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Wet air co-oxidation of decabromodiphenyl ether (BDE209) and tetrahydrofuran
Journal of Hazardous Materials 169 (2009) 1146–1149
Contents lists available at ScienceDirect
Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat
Short communication
Wet air co-oxidation of decabromodiphenyl ether (BDE209) and tetrahydrofuran Hongxia Zhao a,b , Feifang Zhang a , Baocheng Qu b , Xingya Xue a , Xinmiao Liang a,∗ a b
Dalian Institute of Chemical Physics, Chinese Academy of Science, Dalian 116023, China Key Laboratory of Industrial Ecology and Environmental Engineering, MOE, Dalian University of Technology, Dalian 116024, China
a r t i c l e
i n f o
Article history: Received 2 September 2008 Received in revised form 14 March 2009 Accepted 18 March 2009 Available online 27 March 2009 Keywords: Co-oxidation BDE209 THF Promotion effect Free radical
a b s t r a c t The wet air co-oxidation (WACO) of a major commercial polybrominated diphenyl ether flame retardant congener, decabromodiphenyl ether (BDE209), was investigated using tetrahydrofuran (THF) as an initiator in a stainless autoclave at temperature range of 120–170 ◦ C and 0.5 MPa oxygen pressure. Compared to the single oxidation of BDE209 under the same conditions, the addition of THF in the reaction system greatly improved the removal efficiency of BDE209. The effect of temperature on the reaction was studied. The removals of BDE209 and Br increased with increasing temperature. In addition, the effect of NaNO2 as the catalyst on the WACO was also investigated and the results showed that the addition of NaNO2 could improve the Br removal efficiency. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Polybrominated diphenyl ethers (PBDEs) have been widely used as flame retardants to reduce the fire risk on plastics, carpets, electronic equipment, textiles and building materials around the world [1]. PBDEs are structurally similar to polychlorinated biphenyls (PCBs) with the same nomenclature and number (209) of congeners [2]. At present, they have been found in a wide range of environmental and biological samples including birds, edible marine organisms, marine mammals and human beings [3,4]. Environmental monitoring for the past 20 years has shown that PBDEs are persistent in sediment and bioaccumulate in tissues [5]. Levels in human milk are increasing [6], as are levels in organisms that inhabit in the deep oceans [5,7]. Although the acute toxicity of PBDEs is thought to be low relative to polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and co-planar PCBs, they are proven endocrine disruptors that destroy thyroid hormone balance and cause developmental problems [8]. It is reported that pentaBDEs are the most toxic, causing developmental toxicity at concentrations starting at 0.8 mg kg−1 body weight [9], while octaBDEs are teratogens and decaBDE is classified by the U.S. EPA as a possible human carcinogen [10]. Therefore, to suppress the accumulation of these compounds in the environment, development of techniques for decomposing them to harmless or lower toxic species is desirable.
However, few published studies are available regarding biotic and abiotic degradation of PBDEs. Debromination of BDE209 and an octaBDE mixture was observed with anaerobic bacteria including Sulfurospirillum multivorans and Dehaloccoides species [11]. In sediments, BDE209 can be biotransformed into lower mass PBDE congeners and its debromination half-life in sediments was over a decade [12]. Chemical reduction degradation with zerovalent iron and photolytic decomposition of PBDEs are proposed, respectively [13–15]. However, the wet air oxidation (WAO) of PBDEs is not well documented. WAO aiming at treating persistent organic pollutants in industrial wastewaters has been actively explored. Numerous methods have been investigated to increase the oxidation rate and effectiveness of WAO processes. Besides catalytic WAO processes [16], co-oxidation is another important way to increase oxidation rate. Since some compounds are very difficult to be oxidized under moderate reaction conditions, more easily oxidisable compounds may initiate the more difficultly oxidisable compounds. Therefore, wet air co-oxidation (WACO) has drawn more and more attention of researchers [17–19]. In this paper, the WACO of a major commercial polybrominated diphenyl ether flame retardant congener, BDE209, was studied with THF as an initiator for the first time. The aim of the present work was to gain experimental information about the simultaneous BDE209 and THF wet air co-oxidation. 2. Experimental 2.1. Chemicals and standards
∗ Corresponding author. Tel.: +86 411 84707965. E-mail address: [email protected] (X. Liang). 0304-3894/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2009.03.089
The technical product of BDE209 was purchased from Accustandard, Inc. (New Haven, CT, USA). A total of 39 PBDE standards
H. Zhao et al. / Journal of Hazardous Materials 169 (2009) 1146–1149
were bought for the identification of low brominated reaction products, among them 10 PBDE congeners containing BDE30, -32, -35, -37, -75, -116, -155, -166, -181 and -190 in nonane solution were obtained from Cambridge Isotope Laboratories (Andover, MA, USA). PBDE-MXE containing BDE3, -7, -15, -17, -28, -47, -49, -71, -66, -99, -77, -85, -100, -119, -126, -138, -153, -154, -156, -183, -184, -191, -196, -197, -206 and -207 in nonane solution was purchased from Wellington Laboratories (Guelph, Ontario, Canada). NaNO2 , Na2 SO4 , DMSO, THF and ethyl acetate (Tedia Co.) were of analytical grade and were used without further purification. Water was prepared with a Milli-Q water purification system (Millipore, Milford, MA, USA) throughout all experiments. 2.2. Wet air co-oxidation The WACO of BDE209 with THF as an initiator was carried out in a 50 mL of Teflon-lined stainless steel autoclave equipped with a magnetic stirrer. The reaction temperature was measured using a thermocouple and controlled by a PID regulator. 96 g mL−1 BDE209 solution was added to the autoclave. The autoclave was closed and charged with pure oxygen to 0.5 MPa and heated to the desired temperature. The stirring speed was set at 500 r min−1 . After reaction (heating time included), the autoclave was cooled to room temperature with a water bath. Carefully depressurized, it was sampled for further analysis. 2.3. Determination of calibration curve Commercially available standards of BDE209 (9.6 mg) was dissolved in 100 mL of THF solution, and used as standard stock solutions for generating calibration curves. The stock solutions were diluted 1/5, 1/10, 1/25 and 1/100 times in THF to afford 19.2 g mL−1 , 9.6 g mL−1 , 3.84 g mL−1 and 0.96 g mL−1 solutions of BDE209. These four standard solutions and the stock solution were injected to generate a five-point calibration curve for the standard compounds using GC-ECD. Standard curve was linear with R2 = 0.9998. Peak areas of the target compound were within the linear range of the curve. Relative standard deviations for two injections were less than 2%. Using the similar dilution method, a five-point calibration curve for Br− was obtained by IC at the concentration range from 0.8 g mL−1 to 80 g mL−1 and the linear regression coefficient (R2 ) was 0.998. 2.4. Sample preparation and analysis After WACO, 5 mL aliquot of reaction solution was removed from the autoclave by disposable plastic syringe and subjected to a liquid–liquid extraction with an equal volume of ethyl acetate in a 15-mL glass tube. The mixture was vortexed for 3 min and shaked 1 h in order to extract the PBDEs into the ethyl acetate phase. After Na2 SO4 dryness, the extraction organic phase was transferred to GC vial for analysis. The inorganic phase was used to analyze the Br− by IC. BDE209 and its low brominated degradation products were separated using an Agilent 6890GC (Palo Alto, CA, USA) equipped with a fused silica DB-5 column ((5% phenyl) methylpolysiloxane, 30 m × 320 m i.d., 0.25 m film thickness, J&W Scientific, Inc., Folsom, CA, USA), and an Agilent 7683 Series automatic liquid sampler and injector. A 1-L injection, made in the split mode (20:1), was employed for all samples. These brominated compounds were monitored with a 63 Ni ECD detector. Nitrogen was used as the carrier and makeup gas. The temperature program was as follow: 90 ◦ C (2.0 min), 30 ◦ C min−1 , 200 ◦ C, 1.5 ◦ C min−1 , 325 ◦ C (7.0 min). HP Chemstation software was used to collect and process data from the GC-ECD. Br− was identified and quantified by means of non-suppressed ion chromatography (SCL-10Asp, Shimadzu),
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equipped with a Shimpack IC-A3 (150 mm × 4.6 mm i.d.) chromatographic column and a COD-10Avp conductivity detector. The mobile phase, containing 8 mM p-hydroxybenzoic acid, 3.2 mM bis–tris, and 50 mM boric acid, was pumped at a flow rate of 1.0 mL min−1 . Identification of BDE209 and its low brominated degradation products were achieved by the following two methods: (1) comparing the retention times to those of the authentic standard compounds on GC-ECD within ±0.1 and (2) comparing the RRTs to the published retention-time database of 126 PBDE congeners and two Bromkal technical mixtures on seven capillary gas chromatographic columns [20]. Determination of extraction recovery was made by quantification of BDE209 congeners at low (3.84 g mL−1 ) and high (96 g mL−1 ) concentrations. BDE209 extraction recoveries ranged from 60% to 70% for the low and high spike trials. 3. Results and discussion 3.1. Preliminary experiments Single oxidation of BDE209 was carried out at 150 ◦ C and 0.5 MPa oxygen pressure for 4 h. The result showed no significant BDE209 removal was obtained. When the volume ratio of THF to H2 O was 0.1, only 2% of BDE209 were removed after 4 h. With the THF increasing (volume ratio: 0.1, 0.4, 0.6 and 1), BDE209 and Br removal were increased with 2%, 40%, 95%, 100% and 0%, 3%, 18%, 40%, respectively. These results indicated the addition of THF promoted the destruction of BDE209. Thus, the co-oxidation of BDE209 and THF were systematically investigated. Fig. 1 shows the GC chromatogram of BDE209 degradation before and after adding THF. 3.2. Effect of temperature To evaluate the influence of temperature, WACO was studied at temperatures between 120 ◦ C and 170 ◦ C. And the rest of the reaction conditions were fixed (0.5 MPa oxygen pressure, 4 h of reaction time, THF/H2 O = 1:1). With the increasing of the reaction temperature, BDE209 removal markedly increased. As shown in Fig. 2, when the temperature was 120 ◦ C, only 6% BDE209 removal was obtained. Raising the temperature to 140 ◦ C led to 91% removal. When the temperature was up to 150 ◦ C, BDE209 removal efficiency reached to 100%. The temperature also had a great effect on the Br removal. For instance, when the temperature was 120 ◦ C, almost no Br removal was found. With the temperature increasing, the Br removal also increased. When the temperature was raised to 170 ◦ C, the Br removal reached to 84%. From the above results we concluded that higher temperatures were favorable for the WACO of BDE209 and THF. However, from the practical point of view, higher temperatures lead to higher operating costs and severer corrosion problems. Thus we considered 150 ◦ C as the optimum temperature for the study of the WACE of BDE209 and THF. 3.3. Effect of amount of NaNO2 In the previous papers, we reported that NaNO2 exhibited the high catalytic capacity to activate molecular oxygen to destroy some pollutants [21,22]. Here we wanted to further study the effect of NaNO2 on this co-oxidation reaction. Fig. 3 shows the effect of NaNO2 on BDE209 at 150 ◦ C, 0.5 MPa oxygen pressure, THF/H2 O = 1:1 and 2 h of reaction time. From Fig. 3, it can be seen that the increase of NaNO2 amount has basically no effect on BDE209 removal, but influences Br removal. The Br removal was only 16% without NaNO2 . When the NaNO2 was added and the molar ratio of NaNO2 to BDE209 was 0.01, the Br removal increased to 29%. With the NaNO2 amount increasing, the Br removal increased. When 100% molar ratio of NaNO2 (based on
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H. Zhao et al. / Journal of Hazardous Materials 169 (2009) 1146–1149
Fig. 1. GC chromatogram of BDE209 at the reaction condition (150 ◦ C, 0.5 MPa oxygen pressure and 4 h of reaction time): (a) GC chromatogram without THF; (b) GC chromatogram with THF; (c) the magnified GC chromatogram of (b) from 26 min to 65 min. Table 1 BDE209 wet air co-oxidation products at 150 ◦ C, 0.5 MPa and 4 h. Congeners with identical RTs as reaction products
Br atoms
197, one additional OCTA 183, 184, five additional HEPTAs 138, 154, six additional HEXAs 99, 126, three additional PENTAs 77, two additional TETRAs
8 7 6 5 4
BDE209, corresponding to 1:1 molar ratio of NaNO2 to BDE209) was added to the WACE system, the Br removal increased to 46%. These results indicated the addition of NaNO2 could promote the debromination of BDE209. 3.4. Identification of low brominated degradation products of BDE209 Fig. 2. Influence of temperature on BDE209 and Br removals at 0.5 MPa and 4 h of reaction time.
Fig. 1b shows the chromatogram of degradation products at 150 ◦ C, 0.5 MPa oxygen pressure, 4 h of reaction time and THF/H2 O = 1:1. Fig. 1c shows the magnified chromatogram of degradation products. From Fig. 1b, it can be seen that there appear some peaks from 26 min to 65 min comparing with Fig. 1a. These reaction products were mainly assigned to 4–8 brominated compounds by comparing the RRTs to those of authentic standards or the published retention-time database (Table 1). When the reaction temperature was increased to 170 ◦ C, these peaks became smaller and almost disappeared. Therefore, it was initially concluded that BDE209 in the WACE system was easy to remove bromine. At present, the degradation mechanism of BDE209 in this reaction system is still not positively clear. However, as we know, for WAO, the reactions generally proceed according to a free-radical mechanism. During the initiation period, the free-radical concentration increasing can make the reaction proceed rapidly. We speculated since the THF amount was far higher than that of the BDE209 in the present system, a big amount of and were formed in the initiation period and could provide enough free radicals to initiate the oxidation of BDE209. Thus, the debromination of BDE209 can be completed rapidly. 4. Conclusion
Fig. 3. Influence of NaNO2 on BDE209 and Br removals at 150 ◦ C, 0.5 MPa and 4 h of reaction time.
In this investigation, the WACO degradation of BDE209 was studied with THF as an initiator. The results showed that under moderate condition (150 ◦ C, 0.5 MPa oxygen pressure), the addition of THF to
H. Zhao et al. / Journal of Hazardous Materials 169 (2009) 1146–1149
the same system obviously improved the BDE209 reduction. Temperature was important in the simultaneous reaction. When the temperature was increased from 120 ◦ C to 170 ◦ C, the BDE209 and Br removals were increased from 6% to 100% and 0% to 84%, respectively. In addition, the effect of NaNO2 as the catalyst on the WACO was investigated and the results showed that the addition of NaNO2 could improve the Br removal. Further researches about decreasing amount of THF in reaction system and catalytic co-oxidation are being carried out in our laboratory. Acknowledgements We are indebted to Prof. Renhua Liu for his contributions to this work. This research was supported by National Natural Science Foundation of China (20707026). References [1] World Health Organization, Brominated Dihenyl Ethers. IPCS, Environmental Health Criteria, Geneva, 1994, p. 162. [2] K. Ballschmiter, R. Bacher, A. Mennel, R. Fischer, U. Riehle, M. Swerev, The determination of chlorinated biphenyls, chlorinated dibenzodioxins, and chlorinated dibenzofurans by GC–MS, Journal of High Resolution Chromatography 15 (1992) 260–270. [3] A. Covaci, S. Voorspoelsa, J. de Boerb, Determination of brominated flame retardants, with emphasis on polybrominated diphenyl ethers (PBDEs) in environmental and human samples—a review, Environment International 29 (2003) 735–756. [4] B.X. Mai, S.J. Chen, X.J. Luo, L.G. Chen, Q.S. Yang, G.Y. Sheng, P.G. Peng, J.M. Fu, E.Y. Zeng, Distribution of polybrominated diphenyl ethers in sediments of the Pearl River delta and adjacent South China Sea, Environmental Science and Technology 39 (2005) 3521–3527. [5] J.M. Luross, M. Alaee, D.B. Sergeant, D.M. Whittle, K.R. Solomon, Spatial and temporal distribution of polybrominated diphenyl ethers in lake trout from the Great Lakes, Organohalogen Compounds 47 (2000) 73–76. [6] C. Schröter-Kermani, D. Helm, T. Herrmann, O. Päpke, The German environmental specimen bank—application in trend monitoring of polybrominated diphenyl ethers in human blood, Organohalogen Compounds 47 (2000) 49–52. [7] G.A. Stern, M.G. Ikonomou, Temporal trends of polybrominated diphenyl ethers in SE Baffin beluga: increasing evidence of long range atmospheric transport, Organohalogen Compounds 47 (2000) 81–84.
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[8] P. Eriksson, E. Jakobsson, A. Fredriksson, Developmental neurotoxicity of brominated flame-retardants, polybrominated diphenyl ethers and tetrabromo-bisphenol A, Organohalogen Compounds 35 (1998) 375–377. [9] P. Eriksson, E. Jakobsson, A. Fredriksson, Brominated flame retardants: a novel class of developmental neurotoxicants in our environment? Environmental Health Perspectives 109 (2001) 903–908. [10] P.O. Darnerud, G.S. Eriksen, T. Jóhannesson, P.B. Larsen, M. Viluksela, Polybrominated diphenyl ethers: occurrence, dietary exposure, and toxicology, Environmental Health Perspectives 109 (2001) 49–68. [11] J.Z. He, K.R. Robrock, L. Alvarez-Cohen, Microbial reductive debromination of polybrominated diphenyl ethers (PBDEs), Environmental Science and Technology 40 (2006) 4429–4434. [12] J.A. Tokarz, M.Y. Ahn, J. Leng, T.R. Filley, L. Nies, Reductive debromination of polybrominated diphenyl ethers in anaerobic sediment and a biomimetic system, Environmental Science and Technology 42 (2008) 1157–1164. [13] Y.S. Keum, Q.X. Li, Reductive debromonation of polybrominated diphenyl ethers by zerovalent iron, Environmental Science and Technology 39 (2005) 2280–2286. [14] B.C. Juan, T.J. Chad, H. Inez, Solar photodecomposition of decabromodiphenyl ether: products and quantum yield, Environmental Science and Technology 38 (2004) 4149–4156. [15] F. Lei, H. Jun, Y. Gang, W. Lining, Photochemical degradation of six polybrominated diphenyl ether congeners under ultraviolet irradiation in hexane, Chemosphere 71 (2008) 258–267. [16] R. Andreozzi, V. Caprio, A. Insola, R. Marotta, Advanced oxidation processes (AOP) for water purification and recovery, Catalysis Today 53 (1999) 51–59. [17] R.V. Shende, J. Levec, Wet oxidation kenetics of refractory low molecular mass carboxylic acids, Industrial and Engineering Chemistry Research 38 (1999) 3830–3837. [18] J. Vicente, M. Diaz, Thiocyanate/phenol wet oxidation interactions, Environmental Science and Technology 37 (2003) 1457–1462. [19] D.M. Fu, J.P. Chen, X.M. Liang, Wet air oxidation of nitrobenzene enhanced by phenol, Chemosphere 59 (2005) 905–908. [20] P. Korytar, A. Covaci, J. de Boer, A. Gelbin, U.A.T. Brinkman, Retention-time database of 126 polybrominated diphenyl ether congeners and two Bromkal technical mixtures on seven capillary gas chromatographic columns, Journal of Chromatography A 1065 (2005) 239–249. [21] X. Liang, D. Fu, R. Liu, Q. Zhang, T.Y. Zhang, X. Hu, Highly efficient NaNO2 catalyzed destruction of trichlorophenol using molecular oxygen, Angewandte Chemie International Edition 44 (2005) 5520–5523. [22] L. Wang, F. Zhang, R. Liu, T.Y. Zhang, X. Xue, Q. Xu, X. Liang, FeCl3 /NaNO2 : an efficient photocatalyst for the degradation of aquatic steroid estrogens under natural light irradiation, Environmental Science and Technology 41 (2007) 3747–3751.
Contents lists available at ScienceDirect
Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat
Short communication
Wet air co-oxidation of decabromodiphenyl ether (BDE209) and tetrahydrofuran Hongxia Zhao a,b , Feifang Zhang a , Baocheng Qu b , Xingya Xue a , Xinmiao Liang a,∗ a b
Dalian Institute of Chemical Physics, Chinese Academy of Science, Dalian 116023, China Key Laboratory of Industrial Ecology and Environmental Engineering, MOE, Dalian University of Technology, Dalian 116024, China
a r t i c l e
i n f o
Article history: Received 2 September 2008 Received in revised form 14 March 2009 Accepted 18 March 2009 Available online 27 March 2009 Keywords: Co-oxidation BDE209 THF Promotion effect Free radical
a b s t r a c t The wet air co-oxidation (WACO) of a major commercial polybrominated diphenyl ether flame retardant congener, decabromodiphenyl ether (BDE209), was investigated using tetrahydrofuran (THF) as an initiator in a stainless autoclave at temperature range of 120–170 ◦ C and 0.5 MPa oxygen pressure. Compared to the single oxidation of BDE209 under the same conditions, the addition of THF in the reaction system greatly improved the removal efficiency of BDE209. The effect of temperature on the reaction was studied. The removals of BDE209 and Br increased with increasing temperature. In addition, the effect of NaNO2 as the catalyst on the WACO was also investigated and the results showed that the addition of NaNO2 could improve the Br removal efficiency. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Polybrominated diphenyl ethers (PBDEs) have been widely used as flame retardants to reduce the fire risk on plastics, carpets, electronic equipment, textiles and building materials around the world [1]. PBDEs are structurally similar to polychlorinated biphenyls (PCBs) with the same nomenclature and number (209) of congeners [2]. At present, they have been found in a wide range of environmental and biological samples including birds, edible marine organisms, marine mammals and human beings [3,4]. Environmental monitoring for the past 20 years has shown that PBDEs are persistent in sediment and bioaccumulate in tissues [5]. Levels in human milk are increasing [6], as are levels in organisms that inhabit in the deep oceans [5,7]. Although the acute toxicity of PBDEs is thought to be low relative to polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and co-planar PCBs, they are proven endocrine disruptors that destroy thyroid hormone balance and cause developmental problems [8]. It is reported that pentaBDEs are the most toxic, causing developmental toxicity at concentrations starting at 0.8 mg kg−1 body weight [9], while octaBDEs are teratogens and decaBDE is classified by the U.S. EPA as a possible human carcinogen [10]. Therefore, to suppress the accumulation of these compounds in the environment, development of techniques for decomposing them to harmless or lower toxic species is desirable.
However, few published studies are available regarding biotic and abiotic degradation of PBDEs. Debromination of BDE209 and an octaBDE mixture was observed with anaerobic bacteria including Sulfurospirillum multivorans and Dehaloccoides species [11]. In sediments, BDE209 can be biotransformed into lower mass PBDE congeners and its debromination half-life in sediments was over a decade [12]. Chemical reduction degradation with zerovalent iron and photolytic decomposition of PBDEs are proposed, respectively [13–15]. However, the wet air oxidation (WAO) of PBDEs is not well documented. WAO aiming at treating persistent organic pollutants in industrial wastewaters has been actively explored. Numerous methods have been investigated to increase the oxidation rate and effectiveness of WAO processes. Besides catalytic WAO processes [16], co-oxidation is another important way to increase oxidation rate. Since some compounds are very difficult to be oxidized under moderate reaction conditions, more easily oxidisable compounds may initiate the more difficultly oxidisable compounds. Therefore, wet air co-oxidation (WACO) has drawn more and more attention of researchers [17–19]. In this paper, the WACO of a major commercial polybrominated diphenyl ether flame retardant congener, BDE209, was studied with THF as an initiator for the first time. The aim of the present work was to gain experimental information about the simultaneous BDE209 and THF wet air co-oxidation. 2. Experimental 2.1. Chemicals and standards
∗ Corresponding author. Tel.: +86 411 84707965. E-mail address: [email protected] (X. Liang). 0304-3894/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2009.03.089
The technical product of BDE209 was purchased from Accustandard, Inc. (New Haven, CT, USA). A total of 39 PBDE standards
H. Zhao et al. / Journal of Hazardous Materials 169 (2009) 1146–1149
were bought for the identification of low brominated reaction products, among them 10 PBDE congeners containing BDE30, -32, -35, -37, -75, -116, -155, -166, -181 and -190 in nonane solution were obtained from Cambridge Isotope Laboratories (Andover, MA, USA). PBDE-MXE containing BDE3, -7, -15, -17, -28, -47, -49, -71, -66, -99, -77, -85, -100, -119, -126, -138, -153, -154, -156, -183, -184, -191, -196, -197, -206 and -207 in nonane solution was purchased from Wellington Laboratories (Guelph, Ontario, Canada). NaNO2 , Na2 SO4 , DMSO, THF and ethyl acetate (Tedia Co.) were of analytical grade and were used without further purification. Water was prepared with a Milli-Q water purification system (Millipore, Milford, MA, USA) throughout all experiments. 2.2. Wet air co-oxidation The WACO of BDE209 with THF as an initiator was carried out in a 50 mL of Teflon-lined stainless steel autoclave equipped with a magnetic stirrer. The reaction temperature was measured using a thermocouple and controlled by a PID regulator. 96 g mL−1 BDE209 solution was added to the autoclave. The autoclave was closed and charged with pure oxygen to 0.5 MPa and heated to the desired temperature. The stirring speed was set at 500 r min−1 . After reaction (heating time included), the autoclave was cooled to room temperature with a water bath. Carefully depressurized, it was sampled for further analysis. 2.3. Determination of calibration curve Commercially available standards of BDE209 (9.6 mg) was dissolved in 100 mL of THF solution, and used as standard stock solutions for generating calibration curves. The stock solutions were diluted 1/5, 1/10, 1/25 and 1/100 times in THF to afford 19.2 g mL−1 , 9.6 g mL−1 , 3.84 g mL−1 and 0.96 g mL−1 solutions of BDE209. These four standard solutions and the stock solution were injected to generate a five-point calibration curve for the standard compounds using GC-ECD. Standard curve was linear with R2 = 0.9998. Peak areas of the target compound were within the linear range of the curve. Relative standard deviations for two injections were less than 2%. Using the similar dilution method, a five-point calibration curve for Br− was obtained by IC at the concentration range from 0.8 g mL−1 to 80 g mL−1 and the linear regression coefficient (R2 ) was 0.998. 2.4. Sample preparation and analysis After WACO, 5 mL aliquot of reaction solution was removed from the autoclave by disposable plastic syringe and subjected to a liquid–liquid extraction with an equal volume of ethyl acetate in a 15-mL glass tube. The mixture was vortexed for 3 min and shaked 1 h in order to extract the PBDEs into the ethyl acetate phase. After Na2 SO4 dryness, the extraction organic phase was transferred to GC vial for analysis. The inorganic phase was used to analyze the Br− by IC. BDE209 and its low brominated degradation products were separated using an Agilent 6890GC (Palo Alto, CA, USA) equipped with a fused silica DB-5 column ((5% phenyl) methylpolysiloxane, 30 m × 320 m i.d., 0.25 m film thickness, J&W Scientific, Inc., Folsom, CA, USA), and an Agilent 7683 Series automatic liquid sampler and injector. A 1-L injection, made in the split mode (20:1), was employed for all samples. These brominated compounds were monitored with a 63 Ni ECD detector. Nitrogen was used as the carrier and makeup gas. The temperature program was as follow: 90 ◦ C (2.0 min), 30 ◦ C min−1 , 200 ◦ C, 1.5 ◦ C min−1 , 325 ◦ C (7.0 min). HP Chemstation software was used to collect and process data from the GC-ECD. Br− was identified and quantified by means of non-suppressed ion chromatography (SCL-10Asp, Shimadzu),
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equipped with a Shimpack IC-A3 (150 mm × 4.6 mm i.d.) chromatographic column and a COD-10Avp conductivity detector. The mobile phase, containing 8 mM p-hydroxybenzoic acid, 3.2 mM bis–tris, and 50 mM boric acid, was pumped at a flow rate of 1.0 mL min−1 . Identification of BDE209 and its low brominated degradation products were achieved by the following two methods: (1) comparing the retention times to those of the authentic standard compounds on GC-ECD within ±0.1 and (2) comparing the RRTs to the published retention-time database of 126 PBDE congeners and two Bromkal technical mixtures on seven capillary gas chromatographic columns [20]. Determination of extraction recovery was made by quantification of BDE209 congeners at low (3.84 g mL−1 ) and high (96 g mL−1 ) concentrations. BDE209 extraction recoveries ranged from 60% to 70% for the low and high spike trials. 3. Results and discussion 3.1. Preliminary experiments Single oxidation of BDE209 was carried out at 150 ◦ C and 0.5 MPa oxygen pressure for 4 h. The result showed no significant BDE209 removal was obtained. When the volume ratio of THF to H2 O was 0.1, only 2% of BDE209 were removed after 4 h. With the THF increasing (volume ratio: 0.1, 0.4, 0.6 and 1), BDE209 and Br removal were increased with 2%, 40%, 95%, 100% and 0%, 3%, 18%, 40%, respectively. These results indicated the addition of THF promoted the destruction of BDE209. Thus, the co-oxidation of BDE209 and THF were systematically investigated. Fig. 1 shows the GC chromatogram of BDE209 degradation before and after adding THF. 3.2. Effect of temperature To evaluate the influence of temperature, WACO was studied at temperatures between 120 ◦ C and 170 ◦ C. And the rest of the reaction conditions were fixed (0.5 MPa oxygen pressure, 4 h of reaction time, THF/H2 O = 1:1). With the increasing of the reaction temperature, BDE209 removal markedly increased. As shown in Fig. 2, when the temperature was 120 ◦ C, only 6% BDE209 removal was obtained. Raising the temperature to 140 ◦ C led to 91% removal. When the temperature was up to 150 ◦ C, BDE209 removal efficiency reached to 100%. The temperature also had a great effect on the Br removal. For instance, when the temperature was 120 ◦ C, almost no Br removal was found. With the temperature increasing, the Br removal also increased. When the temperature was raised to 170 ◦ C, the Br removal reached to 84%. From the above results we concluded that higher temperatures were favorable for the WACO of BDE209 and THF. However, from the practical point of view, higher temperatures lead to higher operating costs and severer corrosion problems. Thus we considered 150 ◦ C as the optimum temperature for the study of the WACE of BDE209 and THF. 3.3. Effect of amount of NaNO2 In the previous papers, we reported that NaNO2 exhibited the high catalytic capacity to activate molecular oxygen to destroy some pollutants [21,22]. Here we wanted to further study the effect of NaNO2 on this co-oxidation reaction. Fig. 3 shows the effect of NaNO2 on BDE209 at 150 ◦ C, 0.5 MPa oxygen pressure, THF/H2 O = 1:1 and 2 h of reaction time. From Fig. 3, it can be seen that the increase of NaNO2 amount has basically no effect on BDE209 removal, but influences Br removal. The Br removal was only 16% without NaNO2 . When the NaNO2 was added and the molar ratio of NaNO2 to BDE209 was 0.01, the Br removal increased to 29%. With the NaNO2 amount increasing, the Br removal increased. When 100% molar ratio of NaNO2 (based on
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Fig. 1. GC chromatogram of BDE209 at the reaction condition (150 ◦ C, 0.5 MPa oxygen pressure and 4 h of reaction time): (a) GC chromatogram without THF; (b) GC chromatogram with THF; (c) the magnified GC chromatogram of (b) from 26 min to 65 min. Table 1 BDE209 wet air co-oxidation products at 150 ◦ C, 0.5 MPa and 4 h. Congeners with identical RTs as reaction products
Br atoms
197, one additional OCTA 183, 184, five additional HEPTAs 138, 154, six additional HEXAs 99, 126, three additional PENTAs 77, two additional TETRAs
8 7 6 5 4
BDE209, corresponding to 1:1 molar ratio of NaNO2 to BDE209) was added to the WACE system, the Br removal increased to 46%. These results indicated the addition of NaNO2 could promote the debromination of BDE209. 3.4. Identification of low brominated degradation products of BDE209 Fig. 2. Influence of temperature on BDE209 and Br removals at 0.5 MPa and 4 h of reaction time.
Fig. 1b shows the chromatogram of degradation products at 150 ◦ C, 0.5 MPa oxygen pressure, 4 h of reaction time and THF/H2 O = 1:1. Fig. 1c shows the magnified chromatogram of degradation products. From Fig. 1b, it can be seen that there appear some peaks from 26 min to 65 min comparing with Fig. 1a. These reaction products were mainly assigned to 4–8 brominated compounds by comparing the RRTs to those of authentic standards or the published retention-time database (Table 1). When the reaction temperature was increased to 170 ◦ C, these peaks became smaller and almost disappeared. Therefore, it was initially concluded that BDE209 in the WACE system was easy to remove bromine. At present, the degradation mechanism of BDE209 in this reaction system is still not positively clear. However, as we know, for WAO, the reactions generally proceed according to a free-radical mechanism. During the initiation period, the free-radical concentration increasing can make the reaction proceed rapidly. We speculated since the THF amount was far higher than that of the BDE209 in the present system, a big amount of and were formed in the initiation period and could provide enough free radicals to initiate the oxidation of BDE209. Thus, the debromination of BDE209 can be completed rapidly. 4. Conclusion
Fig. 3. Influence of NaNO2 on BDE209 and Br removals at 150 ◦ C, 0.5 MPa and 4 h of reaction time.
In this investigation, the WACO degradation of BDE209 was studied with THF as an initiator. The results showed that under moderate condition (150 ◦ C, 0.5 MPa oxygen pressure), the addition of THF to
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the same system obviously improved the BDE209 reduction. Temperature was important in the simultaneous reaction. When the temperature was increased from 120 ◦ C to 170 ◦ C, the BDE209 and Br removals were increased from 6% to 100% and 0% to 84%, respectively. In addition, the effect of NaNO2 as the catalyst on the WACO was investigated and the results showed that the addition of NaNO2 could improve the Br removal. Further researches about decreasing amount of THF in reaction system and catalytic co-oxidation are being carried out in our laboratory. Acknowledgements We are indebted to Prof. Renhua Liu for his contributions to this work. This research was supported by National Natural Science Foundation of China (20707026). References [1] World Health Organization, Brominated Dihenyl Ethers. IPCS, Environmental Health Criteria, Geneva, 1994, p. 162. [2] K. Ballschmiter, R. Bacher, A. Mennel, R. Fischer, U. Riehle, M. Swerev, The determination of chlorinated biphenyls, chlorinated dibenzodioxins, and chlorinated dibenzofurans by GC–MS, Journal of High Resolution Chromatography 15 (1992) 260–270. [3] A. Covaci, S. Voorspoelsa, J. de Boerb, Determination of brominated flame retardants, with emphasis on polybrominated diphenyl ethers (PBDEs) in environmental and human samples—a review, Environment International 29 (2003) 735–756. [4] B.X. Mai, S.J. Chen, X.J. Luo, L.G. Chen, Q.S. Yang, G.Y. Sheng, P.G. Peng, J.M. Fu, E.Y. Zeng, Distribution of polybrominated diphenyl ethers in sediments of the Pearl River delta and adjacent South China Sea, Environmental Science and Technology 39 (2005) 3521–3527. [5] J.M. Luross, M. Alaee, D.B. Sergeant, D.M. Whittle, K.R. Solomon, Spatial and temporal distribution of polybrominated diphenyl ethers in lake trout from the Great Lakes, Organohalogen Compounds 47 (2000) 73–76. [6] C. Schröter-Kermani, D. Helm, T. Herrmann, O. Päpke, The German environmental specimen bank—application in trend monitoring of polybrominated diphenyl ethers in human blood, Organohalogen Compounds 47 (2000) 49–52. [7] G.A. Stern, M.G. Ikonomou, Temporal trends of polybrominated diphenyl ethers in SE Baffin beluga: increasing evidence of long range atmospheric transport, Organohalogen Compounds 47 (2000) 81–84.
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