Science of the Total Environment 511 (2015) 138–144 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv 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,⁎ a Wadsworth 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 Faculty of Chemistry, Hanoi University of Science, Vietnam National University, 19 Le Thanh Tong, Hoan Kiem, Hanoi, Viet Nam c Biochemistry Department, Faculty of Science and Experimental Biochemistry Unit, King Fahd Medical Research Center, King Abdulaziz University, Jeddah 21589, Saudi Arabia b 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/m3 with 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 3.18 μg/kg-bw/d a r t i c l e i n f o Article history: Received 10 October 2014 Received in revised form December 2014 Accepted December 2014 Available online xxxx Editor: Adrian Covaci Keywords: Siloxane Indoor air Inhalation exposure PDMS Cyclic methylsiloxane D5 a b s t r a c t 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 from b12 μg g−1 (for octamethyltrisiloxane [L3], decamethyltetrasiloxane [L4]) to 2420 μg g−1 (for decamethylcyclopentasiloxane [D5]) and from 1.05 ng m−3 to 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−3 in laboratories to 6210 ng m−3 in salons, with an overall mean concentration of 1470 ng m−3 in 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 0.27 μ g/kg-bw/day, respectively © 2014 Elsevier B.V All rights reserved Introduction Siloxanes are organo-silicone compounds and consist of – (CH3)2SiO – structural units Two major groups of siloxanes of commercial significance 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 ⁎ Corresponding author at: Wadsworth Center, Empire State Plaza, PO Box 509, Albany, NY 12201-0509, USA E-mail address: Kurunthachalam.Kannan@health.ny.gov (K Kannan) http://dx.doi.org/10.1016/j.scitotenv.2014.12.022 0048-9697/© 2014 Elsevier B.V All rights reserved 9380, 81,800, 43,100, and 846 μg g− respectively; skin lotions contained total linear siloxanes at concentrations (sum of L4 to L14) as high as 73,000 μg g−1 (i.e., 7.3% by weight; Horii and Kannan, 2008) The total cyclic siloxane concentrations (D6 to D25) in siliconized rubber products marketed for food contact use were in the range of 3310 to 14,700 μg 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) T.M Tran, K Kannan / Science of the Total Environment 511 (2015) 138–144 Accumulation of D5 in fish 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 170 μg m−3 (Pieri et al., 2013) Another study reported a median concentration of 2200 ng m−3 for the sum of D4, D5, and D6 concentrations in indoor air samples from Chicago, Illinois, USA (Yucuis et al., 2013) A guidance value of 4000 μg m−3 and a precautionary guideline value of 400 μg m−3 were recommended for the sum of D3 to D6 in indoor air in Germany (German Environment 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 preovulatory 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; ConpanioniDamas et al., 2014) In this study, by use of a combination of quartz fiber filters 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 determine five 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 Materials and methods 2.1 Standards Hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6), with a purity of N95%, were purchased from Tokyo Chemical Industry, Inc (Wellesley Hills, MA, USA) Octamethyltrisiloxane (L3) (98%), decamethyltetrasiloxane (L4) (97%), and dodecamethylpentasiloxane (L5) (97%) were purchased from Sigma-Aldrich (St Louis, MO, USA) Polydimethylsiloxane (PDMS) 200 fluid (viscosity of 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 Biosciences, Inc (Brea, CA, USA), and these two compounds were used as surrogate standards All standards were dissolved in hexane The 139 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 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 quartz fiber filters (Whatman, grade QM-A, pore size: 2.2 μm 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 quartz fiber filters were kept in an oven at 100 °C until use The quartz fiber filters 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 quartz fiber filter 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 a flow rate of L per minute The total volume of air collected from each location ranged from 3.6 m3 to 7.2 m3 Air samples (both PUFs and filters) were kept at − 18 °C until analysis The samples were kept for no longer than 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 and filters) were spiked with 100 ng of M4Q and 13C-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 The extraction was performed twice, with 100 mL of solvent mixture for the first extraction and 80 mL for the second The extracts were concentrated in a rotary evaporator at 40 °C to approximately mL The solution was then transferred into a 12-mL glass tube and concentrated by a gentle stream of nitrogen to exactly mL and transferred into a GC vial The particulate samples were extracted by shaking glass fiber filters with a mixture of DCM and hexane (3:1; 20 mL; v:v) each time for min, which was performed three times The extract was concentrated in a rotary evaporator and then by a gentle stream of nitrogen to exactly mL The extract was then transferred into a GC vial 2.3 Instrumental analysis Analysis was performed on an Agilent Technologies 6890 gas chromatograph (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 × 0.25 μm film thickness) Samples were injected in the splitless mode, and the injection volume was μL The oven temperature was programmed from 40 °C (held for min) to 220 °C at 20 °C/min, increased to 280 °C at °C/min (held for 10 min), and 140 T.M Tran, K Kannan / Science of the Total Environment 511 (2015) 138–144 held for at 300 °C Ion fragment m/z 207 was monitored for D3, m/z 281 for D4, D7, and L5, m/z 355 for D5, and m/z 341 for D6 Ion fragment m/z 147 was used for confirmation of L6 and L7 Ion fragment m/z 207 was monitored for confirmation of L4 and m/z 221 for the other siloxanes (Horii and Kannan, 2008; Badjagbo et al., 2009; Zhang et al., 2011; Bletsou et al., 2013) Ion fragment m/z 281 was monitored for M4Q and m/z 360 for 13C-D5 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 Statistical significance was set at p b 0.05 Results and discussion 2.4 Quality assurance and quality control 3.1 Concentrations of siloxanes in particulate phase 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 Solvents 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 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 ng/mL to 500 ng/mL for individual siloxanes (R2 N 0.995) 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 and 13C-D5, D3, D4, D5, D6, L3, L4, and L5 were spiked into blank PUF plugs and a glass fiber filter and passed through the entire analytical procedure The recoveries of target compounds spiked into PUFs and filters are shown in Table 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 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 The concentrations of individual siloxanes in the particulate phase (Table 2) were calculated based on the weight of the airborne particle collected in a glass fiber filter (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 34,300 μg g−1 (mean: 2420) and the concentrations of L8 ranged from below MQL to 12,700 μg 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 deposition, 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 of five cyclic and nine linear siloxanes in the particulate phase of indoor air was 6000 μg 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 explains 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 in Table 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 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) MDL (ng m D3 D4 D5 D6 D7 L3 L4 L5 L6 L7 L8 L9 L10 L11 M4Q 13 C-D5 0.06 0.08 0.06 0.06 0.19 0.14 0.14 0.14 0.19 0.19 0.56 0.56 0.83 0.83 – – −3 ) Recoveries, % (n = 8) MQL (ng m 0.22 0.28 0.22 0.22 0.56 0.83 0.83 0.56 0.83 0.83 1.94 1.94 2.22 2.22 – – −3 ) Range Mean RSD MDL (ng g−1) MQL (ng g−1) Range Mean RSD 66.0–84.9 85.4–121 88.7–126 93.9–123 – 75.5–110 93.6–123 82.5–116 – – – – – – 87.5–120 84.4–122 73.4 105 109 109 – 93.9 112 103 – – – – – – 104 106 7.3 13.1 14.7 11.9 – 10.6 12.7 11.9 – – – – – – 10.4 14.4 0.8 1.2 0.8 0.8 2.8 2.0 2.0 2.0 2.0 2.0 8.0 8.0 12.0 12.0 – – 3.2 4.0 3.2 3.2 8.0 12.0 12.0 8.0 12.0 12.0 28.0 28.0 32.0 32.0 – – 77.5–105 86.6–119 98.4–125 80.7–115 – 79.5–112 78.0–122 96.9–120 – – – – – – 90.8–116 83–115 91.2 106 116 99.7 – 96.9 104 110 – – – – – – 101 97.6 9.8 11.8 8.6 12.2 – 12.0 15.6 8.7 – – – – – – 8.7 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 m3 and the average weight of airborne particle collected, which was 0.25 mg RSD: relative standard deviation Table Concentrations of individual siloxanes in the particulate phase of indoor air samples collected from various locations in Albany, New York, USA (μg g−1) Homes n = 20 Offices n=7 Laboratories n = 13 Schools n=6 Public places n=8 Total n = 60 D3 D4 D5 D6 D7 L3 L4 L5 L6 L7 L8 L9 L10 L11 Σ Sil 8.59–38.9 24.3 100 17.6–66.3 42.7 100 13–131 40.9 100 15.3–41.6 27.7 100 21–34.5 26.7 100 6.43–37.6 14.6 100 6.43–131 29.3 100 17.9–169 47.6 100 19.2–50.4 35 100 13.9–108 49.7 100 24–400 153 100 145–1680 665 100 13.4–75 37.6 100 13.4–1680 118 100 127–12,400 1590 100 40.4–2100 795 100 29.3–394 167 100 258–17,300 5610 100 849–34,300 10,400 100 41–2950 1230 100 29.3–34,300 2420 100 28.8–842 188 100 60.1–702 262 100 9.42–106 47.1 100 66.3–1500 565 100 147–2450 955 100 59.8–652 240 100 9.42–2450 287 100 17.6–438 104 100 20.9–656 231 100 10.3–319 79.8 100 34.3–443 275 100 37.4–432 213 100 7–271 76.1 100 7–656 138 100 n.d.–12.2 b12 25 n.d.–15.6 b12 14.3 n.d.–179 27.3 76.9 n.d n.d – n.d n.d – n.d n.d – n.d.–179 b12 26.7 n.d.–29.8 b12 30 n.d.–15.6 b12 42.9 n.d n.d – n.d.–20 b12 50 n.d.–34.5 14 83.3 n.d.–19.9 b12 25 n.d.–34.5 b12 36.7 n.d.–251 40.3 80 n.d.–93.3 32.8 85.7 n.d.–408 41.5 46.2 n.d.–211 64.8 66.7 23.1–264 103 100 9.6–33 19 100 n.d.–408 45.6 76.7 n.d–1270 184 85 n.d.–330 81 28.6 n.d.–22.7 6.13 53.8 10.7–741 292 100 267–1320 662 100 59.6–872 281 100 n.d.–1320 205 76.7 23.5–1950 390 100 12.8–1720 511 100 n.d.–64.4 31.3 84.6 36.8–3390 1060 100 654–3670 2230 100 b12–514 340 100 n.d.–3670 570 95 53.7–2550 987 100 b28–2260 787 100 n.d.–77.7 36.6 76.9 98.3–3690 1350 100 2210–12,700 6710 100 78.8–1640 666 100 n.d.–12,700 1320 95 b28–1920 435 100 b28–250 128 100 n.d.–32.3 b28 46.2 n.d.–345 201 83.3 468–12,700 4320 100 n.d.–146 67.9 75 n.d.–12,700 623 78.3 n.d.–374 86.9 75 n.d.–53.7 b32 14.3 n.d.–104 b32 7.69 n.d.–127 58.1 50 175–4530 1600 100 n.d.–45.6 b32 25 n.d.–4530 202 46.7 n.d n.d – n.d n.d – n.d n.d – n.d n.d – n.d.–295 145 83.3 n.d n.d – n.d.–295 b32 8.33 – 4100 – – 2940 – – 567 – – 9680 – – 28,000 – – 3000 – – 6000 – Freq %: frequency of siloxanes detectable in particulate phase n.d.: not detectable “b”: below the limit of quantification of the method Σ Sil.: the total concentrations of all siloxanes D3–D7 and L3–L11 Table Concentrations of individual siloxanes in the vapor phase of indoor air samples collected from various locations in Albany, New York, USA (ng.m−3) Homes n = 20 Offices n=7 Laboratories n = 13 Schools n=6 Salons n=6 Public places n=8 Total n = 60 Range Mean Freq % Range Mean Freq % Range Mean Freq % Range Mean Freq % Range Mean Freq % Range Mean Freq % Range Mean Freq % D3 D4 D5 D6 D7 L3 L4 L5 L6 L7 L8 L9 L10 L11 Σ Sil 3.46–68.6 21.6 100 1.96–5.99 8.00 100 3.76–61.3 15.7 100 6.25–20.2 13.4 100 6.34–16.1 10.6 100 12.6–43.2 22.1 100 3.46–68.6 16.9 100 4.37–210 50.9 100 0.06–7.8 23.06 85.7 5.27–87.5 31.6 100 12.8–245 76.1 100 193–722 446 100 34.3–501 196 100 3.58–722 105 100 18–812 263 100 6.36–92.5 74.54 100 15.8–163 70.5 100 111–1020 349 100 375–3710 2500 100 236–2420 1090 100 12.7–3710 543 100 7.91–240 50.9 100 3.09–30.7 26.64 100 4.68–111 23.9 100 10.5–136 76.8 100 121–885 374 100 4.1–283 144 100 4.1–885 89.5 100 7.03–157 39.8 100 2.92–46.2 34.56 100 n.d.–59.4 11.5 61.5 4.23–58.3 27.4 100 8.3–65.7 31.4 100 3.71–140 71.3 100 n.d.–157 35.2 91.7 n.d.–5.62 b0.83 35 n.d.–1.29 b0.83 14.3 n.d.–53.5 4.54 23.1 n.d n.d – n.d.–2.65 b 0.83 83.3 n.d.–2.96 b0.83 100 n.d.–53.4 1.58 91.7 n.d.–8.39 b0.83 25 n.d n.d – n.d.–3.68 b0.83 30.8 n.d.–2.54 b0.83 14.3 n.d.–8.87 3.34 50 n.d.–5.69 b0.83 12.5 n.d.–8.87 b0.83 28.3 n.d.–106 12.7 45 n.d.–49.2 15.43 42.9 n.d.–38.8 9.11 38.5 n.d.–3.55 1.16 33.3 1.68–28.3 15.1 100 n.d.–31.8 12.2 75 n.d.–106 11.2 55 n.d.–191 31.1 55 n.d.–13.7 9.12 57.1 n.d.–92.3 12.6 38.5 n.d.–40.3 10.6 50 7.12–150 90.9 100 4.77–424 158 100 n.d.–424 45.3 58.3 n.d.–175 42.3 50 n.d.–68.6 42.05 71.4 n.d.–8.95 0.82 7.69 n.d.–103 39.6 66.7 56.7–510 312 100 n.d.–368 159 62.5 n.d.–510 75.6 51.7 n.d.–219 30.1 25 n.d n.d – n.d.–134 10.7 7.69 n.d.–120 38.9 50 35.7–346 111 100 n.d.–51.5 8.77 62.5 n.d.–346 28.5 30 n.d n.d – n.d n.d – n.d n.d – n.d n.d – n.d.–48.9 20.3 50 n.d n.d – n.d.–48.9 2.47 6.67 n.d n.d – n.d n.d – n.d n.d – n.d n.d – n.d n.d – n.d n.d – n.d n.d – n.d n.d – n.d n.d – n.d n.d – n.d n.d – n.d n.d – n.d n.d – n.d n.d – – 546 – – 236 – – 193 – – 636 – – 3920 – – 1870 – – 956 – T.M Tran, K Kannan / Science of the Total Environment 511 (2015) 138–144 Salons n=6 Range Mean Freq % Range Mean Freq % Range Mean Freq % Range Mean Freq % Range Mean Freq % Range Mean Freq % Range Mean Freq % n.d.: not detectable Freq %: frequency of siloxanes detectable in indoor air “b”: below the limit of quantification of the method Σ Sil.: the total concentrations of all siloxanes D3–D7 and L3–L11 141 142 T.M Tran, K Kannan / Science of the Total Environment 511 (2015) 138–144 Fig Concentrations of individual siloxanes in the vapor and particulate phases of indoor air (n = 60) from Albany, New York, USA phase can be explained by their high vapor pressure (see Latimer 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 microenvironments studied, L8 and L9 concentrations were 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 explain the preferential partitioning of L10 and L11 to the particulate phase It is also worth to note that retention of siloxanes onto glass fiber filter 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−3 found in laboratories and 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−3 for 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 240 μg m−3 for Italy and from 78 to 350 μg m−3 for the UK) (Pieri et al., 2013) Companioni-Damas et al (2014) reported D5 concentrations as high as 293,000 ng m−3 in homes and 2850 ng m−3 in 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− for D4 (mean: 116 ng m − 3) and from 19 to 5130 ng m − for D5 (mean: 721 ng m− ) The sum concentrations of D4 and D5 accounted for ≥ 82% of the total of five 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 ng m− (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 the five 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 (2890 μg g−1 for D5 and 141 μg g−1 for 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 averaged 91 and 3.2 for indoor and outdoor air, respectively (Yucuis et al., 2013) – 1040 – – 510 – – 249 – – 1240 – – 6210 – – 1990 – – 1470 – Total n = 60 Public places n=8 Salons n=6 Schools n=6 Laboratories n = 13 Offices n=7 n.d.: not detectable freq %: frequency of siloxanes detectable in indoor air “b”: below the limit of quantification of the method Σ Sil.: the total concentrations of all siloxanes D3–D7 and L3–L11 L11 n.d n.d – n.d n.d – n.d n.d – n.d n.d – n.d.–38.1 19 83.3 n.d n.d – n.d.–38.1 2.44 8.33 n.d.–58.7 12.4 75 n.d.–6.57 b2.22 14.3 n.d.–14.4 b2.22 7.69 n.d.–38.6 9.88 50 19.2–576 167 100 n.d.–2.37 b2.22 25 n.d.–576 22.5 46.7 L10 2.8–513 94.7 100 3.72–256 89.1 100 n.d.–13.6 3.77 69.2 4.94–170 88.1 100 194–792 520 100 b0.83–385 175 100 n.d.–792 127 95 L9 L8 6.48–442 145 100 n.d.–266 74.7 71.4 n.d.–140 14 61.5 6.85–440 168 100 282–1090 709 100 3.25–80 41.1 100 n.d.–1090 153 98.3 L7 L6 n.d.–379 56 85 n.d.–53.8 16.2 42.9 n.d.–93.5 13.2 46.2 2.1–65 25.7 100 41–235 147 100 23–426 166 100 n.d.–426 62.7 80 n.d.–133 17.7 80 n.d.–103 18.4 57.1 0.1–84.2 13.4 53.9 n.d.–11.5 4.14 66.7 5.1–41.3 22.7 100 b0.56–33 12.9 100 n.d.–133 15.4 81.7 L5 L4 n.d.–12.1 1.33 35 n.d.–1.86 b0.83 28.6 n.d.–3.78 b0.83 30.8 n.d.–2.64 1.22 66.7 n.d.–11.1 4.96 83.3 n.d.–5.79 b0.83 37.5 n.d.–12.1 1.41 51.7 n.d.–5.72 1.54 75 n.d.–2.69 b0.83 71.4 n.d.–54 7.72 92.3 n.d n.d – n.d.–2.75 1.0 83.3 b0.83–3.1 b0.83 100 b0.83–54 2.5 75 L3 D7 12.5–197 52.9 100 8.16–143 55.5 100 3.1–71.2 17.8 100 20.8–73.8 46.6 100 20.7–92.2 48.4 100 5.92–144 73.8 100 3.1–197 47.3 100 14.9–311 75.4 100 13.6–122 50.8 100 5.73–121 28.9 100 34.7–196 107 100 160–1040 444 100 6.26–297 151 100 5.73–1040 113 100 D6 D5 40.4–1840 446 100 39–428 150 100 19–170 87.6 100 197–1770 649 100 530–5130 3200 100 251–2470 1140 100 19–5130 721 100 8.4–216 56.7 100 6.19–82.6 26.5 100 7.29–89.1 38 100 20–29 98.9 100 206–752 495 100 35.4–505 199 100 6.19–752 116 100 D4 D3 5.07–70.5 24.6 100 5.88–17.2 12.2 100 5.20–74.2 20.4 100 7.6–25.1 15.9 100 8.44–19.2 13 100 13.1–43.6 22.6 100 5.07–74.2 20 100 Range Mean Freq % Range Mean freq % Range Mean Freq % Range Mean Freq % Range Mean Freq % Range Mean Freq % Range Mean Freq % Homes n = 20 Table Total concentration of cyclic and linear siloxanes in bulk indoor air (ng m−3) (sum of particulate and vapor phases) from Albany, New York, USA 143 0.4–299 57.7 100 n.d.-28.2 12.6 71.4 n.d.–3.99 b1.94 23.1 n.d.–104 28 66.7 50.2–869 420 100 b1.94–7.9 3.55 100 n.d.–869 66.2 78.3 Σ Sil T.M Tran, K Kannan / Science of the Total Environment 511 (2015) 138–144 Fig Mean concentrations of total siloxanes (vapor plus particulate phases) in indoor air samples from six categories of sampling locations in Albany, New York, USA 3.5 Human exposure to siloxanes via inhalation On the basis of the average inhalation rate of 13 m3 day−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): 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 Environmental Protection Agency Child-Specific Exposure Factors Handbook, 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 0.27 μg/kg-bw/day, respectively D5 contributed to the highest daily exposures, with 1.56, 0.78, 0.37, 0.16, and 0.13 μg/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 microenvironments Furthermore, a study by Utell 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−1 for 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 144 T.M Tran, K Kannan / Science of the Total Environment 511 (2015) 138–144 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 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 at http://dx doi.org/10.1016/j.scitotenv.2014.12.022 References Badjagbo, K., Furtos, A., Alaee, M., Moore, S., Sauvé, S., 2009 Direct analysis of 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cyclic and linear siloxanes in sediment from Songhua river and in sewage sludge from wastewater treatment plants, Northeastern China Arch Environ Contam Toxicol 60, 204–211  ... objectives of this study were to determine five 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. .. than the concentrations reported in indoor dust from China (Lu et al., 2010) The sum of mean concentration of five cyclic and nine linear siloxanes in the particulate phase of indoor air was 6000... explains 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 in