Traditional and emerging organophosphate esters (OPEs) in indoor dust of Nanjing, eastern China: Occurrence, human exposure, and risk assessment

Journal Pre-proof Traditional and emerging organophosphate esters (OPEs) in indoor dust of Nanjing, eastern China: Occurrence, human exposure, and risk assessment

Luming Zhao, Yayun Zhang, Yirong Deng, Kang Jian, Jianhua Li, Miaolei Ya, Guanyong Su PII:

S0048-9697(20)30002-4

DOI:

https://doi.org/10.1016/j.scitotenv.2020.136494

Reference:

STOTEN 136494

To appear in:

Science of the Total Environment

Received date:

26 November 2019

Revised date:

31 December 2019

Accepted date:

1 January 2020

Please cite this article as: L. Zhao, Y. Zhang, Y. Deng, et al., Traditional and emerging organophosphate esters (OPEs) in indoor dust of Nanjing, eastern China: Occurrence, human exposure, and risk assessment, Science of the Total Environment (2018), https://doi.org/10.1016/j.scitotenv.2020.136494

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© 2018 Published by Elsevier.

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Traditional and emerging organophosphate esters (OPEs) in indoor dust of Nanjing, eastern China: Occurrence, human exposure, and risk assessment

Luming Zhaoa,#, Yayun Zhanga,#, Yirong Dengb,c#, Kang Jiana, Jianhua Lia, Miaolei Yaa, Guanyong Sua,*

a

Jiangsu Key Laboratory of Chemical Pollution Control and Resources Reuse, School of Environmental and

Biological Engineering, Nanjing University of Science and Technology, Nanjing 210094, P. R. China b

Guangdong Provincial Academy of Environmental Science, Guangdong Key Laboratory of Contaminated

Sites Environmental Management and Remediation, Guangzhou 510045, P.R. China

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Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, P.R. China

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* Corresponding author: Guanyong Su;

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Tel.: 1-395-176-3661;

These authors contribute this work equally.

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#

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Email: [email protected]

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c

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Abstract

Here, fifteen OPEs were investigated in n = 50 floor dust samples collected from six types of indoor spaces in Nanjing, eastern China, in the year 2018. Ten OPEs, including tris(2-chloroethyl) phosphate (TCEP), tris(2-chloroisopropyl) phosphate (TCIPP), tris(1,3-dichloro-isopropyl) phosphate (TDCIPP), tris(2-ethylhexyl) phosphate (TEHP), tris(2-butoxyethyl) phosphate (TBOEP), 2-ethylhexyl-diphenyl phosphate (EHDPP), triphenyl phosphate (TPHP), tris(methyl-phenyl) phosphate (TMPP), 4-biphenylyl diphenyl phosphate (4-BPDP) and tris(2-biphenylyl) phosphate (TBPP), were detected in at least one of the analyzed samples (> method limits of quantification). Regardless of indoor spaces, EHDPP (34% of Σ8OPEs, mean: 1.43 μg/g) and TDCIPP (19%, 0.81 μg/g) were the ascendant OPEs in indoor floor dust. 4-BPDP and

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TBPP were detectable in indoor floor dust samples, but at relatively low detection frequencies with 2 % and 10 %, respectively. Various indoor microenvironments exhibited different pollution characteristics of OPEs.

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Floor dust collected from electronic product maintenance centers contained the richest OPE contaminants

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with highest mean Σ8OPEs concentration of 7.92 μg/g. On the basis of measured Σ10OPEs concentrations in dust sample, we estimated daily intake via floor dust ingestion to be 1.37, 0.75 and 1.24 ng/kg BW/day for

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electronic engineers, undergraduates, and graduate students under mean-exposure scenario, respectively.

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Overall, our study reported the occurrence of 4-BPDP and TBPP in environmental samples for the first time, and demonstrated that indoor floor dust ingestion exposure does values were far less than reference dosage

Risk Information System.

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values of oral toxicity proposed by United States Environmental Protection Agency (USEPA) Integrated

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Keywords: Organophosphate esters (OPEs), Indoor floor dust, 4-Biphenylyl diphenyl phosphate (4-BPDP), Tris(2-biphenylyl) phosphate (TBPP), Dietary intake assessment

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1. Introduction

Organophosphate esters (OPEs) are a class of chemicals containing the basic chemical structure of phosphate esters, which are usually added into commercial materials (such as plastics, rubber, textiles, paper products and building materials) as functional additives (van der Veen and de Boer, 2012). OPEs could be halogenated and halogen-free esters, which can be found in different industrial applications (Wei et al., 2015). Specifically, halogenated OPEs are predominantly used as flame retardants (FRs) to prevent or slow ignition of materials, whereas halogen-free OPEs are primarily used as plasticizers, stabilizers, antifoaming, or wetting agents (Andresen et al., 2004; Marklund et al., 2003). Most of OPEs are physically added into host materials and not chemically bonded to polymer products (Rodriguez et al., 2006), indicating that OPEs

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are easily released into the environment throughout their lifecycle, i.e. production, use, and disposal (van der Veen and de Boer, 2012). In recent years, OPEs have been receiving even more environmental attention

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given that several halogenated flame retardants (HFRs) were listed as Persistent Organic Pollutants (POPs)

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(UNEP, 2017), and that several OPEs have been proposed as chemical substitutes/replacements for these phase-out HFRs (Iqbal et al., 2017).

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Previous studies have addressed adverse effects of OPEs, including carcinogenicity (Wei et al., 2015),

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genotoxicity (Shen et al., 2019; Su et al., 2014), cardiotoxicity (McGee et al., 2013), dermatitis (Camarasa and Serra-Baldrich, 1992; McGee et al., 2013), as well as reproductive toxicity (Camarasa and

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Serra-Baldrich, 1992; Li et al., 2015). Specifically, tris(2-chloroethyl) phosphate (TCEP) and tris(2-chloroisopropyl) phosphate (TCIPP) exposure might affect the neurological development of zebrafish

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embryos/larvae though downregulating the expression of selected genes and proteins related to neurodevelopment (e.g., mbp, syn2a, and 1-tubulin) (Li et al., 2019b). What’s worse, triphenyl phosphate (TPHP) at environmentally relevant concentrations was recently reported to cause a reduced successful mating rate and decreased fertilization and hatching rates in Japanese Medaka (Oryzias latipes) (Li et al., 2018b), and exposure to environmentally relevant concentrations of tris(1,3-dichloro-isopropyl) phosphate (TDCIPP) caused a time-dependent change on expressions of genes involved in the hormone/insulin-like growth factor (GH/IGF) axis of female zebrafish (Danio rerio) (Zhu et al., 2017). Given the increasing reports on adverse effects from OPEs, it is critical to consistently identify and monitor the occurrence of OPEs in various environmental samples. OPEs are ubiquitous in various environmental media (Bollmann et al., 2012; Giulivo et al., 2017; Li et al., 2019c; Tao et al., 2016; Wang et al., 2018; Zeng et al., 2014) and biotic matrices (Li et al., 2019a; Ma et al., 2019; She et al., 2013; Sundkvist et al., 2010), potentially posing a serious risk to human health regarding exposure to OPEs in environments. Very recently, Zhang et al. (2019) developed an untargeted screening strategy for analysis of possible organic chemicals currently-used in extracts of smartphone

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screens, and identified three chemicals that shared exact same backbone structures with aryl OPEs . These three chemicals were tri(2,4-di-t-butylphenyl) phosphate (TDtBPP; CAS No. 95906-11-9), 2-biphenylyl diphenyl phosphate (2-BPDP; 132-29-6), and tris (2-biphenyl) phosphate (TBPP; 132-28-5). However, there is a dearth of information regarding their occurrence in real environmental samples. Venier et al. (2018) recently reported the occurrence of TDtBPP in e-waste dust and its application in foam and fabric samples (Wu et al., 2019); so far, there are no known reports on the environmental occurrence of 2-BPDP and TBPP. As compared to dietary and inhalation exposures, dust ingestion is proposed as a more important pathway of exposure to flame retardants for humans, given that 1) where people live and work is equipped with lots of furniture and electric/electronic instruments that contain high concentrations of FRs; and 2) FRs

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could be emitted from the equipment through evaporation or abrasion (de Boer et al., 2016). Organophosphate flame retardants (OPFRs) and replacement brominated flame retardants (RBFRs) were

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ubiquitous in house dust during the polybrominated diphenyl ether (PBDE) phase-out (Percy et al., 2020),

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and recent studies have reported extremely high concentrations of OPEs in indoor dust samples (Guan et al., 2019; Tan et al., 2018). For instance, geometric mean concentrations of OPFRs in dust collected from the

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homes of Cincinnati (USA) between 2003 and 2006 were reported to be 2.14 μg/g (TCIPP), 1.84 μg/g

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(TDCIPP), 1.07 μg/g (TPHP), and 0.67 μg/g (TCEP), respectively, present at approximately one order of magnitude higher than RBFRs (Percy et al., 2020). Two novel groups of OPEs with analogous structure to

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TPHP, isopropylated and tertbutylated triarylphosphate ester (ITP and TBTPP) isomers, were detected in 100 % of house dust from Guangzhou (China) and Carbondale (America). Although the levels of ΣITPs and

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ΣTBTPPs were generally ten times than those of TPHP in the same dust samples, the broad occurrences of these isomers in house dust from the two locations likely suggested their wide applications in household consumer products (Guan et al., 2019). Again, there is no information regarding the environmental occurrences and human exposure risks of the newly identified 2-BPDP and TBPP so far. However, the novel OPEs are worthy of attention due to their possibly wide applications. In this study, in allusion to fifteen target OPEs including tris(2-chloroethyl) phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCIPP), TDCIPP, triethyl phosphate (TEP), tripropyl phosphate (TPrP), tributyl phosphate (TNBP), tris(2-ethylhexyl) phosphate (TEHP), tris(2-butoxyethyl) phosphate (TBOEP), 2⁃ ethylhexyl diphenyl phosphate (EHDPP), TPHP, tricresyl phosphate (TMPP), 2-biphenylyl diphenyl (2-BPDP), 3-biphenylyl diphenyl phosphate (3-BPDP), 4-biphenylyl diphenyl phosphate (4-BPDP), and tris (2-biphenyl) phosphate (TBPP) were analyzed in n=50 flood dust samples from Nanjing, eastern China. The specific objectives were described following as 1) to examine whether two newly identified OPEs were detectable in real environments or not; 2) to analyze the concentrations and distributions of all fifteen OPEs in n = 50 floor dust samples collected from six indoor places (including electronic product maintenance

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center, teaching building, laboratory building, hotel, dormitory and residence) collected from Nanjing, eastern China; 3) to characterize compositional profiles of OPEs in six indoor spaces; and 4) to estimate exposure risks of OPEs via dust ingestion for three categories of crowds.

2. Materials and methods 2.1 Materials Pure standards of eleven target OPEs and five deuterated surrogates (d12-TCEP, d15-TDCIPP, d15-TEP, d27-TNBP, d15-TPHP) were purchased from Sigma-Aldrich (St. Louis, MO, United States), AK Scientific (Union City, CA, U.S.A.), or TCI America (Portland, OR, United States). Four target OPEs (2-BPDP,

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3-BPDP, 4-BPDP, and TBPP) were synthesized in our laboratory, and detailed information regarding their synthesis can be found in our previous publication (Zhang et al., 2019). The chemical structures, chemical

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abstracts service registry number (CASRN), and physicochemical properties of targeted OPEs are listed in

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Table S1. All solvents used for this study were high performance liquid chromatography grade, and purchased from Tedia (Fairfield, OH, U.S.A.), LiChrosolv (Darmstadt, Germany), J&K (Beijing, China), or

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Alfa Aesar (Ward Hill, MA, U.S.A.). CNWBOND silica gel solid phase extraction (CNWBOND Si SPE)

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2.2 Sample collection

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cartridge (500mg, 6mL) were purchased from CNW Technologies (Shanghai, China).

Nanjing is an important central city in the Yangtze delta economic circle, eastern China, and this city is

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located between 31°14″ to 32°37″N and 118°22″ to 119°14″E. The newest statistics information suggests that the resident population of Nanjing was 8.44 million in the year 2018. Fifty individual floor dust samples were collected from six indoor spaces under normal use conditions on workdays in Nanjing between November and December, 2018. The distribution of sampling sites is given in Table 1. The samples were collected by a whirlwind car dust collector (CARCHAT DIVI-V401), and then placed in a polyethylene (PE) specimen collection zipper bag, and brought to laboratory immediately. Each dust sample was sieved with a 10 mesh (pore size: 2.0 mm) stainless steel sieve, and then stored (grain size < 2.0 mm) in brown glass jar sealed with aluminum foil and PE screw cap at -20 °C until further analysis.

2.3 Sample preparation and instrumental analysis For determination of concentrations of OPEs in dust samples, 0.5 g sodium sulfate (Na2SO4), 0.1 g sodium chloride (NaCl), approximately 50 mg of indoor floor dust sample, 10 ng of internal standards (IS), and 2 mL mixture of dichloromethane and hexane (DCM:HEX; 1:1, v/v) were added into clean glass centrifuge tube (10 mL) and mixed well with vortex. Then, the sample was in ultrasonic-assisted extraction

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for 10 min at 20 °C, and centrifuged for 5 min at 4500 rpm. The supernatant was transferred into a clean glass centrifuge tube (10 mL). Same extraction was conducted for other two time, and three extracts were combined. Then, the combined extract was concentrated to approximately 100 μL under gentle nitrogen at 40 °C, and then mixed with 0.4 mL fresh acetone (ACE). The extract was further purified through a CNWBOND Si SPE cartridge, which was preconditioned in sequence with 6 mL of ACE, 8 mL of acetonitrile, and 6 mL of mixture of ACE and ethyl acetate (ACE:EA; 4:1, v/v). After the sample was loaded, the glass centrifuge tube was washed with 0.5, 0.5, and 1 mL of mixture of ACE:EA (4:1, v/v). Subsequently, target OPEs were eluted out with 2 mL of ACE:EA (4:1, v/v) twice. The final extract was dried under gentle nitrogen at 40 °C, and then re-dissolved in 100 μL of 2,2,4-trimethylpentane (TMP). The

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supernatant was carefully transferred into a brown glass vial and stored at -20 °C prior to instrumental analysis.

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Concentrations of sixteen OPEs were targeted and quantified on a Thermo Fisher Scientific Trace 1300

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gas chromatograph coupled to an ISQ LT single quadrupole mass spectrometry (GC-MS, MA, U.S.A.) operated in electron impact ionization (EI) source and selected ion monitor (SIM) mode. The GC-MS was

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equipped with TG-5MS section (30 m × 0.32 mm i.d.×0.25 μm film thickness) column. One μL of sample

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was injected in GC in splitless mode at 285 °C. High purity Helium (He) was utilized as a carrier gas with a flow rate of 1.2 mL/min. GC oven temperature was set to an initial temperature of 50 °C for 3 min and

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raised to 100 °C at a rate of 20 °C/min (held for 3 min), and raised to 230 °C at a rate of 12 °C/min (held for 4 min), then raised to 260 °C at a rate of 5 °C/min; increased at a rate of 10 °C/min to the final temperature

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of 300 °C (hold for 14 min). The transfer line and ion source temperature were 300 °C and 230 °C, respectively. Specific quantification and qualification ions for all fifteen target OPEs are provided in Table S1.

2.4 Quality assurance and quality control Before the analysis of n=50 indoor dust samples, four replicates of spiked dust composite (with 10 ng for each OPE standard and IS) and one matrix blank (with only ISs) were analyzed to ensure good recoveries of target OPEs. The recoveries ranged from 70% (TCIPP) to 168% (TEP), with relative standard deviations (RSDs) less than 28% (Table S2). The linearity range of quantitative calibration curve was obtained from 1 to 200 ng/mL (R2 > 0.98). The method limit of quantification (mLOQ) or method limit of detection (mLOD) were set to the analyte response to a signal-to-noise ratio (S/N) of ten and three respectively in the lowest standard mixture working solution. We did observe procedural contamination for several target OPEs, i.e. TCIPP, TEHP, EHDPP, TPHP (see details in Table S2). When the target compounds were found in the procedural blanks, the mLOQ and mLOD were calculated from the mean

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blank values plus five and three times the standard deviation of the blanks, respectively. The mLOQs of the halogenated OPEs, alkyl-OPEs, and aryl-OPEs ranged of 0.3 ~ 3.1, 1.1 ~ 109, and 1.5 ~ 54 ng/g in dust, respectively (Table S2). Procedural contamination was evaluated by running a blank of the whole process (no dust sample) with every batch of 6 ~ 12 samples. TCIPP, TEHP, EHDPP and TPHP exhibited procedural blanks with a range of ND ~ 45 (TEHP) ng/mL. All the reported concentrations have been deduced by the blank samples. Only TCIPP (0.9 ng/mL) and EHDPP (0.3 ng/mL) were detected in PE zipper bag using dust collection, and their levels in zipper bag were far below dust. Moreover, the packaged dust samples were brought to laboratory and sieved immediately. Hence, the influence of PE zipper bag

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could be neglected.

2.5 Estimated daily intake (EDI) and risk assessment

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By assuming 82% bioavailability factors of OPEs through dust ingestion (Fang and Stapleton, 2014),

according to the following formula (Tan et al., 2019):

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the daily intake of individual OPEs through indoor floor dust ingestion to three crowds was estimated

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𝐶 × 𝐷𝐼𝑅 × 𝑡 × 82% (1) 𝐵𝑊 where EDI represents the estimated daily intake (ng/kg BW/day); C is a chemical’s concentration in indoor

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𝐸𝐷𝐼 = ∑

BW is body weight (kg).

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dust (ng/g); DIR is the dust ingestion rate (g/h); t is the time spent in different indoor spaces per day (h/day);

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Regarding the human health risk assessment, we have inquired the time spent in different indoor spaces throughout the course of a whole day for the three types of crowds via questionnaire surveys (Li et al., 2018a). In total, n=135 volunteers (30 electronic engineers, 79 undergraduates, and 26 graduate students) have given their answers on the questions (i.e. sex, age, body weight, occupation, time spent indifferent indoor environments, dormitory) listed in Table S3. Average time spent in different indoor spaces for target crowds showed in Table S4 were used. Besides, the average body weight of the Chinese population (58.7 kg) was used for EDI (Yang et al., 2005). Human health risk assessment was assessed with hazard quotient (HQ) and hazard index (HI) values, they were calculated by the formula as follow (Ding et al., 2018): 𝐻𝑄 =

𝐸𝐷𝐼 𝑅𝑓𝐷

𝐻𝐼 = ∑ 𝐻𝑄

(2) (3)

where RfD is the reference dosage values of oral toxicity (ng/kg BW/day) for chemical, and they were summarized in our previous studies and listed in Table 2 (Zhao et al., 2019).

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2.6 Statistical analysis

The statistical analyses and data visualization were performed with Excel 2019 (Microsoft Inc., Redmond, WA, USA) and GraphPad Prism 8 (GraphPad Software Inc., San Diego, CA, USA). Unpaired t-test and one-way analysis of variance (ANOVA) were used for analysis of significant difference among two groups and more than two groups, respectively. Pearson correlation analysis was used for correlation analysis. Target compounds with detection frequencies (DFs) below 40% in individual indoor space were excluded from our statistical analyses, the rest measured values below mLOQ or mLOD were replaced by

3. Results and discussion

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3.1. Levels and distributions of OPEs in Chinese indoor dust

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the mLOQ/√2 or mLOD/√2 for computation and analysis purpose.

Information regarding statistical analysis of levels of OPEs in indoor floor dust are summarized in

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Table S5 and Table S6, and the corresponding box-whisker plots are shown in Fig. 1 and 2. It is noticeable,

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however, that five (TEP, TPrP, TNBP, 2-BPDP, and 3-BPDP) out of the target fifteen OPEs were not detected in any of the samples (< mLODs values). Hence, they were not taken into account this installment

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of the article. With regard to the other OPEs, three halogenated OPEs (TCEP, TCIPP, TDCIPP), two alkyl-OPEs (TEHP, TBOEP) and five aryl-OPEs (EHDPP, TPHP, TMPP, 4-BPDP and TBPP) were

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detected in dust samples with DFs of 98 ~ 100%, 34 ~ 68%, and 2 ~ 100%, respectively. The most

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frequently detected OPEs were TCEP, TCIPP, EHDPP, and TPHP (DFs = 100%). The high DFs of OPEs in floor dust indicated a broad range of OPEs extensively applied in commercial products in indoor environments of Nanjing, eastern China.

The concentrations of target OPEs distributed in individual indoor floor dust samples were presented in Fig. S1. There were big gaps in levels and profiles of OPEs among individual samples. The concentrations of TBPP in the floor dust were very variable with a high coefficient of variance (CV) of 629%, whereas TCEP (126%), and TPHP (129%) were least changeable. The concentrations of Σ10OPEs (sum of the ten target OPEs) in dust samples ranged from 0.04 to 29.2 μg/g (mean ± SD: 4.34 ± 5.90 μg/g , median: 2.52 μg/g ). The highest concentration of Σ10OPEs was found in a laboratory (L14: 29.2 μg/g) where TEHP (10.6 μg/g ), TBOEP (1.62 μg/g) and EHDPP (14.1 μg/g) also had maximum detectable concentration, while the lowest level of Σ10OPEs was detected at a classroom (T3: 0.04 μg/g). Two aryl-OPEs (4-BPDP and TBPP) exhibited relatively lower DFs of 2 % and 10 %, respectively. They were only detected in one (L5) and five (L7 ~ 9, L12 and L14) dust samples from laboratory building, respectively. This is the first report on detection of 4-BPDP and TBPP in environmental samples. These two

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target compounds were beyond our following statistical analyses due to their DFs below 40% in each individual indoor space. Generally, among different classes of OPEs, aryl-OPEs were the most prominent OPEs measured in floor dust, followed by halogenated OPEs and alkyl-OPEs, the concentrations of ∑3aryl-OPEs, ∑3halogenated OPEs and ∑2alkyl-OPEs ranged from 0.01 ~ 15.8 (mean: 2.02) μg/g, 0.02 ~ 20.0 (1.57) μg/g and ND ~ 12.2 (0.63) μg/g and accounted for 48%, 37% and 15% of Σ8OPEs, respectively. Regardless of the sampling indoor space, the mean concentration of individual OPEs contributed to the Σ8OPEs was ranked from highest to lowest as following: EHDPP (34% of Σ8OPEs, mean: 1.43 μg/g), TDCIPP (19%, 0.81 μg/g), TCIPP (14%, 0.59 μg/g), TEHP (11%, 0.47 μg/g), TPHP (11%, 0.46 μg/g), TCEP (4.1%, 0.17 μg/g),

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TBOEP (3.8%, 0.16 μg/g), TMPP (3.1%, 0.13 μg/g). As shown in Table S7, the levels of EHDPP in floor dust were significantly higher than TCEP (one-way ANOVA: p < 0.01) and TMPP (p < 0.01). The high DFs

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and levels of OPEs in indoor dust in this study may be attributed to the less volatile compounds partitioning

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more to the floor dust (particle phase) on account of their relatively lower vapor pressures and higher octanol-air partition coefficient (KOA) values (Tao et al., 2016). In addition, the potential persistence and/or

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possible range of application in commercial products in the indoor spaces might be the reasons which lead to

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the differences in detection results among target OPEs (Covaci et al., 2011; Derek and Philip, 2006). Table S8 lists the results of Pearson correlation analysis among individual concentrations of OPEs in

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floor dust from 50 indoor places. TPHP concentrations in samples correlated moderately and significantly with TDCIPP (Pearson correlation analysis: r = 0.457, p < 0.001), TBOEP (r = 0.753, p < 0.001) and

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EHDPP (r = 0.630, p < 0.001). In addition, the levels of TBOEP showed significant correlation with EHDPP (r = 0.785, p < 0.001), TDCIPP (r = 0.438, p < 0.05), and TEHP (r = 0.658, p < 0.001), respectively. Moreover, EHDPP versus TEHP (r = 0.638, p < 0.001), TMPP versus TCEP (r = 0.312, p < 0.05), ∑3aryl-OPEs versus ∑2alkyl-OPEs (r = 0.619, p < 0.001) were correlated positively and significantly. These OPEs in indoor floor dust samples with significantly positive correlations suggested that they shared possible common sources.

3.2. Contamination profiles of OPEs in dust from different microenvironments The congener profiles of OPEs were compared in floor dust sampled from six types of indoor spaces investigated in this study (Fig. S1 and Fig. 3). Floor dust collected from electronic product maintenance center contained the highest mean Σ8OPEs concentration (mean: 7.92 ng/g; range: 3.20 ~ 28.2 μg/g), followed by those from laboratory building (5.79 μg/g; 0.41 ~ 29.1 μg/g), dormitory (4.33 μg/g; 0.60 ~ 14.1 μg/g), residence (3.20 μg/g; 2.00 ~ 4.57 μg/g), teaching building (1.24 μg/g; 0.03 ~ 6.62 μg/g) and hotel (1.20 μg/g; 0.32 ~ 1.77 μg/g). This may be due to strict fire-safety regulations in public buildings (China,

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2006; China, 2012), types and quantities of indoor consumer goods, and the frequency of cleaning (Wu et al., 2016). Moreover, the reason for the highest levels of OPEs found in electronic product maintenance center could be release of these substances during disassembly and maintenance processes. There were either no significant differences (one-way ANONA: p > 0.05) or no significant correlations (Pearson correlation analysis: p > 0.05) for Σ8OPEs concentrations among the investigated microenvironments in our study (Table S9 and S10). Overall, aryl-OPEs were the dominant compounds (mean contribution to Σ8OPEs: > 40%) found in teaching building, laboratory building, hotel, dormitory, and residence. Halogenated OPEs were predominant in electronic product maintenance center (53%). Concretely speaking, in electronic product

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maintenance center, TDCIPP (mean: 3.47 μg/g, contribution: 44% of Σ8OPEs) was the predominant compound, followed by EHDPP (1.82 μg/g, 23%). In teaching building, EHDPP, detected as the ascendant

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contaminant with mean concentration of 0.69 ng/g, accounted for 55% of mean Σ8OPE concentrations.

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Furthermore, EHDPP was also the major contributor in dormitory (2.34 μg/g, 54%) and residence (1.17 μg/g, 37%), followed by TCIPP (0.92 μg/g, 21%) and TPHP (0.68 μg/g, 21%), respectively. The distributions of

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OPEs in laboratory building and hotel were relatively uniform, and all target OPEs accounted below 28% of

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mean Σ8OPE concentrations. It might be attributed to application preferences of OPEs among various indoor environments (van der Veen and de Boer, 2012). EHDPP was identified as the most abundant compound in

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most of indoor spaces (including teaching building, laboratory building, dormitory, residence). EHDPP is frequently used in hydraulic fluids, PVC and food packaging (van der Veen and de Boer, 2012). Occurrence

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of chlorinated OPEs (TCEP, TCIPP and TDCIPP) in indoor dust may be ascribed that they are commonly used in flexible and rigid polyurethane foam (PUF) (Stapleton et al., 2009), and Truong et al further confirmed that spray foam insulation was a large source of TCIPP to the indoor environment (Truong et al., 2017). TPHP is one of the most effective additive FRs in many polymers and is commonly used in combination with halogenated and non-halogenated FR mixtures such as Firemaster 550 (FM 550) where some of its main uses are in plasticizers in hydraulic fluids, PVC, lubricants, electronic equipment and building materials (Stapleton et al., 2008; van der Veen and de Boer, 2012). Compared with the similar microenvironment floor dust reported in other reports (Table S11), the levels of OPEs in our investigated floor dust was comparable with the research results in China (He et al., 2015; Sun et al., 2019; Zheng et al., 2015), Saudi Arabia (Ali et al., 2016), Kuwaiti (Ali et al., 2013), Czech Republic (Vykoukalova et al., 2017), Norway (Xu et al., 2016), Canada (Vykoukalova et al., 2017) and New Zealand (Ali et al., 2012), and approximately one magnitude lower than America (Dodson et al., 2017; Vykoukalova et al., 2017), Japan (Mizouchi et al., 2015) and some parts of Europe such as Germany (Zhou et al., 2017), Sweden (Luongo and Ostman, 2016) and United Kingdom (Brommer and Harrad, 2015),

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whereas much higher than Egypt (Abdallah and Covaci, 2014) and some Asian countries like Pakistan (Ali et al., 2013; Ali et al., 2014) and Philippines (Kim et al., 2013). Especially, the concentrations of OPEs in dust from dormitory were lower while corresponding with the other indoor spaces (including residence office and public place) in our study (He et al., 2016). The substantial differences among OPEs concentrations in indoor dust reported in different countries more likely reflect differences in the extent to which OPEs were used in indoor consumer materials, the flammability standards of each country and different environmental conditions (Shoeib et al., 2019). For instance, Tao et al. (2019) concluded that TBOEP was overwhelming in indoor floor dust, with 97% of median percent contribution to Σ 10OPEs in Sweden. They found that all office floors were equipped with polyvinyl chloride (PVC) plastic and treated

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regularly with polish, and TBOEP was widely used in floor polishes, same results were reported in samples from Japan (Mizouchi et al., 2015). Nevertheless, in Istanbul, ceramic flooring is most commonly used,

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frequent floor washing could explain the relatively low DFs of TBOEP in these dust samples as OPEs are

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quite soluble and are easily washed away in China (Saini et al., 2016). In all studies, chlorinated-OPEs were relatively abundant in dust compared to other OPEs, which can be possibly explained by the reason that they

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were more persistent in environment.

3.3. Human exposure assessment and health risks

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The EDIs of OPEs via indoor floor dust ingestion for humans were calculated with formula (1) on the basis of the United States Environmental Protection Agency (USEPA) risk assessment model, and three

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exposure scenarios (including low-, mean- and high-exposure scenarios) for electronic engineers, undergraduates and graduate students in Nanjing, China are displayed in Table 2 and Fig. 4. Low-exposure scenario was estimated with average dust ingestion rate (20 mg/day) and 5th percentile of OPEs concentrations detected in dust; mean-exposure scenario was calculated using high dust ingestion rate (50 mg/day) and mean concentrations of OPE detected in dust, which is applicable to most of the population; high-exposure scenario was estimated with high dust ingestion rate (50 mg/day) and 95th percentile of OPEs concentrations detected in dust (Ali et al., 2013; Tan et al., 2019). Dust ingestion exposure does (EDI-ing) of ∑10OPEs for different crowds were between 0.11 ~ 0.68, 0.75 ~ 1.37, and 6.16 ~ 9.08 ng/kg BW/day under low-, mean- and high-exposure scenario, respectively. As for general scenario (mean-exposure), EHDPP was the major contributor of human exposure to ∑10OPEs through floor dust ingestion for electronic engineer (27%), undergraduate (52%) and graduate student (38%), while TDCIPP was also the principal contributors of human exposure to OPEs through floor dust ingestion for electronic engineer with 32% of Σ10OPEs. Additionally, throughout a whole day, electronic product maintenance center, dormitory and laboratory building were the preponderant exposure source of OPEs for

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electronic engineer, graduate student and undergraduate, accounting for 68%, 82% and 55% of total exposed quantity. With regard to the three groups of people involved in this study, even in the worst scenario case (high-exposure), ranges of the HQ and HI were 0.4 ~ 84‱ and 63 ~ 104‱ , respectively. In other words, the EDI-ing of individual OPE was 2 ~ 5 orders of magnitude lower than its homologous reference dosage value of oral toxicity (RfD). To the best of our knowledge, no significant adverse health effects were noticed in OPEs exposure via indoor floor dust ingestion for Chinese adults. Dietary intake is another principal exposure source pathway for many organic substances, and the EDI-ing of OPEs in this research were dozens of times lower compared to the dietary intake exposure does

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in our previous study (Zhao et al., 2019). However, studies have also showed that ingestion of indoor floor dust can be a significant exposure pathway for OPEs and cannot be ignored attributed that high measured

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levels and DFs of OPEs in indoor floor dust can contribute to high human occupational exposure to OPEs in

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specific working conditions, such as automobile parts shops, electronics, and nail salons/shops that sell nail polish (Ali et al., 2013; Kim et al., 2019). Whereas ingestion was more important for the more volatile OPEs

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such as TCEP and TMPP (Xu et al., 2016). The consumption of OPEs is expected to increase in the future

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due to the regulations on brominated flame retardants in consumer products. Therefore, further studies are warranted to investigate the exposure of OPEs from diverse types of consumer products and

4. Conclusion

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therefore warranted.

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microenvironments. Further studies of occupational groups exposure to these semi-volatile chemicals are

All in all, ten out of the target fitteen OPEs were measurable above mLOQs in at least one of n=50 floor dust samples collected from six indoor microenvironments in Nanjing, eastern China, in the year 2018. 4-BPDP and TBPP were first detected in environmental samples. EHDPP (34% of Σ8OPEs, mean: 1.43 μg/g) and TDCIPP (19%, 0.81 μg/g) were the prominent OPEs. The highest mean Σ8OPEs concentration was detected in floor dust samples collected from electronic product maintenance center (mean: 7.92 μg/g). Various indoor microenvironments exhibited different pollution characteristics of OPEs. Furthermore, the estimated values of dust ingestion mean-exposure to OPEs were 1.37, 0.75 and 1.24 ng/kg BW/day for electronic engineer, undergraduates, and graduate students, respectively. EHDPP and TDCIPP were the main contributors, whilst electronic product maintenance center, laboratory building and dormitory were the major exposure sources. Even in the high-exposure scenario, indoor floor dust ingestion exposure does values were far less than RfDs with hazard index≪1, which means that there were almost not deleterious effects of human health for three investigated crowds inhabiting in Nanjing exposed through indoor floor

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dust. However, the consumption of OPEs is expected to increase in the future due to the regulations on traditional HFRs in consumer products, and we emphasize the importance of continued monitoring the exposure of OPEs via various indoor atmospheric microenvironments. Here, it should be noted that sample sizes in our present study were quite small for individual microenvironment spaces, especially for hotel and residence. Further monitoring studies of OPEs should be encouraged to conduct based on larger sizes of indoor dust samples, as well as include more comprehensive inhalation exposure sources, i.e. indoor air, outdoor air, and dust samples.

Acknowledgments

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This research was supported by the National Natural Science Foundation of China (Grant 21976088), Natural Science Foundation of Jiangsu Province (Grant No. BK20170830 and BK20180498), and the

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Fundamental Research Funds for the Central Universities (Grant No. 30919011101). Y. Deng was supported

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by the National Key Research and Development Program of China (Grant No.2018YFC1800806, and 2018YFC1800205). Dr. Su appreciates the support from the programs of “Thousand Talents Plan” and

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“Jiangsu Provincial Distinguished Professorship”.

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Journal Pre-proof Table 1. Description of sampling sites in different indoor spaces. Indoor Spaces (n=50) Electronic Product Maintenance Center (E1 ~ E7, n=7) Working/Learning Place Teaching Building (T1 ~ T11, n=11) (n=32) Laboratory Building (L1 ~ 14, n=14) Hotel (H1 ~ H4, n=4) Living Place Dormitory (D1 ~ D10, n=10) (n=18) Residence (R1 ~ R4, n=4)

Journal Pre-proof Table 2a. Exposure risk assessment of OPEs via dust ingestion by specific crowds under different exposure scenarios on basis of various OPEs. Detailed information regarding the OPE concentrations can be found in Table S5 and Table S6 of supporting information. Crowd Exposure Scenario a

Electronic Engineer Low b

Undergraduate

Graduate Student

RfD d

Mean

High

Low

Mean

High

Low

Mean

High

0.03 (0.1) 0.12 (0.3) 0.44 (2.9) 0.12 (0.03) 0.06 (0.4)

0.10 (0.4) 0.53 (1.5) 4.11 (27) 0.52 (0.1) 0.31 (2.1)

0.005 (0.02) 0.02 (0.1) 0.01 (0.04) 0.01 (0.003) 0.0005 (0.003)

0.02 (0.1) 0.15 (0.4) 0.02 (0.2) 0.06 (0.02) 0.01 (0.1)

0.15 (0.7) 1.51 (4.2) 0.15 (1.0) 0.51 (0.1) 0.11 (0.8)

0.01 (0.0) 0.03 (0.1) 0.01 (0.1) 0.01 (0.003) 0.001 (0.003)

0.05 (0.2) 0.21 (0.6) 0.11 (0.8) 0.16 (0.05) 0.04 (0.3)

0.33 (1.5) 1.77 (4.9) 1.07 (7.1) 1.39 (0.4) 0.38 (2.5)

2200 3600 1500 35000 1500

c

EDI , ng/kg BW/day (HQ /HI , ‱ ) TCEP 0.02 (0.1) TCIPP 0.07 (0.2) TDCIPP 0.06 (0.4) TEHP 0.04 (0.01) TBOEP 0.03 (0.2)

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EHDPP

0.15 (2.5)

0.38 (6.3)

1.72 (29)

0.02 (0.3)

0.39 (6.5)

4.49 (75)

0.04 (0.6)

0.48 (8.0)

5.02 (84)

600

TPHP TMPP

0.10 (0.1) 0.01 (0.1)

0.19 (0.3) 0.03 (0.3)

0.93 (1.3) 0.20 (1.5)

0.01 (0.02) 0.002 (0.01)

0.08 (0.1) 0.01 (0.1)

0.81 (1.2) 0.06 (0.5)

0.03 (0.04) 0.004 (0.03)

0.13 (0.2) 0.04 (0.3)

1.04 (1.5) 0.33 (2.5)

7000 1300

4-BPDP

0 (—)

0 (—)

0 (—)

0 (—)

0 (—)

0 (—)

0 (—)

0 (—)

0.002 (—)

na e

TBPP ∑Halogenated OPEs ∑Alkyl-OPEs

0 (—) 0.09 (0.2) 0.27 (2.7)

0 (—) 0.18 (0.5) 0.60 (6.8)

0 (—) 0.74 (2.2) 2.71 (31)

0 (—) 0.01 (0.01) 0.03 (0.3)

0 (—) 0.07 (0.1) 0.48 (6.7)

0 (—) 0.55 (0.9) 5.22 (76)

0 (—) 0.01 (0.0) 0.10 (0.7)

0.03 (—) 0.20 (0.3) 0.67 (8.4)

0.29 (—) 1.64 (2.9) 6.28 (88)

na — —

∑Aryl-OPEs

0.68 (3.6)

1.37 (11)

7.85 (63)

0.11 (0.5)

0.75 (7.5)

6.16 (83)

0.26 (0.9)

1.24 (10)

9.08 (104)

—

∑OPEs

1725 (358)

2785 (1065)

12231 (6299)

110 (46)

754 (747)

6160 (8320)

1246 (85)

13011 (1032)

190954 (10414)

—

EDI: Estimated daily intake via dust ingestion. HQ: Hazard quotient. c HI: Hazard index. d RfD: Reference dosage values of oral toxicity. e na: Not available.

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Journal Pre-proof Table 2b. Exposure risk assessment of OPEs via dust ingestion by specific crowds under different exposure scenarios on basis of various indoor spaces. Crowd Exposure Scenario

Electronic Engineer

Undergraduate

Graduate Student

Low

Mean

High

Low

Mean

High

Low

Mean

High

0.38

0.93

6.34

—

—

—

—

—

—

— — —

— — —

— — —

0.02 — 0.09

0.13 — 0.62

1.15 — 5.01

— 0.18 0.08

— 0.69 0.56

— 4.60 4.48

Residence

0.30

0.44

1.50

—

—

—

—

—

—

Total

0.68

1.37

7.85

0.11

0.75

6.16

0.26

1.24

9.08

a

EDI (ng/kg BW/day) Electronic Product Maintenance Center Teaching Building Laboratory Building Dormitory

a

EDI: Estimated daily intake via dust ingestion.

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Pre-proof Fig. 1. Box-whisker plot of OPE concentrations (μg/g) in floor Journal dust samples collected from n=6 different indoor spaces including electronic product maintenance center, teaching building, laboratory building, hotel, dormitory, and residence. In the box-whisker plot, box represents 1−3 quartiles; midcourt line represents median; ⊗ represents arithmetic mean; bottom bar represents 1 st quartile -1.5 × interquartile range (IQR); top bar represents 3 rd quartile + 1.5 × IQR; dot represents outliers. Detailed OPE concentrations can be found in Table S5 and Table S6 of the supporting information.

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Journal Fig. 2. Box-whisker plot of OPE concentrations (μg/g)Pre-proof in floor dust samples collected from working/learning, living, or all spaces. In the box-whisker plot, box represents 1−3 quartiles; midcourt line represents median; ⊗ represents arithmetic mean; bottom bar represents 1 st quartile -1.5 × interquartile range (IQR); top bar represents 3 rd quartile + 1.5 × IQR; dot represents outliers.

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Journal Pre-proof Fig. 3. Contaminant profiles of OPEs in floor dust samples collected from different indoor spaces.

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Journal Pre-proof Fig. 4. Contributions of OPEs (a) and exposed situations (b) to the total estimated daily per capita intakes via indoor floor dust ingestion for the three target crowds.

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Graphical Abstract

Journal Pre-proof Highlights  Fifteen OPEs were analyzed in n=50 Chinese indoor dust samples.  4-BPDP and TBPP were detected in environments for the first time.  OPE concentrations were dominated by EHDPP, TPHP, TDCIPP, TCIPP, and TCEP.  Dust from electronic product maintenance centers contained the highest OPE levels.

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 Dust ingestion of OPEs was less than reference dosage values proposed by USEPA.