Environ Sci Pollut Res DOI 10.1007/s11356-014-3741-7
RESEARCH ARTICLE
Model for photodegradation of polybrominated diphenyl ethers M. Vesely & Z. Vajglova & P. Kotas & J. Kristal & R. Ponec & V. Jiricny
Received: 14 January 2014 / Accepted: 17 October 2014 # Springer-Verlag Berlin Heidelberg 2014
Abstract Polybrominated diphenyl ethers (PBDE) were, and in some countries still are, used as flame retardants for plastic materials. When released from plastics, PDBE cause harm to the environment. This creates the incentive for further investigation of the PBDE degradation. This work focused on a formulation of a PBDE photodegradation model based on the PBDE properties obtained by the quantum chemical calculations. The proposed model predicted degradation routes of arbitrary PBDE congener. The routes of selected congeners were validated by the two independently published data sets and showed the high fitting degree. The model can be easily modified for any reactor system if the initial reaction rate constant of one congener is available for the given system.
Keywords Polybrominated diphenyl ethers . Photodegradation model . Quantum chemical calculation
Responsible editor: Philippe Garrigues M. Vesely : Z. Vajglova : J. Kristal (*) : R. Ponec : V. Jiricny Institute of Chemical Process Fundamentals, AS CR, v. v. i., Rozvojova 135, 165 02 Prague 6, Czech Republic e-mail: [email protected] M. Vesely Institute of Chemical Technology, Technicka 5, 166 28 Prague 6, Czech Republic P. Kotas Global Change Research Centre, AS CR, v. v. i., Branisovska 31, 375 05 Ceske Budejovice, Czech Republic P. Kotas Department of Ecosystem Biology, Faculty of Science, University of South Bohemia, Branisovska 31, 370 05 Ceske Budejovice, Czech Republic
Introduction Polybrominated diphenyl ethers (PBDE) are chemical specialties produced since the 1970s. As additives, PBDE are present in a wide range of materials (e.g., plastic materials, heat insulation, polyurethane foam, textile fabric etc.) where they decrease the flammability of the material. PBDE possess aromatic character and represent a structural analog of the polychlorinated biphenyls (PCB) (Fig. 1). PBDE have 209 possible congeners and, according to the IUPAC nomenclature, their numbering is identical with PCB (Ballschmiter and Zell 1980). In 2004, EU banned the use of the PBDE mixture containing the tetra-, penta-, and octaBDE due to their severe environmental impact (Konstantinov et al. 2008). The estimated total PBDE production varies around 60,000 t per year (Hites 2004), and the dominating product is the decaBDE (BDE 209). Due to the continuous use of various mixtures of PBDE, they have been gradually released into the environment (Crosse et al. 2012; Besis and Samara 2012). In particular, the lower brominated PBDE are extremely persistent and being highly lipophilic, they pose a high risk of their bioaccumulation in organic fat tissue, or waste waters and sediments (Barraj et al. 2005). Despite the low concentration of PBDE accumulated in matrices (about ppb in fats), it is particularly alarming that over a longer perspective this concentration increases. Even more alarming is the fact that detectable PBDE concentrations were found even in human milk (de Wit 2002) or in settled indoor dust (Kefeni and Okonkwo 2013). In relation to the human toxicity, PBDE were classified by the US.EPA as teratogens and possible carcinogens (Eriksson et al. 2001) and endocrine disruptors (Orazio and Peterman 2005; Barraj et al. 2005). Because of the significant environmental impact of PBDE, there is a need to study the ways of the PBDE degradation. The possible degradation routes are the reductive and
Environ Sci Pollut Res O
Bry
Brx
Cly
Clx
This work focused on the quantum chemical calculation of the PBDE properties and their subsequent utilization for the formulation of the PBDE photodegradation model, including the degradation routes of selected congeners.
x + y = 1 - 10 PBDE
PCB
Fig. 1 Structure similarity of PBDE and PCB
electrochemical debromination, pyrolysis, active sludge biodegradation, microwave degradation, wet air oxidation, oxidative transformation, and the dominating photochemical degradation (WHO/ICPS 1994; Shih and Tai 2010; Bastos et al. 2008).
Photochemical degradation PBDE absorb ultraviolet light. The energy generated by the UV light absorption brings about gradual loss of the bromine atoms from the PBDE molecule. The reaction quantum yield depends on factors such as light intensity, wavelength, initial substrate concentration, and solvent. Zeng (Zeng et al. 2008) assumed the quantum yield for PBDE photodegradation to be constant. Shih (Shih and Wang 2009) studied the effect of the light intensity, wavelength, and the initial PBDE concentration on the rate of the degradation reaction. The BDE 209 was used as main substrate, and the reaction rate constant was determined for this congener. The reaction rate constant for the BDE 209 is affected by the light intensity, the higher the light intensity the higher the rate constant. No effect of the initial PBDE concentration on the reaction rate constant was observed, which corresponds to the kinetics of the pseudo-first order reaction. This is in agreement also with the analysis of the photoreaction quantum yield, that is practically constant over a wide range of reaction conditions (Bezares-Cruz et al. 2004). The analysis of the products of the photochemical degradation showed that the debromination is taking place preferably in the para position and the least preferred is the meta position with regard to the oxygen atom in the BDE 209 molecule (Shih and Wang 2009; Eriksson et al. 2004). A possible mechanism of the photodegradation was explained by Xie (Xie et al. 2009). From the technological point of view, the PBDE degradation is facing the problem of extremely low PBDE concentrations in the environmental samples. One of the alternatives to deal with this fact is to study the ways of increasing the PBDE concentration in the solvent prior to the decontamination process. One way would be the identification of a suitable sorption material. Another option is the extraction of the PBDE with the subsequent concentration of the PBDE organic solution. However, the disadvantage of the extraction process is the risk of the contamination of water with organic solvents.
Computation methods The quantum chemical calculations of the thermodynamic properties and other parameters of the studied series of PBDE congeners were carried out using the Austin method 1 (AM1) implemented in the Spartan 08 software (Spartan ‘08 2009) (gas state at 298.15 K and 101.325 kPa). The energies of the selected congeners in the excited state have been computed via calculation on excited states using singleexcitation (CIS) in Gaussian (Frisch et al. 2007; Gaussian 98 1998).
Photochemical degradation model The mechanism of PBDE photodegradation was studied by several authors (Bezares-Cruz et al. 2004; Eriksson et al. 2004). They found that the reaction follows the pseudo-first order kinetics with the dominating role of the dissociation of C-Br bond in the first excited state of corresponding congeners. The photochemical nature of the process was also demonstrated in Xie et al. (2009) where the authors described the correlation between the logarithm of the photodegradation reaction rate constant and the reciprocal wavelength of the UV transition into the first excited singlet state. The decisive factor in photodegradation is apparently the dissociation of the C-Br bond in the photoreactive excited state. In the formulated model, we assumed that the key to the elucidation of the observed differences of photodegradation of individual congeners was the knowledge of the dissociation energy of the C-Br bond in the photoreactive excited state of the corresponding congeners. However, obtaining these quantities was, in view of the extent of the studied series and the size of individual PBDE, beyond the current capabilities of theoretical calculation. To overcome the problem of solving the relative rates of photodegradation, we adopted the following simplifying assumption, namely, that within the group of the structurally similar compounds there exists a parallel between the magnitudes of the dissociation energies of the C-Br bond in the excited and the ground state. The possibility of utilizing the characteristics obtained by calculation in the ground state for the description of the molecule in the excited state has been also confirmed for chlorinated methanes and chlorinated benzenes (Chatterjee 2011).
Environ Sci Pollut Res Table 2 Review of most stable and least stable congeners
10
5 4
6
9
11
3
1
8
12
7
2
Group Most stable
Congener Number ΔG0f Congener Number ΔG0f of ortho [kJ/mol] of ortho [kJ/mol] Br Br
13
O
Fig. 2 Position labeling in PBDE molecule
The fact that the dissociation energies may be obtained for molecules in the ground state, from the thermodynamic parameters ΔH0f and or ΔG0f opens the way to explaining the differences in the rates of degradation of individual PBDE by means of the given thermodynamic experimental data. These, if not available as experimental data, may be obtained by quantum chemical calculations using Eq. (1). ΔH 0f i − ΔH 0f j k im ¼ exp −RT k mj
Mono Di Tri Tetra Penta Hexa
BDE 3 BDE 13 BDE 37 BDE 77 BDE 126 BDE 169
0 0 0 0 0 0
168.6 177.9 204.2 216.7 245.4 273.0
BDE 1 BDE 4 BDE 19 BDE 54 BDE 104 BDE 165
1 2 3 4 4 2
181.4 202.4 238.0 271.6 297.8 343.6
Hepta Octa Nona Deca
BDE 191 BDE 194 BDE 206 BDE 209
2 2 3 4
309.3 337.1 380.9 414.0
BDE 186 BDE 204 BDE 208 BDE 209
4 4 4 4
350.2 384.5 392.5 414.0
! ð1Þ
The kinetics of photodegradation of each congener, i, may be obtained by means of Eq. (2), where [i] designates concentration of the given congener i and Σki is the overall reaction rate constant of degradation of the given PBDE. Congener i is degraded to several lower congeners j with the specific reaction rate constant, kji, and Σki is then the sum of the specific reaction rate constants. However, a given congener i may be also a degradation product of a higher congener m. Therefore, the reaction rate equation for a given congener i contains
Table 1 Comparison of optimization for BDE 51 and BDE 166; PBDE position labeling is shown in Fig. 2 Congener
Least stable
Bond length [Å]
Bond angle [°]
C1-O7
O7-C8
C1-O7-C8
AM1 HF/STO-3G HF/3-21G* HF/6-31G* B3LYP/3-21G*
1.391 1.405 1.385 1.362 1.404
1.395 1.407 1.380 1.356 1.398
118.9 115.7 123.0 120.8 120.5
X-ray (Eriksson and Hu 2002a) AM1 HF/STO-3G HF/3-21G* HF/6-31G* B3LYP/3-21G* X-ray (Eriksson and Hu 2002b)
1.395
1.397
115.7
1.392 1.405 1.373 1.348 1.393 1.391
1.395 1.409 1.398 1.371 1.415 1.414
116.5 115.6 122.9 121.5 119.9 116.7
another term, αmikim[m], describing the production of congener i where [m] is the concentration of the original congener m, kim is the specific reaction rate constant of degradation of congener m to i and αmi is the number of potential routes for this reaction. The calculation of ki itself is given in Eq. (3) where kji is the specific reaction rate constant of degradation of congener i to lower congener j and αij is the number of potential routes for this debromination. d ½i ¼ −∑k i ½i þ αmi k im ½m dt
ð2Þ
k i ¼ ∑αi j k ij
ð3Þ
0
BDE 166
−1 −1.5
log(k) [−]
BDE 51
−0.5
−2 −2.5 −3 −3.5 −4 −4.5 −5
4.3
4.4
4.5
4.6
4.7
1/λ [1/nm]
4.8
4.9 −3
x 10
Fig. 3 Dependence of predicted reaction rate constants on computed wavelengths via CIS
Environ Sci Pollut Res
For the purpose of solving these equations, a MATLAB program was written to specify the congeners to which a given congener may be degraded as well as those from which the given congener could be produced. Part of this program was the determination of the number of routes for the given degradation. The inputs for the model were the relative concentrations of congeners PBDE and the reaction rate constant of
a
Model 100 90 80
Abundance [%]
70 60 deca nona octa hepta hexa
50 40 30 20 10 0
0
1
5
10
20
40
60
Time [min]
b
Shih 100 90 80 70
Abundance [%]
Fig. 4 Predicted products of photodegradation of BDE 209 after 60 min, reaction rate constant k209 =0.12 min-1 taken from Shih and Wang (2009)
degradation for BDE 209, k209 =1. The outputs were the relative concentrations of individual congeners in time. All the calculated values of ΔH0f and ki used in our model are listed in the Appendix. These presented data can be easily utilized for the prediction of the PBDE degradation routes in different photochemical reactors if the reaction rate of an arbitrary congener is known for the given reactor.
deca nona octa hepta hexa penta unknow
60 50 40 30 20 10 0
0
1
5
10
Time [min]
20
40
60
Environ Sci Pollut Res
Geometry of BDE 51 and BDE 166 was described experimentally (Eriksson and Hu 2002a, b). In this work, these results were used for the selection of the appropriate method for the calculation of the quantum chemical properties of PBDE congeners. To do this, we calculated the geometry of BDE 51 and BDE 166 using the following methods: semi-empirical method AM1, ab initio Hartree-Fock method (HF), and Density Functional Theory (DFT). Both molecules were optimized with HF/STO-3G, HF/3-21G*, HF/6-31G*, and B3LYP/321G*. The PBDE position labeling is shown in Fig. 2. Comparison of the computed data with the measured diffraction analysis (Table 1) showed a good agreement of experimental data with results computed by the AM1 method at the lowest computational requirements. Therefore, all the 209 congeners were computed by the AM1 method. Stability of PBDE Thermodynamic properties calculated by the AM1 method were used to assess the stability of PBDE congeners. The relative stability of individual congeners may be characterized by computed ΔG0f and ΔH0f . Gibbs free energy equation was used for ΔG0f . In fact, the lower ΔG0f , the greater is the thermodynamic stability. As may be seen in Table 2, ΔG0f grows with the number of bromines in the molecule of PBDE. With the same number of bromines, the difference in ΔG0f is caused by the different number of bromines in the ortho positions. With the growing number of these positions, ΔG 0f again increases. From this, it follows that substituted ortho positions decrease the thermodynamic stability of congeners. Higher energies of such congeners may be explained by steric effects. The most stable and the least stable congeners for characteristic groups of PBDE are given in Table 1. From the analysis of calculated ΔG0f , it follows that the relatively least stable congener is BDE 209. Another justification of the assumption of the least thermodynamic stability of BDE 209 is the fact that BDE 209 became the most widely used fire retardant on the basis of
BDE 28 BDE 15
0.9
0
Relative concentration; C / C [−]
Selection of the PBDE geometry optimization method
Degradation products of BDE 28 1
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0
5
10
15
20
Time [h] Degradation products of BDE 47 1
Relative concentration; C / C [−] 0
In the following sections, we present the results related to the PBDE degradation model. Firstly, we selected an appropriate quantum chemical method for calculation of thermodynamic properties of all PBDE congeners. Based on the calculated thermodynamic properties, we discussed the stability of PBDE congeners. Secondly, the results of the formulated PBDE degradation model are presented.
PBDE. One must not forget, however, that even though BDE 209 is the least stable PBDE congener, it is still a strongly persistent substance.
BDE 47 BDE 28 BDE 15
0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0
2
4
6
8
10
Time [h] Degradation products of BDE 99 1
Relative concentration; C / C [−] 0
Results and discussion
BDE 99 BDE 66 BDE 47 BDE 28
0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0
2
4
6
8
10
Time [h] Fig. 5 Time dependence of the relative concentration of selected congeners during degradation of BDE 28, BDE 47, and BDE 99; experimental data (Fang et al. 2008) (markers), presented model (lines)
Environ Sci Pollut Res
PBDE degradation results
Model validation against the experimental data
Justification of the calculations in the ground state
We formulated the model for the general case of k209 =1. For the direct comparison of our degradation model and experimental data at the identical time scale, the knowledge of the experimental reaction rate constant is necessary. To verify our model, we use a published reaction rate constant k209 = 0.12 min−1 (Shih and Wang 2009), relevant for the degradation in hexane with BDE 209 initial concentration of 12.5 mg/L. Another experimental dataset (Fang et al. 2008) was used for comparison of degradation product from three individual congeners—BDE 28, BDE 47, and BDE 99. Published values (Fang et al. 2008) of experimental reaction rate constant were supplied to the model of photochemical degradation and the relative concentrations of the degradation components were calculated. The composition of the reaction mixture after 1, 5, 10, 20, 40, and 60 min of the BDE 209 degradation is shown in Fig. 4. The comparison of the
The justification of the simplifying assumption of the proportionality of the dissociation energies of the C-Br bond in the ground and excited state was verified by the correlation between the logarithm of the reaction rate constants calculated from the presented model and the excitation energies of UV transition to the first excited singlet state. The wavelengths were calculated using the CIS involving the mono excited configuration. For the calculation of the wavelengths, we used the congeners from all congener groups. From Fig. 3, it is evident that the calculated log(k) values based on AM1 calculations clearly correlate with the excitation energies calculated by CIS. The linear dependence of the log(k) on the inversed wavelength is in agreement with published data (Eriksson et al. 2004; Xie et al. 2009). Fig. 6 Predicted degradation routes of BDE 209; major products (rectangular box), common products (no designation), and minor products (underlined)
209
207
206
194
195
196
197
199
198
171
170
128
208
201
200
176
175
129
131
132
137
139
158
84
82 88
40
41
109
42
44
45
47
55
16
17
20
4
5
6
7
11
12
1
134
87
85
105
184
2
202
203
204
205
Environ Sci Pollut Res
Prediction of degradation routes
results of our model and the experimental data (Shih and Wang 2009) shows the good qualitative agreement. The representation of the individual groups follows the similar trends. The model results are in qualitative agreement with the experiment. The model results are slightly shifted to the longer times. This difference can be attributed to the uncertainties in the determination in the experimental reaction rate constant. Other authors also described similar dependences for the degradation of BDE 209 to lower congeners (Sun et al. 2009) and for degradation to the higher congeners (Christiansson et al. 2009). Also, photochemical degradation of lower brominated congeners is described very well by our model. The results for degradation of BDE 28, BDE 47, and BDE 99 dissolved in hexane are shown in Fig. 5 for both the experiment (Fang et al. 2008) and our model. Degradation of the lower brominated congeners seems to be quicker than the prediction, but the degradation of the individual congeners is still predicted by the model very well qualitatively. The concentration curves of the selected congeners essentially overlap each other in both the experiment and model.
194
195
170
128
a
b
c
206
207
208
198
196
171
180
129
131
85
82
187
137
138
42 52
56
60
66
197
139
5
4 8
45
82
84
85
91
105
55
17
1
12
2
22
21
33
28
5
6
8
7
12
2
144
136
82
83
84
87
88
109
41
44
45
16
17
20
55
20
4
1
132
60
40
28
179
131
130
129
77
7
176
175
202
45
42
41 47
200
132
88
40
55
6 11
199
134
105
22
20
198
158
139
16
17
16
131
129 137
204
184
176
171
128
199
163
44
49
195
149
91 95
47
205
191
147
87
41
40
183
158
156
153
203
201
146
144
141
The degradation routes of BDE 209, BDE 208, BDE 207, and BDE 206 were predicted by our model and are shown in Figs. 6 and 7. These four congeners were selected since they were frequently present in the commercial PBDE mixtures. In the degradation routes diagrams, the following labeling is used. In each congener group, we selected the congener with the highest concentration as a reference point. The congeners were labeled as major if their maximum concentration reached above 50 % of the reference concentration. The congeners were labeled as common if their maximum concentration was between 40 and 50 % of the reference concentration. The congeners were labeled as minor if their occurrence was predicted and their maximum concentration was below 40 % of the reference concentration. The minor category was used for the first and second degradation step for BDE 209 and only for the first degradation step for nonaBDE. In the further degradation steps, the broad spectrum of subsequent congeners is formed, and the diagram would be too complicated. Therefore, the minor category is not shown.
4
5
7
6
1
11
2
3
Fig. 7 Predicted degradation routes of a BDE 206, b BDE 207, and c BDE 208; major products (rectangular box), common products (no designation), and minor products (underlined)
Environ Sci Pollut Res
a
b
BDE 206 1 mono di tri tetra penta hexa hepta octa nona all
0.8
c / c0 [−]
BDE 207 1
0.6
0.4
mono di tri tetra penta hexa hepta octa nona all
0.8
c / c0 [−]
Fig. 8 Degradation profiles of specific congeners a BDE 206, b BDE 207, c BDE 208, and d BDE 209
0.6
0.4
0.2
0.2
0
0 10
−1
0
10
10
1
10
2
3
10
10
4
10
−1
10
0
10
Time [h]
c
d
BDE 208 1
mono di tri tetra penta hexa hepta octa nona all
0.8 0.7
10
2
10
3
10
4
0.6 0.5 0.4 0.3 0.2
BDE 209
1
mono di tri tetra penta hexa hepta octa nona deca all
0.8
c / c0 [−]
0.9
c / c0 [−]
1
Time [h]
0.6
0.4
0.2
0.1 0 10
−1
0
10
10
1
10
2
10
3
0
4
10
10
−1
Predicted routes of degradation for BDE 209 correspond with the published experimental work (Sun et al. 2009). The first predicted step of BDE 206 degradation and the relative compositions qualitatively agree with another published experimental data (Davis and Stapleton 2009); the identical congeners were predicted and found experimentally. For both BDE 207 and 208, Davis experimentally found one major Table 3 Effect of the reaction rate constant magnitude on BDE 209 degradation profile BDE group 0.1 k BDE 209 A
tmax
1 k BDE 209
10 k BDE 209
A
A
tmax
Tetra Tri Di Mono
3.22 5.02 8.90 16.18 33.69
4.67 8.52 14.21 25.49 44.27
1.02 1.59 2.82 5.12 10.65
1.48 2.69 4.49 8.06 14.00
tmax 0.32 0.50 0.89 1.62 3.3
0
10
1
10
2
10
3
10
4
congener (BDE 200 and BDE 201 for BDE 207 and 208, respectively) that was not predicted by our model. This difference can be attributed to the small difference in the calculated values of ΔH0f between the given nona- and octa-congeners. Consequently, the small difference of enthalpies could cause the different predicted composition of the reaction mixture. Nonetheless, we can conclude that the agreement between the experimental data (Sun et al. 2009; Davis and Table 4 Characteristics of degradation profiles of specific congeners BDE 206, BDE 207, and BDE 208 BDE group
BDE 208 A
Nona Octa Hepta Hexa Penta
10
Time [h]
Time [h]
BDE 207 tmax
A
BDE 206 tmax
A
tmax
0.47 0.85 1.42 2.55 4.43
Octa Hepta Hexa Penta
1.7 2.9 4.3 9.4
2.2 4.4 7.7 13.6
1.9 2.8 5.3 10.5
2.4 4.6 8.2 14.1
1.7 3.0 5.5 11.5
2.1 4.2 7.8 14.1
75.52 75.12 23.88 23.75 7.55 7.51 174.45 135.79 55.17 42.94 17.44 13.58 524.98 541.42 166.01 162.67 52.50 51.44 1,758.75 1,055.56 556.05 333.80 175.87 105.56
Tetra Tri Di Mono
21.6 50.4 145.2 549.5
23.1 40.4 146.9 323.4
22.4 55.2 169.5 567.0
23.3 41.8 164.4 326.8
26.6 57.5 172.9 548.5
25.3 47.2 171.5 339.1
A area under the concentration profile curve, tmax time of maximum concentration of a given congener group
A area under the concentration profile curve, tmax time of maximum concentration of a given congener group
Environ Sci Pollut Res
Stapleton 2009) and our model is very good as most of the p r e di c t e d de gr ad at i o n p r o du c t s w e r e c on f i r m e d experimentally. The predicted degradation route of BDE 209 is in agreement with the routes of nonaBDE with respect to their relative abundance. The analysis of the individual congener structure, and their relative abundance (Fig. 5), revealed the easiest degradation of the C-Br bond in the ortho position; on the other hand, the product of degradation of the C-Br bond in the para position is minor. This result was in accordance with the calculated ΔG0f values (Table 2) and was in agreement with the findings of Shih (Shih and Wang 2009). Degradation profiles of specific congeners are shown in Fig. 8 and their characteristics in Tables 3 and 4. The comparison of the tmax differences for the different PDBE groups documented the lower disposition for degradation of the lower brominated congeners. The time needed for the degradation of the whole group increased exponentially with the decreasing number of bromine in the PBDE molecule. This was again in accordance with the calculated ΔG0f values. The comparison of the concentration of the given PBDE groups (BDE 206, BDE 207, and BDE 208) confirmed the fact that the total degradation time was affected by the structure of the starting congener. If the starting congener contained more bromines in the para position (BDE 206), its degradation proceeded slower than if the starting congener contained more bromines in the ortho position (BDE 208). If the starting congener contained the bromine in the both para and ortho positions (BDE 207), its degradation proceeded at the intermediate rate. As a result, for the lower brominated groups (tetra and lower), there was a clearly decreasing trend in tmax: tmax(206)>tmax(207)>tmax(208). This was again in accordance with the calculated ΔG0f values indicating that BDE 206 and BDE 208 are the most and least stable congener, respectively, in the nonaBDE group. Effect of the reaction rate constant magnitude on BDE 209 degradation profile is shown in Table 3. Three different magnitudes of reaction rate constant were used to show that the absolute value of the reaction rate constant has no effect on the composition of the reaction mixture. Relative concentrations of the individual PBDE group as well as the tmax values were constant for all three values of the reaction rate constant. This was in accordance with the assumption of the pseudo-first order kinetics.
Conclusions The presented work was focused on the formulation of a mathematical model for the photochemical degradation of the polybrominated diphenyl ethers. Using the Spartan
software, the selected thermodynamic properties of individual congeners of PBDE were computed using the AM1 method. The energies of selected congeners in the excited state were computed using CIS. On the basis of the computed PBDE properties, a model was formulated describing the photochemical degradation of PBDE. The model results were compared with the published experimental data, and the good agreement was found in terms of the concentration time dependence and the mixture composition during the BDE 209 degradation. The proposed model was then used for prediction of the degradation routes of BDE 99, BDE 47, and BDE 28 The qualitative agreement between the published experimental data and our model is good. The analysis of the individual congener structure, and their relative abundance revealed the easiest degradation of the CBr bond in the ortho position. If the starting congener contained more bromines in the para position (BDE 206), its degradation proceeded slower than if the starting congener contained more bromines in the ortho position (BDE 208). The results also indicated the lower disposition for photochemical degradation of the lower brominated congeners. If the initial degradation reaction rate is known for any arbitrary congener, the proposed model is able to predict the time needed for the degradation of the given congener to the desired level under different conditions (reactors). The values of ki and ΔH0f needed as the model inputs are presented in the “Appendix.”
Nomenclature Symbol
Unit
Description
A BDE c c0 EU GC HOMO IUPAC ki kim
– – mmol/l mmol/l – – – – s−1 s−1
Kow LUMO PBDE PCB QSAR
– – – – –
Area under the concentration profile curve Brominated diphenyl ether Actual concentration Initial concentration European Union Gas chromatography Highest occupied molecular orbital International Union of Pure and Applied Chemistry Degradation rate constant of congener i Specific degradation rate constant of congener m to congener i Octanol-water distribution coefficient Lowest unoccupied molecular orbital Polybrominated diphenyl ether Polychlorinated biphenyl Quantitative structure-activity relationship
R T
J/mol/K Universal gas constant K Thermodynamic temperature
Environ Sci Pollut Res tmax US EPA UV Α αmi
H – – A3 –
ΔG0f ΔH0f λmax
kJ/mol kJ/mol nm
Time of PBDE concentration maximum United States Environmental Protection Agency Ultraviolet light Polarizability Number of possible ways to formation of congener i from m Gibbs free energy of formation Standard enthalpy of formation Wavelength of maximal absorbance of UV
Acknowledgments The work has been carried out in the frame of the Czech Science Foundation project no. 104/09/0800. J. Kristal also acknowledges support by the Czech Science Foundation project no. P105/12/0664.
Appendix
Table 5 Specific reaction rate constants for all PBDE congeners
No.
k [s−1]
1 2 3 4 5 6 7 8 9 10 11
9.37e-006 5.89e-007 7.86e-007 3.08e-005 4.82e-004 1.45e-005 3.43e-005 1.10e-005 2.93e-005 3.41e-005 2.15e-006
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
5.74e-005 2.16e-006 4.60e-006 2.30e-006 7.93e-004 7.15e-005 7.10e-005 8.07e-005 7.44e-004 2.84e-003 5.27e-004 1.46e-003 9.65e-004 5.37e-005 4.60e-005 5.21e-005 3.97e-005 2.77e-004
30 31
1.23e-004 3.39e-005
Table 5 (continued) No.
k [s−1]
32 33 34
3.68e-005 8.55e-005 2.72e-005
35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52
9.47e-005 1.08e-005 8.53e-005 1.51e-003 9.11e-006 2.34e-003 4.42e-003 9.50e-004 2.41e-003 1.27e-003 1.56e-003 1.36e-003 1.23e-004 4.07e-004 1.36e-004 2.29e-004 1.48e-004 1.44e-004
53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71
1.60e-004 1.78e-004 4.60e-003 9.42e-004 2.25e-003 1.12e-003 1.46e-003 3.59e-003 1.41e-002 6.69e-003 1.63e-003 1.08e-003 5.54e-003 1.66e-004 4.46e-004 8.74e-005 1.87e-004 1.69e-004 1.49e-004
72 73 74 75 76 77 78 79 80
7.92e-005 8.69e-005 3.66e-004 1.43e-004 1.75e-003 2.76e-004 2.38e-003 1.75e-004 3.25e-005
Environ Sci Pollut Res Table 5 (continued)
Table 5 (continued) No.
k [s−1]
No.
k [s−1]
81 82 83
2.18e-003 8.71e-003 5.42e-003
130 131 132
1.64e-002 1.96e-002 1.42e-002
84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101
4.31e-003 5.81e-003 1.96e-002 7.42e-003 1.05e-002 6.97e-003 2.78e-003 1.84e-003 3.63e-003 8.91e-003 3.99e-003 2.52e-003 2.61e-003 1.96e-003 1.72e-003 5.82e-004 3.17e-004 6.85e-004
133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150
1.09e-002 1.64e-002 9.34e-003 7.58e-003 2.70e-002 1.03e-002 1.39e-002 8.94e-003 3.32e-002 8.51e-002 2.86e-002 1.77e-002 1.62e-002 4.98e-003 1.02e-002 4.67e-003 3.51e-003 3.28e-003
102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120
6.38e-004 3.82e-004 4.20e-004 6.22e-003 2.31e-002 7.78e-003 1.15e-002 2.74e-003 1.84e-003 3.41e-003 8.29e-003 2.24e-003 1.93e-002 8.88e-003 6.00e-002 6.25e-003 7.94e-004 3.41e-004 7.38e-004
151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169
1.38e-002 1.43e-002 1.67e-003 1.06e-003 7.09e-004 3.18e-002 1.43e-002 1.60e-002 3.80e-002 9.80e-002 1.98e-002 8.28e-003 9.90e-003 5.79e-003 1.29e-002 8.06e-002 5.07e-003 3.29e-003 1.10e-002
121 122 123 124 125 126 127 128 129
2.93e-004 4.09e-003 2.54e-003 2.87e-003 2.12e-003 3.74e-003 3.77e-003 1.88e-002 3.43e-002
170 171 172 173 174 175 176 177 178
5.92e-002 3.78e-002 6.02e-002 1.48e-001 5.05e-002 3.58e-002 3.10e-002 3.48e-002 3.04e-002
Environ Sci Pollut Res Table 6 (continued)
Table 5 (continued)
Table 6 Values of ΔH0f for all PBDE congeners
No.
k [s−1]
No.
ΔH0f [kJ/mol]
179 180 181
2.82e-002 4.55e-002 1.16e-001
182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199
3.81e-002 2.50e-002 2.14e-002 1.44e-001 1.22e-001 1.71e-002 1.72e-002 6.00e-002 1.38e-001 3.22e-002 1.71e-001 2.06e-002 1.49e-001 2.23e-001 1.04e-001 7.23e-002 2.54e-001 1.05e-001
200 201 202 203 204 205 206 207 208 209
2.19e-001 7.18e-002 6.81e-002 2.02e-001 1.69e-001 2.46e-001 4.59e-001 3.56e-001 3.98e-001 1.00e+000
No.
ΔH0f [kJ/mol]
1 2 3 4 5 6 7 8 9 10 11 12 13
79.215 68.535 66.425 116.330 107.950 104.330 104.820 100.290 106.240 117.580 92.260 95.540 91.880
14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62
96.190 90.220 145.775 142.535 144.775 157.235 135.545 138.205 131.485 138.625 149.605 133.455 134.135 145.345 131.215 135.835 146.195 132.405 142.665 132.475 133.285 123.455 124.305 121.215 126.745 122.545 176.520 175.180 173.990 175.910 175.710 190.690 190.220 171.660 172.990 173.200 189.450 183.620 171.510 184.970 201.700 166.020 162.680 166.160 164.010 177.080 164.300 170.250 182.340
Environ Sci Pollut Res Table 6 (continued)
Table 6 (continued) No.
ΔH0f [kJ/mol]
No.
ΔH0f [kJ/mol]
63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111
164.860 174.510 183.400 162.210 164.200 163.300 173.800 160.040 173.050 164.130 174.400 162.520 173.890 163.280 151.580 154.820 153.400 151.910 153.550 206.045 206.805 219.025 205.115 207.335 204.715 221.235 216.735 205.595 215.965 206.505 221.915 217.305 216.975 233.645 204.285 217.955 203.765 217.145 202.845 214.365 216.005 231.945 195.065 198.855 194.125 195.215 210.125 204.845 194.105
112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160
210.385 206.495 195.835 221.455 214.875 208.195 193.025 204.045 194.795 202.915 194.385 193.805 193.455 204.115 184.185 185.535 237.830 238.790 238.880 251.690 248.910 238.340 252.340 249.520 264.840 238.520 237.120 248.940 248.020 237.420 256.280 248.910 250.170 265.560 235.970 249.350 248.350 248.540 263.640 250.780 266.890 234.610 245.910 259.050 227.970 224.710 238.170 229.410 242.630
Environ Sci Pollut Res Table 6 (continued)
References No.
ΔH0f
161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209
226.400 226.430 238.520 252.980 276.100 258.230 234.650 244.610 214.010 271.835 282.095 270.645 289.045 281.545 282.275 297.425 285.265 283.065 298.595 270.495 286.455 280.595 282.385 295.825 285.615 300.895 283.515 297.095 296.895 273.535 269.955 272.665 270.625 304.060 319.770 317.450 329.430 318.110 332.820 330.850 318.390 338.470 313.420 335.690 305.730 353.085 365.565 366.515 401.170
[kJ/mol] Ballschmiter K, Zell M (1980) Analysis of polychlorinated-biphenyls (PCB) by glass-capillary gas-chromatography—composition of technical aroclor-PCB and clophen-PCB mixtures. Fresenius Z Anal Chem 302(1):20–31 Barraj L, van den Berg M, Darnerud PO, Feeley M, Lilienthal H, Papke O, Bolger M, Tohyama C (2005) Polybrominated diphenyl ethers. Exponent, Washington DC Bastos PM, Eriksson J, Vidarson J, Bergman A (2008) Oxidative transformation of polybrominated diphenyl ether congeners (PBDEs) and of hydroxylated PBDEs (OH-PBDEs). Environ Sci Pollut Res 15(7):606–613. doi:10.1007/s11356-008-0045-9 Besis A, Samara C (2012) Polybrominated diphenyl ethers (PBDEs) in the indoor and outdoor environments—a review on occurrence and human exposure. Environ Pollut 169:217–229. doi:10.1016/j. envpol.2012.04.009 Bezares-Cruz J, Jafvert CT, Hua I (2004) Solar photodecomposition of decabromodiphenyl ether: products and quantum yield. Environ Sci Technol 38(15):4149–4156. doi:10.1021/es0498608o Chatterjee A (2011) Excited state reactivity index theory application for small moieties. Int J Quantum Chem 111(14):3821–3830. doi:10. 1002/qua.22941 Christiansson A, Eriksson J, Teclechiel D, Bergman A (2009) Identification and quantification of products formed via photolysis of decabromodiphenyl ether. Environ Sci Pollut Res 16(3):312–321. doi:10.1007/s11356-009-0150-4 Crosse JD, Shore RF, Jones KC, Pereira MG (2012) Long term trends in PBDE concentrations in gannet (Morus bassanus) eggs from two UK colonies. Environ Pollut 161:93–100. doi:10.1016/j.envpol. 2011.10.003 Davis EF, Stapleton HM (2009) Photodegradation pathways of nonabrominated diphenyl ethers, 2-ethylhexyltetrabromobenzoate and Di(2-ethylhexyl)tetrabromophthalate: identifying potential markers of photodegradation. Environ Sci Technol 43(15):5739– 5746. doi:10.1021/es901019w de Wit CA (2002) An overview of brominated flame retardants in the environment. Chemosphere 46(5):583–624 Eriksson L, Hu JW (2002a) 2,3,4,5,6-Pentabromophenyl phenyl ether. Acta Crystallogr E-Struct Rep Online 58:O794–O796. doi:10.1107/ s1600536802010942 Eriksson L, Hu JW (2002b) 4-Bromophenyl 2,3,4,5,6-pentabromophenyl ether. Acta Crystallogr E-Struct Rep Online 58:O1147–O1149. doi: 10.1107/s1600536802016926 Eriksson P, Jakobsson E, Fredriksson A (2001) Brominated flame retardants: a novel class of developmental neurotoxicants in our environment? Environ Health Perspect 109(9):903–908 Eriksson J, Green N, Marsh G, Bergman A (2004) Photochemical decomposition of 15 polybrominated diphenyl ether congeners in methanol/water. Environ Sci Technol 38(11):3119–3125. doi:10. 1021/es049830t Fang L, Huang J, Yu G, Wang L (2008) Photochemical degradation of six polybrominated diphenyl ether congeners under ultraviolet irradiation in hexane. Chemosphere 71(2):258–267. doi:10.1016/j. chemosphere.2007.09.041 Frisch AC, Webb PB, Zhao G, Muldoon MJ, Pogorzelec PJ, ColeHamilton DJ (2007) “Solventless” continuous flow homogeneous hydroformylation of 1-octene. Dalton Trans 0 (47): 5531–5538 Gaussian 98 (1998). Gaussian, Inc., Pittsburgh PA Hites RA (2004) Polybrominated diphenyl ethers in the environment and in people: a meta-analysis of concentrations. Environ Sci Technol 38(4):945–956. doi:10.1021/es035082g Kefeni KK, Okonkwo JO (2013) Trace metals, anions and polybromodiphenyl ethers in settled indoor dust and their association.
Environ Sci Pollut Res Environ Sci Pollut Res 20(7):4895–4905. doi:10.1007/s11356-0131469-4 Konstantinov A, Bejan D, Bunce NJ, Chittim B, McCrindle R, Potter D, Tashiro C (2008) Electrolytic debromination of PBDEs in DE-83 (TM) technical decabromodiphenyl ether. Chemosphere 72(8): 1159–1162. doi:10.1016/j.chemosphere.2008.03.046 Orazio C, Peterman P (2005) Brominated flame etardants in the environment. CERC - U. S. Geological Survey Shih YH, Wang CK (2009) Photolytic degradation of polybromodiphenyl ethers under UV-lamp and solar irradiations. J Hazard Mater 165(1– 3):34–38. doi:10.1016/j.jhazmat.2008.09.103 Shih Y-h, Tai Y-t (2010) Reaction of decabrominated diphenyl ether by zerovalent iron nanoparticles. Chemosphere 78(10): 1200–1206 Spartan ‘08 (2009) 1.2.0 edn. Wavefunction, Inc., Irvine
Sun CY, Zhao D, Chen CC, Ma WH, Zhao JC (2009) TiO2-mediated photocatalytic debromination of decabromodiphenyl ether: kinetics and intermediates. Environ Sci Technol 43(1):157–162. doi:10. 1021/es801929a WHO/ICPS (1994) Environmental health criteria 162, brominated diphenyl ethers. WHO, Geneve Xie Q, Chen JW, Shao JP, Chen CE, Zhao HX, Hao C (2009) Important role of reaction field in photodegradation of deca-bromodiphenyl ether: theoretical and experimental investigations of solvent effects. Chemosphere 76(11):1486–1490. doi:10.1016/j.chemosphere.2009. 06.054 Zeng X, Simonich SLM, Robrock KR, Korytar P, Alvarez-Cohen L, Barofsky DF (2008) Development and validation of congenerspecific photodegradation model for polybrominated diphenyl ethers. Environ Toxicol Chem 27(12):2427–2435
RESEARCH ARTICLE
Model for photodegradation of polybrominated diphenyl ethers M. Vesely & Z. Vajglova & P. Kotas & J. Kristal & R. Ponec & V. Jiricny
Received: 14 January 2014 / Accepted: 17 October 2014 # Springer-Verlag Berlin Heidelberg 2014
Abstract Polybrominated diphenyl ethers (PBDE) were, and in some countries still are, used as flame retardants for plastic materials. When released from plastics, PDBE cause harm to the environment. This creates the incentive for further investigation of the PBDE degradation. This work focused on a formulation of a PBDE photodegradation model based on the PBDE properties obtained by the quantum chemical calculations. The proposed model predicted degradation routes of arbitrary PBDE congener. The routes of selected congeners were validated by the two independently published data sets and showed the high fitting degree. The model can be easily modified for any reactor system if the initial reaction rate constant of one congener is available for the given system.
Keywords Polybrominated diphenyl ethers . Photodegradation model . Quantum chemical calculation
Responsible editor: Philippe Garrigues M. Vesely : Z. Vajglova : J. Kristal (*) : R. Ponec : V. Jiricny Institute of Chemical Process Fundamentals, AS CR, v. v. i., Rozvojova 135, 165 02 Prague 6, Czech Republic e-mail: [email protected] M. Vesely Institute of Chemical Technology, Technicka 5, 166 28 Prague 6, Czech Republic P. Kotas Global Change Research Centre, AS CR, v. v. i., Branisovska 31, 375 05 Ceske Budejovice, Czech Republic P. Kotas Department of Ecosystem Biology, Faculty of Science, University of South Bohemia, Branisovska 31, 370 05 Ceske Budejovice, Czech Republic
Introduction Polybrominated diphenyl ethers (PBDE) are chemical specialties produced since the 1970s. As additives, PBDE are present in a wide range of materials (e.g., plastic materials, heat insulation, polyurethane foam, textile fabric etc.) where they decrease the flammability of the material. PBDE possess aromatic character and represent a structural analog of the polychlorinated biphenyls (PCB) (Fig. 1). PBDE have 209 possible congeners and, according to the IUPAC nomenclature, their numbering is identical with PCB (Ballschmiter and Zell 1980). In 2004, EU banned the use of the PBDE mixture containing the tetra-, penta-, and octaBDE due to their severe environmental impact (Konstantinov et al. 2008). The estimated total PBDE production varies around 60,000 t per year (Hites 2004), and the dominating product is the decaBDE (BDE 209). Due to the continuous use of various mixtures of PBDE, they have been gradually released into the environment (Crosse et al. 2012; Besis and Samara 2012). In particular, the lower brominated PBDE are extremely persistent and being highly lipophilic, they pose a high risk of their bioaccumulation in organic fat tissue, or waste waters and sediments (Barraj et al. 2005). Despite the low concentration of PBDE accumulated in matrices (about ppb in fats), it is particularly alarming that over a longer perspective this concentration increases. Even more alarming is the fact that detectable PBDE concentrations were found even in human milk (de Wit 2002) or in settled indoor dust (Kefeni and Okonkwo 2013). In relation to the human toxicity, PBDE were classified by the US.EPA as teratogens and possible carcinogens (Eriksson et al. 2001) and endocrine disruptors (Orazio and Peterman 2005; Barraj et al. 2005). Because of the significant environmental impact of PBDE, there is a need to study the ways of the PBDE degradation. The possible degradation routes are the reductive and
Environ Sci Pollut Res O
Bry
Brx
Cly
Clx
This work focused on the quantum chemical calculation of the PBDE properties and their subsequent utilization for the formulation of the PBDE photodegradation model, including the degradation routes of selected congeners.
x + y = 1 - 10 PBDE
PCB
Fig. 1 Structure similarity of PBDE and PCB
electrochemical debromination, pyrolysis, active sludge biodegradation, microwave degradation, wet air oxidation, oxidative transformation, and the dominating photochemical degradation (WHO/ICPS 1994; Shih and Tai 2010; Bastos et al. 2008).
Photochemical degradation PBDE absorb ultraviolet light. The energy generated by the UV light absorption brings about gradual loss of the bromine atoms from the PBDE molecule. The reaction quantum yield depends on factors such as light intensity, wavelength, initial substrate concentration, and solvent. Zeng (Zeng et al. 2008) assumed the quantum yield for PBDE photodegradation to be constant. Shih (Shih and Wang 2009) studied the effect of the light intensity, wavelength, and the initial PBDE concentration on the rate of the degradation reaction. The BDE 209 was used as main substrate, and the reaction rate constant was determined for this congener. The reaction rate constant for the BDE 209 is affected by the light intensity, the higher the light intensity the higher the rate constant. No effect of the initial PBDE concentration on the reaction rate constant was observed, which corresponds to the kinetics of the pseudo-first order reaction. This is in agreement also with the analysis of the photoreaction quantum yield, that is practically constant over a wide range of reaction conditions (Bezares-Cruz et al. 2004). The analysis of the products of the photochemical degradation showed that the debromination is taking place preferably in the para position and the least preferred is the meta position with regard to the oxygen atom in the BDE 209 molecule (Shih and Wang 2009; Eriksson et al. 2004). A possible mechanism of the photodegradation was explained by Xie (Xie et al. 2009). From the technological point of view, the PBDE degradation is facing the problem of extremely low PBDE concentrations in the environmental samples. One of the alternatives to deal with this fact is to study the ways of increasing the PBDE concentration in the solvent prior to the decontamination process. One way would be the identification of a suitable sorption material. Another option is the extraction of the PBDE with the subsequent concentration of the PBDE organic solution. However, the disadvantage of the extraction process is the risk of the contamination of water with organic solvents.
Computation methods The quantum chemical calculations of the thermodynamic properties and other parameters of the studied series of PBDE congeners were carried out using the Austin method 1 (AM1) implemented in the Spartan 08 software (Spartan ‘08 2009) (gas state at 298.15 K and 101.325 kPa). The energies of the selected congeners in the excited state have been computed via calculation on excited states using singleexcitation (CIS) in Gaussian (Frisch et al. 2007; Gaussian 98 1998).
Photochemical degradation model The mechanism of PBDE photodegradation was studied by several authors (Bezares-Cruz et al. 2004; Eriksson et al. 2004). They found that the reaction follows the pseudo-first order kinetics with the dominating role of the dissociation of C-Br bond in the first excited state of corresponding congeners. The photochemical nature of the process was also demonstrated in Xie et al. (2009) where the authors described the correlation between the logarithm of the photodegradation reaction rate constant and the reciprocal wavelength of the UV transition into the first excited singlet state. The decisive factor in photodegradation is apparently the dissociation of the C-Br bond in the photoreactive excited state. In the formulated model, we assumed that the key to the elucidation of the observed differences of photodegradation of individual congeners was the knowledge of the dissociation energy of the C-Br bond in the photoreactive excited state of the corresponding congeners. However, obtaining these quantities was, in view of the extent of the studied series and the size of individual PBDE, beyond the current capabilities of theoretical calculation. To overcome the problem of solving the relative rates of photodegradation, we adopted the following simplifying assumption, namely, that within the group of the structurally similar compounds there exists a parallel between the magnitudes of the dissociation energies of the C-Br bond in the excited and the ground state. The possibility of utilizing the characteristics obtained by calculation in the ground state for the description of the molecule in the excited state has been also confirmed for chlorinated methanes and chlorinated benzenes (Chatterjee 2011).
Environ Sci Pollut Res Table 2 Review of most stable and least stable congeners
10
5 4
6
9
11
3
1
8
12
7
2
Group Most stable
Congener Number ΔG0f Congener Number ΔG0f of ortho [kJ/mol] of ortho [kJ/mol] Br Br
13
O
Fig. 2 Position labeling in PBDE molecule
The fact that the dissociation energies may be obtained for molecules in the ground state, from the thermodynamic parameters ΔH0f and or ΔG0f opens the way to explaining the differences in the rates of degradation of individual PBDE by means of the given thermodynamic experimental data. These, if not available as experimental data, may be obtained by quantum chemical calculations using Eq. (1). ΔH 0f i − ΔH 0f j k im ¼ exp −RT k mj
Mono Di Tri Tetra Penta Hexa
BDE 3 BDE 13 BDE 37 BDE 77 BDE 126 BDE 169
0 0 0 0 0 0
168.6 177.9 204.2 216.7 245.4 273.0
BDE 1 BDE 4 BDE 19 BDE 54 BDE 104 BDE 165
1 2 3 4 4 2
181.4 202.4 238.0 271.6 297.8 343.6
Hepta Octa Nona Deca
BDE 191 BDE 194 BDE 206 BDE 209
2 2 3 4
309.3 337.1 380.9 414.0
BDE 186 BDE 204 BDE 208 BDE 209
4 4 4 4
350.2 384.5 392.5 414.0
! ð1Þ
The kinetics of photodegradation of each congener, i, may be obtained by means of Eq. (2), where [i] designates concentration of the given congener i and Σki is the overall reaction rate constant of degradation of the given PBDE. Congener i is degraded to several lower congeners j with the specific reaction rate constant, kji, and Σki is then the sum of the specific reaction rate constants. However, a given congener i may be also a degradation product of a higher congener m. Therefore, the reaction rate equation for a given congener i contains
Table 1 Comparison of optimization for BDE 51 and BDE 166; PBDE position labeling is shown in Fig. 2 Congener
Least stable
Bond length [Å]
Bond angle [°]
C1-O7
O7-C8
C1-O7-C8
AM1 HF/STO-3G HF/3-21G* HF/6-31G* B3LYP/3-21G*
1.391 1.405 1.385 1.362 1.404
1.395 1.407 1.380 1.356 1.398
118.9 115.7 123.0 120.8 120.5
X-ray (Eriksson and Hu 2002a) AM1 HF/STO-3G HF/3-21G* HF/6-31G* B3LYP/3-21G* X-ray (Eriksson and Hu 2002b)
1.395
1.397
115.7
1.392 1.405 1.373 1.348 1.393 1.391
1.395 1.409 1.398 1.371 1.415 1.414
116.5 115.6 122.9 121.5 119.9 116.7
another term, αmikim[m], describing the production of congener i where [m] is the concentration of the original congener m, kim is the specific reaction rate constant of degradation of congener m to i and αmi is the number of potential routes for this reaction. The calculation of ki itself is given in Eq. (3) where kji is the specific reaction rate constant of degradation of congener i to lower congener j and αij is the number of potential routes for this debromination. d ½i ¼ −∑k i ½i þ αmi k im ½m dt
ð2Þ
k i ¼ ∑αi j k ij
ð3Þ
0
BDE 166
−1 −1.5
log(k) [−]
BDE 51
−0.5
−2 −2.5 −3 −3.5 −4 −4.5 −5
4.3
4.4
4.5
4.6
4.7
1/λ [1/nm]
4.8
4.9 −3
x 10
Fig. 3 Dependence of predicted reaction rate constants on computed wavelengths via CIS
Environ Sci Pollut Res
For the purpose of solving these equations, a MATLAB program was written to specify the congeners to which a given congener may be degraded as well as those from which the given congener could be produced. Part of this program was the determination of the number of routes for the given degradation. The inputs for the model were the relative concentrations of congeners PBDE and the reaction rate constant of
a
Model 100 90 80
Abundance [%]
70 60 deca nona octa hepta hexa
50 40 30 20 10 0
0
1
5
10
20
40
60
Time [min]
b
Shih 100 90 80 70
Abundance [%]
Fig. 4 Predicted products of photodegradation of BDE 209 after 60 min, reaction rate constant k209 =0.12 min-1 taken from Shih and Wang (2009)
degradation for BDE 209, k209 =1. The outputs were the relative concentrations of individual congeners in time. All the calculated values of ΔH0f and ki used in our model are listed in the Appendix. These presented data can be easily utilized for the prediction of the PBDE degradation routes in different photochemical reactors if the reaction rate of an arbitrary congener is known for the given reactor.
deca nona octa hepta hexa penta unknow
60 50 40 30 20 10 0
0
1
5
10
Time [min]
20
40
60
Environ Sci Pollut Res
Geometry of BDE 51 and BDE 166 was described experimentally (Eriksson and Hu 2002a, b). In this work, these results were used for the selection of the appropriate method for the calculation of the quantum chemical properties of PBDE congeners. To do this, we calculated the geometry of BDE 51 and BDE 166 using the following methods: semi-empirical method AM1, ab initio Hartree-Fock method (HF), and Density Functional Theory (DFT). Both molecules were optimized with HF/STO-3G, HF/3-21G*, HF/6-31G*, and B3LYP/321G*. The PBDE position labeling is shown in Fig. 2. Comparison of the computed data with the measured diffraction analysis (Table 1) showed a good agreement of experimental data with results computed by the AM1 method at the lowest computational requirements. Therefore, all the 209 congeners were computed by the AM1 method. Stability of PBDE Thermodynamic properties calculated by the AM1 method were used to assess the stability of PBDE congeners. The relative stability of individual congeners may be characterized by computed ΔG0f and ΔH0f . Gibbs free energy equation was used for ΔG0f . In fact, the lower ΔG0f , the greater is the thermodynamic stability. As may be seen in Table 2, ΔG0f grows with the number of bromines in the molecule of PBDE. With the same number of bromines, the difference in ΔG0f is caused by the different number of bromines in the ortho positions. With the growing number of these positions, ΔG 0f again increases. From this, it follows that substituted ortho positions decrease the thermodynamic stability of congeners. Higher energies of such congeners may be explained by steric effects. The most stable and the least stable congeners for characteristic groups of PBDE are given in Table 1. From the analysis of calculated ΔG0f , it follows that the relatively least stable congener is BDE 209. Another justification of the assumption of the least thermodynamic stability of BDE 209 is the fact that BDE 209 became the most widely used fire retardant on the basis of
BDE 28 BDE 15
0.9
0
Relative concentration; C / C [−]
Selection of the PBDE geometry optimization method
Degradation products of BDE 28 1
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0
5
10
15
20
Time [h] Degradation products of BDE 47 1
Relative concentration; C / C [−] 0
In the following sections, we present the results related to the PBDE degradation model. Firstly, we selected an appropriate quantum chemical method for calculation of thermodynamic properties of all PBDE congeners. Based on the calculated thermodynamic properties, we discussed the stability of PBDE congeners. Secondly, the results of the formulated PBDE degradation model are presented.
PBDE. One must not forget, however, that even though BDE 209 is the least stable PBDE congener, it is still a strongly persistent substance.
BDE 47 BDE 28 BDE 15
0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0
2
4
6
8
10
Time [h] Degradation products of BDE 99 1
Relative concentration; C / C [−] 0
Results and discussion
BDE 99 BDE 66 BDE 47 BDE 28
0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0
2
4
6
8
10
Time [h] Fig. 5 Time dependence of the relative concentration of selected congeners during degradation of BDE 28, BDE 47, and BDE 99; experimental data (Fang et al. 2008) (markers), presented model (lines)
Environ Sci Pollut Res
PBDE degradation results
Model validation against the experimental data
Justification of the calculations in the ground state
We formulated the model for the general case of k209 =1. For the direct comparison of our degradation model and experimental data at the identical time scale, the knowledge of the experimental reaction rate constant is necessary. To verify our model, we use a published reaction rate constant k209 = 0.12 min−1 (Shih and Wang 2009), relevant for the degradation in hexane with BDE 209 initial concentration of 12.5 mg/L. Another experimental dataset (Fang et al. 2008) was used for comparison of degradation product from three individual congeners—BDE 28, BDE 47, and BDE 99. Published values (Fang et al. 2008) of experimental reaction rate constant were supplied to the model of photochemical degradation and the relative concentrations of the degradation components were calculated. The composition of the reaction mixture after 1, 5, 10, 20, 40, and 60 min of the BDE 209 degradation is shown in Fig. 4. The comparison of the
The justification of the simplifying assumption of the proportionality of the dissociation energies of the C-Br bond in the ground and excited state was verified by the correlation between the logarithm of the reaction rate constants calculated from the presented model and the excitation energies of UV transition to the first excited singlet state. The wavelengths were calculated using the CIS involving the mono excited configuration. For the calculation of the wavelengths, we used the congeners from all congener groups. From Fig. 3, it is evident that the calculated log(k) values based on AM1 calculations clearly correlate with the excitation energies calculated by CIS. The linear dependence of the log(k) on the inversed wavelength is in agreement with published data (Eriksson et al. 2004; Xie et al. 2009). Fig. 6 Predicted degradation routes of BDE 209; major products (rectangular box), common products (no designation), and minor products (underlined)
209
207
206
194
195
196
197
199
198
171
170
128
208
201
200
176
175
129
131
132
137
139
158
84
82 88
40
41
109
42
44
45
47
55
16
17
20
4
5
6
7
11
12
1
134
87
85
105
184
2
202
203
204
205
Environ Sci Pollut Res
Prediction of degradation routes
results of our model and the experimental data (Shih and Wang 2009) shows the good qualitative agreement. The representation of the individual groups follows the similar trends. The model results are in qualitative agreement with the experiment. The model results are slightly shifted to the longer times. This difference can be attributed to the uncertainties in the determination in the experimental reaction rate constant. Other authors also described similar dependences for the degradation of BDE 209 to lower congeners (Sun et al. 2009) and for degradation to the higher congeners (Christiansson et al. 2009). Also, photochemical degradation of lower brominated congeners is described very well by our model. The results for degradation of BDE 28, BDE 47, and BDE 99 dissolved in hexane are shown in Fig. 5 for both the experiment (Fang et al. 2008) and our model. Degradation of the lower brominated congeners seems to be quicker than the prediction, but the degradation of the individual congeners is still predicted by the model very well qualitatively. The concentration curves of the selected congeners essentially overlap each other in both the experiment and model.
194
195
170
128
a
b
c
206
207
208
198
196
171
180
129
131
85
82
187
137
138
42 52
56
60
66
197
139
5
4 8
45
82
84
85
91
105
55
17
1
12
2
22
21
33
28
5
6
8
7
12
2
144
136
82
83
84
87
88
109
41
44
45
16
17
20
55
20
4
1
132
60
40
28
179
131
130
129
77
7
176
175
202
45
42
41 47
200
132
88
40
55
6 11
199
134
105
22
20
198
158
139
16
17
16
131
129 137
204
184
176
171
128
199
163
44
49
195
149
91 95
47
205
191
147
87
41
40
183
158
156
153
203
201
146
144
141
The degradation routes of BDE 209, BDE 208, BDE 207, and BDE 206 were predicted by our model and are shown in Figs. 6 and 7. These four congeners were selected since they were frequently present in the commercial PBDE mixtures. In the degradation routes diagrams, the following labeling is used. In each congener group, we selected the congener with the highest concentration as a reference point. The congeners were labeled as major if their maximum concentration reached above 50 % of the reference concentration. The congeners were labeled as common if their maximum concentration was between 40 and 50 % of the reference concentration. The congeners were labeled as minor if their occurrence was predicted and their maximum concentration was below 40 % of the reference concentration. The minor category was used for the first and second degradation step for BDE 209 and only for the first degradation step for nonaBDE. In the further degradation steps, the broad spectrum of subsequent congeners is formed, and the diagram would be too complicated. Therefore, the minor category is not shown.
4
5
7
6
1
11
2
3
Fig. 7 Predicted degradation routes of a BDE 206, b BDE 207, and c BDE 208; major products (rectangular box), common products (no designation), and minor products (underlined)
Environ Sci Pollut Res
a
b
BDE 206 1 mono di tri tetra penta hexa hepta octa nona all
0.8
c / c0 [−]
BDE 207 1
0.6
0.4
mono di tri tetra penta hexa hepta octa nona all
0.8
c / c0 [−]
Fig. 8 Degradation profiles of specific congeners a BDE 206, b BDE 207, c BDE 208, and d BDE 209
0.6
0.4
0.2
0.2
0
0 10
−1
0
10
10
1
10
2
3
10
10
4
10
−1
10
0
10
Time [h]
c
d
BDE 208 1
mono di tri tetra penta hexa hepta octa nona all
0.8 0.7
10
2
10
3
10
4
0.6 0.5 0.4 0.3 0.2
BDE 209
1
mono di tri tetra penta hexa hepta octa nona deca all
0.8
c / c0 [−]
0.9
c / c0 [−]
1
Time [h]
0.6
0.4
0.2
0.1 0 10
−1
0
10
10
1
10
2
10
3
0
4
10
10
−1
Predicted routes of degradation for BDE 209 correspond with the published experimental work (Sun et al. 2009). The first predicted step of BDE 206 degradation and the relative compositions qualitatively agree with another published experimental data (Davis and Stapleton 2009); the identical congeners were predicted and found experimentally. For both BDE 207 and 208, Davis experimentally found one major Table 3 Effect of the reaction rate constant magnitude on BDE 209 degradation profile BDE group 0.1 k BDE 209 A
tmax
1 k BDE 209
10 k BDE 209
A
A
tmax
Tetra Tri Di Mono
3.22 5.02 8.90 16.18 33.69
4.67 8.52 14.21 25.49 44.27
1.02 1.59 2.82 5.12 10.65
1.48 2.69 4.49 8.06 14.00
tmax 0.32 0.50 0.89 1.62 3.3
0
10
1
10
2
10
3
10
4
congener (BDE 200 and BDE 201 for BDE 207 and 208, respectively) that was not predicted by our model. This difference can be attributed to the small difference in the calculated values of ΔH0f between the given nona- and octa-congeners. Consequently, the small difference of enthalpies could cause the different predicted composition of the reaction mixture. Nonetheless, we can conclude that the agreement between the experimental data (Sun et al. 2009; Davis and Table 4 Characteristics of degradation profiles of specific congeners BDE 206, BDE 207, and BDE 208 BDE group
BDE 208 A
Nona Octa Hepta Hexa Penta
10
Time [h]
Time [h]
BDE 207 tmax
A
BDE 206 tmax
A
tmax
0.47 0.85 1.42 2.55 4.43
Octa Hepta Hexa Penta
1.7 2.9 4.3 9.4
2.2 4.4 7.7 13.6
1.9 2.8 5.3 10.5
2.4 4.6 8.2 14.1
1.7 3.0 5.5 11.5
2.1 4.2 7.8 14.1
75.52 75.12 23.88 23.75 7.55 7.51 174.45 135.79 55.17 42.94 17.44 13.58 524.98 541.42 166.01 162.67 52.50 51.44 1,758.75 1,055.56 556.05 333.80 175.87 105.56
Tetra Tri Di Mono
21.6 50.4 145.2 549.5
23.1 40.4 146.9 323.4
22.4 55.2 169.5 567.0
23.3 41.8 164.4 326.8
26.6 57.5 172.9 548.5
25.3 47.2 171.5 339.1
A area under the concentration profile curve, tmax time of maximum concentration of a given congener group
A area under the concentration profile curve, tmax time of maximum concentration of a given congener group
Environ Sci Pollut Res
Stapleton 2009) and our model is very good as most of the p r e di c t e d de gr ad at i o n p r o du c t s w e r e c on f i r m e d experimentally. The predicted degradation route of BDE 209 is in agreement with the routes of nonaBDE with respect to their relative abundance. The analysis of the individual congener structure, and their relative abundance (Fig. 5), revealed the easiest degradation of the C-Br bond in the ortho position; on the other hand, the product of degradation of the C-Br bond in the para position is minor. This result was in accordance with the calculated ΔG0f values (Table 2) and was in agreement with the findings of Shih (Shih and Wang 2009). Degradation profiles of specific congeners are shown in Fig. 8 and their characteristics in Tables 3 and 4. The comparison of the tmax differences for the different PDBE groups documented the lower disposition for degradation of the lower brominated congeners. The time needed for the degradation of the whole group increased exponentially with the decreasing number of bromine in the PBDE molecule. This was again in accordance with the calculated ΔG0f values. The comparison of the concentration of the given PBDE groups (BDE 206, BDE 207, and BDE 208) confirmed the fact that the total degradation time was affected by the structure of the starting congener. If the starting congener contained more bromines in the para position (BDE 206), its degradation proceeded slower than if the starting congener contained more bromines in the ortho position (BDE 208). If the starting congener contained the bromine in the both para and ortho positions (BDE 207), its degradation proceeded at the intermediate rate. As a result, for the lower brominated groups (tetra and lower), there was a clearly decreasing trend in tmax: tmax(206)>tmax(207)>tmax(208). This was again in accordance with the calculated ΔG0f values indicating that BDE 206 and BDE 208 are the most and least stable congener, respectively, in the nonaBDE group. Effect of the reaction rate constant magnitude on BDE 209 degradation profile is shown in Table 3. Three different magnitudes of reaction rate constant were used to show that the absolute value of the reaction rate constant has no effect on the composition of the reaction mixture. Relative concentrations of the individual PBDE group as well as the tmax values were constant for all three values of the reaction rate constant. This was in accordance with the assumption of the pseudo-first order kinetics.
Conclusions The presented work was focused on the formulation of a mathematical model for the photochemical degradation of the polybrominated diphenyl ethers. Using the Spartan
software, the selected thermodynamic properties of individual congeners of PBDE were computed using the AM1 method. The energies of selected congeners in the excited state were computed using CIS. On the basis of the computed PBDE properties, a model was formulated describing the photochemical degradation of PBDE. The model results were compared with the published experimental data, and the good agreement was found in terms of the concentration time dependence and the mixture composition during the BDE 209 degradation. The proposed model was then used for prediction of the degradation routes of BDE 99, BDE 47, and BDE 28 The qualitative agreement between the published experimental data and our model is good. The analysis of the individual congener structure, and their relative abundance revealed the easiest degradation of the CBr bond in the ortho position. If the starting congener contained more bromines in the para position (BDE 206), its degradation proceeded slower than if the starting congener contained more bromines in the ortho position (BDE 208). The results also indicated the lower disposition for photochemical degradation of the lower brominated congeners. If the initial degradation reaction rate is known for any arbitrary congener, the proposed model is able to predict the time needed for the degradation of the given congener to the desired level under different conditions (reactors). The values of ki and ΔH0f needed as the model inputs are presented in the “Appendix.”
Nomenclature Symbol
Unit
Description
A BDE c c0 EU GC HOMO IUPAC ki kim
– – mmol/l mmol/l – – – – s−1 s−1
Kow LUMO PBDE PCB QSAR
– – – – –
Area under the concentration profile curve Brominated diphenyl ether Actual concentration Initial concentration European Union Gas chromatography Highest occupied molecular orbital International Union of Pure and Applied Chemistry Degradation rate constant of congener i Specific degradation rate constant of congener m to congener i Octanol-water distribution coefficient Lowest unoccupied molecular orbital Polybrominated diphenyl ether Polychlorinated biphenyl Quantitative structure-activity relationship
R T
J/mol/K Universal gas constant K Thermodynamic temperature
Environ Sci Pollut Res tmax US EPA UV Α αmi
H – – A3 –
ΔG0f ΔH0f λmax
kJ/mol kJ/mol nm
Time of PBDE concentration maximum United States Environmental Protection Agency Ultraviolet light Polarizability Number of possible ways to formation of congener i from m Gibbs free energy of formation Standard enthalpy of formation Wavelength of maximal absorbance of UV
Acknowledgments The work has been carried out in the frame of the Czech Science Foundation project no. 104/09/0800. J. Kristal also acknowledges support by the Czech Science Foundation project no. P105/12/0664.
Appendix
Table 5 Specific reaction rate constants for all PBDE congeners
No.
k [s−1]
1 2 3 4 5 6 7 8 9 10 11
9.37e-006 5.89e-007 7.86e-007 3.08e-005 4.82e-004 1.45e-005 3.43e-005 1.10e-005 2.93e-005 3.41e-005 2.15e-006
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
5.74e-005 2.16e-006 4.60e-006 2.30e-006 7.93e-004 7.15e-005 7.10e-005 8.07e-005 7.44e-004 2.84e-003 5.27e-004 1.46e-003 9.65e-004 5.37e-005 4.60e-005 5.21e-005 3.97e-005 2.77e-004
30 31
1.23e-004 3.39e-005
Table 5 (continued) No.
k [s−1]
32 33 34
3.68e-005 8.55e-005 2.72e-005
35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52
9.47e-005 1.08e-005 8.53e-005 1.51e-003 9.11e-006 2.34e-003 4.42e-003 9.50e-004 2.41e-003 1.27e-003 1.56e-003 1.36e-003 1.23e-004 4.07e-004 1.36e-004 2.29e-004 1.48e-004 1.44e-004
53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71
1.60e-004 1.78e-004 4.60e-003 9.42e-004 2.25e-003 1.12e-003 1.46e-003 3.59e-003 1.41e-002 6.69e-003 1.63e-003 1.08e-003 5.54e-003 1.66e-004 4.46e-004 8.74e-005 1.87e-004 1.69e-004 1.49e-004
72 73 74 75 76 77 78 79 80
7.92e-005 8.69e-005 3.66e-004 1.43e-004 1.75e-003 2.76e-004 2.38e-003 1.75e-004 3.25e-005
Environ Sci Pollut Res Table 5 (continued)
Table 5 (continued) No.
k [s−1]
No.
k [s−1]
81 82 83
2.18e-003 8.71e-003 5.42e-003
130 131 132
1.64e-002 1.96e-002 1.42e-002
84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101
4.31e-003 5.81e-003 1.96e-002 7.42e-003 1.05e-002 6.97e-003 2.78e-003 1.84e-003 3.63e-003 8.91e-003 3.99e-003 2.52e-003 2.61e-003 1.96e-003 1.72e-003 5.82e-004 3.17e-004 6.85e-004
133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150
1.09e-002 1.64e-002 9.34e-003 7.58e-003 2.70e-002 1.03e-002 1.39e-002 8.94e-003 3.32e-002 8.51e-002 2.86e-002 1.77e-002 1.62e-002 4.98e-003 1.02e-002 4.67e-003 3.51e-003 3.28e-003
102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120
6.38e-004 3.82e-004 4.20e-004 6.22e-003 2.31e-002 7.78e-003 1.15e-002 2.74e-003 1.84e-003 3.41e-003 8.29e-003 2.24e-003 1.93e-002 8.88e-003 6.00e-002 6.25e-003 7.94e-004 3.41e-004 7.38e-004
151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169
1.38e-002 1.43e-002 1.67e-003 1.06e-003 7.09e-004 3.18e-002 1.43e-002 1.60e-002 3.80e-002 9.80e-002 1.98e-002 8.28e-003 9.90e-003 5.79e-003 1.29e-002 8.06e-002 5.07e-003 3.29e-003 1.10e-002
121 122 123 124 125 126 127 128 129
2.93e-004 4.09e-003 2.54e-003 2.87e-003 2.12e-003 3.74e-003 3.77e-003 1.88e-002 3.43e-002
170 171 172 173 174 175 176 177 178
5.92e-002 3.78e-002 6.02e-002 1.48e-001 5.05e-002 3.58e-002 3.10e-002 3.48e-002 3.04e-002
Environ Sci Pollut Res Table 6 (continued)
Table 5 (continued)
Table 6 Values of ΔH0f for all PBDE congeners
No.
k [s−1]
No.
ΔH0f [kJ/mol]
179 180 181
2.82e-002 4.55e-002 1.16e-001
182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199
3.81e-002 2.50e-002 2.14e-002 1.44e-001 1.22e-001 1.71e-002 1.72e-002 6.00e-002 1.38e-001 3.22e-002 1.71e-001 2.06e-002 1.49e-001 2.23e-001 1.04e-001 7.23e-002 2.54e-001 1.05e-001
200 201 202 203 204 205 206 207 208 209
2.19e-001 7.18e-002 6.81e-002 2.02e-001 1.69e-001 2.46e-001 4.59e-001 3.56e-001 3.98e-001 1.00e+000
No.
ΔH0f [kJ/mol]
1 2 3 4 5 6 7 8 9 10 11 12 13
79.215 68.535 66.425 116.330 107.950 104.330 104.820 100.290 106.240 117.580 92.260 95.540 91.880
14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62
96.190 90.220 145.775 142.535 144.775 157.235 135.545 138.205 131.485 138.625 149.605 133.455 134.135 145.345 131.215 135.835 146.195 132.405 142.665 132.475 133.285 123.455 124.305 121.215 126.745 122.545 176.520 175.180 173.990 175.910 175.710 190.690 190.220 171.660 172.990 173.200 189.450 183.620 171.510 184.970 201.700 166.020 162.680 166.160 164.010 177.080 164.300 170.250 182.340
Environ Sci Pollut Res Table 6 (continued)
Table 6 (continued) No.
ΔH0f [kJ/mol]
No.
ΔH0f [kJ/mol]
63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111
164.860 174.510 183.400 162.210 164.200 163.300 173.800 160.040 173.050 164.130 174.400 162.520 173.890 163.280 151.580 154.820 153.400 151.910 153.550 206.045 206.805 219.025 205.115 207.335 204.715 221.235 216.735 205.595 215.965 206.505 221.915 217.305 216.975 233.645 204.285 217.955 203.765 217.145 202.845 214.365 216.005 231.945 195.065 198.855 194.125 195.215 210.125 204.845 194.105
112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160
210.385 206.495 195.835 221.455 214.875 208.195 193.025 204.045 194.795 202.915 194.385 193.805 193.455 204.115 184.185 185.535 237.830 238.790 238.880 251.690 248.910 238.340 252.340 249.520 264.840 238.520 237.120 248.940 248.020 237.420 256.280 248.910 250.170 265.560 235.970 249.350 248.350 248.540 263.640 250.780 266.890 234.610 245.910 259.050 227.970 224.710 238.170 229.410 242.630
Environ Sci Pollut Res Table 6 (continued)
References No.
ΔH0f
161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209
226.400 226.430 238.520 252.980 276.100 258.230 234.650 244.610 214.010 271.835 282.095 270.645 289.045 281.545 282.275 297.425 285.265 283.065 298.595 270.495 286.455 280.595 282.385 295.825 285.615 300.895 283.515 297.095 296.895 273.535 269.955 272.665 270.625 304.060 319.770 317.450 329.430 318.110 332.820 330.850 318.390 338.470 313.420 335.690 305.730 353.085 365.565 366.515 401.170
[kJ/mol] Ballschmiter K, Zell M (1980) Analysis of polychlorinated-biphenyls (PCB) by glass-capillary gas-chromatography—composition of technical aroclor-PCB and clophen-PCB mixtures. Fresenius Z Anal Chem 302(1):20–31 Barraj L, van den Berg M, Darnerud PO, Feeley M, Lilienthal H, Papke O, Bolger M, Tohyama C (2005) Polybrominated diphenyl ethers. Exponent, Washington DC Bastos PM, Eriksson J, Vidarson J, Bergman A (2008) Oxidative transformation of polybrominated diphenyl ether congeners (PBDEs) and of hydroxylated PBDEs (OH-PBDEs). Environ Sci Pollut Res 15(7):606–613. doi:10.1007/s11356-008-0045-9 Besis A, Samara C (2012) Polybrominated diphenyl ethers (PBDEs) in the indoor and outdoor environments—a review on occurrence and human exposure. Environ Pollut 169:217–229. doi:10.1016/j. envpol.2012.04.009 Bezares-Cruz J, Jafvert CT, Hua I (2004) Solar photodecomposition of decabromodiphenyl ether: products and quantum yield. Environ Sci Technol 38(15):4149–4156. doi:10.1021/es0498608o Chatterjee A (2011) Excited state reactivity index theory application for small moieties. Int J Quantum Chem 111(14):3821–3830. doi:10. 1002/qua.22941 Christiansson A, Eriksson J, Teclechiel D, Bergman A (2009) Identification and quantification of products formed via photolysis of decabromodiphenyl ether. Environ Sci Pollut Res 16(3):312–321. doi:10.1007/s11356-009-0150-4 Crosse JD, Shore RF, Jones KC, Pereira MG (2012) Long term trends in PBDE concentrations in gannet (Morus bassanus) eggs from two UK colonies. Environ Pollut 161:93–100. doi:10.1016/j.envpol. 2011.10.003 Davis EF, Stapleton HM (2009) Photodegradation pathways of nonabrominated diphenyl ethers, 2-ethylhexyltetrabromobenzoate and Di(2-ethylhexyl)tetrabromophthalate: identifying potential markers of photodegradation. Environ Sci Technol 43(15):5739– 5746. doi:10.1021/es901019w de Wit CA (2002) An overview of brominated flame retardants in the environment. Chemosphere 46(5):583–624 Eriksson L, Hu JW (2002a) 2,3,4,5,6-Pentabromophenyl phenyl ether. Acta Crystallogr E-Struct Rep Online 58:O794–O796. doi:10.1107/ s1600536802010942 Eriksson L, Hu JW (2002b) 4-Bromophenyl 2,3,4,5,6-pentabromophenyl ether. Acta Crystallogr E-Struct Rep Online 58:O1147–O1149. doi: 10.1107/s1600536802016926 Eriksson P, Jakobsson E, Fredriksson A (2001) Brominated flame retardants: a novel class of developmental neurotoxicants in our environment? Environ Health Perspect 109(9):903–908 Eriksson J, Green N, Marsh G, Bergman A (2004) Photochemical decomposition of 15 polybrominated diphenyl ether congeners in methanol/water. Environ Sci Technol 38(11):3119–3125. doi:10. 1021/es049830t Fang L, Huang J, Yu G, Wang L (2008) Photochemical degradation of six polybrominated diphenyl ether congeners under ultraviolet irradiation in hexane. Chemosphere 71(2):258–267. doi:10.1016/j. chemosphere.2007.09.041 Frisch AC, Webb PB, Zhao G, Muldoon MJ, Pogorzelec PJ, ColeHamilton DJ (2007) “Solventless” continuous flow homogeneous hydroformylation of 1-octene. Dalton Trans 0 (47): 5531–5538 Gaussian 98 (1998). Gaussian, Inc., Pittsburgh PA Hites RA (2004) Polybrominated diphenyl ethers in the environment and in people: a meta-analysis of concentrations. Environ Sci Technol 38(4):945–956. doi:10.1021/es035082g Kefeni KK, Okonkwo JO (2013) Trace metals, anions and polybromodiphenyl ethers in settled indoor dust and their association.
Environ Sci Pollut Res Environ Sci Pollut Res 20(7):4895–4905. doi:10.1007/s11356-0131469-4 Konstantinov A, Bejan D, Bunce NJ, Chittim B, McCrindle R, Potter D, Tashiro C (2008) Electrolytic debromination of PBDEs in DE-83 (TM) technical decabromodiphenyl ether. Chemosphere 72(8): 1159–1162. doi:10.1016/j.chemosphere.2008.03.046 Orazio C, Peterman P (2005) Brominated flame etardants in the environment. CERC - U. S. Geological Survey Shih YH, Wang CK (2009) Photolytic degradation of polybromodiphenyl ethers under UV-lamp and solar irradiations. J Hazard Mater 165(1– 3):34–38. doi:10.1016/j.jhazmat.2008.09.103 Shih Y-h, Tai Y-t (2010) Reaction of decabrominated diphenyl ether by zerovalent iron nanoparticles. Chemosphere 78(10): 1200–1206 Spartan ‘08 (2009) 1.2.0 edn. Wavefunction, Inc., Irvine
Sun CY, Zhao D, Chen CC, Ma WH, Zhao JC (2009) TiO2-mediated photocatalytic debromination of decabromodiphenyl ether: kinetics and intermediates. Environ Sci Technol 43(1):157–162. doi:10. 1021/es801929a WHO/ICPS (1994) Environmental health criteria 162, brominated diphenyl ethers. WHO, Geneve Xie Q, Chen JW, Shao JP, Chen CE, Zhao HX, Hao C (2009) Important role of reaction field in photodegradation of deca-bromodiphenyl ether: theoretical and experimental investigations of solvent effects. Chemosphere 76(11):1486–1490. doi:10.1016/j.chemosphere.2009. 06.054 Zeng X, Simonich SLM, Robrock KR, Korytar P, Alvarez-Cohen L, Barofsky DF (2008) Development and validation of congenerspecific photodegradation model for polybrominated diphenyl ethers. Environ Toxicol Chem 27(12):2427–2435
