Hydroxylated PBDEs and brominated phenolic compounds in particulate matters emitted during recycling of waste printed circuit boards in a typical e-waste workshop of South China

Environmental Pollution 177 (2013) 71e77

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Hydroxylated PBDEs and brominated phenolic compounds in particulate matters emitted during recycling of waste printed circuit boards in a typical e-waste workshop of South China Zhaofang Ren a, b, Xinhui Bi a, *, Bo Huang a, b, Ming Liu a, b, Guoying Sheng a, Jiamo Fu a, c a State Key Laboratory of Organic Geochemistry, Guangdong Province Key Laboratory of Utilization and Protection of Environmental Resource, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, PR China b Graduate University of Chinese Academy of Sciences, Beijing 100039, PR China c School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444, PR China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 12 November 2012 Received in revised form 23 January 2013 Accepted 27 January 2013

The hydroxylated PBDEs (OH-PBDEs) and brominated phenolic compounds in aerosol samples from a printed circuit boards recycling workshop were characterized. The results show that OH-PBDEs, which are naturally occurring compounds or metabolism of PBDEs, could also be emitted from the e-waste recycling. Five OH-PBDEs, several unidentified mono-OH-PBDE and di-OH-PBDE congeners were P detected. The concentration of OH-PBDEs was 1.74e4.22 ng m
3 (average of 2.66 ng m
3), with 6-OH
3 BDE-47 (0.329 ng m ) as the most abundant identified congener. The total concentration of di- to tribrominated phenols (BPs) was 18.8e32.0 ng m
3 (average of 26.3 ng m
3) with 2,4,6-triBP as the most abundant congener. These findings suggest that the recycling of printed circuit boards represent a strong source of OH-PBDEs and BPs to the atmosphere. Additionally, some phenolic compounds including brominated bisphenol A, hydroxylated polybrominated biphenyl species and etc. were also identified. Ó 2013 Elsevier Ltd. All rights reserved.

Keywords: Hydroxylated polybrominated diphenyl ethers Bromophenols Printed circuit boards E-waste POPs

1. Introduction Electronic waste (e-waste) refers to an obsolete electronic device and its parts, such as computers, printers, mobile phones, television sets. With the rapid development of the electronics industry, e-waste is generated in large quantities around the world and it has become a global problem, particularly in China, where most e-waste produced worldwide is illegally imported for “recycling”. Printed circuit boards are used in most electrical and electronic products, and consist of a heterogeneous mixture of organic materials, metals, glass fibers and some toxic substances, such as brominated flame retardants (BFR), polyvinyl chloride and heavy metals (Wu and Zhang, 2010). During the recycling process, these toxic substances might be emitted into the environment (Leung et al., 2007). Polybrominated diphenyl ethers (PBDEs) are used extensively in the electrical and electronic products as flame retardants. Hydroxylated PBDEs (OH-PBDEs), which are a relatively new group of phenolic compounds, have been detected in biological samples including fish (Marsh et al., 2004; Valters et al., 2005), algae

* Corresponding author. E-mail address: [email protected] (X. Bi). 0269-7491/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.envpol.2013.01.034

(Malmvarn et al., 2005, 2008), birds (Verreault et al., 2005), rats and mice (Malmberg et al., 2005; Qiu et al., 2007), as well as human blood (Chang et al., 2010; Qiu et al., 2009; Yu et al., 2010). It has been shown that OH-PBDEs can be naturally formed in marine algae or by their associated microorganisms (Malmvarn et al., 2005, 2008; Unson et al., 1994). Studies in animals suggest that OH-PBDEs are metabolic products of PBDEs (Hamers et al., 2008; Malmberg et al., 2005; Stapleton et al., 2009). Recently, it also has been suggested that demethylation of naturally produced methoxylated PBDEs (MeO-PBDEs) may result in OH-PBDEs in the environment (Wan et al., 2010, 2009; Wiseman et al., 2011). Additionally, gas phase reactions of mono- and di-BDEs with present of OH radicals could yield bromophenols with OH-PBDEs as intermediates (Raff and Hites, 2006). Ueno et al. (2008) examined OH-PBDEs in surface water and precipitation, and suggested that the reaction between PBDEs and atmospheric OH radicals probably yield OH-PBDEs. OHPBDEs are reported to be more toxic than PBDEs and the biological systems effected are the disruption of thyroid hormone homeostasis, neurotoxic, oxidative phosphorylation and sex hormone steroidogenesis (Canton et al., 2008; Dingemans et al., 2008; Meerts et al., 2001). Because of their severe toxicity, the study on OHPBDEs has been intensive, however, to our best knowledge, no study has taken place on the anthropogenic emission sources.

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Z. Ren et al. / Environmental Pollution 177 (2013) 71e77

Brominated phenols (BPs) are a group of compounds extensively used as flame retardants, or intermediates for the production of flame retardants (Knob et al., 2010). BPs may be released into the environment as the major degradation products of other BFRs (Sim et al., 2009), or as the products of the gas phase reaction between PBDEs and OH radicals (Raff and Hites, 2006). Additionally, BPs can also be formed by several marine organisms and have been identified as a key natural flavor component of marine fish (Hassenklover et al., 2006; Whitfield et al., 1998). Some BPs (2,4diBP, 2,4,5-triBP and 2,4,6-triBP) were the metabolites of PBDEs in mice (Qiu et al., 2007). BPs may play a role in chemical defense and deterrence to ecology (Woodin et al., 1997). They are suspected to be a disruptor of hormone system by showing a thyroid hormonelike activity (Legler and Brouwer, 2003), could bind to the human estrogen receptor and may interfere with the endocrine systems (Hassenklover et al., 2006; Olsen et al., 2002). Meanwhile, BPs are the precursors of polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) (Evans and Dellinger, 2005). Guiyu, a small town in Guangdong Province, in the south of China, has emerged as an intensive e-waste recycling center since 1995 (An et al., 2011). It has a total area of 52 km2 with a population of 150,000, and processes about 70% of the world’s exported ewaste. Previous studies showed that Guiyu is one of the most PBDEand PBDD/F-polluted places around the world (An et al., 2011; Li et al., 2007). The concentrations of PBDEs and PBDD/Fs in Guiyu were about 58e691 and 30 times higher than the other urban sites (Deng et al., 2007; Li et al., 2007). Waste printed circuit boards recycling is one of the major recycling activities engaged in Guiyu. The methods used to recycle printed circuit boards include heating them over a grill on a stove burning honeycombed coal briquettes or by an electrothermal machine. During the heating process, plenty of toxic substances such as PBDEs, polychlorinated dibenzop-dioxins and dibenzofurans (PCDD/Fs) and PBDD/Fs as well as heavy metals were released into the environment. In this study, the particulate matter (PM) samples were collected from a typical workshop of Guiyu engaged in the recycling of printed circuit boards. In the parallel study, we present the levels and characteristics of PBDEs, PCDD/Fs and PBDD/Fs (Ren et al., submitted for publication). Here we present the data of OH-PBDEs and BPs. The aims of this present study were 1) to identify OH-PBDEs, BPs and other brominated phenolic compounds in the indoor particles of this workshop; 2) to characterize the levels and patterns of OHPBDEs and BPs; and 3) to gain insight into a possible formation mechanism of brominated phenolic compounds during the waste printed circuit boards recycling. 2. Materials and methods 2.1. Sample collection The PM samples were collected in September, 2007 from the typical workshop (23.324 N, 116.367 E) in Guiyu town. During the sampling process, the workers removed electronic components from circuit boards by heating over grills on stoves burning honeycombed coal briquettes. The sampling site and methodology has been described elsewhere (Bi et al., 2010). Briefly, the sampler was placed close to the middle of 24 stoves in the workshop, and about 1.5 m away from one side of a worker in order to allow the operation to run as normal. PM samples were collected on quartz fiber filters using a high volume air sampler operating at flow rate of 250e 278 L min
1 for 8e10 h. During the sampling period, average ambient temperature and relative humidity were 27.0  1.2  C and 83.5  7.4%, respectively. After sampling, the filters were wrapped with prebaked aluminum foils and then transported to the laboratory and stored at
40  C until analysis. 2.2. Extraction and cleanup Extraction and isolation of phenolic faction and neutral faction were based on the method described by Ueno et al. (2008), with some modifications. An aliquot of filter samples (1/4) were spiked with a mixture of recovery standards (BDEs-51, -128, 13C-BDE-209 and 13C-40 -OH-PCB-79) and then Soxhlet extracted with

dichloromethane (DCM) for 48 h. The solvent extract was concentrated to 1 mL and HCl was added to lower the pH before another extraction with 2-propanol and 1:1 (v/v) methyl tert-butyl ether (MTBE)/hexane mixture. The organic layer was separated, washed with a 3% KCl solution, and raised pH using 1:1 (v/v) 1 M KOH solution/ethanol for partitioning phenolic and neutral fractions. The aqueous phenolic phase was separated and acidified with concentrated H2SO4 in order to extract OHPBDEs and BPs into a 50% MTBE in hexane solution. The phenolic compounds were derivatized to methoxylated compounds (MeO-PBDEs and MeO-BPs) by diazomethane. Both of phenolic and neutral fractions (containing PBDEs) were cleaned up using concentrated H2SO4, milli-Q water and then dried with anhydrous Na2SO4. Finally, the extracts were put through a gel permeation chromatography (GPC) column (Biobeads S-X3) followed by the addition of internal standards (BDE-69, PCB-30 and 13C-PCB208). 2.3. Instrument analysis The samples were analyzed by a Shimadzu model 2010 gas chromatograph (GC) coupled with a QP2010 mass spectrometer (MS) (Shimadzu, Japan) via a 30 m DB5MS (0.25 mm i.d., 0.10 mm film thickness, J&W Scientific) capillary column. The MS was operated in electronic capture negative ionization (ECNI) and selected ion monitoring (SIM) modes. The ion fragments m/z 79 and 81 ([Br]
) were monitored for all target compounds. For OH-PBDEs, helium was used as the carrier gas at a flow rate of 1.5 mL/min. The injection was conducted in splitless mode at 250  C with an injection volume of 1 mL. Column temperature started at 150  C maintained for 2 min, and ramped to 245  C at 2  C/min, held for 2 min, then to 300  C at 20  C/min, held for 5 min. For BPs, column temperature started at 100  C, held for 5 min, then ramped to 180  C at 3  C/min, held for 2 min, and to 220  C at 2  C/min, held for 2 min, and finally to 300  C at 25  C/min, held for 5 min. The helium was chosen as the carrier gas at a flow rate of 1.2 mL/min. Gas chromatographyetandem mass spectrometry (GCe MSeMS) operated on a TSQ Quantum XLS system (Thermo Fisher Scientific, USA) in scan mode was also employed to further identify the analytes in the samples. The detailed instrumental conditions are provided in Supporting Information. 2.4. Quality assurance/quality control (QA/QC) All samples were spiked with 13C12-labeled recovery standard (13C-40 -OH-PCB79). Recovery of 13C-40 -OH-PCB-79 for the whole procedure was 47.1e179.3% (QA, n ¼ 12). Three solvent blanks and matrix blanks were analyzed to check for contamination from the laboratory, equipment and matrix. No target OH-PBDEs were detected in the blanks, only small amount of 2,4,6-triBP and TBBPA were detected in the blanks with levels less than 0.1% of the mass in the samples. Six spike experiments (13 OH-PBDE, 5 BP standards and TBBPA with 3 levels spiked into six filters) were performed to evaluate the recoveries of the method. Recoveries ranged from 52.1% to 179% for 12 OH-PBDE congeners (containing three to six bromine atoms), and 48.1%e82.6% for BPs except for TBBPA, which was only 22.8%. Thus, the quantification of TBBPA wasn’t carried out due to its low recovery, as well as for mono-BPs, the recoveries of which were less than 17%. The relative difference for individual OH-PBDE and BP congeners in paired duplicate samples was <17% and <15%, respectively. It is noted that OH-PBDE congener with two bromine atoms were not detected in all matrix spiked samples. This might suggest that the low brominated OH-PBDE congeners could not be derivatized by diazomethane or need more reaction time like low chlorinated hydroxylated polychlorinated biphenyls (OH-PCBs) (Sandau, 2000). The limit of detection (LODs), defined as a signal-to-noise ratio of greater than 3, ranged from 0.013 to 0.067 pg m
3 for OH-PBDEs and 0.31e 0.44 pg m
3 for BPs based on the average volume (150 m3). Detailed information on quality assurance and control during analytical procedures are presented in Supporting Information.

3. Results and discussion 3.1. Identification of target compounds Fig. 1 shows a representative SIM chromatogram (recorded by ions m/z 79 and 81) for phenolic fraction of an aerosol sample collected at the waste printed circuit boards recycling workshop. This is the first report, to our knowledge, on the identification of OH-PBDEs, BPs and other compounds containing both bromines and hydroxyl groups in PM emitted from the e-waste recycling activities. Structural identification of these compounds was completed by a) comparison with the best fit pattern in the NIST library and with published MS data (Barontini et al., 2004; Blazso et al., 2002; Hites, 2008), b) comparison with authentic standards, c) comparison with mass spectra data of GCeMS, and d) interpretation of mass spectrometric fragmentation patterns.

44-OH-BDE-90

OH-tetraPBB

6'-OH-BDE-99

tribromobisphenol A di-OH-tetraPBB1

penta-BDE2 OH-pentaPBB

3-OH-BDE-47 5-OH-BDE-47 OH-tetraBDE2

etra-BDE3

6-OH-BDE-47 OH-tetraBDE1

OH-triBDE2

tetra-BDE2

di-OH-triPBB2

di-OH-triPBB1 tetra-BDE1 -triBDE1

OH-monoPBB1

DE-69 romobisphenol A

20

i-OH-diBDE1 di-OH-diBDE2 di-OH-diBDE3 di-OH-diBDE4

16

2-Bromo-4-(1-methylethenyl)phenol

50000

2,6-dibromophenol

100000

2,4-dibromophenol

150000

di-OH-monoBDE

2,4,6-tribromophenol

phenolic fraction

4-bromophenol

Relative abundance

200000

73

TBBPA

Z. Ren et al. / Environmental Pollution 177 (2013) 71e77

0

8

12

24

28

32

36

40

44

48

52

56

Time (min)

Fig. 1. Typical selected-ion monitoring (SIM) chromatogram for phenolic fraction of an aerosol sample from waste printed circuit boards recycling workshop in ECNI mode, recorded by ion m/z: 79/81 (diazomethane derivatized).

The results are summarized in Table 1 and the identification methods used for each of the identified compounds are also included in the table. OH-PBDEs and di-OH-PBDEs. Five OH-PBDE congeners (6-OHBDE-47, 3-OH-BDE-47, 5-OH-BDE-47, 60 -OH-BDE-99, and 4-OHBDE-90) were identified using the authentic standards (Fig. 1), and the mass spectra of these compounds in the samples and in the authentic standards were presented in Fig. S1 and 2 in the Supporting Information. Several compounds, assigned to be monoOH-PBDEs and di-OH-PBDEs were also detected, however, their structures could not be identified in the present study because of an absence of authentic standards. It is suggested that meta-methoxysubstituted PBDEs does not contain fragment ions of [M
CH3]þ or [M
BrCH3]þ, but with the base peak at [M
2Br]þ, para-methoxysubstituted PBDEs shows a fragment at [M
CH3]þ, a molecular ion as the base peak, and no [M
BrCH3]þ, while ortho-methoxysubstituted PBDEs contain a [M
BrCH3]þ, but not [M
CH3]þ (Malmberg et al., 2005; Marsh et al., 2004). Therefore, position of the hydroxylated group in the unidentified monohydroxylated PBDE congeners was suggested based on the characteristic fragmentation pattern of their EI mass spectra. EI mass spectra of the four unidentified OH-PBDEs are listed in Fig. 2. One meta-OHtriBDE (OH-triBDE1, Fig. 1(a)), one para-OH-triBDE (OH-triBDE2, Fig. 1(b)), and two ortho-OH-tetraBDE congeners (OH-tetraBDE1 and OH-tetraBDE2, Fig. 1(c) and (d)) were tentatively assigned. Six di-OH-PBDE congeners containing one to three bromines were assigned by the fragmentation interpretation (see Fig. S3 in Supporting Information). Di-OH-PBDEs presented the molecular ions and characterized with fragment ions [M
CH3]þ, meanwhile with congeners either contained the fragment ions of [M
2CH3]þ or [M
BrCH3]þ or [M
2BrCH3]þ etc. Bromophenols and brominated bisphenol A species. Four BP congeners (4-monoBP, 2,6-diBP, 2,4-diBP, and 2,4,6-triBP) were identified based on the authentic standards available. Three brominated bisphenol A congeners (TBBPA, tribromobisphenol A, and bromobisphenol A) were identified by comparing their mass spectra (Fig. S4) with mass spectrum of TBBPA standard and the MS data reported by Blazso et al. (2002) and Barontini et al. (2004). The identification of 2-bromo-4-(1-methylethenyl)phenol was also achieved in this study (see mass spectrum reported in Fig. S5). OH-PBBs and di-OH-PBBs. Neither a NIST spectrum, nor a standard for hydroxylated polybrominated biphenyl (OH-PBB) and dihydroxylated polybrominated biphenyl (di-OH-PBB) were available. Therefore, the identification of OH-PBBs and di-OH-PBBs was conducted similarly to di-OH-PBDEs, based on the interpretation of

their mass spectra fragmentation (see Fig. S6 and 7). Both OH-PBBs and di-OH-PBBs showed their molecular ions in the chromatograph. It is noted that the fragmentation patterns of OH-PBBs are not uniform (Fig. S6), and di-OH-PBBs generally characterized by the fragment ions of [M
CH3]þ and [M
BrCH3]þ (Fig. S7). In addition, fragment ions of several peaks in EI mass spectra were very similar to that of PBDEs in a previous study (Hites, 2008). The emergence of PBDEs in phenolic fraction might be explained by the fact that the neutral compounds and phenolic compounds could not be thoroughly separated. However, their concentrations were extremely low compared to PBDEs in neutral fraction. 3.2. Levels and patterns of OH-PBDEs and BPs OH-PBDEs and BPs were detected in all samples and their conP centrations are presented in Table 2. The concentrations of OHPBDEs (identified and unidentified congeners) ranged from 1.75 to P 4.22 ng m
3, with an average of 2.66 ng m
3. BPs concentrations P were more than 10 times higher than OH-PBDEs, ranged from 18.8 to 32.0 ng m
3, with an average of 26.3 ng m
3. The comparison of relative abundance of the identified OHPBDE congeners found in this study, with that in plasma of pelagic fish species from the Detroit River (Valters et al., 2005), human serum samples from e-waste dismantling region (Ren et al., 2011), and snow and rain samples from Ontario, Canada (Ueno et al., 2008) are present in Fig. 3. It can be seen that the OH-PBDE congener patterns were different. Tetra- and penta-brominated OH-PBDEs were the major components in snow and rain samples collected from Ontario, Canada, and 5-OH-BDE-47 was the major congener (Ueno et al., 2008) (Fig. S8). OH-PBDEs detected in biotic environment generally contain three to nine bromines. In the plasma of fish from the Detroit River, the profile was generally dominated by 6-OH-BDE-47 with lesser amounts of 20 -OH-BDE-68, 40 -OH-BDE-49, and 4-OH-BDE-42 (Valters et al., 2005). The dominant OH-PBDEs in the human serum of the e-waste dismantling workers were mainly highly-brominated congeners (Fig. 3), such as 6-OH-BDE-196, 6-OH-BDE-199 and 60 -OH-BDE-206 (Ren et al., 2011; Yu et al., 2010). However, in this study, 6-OH-BDE-47 (0.329 ng m
3) was the most abundant identified OH-PBDE congener, accounting for 31.0% of the total concentration of the five identified OH-PBDE congeners, followed by 5-OH-BDE-47 (30.8%) and 3-OH-BDE-47 (16.7%) (Fig. 3). This different pattern might be explained by the fact that amounts of tri- to tetra-PBDEs mainly distributed in the gas phase in the circuit boards recycling workshops (An et al., 2011) and OH-PBDEs were results of the

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Z. Ren et al. / Environmental Pollution 177 (2013) 71e77

Table 1 Results of GCeMS analysis performed on the phenolic fraction in particle samples from waste printed circuit boards recycling workshop. Compound

Molecular weight

Identified by the means of

Identified also by:

173 252 213

252 249 265 331 281 265 361 361 361 361 307

15 16

Di-OH-triPBB1 Tetra-BDE1

423 486

17

423

18

OH-triBDE1 (meta-substituted) Tetra-BDE2

NIST library and use of standard NIST library and use of standard Analysis of mass spectrum and comparison with the MS data reported by Barontini et al. (2004) NIST library and use of standard Analysis of mass spectrum Analysis of mass spectrum NIST library and use of standard Analysis of mass spectrum Analysis of mass spectrum Analysis of mass spectrum Analysis of mass spectrum Analysis of mass spectrum Analysis of mass spectrum Analysis of mass spectrum and comparison with the MS data reported by Barontini et al. (2004) Analysis of mass spectrum Analysis of mass spectrum and comparison with the MS data reported by Hites (2008) Analysis of mass spectrum

Barontini et al. (2004) and Blazso et al. (2002)

4 5 6 7 8 9 10 11 12 13 14

4-Bromophenol 2,6-dibromophenol 2-Bromo-4(1-methylethenyl) phenol 2,4-dibromophenol OH-mono-PBB Di-OH-monoPBB1 2,4,6-tribromophenol Di-OH-monoBDE Di-OH-monoPBB2 Di-OH-diBDE1 Di-OH-diBDE2 Di-OH-diBDE3 Di-OH-diBDE4 Bromobisphenol A

486

19

Tetra-BDE3

486

20 21

Di-OH-triPBB2 OH-triBDE2 (para-substituted) Di-OH-triBDE 6-OH-BDE-47

448 423

Analysis of mass spectrum and comparison with the MS data reported by Hites (2008) Analysis of mass spectrum and comparison with the MS data reported by Hites (2008) Analysis of mass spectrum Analysis of mass spectrum

439 502

Analysis of mass spectrum NIST library and use of standard

1 2 3

22 23

24

502

Analysis of mass spectrum

25

OH-tetraBDE1 (ortho-substituted) 3-OH-BDE-47

502

NIST library and use of standard

26

Penta-BDE1

565

27

5-OH-BDE-47

502

Analysis of mass spectrum and comparison with the MS data reported by Hites (2008) NIST library and use of standard

28

502

Analysis of mass spectrum

29

OH-tetraBDE2 (ortho-substituted) Penta-BDE2

565

30 31

OH-pentaPBB Tribromobisphenol A

565 465

32 33 34 35 53.0 36 37 38

Di-OH-tetraPBB1 Di-OH-tetraPBB2 60 -OH-BDE-99 OH-tetraPBB TBBPA 4-OH-BDE-90 OH-hexaPBB Di-OH-pentaPBB

502 502 581 486 544 581 644 581

Analysis of mass spectrum and comparison with the MS data reported by Hites (2008) Analysis of mass spectrum Analysis of mass spectrum and comparison with the MS data reported by Barontini et al. (2004) Analysis of mass spectrum Analysis of mass spectrum NIST library and use of standard Analysis of mass spectrum NIST library and use of standard NIST library and use of standard Analysis of mass spectrum Analysis of mass spectrum

reaction between PBDEs and OH radicals in the gas phase (Raff and Hites, 2006). It was reported that OH-PBDE metabolites from laboratory studies in animals were dominated by hydroxyl groups in the meta or para positions (Malmberg et al., 2005; Marsh et al., 2006; Qiu et al., 2007). Ortho OH-substituted OH-PBDEs have been identified as naturally occurring formulations in marine organisms such as sponges, tunicates, and algae (Fu et al., 1995; Malmvarn et al.,

Barontini et al. (2004) and Blazso et al. (2002)

Barontini et al. (2004) and Blazso et al. (2002)

Barontini et al. (2004) and Blazso et al. (2002)

Fu et al. (1995), Hovander et al. (2002), Malmberg et al. (2005), Malmvarn et al. (2005), Marsh et al. (2006), Ueno et al. (2008), Valters et al. (2005), Verreault et al. (2005), Zeng et al. (2012)

Malmberg et al. (2005), Ueno et al. (2008), Valters et al. (2005), Verreault et al. (2005), Zeng et al. (2012)

Ueno et al. (2008), Valters et al. (2005), Zeng et al. (2012)

Barontini et al. (2004), Blazso et al. (2002)

Zeng et al. (2012) Barontini et al. (2004) Ueno et al. (2008)

2005; Unson et al., 1994). OH-PBDEs in the abiotic samples (surface water and precipitation) were dominated by ortho substituted congeners (Ueno et al., 2008). In this study, two of the five identified OH-PBDE congeners were substituted in ortho position, other two congeners were in meta position, and another one were substituted in para position. Therefore, it needs be very prudent to deduce the origins of OH-PBDEs solely by using the hydroxyl group substituted position.

(a) OH-triBDE1 275.29 277.09 [M-2Br]+

[M-2BrCH3]+

Relative abundance

259.27

206.60

[M]+ 436.66 279.05

231.99

325.12

170 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%

meta-substituted Relative abundance

100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%

222

275

(c) OH-tetraBDE1

352.65

331

515.54

513.87

431.38 438.99 401.85

389

ortho-substituted

[M]+ 517.75

[M-BrCH3]+ 419.52

511.87 405.36 435.40

488.07 519.51

400

452

509

566

621

677

75

(b) OH-triBDE2

100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%

para-substituted

258.97

418.77

[M-CH3]+

[M-2BrCH3]+

433.82 [M]+ 195.04 178.98

170

451

Relative abundance

Relative abundance

Z. Ren et al. / Environmental Pollution 177 (2013) 71e77

354.83 338.82 261.98 257.99 229.93 274.04

219

272

327

385

441

499

ortho-substituted

515.68 513.69

437.81

356.89

(d) OH-tetraBDE2

100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%

416.78

[M]+

421.74 517.70 [M-BrCH3]+

483.71

519.72 577.60 590.62

449.22

400

454

513

568

625

682

Fig. 2. Mass spectra of unidentified OH-BDEs (a: OH-triBDE1; b: OH-triBDE2; c: OH-tetraBDE1; d: OH-tetraBDE2) in particle samples from waste printed circuit boards recycling workshop (diazomethane derivatized).

The most abundant BP congener was 2,4,6-triBP, accounting for 65.0% of the total BPs concentration, followed by 2,4-diBP (32.1%) and 2,6-diBP (2.81%). This BPs profile was quite different from that in mouse plasma exposed to commercial PBDE mixture, in which 2,4,5-triBP was the most abundant congener, accounting for 49.8e 56.3% of the three detected BP congeners (2,4-diBP, 2,4,5-triBP and 2,4,6-triBP), whereas 2,4,6-triBP was only accounted for 3.43e 3.76% (Qiu et al., 2007). This difference might be due to the different formation pathways of BPs in mouse plasma from this study. In the mouse plasma samples, 2,4,5-triBP and 2,4-diBPs were thought to be metabolites of BDE-47 and -99 (Qiu et al., 2007). While in this study, BPs could be directly released as flame retardant compounds or formed via other pathways.

Table 2 Concentration of OH-PBDEs and BPsa in PMb emitted from printed circuit boards recycling in Guiyu (ng m3). Compounds

No 1

No 2

No 3

No 4

Average

OH-triBDE1 OH-triBDE2 6-OH-BDE-47 OH-tetraBDE1 3-OH-BDE-47 5-OH-BDE-47 OH-tetraBDE2 60 -OH-BDE-99 4-OH-BDE-90 P OH-PBDEs Pidentified OH-PBDEs 2,6-diBP 2,4-diBP 2,4,6-triBP P BPs P OH-PBDEs þ BPs P PBDEsc Pprecursors PBDEs P P identified OH-PBDEs/ precursors PBDEs P P OH-PBDEs/ PBDEs

0.379 1.94 0.377 0.080 0.245 0.469 0.132 0.080 0.247 1.42 3.95 0.67 9.14 22.2 32.0 35.9 820 1471 0.17%

0.572 0.233 0.384 0.095 0.224 0.396 0.106 0.146 0.158 1.31 2.31 0.99 12.0 5.84 18.8 21.1 404 785 0.32%

0.384 0.038 0.351 0.071 0.148 0.298 0.068 0.083 0.111 0.99 1.55 1.07 10.3 16.2 27.6 29.2 369 815 0.27%

0.159 1.34 0.203 0.045 0.093 0.146 0.030 0.067 0.023 0.532 2.11 0.24 2.25 24.1 26.6 28.7 266 720 0.20%

0.374 0.889 0.329 0.073 0.178 0.327 0.084 0.094 0.135 1.06 2.48 0.74 8.43 17.1 26.3 28.8 465 948 0.23%

0.27%

0.29%

0.19%

0.29%

0.26%

a b c

BPs: bromophenols. PM: particulate matters. P precursors PBDEs ¼ BDE-47 þ BDE-99.

3.3. Formation mechanisms of OH-PBDEs and BPs In the workshop, the waste printed circuit boards were recycled by heating over a grill on a stove. During the heating process, plenty of organic chemicals as well as POPs and flame retardants can be released into the environment via two pathways: a) direct evaporation and b) oxidation reaction of precursor compounds (Bi et al., 2010). As for OH-PBDEs, there was no evidence to show that they are used in the waste printed circuit boards or other e-waste material. Therefore, OH-PBDEs most likely were formed via the oxidation reaction of precursors during the e-waste recycling. Monohydroxylated PBDEs can be formed via direct hydroxylation or by a 1,2-shift of a bromine atom after epoxidation of the parent PBDE congener (Malmberg et al., 2005). Possibly, BDE-47 and -99 were the main precursors of OH-PBDEs identified in the present study since they are the most abundant PBDE congeners (Ren et al., submitted for publication). The ratios of identified OH-PBDEs to precursor PBDEs were calculated (Table 2) in order to evaluate the transformation efficiency from precursor PBDEs to OH-PBDEs. The calculated ratios were from 0.17% to 0.32%, with an average transP P formation ratio of 0.23%. The ratios of OH-PBDEs to PBDEs ranged from 0.19% to 0.29%, and average of 0.26%. These transformation ratios were much lower compared to the ratios found in the abiotic environment, which ranged from 1% to 30% in snow, 1%e 20% in rain, and 3%e40% in water samples (Ueno et al., 2008). This could be explained by the different environmental conditions. Under the conditions with high temperature and high radical concentrations, OH-PBDEs could also be consumed by the secondary reaction with OH radicals since they have faster OH rate constant compare to PBDEs (Raff and Hites, 2006). Di-OH-PBDEs could be generated during this process, which were evidenced by the identification of several di-OH-PBDEs in this study (Fig. 1). Additionally, BPs were suggested to be a possible source of OHPBDEs in the natural aquatic systems through photochemical approaches (Liu et al., 2011), which may result in the low transformation ratios of PBDEs to OH-PBDEs. The formation mechanism of BPs might be slightly complicated compared to that of OH-PBDEs. As a widely used flame retardant

76

Z. Ren et al. / Environmental Pollution 177 (2013) 71e77

100% 90%

Relative abundance

80% 70%

2'-OH-BDE-68 4'-OH-BDE49 6’-OH-BDE-99 6-OH-BDE-137

60%

6-OH-BDE-47 4-OH-BDE-42 4-OH-BDE-90 6-OH-BDE-196

3-OH-BDE-47 6-OH-BDE-90 6-OH-BDE-85 6-OH-BDE-199

5-OH-BDE-47 6-OH-BDE-99 2-OH-BDE-123 6'-OH-BDE-206

Abiotic environment

Biotic environment

50% 40% 30% 20% 10% 0% a

largemouth bass

longnose gar a

human sermb

snow c

rain c

this study

a

Fig. 3. Comparison of OH-PBDE congeners detected in this study with that in biotic and abiotic environment ( Data from Valters et al. (2005); bData from Ren et al. (2011); cData from Ueno et al. (2008)).

compounds (Knob et al., 2010), BPs are probably released into the environment via direct evaporation during the heating process of waste printed circuit boards recycling. On the other hand, previous study on the thermal behavior of TBBPA showed that the main volatile products generated in the thermal degradation process were BPs and brominated bisphenol A species, and the degradation became vital at temperatures equal or higher than 250  C (Barontini et al., 2004). In this workshop, the waste printed circuit boards were heated over coal-stoves and the heating temperature was about 250e300  C. Therefore, a lot of BPs and brominated bisphenol A might be produced through the TBBPA decomposition. Plenty of TBBPA and brominated bisphenol A were observed in this study (Fig. 1), though they were not quantified for the low recovery and lack of corresponding authentic standards, this still can be an evidence providing this formation pathway is possible. Additionally, BPs have also been characterized as products of PBDEs with 1e 2 bromines reacted with OH radicals in the gas phase (yields up to 20% relative to the amount of PBDEs consumed) via the breaking of diphenyl ether bond (Raff and Hites, 2006). Similarly to OH-PBDEs, no evidences show that the e-waste material contained OH-PBBs and di-OH-PBBs. Therefore, they are probably produced by oxidation reaction of precursor compounds. Rayne et al. (2006) found that OH-PBBs (20% yield) were generated through the photolysis of BDE-153, and Erickson et al. (2012) observed di-OH-PBBs as photoproducts of OH-PBDEs. In this workshop, high BDE-153 and OH-PBDEs concentrations associated with PM were observed (Ren et al., submitted for publication). Thus, these two compounds possibly were produced during the waste printed circuit boards recycling. 4. Conclusions OH-PBDEs, BPs and other brominated phenolic compounds in the particle samples were investigated in a workshop engaged in recycling waste printed circuit boards in Guiyu, South of China. The results show that tri- to penta-brominated OH-PBDEs and mono- to tri-brominated BPs were abundant in the PM samples. 6-OH-PBDE47 and 2,4,6-triBP were the most abundant identified OH-PBDE and BP congeners, respectively. The results suggest that these compounds can be formed not only by enzymatic or photochemical reaction, but also by direct emissions from a point source. OHPBDEs are most likely to be formed via the oxidation reaction of PBDEs and/or BPs, while BPs are probably released through the direct evaporation or produced from decomposition or the gas

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