Theoretical Investigation on Mechanistic and Kinetic Transformation

(1-4) Hence, PBDEs degradation and metabolites, as well as derivatives elicit ... BDE99 is frequently detected in air dust and other medias and usuall...
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Theoretical Investigation on Mechanistic and Kinetic Transformation of 2,2′,4,4′,5-Pentabromodiphenyl Ether Haijie Cao, Dandan Han, Mingyue Li, Xin Li, Maoxia He,* and Wenxing Wang Environment Research Institute, Shandong University, Jinan 250100, P. R. China S Supporting Information *

ABSTRACT: This study investigates the decomposition of 2,2′,4,4′,5-pentabrominated diphenyl ether (BDE99), a commonly detected pollutant in the environment. Debromination channels yielding tetrabrominated diphenyl ethers and hydrogen abstracting aromatic bromine atom formations play significant roles in the reaction of BDE99 + H, in which the former absolutely predominates bimolecular reactions. Polybrominated dibenzo-p-dioxins (PBDDs) and polybrominated dibenzofurans (PBDFs) can be produced during BDE99 pyrolysis, especially for PBDFs under inert conditions. The expected dominant pathways in a closed system are debromination products and PBDF formations. The bimolecular reaction with hydroxyl radical mainly leads to hydroxylated BDE99s rather than hydroxylated tetrabrominated diphenyl ethers. PBDDs are then generated from orthohydroxylated PBDEs. HO2 radical reactions rarely proceed. The total rate constants for the BDE99 reaction with hydrogen atoms and hydroxyl radicals exhibit positive dependence on temperature with values of 1.86 × 10−14 and 5.24 × 10−14 cm3 molecule−1 s−1 at 298.15 K, respectively.

1. INTRODUCTION Polybrominated diphenyl ethers (PBDEs) are widely used brominated flame retardants (BFRs), which are being phased out because of their potential hazards to humans. However, PBDEs remain as ubiquitous pollutants worldwide because of their stability, persistence, accumulation, and migration.1−4 Hence, PBDEs degradation and metabolites, as well as derivatives elicit increasing attention. PBDEs are frequently detected in various samples (e.g., human tissues, fluids, sewage sludge, air, and water)5−9 and expected to exist in the environment at extended periods.10 Therefore, knowledge on the kinetic properties and removal pathways of PBDEs is crucial. Furthermore, 2,2′,4,4′,5-pentabromodiphenyl ether (BDE99) was a major component of commercial pentabrominated diphenyl ethers. BDE99 is frequently detected in air dust and other medias and usually acts as a dominant congener.11−14 Similar to other PBDEs, BDE99 exhibits an evident ichthyotoxic effect,15 which causes learning disorders and disturbs thyroid hormones.16 BDE99 in hepatocytes can be metabolized to form hydroxylated PBDEs (OH-PBDEs), which are more toxic than the parent compound.17−20 Although BDE99 can be metabolized in vivo, BDE99 degradation has not been observed in soil,21 which may be a reason behind the high BDE99 concentrations in sediment and soil samples.22 PBDEs debromination has been well-investigated experimentally, and the generation of sub-PBDEs are mostly observed together with different catalysts (e.g., UV irritation and zero iron).23−29 Production, utilization, treatment, and recycling of PBDEs lead to the formation of notorious contaminant polybrominated dibenzo-p-dioxins (PBDDs)/ polybrominated dibenzofurans (PBDFs).30−32 PBDEs can © XXXX American Chemical Society

also feasibly react with air oxidants and be converted into corresponding derivatives. The rate constants of several monoto tetra-BDEs with hydroxyl radical have been determined experimentally33 or theoretically.34−36 Given the limited oxidation data of higher brominated PBDEs, the roles of hydroxyl radicals in the decomposition of higher brominated PBDEs require further investing ation. Computational methods will compensate for the invisible reaction mechanisms. In this study, the bimolecular decomposition of BDE99 with hydrogen atoms, hydroxyls, and HO2 radicals are investigated with regard to active radicals in combustion chemistry. This research presents the available mechanism involved in BDE99 debromination. The formation of PBDDs and PBDFs are also discussed in detail. The calculated results will provide researchers with further understanding about the removal of PBDEs from the environment. This information will facilitate the development of appropriate degradation methods under optimal conditions.

2. COMPUTATIONAL METHODS Gaussian 09 packages37 were used to perform all the calculations. The MPWB1K functional38 was selected for quantum calculations. In our previous work,39,40 the reliability of this method was proven appropriate (time-saving and accurate) in calculations involving PBDE components. The geometries of all the stable points (reactants, intermediates, and products) and transition states were optimized at the MPWB1K/6-31+G(d,p) level. Harmonic vibrational frequenReceived: April 28, 2015 Revised: May 22, 2015

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Figure 1. Schematic self-decomposition of BDE99. ΔrE (kcal/mol) represents the reaction heat.

Figure 2. Schematic mechanism of addition reactions between BDE99+H. Units of reaction heats (ΔrE) and activation energies (ΔE*) are kcal/mol.

cies and zero-point vibrational energies were calculated at the same level. Intrinsic reaction coordinates41,42 were calculated to verify the connections between the minima and the transition states. The single-point energies of the higher level were calculated at the theoretical MPWB1K/6-311+G(3df,2p). Then

the rovibrational frequencies and the energies were used to calculate the rate constants via canonical transition state theory (TST).43 Quantum tunneling effect from the asymmetrical Eckart barrier was included. TST rate constants were obtained B

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Figure 3. Schematic mechanism of abstraction reactions between BDE99 and H. Units of reaction heat (ΔrE) and activation energy (ΔE*) are kcal/ mol.

shown in Figure 2, whereas those of abstraction channels are depicted in Figure 3. Additions to the ipso-C sites proceeded moderately, which generated IM15 and IM18 via similar activation energies. Through the thermodynamic preferred fission of C(H)−O bonds, IM15 and IM18 decomposed into 1,2,4-tribromobenzene (P1) + 2,4-dibromophenoxy radical (IM2) and 1,3-dibromobenzene (P5) + 2,4,5-tribromophenoxy radical (IM9), respectively. These reactions released large amounts of energy. Hydrogen addition to the C(Br) site released bromine atoms, which resulted in tetrabromodiphenyl ethers (TetraBDEs) with high exothermicity (∼30 kcal/mol). Among the initial addition reactions, hydrogen addition to C(H) sites were preferred with lower activation energies, which led to the formation of H-adducts (IM16, IM17, IM19, IM20, and IM21). Hydrogen migrations from C(H2) groups to C(Br) sites also led to the formation of TetraBDEs and bromine atoms with high activation energies. Hydrogen atoms preferred to abstract bromine atoms rather than aromatic hydrogen (Figure 3). Obviously, the activation energies were competitive with the addition reactions at C(Br) sites. This behaved similarly to the system of H + bromobenzene.34 The formation of HBr and phenyl radicals (IM3−IM7) was slightly exothermic. Moreover, ortho-position radicals (IM3, IM6, IM10, and IM13) can transfer to PBDFs. The temperature-dependent rate constants of bimolecular reactions have been investigated and were fitted to a modified three-parameter Arrhenius expression within 250 to 1000 K interval (Table 1). All the rate constants exhibited positive temperature dependence. The total rate constant of BDE99 + H ranged from 5.75 × 10−14 cm3 molecule−1 s−1 at 298.15 K to 2.19 × 10−11 cm3 molecule−1 s−1 at 1000 K. At room temperature, the orders of the rate constants generally agreed with the activation energies. Hydrogen addition to the C(H) sites dominated the whole bimolecular reactions, which

using the Thermo program of the recently developed MultiWell software.44,45

3. RESULTS AND DISCUSSION The structure of BDE99 with atom numbers is shown in Figure S1 of the Supporting Information. The phenyl ring with three bromine atoms is denoted as ring 1, whereas the other phenyl ring is ring 2. The highest occupied molecular orbital of BDE99 was located in ring 1, whereas the lowest unoccupied molecular orbital consisted of the atoms in ring 2 (Figure S2 of the Supporting Information). The barrierless self-decomposition potential of BDE99 was initially investigated through the reaction heats (Figure 1). For convenience, IM’s and TS’s denote the intermediates and transition states, respectively. The cleavages of C−H bonds and the generation of aromatic radicals (IM10−IM14) incurred a high endoergicity of ∼112 kcal/mol. The rupture of C−Br bonds absorbed less energy than the breaking of C−H bonds. The fission of C−O bonds required the least energy absorption, which implied a significant generation of brominated phenol radicals and brominated benzene radicals during the initial self-decomposition of PBDEs. 3.1. Bimolecular Reactions of BDE99. Reaction with Hydrogen Atoms. Hydrogen atoms play significant roles in the transformation of many compounds, especially during combustion progression. PBDE pyrolysis mainly forms debromination products, indicating a replacement activity of hydrogen and bromine atoms.23−26,29 Most environmental PBDEs result from the debromination of higher BDEs (e.g., Deca-BDE). Thus, H-reducing reactions are important to treat PBDEs. Hydrogen reaction with the selected BDE99 reactant was investigated, which branched into 22 channels. The reaction heats and activation energies of hydrogen addition routes are C

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shown in Table S2 of the Supporting Information. Apparently, hydrogen migrations proceeded slowly at 298.15 K but increased rapidly with temperature. At high temperatures, these processes will significantly participate in the formation of low brominated congeners. The formation of PBDDs required oxygen atom insertion in the ortho-position of the ether bond. Therefore, at high temperatures (e.g., >900 K), PBDFs were the dominant products rather than PBDDs under inert gas conditions. Bimolecular Reaction with Hydroxyl Radical. OH-PBDEs are evidently important products in recycling waste printed circuit boards.46 Hence, hydroxylation of PBDEs is a significant source of OH-PBDEs. The detailed parameters of the oxidation reactions of BDE99 and hydroxyl radicals (·OH) are shown in Figure 4. All the ·OH addition reactions to BDE99 were exothermic with moderate activation energies. IM21 and IM24 were the intermediates formed via ·OH addition to ipso-C atoms. The activation energy of IM21 was extremely lower than that of IM24. Thus, hydroxyl radical addition was preferred for the ipso-C atom of ring 1. The activation energies of hydroxyl radical addition to C(Br) sites ranged from 4.52 to 7.14 kcal/mol. These processes were deeply exothermic (29.68 to 32.11 kcal/mol). Bromine atoms were also released simultaneously, leading to the formation of hydroxylated TetraBDEs (OH-TetraBDEs). ·OH addition to C(H) sites should overcome lower activation energies, varying from 0.26 to 3.72 kcal/mol. The corresponding intermediates (OH-adducts, IM22, IM23, IM25, IM26, and IM27) were then formed, followed by the removal of hydrogen atoms through O2 molecules in the air. Stable hydroxylated BDE99s (OHBDE99s) were produced once H atoms were abstracted by O2. These pathways were barrierless, and OH-BDE99s were the preferred products. ·OH can also abstract the phenyl hydrogen of BDE99. However, these processes incurred higher activation energies of 6.27 to 7.96 kcal/mol (Figure S3 of the Supporting Information). Despite our optimal attempts, we failed to locate the transition states of the ·OH abstracting bromine atoms of BDE99. Compared with the activation energies of elementary reactions, ·OH prefers to add to the phenyl ring with three bromine atoms. This is contrary to the results of 2,4dibromodiphenyl ether39 and 2,4,4′-tribromodiphenyl ether,40 indicating that higher brominated PBDEs have some different properties and should be investigated carefully. The rate constants (Table 1) were positively dependent on temperature, and the branching ratios are summarized in Table S3 of the Supporting Information. The total rate constant of BDE99 + ·OH was 5.24 × 10−14 cm3 molecule−1 s−1 at room temperature, which was approximately 2 orders of magnitude lower than the experimental data of mono- and dibrominated diphenyl ethers.33 Compared with the results of other PBDEs, the rate constants decreased moderately as the degree of bromine substitution of PBDEs increased (Table S4 of the Supporting Information).36,39,40 The atmospheric lifetime of BDE99 due to tropospheric ·OH (1 × 106 molecules cm−3) is 5.30 × 103 hours. The atmospheric lifetime of BDE99 is considerably longer than low brominated congeners (Table S4 of the Supporting Information). In contrast to the bimolecular reaction of BDE99 + H, the rate constants of ·OH addition to ipso-C atoms were more significant than the addition to C(Br) sites. Hydrogen abstraction reactions barely contributed to the total rate constant. Among the studied intervals of temperature, the hydroxyl radical addition to C(H) sites dominated the bimolecular reaction, although the branching ratio decreased

Table 1. Parameters Involved in the Modified Arrhenius Expression k(T) = ATn exp{−[(Ea)/(RT)]} at the Interval of 250−1000 Ka A

reaction BDE99 + H → IM15 BDE99 + H → P2 + Br BDE99 + H → IM16 BDE99 + H → P3 + Br BDE99 + H → P4 + Br BDE99 + H → IM17 BDE99 + H → IM18 BDE99 + H → P6 + Br BDE99 + H → IM19 BDE99 + H → P7 + Br BDE99 + H → IM20 BDE99 + H → IM21 BDE99 + H → IM3 + HBr BDE99 + H → IM4 + HBr BDE99 + H → IM5 + HBr BDE99 + H → IM6 + HBr BDE99 + H → IM7 + HBr BDE99 + H → IM10 + H2 BDE99 + H → IM11 + H2 BDE99 + H → IM12 + H2 BDE99 + H → IM13 + H2 BDE99 + H → IM14 + H2 BDE99 + ·OH → IM21 BDE99 + ·OH → P9 BDE99 + ·OH → IM22 BDE99 + ·OH → P11 BDE99 + ·OH → P12 BDE99 + ·OH → IM23 BDE99 + ·OH → IM24 BDE99 + ·OH → P14 BDE99 + ·OH → IM25 BDE99 + ·OH → P16 BDE99 + ·OH → IM26 BDE99 + ·OH → IM27 IM3 → P19 + Br IM3 → IM28

1.46 3.46 1.26 7.32 1.03 2.28 3.02 4.09 2.78 2.43 1.31 3.28 2.26 2.58 2.06 7.74 8.05 1.69 1.36 1.74 1.06 1.90 2.20 3.06 4.79 1.47 1.21 3.49 2.96 6.06 1.42 2.16 8.95 6.88 3.52 3.79

× × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × ×

−20

10 10−22 10−18 10−23 10−22 10−18 10−20 10−22 10−18 10−22 10−18 10−19 10−15 10−15 10−15 10−16 10−16 10−18 10−18 10−18 10−18 10−18 10−21 10−21 10−21 10−21 10−21 10−21 10−21 10−21 10−20 10−21 10−21 10−21 1010 1010

n

Ea/R

2.86 3.46 2.30 3.64 3.53 2.19 2.74 3.36 2.17 3.41 2.27 2.50 1.46 1.54 1.51 1.65 1.59 2.46 2.47 2.44 2.36 2.38 2.75 2.71 2.69 2.72 2.72 2.51 2.53 2.63 2.55 2.65 2.49 2.57 0.34 0.37

2631.33 2230.55 1380.55 2186.12 2290.78 1371.47 2861.06 2695.18 1608.81 2817.05 1670.48 1800.83 3834.87 3641.45 3625.37 3698.70 3651.77 7754.96 7789.33 7892.78 8142.21 7763.59 −37.48 1629.77 539.08 1781.61 2163.20 −460.44 1789.17 2943.86 634.02 2511.63 559.76 1244.67 6447.69 3850.56

Unit of A is cm3 molecule−1 s−1 for bimolecular reactions and s−1 for unimolecular reactions.

a

contributed 98% of the total rate constant, similar to the results of the H + bromobenzene system.34 The difference between H + BDE99 and H + bromobenzene exhibited in the branching ratios of addition channel and abstraction channel. In the system of H + bromobenzene, addition channels dominated the reaction within 250−2000 K.34 In the system of H + BDE99, the branching ratio of the addition channel decreased steadily with temperature and reduced to 45% of the whole value (Table S1 of the Supporting Information). By contrast, hydrogen abstracting bromine atoms and hydrogen addition to C(Br) sites became dominant channels at high temperatures (Table S1 of the Supporting Information). Hydrogen addition to ipso-C atoms evidently processed slowly, whereas the abstraction of phenyl hydrogen atoms was negligible. The rate constants for the hydrogen migration reactions of Hadducts were also calculated. However, fitting these values to the modified Arrhenius expression was inappropriate because of the huge error between the fitted data and the calculated values, especially at low temperatures. The nonfitted rate constants are D

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Figure 4. Schematic mechanism of bimolecular reactions between BDE99 and OH radical. Units of reaction heat (ΔrE) and activation energy (ΔE*) are kcal/mol.

at the ortho-position of ether bonds (IM3, IM6, IM10, and IM13) were PBDF precursors (Figure 5).34 Two channels leading to different PBDFs were available for IM3, that is, attacking the ortho-C(Br) site or ortho-C(H) site of the other phenyl ring. Moreover, 2,3,8-tribromodibenzofuran (2,3,8TriBDF, P24) was generated through a concerted process, where bromine atoms were released coupled with the bond association of C−C. This process was deeply exothermic by 43.84 kcal/mol with a 13.06 kcal/mol activation energy. The formation of 2,3,6,8-tetrabromodibenzofuran (2,3,6,8-TetraBDF, P25) proceeded with a stepwise mechanism, which was initiated by the association of the C−C(H) bond. After releasing a hydrogen atom, 2,3,6,8-TetraBDF (P25) was formed. The self-decomposition of IM35 faced high activation energy and was endothermic. Hence, 2,3,8-TriBDF was the dominant product in this closed system instead of 2,3,6,8TetraBDF. However, in the case of bromine atoms, IM35 to P25 transformation was strongly prompted via barrierless reaction. The process of IM35 + Br → P25 + HBr released substantial energy of 75.92 kcal/mol. The association of IM3 with oxygen molecules was preferred in an oxidative atmosphere, leading to the formation of peroxyl radical intermediate (IM36). The isomerization of IM36 was divided into four endoergic channels. Terminal oxygen atom addition to the ipso-C atom of the same phenyl ring incurred the highest activation energy of 44.73 kcal/mol and absorbing energy of 35.39 kcal/mol. Addition of the other ring to ortho-C atoms was much easier, but the favored pathway was the one toward IM40 because this pathway exhibited the lowest

moderately with temperature. TetraBDEs (P9, P11, P12, P14, and P16), which resulted from the hydroxyl group substituting bromine atoms of BDE99, were not major products. The yield of OH-TetraBDEs was quite minimal and even negligible at room temperature. Thus, ·OH preferred to react with nonsubstituted carbon atoms of BDE99 to produce OHadducts, which were then stabilized through the O2 abstraction of the H atoms. Considering the rate of determining steps, OHBDE99s were preferred products instead of OH-TetraBDEs in the presence of oxygen. Oxidation by HO2 Radical. Bimolecular reactions of BDE99 + HO2· were all endothermic and incurred high activation energies (Figure S5 of the Supporting Information), indicating lower feasibility of these reactions. The steric hindrance between HO2· and phenyl rings was seemingly enhanced, whereas the inactivation effect of Br atoms was weakened. The kinetic results (Table S4 of the Supporting Information) confirmed this assumption. The rate constant of BDE99+HO2· showed moderately positive dependence on temperature and was determined to be 4.53 × 10−27 cm3 molecule−1 s−1 at room temperature, negligible compared with the rate constant of BDE99 + ·OH/H. Although the ambient concentration of HO2· is higher than ·OH by ∼100 times, HO2· barely contributes to BDE99 decomposition. At 298 K, the HO2·determined an atmospheric lifetime of BDE99 was 6.13 × 1014 hours. 3.2. Formation of PBDDs/PBDFs. Thermal treatments of materials containing PBDEs are evidenced producing hazardous PBDDs and PBDFs.47,48 The phenyl-type radical intermediates E

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Figure 5. Reaction parameters involved in the formation of PBDD/Fs from IM3. Units of reaction heat (ΔrE) and activation energy (ΔE*) are kcal/ mol.

1,2,4,8-tetrabromodibenzofuran, and 1,2,4,6,8-pentabromodibenzofuran) emerged after a series of stepwise reactions. In addition to the aforementioned reactions, PBDDs can form through the decomposition of ortho-position OH-PBDEs, as confirmed both experimentally60 and theoretically. Figure S8 of the Supporting Information depicts the mechanism of PBDDs resulting from four ortho-OH-PBDEs which has been verified experimentally49 and theoretically.40,50 Removal of phenoxyl hydrogen atoms led to essential intermediates, which were precursors of PBDDs. PBDDs formed after different ringclosing reactions. Sub-brominated PBDDs were evidently preferred products.

activation energy (14.15 kcal/mol) and a slight endoergicity (2.99 kcal/mol). The decomposition of IM40 branched into two channels. Through the fission of O−O bond and the association of O−C(Br) bond, IM41 was produced, followed by oxygen attacking the C(H) site. Hydrogen migration from aromatic rings to cyclo-oxygen atoms underwent moderate activation energy, leading to the formation of hydroxylated intermediate IM43. Subsequently, 1,3,7,8-tetrabromodibenzo-pdioxin (P27) was produced through the release of hydroxyl radicals. IM40 to IM44 transformation proceeded with the rupture of O−O bonds and association of O−C(H) bonds. This process showed similar energy barriers and reaction heats with the channel toward IM41. IM45 was formed via O−C(Br) bond association. Bromine atom migration from aromatic ring to cyclo-oxygen underwent high activation energy. After the removal of the OBr radical, 2,3,7-tribromodibenzo-p-dioxin (P28) was formed. The transformations from other ortho-position radical intermediates to PBDDs/PBDFs are illustrated in Figures S5−S7 of the Supporting Information. These reactions showed similar trends to the reaction of IM3. The formation of PBDDs and PBDFs exhibited similar trends from a different phenyltype radical intermediate. The results were in agreement with a study on the reaction of phenyl-type radical intermediate from 2,2′-dibromodiphenyl ether.34 In a word, the number and position of bromine atoms have little impact on the formation of PBDFs and PBDDs from phenyl-type intermediates. In a word, four PBDDs (2,3,7-tribromodibenzo-p-dioxin, 1,3,7,8tetrabromodibenzo-p-dioxin, 1,2,4,8-tetrabromodibenzo-p-dioxin, and 1,2,4,6,8-pentabromodibenzo-p-dioxin) and four PBDFs (2,3,8-tribromodibenzofuran, 2,3,6,8-tetrabromodibenzofuran,

4. CONCLUSIONS Hydroxyl radical- or hydrogen atom-initiated BDE99 transformations are important pathways in BDE99 decomposition. In contrast to BDE28 reactions, higher brominated phenyl rings are more reactive. In this study, hydrogen atoms preferred to attack C(H) sites and dominated the reaction at low temperatures. The removal of the bromine atom through the hydrogen atom became competitive as the branching ratio increased at high temperatures. The fission of ether bonds were insignificant at 250 to 1000 K. Hydrogen migrations of Hadducts, which formed TetraBDEs, were highly prompted by temperature. Sub-brominated PBDEs, which can be major products at low-temperature PBDFs, were important at high temperatures. PBDDs were available in the presence of oxygen molecules. For OH-initiated oxidation of BDE99, OH-BDE99s were the major components of OH-PBDEs in the presence of oxygen molecules. PBDDs can be generated through further reaction of OH-PBDEs. Thus, the reaction between BDE99 F

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(11) Birgul, A.; Katsoyiannis, A.; Gioia, R.; Crosse, J.; Earnshaw, M.; Ratola, N.; Jones, K. C.; Sweetman, A. J. Atmospheric polybrominated diphenyl ethers (PBDEs) in the United Kingdom. Environ. Pollut. 2012, 169, 105−111. (12) Butt, C. M.; Diamond, M. L.; Truong, J.; Ikonomou, M. G.; Ter Schure, A. F. H. Spatial distribution of polybrominated diphenyl ethers in southern Ontario as measured in indoor and outdoor window organic films. Environ. Sci. Technol. 2004, 38, 724−731. (13) Muenhor, D.; Harrad, S. Within-room and within-building temporal and spatial variations in concentrations of polybrominated diphenyl ethers (PBDEs) in indoor dust. Environ. Int. 2012, 47, 23− 27. (14) Schreder, E. D.; La Guardia, M. J. Flame retardant transfers from US households (dust and laundry wastewater) to the aquatic environment. Environ. Sci. Technol. 2014, 48, 11575−11583. (15) Suyama, T. L.; Cao, Z. Y.; Murray, T. F.; Gerwick, W. H. Ichthyotoxic brominated diphenyl ethers from a mixed assemblage of a red alga and cyanobacterium: Structure clarification and biological properties. Toxicon 2010, 55, 204−210. (16) Blanco, J.; Mulero, M.; Heredia, L.; Pujol, A.; Domingo, J. L.; Sanchez, D. J. Perinatal exposure to BDE-99 causes learning disorders and decreases serum thyroid hormone levels and BDNF gene expression in hippocampus in rat offspring. Toxicology 2013, 308, 122−128. (17) Dingemans, M. M. L.; de Groot, A.; van Kleef, R. G. D. M.; Bergman, A.; van den Berg, M.; Vijverberg, H. P. M.; Westerink, R. H. S. Hydroxylation increases the neurotoxic potential of BDE-47 to affect exocytosis and calcium homeostasis in PC12 cells. Environ. Health. Persp. 2008, 116, 637−643. (18) Dingemans, M. M. L.; van den Berg, M.; Westerink, R. H. Neurotoxicity of brominated flame retardants: (in)direct effects of parent and hydroxylated polybrominated diphenyl ethers on the (developing) nervous system. Environ. Health. Persp. 2011, 119, 900− 907. (19) Leijs, M. M.; Koppe, J. G.; Olie, K.; van Aalderen, W. M. C.; de Voogt, P.; ten Tusscher, G. W. Effects of dioxins, PCBs, and PBDEs on immunology and hematology in adolescents. Environ. Sci. Technol. 2009, 43, 7946−7951. (20) Stapleton, H. M.; Kelly, S. M.; Pei, R.; Letcher, R. J.; Gunsch, C. Metabolism of polybrominated diphenyl ethers (PBDEs) by human hepatocytes in vitro. Environ. Health. Persp. 2009, 117, 197−202. (21) Wong, F.; Kurt-Karakus, P.; Bidleman, T. F. Fate of brominated flame retardants and organochlorine pesticides in urban soil: volatility and degradation. Environ. Sci. Technol. 2012, 46, 2668−2674. (22) Zeng, Y. H.; Luo, X. J.; Yu, L. H.; Chen, H. S.; Wu, J. P.; Chen, S. J.; Mai, B. X. Using compound-specific stable carbon isotope analysis to trace metabolism and trophic transfer of PCBs and PBDEs in fish from an e-waste site, south China. Environ. Sci. Technol. 2013, 47, 4062−4068. (23) Fang, Z.; Qiu, X.; Chen, J.; Qiu, X. Debromination of polybrominated diphenyl ethers by Ni/Fe bimetallic nanoparticles: influencing factors, kinetics, and mechanism. J. Hazard. Mater. 2011, 185, 958−969. (24) Li, A.; Tai, C.; Zhao, Z.; Wang, Y.; Zhang, Q.; Jiang, G.; Hu, J. Debromination of decabrominated diphenyl ether by resin-bound iron nanoparticles. Environ. Sci. Technol. 2007, 41, 6841−6846. (25) Kim, Y. M.; Murugesan, K.; Chang, Y. Y.; Kim, E. J.; Chang, Y. S. Degradation of polybrominated diphenyl ethers by a sequential treatment with nanoscale zero valent iron and aerobic biodegradation. J. Chem. Technol. Biotechnol. 2012, 87, 216−224. (26) Rayne, S.; Wan, P.; Ikonomou, M. Photochemistry of a major commercial polybrominated diphenyl ether flame retardant congener: 2,2′,4,4′,5,5′-hexabromodiphenyl ether (BDE153). Environ. Int. 2006, 32, 575−585. (27) Sun, C. Y.; Zhao, D.; Chen, C. C.; Ma, W. H.; Zhao, J. C. TiO2mediated photocatalytic debromination of decabromodiphenyl ether: kinetics and intermediates. Environ. Sci. Technol. 2009, 43, 157−162.

and HO2 radicals barely contributed to the BDE99 removal because of the small rate constant.

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ASSOCIATED CONTENT

S Supporting Information *

Geometry structure, molecular orbitals, schematic representation, reaction parameters, branching ratios, rate constants, and table of parameters. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpca.5b04022.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: 86-531-8836 1990. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported financially by the National Natural Science Foundation of China (Grants 21337001 and 21477065) and the Fundamental Research Funds of Shandong University (Grant 2014JC014).

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REFERENCES

(1) Gouin, T.; Thomas, G. O.; Cousins, I.; Barber, J.; Mackay, D.; Jones, K. C. Air-surface exchange of polybrominated diphenyl ethers and polychlorinated biphenyls. Environ. Sci. Technol. 2002, 36, 1426− 1434. (2) Ter Schure, A. F. H.; Larsson, P.; Agrell, C.; Boon, J. P. Atmospheric transport of polybrominated diphenyl ethers and polychlorinated biphenyls to the Baltic sea. Environ. Sci. Technol. 2004, 38, 1282−1287. (3) Tomy, G. T.; Palace, V. P.; Halldorson, T.; Braekevelt, E.; Danell, R.; Wautier, K.; Evans, B.; Brinkworth, L.; Fisk, A. T. Bioaccumulation, biotransformation, and biochemical effects of brominated diphenyl ethers in juvenile lake trout (Salvelinus namaycush). Environ. Sci. Technol. 2004, 38, 1496−1504. (4) Wan, Y.; Hu, J. Y.; Zhang, K.; An, L. H. Trophodynamics of polybrominated diphenyl ethers in the marine food web of Bohai Bay, North China. Environ. Sci. Technol. 2008, 42, 1078−1083. (5) Bodin, N.; Abarnou, A.; Fraisse, D.; Defour, S.; Loizeau, V.; Le Guellec, A. M.; Philippon, X. PCB, PCDD/F and PBDE levels and profiles in crustaceans from the coastal waters of Brittany and Normandy (France). Mar. Pollut. Bull. 2007, 54, 657−668. (6) Cincinelli, A.; Martellini, T.; Misuri, L.; Lanciotti, E.; Sweetman, A.; Laschi, S.; Palchetti, I. PBDEs in Italian sewage sludge and environmental risk of using sewage sludge for land application. Environ. Pollut. 2012, 161, 229−234. (7) Crosse, J. D.; Shore, R. F.; Wadsworth, R. A.; Jones, K. C.; Pereira, M. G. Long-term trends in PBDEs in sparrowhawk (Accipiter nisus) eggs indicate sustained contamination of UK terrestrial ecosystems. Environ. Sci. Technol. 2012, 46, 13504−13511. (8) Kierkegaard, A.; Bignert, A.; Sellstrom, U.; Olsson, M.; Asplund, L.; Jansson, B.; de Wit, C. A. Polybrominated diphenyl ethers (PBDEs) and their methoxylated derivatives in pike from Swedish waters with emphasis on temporal trends, 1967−2000. Environ. Pollut. 2004, 130, 187−198. (9) Petreas, M.; Nelson, D.; Brown, F. R.; Goldberg, D.; Hurley, S.; Reynolds, P. High concentrations of polybrominated diphenylethers (PBDEs) in breast adipose tissue of California women. Environ. Int. 2011, 37, 190−197. (10) Fu, J.; Wang, T.; Wang, P.; Qu, G.; Wang, Y.; Zhang, Q.; Zhang, A.; Jiang, G. Temporal trends (2005−2009) of PCDD/Fs, PCBs, PBDEs in rice hulls from an e-waste dismantling area after stricter environmental regulations. Chemosphere 2012, 88, 330−335. G

DOI: 10.1021/acs.jpca.5b04022 J. Phys. Chem. A XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry A (28) Zhao, S.; Ma, H.; Wang, M.; Cao, C.; Xiong, J.; Xu, Y.; Yao, S. Study on the mechanism of photo-degradation of p-nitrophenol exposed to 254 nm UV light. J. Hazard. Mater. 2010, 180, 86−90. (29) Zhuang, Y.; Ahn, S.; Luthy, R. G. Debromination of polybrominated diphenyl ethers by nanoscale zerovalent iron: pathways, kinetics, and reactivity. Environ. Sci. Technol. 2010, 44, 8236−8242. (30) Gullett, B. K.; Wyrzykowska, B.; Grandesso, E.; Touati, A.; Tabor, D. G.; Ochoa, G. S. PCDD/F, PBDD/F, and PBDE emissions from open burning of a residential waste dump. Environ. Sci. Technol. 2010, 44, 394−399. (31) 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. (32) Takigami, H.; Suzuki, G.; Hirai, Y.; Sakai, S. Transfer of brominated flame retardants from components into dust inside television cabinets. Chemosphere 2008, 73, 161−169. (33) Raff, J. D.; Hites, R. A. Gas-phase reactions of brominated diphenyl ethers with OH radicals. J. Phys. Chem. A 2006, 110, 10783− 10792. (34) Altarawneh, M.; Dlugogorski, B. Z. A mechanistic and kinetic study on the formation of PBDD/Fs from PBDEs. Environ. Sci. Technol. 2013, 47, 5118−5127. (35) Wang, S.; Hao, C.; Gao, Z.; Chen, J.; Qiu, J. Effects of excitedstate structures and properties on photochemical degradation of polybrominated diphenyl ethers: a TDDFT study. Chemosphere 2012, 88, 33−38. (36) Zhou, J.; Chen, J.; Liang, C. H.; Xie, Q.; Wang, Y. N.; Zhang, S.; Qiao, X.; Li, X. Quantum chemical investigation on the mechanism and kinetics of PBDE photooxidation by ·OH: a case study for BDE15. Environ. Sci. Technol. 2011, 45, 4839−4845. (37) Frisch, M.; Trucks, G.; Schlegel, H. B.; Scuseria, G.; Robb, M.; Cheeseman, J.; et al. Gaussian 09, revision A. 02, Gaussian. Inc.: Wallingford, CT, 2009, 200. (38) Zhao, Y.; Truhlar, D. G. Hybrid meta density functional theory methods for thermochemistry, thermochemical kinetics, and noncovalent interactions: The MPW1B95 and MPWB1K models and comparative assessments for hydrogen bonding and van der Waals interactions. J. Phys. Chem. A 2004, 108, 6908−6918. (39) Cao, H. J.; He, M. X.; Han, D. D.; Sun, Y. H.; Zhao, S. F.; Ma, H. J.; Yao, S. D. Mechanistic and kinetic study on the reaction of 2;4dibrominated diphenyl ether (BDE-7) with OH radicals. Comput. Theor. Chem. 2012, 983, 31−37. (40) Cao, H. J.; He, M. X.; Han, D. D.; Li, J.; Li, M. Y.; Wang, W. X.; Yao, S. D. OH-Initiated oxidation mechanisms and kinetics of 2,4,4′tribrominated diphenyl ether. Environ. Sci. Technol. 2013, 47, 8238− 8247. (41) Gonzalez, C.; Schlegel, H. B. An improved algorithm for reaction path following. J. Chem. Phys. 1989, 90, 2154−2161. (42) Gonzalez, C.; Schlegel, H. B. Reaction path following in massweighted internal coordinates. J. Phys. Chem. 1990, 94, 5523−5527. (43) Pechukas, P. Transition state theory. Annu. Rev. Phys. Chem. 1981, 32, 159−177. (44) Barker, J. R.; Ortiz, F. N.; Preses, M. J.; Lohr, L. L.; Maranzana, A.; Stimac, J. P.; Nguyen, T. L.; Kumar, T. J. D. MultiWell-2014.1 Software; University of Michigan, Ann Arbor: MI, 2014, http://aoss. engin.umich.edu/multiwell/. (45) Barker, J. R. Multiple-well, multiple-path unimolecular reaction systems. I. MultiWell computer program suite. Int. J. Chem. Kinet. 2001, 33, 232−245. (46) Ren, Z.; Bi, X.; Huang, B.; Liu, M.; Sheng, G.; Fu, J. Hydroxylated PBDEs and brominated phenolic compounds in particulate matters emitted during recycling of waste printed circuit boards in a typical e-waste workshop of South China. Environ. Pollut. 2013, 177, 71−77. (47) Ebert, J.; Bahadir, M. Formation of PBDD/F from flameretarded plastic materials under thermal stress. Environ. Int. 2003, 29, 711−716.

(48) Wyrzykowska-Ceradini, B.; Gullett, B. K.; Tabor, D.; Touati, A. PBDDs/Fs and PCDDs/Fs in the raw and clean flue gas during steady state and transient operation of a municipal waste combustor. Environ. Sci. Technol. 2011, 45, 5853−5860. (49) Steen, P. O.; Grandbois, M.; McNeill, K.; Arnold, W. A. Photochemical formation of halogenated dioxins from hydroxylated polybrominated diphenyl ethers (OH-PBDEs) and chlorinated derivatives (OH-PBCDEs). Environ. Sci. Technol. 2009, 43, 4405− 4411. (50) Cao, H. J.; He, M. X.; Sun, Y. H.; Han, D. D. Mechanical and kinetic studies of the formation of polyhalogenated dibenzo-p-dioxins from hydroxylated polybrominated diphenyl ethers and chlorinated derivatives. J. Phys. Chem. A 2011, 115, 13489−13497.

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DOI: 10.1021/acs.jpca.5b04022 J. Phys. Chem. A XXXX, XXX, XXX−XXX