DSpace at VNU: A survey of cyclic and linear siloxanes in indoor dust and their implications for human exposures in twelve countries

Environment International 78 (2015) 39–44

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Environment International
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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.

1. 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: (K. Kannan).

/>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 2 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.
2. 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 1. 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 4 °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 min 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
5 mL mixture of dichloromethane (DCM) and hexane (3:1, v:v) for
5 min. Samples were then centrifuged at 2000 g for 5 min (Eppendorf
Centrifuge 5804, Hamburg, Germany), and the supernatant was
transferred to a 12 mL glass tube. The extraction was repeated
twice, with 3 mL of DCM: hexane mixture (3:1) for the second time
and 3 mL hexane for the third time. The extracts were concentrated
to 1 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
2 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 5 °C/min
(held for 10 min) and then held for 5.0 min 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 1

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.

3. 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 2 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 2
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. 1. Median concentrations (ng/g) of total siloxanes (sum of 5 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. 2. 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. 3. 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. 3. 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): 8 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 3 to 5 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 3
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
Center, New York State Department of Health. Its contents are solely
the responsibility of the authors and do not necessarily represent the official views of the CDC.
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.envint.2015.02.011.
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