Photodegradation Pathways of Nonabrominated Diphenyl Ethers, 2

Jul 8, 2009 - Response to “Comment on 'Photodegradation Pathways of Nonabrominated Diphenyl Ethers, 2-Ethylhexyltetrabromobenzoate, and Di(2-ethylhe...
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Environ. Sci. Technol. 2009, 43, 5739–5746

Photodegradation Pathways of Nonabrominated Diphenyl Ethers, 2-Ethylhexyltetrabromobenzoate and Di(2-ethylhexyl)tetrabromophthalate: Identifying Potential Markers of Photodegradation ELIZABETH F. DAVIS AND HEATHER M. STAPLETON* Duke University, Nicholas School of the Environment, Durham, North Carolina 27708

Received April 3, 2009. Revised manuscript received June 11, 2009. Accepted June 24, 2009.

Photodegradation kinetics of several polybrominated diphenyl ethers (PBDEs), particularly decabromodiphenyl ether (BDE 209), have been reported in various matrixes, demonstrating that it photodegrades primarily via debromination. However, it has been difficult to determine the primary pathways by which bromine is cleaved from BDE 209 to form nona- and octabrominated congeners. In this study, photodegradation of the three nonaBDE congeners (i.e., BDE 206, 207, and 208) was examined individually in three different solvents exposed to natural sunlight and then analyzed to identify the primary degradation products. Rapid degradation of nonaBDEs (halflives ranging from 4.25 to 12.78 min) was observed coincident with formation of octa- and heptabrominated PBDEs. BDE 207 photodegraded most rapidly while BDE 206 photodegraded the slowest. The photodegradation pathways of each nonaBDE congener were consistent among the different solvent matrixes tested; however, mass balances were found to vary with the type of solvent used in the experiment (recovery ranging from 76 to 95%). The octabrominated congener, BDE 202, and the ratio of BDE 197 to BDE 201, were identified as congeners that may serve as environmental markers of photolytic debromination of decaBDE. Additional photodegradation studies were conducted with two new brominated flame retardants used in replacements for pentaBDE mixtures: 2-ethylhexyltetrabromobenzoate (TBB) and di(2-ethylhexyl)tetrabromophthalate (TBPH). Both TBB and TBPH underwent photolysis more slowly than nonaBDEs (half-lives ranging from 85.70 to 220.17 min) and primarily formed debrominated products.

Introduction Polybrominated diphenyl ethers (PBDEs) have historically been the most widely used class of brominated flame retardants (BFRs), being applied as additives to combustible materials such as polyurethane foam, plastics, and textiles in order to decrease flammability (1). PBDEs have received a great deal of attention due to their persistence and potential toxicity; additionally, they have been detected globally in * Corresponding author e-mail: [email protected]. 10.1021/es901019w CCC: $40.75

Published on Web 07/08/2009

 2009 American Chemical Society

humans, wildlife, and environmental media (2). As a result, two of the three commercial PBDE mixtures, pentaBDE and octaBDE, were banned in Europe and voluntarily phased out in the United States in 2004 (3). The third commercial mixture, decaBDE (which consists primarily of the fully brominated diphenyl ether congener, BDE 209) remains one of the most heavily used BFRs worldwide. However, decaBDE has recently begun to face restrictions in the United States and elsewhere (4-6). Several studies have shown that BDE 209 can undergo photolytic degradation in solvents when exposed to UV radiation and/or natural sunlight (7-10). Generally, these studies all suggest that decaBDE undergoes reductive debromination, forming less brominated congeners which can be more recalcitrant to further breakdown. This breakdown pattern is of some concern as the lower brominated PBDE congeners formed as a result of debromination are generally more persistent, bioaccumulative, and toxic (11, 12). The photodegradation of decaBDE has been investigated in a wide variety of natural and artificial matrixes. Soderstrom et al. exposed decaBDE in toluene, silica gel, sand, soil, and sediment to artificial UV radiation; photodegradation kinetics were highly variable among the different matrixes, with halflives ranging from less than 15 min (toluene) to 200 h (soil) (8). Additionally, Stapleton et al. calculated a half-life of 301 h for decaBDE photodegradation in house dust (7). These variations in degradation rates between sample matrixes have been explained by differences in the radiation shielding of the matrix, as well as the presence of light coabsorbers in different matrixes (7, 8). Several studies have investigated photodegradation reactions in artificial matrixes such as solvents, which facilitate photodegradation kinetics by providing minimal radiation shielding as well as even exposure to light sources. Thus, more can be learned about the basic chemical behaviors of individual PBDE congeners. Six PBDEs (BDE 28, 47, 99, 100, 153, and 183) have been shown to undergo reductive photodegradation in hexane (10). Eriksson et al. investigated the photodegradation kinetics of 15 PBDE congeners in different solvents exposed to UV light, determined the major products of BDE 209 degradation, and examined the photodegradation kinetics of all three nonaBDEs (2,2′,3,3′,4,4′, 5,5′,6-nonabrominated diphenyl ether (BDE 206), 2,2′,3,3′,4,4′, 5,6,6′-nonabrominated diphenyl ether (BDE 207), and 2,2′,3,3′, 4,5,5′,6,6′-nonabrominated diphenyl ether (BDE 208); see Figure 1 for structures) in methanol and methanol/water (9). These studies have shown that decaBDE debrominates rapidly in solvents. However, it is quite difficult to trace the pathways by which BDE 209 degrades through sequential removal of the bromine atoms. The rapid formation of all three nonaBDEs and several octaBDEs from photodegradation of decaBDE makes it impossible to determine how the individual nonaBDEs degrade to specific octaBDE congeners. This pathway may only be elucidated by an experimental determination of the photodegradation products of nonaBDEs. More information is needed on the specific products and relative kinetics of nonaBDE photodegradation reactions in order to better understand the environmental debromination of decaBDE. Due to the growing restrictions on PBDEs, there has been an increased use of alternate types of BFRs in order to comply with federal fire safety standards. Among these alternate BFRs currently in use are 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (TBB) and di(2-ethylhexyl)-2,3,4,5-tetrabromophthalate (TBPH), the brominated components of the commercial fire retardant mixture Firemaster 550 (FM 550) (13) (See Figure VOL. 43, NO. 15, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 1. Structures of (A) BDE 206, (B) BDE 207, (C) BDE 208, (D) TBB, and (E) TBPH. 1 for structures). TBB and TBPH are also present in the fire retardant mixture known as BZ 54, and TBPH alone is found in a commercial mixture known as DP-45, all of which are manufactured by Chemtura Inc. (14). These previously unstudied compounds were recently detected in indoor dust and San Francisco Bay area biosolids (13, 15). TBPH is a tetrabrominated analogue of di(2-ethylhexyl)-phthalate (DEHP), a common plasticizer now heavily restricted in children’s toys due to its endocrine disrupting effects (16, 17); thus, reductive debromination of TBPH may result in the formation of compounds with properties similar to those of DEHP. No studies to date have evaluated the photodegradation potential or environmental fates of TBPH or TBB; however, these compounds share many similar structural characteristics with PBDEs (e.g., aromatic rings, bromination) and thus may be expected to behave similarly to PBDEs in the environment. The present study was undertaken to determine the relative degradation rates of the three nonaBDE congeners in solvents and to identify their primary degradation products. Additional objectives of this study were to examine the mass balance of the nonaBDEs following photodegradation and to determine if any identifiable degradation products could serve as “markers” of environmental debromination of decaBDE. Here, we refer to “markers” as any photodegradation product of both decaBDE and nonaBDEs that can be found in environmental samples that would not have a commercial source. Furthermore, we included TBB and TBPH in this study as they are becoming more prevalent in the environment and nothing is known about their potential photodegradation behavior.

Materials and Methods Materials. All solvents used in these experiments (hexane, toluene, tetrahydrofuran, and methanol) were chromatography-grade. Clear 4 mL glass vials (screw thread with PTFE caps) with high UV transmittance were purchased from VWR Scientific (West Chester, Pennsylvania). Standards for the three nonaBDE congeners 2,2′,3,3′,4,4′,5,5′,6-nonabrominated diphenyl ether (BDE 206), 2,2′,3,3′,4,4′,5,6,6′-nonabro5740

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minated diphenyl ether (BDE 207), and 2,2′,3,3′,4,5,5′,6,6′nonabrominated diphenyl ether (BDE 208) and the standards for 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (TBB) and di(2ethylhexyl)-2,3,4,5-tetrabromophthalate (TBPH) (all 50 µg/ mL) were purchased from Wellington Laboratories (Guelph, Ontario). The BDE 209 standard (2.156 µg/mL) was prepared from neat BDE 209 purchased from AccuStandard (New Haven, Connecticut). Internal and recovery standards 4′fluoro2,3′,4,6-tetrabromodiphenyl ether (F-BDE 69), 4′fluoro2,3,3′,4,5,6-hexabromodiphenyl ether (F-BDE 160), and 4′,6difluoro-2,2′,3,3′,4,5,5′,6-octabromodiphenyl ether (F-BDE 201) were purchased from Chiron (Trondeheim, Norway); the 13C labeled BDE 209 internal standard was purchased from Wellington Laboratories. Standards. The stock standards of BDE 206, BDE 207, and BDE 208 were diluted to concentrations of 24.42 ( 1.20 µg/mL, 20.88 ( 1.32 µg/mL, and 19.99 ( 3.97 µg/mL, respectively, which were determined using gas chromatography/mass spectrometry operated in electron capture negative ionization mode (GC/ECNI-MS) using previously published methods (7). The TBB and TBPH stock standards were each diluted from 50 µg/mL to final concentrations of 1.0 µg/mL each. All standards were >98% pure. Sample Preparation. To prepare each sample, an aliquot of a given standard (diluted nonaBDE standards: 25 µL; diluted TBB and TBPH standards: 500 µL; stock BDE 209 standard: 150 µL) was added to the bottom of a clear 4 mL glass vial, followed by 1 mL of toluene, methanol, or tetrahydrofuran (THF) such that the starting concentration of the analyte in each vial was approximately 500 ng/mL (or in the case of BDE 209, approximately 300 ng/mL). The vial was then capped and the contents were briefly vortexed. Sunlight exposure experiments were conducted for BDE 206, BDE 207, BDE 208, BDE 209, TBB, and TBPH in each of the three solvents. The BDE 209 experiment was included in order to better compare the kinetics data from our experiments with the published values for BDE 209. The actual average starting concentrations (n ) 9) of BDE 206, BDE 207, BDE 208, BDE 209, TBB, and TBPH in the samples were verified using GC/ECNI-MS, and were found to be 454.06 (

31.99, 408.54 ( 41.67, 427.20 ( 28.50, 216.71 ( 5.13, 426.06 ( 43.05, and 426.80 ( 42.86 ng/mL, respectively. Sunlight Exposure. Exposure was conducted outside the Levine Science Research Center building at Duke University in Durham, North Carolina (35°59′19′′ latitude, 78°54′26′′ longitude). All samples were exposed to sunlight between the summer and early fall of 2008. Vials were placed outside on a foil-lined tray for direct sunlight exposure. At predetermined time points (nonaBDEs and deca-BDE: 2, 5, 15, and 30 min; TBB and TBPH: 5, 15, 30, 60, and 240 min), three vials of each treatment were removed from the tray, wrapped in aluminum foil, and stored in the laboratory until analysis. Average hourly incident solar radiation (W/m2) readings recorded using a pyranometer and average hourly temperature readings (°C) were obtained from a weather station maintained by the National Oceanic and Atmospheric Administration (NOAA), approximately 8 miles from the site of exposure. This latter information, presented in the Supporting Information, allowed us to compensate for any variations in incident solar radiation experienced from running the experiments on different days with different sunlight radiation levels. Analysis. Samples were analyzed using our previously published methods (7, 13). Further details concerning the standards used and GC/MS conditions can be found in the Supporting Information. A subsample of the nonaBDE samples was analyzed using liquid chromatography/tandem mass spectrometry (LC/MS/MS) in an effort to determine whether hydroxylated PBDEs and brominated phenols were formed. Additionally, selected nonaBDE samples in toluene were analyzed for brominated dibenzodioxins and dibenzofurans (PBDDs/Fs) using high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS) (18). Quality Analysis/Quality Control. All sample treatments were prepared in triplicate at each time point, along with three laboratory blanks containing just the solvent. During the exposure period, three vials of each treatment were wrapped in foil and placed outside with the sunlight exposed samples as outdoor controls. Additionally, three vials of each treatment were wrapped in foil and kept at room temperature in the laboratory as indoor controls. All samples and controls were extracted and analyzed at the same time. Instrument detection limit (three times the signal in the blanks) ranged from 0.07 ng (BDE 153) to 1.5 ng (BDE 209). All compounds monitored were either not detected or below the instrument detection limit in all blanks, and thus blank correction was not required. Recovery of the F-BDE 160 internal standard in the nonaBDE samples averaged 98% ( 13%. Recovery of the F-BDE 201 internal standard in the TBB and TBPH samples averaged 98% ( 6%. Data and Statistical Analysis. The indoor control samples were treated as the initial time point (0 min sunlight exposure) in the sunlight experiments. To determine whether any photodegradation took place in the absence of sunlight (i.e., in the outdoor controls relative to the indoor controls the initial time point), statistical tests were performed using the programming language R (version 2.6.0). For all sample treatments, the means of the initial samples and the means of the controls were not significantly different at p < 0.05. Thus, no degradation occurred in the controls relative to the initial samples. To calculate photodegradation rate constants and halflives, concentration data for each analyte over time were fit to a first-order degradation model (Ct ) C0 e-kt, where Ct represents the concentration at a given time t, C0 is the initial concentration, and k is the degradation rate constant).

TABLE 1. Photodegradation Kinetics Calculated for BDEs 206, 207, 208, and 209, TBB, and TBPH analyte

BDE 206

BDE 207

BDE 208

BDE 209

TBB

TBPH

solvent Toluene Methanol THF Toluene Methanol THF Toluene Methanol THF

raw ka (min-1)

normalized kb, × corrected t1/2c 10-4 (min-1W-1m2) (min)

NonaBDEs 0.151 1.78 0.0678 0.797 0.0307 0.789 0.202 2.37 0.119 1.40 0.0546 1.40 0.181 2.13 0.0960 1.13 0.0460 1.18

BDE 209 Toluene 0.108 2.78 Methanol 0.0554 1.42 THF 0.0751 1.93 Toluene Methanol THF Toluene Methanol THF

TBB and TBPH 0.0218 0.0621 0.0135 0.107 0.0149 0.118 0.0240 0.0684 0.00580 0.0458 0.00760 0.0600

5.67 12.65 12.78 4.25 7.20 7.18 4.74 8.93 8.53 3.62 7.08 5.22 162.34 94.59 85.70 147.46 220.17 168.03

a Calculated rate constants based on raw data. Calculated rate constants normalized to cumulative incident solar radiation during exposure period. c Half-lives were calculated using the normalized rate constants and assuming an average solar radiation value for an early fall day in Durham, North Carolina (687.5 W/m2). b

Results and Discussion NonaBDE Photodegradation Kinetics. Initial experiments were carried out to examine the photodegradation pathways of the nonaBDE congeners BDE 206, BDE 207, and BDE 208 in three different solvents exposed to natural sunlight. All three nonaBDE congeners underwent rapid photodegradation in methanol, toluene, and THF, albeit at different rates. Decay plots for the nonaBDEs are shown in Figure S1 in the Supporting Information. Because experiments were conducted at different time periods between mid summer and early fall, the incident solar radiation levels varied among the experiments. To compensate for this variable, we normalized the observed rate constants to the cumulative solar radiation monitored during the specific exposure periods (i.e., the average hourly solar radiation values obtained from NOAA; see Tables 1 and S1 in the Supporting Information). Thus, all kinetic values are reported in units of min-1 W-1 m2. To compare half-lives among the analytes and treatments, normalized rate constants were then multiplied by the value 687.5 W/m2, an average daily solar radiation value for an autumn day in Durham, North Carolina. The values for the uncorrected and corrected rate constants, along with the calculated half-lives, are presented in Table 1. BDE 207 experienced the most rapid photodegradation whereas BDE 206 was consistently found to have the slowest photodegradation rates in all three solvents. This finding is in agreement Eriksson et al.’s discovery that, of the three nonaBDE congeners, BDE 207 photodegraded fastest whereas BDE 206 photodegraded slowest (9). This finding is in contrast with modeled data from the literature. Specifically, Zeng et al. modeled photodegradation rate constants of nonaBDEs relative to BDE 209 and estimated that BDE 207 had the lowest calculated rate constant of the three congeners while BDE 206 had the highest rate constant (19). Another study using theoretical calculations of Gibbs free energy of PBDE congeners determined that, of the nonaBDE homologue group, BDE 206 was predicted to be the least thermodyVOL. 43, NO. 15, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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namically stable and BDE 207 to be the most stable (20). Thus, experimental and modeled kinetics data for nonaBDEs are in contrast with one another. Based on the normalized rate constants calculated in our study, all three nonaBDEs degraded fastest in toluene and each nonaBDE degraded at approximately the same rate in methanol as in THF (See Table 1). This is in contrast with the results of Eriksson et al., which compared experimental photodegradation rate constants for BDE 207 in methanol and in THF and found that BDE 207 reacted 1.4 times faster in THF than in pure methanol (9). BDE 209 underwent photodegradation more rapidly than any of the nonaBDEs; this is in keeping with previous studies that reported an increasing photodegradation rate with increasing degree of bromination (9, 10). We calculated half-lives of 3.62, 7.08, and 5.22 min for BDE 209 in toluene, methanol, and THF, respectively; previous studies have reported a half-life of 90%, indicating that reductive debromination was the most dominant photodegradation pathway in this solvent. For BDE 207 and BDE 208, the mass balance recovery in THF was 79-86%. The mass balance was least conserved in toluene for all three solvents with a mass balance recovery in toluene ranging from 76 to 81% among the congeners. Thus, as little as 76% of the loss of BDE 206 in toluene can be attributed to reductive debromination, with the other 24% possibly being lost to formation of unknown degradation products. Because all three nonaBDEs have low modeled vapor pressures (log PL ) -7.5), loss by volatilization is unlikely (30). In an effort to identify degradation products which may not be detectable by GC/MS (such as hydroxylated PBDEs and brominated phenols), selected toluene samples (indoor controls and samples irradiated for 5 min) were analyzed using LC/MS/MS, first monitoring for known ion fragments of specific hydroxylated PBDEs and then in full scan. No identifiable peaks appeared in the 5 min samples 5744

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relative to the controls. Additionally, polybrominated dibenzofurans (PBDFs), which are known to be more toxic than PBDEs, have previously been confirmed as photodegradation products of PBDEs in plastics (21). Selected samples from the toluene treatment were analyzed using HRGC/HRMS for PBDDs/Fs; however, all PBDDs/DFs monitored were below detection limits (which ranged from 0.01 pg/µL for triBDDs/ DFs to 2.8 pg/µL for octaBDDs/DFs). TBB and TBPH Photodegradation. TBB and TBPH are new flame retardants, and to our knowledge, their photodegradation potential had not yet been investigated prior to this study. Since standards were available, we included these compounds in this photodegradation experiment. Both TBB and TBPH underwent photodegradation in all three solvents, and data were fit to first-order decay models (Figure S1 in the Supporting Information); reaction rate constants and half-lives are reported in Table 1. TBB and TBPH photodegraded more slowly than the nonaBDEs in all three solvents, and the rate constants were consistently an order of magnitude lower than those calculated for the nonaBDEs. This difference may be explained in part by the lower aromatic character of TBB and TBPH relative to the nonaBDEs. In all solvents except toluene, TBB was photodegraded more rapidly than TBPH. TBB degraded fastest in tetrahydrofuran and slowest in toluene, while TBPH degraded fastest in toluene and slowest in methanol. These differences in photodegradation kinetics may be explained by structural differences resulting in greater steric hindrance for indirect photolysis of TBPH than of TBB. In an effort to qualitatively identify photodegradation products, the full scan ECNI/MS spectra of TBB and TBPH samples in all three solvents were examined as no authentic standards are available and little is known about degradation of these compounds. The major products identified for TBB and TBPH were consistent between solvents and are shown in Figure 3. The mass spectra of the degradation products identified are provided in the Supporting Information. We identified several peaks in the chromatograms that eluted earlier than the parent compound and displayed a strong 1:1 ratio of ions 79/81, indicating that brominated degradation products were formed. In the case of TBB, peaks 1 and 2 had strong bromine signals. In the full scan spectra for these compounds, peaks were identified at 233 and 280 amu, but no clear molecular ion peak could be discerned; however, based on isotope clusters, it appears that these products are dibrominated TBB analogues. Peaks 3 and 4 both had approximate molecular weights of 391, suggesting that these two peaks represent different isomers of a dibrominated analogue of TBB. Peak 5 had an approximate molecular weight of 470 amu, indicating that it is a tribrominated analogue of TBB. Peak 6 was present in the controls but increased in abundance over the irradiance period; this peak lacked a bromine signal and had an approximate molecular weight of 390 amu. The identity of this compound is unknown. In the case of TBPH, di- and tribrominated analogues of TBPH (most of which were also missing both alkane branches) were the most dominant photodegradation products. These products were identified by both molecular ion fragments and by the ion cluster patterns. Three dibrominated and two tribrominated isomers appear to have been formed through the degradation of TBPH. These results suggest that, like PBDEs, TBB and TBPH can undergo sequential reductive debromination. For both TBB and TBPH, peaks of nonbrominated degradation products were identified, but the structures cannot yet be specified; additional studies are planned to further investigate the different possible photodegradation pathways and products of TBB and TBPH. In summary, this study demonstrated that nonaBDE congeners will photodegrade primarily via reductive debro-

This material is available free of charge via the Internet at http://pubs.acs.org.

Literature Cited

FIGURE 3. GC/ECNI-MS TIC chromatograms of (A) TBB in methanol after 60 min of sunlight exposure and (B) TBPH in methanol after 240 min of exposure; peaks of their primary photodegradation products are labeled with molecular formulas and peak numbers.

mination to form less brominated congeners. By knowing the pathways of nonaBDE degradation, we can identify the octa- and heptaBDE congeners which may be useful for tracking potential degradation of decaBDE under environmentally relevant conditions. Our results indicate that the octabrominated congener BDE 202, as well as the ratio of BDE 197 to BDE 201, may serve as useful markers of environmental debromination of decaBDE. In addition, this study reports the first observation of the photodegradation of TBB and TBPH via debromination reactions and is the first study to identify some of their photodegradation products. These emerging BFRs have been shown to photodegrade more slowly than decaBDE or nonaBDEs; this finding suggests that TBB and TBPH may be more persistent, at least photolytically, than higher brominated PBDE congeners in the environment.

Acknowledgments We would like to thank Drs. Dennis Tabor, Barbara Wyrzykowska, and Brian Gullett at the U.S. EPA in Research Triangle Park, NC for the GC/HRMS analysis.

Supporting Information Available Method information and a table containing solar radiation and temperature data, as well as several figures (the degradation curves of the starting compounds and full scan ECNI-MS spectra of TBB and TBPH degradation products).

(1) Hale, R.; Alaee, M.; Manchester-Neesvig, J.; Stapleton, H.; Ikonomou, M. Polybrominated diphenyl ether flame retardants in the North American environment. Environ. Int. 2003, 29, 771–779. (2) de Wit, C. An overview of brominated flame retardants in the environment. Chemosphere 2002, 46, 583–624. (3) Tullo, A. Great lakes to phase out two flame retardants. Chem. Eng. News 2003, 81, 13–13. (4) An act relating to phasing out the use of polybrominated diphenyl ethers. HB 1024. 22 July 2007. Revised Code of Washington, 2007. Available at http://apps.leg.wa.gov/documents/billdocs/200708/Pdf/Bills/Session%20Law%202007/1024-S.SL.pdf. (5) An Act to Protect Pregnant Women and Children from Toxic Chemicals Released into the Home. LD 1658. 20 September 2007. Maine Revised Statues, 2007. Available at http://janus. state.me.us/legis/ros/lom/lom123rd/pdf/PUBLIC296.pdf. (6) Parliament v. Commission, Judgment Joined Cases C-14/06, C-295/06. European Court of Justice, 01 April 2008. (7) Stapleton, H.; Dodder, N. Photodegradation of decabromodiphenyl ether in house dust by natural sunlight. Environ. Toxicol. Chem. 2008, 27, 306–312. (8) Soderstrom, G.; Sellstrom, U.; de Wit, C.; Tysklind, M. Photolytic debromination of decabromodiphenyl ether (BDE 209). Environ. Sci. Technol. 2004, 38, 127–132. (9) Eriksson, J.; Green, N.; Marsh, G.; Bergman, Å. Photochemical decomposition of 15 polybrominated diphenyl ether congeners in methanol/water. Environ. Sci. Technol. 2004, 38, 3119–3125. (10) Fang, L.; Huang, J.; Yu, G.; Wang, L. Photochemical degradation of six polybrominated diphenyl ether congeners under ultraviolet irradiation in hexane. Chemosphere 2008, 71, 258–267. (11) Meerts, I.; Letcher, R.; Hoving, S.; Marsh, G.; Bergman, Å.; Lemmen, J.; van der Burg, B.; Brouwer, A. in vitro estrogenicity of polybrominated diphenyl ethers, hydroxylated PBDEs, and polybrominated bisphenol A compounds. Environ. Health Perspect. 2001, 109, 339–407. (12) Stapleton, H.; Letcher, R.; Li, J.; Baker, J. Dietary accumulation and metabolism of polybrominated diphenyl ethers by juvenile carp (Cyprinus carpio). Environ. Toxicol. Chem. 2004, 23, 1939– 1946. (13) Stapleton, H.; Allen, J.; Kelly, S.; Konstantinov, A.; Klosterhaus, S.; Watkins, D.; McClean, M.; Webster, T. Alternate and new brominated flame retardants detected in U.S. house dust. Environ. Sci. Technol. 2008, 42, 6910–6916. (14) Great Lakes, DP-45. Great Lakes Chemical Co., 2004. http:// www.pa.greatlakes.com/freb/common/pdf/DP_45_ds.pdf. (15) Klosterhaus, S. Characterization of the brominated chemicals in a PentaBDE replacement mixture and their detection in biosolids collected from two San Francisco Bay area wastewater treatment plants. Poster, BFR 2008, 10th Annual Workshop on Brominated Flame Retardants. (16) US Consumer Product Safety Commission. Consumer Product Safety Improvement Act, Section 108. (17) Swan, S. Environmental phthalate exposure in relation to reproductive outcomes and other health endpoints in humans. Environ. Res. 2008, 108, 177–184. (18) Wyrzykowska, B.; Gullett, B.; Tabor, D.; Touati, A. Levels of brominated diphenylether, dibenzo-p-dioxin, and dibenzofuran in flue gases of a municipal waste combustor. Organohalogen Compd. 2008, 70, 182–185. (19) Zeng, X.; Massey Simonich, S.; Robrock, K.; Koryta´r, P.; AlvarezCohen, J.; Barofsky, D. Development and validation of a congener-specific photodegradation model for polybrominated diphenyl ethers. Environ. Toxicol. Chem. 2008, 27, 2427–2435. (20) Grabda, M.; Oleszek-Kudlak, S.; Shibata, E.; Nakamura, T. Theoretical calculations of thermodynamic properties of brominated flame retardants. Organohalogen Compd. 2006, 68, 1983–1986. (21) CRC Handbook of Chemistry and Physics, 89th ed.; CRC Press: Boca Raton, FL., 2008. (22) Schwarzenbach, R.; Gschwend, P.; Imboden, D. Environmental Organic Chemistry; John Wiley & Sons: Hoboken, NJ, 2003. (23) Kajiwara, N.; Noma, Y.; Takigami, H. Photolysis studies of technical decabromodiphenyl ether (DecaBDE) and ethane (DeBDethane) in plastics under natural sunlight. Environ. Sci. Technol. 2008, 42, 4404–4409. VOL. 43, NO. 15, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

9

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(24) Bezares-Cruz, J.; Jafvert, C.; Hua, I. Solar photodecomposition of decabromodiphenyl ether: products and quantum yield. Environ. Sci. Technol. 2004, 38, 4149–4156. (25) Stapleton, H.; Alaee, M.; Letcher, R.; Baker, J. Debromination of the flame retardant decabromodiphenyl ether by juvenile carp (Cyprinus carpio) following dietary exposure. Environ. Sci. Technol. 2004, 38, 112–119. (26) Konstantinov, A.; Bejan, D.; Bunce, N.; Chittim, B.; McCrindle, R.; Potter, D.; Tashiro, C. Electrolytic debromination of PBDEs in DE-83TM technical decabromodiphenyl ether. Chemosphere 2008, 72, 1159–1162. (27) Sun, C.; Zhao, D.; Chen, C.; Ma, W.; Zhao, J. TiO2-Mediated photocatalytic debromination of decabromodiphenyl ether: kinetics and intermediates. Environ. Sci. Technol. 2009, 43, 157– 162.

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(28) La Guardia, M.; Hale, R.; Harvey, E. Detailed polybrominated diphenyl ether (PBDE) congener composition of the widely used penta-, octa-, and deca-PBDE technical flame-retardant mixtures. Environ. Sci. Technol. 2006, 40, 6247–6254. (29) La Guardia, M.; Hale, R.; Harvey, E. Evidence of debromination of decabromodiphenyl ether (BDE-209) in biota from a wastewater receiving stream. Environ. Sci. Technol. 2007, 41, 6663– 6670. (30) Wang, Z.; Zeng, X.; Zhai, Z. Prediction of supercooled liquid vapor pressures and n-octanol/air partition coefficients for polybrominated diphenyl ethers by means of molecular descriptors from DFT method. Sci. Total Environ. 2008, 389, 296–305.

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