Measurement of Vapor Pressures of Selected PBDEs

Article pubs.acs.org/jced

Measurement of Vapor Pressures of Selected PBDEs, Hexabromobenzene, and 1,2-Bis(2,4,6-tribromophenoxy)ethane at Elevated Temperatures Hidetoshi Kuramochi,*,† Hidetaka Takigami,† Martin Scheringer,‡ and Shin-ichi Sakai§ †

Center for Material Cycles and Waste Management Research, National Institute for Environmental Studies, Tsukuba, Ibaraki, 305-8506, Japan ‡ Institute for Chemical and Bioengineering, Swiss Federal Institute of Technology, ETH Zurich, HCI G127, CH 8093, Zurich, Switzerland § Environment Preservation Research Center, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501, Japan ABSTRACT: Vapor pressures (pi) of selected brominated flame retardants (BFRs), such as three polybrominated diphenyl ethers, PBDEs, 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47), 2,2′,4,4′,5pentabromodiphenyl ether (BDE-99), and 2,2′,4,4′,5,5′-hexabromodiphenyl ether (BDE-153), and two non-PBDE BFRs, hexabromobenzene (HBB) and 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) in the temperature range of (313 to 423) K, were measured by the gas saturation method. The standard uncertainties of temperature and vapor pressure measurements were estimated to be within ± 0.08 K and typically ca. ± 3.9 %, respectively. The temperature dependence of pi, namely, enthalpy of sublimation (ΔsubH), was determined by fitting the experimental data with the Clausius−Clapeyron equation. From the equation and our previous works on water solubility, pi and Henry’s law constant at 298 K for those BFRs were predicted. On the basis of these results, the environmental partitioning characteristics were also discussed.

1. INTRODUCTION The RoHS Directive (Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment) bans the use of polybromodiphenyl ethers (PBDEs) except for decabromodiphenyl ether (BDE-209) in the European Union. In addition, some PBDEs have been newly listed as persistent organic pollutants (POPs) in the Stockholm Convention. Recently, in the United States, three companies have agreed to phase out production and sale of BDE-209 for most uses by 2013.1 Therefore, research and development on non-PBDE flame retardants used as alternatives to PBDEs receives increasing attention. Other brominated flame retardants (BFRs) and organophosphorus flame retardants have been used as replacements for PBDEs. However, environmental contaminations caused by such alternatives have been reported by many research groups. Focusing on bis-(2,4,6-tribromophenyl)ethane (BTBPE) and hexabromobenzene (HBB) as alternatives, the concentration of BTBPE and HBB in air and precipitation samples at various sites around the Great Lakes was quantified.2 These compounds were found in the egg pools of herring gulls in the Great Lakes.3 In the European Arctic area, the spatial distribution of both alternatives was reported.4 In terms of protection against such new contamination, it is necessary to obtain a better understanding of the environmental behavior of the alternatives and PBDEs and human exposure to them. © 2013 American Chemical Society

Therefore, the physicochemical properties of those compounds, e.g., vapor pressure (pi), water solubility (Sw), and 1-octanol/ water partition coefficient (Kow), are of importance for the understanding of the environmental fate and human exposure. In our previous works,5−8 we measured the properties of PBDEs and non-PBDE BFRs. However, there is little experimental data on vapor pressure, pi, for these BFRs. Even if the pi values are available, they are often determined by an indirect measurement method.9,10 We consider that the value measured by a direct measurement method should be available as Fu and Suuberg reported vapor pressures of some other PBDEs measured by a direct measurement method.11,12 In this work, therefore, pi of three PBDEs and two nonPBDE BFRs at different temperatures from 313 K to 423 K was measured using the gas saturation method. The enthalpy of sublimation for each substance was determined by fitting the measured pi data with the Clausius−Clapeyron equation to predict their vapor pressure at 298 K (pio). In addition, Henry’s law constant (Hw) of these compounds at 298 K was derived from the pio data and our previous Sw data. Finally, not only air−water partitioning but also persistence and long-range Received: June 3, 2013 Accepted: November 21, 2013 Published: December 13, 2013 8

dx.doi.org/10.1021/je400520e | J. Chem. Eng. Data 2014, 59, 8−15

Journal of Chemical & Engineering Data

Article

Table 1. Description of the Brominated Flame Retardants Used in the Experiments

a

chemical name

source

puritya

analysis method

2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) 2,2′,4,4′,5-pentabromodiphenyl ether (BDE-99) 2,2′,4,4′,5,5′-hexabromodiphenyl ether (BDE-153) hexabromobenzene (HBB) 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE)

AccuStandard AccuStandard AccuStandard Sigma-Aldrich Kanto Chemical

1.00 0.983 0.993 0.98 0.95b

GC/MSc GC/MSc GC/MSc GC/MSc GC/MSc

The purities except for BTBPE are given by the suppliers. bDetermination in this study. cGas chromatograph mass spectrometer.

controlled gas oven at a constant flow rate of 20 cm3·min−1 or 40 cm3·min−1. In the generator column, saturated vapor of the sample chemical was generated. The sample compound in the saturated vapor was trapped in a mini stainless steel column and a Sep-Pak PS-Air cartridge (Waters Corporation, Milford, MA, USA). The amount of chemical in the traps, Q, was determined as follows: For PBDEs and HBB, following acetonitrile extraction of the adsorbed sample from both the traps, the concentration of the extraction solution was analyzed using a Waters Associates Separation Module 2695 HPLC system with a model 2487 variable-wavelength ultraviolet detector (Waters Corporation, Milford, MA, USA) under isocratic conditions. The HPLC-UV analytical condition was the same as that in our previous paper.6,7 The Q value was calculated from the concentration of sample chemical and the volume eluted from the traps. For BTBPE, acetonitrile extraction and HPLC-UV analysis were replaced with toluene extraction and GC/MS analysis, respectively. The GS/MC

transport potential, which are key parameters for environmental hazard assessment, were estimated using EPIsuite,13 and the OECD Pov and LRTP Screening Tool.14,15

2. MATERIALS AND METHODS 2.1. Chemicals. The following PBDEs were used in this study: 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47), 2,2′,4,4′,5-pentabromodiphenyl ether (BDE-99), and 2,2′,4,4′,5,5′-hexabromodiphenyl ether (BDE-153) purchased from AccuStandard Inc. (New Haven, CT, USA). Hexabromobenzene (HBB) and 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) were included as BFRs for the replacement of PBDEs. HBB was purchased from Sigma-Aldrich Co. (St. Louis, MO, USA), and technical grade BTBPE was supplied from Kanto Chemical Co., Inc. (Tokyo, Japan). The details about the chemicals used in this study are listed in Table 1. All flame retardants were used without further purification. 2.2. Vapor Pressure (pi) Measurement. Although several methods can be used to measure very low vapor pressure of up to 10−5 Pa, the gas saturation method was used in this work, as shown in Figure 1, due to its ability to mitigate the effect of

Figure 1. Schematic description of the apparatus used in our gas saturation method.

impurity compounds on vapor pressure measurements via chromatographic analysis of vaporized compounds. The apparatus is based on the OECD (Organization for Economic Cooperation and Development) Guideline for the Testing of Chemicals16 and an earlier work.17 In this method, first, a generator column to generate a saturated vapor is set up as follows; a stainless steel column (2.2 (i.d.) × 600 (length) mm) was packed with 60 to 80 mesh glass beads (Chromosorb AWA; Chromatography Research Supplies, Louisville, KY, USA), coated with solid sample compound. The weight ratio of the solid sample to glass beads was about 0.2 %. The procedure of washing and coating glass beads before the preparation of the generator column was carried out according to that in our previous works.6,7 Next, pure nitrogen gas was flowed as a carrier gas into the generator column in a thermostatically

Figure 2. Vapor pressures (pi) of anthracene (A) and pyrene (B) as a function of temperature. Solid circles, this work for anthracene; open circles, refs for anthracene;20−25 solid triangles, this work for pyrene; open triangles, refs for pyrene.23−27 9


308.62 313.70 323.59 333.63 343.60

crystal crystal crystal crystal crystal

10

a

0.00364 (0.053) 0.0141 (0.017) 0.0456 (0.032) 0.121 (0.040) 0.329 (0.016) 0.827 (0.012)

Pa

pi

313 318 323 328 333 338 343 348 353 358 363

K

crystal crystal crystal crystal crystal crystal crystal

311.13 320.10 330.14 341.18 346.14 357.14 366.17

K

T

ref 23

0.0058 0.0105 0.0193 0.039 0.0675 0.0987 0.1688 0.3056 0.5252 0.9247 1.244

Pa

0.00209 0.00863 0.0243 0.0852 0.164 0.428 0.945

Pa

pi

crystal crystal crystal

298 323 348

K

crystal crystal

condensed phase

condensed phase

T

condensed phase

crystal crystal crystal crystal crystal crystal crystal crystal crystal crystal crystal

condensed phase

ref 21

T

pi

ref 20

303.2 312.49

K

T

ref 24

0.00106 0.023 0.322

Pa

pi

0.00107 0.00334

Pa

pi

crystal crystal crystal crystal crystal crystal

condensed phase

crystal crystal crystal crystal crystal crystal crystal crystal crystal

Pa

pi

crystal crystal crystal crystal crystal crystal crystal

322.0 337.1 342.1 347.1 352.3 356.8 362.1 372.0 381.4

K

T Pa

pi

300.9 312.9 320.8 327.8 333.3 345.9 347.3

K

T

ref 23

0.00895 0.0531 0.0943 0.147 0.227 0.339 0.599 1.30 2.81

condensed phase

ref 25

0.00102 0.035 0.0849 0.267 0.359 0.588

condensed phase

pyrene

293.2 323.3 333.2 343.2 348.2 353.7

K

T

ref 22

anthracene


condensed phase

0.00114 0.00575 0.0162 0.0355 0.0620 0.204 0.258

Pa

pi

348 361 364 369 377 384

K

T

ref 26

crystal crystal crystal crystal crystal

condensed phase

0.2118 0.508 0.717 1.034 2.016 3.871

Pa

pi

285.5 292.4 298.2 303.3 308.1

K

T

ref 24

crystal crystal crystal crystal

353.26 363.25 373.26 383.29

K

T

322.2 327.0 329.1 333.4 336.3 338.7 340.4 341.2 342.3 343.6 344.2 346.4 348.2

K

T

ref 25

ref 27

crystal crystal crystal crystal crystal crystal crystal crystal crystal crystal crystal crystal crystal

condensed phase

condensed phase

0.000160 0.000371 0.000826 0.00150 0.00264

Pa

pi

Standard uncertainties u are u(T) = ± 0.05 K, and u(pi) differs among temperatures and samples. Therefore, all the values in the parentheses in columns pi are given as ur(pi).

K

313.61 323.81 333.53 343.36 353.24 363.63


T

condensed phase

Pa

pi

0.00279 (0.034) 0.00541 (0.013) 0.0183 (0.016) 0.0599 (0.029) 0.164 (0.029)

this work

K

condensed phase

T

this work

Table 2. Vapor Pressures of Anthracene and Pyrene at Different Temperaturesa

0.30 0.764 1.853 4.360

Pa

pi

0.0160 0.0260 0.0333 0.0491 0.072 0.0943 0.110 0.119 0.131 0.141 0.164 0.192 0.260

Pa

pi

Journal of Chemical & Engineering Data Article


Pa

2.54·10−4 9.18·10−4 3.16·10−3 8.63·10−3 2.42·10−2 7.18·10−2

(0.021) (0.031) (0.022) (0.026) (0.035) (0.041) crystal crystal crystal crystal liquid liquid

condensed phase 323.60 333.51 343.46 353.50 363.39 373.56

K

T

1.32·10−4 5.35·10−4 1.82·10−3 4.86·10−3 1.29·10−2 4.24·10−2

Pa

pi

(0.010) (0.013) (0.025) (0.005) (0.019) (0.026) crystal crystal crystal crystal crystal crystal

condensed phase

343.44 353.11 363.19 373.17 383.16 392.81

11

2.25·10−5 1.29·10−4 4.26·10−4 1.37·10−3 4.43·10−3 1.50·10−2

Pa

pi

(0.050) (0.029) (0.030) (0.028) (0.015) (0.006) crystal crystal crystal crystal crystal crystal

condensed phase

363.28 373.39 383.22 392.95 402.92 412.93

K

T

2.33·10−3 7.39·10−3 1.78·10−2 4.48·10−2 1.16·10−1 2.55·10−1

Pa

pi

hexabromobenzene (HBB)

(0.024) (0.029) (0.025) (0.039) (0.039) (0.029)


condensed phase

373.38 383.23 392.86 403.16 412.64 422.81

pio/Pae pio,sl/Pae pio,sl [lit]/Pae ΔsubH/kJ·mol−1e ΔfusH/kJ·mol−1e Tm/Ke Hw/Pa·m3 mol−1e Sw/mg·L−1e

2,2′,4,4′,5-pentabromodiphenyl ether (BDE-99) 3.67·10−6 2.17·10−5 6.82·10−5,b 1.76·10−5c 115 27.5 355.0 4.74·10−1 4.37·10−3

2,2′,4,4′-tetrabromodiphenyl ether (BDE-47)

3.26·10−5 1.03·10−4 3.19·10−4,b 1.86·10−4c 105 17.3 356.9 1.08 1.47·10−2

1.28·10−8 6.10·10−7 8.43·10−6,b 2.09·10−6c 143 30.2 436.6 1.63·10−1 5.04·10−5

2,2′,4,4′,5,5′-hexabromodiphenyl ether (BDE-153)

4.84·10−7 7.07·10−5 7.50·10−4c 118 24.6 598.8 2.43 1.10·10−4


K

T

(0.050) (0.027) (0.041) (0.021) (0.019) (0.044)

167 36.8a 500.4a 5.56·10−2 2.79·10−7d

2.26·10−11 9.12·10−9

1,2-bis(2,4,6-tribromo-phenoxy)ethane (BTBPE)

2.09·10−5 7.87·10−5 2.38·10−4 8.68·10−4 3.44·10−3 1.10·10−2

Pa

pi

1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE)

Measured in this research. Standard uncertainties u for Tm and ΔfusH are u(T) = 0.5 K, and u(pi) = 1.8 kJ·mol−1. bWong et al.9 cTittlemier et al.10 dEstimated value by the UNIFAC model.7 e pio, vapor pressure at 298 K; pio,sl, subcooled liquid vapor pressure at 298 K; ΔsubH, enthalpy of sublimation; ΔfusH, enthalpy of fusion; Tm, melting point; Hw, Henry’s law constant; Sw, water solubility.

a

K

T


Standard uncertainties u are u(T) = ± 0.08 K, and u(pi) differs among temperatures and samples. Therefore, all the values in the parentheses in column pi are given as ur(pi).

crystal crystal crystal crystal crystal liquid

pi

2,2′,4,4′,5-pentabromodiphenyl ether (BDE-99)

Table 4. Physicochemical Properties for Three PBDEs and Two Non-PBDE BFRs

a

K

313.54 323.60 333.47 343.36 353.37 363.45

condensed phase

T


Table 3. Vapor Pressure (pi) of Three PBDEs and Two Non-PBDE Brominated Flame Retardantsa

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12

a

Estimated value by the UNIFAC model.7 bMw, molecular weight; t1/2, air, half-life in air; t1/2, water, half-life in water; t1/2, soil, half-life in soil; Kow, 1-octanol/water partition coefficient; Kaw, air/water partition coefficient; Pov, overall persistence; CTD, characteristic travel distance; TE, transfer efficiency.

551.49 11 207 17 280 34 560 6.07 −3.01 2033 21 033 257 643.58 554 17 280 34 560 8.05 −4.63 2075 2883 12.6 564.69 233 17 280 34 560 7.35 −3.72 2073 2732 9.33 485.79 128 5760 11 520 6.78 −3.36 690 2053 3.66

3. RESULTS AND DISCUSSION To verify the consistency of the gas saturation method, pi of anthracene (≥ 99 %, Aldrich) and pyrene (≥ 99 %, Aldrich) between 308 K and 363 K was measured. In this measurement, a Waters Associates model 2475 fluorescence detector (Waters Corporation, Milford, MA, USA) was used to quantify the amount of vaporized anthracene as well as pyrene from the generator column. The optimal excitation/emission wavelengths for anthracene and pyrene were 248 nm/400 nm and 238 nm/398 nm, respectively. The vapor pressures of both polyaromatic compounds at various temperatures have been measured by many researchers, and thus compared with literature data,20−27 as shown in Figure 2 and Table 2. These obtained values were in good agreement with the literature data. The coefficient of variation for the experimental data at each temperature was within 2


Table 5. Input Parameters and Calculation Results by OECD Pov and LRTP Screening Tool


where V is the nitrogen gas volume flowed through the generator column, Mw is the molecular weight of the sample, and R is the ideal gas constant. For the determination of pi at each temperature, three or four generator columns were used. In comparing the obtained vapor pressure values with the literature data of subcooled liquid vapor pressures, the fugacity ratio must be calculated from the enthalpy of fusion (ΔfusH) and melting point (Tm). Both values for the present compounds except for BTBPE have been measured in our previous works.6,7 Therefore, Tm and ΔfusH of BTBPE were measured with a SII DSC 6200 differential scanning calorimeter (Seiko Instruments, Chiba, Japan). The weight of a sample (BTBPE) in the DSC cell was carefully measured on an analytical balance (Mettler-Toledo Co.). The sample was frozen at less than 200 K and was then heated up to 600 K on the DSC apparatus. The rate of heating was fixed at 5 K·min−1. 2.3. Model and Calculation. The OECD Pov and LRTP Screening Tool was used for the evaluation of the persistence and long-range transport potential (LRTP) of the measured BFRs. For each BFR, the tool requires the three degradation half-lives in air, water, and soil and also two partition coefficients, log Kow and log Kaw (= Hw/RT), as chemical-specific input data. Whereas log Kow and Hw are available from our previous works6,7 and the present results, respectively, measured data for the degradation half-lives are not available. Therefore, the half-lives for each BFR were estimated with EPI-Suite. To estimate the half-life in water (t1/2, water), however, the biodegradation score obtained from BIOWIN3 in EPI-Suite was converted to t1/2, water according to the scheme by Aronson et al.19 The tool provides the overall persistence (Pov; unit: days) and two kinds of long-range transport potentials such as characteristic travel distance (CTD; unit: km) and transfer efficiency (TE; unit: %) as output. Pov is a measure of the time scale of degradation of the chemical in the whole environment. CTD represents a transportoriented metric of LRTP. It is the distance from the source point to the point at which the chemical’s concentration at the source has decreased to 37 %. TE is a target-oriented LRTP indicator, which is defined as a ratio of emission flux from the source region to deposition flux into a remote region (target region). Details of these parameters are described in the paper by Wegmann et al.15

Mw/g·mol−1b t1/2, air/hb t1/2, water/hb t1/2, soil/hb log Kowb log Kawb Pov/daysb CTD/kmb TE/%b

(1)

2,2′,4,4′,5-pentabromodiphenyl ether (BDE-99)

Q RT V Mw


pi =

1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE)

analysis using an Agilent 7890A/5975C GC-MS (Agilent Technologies, Santa Clara, CA) was performed according to an early work.18 Finally, the pi value was determined by

687.64 8.64 17 280 34 560 8.99a −4.65 2075 2744 11.6

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where ΔsubS denotes the entropy of sublimation. The ΔsubH values are listed in Table 4. The ΔsubH value of BDE-153 and BTPBE was 1.2- to 1.6-fold higher than that of the others. It indicates that the intermolecular interaction in the pure solid of both compounds is stronger than that of the others. In addition, vapor pressure at 298 K (pio) and subcooled liquid vapor pressure at 298 K (pio,sl) values were estimated by the Clausius−Clapeyron equation and the fugacity ratio derived from the enthalpy of fusion (ΔfusH) and melting point (Tm) measured in our previous works.6,7 The calculated values are summarized in Table 4. pio values of the present BFRs ranged from 3.26·10−5 Pa to 2.26·10−11 Pa. Especially, the pio value of BTBPE was much lower than that of the others by 2 to 6 orders of magnitude, which indicates that BTBPE has the lowest air emission potential at room temperature. With respect to pio,sl, the calculated value was compared with the literature data obtained by indirect methods9,10, as shown in Table 4. The pio,sl values of BDE-47 and -99 were in good agreement with the literature data,9,10 whereas pio,sl values of BDE-153 and HBB were lower than the literature values by up to 1 order of magnitude. Overall, we consider the agreement of our results for pio,sl with earlier results obtained with indirect methods, in particular, for BDE-47, BDE-99, and also BDE-153, as an indication that indirect methods are reasonable for very low vapor pressures of up to 10−4 Pa or 10−5 Pa. On the basis of our previous water solubility (Sw) data of PBDEs and HBB6,7 and their pio values, Henry’s law constant (Hw) values of these chemicals were estimated by

% to 6 %. These results demonstrate that our apparatus can provide reliable experimental values for low vapor pressures. The experimental results for BFRs are shown in Table 3. In the case of the three PBDEs (BDE-47, -99, and -153), as the bromine number in the molecular structure increased, pi values significantly decreased by 1 or 2 orders of magnitude. Results for HBB and BTBPE, which are hexabromo compounds like BDE-153, show that pi values of HBB were higher than those of BDE-153, whereas pi values of BTBPE were much lower than those of BDE-153. From the experimental data, the enthalpy of sublimation (ΔsubH), namely, temperature dependence of pi, was calculated by fitting the plots of pi against the reciprocal temperature (1/T), as shown in Figure 3, using the Clausius−Clapeyron equation ln pi = −

ΔsubH Δ S + sub RT R

(2)

Hw =

pio Sw

(3)

Since the Sw value of BTBPE is not available, it was estimated by the UNIFAC model with our parameter sets for the bromine group.7 The Hw values are listed in Table 4. For the PBDEs, Hw decreased with an increase in bromine content. Therefore, PBDEs with higher bromine numbers have less partition potential from water to air. The Hw value of HBB was higher than that of BDE-47, and thus, HBB is considered to be transferred more easily from water to air. In contrast, the Hw value of BTBPE was the lowest of the present BFRs. However, the value was relatively close to that of

Figure 3. Vapor pressures of three PBDEs and two non-PBDE brominated flame retardants. Open squares, BDE-47; open circles, BDE-99; open triangles, BDE-153; gray triangles, HHB; black triangles, BTBPE.

Figure 4. Pov and LRTP (characteristic travel distance (A) and transfer efficiency (B)) of three PBDEs as well as HBB and BTBPE calculated by the OECD Pov and LRTP Screening Tool. Open square, BDE-47; open circle, BDE-99; open triangle, BDE-153; gray triangle, HHB; black triangle, BTBPE. 13



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BDE-153. In other words, although pio of BTBPE was much lower than pio of BDE-153 by 2 orders of magnitude, BTBPE has a similar partition potential of BDE-153 from water to air. The physicochemical properties listed in Table 4 were used to estimate the overall persistence (Pov) and long-range transport potential (LRTP) of the present BFRs. Pov, characteristic travel distance (CTD), and transfer efficiency (TE) were calculated using the OECD Pov and LRTP Screening Tool. The degradation half-lives and partition coefficients used as input parameters are summarized in Table 5. The calculated results for Pov and LRTP are also listed in Table 5 and further shown in Figure 4. In this study, we focus on BTBPE and HBB, namely, the alternatives to PBDEs, since it is well-known that the three PBDEs have high persistence and LRTP. As shown in Figure 4, the Pov and CTD and TE results are located above the vertical line and near or above horizontal line, which indicate Pov and CTD values of POPs reference substances as reported by Klasmeier et al.28 The Pov values for both alternatives are higher than that of BDE-47 and similar to those of BDE-99 and BDE-153. In terms of CTD and TE, the values of BTBPE were the same as those of BDE-153, whereas those of HBB exceeded the others by 1 order of magnitude. It should be noted that both characteristics of HBB and BTBPE were higher than those of the three PBDEs included here and similar to those of the PBDEs that have been included as POPs in the Stockholm Convention on POPs.

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4. CONCLUSIONS Vapor pressures of three PBDEs (BDE-47, -99, and -153) and two non-PBDE BFRs (BTBPE and HBB) were measured at different temperatures from 313 K to 423 K by the gas saturation method. The vapor pressures measured ranged from 2·10−5 Pa to 1·10−2 Pa. The enthalpy of sublimation for each chemical was obtained from the measured vapor pressures by means of the Clausius−Clapeyron equation. The sublimation enthalpy of BDE-153 and BTBPE was higher than that of the others by a factor of 1.2 to 1.6. The vapor pressure and Henry’s law constant at 298 K for the compounds were derived from the present results and our previous works. The lowest and highest vapor pressure values at 298 K were 3.17·10−5 Pa for BDE-47 and 2.26·10−11 Pa for BTBPE, respectively. In addition, the persistence and long-range transport potential (LRTP) were estimated using the OECD Pov and LRTP Screening Tool. The estimated results indicate that HBB and BTBPE as well as three PBDEs have similar or even higher persistence and LRTP than acknowledged persistent organic pollutants.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Funding

The work described in this paper was funded by the Japanese Ministry of the Environment, Waste Management and Recycling Department, Waste Management Division. Notes

The authors declare no competing financial interest.

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REFERENCES

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Measurement of Vapor Pressures of Selected PBDEs

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