Environment International 78 (2015) 39–44 Contents lists available at ScienceDirect Environment International journal homepage: www.elsevier.com/locate/envint A survey of cyclic and linear siloxanes in indoor dust and their implications for human exposures in twelve countries Tri Manh Tran a,b, Khalid O Abualnaja c, Alexandros G Asimakopoulos a, Adrian Covaci d, Bondi Gevao e, Boris Johnson-Restrepo f, Taha A Kumosani g, Govindan Malarvannan d, Tu Binh Minh b, Hyo-Bang Moon h, Haruhiko Nakata i, Ravindra K Sinha j, Kurunthachalam Kannan a,c,⁎ a Wadsworth Center, New York State Department of Health, and 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 b Faculty of Chemistry, Hanoi University of Science, Vietnam National University, Hanoi, 19 Le Thanh Tong, Hoan Kiem, Hanoi, Viet Nam c Biochemistry Department, Faculty of Science, Experimental Biochemistry Unit, King Fahd Medical Research Center and Bioactive Natural Products Research Group, King Abdulaziz University, Jeddah, Saudi Arabia d Toxicological Center, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk-Antwerp, Belgium e Environmental Management Program, Environment and Life Sciences Center, Kuwait Institute for Scientific Research, P.O Box 24885, Safat 13109, Kuwait f Environmental and Chemistry Group, Sede San Pablo, University of Cartagena, Cartagena, Bolívar 130015, Colombia g Biochemistry Department, Faculty of Science, Experimental Biochemistry Unit, King Fahd Medical Research Center and Production of Bioproducts for Industrial Applications Research Group, King Abdulaziz University, Jeddah, Saudi Arabia h Department of Marine Sciences and Convergent Technology, College of Science and Technology, Hanyang University, Ansan, South Korea i Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan j Department of Zoology, Patna University, Patna, 800 005, India a r t i c l e i n f o Article history: Received 10 December 2014 Received in revised form 19 February 2015 Accepted 23 February 2015 Available online xxxx Keywords: Siloxanes Dust Exposure D5 Silicone a b s t r a c t Siloxanes are used widely in a variety of consumer products, including cosmetics, personal care products, medical and electrical devices, cookware, and building materials Nevertheless, little is known on the occurrence of siloxanes in indoor dust In this survey, five cyclic (D3–D7) and 11 linear (L4–L14) siloxanes were determined in 310 indoor dust samples collected from 12 countries Dust samples collected from Greece contained the highest concentrations of total cyclic siloxanes (TCSi), ranging from 118 to 25,100 ng/g (median: 1380), and total linear siloxanes (TLSi), ranging from 129 to 4990 ng/g (median: 772) The median total siloxane (TSi) concentrations in dust samples from 12 countries were in the following decreasing order: Greece (2970 ng/g), Kuwait (2400), South Korea (1810), Japan (1500), the USA (1220), China (1070), Romania (538), Colombia (230), Vietnam (206), Saudi Arabia (132), India (116), and Pakistan (68.3) TLSi concentrations as high as 42,800 ng/g (Kuwait) and TCSi concentrations as high as 25,000 ng/g (Greece) were found in indoor dust samples Among the 16 siloxanes determined, decamethylcyclopentasiloxane (D5) was found at the highest concentration in dust samples from all countries, except for Japan and South Korea, with a predominance of L11; Kuwait, with L10; and Pakistan and Romania, with L12 The composition profiles of 16 siloxanes in dust samples varied by country TCSi accounted for a major proportion of TSi concentrations in dust collected from Colombia (90%), India (80%) and Saudi Arabia (70%), whereas TLSi predominated in samples collected from Japan (89%), Kuwait (85%), and South Korea (78%) Based on the measured median TSi concentrations in indoor dust, we estimated human exposure doses through indoor dust ingestion for various age groups The exposure doses ranged from 0.27 to 11.9 ng/kg-bw/d for toddlers and 0.06 to 2.48 ng/kg-bw/d for adults © 2015 Elsevier Ltd All rights reserved Introduction Organosilicons are compounds that contain carbon–silicon bonds Among the various types of organosilicon compounds in commerce, methyl siloxanes are widely used in industrial and consumer products ⁎ Corresponding author at: Wadsworth Center, Empire State Plaza, P.O Box 509, Albany, NY 12201-0509, USA E-mail address: kkannan@wadsworth.org (K Kannan) http://dx.doi.org/10.1016/j.envint.2015.02.011 0160-4120/© 2015 Elsevier Ltd All rights reserved Methyl siloxanes, depending on the structure, can be divided into cyclic and linear siloxanes The most widely used methyl siloxanes include polydimethyl siloxane (PDMS) and volatile methyl siloxanes (VMSs) The total worldwide production of siloxanes in 2002 was million tons, of which 34% were used in North America, 33% in Western Europe, 28% in Asia, and 5% in the rest of the world (Brooke et al., 2009a,b,c) Siloxanes are used in products due to their low surface tension, high thermal stability, and smooth texture The concentrations of siloxanes 40 T.M Tran et al / Environment International 78 (2015) 39–44 on the order of several percentages by weight (as high as 7.3% for linear siloxanes and 8.2% for cyclic siloxanes) have been reported in personal care and household products (Horii and Kannan, 2008; Wang et al., 2009) Remarkable concentrations of octamethylcyclotetrasiloxane (D4; 72.9 μg/g), D5 (1110 μg/g), and total linear siloxanes (L4–L14; 1.02 mg/g) were reported in shampoos and hair conditioners in China (Lu et al., 2011) Siloxanes were also found in siliconized rubber products (Kawamura et al., 2001), electrical devices, healthcare products, cosmetics, cookware, sealants, and household cleaning products (Watts et al., 1995; Environment Canada, 2011) The occurrence of siloxanes in environmental media was reported in several earlier studies The mean concentration of total siloxanes (5 cyclic and 15 linear) in sludge samples from wastewater treatment plants in South Korea was 45.7 μg/g (Lee et al., 2014) Influent wastewater and sewage sludge collected from Greece contained 17 siloxanes at mean concentrations of 20 μg/L and 75 mg/kg, respectively (Bletsou et al., 2013) Cyclic and linear siloxanes were found in sediment and wastewater collected from China (Zhang et al., 2011), Spain (Sanchís et al., 2013), and Canada (Wang et al., 2013) Indoor and outdoor air samples collected from Chicago contained a median concentration of 2200 and 280 ng/m3, respectively, for the sum of D4, D5, and dodecamethylcyclohexasiloxane (D6) (Yucuis et al., 2013) Linear and cyclic siloxanes were reported in indoor air from Italy and the UK at concentrations ranging from 18 to 240 ng/m3 and 78 to 350 ng/m3, respectively (Pieri et al., 2013) Owing to their widespread use in consumer products, there is a great potential for the occurrence of elevated concentrations of siloxanes in indoor dust Thus far, only one study, from China, reported the concentrations of total siloxanes as high as 21,000 ng/g in indoor dust (Lu et al., 2010) Several studies have reported toxicity, especially reproductive and endocrine effects, of siloxanes in laboratory animals (Burns-Naas et al., 1998; Burn-Naas et al., 2002; McKim et al., 2001; He et al., 2003; Meeks et al., 2007; Quinn et al., 2007a,b; Siddiqui et al., 2007) A risk assessment conducted in Canada indicated that D5 met the criteria for persistence (Environment Canada, 2011) The environmental distribution, fate, and toxicity of siloxanes have been under scrutiny by several environmental and public health agencies in various countries in recent years There is a lack of information with regard to the sources of human exposure to siloxanes In this study, we surveyed the composition and distribution of five cyclic and 11 linear siloxanes in indoor dust collected from 12 countries Human exposure to siloxanes through dust ingestion was estimated for infants, toddlers, children, teenagers, and adults based on the measured median TSi concentrations in dust Materials and methods 2.1 Standards Hexamethylcyclotrisiloxane (D3), D4, D5, and D6, with a purity of N95%, were obtained from Tokyo Chemical Industry (Wellesley Hills, MA) Decamethyltetrasiloxane (L4) (97%) and dodecamethylpentasiloxane (L5) (97%) were purchased from Sigma-Aldrich (St Louis, MO) PDMS 200 fluid (viscosity of 5cSt) that contained octadecamethylcycloheptasiloxane (D7), linear tetradecamethylhexasiloxane (L6), and other linear polydimethyl siloxanes (L7, L8, L9, L10, and L11) were purchased from Sigma-Aldrich Tetrakis-(trimethylsiloxy)-silane (M4Q) of 97% purity was from Sigma-Aldrich Decamethylcyclopentasiloxane-[2, 4, 6, 8, 10-13C5] 99% atom 13C (13C-D5) of 98% purity was from Bristlecone Biosciences, Inc (Brea, CA) M4Q and 13C-D5 were used as internal standards All standards were dissolved in hexane The composition of PDMS was determined in an earlier study (Horii and Kannan, 2008), and this mixture, with known composition and content, was used in the determination of concentrations of linear siloxanes 2.2 Sample collection Indoor dust samples were collected from 12 countries, including China (n = 18), Colombia (n = 28), Greece (n = 28), India (n = 28), Japan (n = 13), Kuwait (n = 28), Pakistan (n = 28), Romania (n = 23), Saudi Arabia (n = 28), South Korea (n = 28), the USA (n = 22), and Vietnam (n = 38) during 2010–2014 The details of the sampling locations are shown in Table Floor dust samples were collected by a vacuum cleaner or by sweeping the floor with a (non-siliconized) brush directly Dust samples from offices, laboratories, and cars were available for certain countries Samples were stored in polyethylene bags or glass jars at °C in the dark until analysis 2.3 Sample preparation Prior to the analysis, all dust samples were sieved through a 150 μm sieve and homogenized One hundred nanograms of M4Q and 13C-D5 were spiked as internal standards onto 150–200 milligrams of dust samples The spiked dust samples were equilibrated for 30 at room temperature The extraction procedure was similar to that described earlier (Horii and Kannan, 2008; Lu et al., 2010), with slight modifications The dust samples were extracted by shaking in an orbital shaker (Eberbach Corporation, Ann Arbor, MI) with mL mixture of dichloromethane (DCM) and hexane (3:1, v:v) for Samples were then centrifuged at 2000 g for (Eppendorf Centrifuge 5804, Hamburg, Germany), and the supernatant was transferred to a 12 mL glass tube The extraction was repeated twice, with mL of DCM: hexane mixture (3:1) for the second time and mL hexane for the third time The extracts were concentrated to mL under a gentle stream of nitrogen and then filtered through a regenerated cellulose membrane filter (Phenomenex Inc., Torrance, CA, pore size: 0.2 μm), and transferred into a gas chromatography (GC) vial 2.4 Instrumental analysis Analysis was performed on an Agilent Technologies 6890 GC interfaced with a 5973 mass spectrometer (MS) Separation of siloxanes was achieved by an HP-5MS capillary column (Agilent, Santa Clara, CA; 30 m × 0.25 mm i.d × 0.25 μm film thickness) Samples were injected into the splitless mode, and the injection volume was μL The oven temperature was programmed from 40 °C (held for 2.0 min) to 220 °C at 20 °C/min, increased to 280 °C at °C/min (held for 10 min) and then held for 5.0 at 300 °C Injector and detector temperatures were 200 °C and 300 °C, respectively 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 the confirmation of L6 and L7 Ion fragment m/z 207 was monitored for the confirmation of L4 and m/z 221 for the other siloxanes Ion fragment m/z 281 was monitored for M4Q and m/z 360 for 13C-D5 (Horii and Kannan, 2008; Badjagbo et al., 2009; Zhang et al., 2011; Bletsou et al., 2013) 2.5 Quality assurance and quality control Contamination of siloxanes from materials and laboratory products has been examined in our laboratory (Horii and Kannan, 2008; Lu et al., 2010; Bletsou et al., 2013), and considerable efforts to reduce background levels of siloxane contamination were made (Lu et al., 2011) All glassware were baked at 450 °C for 20 h and placed in an oven at 100 °C until use The GC vials were capped with aluminum foil (instead of Teflon® or rubber/silicon), and the solvents were dispensed directly from new glass bottles (i.e., a solvent-bottle that was kept open for more than a day was not used) Prior to instrumental analysis, hexane was injected into the GC–MS until the background levels of T.M Tran et al / Environment International 78 (2015) 39–44 41 Table Details of indoor dust samples collected from various countries Countries Cities Locations Period China (n = 18) Colombia (n = 28) Greece (n = 28) India (n = 28) Japan (n = 13) Kuwait (n = 28) Pakistan (n = 28) Romania (n = 23) Saudi Arabia (n = 28) South Korea (n = 28) USA (n = 22) Vietnam (n = 38) Shanghai Cartagena Athens, Erateini, Komotini Patna Kumamoto, Nagasaki, Fukuoka, Saitama, Saga Kuwait Faisalabad Iasi Jeddah Ansan, Anyang Albany Hanoi, Hatinh, Hungyen, Thaibinh Homes, laboratories Homes Homes Homes Homes, offices Homes, cars Homes, cars, offices Homes Homes, cars, air conditioners Homes, laboratories, offices Homes, laboratories, offices Homes, laboratories, offices 2010–2011 2014 2014 2014 2012 2013 2011–2012 2012 2013 2012 2014 2014 siloxanes became stable Hexane also was injected before every sample as a check for background contamination and carry-over (Bletsou et al., 2013) We analyzed dust samples collected from the same homes with vacuum cleaners and sweeping the floors (n = 3) and found no difference in siloxane levels between the two methods of sampling (coefficient of variation was below ±5%) The calibration curve was linear over a concentration that ranged from 0.5 to 500 ng/mL for individual siloxanes, for which the correlation coefficient (r) was greater than 0.995 D3, D4, D5, and D6 were found at respective concentration ranges of 5.5–20 ng (mean: 6.5), 9–46 ng (mean: 13.5), 11–39.7 ng (mean: 16.0), and 6–30 ng (mean: 8.5) in procedural blanks analyzed with each batch of 12–14 samples Other siloxanes were not found in procedural blanks All of the reported concentrations of siloxanes in dust samples were subtracted from the mean values found in procedural blanks One hundred nanograms of 13C-D5 and M4Q were spiked into every sample and passed through the entire analytical procedure The average recoveries of 13C-D5 and M4Q (for all procedural blanks and samples) ranged from 75.3 to 118% (RSD: 9.3%) and 77.5 to 115% (RSD: 12.6%), respectively The mean recoveries of target compounds in spiked dust samples (i.e., matrix spikes) were 67.2–121% (RSD: 9.7%) The limits of quantification (LOQs) were determined based on the lowest point in the calibration standard with a signalto-noise ratio of 10; an average sample weight of 200 mg, and the dilution factors were included in the calculation of LOQ LOQs were 2.0 ng/g for D3, D5, and D7; 3.0 ng/g for D4 and L4 to L9; 4.0 ng/g for D6, L10, and L11; and 6.0 ng/g for L12 to L14 For concentrations below the LOQ, a value of one-half the LOQ was assigned for statistical analysis Data analysis was conducted using Microsoft Excel (Microsoft Office 2010) and Graph Pad Prism V 5.0 Statistical significance was set at p b 0.05 Results and discussion 3.1 Concentrations of total siloxanes in indoor dust Five cyclic (D3–D7) and 11 linear siloxanes (L4–L14) were found in 310 indoor dust samples collected from 12 countries during 2010–2014 (Table S1) Total siloxanes (TSi) refer to the sum of five cyclic and 11 linear siloxanes (Table and Fig 1) The concentrations of TSi in indoor dust samples varied between countries, although the overall differences were not statistically significant (p N 0.05) Indoor dust samples collected from Greece contained the highest concentrations of TSi (median: 2970 ng/g), followed by samples from Kuwait (median: 2400), South Korea (1810), Japan (1500), the USA (1220), China (1070), Romania (538), Colombia (230), Vietnam (206), and Saudi Arabia (132) A TSi concentration as high as 42,800 ng/g was found in dust samples collected from Kuwait The lowest concentrations of TSi were found in dust samples collected from India (median: 116 ng/g) and Pakistan (median: 68.3 ng/g) The median concentration of TSi found in indoor dust from Greece (highest) was 25 times higher than the concentrations found for India (second lowest) and 43 times higher than the concentrations found for Pakistan (lowest) The country-specific differences in the concentrations of siloxanes in indoor dust can be attributed to the consumption and usage patterns of siloxanes between countries Further, the difference also reflects the usage pattern of personal care products among various countries Personal care products, especially skin care products, are the major sources of siloxanes in the indoor environments (Horii and Kannan, 2008) The TSi concentrations measured in indoor dust samples from homes, laboratories, and offices in South Korea, the USA, and Vietnam were compared (Fig 2); the dust samples collected from homes contained the highest TSi concentrations The median concentrations Table Concentrations of total cyclic siloxanes (TCSi), total linear siloxanes (TLSi), and total siloxanes (TSi) in indoor dust collected from 12 countries (ng/g) Countries China (n = 18) Colombia (n = 28) Greece (n = 28) India (n = 28) Japan (n = 13) Kuwait (n = 28) Pakistan (n = 28) Romania (n = 23) Saudi Arabia (n = 28) South Korea (n = 28) USA (n = 22) Vietnam (n = 38) TCSi TLSi TSi Mean Median Range Mean Median Range Mean Median Range 458 304 4100 90.4 296 847 118 317 194 430 587 111 362 193 1380 87.3 156 354 30.3 192 68.7 326 296 94.3 95.3–1350 81–1700 118–25,100 n.d.–244 42.9–757 50.3–10,400 n.d.–1870 31.7–1800 12–2930 54–1700 69–3660 n.d.–336 627 198 1490 112 3950 3940 2570 1700 262 2190 882 179 471 21.5 772 21.5 1300 2060 21.5 235 29.6 1190 623 97.7 21.5–2350 n.d.–1080 129–4990 n.d.–562 248–29,000 246–42,400 n.d.–25,800 n.d.–12,000 n.d.–2160 131–9010 36.8–4110 n.d.–733 1090 502 5590 202 4240 4780 2690 2020 456 2620 1470 291 1070 230 2970 116 1500 2400 68.3 538 132 1810 1220 206 117–2670 102–2730 384–30,100 n.d.–657 321–29,400 476–42,800 n.d.–25,900 88.7–12,200 33.5–3040 335–9340 114–4950 n.d.–943 TCSi, TLSi, and TSi: Total concentrations of five cyclic siloxanes (D3–D7), eleven linear siloxanes (L4–L14), and sixteen siloxanes (sum of cyclic and linear) in indoor dust, respectively n.d.: not detected 42 T.M Tran et al / Environment International 78 (2015) 39–44 Fig Median concentrations (ng/g) of total siloxanes (sum of cyclic plus 11 linear siloxanes) in homes dust collected from 12 countries Values in parentheses (next to country) refer to the number of samples of TSi in dust from the US homes (1450 ng/g) were 1.5 to 3.5 times higher than the concentrations found in laboratories (1050 ng/g) and offices (423 ng/g) Higher concentrations of siloxanes in dust from homes than in offices and laboratories from the USA and Korea further suggest that personal care products and household products are the major sources of siloxanes in the indoor environment There existed a considerable difference in mean and median concentrations of TSi in dust samples collected from Pakistan (mean: 2690 ng/g; median: 68.3 ng/g) This difference can be explained by elevated concentrations of TLSi (median: 4670 ng/g) found in car dust samples (n = 7), which accounted for 99% of the TSi concentrations (median: 4710 ng/g) Dust from homes in Pakistan contained significantly lower TSi concentrations (median: 60.5 ng/g) 3.2 Composition profiles of cyclic and linear siloxanes in dust The detection frequencies and concentrations of individual siloxanes determined in indoor dust are shown in Table S1 Among the five cyclic siloxanes analyzed, D5 was found at 100% frequency in dust from all countries, except for samples collected from India (79%), Pakistan (50%), Saudi Arabia (75%), and Vietnam (82%) Overall, D5 was also the predominant siloxane found in indoor dust The highest D5 concentration was found in samples from Greece, ranging from 60 to 24,600 ng/g (median: 1200), followed by the USA (range: 6.34 to 1740 ng/g and median: 159 ng/g) The lowest concentration of D5 was found in dust samples from Pakistan (range: LOQ to 371 ng/g; median b LOQ), followed Fig Comparison of total siloxane concentrations in indoor dust from homes, laboratories, and offices in South Korea, USA, and Vietnam by Vietnam (median: 16.6 ng/g), and India (median: 22.1 ng/g) D3, D4, and D6 also were found in indoor dust samples collected from all countries with detection frequencies and concentrations lower than those of D5 The highest concentrations of D6 were found in dust samples from China (median: 131 ng/g) and D3 was found in dust samples from Kuwait (median: 29.4 ng/g) D4 was found at the highest concentration in samples from Greece (median: 65.8 ng/g) Personal care products, especially deodorants and antiperspirants, contained D5 concentrations as high as 14.3% by weight (Horii and Kannan, 2008) Horii and Kannan (2008) also reported the predominance of D5 in hair care products and cosmetics from the USA Among linear siloxanes, L8, L9, and L10 were found at higher detection frequencies than the other linear siloxanes analyzed L8, L9, and L10 were found at 100% in indoor dust samples from Greece, Japan, Kuwait, and South Korea L10 was measured at the highest concentrations, ranging from 83.9 to 22,100 ng/g (median: 537), followed by L9 (20.8 to 15,300 ng/g with a median value of 287) in dust samples from Kuwait L11 and L12 were found in all samples from Japan at the highest concentrations, which ranged from 45.5 to 7940 ng/g (median: 389) for L11 and from 33.9 to 7720 ng/g (median: 337) for L12 L4, L5, L13, and L14 were less frequently detected in dust samples Some dust samples contained elevated concentrations of L12, L13, and L14, which were found at concentrations as high as 8060, 2600, and 580 ng/g, respectively, in car dust samples from Pakistan (Table S1) These results suggested country-specific differences in the profiles of siloxanes in indoor dust samples Similar to that for cyclic siloxanes, a major source of linear siloxanes in the indoor environment is personal care products Horii and Kannan (2008) reported TLSi concentrations in personal care and household products in the USA at b 0.059 to 73,000 μg/g (mean: 1690), and that sanitary products (e.g., furniture polish, dish cleaners) contained elevated concentrations of linear siloxanes (b 0.059 to 53,000 μg/g with a mean of 8840) The distribution percentage of TCSi and TLSi in TSi concentrations in indoor dust from various countries is shown in Fig TCSi concentrations in dust samples collected from Colombia, India, and Saudi Arabia accounted for 90, 80 and 70%, respectively, of the TSi concentrations TLSi predominated in dust samples collected from Japan (89%), Kuwait (85%), South Korea (78%), and the USA (68%) TCSi and TLSi contributed almost equally to TSi concentrations in dust samples from China, Greece, Pakistan, Romania, and Vietnam 3.3 Human exposure to siloxanes through indoor dust ingestion A few studies have reported exposure of humans to siloxanes through dermal absorption from the use of personal care products in the USA and China (Horii and Kannan, 2008; Jovanovic et al., 2008; Lu et al., Fig Distribution profiles of total cyclic siloxanes (TCSi; D3–D7) and total linear siloxanes (TLSi; L4–L14) in indoor dust collected from twelve countries Values in parentheses (next to country) refer to the number of samples T.M Tran et al / Environment International 78 (2015) 39–44 2011) and inhalation of indoor air in the UK (Pieri et al., 2013) The reported daily intake of TSi through indoor dust ingestion in China for toddlers and adults was 32.8 and 15.9 ng/d, respectively (Lu et al., 2010) Human exposure to siloxanes through dust ingestion was estimated based on the measured median TSi concentrations in indoor dust, average body weights reported for various age groups, and the dust ingestion rates (Lu et al., 2010; Guo and Kannan, 2011; Liao et al., 2012) The average body weights (bw) reported in the U.S Environmental Protection Agency (EPA) exposure factor handbook were: infants (6–12 months): kg, toddlers (1–6 yrs): 15 kg, children (6–11 yrs): 32 kg, teenagers (11–16 yrs): 57 kg, and adults (≥ 19 yrs): 72 kg (U.S EPA, 2008) The mean dust ingestion rates were 30 mg/d for infants and 60 mg/d for toddlers, children, teenagers, and adults (U.S EPA, 2008) Based on the median TSi concentrations (Table 2), the calculated exposure doses of TSi for infants and toddlers from 12 countries were in the ranges of 0.26 to 11.9 ng/kg-bw/d (Table 3) Infants and toddlers from Greece had the highest exposure to TSi, with the exposure doses at 11.1 and 11.9 ng/kg-bw/d, respectively Among siloxanes, D5 exposure was the highest for infants and toddlers from Greece and the respective doses were 4.50 and 4.80 ng/kg-bw/d Infants and toddlers in Pakistan had the lowest exposure to TSi through indoor dust ingestion (0.26 and 0.27 ng/kg-bw/d, respectively) For adults, indoor dust ingestion contributed to exposure doses to TSi that ranged from 0.06 for Pakistani adults to 2.48 ng/kg-bw/d for Greek adults Overall, these results suggest that TSi exposure through indoor dust ingestion decreases with increased age However, it should be noted that the exposure doses calculated for children are a crude estimate as the dust concentrations for some countries include the office environment A dermal intake value for TSi from the use of personal care products by an adult woman in the USA was estimated at 307 mg/d (Horii and Kannan, 2008) The siloxane exposure doses calculated from dust ingestion were to orders of magnitude lower than the exposure doses from dermal intake through the use of personal care products Furthermore, it has been shown that 0.12–0.3% and 0.05% of the dermally applied dose of D4 and D5, respectively, were absorbed into the systemic circulation (Reddy et al., 2007) A no-observed adverse effect level (NOAEL) of 19 mg/kg/d was reported for D5 based on a 90-day inhalation exposure study in rats (Brooke et al., 2009a,b,c), and the exposure doses estimated from indoor dust ingestion were several orders of magnitude lower than the NOAEL In summary, this is the first survey of siloxanes in indoor dust collected from 12 countries D5, L8, L9, and L10 were found frequently in indoor dust samples at concentrations as high as 42,800 ng/g Dust samples collected from Greece, Kuwait, and Japan contained the highest siloxane concentrations The profiles of siloxanes in dust varied by the country of origin Dust samples collected in homes contained higher TSi concentrations than those from offices and laboratories Based on the median concentrations of siloxanes found in indoor dust, and the dust ingestion rates, the human exposure doses to TSi were calculated Table Estimated human exposure doses (ng/kg-bw/d) to total siloxanes through indoor dust ingestion by infants, toddlers, children, teenagers, and adults in various countries (based on median concentrations) Countries Infants Toddlers Children Teenagers Adults China Colombia Greece India Japan Kuwait Pakistan Romania Saudi Arabia South Korea USA Vietnam 4.01 0.86 11.1 0.44 5.63 9.0 0.26 2.02 0.5 6.79 4.58 0.77 4.28 0.92 11.9 0.46 6.0 9.6 0.27 2.15 0.53 7.24 4.88 0.82 2.01 0.43 5.57 0.22 2.81 4.5 0.13 1.01 0.25 3.39 2.29 0.39 1.13 0.24 3.13 0.12 1.58 2.53 0.07 0.57 0.14 1.91 1.28 0.22 0.89 0.19 2.48 0.10 1.25 2.0 0.06 0.45 0.11 1.51 1.02 0.17 43 to range from 0.27 to 11.9 ng/kg-bw/d for toddlers and 0.06 to 2.48 ng/kg-bw/d for adults This study has several limitations; samples were collected from select cities and the sample size is small for each country The number of samples from various microenvironments is inadequate to discern distribution of siloxanes The exposure assessment of siloxanes through dust ingestion involves several assumptions, which may under- or over-estimate actual exposures Further studies are needed to assess the significance of indoor dust as a source of siloxane exposure in humans Acknowledgments The authors thank Pierina Maza-Anaya, a youth research fellow supported by the Colombian National Science and Technology System, for helping with the collection of dust samples from Colombia; Dr Dilip Kumar Kedia helped with the collection of dust samples from India This study was funded by a grant (1U38EH000464-01) from the Centers for Disease Control and Prevention (CDC, Atlanta, GA) to Wadsworth 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Komotini Patna Kumamoto, Nagasaki, Fukuoka, Saitama, Saga Kuwait Faisalabad Iasi Jeddah Ansan, Anyang Albany Hanoi, Hatinh, Hungyen, Thaibinh Homes, laboratories Homes Homes Homes Homes, of ces... in the profiles of siloxanes in indoor dust samples Similar to that for cyclic siloxanes, a major source of linear siloxanes in the indoor environment is personal care products Horii and Kannan... Occurrence of linear and cyclic volatile methyl siloxanes in indoor air samples (UK and Italy) and their isotopic characterization Environ Int 59, 363–371 Quinn, A. L., Dalu, A. , Meeker, L.S., Jean, P .A. ,