Article pubs.acs.org/est
Particle Size-Specific Distributions and Preliminary Exposure Assessments of Organophosphate Flame Retardants in Office Air Particulate Matter Fangxing Yang,† Jinjian Ding,‡ Wei Huang,† Wei Xie,† and Weiping Liu*,‡ †
Research Center for Air Pollution and Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China ‡ MOE Key Laboratory of Environmental Remediation and Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China S Supporting Information *
ABSTRACT: In this study, the concentrations, size-specific distributions, and preliminary exposure assessments of 10 organophosphate flame retardants (OPFRs) were investigated in suspended particulate matter collected from offices. OPFRs were detected in a range of 5.00−147.77 ng/m3. Tri(chloropropyl) phosphate (TCPP) was the most abundant analog followed by tri(2-chloroethyl) phosphate (TCEP) and triphenyl phosphate (TPhP). Chlorinated OPFRs (TCPP, TCEP, and tris(1,3dichloroisopropyl) phosphate (TDCPP)) contributed to about 77% of the total OPFRs. Size-specific distributions revealed that TCEP, tri-n-propyl phosphate (TnPP), TCPP, and tri-n-butyl phosphate (TnBP) shared a similar distribution pattern with a peak in the fraction 4.7−5.8 μm. A peak was also found in the distributions of tricresyl phosphate (TCrP), 2-ethylhexyl diphenyl phosphate (EHDPP), and tri(2-ethylhexyl) phosphate (TEHP) but in different fractions. A bimodal distribution was observed for TDCPP, TPhP, and tributoxyethyl phosphate (TBEP). The results of mass median aerodynamic diameter (MMAD) indicated that TDCPP, TCrP, and TEHP were mainly located on ultrafine particles (≤1 μm), while TnPP, TBEP, and EHDPP mainly on fine particles (≤2.5 μm). Furthermore, MMADs of OPFRs were found to be positively correlated with their vapor pressures (Vp) (p < 0.01), indicating that OPFR analogs with low Vp were inclined to adsorb on small size particles. Preliminary exposure assessments suggested a low risk of exposure to OPFRs for people working in such offices, and inhaled OPFRs would mainly deposit in the head region of the respiratory tract.
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INTRODUCTION With the phase out of polybrominated diphenyl ether (PBDE) flame retardants (FRs) due to their persistence and bioaccumulative and toxic properties,1 the demand for alternative FRs has been increasing. Organophosphate esters were introduced as replacements and are commonly known as organophosphate flame retardants (OPFRs).2 OPFRs have been widely used as flame retardants, plasticizers, and antifoaming agents in many products including furniture, textiles, cables, building materials, insulation materials, paints, floor polishes, hydraulic fluids, and electronics.3 In most cases, OPFRs are used as additives in products and are not chemically bonded to the original materials. Therefore, OPFRs can be slowly released into the environment by abrasion and volatilization.4,5 Some OPFRs, especially those with chlorinated alkyls, have a low degradation potential and may be persistent in the environment.6 As a result, OPFRs have been detected in various matrices in the environment including air, waters, sediment, and soil.7−12 Studies further suggested © 2013 American Chemical Society
that OPFRs were absorbed into organisms and transferred through food chains,13,14 including accumulation in humans.13,15,16 Although OPFRs may be less toxic to organisms compared with PBDEs,17 adverse effects of OPFRs have still been observed in organisms and humans. For instance, tris(1,3dichloroisopropyl) phosphate (TDCPP) was found to be a mutagen and was recently determined to be potentially neurotoxic.18 Tri-n-butyl phosphate (TnBP) and tri(2-chloroethyl) phosphate (TCEP) also showed neurotoxic properties after chronic exposure.19,20 A recent study reported a link between triphenyl phosphate (TPhP) exposure and a decline in sperm concentration.21 On the basis of potential adverse effects Received: Revised: Accepted: Published: 63
July 18, 2013 November 22, 2013 December 6, 2013 December 6, 2013 dx.doi.org/10.1021/es403186z | Environ. Sci. Technol. 2014, 48, 63−70
Environmental Science & Technology
Article
electronic products but varied in the type and amount of these products. In the offices, the sampling device was placed near the center of the room, and sampling took place at 1 m above the ground. All adjacent doors were closed, but the windows were open, to simulate common conditions during working hours. People were not present in the offices, and the temperature ranged from 16 to 20 °C during the sampling time. An Anderson eight-stage nonviable cascade impactor (Tisch Environmental., Cleves, OH, U.S.A.) with a back-up filter was employed to collect size segregated PM at a flow rate of 28.3 L/ min. The cutoff aerodynamic diameters for each stage were 9.0 μm, respectively. Prior to sampling, glass fiber filters (GFFs) were baked at 550 °C for 4 h to reduce any residual organic matter. A 24 h equilibrium process for GFFs in a desiccator before weighing was used in both pre- and postsample collection. Gravimetric measurements were conducted with a high precision (0.00001 g) balance. The PM was sampled for a continuous 48 h to obtain sufficient PM masses and also to minimize the interday variations. The total sampling air volume was about 81.5 m3 for each sampled office. After weighing, filters were folded, wrapped in aluminum foil, and stored in a refrigerator at −20 °C before analysis. Filters were spiked with 25 ng TnBP-d27 as the recovery surrogate and then Soxhlet extracted with 150 mL n-hexane/ acetone (1:1, v/v) for 24 h. The extract was concentrated to about 2 mL on a vacuumed rotary evaporator (Buchi, Switzerland). A glass column packed with 4 g of Florisil, 4 g of neutral silica gel, and 2 g of anhydrous sodium sulfate, from bottom to top, was used for cleanup. The column was prewashed with 40 mL methanol and 40 mL n-hexane prior to loading the extract. Dichloromethane (150 mL) was used to elute the analytes. The eluted fraction was evaporated to near dryness on the rotary evaporator, transferred to a 2 mL glass vial, and dried under a gentle stream of nitrogen gas. After adding 25 ng TPhP-d15, the analytes were reconstituted to 0.5 mL with methanol. Finally, the sample was passed through a disc filter (0.2 μm, Waters, Milford, MA, U.S.A.) before UPLCMS/MS analysis. UPLC-MS/MS Analysis. Sample analysis was accomplished by an ultraperformance liquid chromatography-tandem electrospray-triple quadrupole mass spectrometry system (Xevo TQ-S, Waters, Milford, MA, U.S.A.). A 2 μL aliquot of sample was injected into a Waters BEH C18 column (2.1 mm × 50 mm, 1.7 μm) coupled with a VanGuard precolumn (C18 column, 2.1 mm × 5 mm, 1.7 μm). A binary eluent of water (A) and acetonitrile (B) both containing 0.1% formic acid was used for the separation of analytes at a flow rate of 0.4 mL/min. The gradient was set as follows (with reference to B): 0 min 10% B, 4 min 50% B, 6 min 50% B, 7 min 100% B, 9 min 100% B, and 10 min 10% B. The mass spectrometry was operated in the positive ion mode with multiple reaction monitoring. The capillary voltage was set to 3.5 kV. Nitrogen was applied as the desolvation gas with a flow of 800 L/h at 400 °C. Argon served as the collision gas. The detection parameters of each analyte are listed in Figure S1 and Table S1 of the Supporting Information. QA/QC. All of the samples were spiked with labeled compounds to monitor recovery. A method blank with each sample batch (nine samples) was included. The recoveries of the labeled compounds were 85.5−109% for OPFRs (Table S1, Supporting Information). The limit of detection (LOD) of OPFRs was defined as three times the signal-to-noise (S/N =
of OPFRs, the U.S. Environmental Protection Agency is conducting full risk assessments on some OPFRs.22 With the widespread use of products containing OPFRs in houses, the occurrence of OPFRs is expected to increase in indoor environments including air, suspended particulate matter (PM), and dust. Levels of OPFRs have been reported in indoor environments, and they are generally higher than under outdoor conditions.6 Therefore, inhalation is believed to be one of main pathways for exposure to OPFRs for people in indoor environments, especially for young children and elderly people who tend to spend more time indoor. Most recent studies considering OPFRs in indoor environments focused on dust and air. In contrast, few surveys reported the occurrence of OPFRs in suspended PM. It is well known that the inhalable particles may induce higher risks because these particles are small enough to reach deep into the lung. Furthermore, previous studies revealed that the risk of toxic chemicals adsorbed on PM depends on the size of particles.23 Therefore, particle size-specific classification may provide improved information for exposure assessments of OPFRs. Offices are important indoor spaces for many people in addition to homes. Working people spend 8 h or more in the office on working days. Therefore, exposure to OPFRs in offices is likely an important pathway of exposure to airborne OPFRs due to the higher levels of OPFRs in offices.6,17 In the present study, we collected suspended particles with different diameters in offices and analyzed the levels and characteristics of 10 OPFRs on the particles. Preliminary exposure assessments were then conducted to evaluate OPFRs exposure for people working in these office spaces.
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MATERIALS AND METHODS Chemicals and Reagents. Standards of TnBP (99.5%), trin-propyl phosphate (TnPP, 99.5%), TCEP (98.5%), and tributoxyethyl phosphate (TBEP, 93.0%) were purchased from Dr. Ehrenstorfer GmbH (Augsburg, Germany). TPhP (100%), tri(chloropropyl) phosphate (TCPP, 99.9%), and TDCPP (97.8%) were obtained from Accustandard (New Haven, CT, U.S.A.). Tri(2-ethylhexyl) phosphate (TEHP, >98%) and 2-ethylhexyl diphenyl phosphate (EHDPP, >90%) were provided by Tokyo Chemical Industry (Tokyo, Japan). Tricresyl phosphate (TCrP, 99%) was obtained from J&K Scientific (Beijing, China). Isotope-labeled standards TnBP-d27 (98−99%) and TPhP-d15 were purchased from Cambridge Isotope Laboratories (Andover, MA, U.S.A.) and Sigma-Aldrich (St. Louis, MO, U.S.A.), respectively. Methanol (LC/MS grade) and dichloromethane (Envi grade) were purchased from Fisher Scientific (Fair Lawn, NJ, U.S.A.) and Anaqua Chemicals Supply Inc. Limited (Houston, TX, U.S.A.), respectively. Acetonitrile and other organic solvents of residue analysis grade were obtained from J. T. Baker (Phillipsburg, NJ, U.S.A.). Florisil (Supelco, 150−250 μm) and silica gel (ICN, 60−200 μm) were heated for activation before use. Analytical grade anhydrous sodium sulfate was prewashed with dichloromethane and activated in 450 °C for 4 h. Stock solutions of analytes and isotope-labeled standards were prepared in methanol and kept at 4 °C. Sample Collection and Preparation. Particulate matter was collected in 10 office rooms during February to April, 2013, in Hangzhou, China. These offices with different areas were located in three buildings that were not adjacent to any industrial activity and at 100 m or more from main traffic roads. The offices were equipped with common office furniture and 64
dx.doi.org/10.1021/es403186z | Environ. Sci. Technol. 2014, 48, 63−70
Environmental Science & Technology
Article
3) and ranged from 0.02 to 0.88 pg/m3. For the results below the LOD, the value was set as half of the LOD in data analysis. Deposition of OPFRs in the Human Respiratory Tract. The deposition efficiency and flux of inhaled OPFRs in the respiratory tract of a normal adult were estimated from the sizespecific distribution of OPFRs using the International Commission on Radiological Protection (ICRP) model.23 The model divides respiratory tract into several regions for consideration of deposition. In the present study, the respiratory tract was divided into three regions, i.e., head, tracheobronchial, and alveoli. The deposition fractions of inhaled particles and OPFRs were calculated in the three regions using a sitting breathing rate of 0.54 m3/h as recommended by ICRP.23 The deposition flux was estimated using the deposition efficiency of the mean diameter in each particle size fraction.24 The mean diameter for size fraction >9.0 μm was assumed to be 10 μm.
Table 1. Concentrations of 10 Target OPFRs Detected in Offices
RESULTS AND DISCUSSION Particulate Matter Concentration and Size Distribution. Particulate matter was detected at a range from 47.1
a
concentration (ng/m3) TCEP TnPP TCPP TDCPP TPhP TnBP TBEP TCrP EHDPP TEHP ∑OPFRs ∑ClOPFRsa ∑ClOPFRs/∑OPFRs
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range
mean
median
1.03−13.38
