6 D7 L3 L4 L5 L6 L7 L8 L9 L10 L11 ΣSil.

Homes Range 8.59–38.9 17.9–169 127–12,400 28.8–842 17.6–438 n.d.–12.2 n.d.–29.8 n.d.–251 n.d–1270 23.5–1950 53.7–2550 b28–1920 n.d.–374 n.d. –

n = 20 Mean 24.3 47.6 1590 188 104 b12 b12 40.3 184 390 987 435 86.9 n.d. 4100

Freq. % 100 100 100 100 100 25 30 80 85 100 100 100 75 – –

Ofﬁces Range 17.6–66.3 19.2–50.4 40.4–2100 60.1–702 20.9–656 n.d.–15.6 n.d.–15.6 n.d.–93.3 n.d.–330 12.8–1720 b28–2260 b28–250 n.d.–53.7 n.d. –

n = 7 Mean 42.7 35 795 262 231 b12 b12 32.8 81 511 787 128 b32 n.d. 2940

Freq. % 100 100 100 100 100 14.3 42.9 85.7 28.6 100 100 100 14.3 – –

Laboratories Range 13–131 13.9–108 29.3–394 9.42–106 10.3–319 n.d.–179 n.d. n.d.–408 n.d.–22.7 n.d.–64.4 n.d.–77.7 n.d.–32.3 n.d.–104 n.d. –

n = 13 Mean 40.9 49.7 167 47.1 79.8 27.3 n.d. 41.5 6.13 31.3 36.6 b28 b32 n.d. 567

Freq. % 100 100 100 100 100 76.9 – 46.2 53.8 84.6 76.9 46.2 7.69 – –

Schools Range 15.3–41.6 24–400 258–17,300 66.3–1500 34.3–443 n.d. n.d.–20 n.d.–211 10.7–741 36.8–3390 98.3–3690 n.d.–345 n.d.–127 n.d. –

n = 6 Mean 27.7 153 5610 565 275 n.d. b12 64.8 292 1060 1350 201 58.1 n.d. 9680

Freq. % 100 100 100 100 100 – 50 66.7 100 100 100 83.3 50 – –

Salons Range 21–34.5 145–1680 849–34,300 147–2450 37.4–432 n.d. n.d.–34.5 23.1–264 267–1320 654–3670 2210–12,700 468–12,700 175–4530 n.d.–295 –

n = 6 Mean 26.7 665 10,400 955 213 n.d. 14 103 662 2230 6710 4320 1600 145 28,000

Freq. % 100 100 100 100 100 – 83.3 100 100 100 100 100 100 83.3 –

Public places Range 6.43–37.6 13.4–75 41–2950 59.8–652 7–271 n.d. n.d.–19.9 9.6–33 59.6–872 b12–514 78.8–1640 n.d.–146 n.d.–45.6 n.d. –

n = 8 Mean 14.6 37.6 1230 240 76.1 n.d. b12 19 281 340 666 67.9 b32 n.d. 3000

Freq. % 100 100 100 100 100 – 25 100 100 100 100 75 25 – –

Total Range 6.43–131 13.4–1680 29.3–34,300 9.42–2450 7–656 n.d.–179 n.d.–34.5 n.d.–408 n.d.–1320 n.d.–3670 n.d.–12,700 n.d.–12,700 n.d.–4530 n.d.–295 –

n = 60 Mean 29.3 118 2420 287 138 b12 b12 45.6 205 570 1320 623 202 b32 6000

Freq. % 100 100 100 100 100 26.7 36.7 76.7 76.7 95 95 78.3 46.7 8.33 –

Freq. %: frequency of siloxanes detectable in particulate phase. n.d.: not detectable.“b”: below the limit of quantiﬁcation of the method.ΣSil.: the total concentrations of all siloxanes D3–D7 and L3–L11

Table 3

Concentrations of individual siloxanes in the vapor phase of indoor air samples collected from various locations in Albany, New York, USA (ng.m⁻³).

D3 D4 D5 D6 D7 L3 L4 L5 L6 L7 L8 L9 L10 L11 ΣSil.

Homes Range 3.46–68.6 4.37–210 18–812 7.91–240 7.03–157 n.d.–5.62 n.d.–8.39 n.d.–106 n.d.–191 n.d.–175 n.d.–219 n.d. n.d. n.d. –

n = 20 Mean 21.6 50.9 263 50.9 39.8 b0.83 b0.83 12.7 31.1 42.3 30.1 n.d. n.d. n.d. 546

Freq. % 100 100 100 100 100 35 25 45 55 50 25 – – – –

Ofﬁces Range 1.96–5.99 0.06–7.8 6.36–92.5 3.09–30.7 2.92–46.2 n.d.–1.29 n.d. n.d.–49.2 n.d.–13.7 n.d.–68.6 n.d. n.d. n.d. n.d. –

n = 7 Mean 8.00 23.06 74.54 26.64 34.56 b0.83 n.d. 15.43 9.12 42.05 n.d. n.d. n.d. n.d. 236

Freq. % 100 85.7 100 100 100 14.3 – 42.9 57.1 71.4 – – – – –

Laboratories Range 3.76–61.3 5.27–87.5 15.8–163 4.68–111 n.d.–59.4 n.d.–53.5 n.d.–3.68 n.d.–38.8 n.d.–92.3 n.d.–8.95 n.d.–134 n.d. n.d. n.d. –

n = 13 Mean 15.7 31.6 70.5 23.9 11.5 4.54 b0.83 9.11 12.6 0.82 10.7 n.d. n.d. n.d. 193

Freq. % 100 100 100 100 61.5 23.1 30.8 38.5 38.5 7.69 7.69 – – – –

Schools Range 6.25–20.2 12.8–245 111–1020 10.5–136 4.23–58.3 n.d. n.d.–2.54 n.d.–3.55 n.d.–40.3 n.d.–103 n.d.–120 n.d. n.d. n.d. –

n = 6 Mean 13.4 76.1 349 76.8 27.4 n.d. b0.83 1.16 10.6 39.6 38.9 n.d. n.d. n.d. 636

Freq. % 100 100 100 100 100 – 14.3 33.3 50 66.7 50 – – – –

Salons Range 6.34–16.1 193–722 375–3710 121–885 8.3–65.7 n.d.–2.65 n.d.–8.87 1.68–28.3 7.12–150 56.7–510 35.7–346 n.d.–48.9 n.d. n.d. –

n = 6 Mean 10.6 446 2500 374 31.4 0b0.83 3.34 15.1 90.9 312 111 20.3 n.d. n.d. 3920

Freq. % 100 100 100 100 100 83.3 50 100 100 100 100 50 – – –

Public places Range 12.6–43.2 34.3–501 236–2420 4.1–283 3.71–140 n.d.–2.96 n.d.–5.69 n.d.–31.8 4.77–424 n.d.–368 n.d.–51.5 n.d. n.d. n.d. –

n = 8 Mean 22.1 196 1090 144 71.3 b0.83 b0.83 12.2 158 159 8.77 n.d. n.d. n.d. 1870

Freq. % 100 100 100 100 100 100 12.5 75 100 62.5 62.5 – – – –

Total Range 3.46–68.6 3.58–722 12.7–3710 4.1–885 n.d.–157 n.d.–53.4 n.d.–8.87 n.d.–106 n.d.–424 n.d.–510 n.d.–346 n.d.–48.9 n.d. n.d. –

n = 60 Mean 16.9 105 543 89.5 35.2 1.58 b0.83 11.2 45.3 75.6 28.5 2.47 n.d. n.d. 956

Freq. % 100 100 100 100 91.7 91.7 28.3 55 58.3 51.7 30 6.67 – – –

n.d.: not detectable. Freq. %: frequency of siloxanes detectable in indoor air.“b”: below the limit of quantiﬁcation of the method.ΣSil.: the total concentrations of all siloxanes D3–D7 and L3–L11

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phase can be explained by their high vapor pressure (seeLatimer et al., 1998). However, it should be noted several environmental factors including temperature, relative humidity, and amount and type of particulate matter can affect partitioning of siloxanes in air (Latimer et al., 1998). Further discussion regarding gas-particle partitioning (Kp) of siloxanes can be found in the Supporting information (Table S3).

The mean ratio for concentrations of D4 between vapor and particulate phases was 4.7, and this ratio was 3.0 and 3.8 for D5 and D6, respectively. In contrast, the high molecular weight siloxanes such as L8 and L9 were found more frequently in the particulate phase. Among all micro- environments studied, L8 and L9 concentrations were 6 and 70 times, respectively, higher in the particulate phase than in the vapor phase.

L10 and L11 were detected only in the particulate phase of all samples.

High molecular weight siloxanes have low vapor pressures, which ex- plain the preferential partitioning of L10 and L11 to the particulate phase. It is also worth to note that retention of siloxanes onto glass ﬁberﬁlter from vapor phase during sampling is not known.

3.3. Siloxanes in bulk indoor air (particulate plus vapor phases)

Total concentrations of individual siloxanes in indoor air were determined by summation of concentrations measured in the particulate and vapor phases on a volumetric (m³) basis (Table 4). The mean concentration of siloxanes was the highest in indoor air samples collected from hair salons and the lowest in laboratories (Fig. 2). Eleven of the 14 target siloxanes were found in all samples from hair salons. L3, L4, L10, and L11 were found less frequently in the air samples. The mean concentration of siloxanes found in hair salons was 6210 ng m⁻³; the next highest concentration was in samples from the public places (1990 ng m⁻³) and schools (1240 ng m⁻³). The mean total concentration of siloxanes in hair salons was 25 times higher than the lowest value of 249 ng m⁻³found in laboratories and 4 times higher than the total mean value for all samples (1470 ng m⁻³). As indicated above, high concentrations in siloxanes in salons can be explained by the extensive use of personal care products in hair salons. The total mean concentration of siloxanes found in our study is similar to that reported by Yucuis et al. (2013), who found a median concentration of 2200 ng m⁻³for the sum of D4, D5, and D6 in indoor air (in laboratories and ofﬁces) from Chicago, Illinois, USA. However, our values are much lower than those of the mean concentrations of eight siloxanes in indoor

air (in homes, ofﬁces, and supermarkets) reported from Italy and the UK (18 to 240μg m⁻³for Italy and from 78 to 350μg m⁻³for the UK) (Pieri et al., 2013).Companioni-Damas et al. (2014)reported D5 concentrations as high as 293,000 ng m⁻³in homes and 2850 ng m⁻³in laboratories in Barcelona, Spain.

3.4. Contribution of D4 and D5 to total siloxane concentrations in indoor air

Among several siloxanes, D4 and D5 were the most widely studied compounds. D4 and D5 were found at the high concentrations in indoor air from Albany and ranged from 6.19 to 752 ng m⁻³for D4 (mean: 116 ng m⁻³) and from 19 to 5130 ng m⁻³ for D5 (mean: 721 ng m⁻³). The sum concentrations of D4 and D5 accounted for≥82% of the total ofﬁve cyclic siloxanes determined in our study.Yucuis et al. (2013)reported D4 levels in indoor air from the Seamans Center for Engineering Arts and Sciences at the University of Iowa (23 to 500 ng m⁻³); these values are similar to what was found in indoor air from Albany. The D5 concentrations at a Swedish rural site ranged from 0.7 to 8 ng m⁻³(Kierkegaard and McLachlan, 2010), which were much lower than the concentrations found in our study.

The ratios of D5 to D4 concentrations have been used in the determination of sources of cyclic siloxanes in the environment (Navea et al., 2011; Yucuis et al., 2013). The D5/D4 ratios in indoor air from Albany were 7.86, 5.68, 1.90, 6.56, 6.45, and 5.73 for homes, ofﬁces, laboratories, schools, hair salons, and public places, respectively. The D5/D4 ratios in indoor air were similar among theﬁve categories of sampling locations, except for the laboratory locations, which had the lowest values (1.90).

High D5/D4 ratios in indoor environments suggest the existence of point sources of cyclic siloxanes. Personal care and household products are the sources of siloxanes in indoor air. The mean concentrations of D5 in personal care products were much higher than those of D4 (2890μg g⁻¹for D5 and 141μg g⁻¹for D4) (Horii and Kannan, 2008).

For the entire sample set of 60 indoor air samples, the ratio of D5/D4 was 6.21. The D5/D4 ratios were reported to range from 2.6 to 4.4 for indoor air samples in three types of commercial buildings in the USA (Shields et al., 1996). A recent study reported that the D5/D4 ratios av- eraged 91 and 3.2 for indoor and outdoor air, respectively (Yucuis et al., 2013).

Fig. 1.Concentrations of individual siloxanes in the vapor and particulate phases of indoor air (n = 60) from Albany, New York, USA.

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3.5. Human exposure to siloxanes via inhalation

On the basis of the average inhalation rate of 13 m³day⁻¹(CEPA, 1994; Pieri et al., 2013), we calculated the inhalation exposure to siloxanes by multiplying the measured concentration (ng m⁻³) with the volume of air inhaled (m³). The results showed that the mean value of exposure of total siloxanes from homes, ofﬁces, laboratories, schools, salons, and public places were 13,500, 6630, 3230, 16,200, 80,700, and 25,900 ng day⁻¹, respectively. The inhalation exposure dose for people in salons was the highest (80,700 ng day⁻¹). The mean daily exposure to total siloxanes from all locations was 19,100 ng day⁻¹. Among several siloxanes measured, D5 exposure was the highest and ranged from 247 to 66,700 ng day⁻¹(mean: 9370 ng day⁻¹). The average inhalation exposure doses for L8, L7, D4, and D6 were 1990, 1650, 1510, and 1470 ng day⁻¹, respectively.

No previous studies have reported human exposure doses of siloxanes by age. Because the average body weights vary with age, infants (b1 yr): 6 kg-bw, toddlers (1–3 yr): 12 kg-bw, children (3–11 yr): 25 kg-bw, teenagers (11–18 yr): 57 kg-bw, and adults: 72 kg-bw (U.S. En- vironmental Protection Agency Child-Speciﬁc Exposure Factors Hand- book, 2008), the calculated exposure doses of total siloxanes for infants, toddlers, children, teenagers, and adults were 3.18, 1.59, 0.76, 0.34, and 0.27μg/kg-bw/day, respectively. D5 contributed to the highest daily exposures, with 1.56, 0.78, 0.37, 0.16, and 0.13μg/kg-bw/day for infants, toddlers, children, teenagers, and adults, respectively. It is worth to note that our exposure doses are approximate values as these are based on average concentrations found in various microenvi- ronments. Furthermore, a study byUtell et al. (1998)reported that only 12% of the inhaled D4 dose was absorbed in systemic circulation and such information may be taken into account when calculating actual exposure doses. However, high doses of inhalation exposure to D4 used in that study may underestimate absorbed fraction of D4.

Jovanovic et al. (2008)reported that the dermal exposure to cyclic siloxanes present in lotions and antiperspirants in the United States was 0.1 and 0.2 mg day⁻¹, respectively; siloxane exposure doses from indoor air calculated in our study were similar to the exposure doses calculated from skin lotions and antiperspirants. Nevertheless, based on a comprehensive analysis of a wide range of personal care products, Horii and Kannan (2008)showed that the daily exposure rate to total siloxanes from personal care products (inhalation, ingestion, and dermal absorption pathways) was 307 mg day⁻¹for the United States women and D5 contributed 162 mg day⁻¹. The inhalation exposure doses of siloxanes calculated in our study were lower than the values reported in Table4 Totalconcentrationofcyclicandlinearsiloxanesinbulkindoorair(ngm−3)(sumofparticulateandvaporphases)fromAlbany,NewYork,USA. D3D4D5D6D7L3L4L5L6L7L8L9L10L11ΣSil. HomesRange5.07–70.58.4–21640.4–184014.9–31112.5–197n.d.–5.72n.d.–12.1n.d.–133n.d.–3792.8–5136.48–4420.4–299n.d.–58.7n.d.– n=20Mean24.656.744675.452.91.541.3317.75694.714557.712.4n.d.1040 Freq.%1001001001001007535808510010010075–– OfﬁcesRange5.88–17.26.19–82.639–42813.6–1228.16–143n.d.–2.69n.d.–1.86n.d.–103n.d.–53.83.72–256n.d.–266n.d.-28.2n.d.–6.57n.d.– n=7Mean12.226.515050.855.5b0.83b0.8318.416.289.174.712.6b2.22n.d.510 freq.%10010010010010071.428.657.142.910071.471.414.3–– LaboratoriesRange5.20–74.27.29–89.119–1705.73–1213.1–71.2n.d.–54n.d.–3.780.1–84.2n.d.–93.5n.d.–13.6n.d.–140n.d.–3.99n.d.–14.4n.d.– n=13Mean20.43887.628.917.87.72b0.8313.413.23.7714b1.94b2.22n.d.249 Freq.%10010010010010092.330.853.946.269.261.523.17.69–– SchoolsRange7.6–25.120–29197–177034.7–19620.8–73.8n.d.n.d.–2.64n.d.–11.52.1–654.94–1706.85–440n.d.–104n.d.–38.6n.d.– n=6Mean15.998.964910746.6n.d.1.224.1425.788.1168289.88n.d.1240 Freq.%100100100100100–66.766.710010010066.750–– SalonsRange8.44–19.2206–752530–5130160–104020.7–92.2n.d.–2.75n.d.–11.15.1–41.341–235194–792282–109050.2–86919.2–576n.d.–38.1– n=6Mean13495320044448.41.04.9622.7147520709420167196210 Freq.%10010010010010083.383.310010010010010010083.3– PublicplacesRange13.1–43.635.4–505251–24706.26–2975.92–144b0.83–3.1n.d.–5.79b0.56–3323–426b0.83–3853.25–80b1.94–7.9n.d.–2.37n.d.– n=8Mean22.6199114015173.8b0.83b0.8312.916617541.13.55b2.22n.d.1990 Freq.%10010010010010010037.510010010010010025–– TotalRange5.07–74.26.19–75219–51305.73–10403.1–197b0.83–54n.d.–12.1n.d.–133n.d.–426n.d.–792n.d.–1090n.d.–869n.d.–576n.d.–38.1– n=60Mean2011672111347.32.51.4115.462.712715366.222.52.441470 Freq.%1001001001001007551.781.7809598.378.346.78.33– n.d.:notdetectable.freq.%:frequencyofsiloxanesdetectableinindoorair.“b”:belowthelimitofquantiﬁcationofthemethod.ΣSil.:thetotalconcentrationsofallsiloxanesD3–D7andL3–L11

Fig. 2.Mean concentrations of total siloxanes (vapor plus particulate phases) in indoor air samples from six categories of sampling locations in Albany, New York, USA.

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the UK (Pieri et al., 2013); the reported siloxane exposure doses for children and adults in the UK were 3.19 and 1.88 mg day⁻¹, respectively.

4. Conclusions

Five cyclic and nine linear siloxanes were determined in 60 indoor air samples from Albany, New York, USA; most siloxanes were found in almost all indoor air samples, and D3, D4, D5, and D6 were found in all samples. Indoor air from hair salons contained the highest concentrations of siloxanes (mean: 6210 ng.m⁻³). D5 was the most abundant compound in indoor air samples (mean: 721 ng.m⁻³). High molecular weight siloxanes (L7, L8, and L9) existed predominantly in the particulate phases than in the vapor phases. The estimated average inhalation exposure dose to total siloxanes in indoor air was 19,100 ng day⁻¹. Acknowledgments

We thank Anthony M. DeJulio for the help with sampling.

Appendix A. Supplementary data

Supplementary data to this article can be found online athttp://dx.

doi.org/10.1016/j.scitotenv.2014.12.022.

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