Polybromobenzene Pollutants in the Atmosphere of North China

Oct 21, 2013 - State Key Joint Laboratory for Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering and Ce...
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Polybromobenzene Pollutants in the Atmosphere of North China: Levels, Distribution, and Sources Yan Lin,† Xinghua Qiu,*,† Yifan Zhao,† Jin Ma,‡ Qiaoyun Yang,† and Tong Zhu† †

State Key Joint Laboratory for Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering and Center for Environment and Health, Peking University, Beijing 100871, P. R. China ‡ State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, P. R. China S Supporting Information *

ABSTRACT: Brominated flame retardants (BFRs) are important persistent organic pollutants. Analysis of BFRs in atmospheric samples in a previous study led us to suspect the presence of unidentified organic bromides, other than polybrominated diphenyl ethers (PBDEs), in the atmosphere. In this study, we identified and quantified polybromobenzenes, a group of organic bromides, in air samples collected through passive sampling in gridded observations in North China. We investigated their concentrations and spatial distribution, and estimated the proportion due to different sources. We detected seven species of polybromobenzenes, including hexabromobenzene (HBB), pentabromotoluene (PBT), pentabromoethylbenzene (PBEB), pentabromobenzene (PeBB), tetrabromobenzenes (TeBBs), and tribromotoluene (TrBT), in all or most of the field samples, indicating widespread occurrence of this class of pollutants. The median concentrations of each pollutant ranged from 20.0 to 144 pg/sample (or from 0.07 to 1.16 pg/ m3), with relatively high concentrations found near e-waste recycling sites, BFR manufacturing sites, and areas of high population density. Positive matrix factorization (PMF) analysis revealed that ∼70% of HBB, PBT, PBEB, and PeBB was from commercial products, while ∼80% of 1,2,3,5-TeBB, 1,2,4,5-TeBB, and 2,4,5-TrBT was linked with BFR manufacturing. This study provides essential information on widespread polybromobenzene pollutants in the atmosphere, particularly TeBBs and TrBT, for which this is the first report of their presence as atmospheric pollutants.

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and several states in America.10 For these control regulations, other unregulated substitutes, such as polybromobenzenes, may be introduced to the market to fill the demand for flame retardants.11,12 Polybromobenzenes belong to a group of organic bromides with one phenyl ring substituted by several bromine atoms. Compared with PBDEs and HBCD, polybromobenzene pollutants have higher vapor pressures and hence are more prone to evaporation into the atmosphere.13,14 Some polybromobenzene pollutants have been shown to bioaccumulate in wildlife,10,15,16 and to be toxic, particularly hepatotoxic. 17,18 Because of their environmental risks, some polybromobenzenes, such as 1,2,4,5-tetrabromobenzene, have been listed in the preregistration list of the Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) framework.19

INTRODUCTION Brominated flame retardants (BFRs) are a large and important group of synthetic chemicals. More than 75 commercial BFRs were reported in 2003 and new compounds are still being produced.1 In particular, additive BFRs such as polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCD) have attracted a great deal of attention over the past decades. PBDEs and HBCD are widely used for fire prevention in domestic and industrial products, with ∼82,000 tons produced globally in 2001.2 These BFRs are not chemically bonded to the products to which they are added, so they can be released into the environment during the lifetime and disposal of the products.3,4 Because of their persistence and potential for long-distance transport through the atmosphere, these pollutants are now ubiquitous in the environment, even in the polar regions.5,6 PBDEs and HBCD are potentially harmful to wildlife and humans due to their bioaccumulation and toxicity.7,8 As a result, tetra-, penta-, hexa-, and hepta-BDEs were incorporated into the Stockholm Convention on Persistent Organic Pollutants for global regulation in 2009, and HBCD was added in 2013.9 Another widely used BFR, i.e., commercial Deca-BDE, has been restricted in Europe © 2013 American Chemical Society

Received: Revised: Accepted: Published: 12761

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Several recent studies have investigated the sources of polybromobenzenes. The most important source of commercially produced polybromobenzenes, such as hexabromobezene (HBB), pentabromotoluene (PBT), and pentabromoethylbenzene (PBEB), is released during production and consumption.11,20 In addition, thermal processes such as steel production and especially incineration of solid waste containing polymeric BFRs or decabromodiphenylethane (DBDPE) have been shown to be sources of polybromobenzene pollutants.3,11,21,22 Electronic waste (e-waste) recycling is a particularly important source of HBB, PBT, and PBEB, and significantly high levels of these pollutants have been found near e-waste sites.23,24 As for other polybromobenzenes, such as pentabromobenzene (PeBB), little information is available on their sources although high environmental levels have been measured.11 China is one of the major BFRs manufacturers in the world,1,11 and high levels of polybromobenzene pollutants have been found in South China.24 In North China, one of the most developed regions with a population of more than 300 million people,25 both the manufacturing of BFRs26 and e-waste recycling27,28 could result in potentially significant pollution by polybromobenzenes. However, little information is available on these pollutants in North China. In a previous study, we used gridded field observations to investigate PBDEs and DBDPE in the atmosphere of North China.26 We measured these pollutants with gas chromatographic-mass spectrometry (GC-MS) with electron capture negative ionization (ECNI) and found many peaks of unknown brominated organic chemicals other than PBDEs. We hypothesized that some of these peaks may belong to polybromobenzenes. To verify this hypothesis, we systematically identified and quantified polybromobenzene pollutants to determine their atmospheric levels, spatial distribution, and potential sources. The polybromobenzene pollutants examined include hexabromobenzene (HBB), pentabromotoluene (PBT), pentabromoethylbenzene (PBEB), pentabromobenzene (PeBB), 1,2,3,5-tetrabromobenzene (1,2,3,5-TeBB), 1,2,4,5-tetrabromobenzene (1,2,4,5-TeBB), and 2,4,5-tribromotoluene (2,4,5-TrBT). This is the first report on the environmental presence of the latter three chemicals.

one polyurethane foam (PUF)-based passive air sampler with duplicate samplers at four sites. All samplers were deployed continually for 90 days, and the entire sampling period ranged from early June to early October 2011. Sample Analysis. We prepared the samples for analysis of polybromobenzene pollutants in the same manner as for analysis of PBDEs and DBDPE as described elsewhere,26 except that we used 13C12−PCB138 as an internal standard for the quantification of polybromobenzenes. Analysis of all target chemicals was performed on an Agilent 7890A-5975C GC-MS. The GC injection port was held at 250 °C with a splitless injection volume of 1 μL. A 30-m DB-5MS column (250 μm i.d., 0.25 μm film thickness; J&W Scientific, Folsom, CA, USA) was used to separate all analytes with a constant flow rate of 1.0 mL min−1. The GC oven temperature program was as follows: held at 90 °C for 1 min; 8 °C min−1 to 280 °C; 20 °C min−1 to 300 °C, and then held for 10 min. For the identification of target chemicals, the following ion couples were monitored with MS operated in electron impact (EI) ionization mode: m/ z 550 and 552 for HBB, m/z 486 and 488 for PBT, m/z 500 and 502 for PBEB, m/z 472 and 474 for PeBB, m/z 394 and 396 for TeBBs, and m/z 328 and 330 for TrBTs. For the quantification of all analytes, 79 and 81 were monitored for all brominated chemicals and m/z 372 and 374 for 13C12−PCB138 with MS operated in electron capture negative ionization (ECNI) mode. The average coefficient of variation in duplicate samples was 9.2% (range 2.3−14.5%) for all analytes. For each batch of eight samples, we prepared one procedural blank. Concentrations of analytes in blank samples (n = 12) were less than 8% of the average value measured in field samples, and recoveries monitored by BDE77 were 93.8 ± 7.5% (mean ± standard deviation; range 83.6−107.7%). Measurements were not corrected for blanks or recovery. Moran’s Index. Moran’s Index (I) is a global test statistic for spatial autocorrelation, which is calculated as follows:29

MATERIALS AND METHODS Chemicals. We acquired chemical standards from the following sources: hexabromobenzene (HBB) and pentabromoethylbenzene (PBEB) from Wellington Laboratories (Guelph, ON, Canada); pentabromotoluene (PBT) from AccuStandard (New Haven, CT, USA); pentabromobenzene (PeBB) and 1,2,3,5-tetrabromobezene (1,2,3,5-TeBB) from Aldrich Chemistry (Milwaukee, WI, USA); 1,2,4,5-tetrabromobenzene (1,2,4,5-TeBB) from Dr. Ehrenstorfer GmbH (Augsburg, Germany); 2,4,5-tribromotuluene (2,4,5-TrBT) from Alfa Aesar (Ward Hill, MA, USA); 2,4,6-tribromotuluene (2,4,6-TrBT) from Apollo Scientific Limited (Manchester, UK); and 13C12−PCB138 from Cambridge Isotope Laboratories (Andover, MA, USA). All solvents used in this study were of residue grade from Fisher Scientific (Fair Lawn, NJ, USA). Sample Collection. The study design and sample collection are reported in detail in previous papers.25,26 Briefly, we assigned 90 grid-based sampling sites in North China with a grid interval of ∼70 km. These sites included various pollution sources, including an e-waste recycling site, BFR manufacturing sites, areas of megacity, and others. At most sites we deployed

where n is the number of sampling sites, Ci and Cj are concentrations observed at sites i and j, respectively, C̅ is the average concentration of all sites, and wij is the spatial weight between sites i and j, which is based on the inversed square of Euclidean distance in this study. The value of Moran’s I varies from −1 to 1, with values approaching 1 or −1 indicating strong correlation within neighborhoods, and values close to zero indicating a random distribution.29,30 PMF Analysis. A positive matrix factorization (PMF) model developed by Paateroet et al.31 was applied to investigate the sources of polybromobenzenes in this study. The principles of the model are described in detail in the Supporting Information. This analysis was conducted using the US-EPA PMF 3.0 version. In addition to commercial sources, thermal processes and byproducts of other BFRs are potential sources of polybromobenzenes.3,11,21,22 Hence, we incorporated BDE209 and DBDPE into the model to represent BFR production and 1,2,3,5,6,7-hexachlorinated naphthalene (PCN67) to represent thermal processes.25,32 In total, 10 pollutants were involved, including seven polybromobenzenes, BDE209, DBDPE, and

n

I=

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(i ≠ j)

12762

n

∑i = 1 ∑ j = 1 wij(Ci − C̅ )(Cj − C̅ ) n × n n n ∑i = 1 ∑ j = 1 wij ∑i = 1 (Ci − C̅ )2 (1)

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Figure 1. Concentrations of seven polybromobenzene pollutants in North China. The solid horizontal line represents the median, and the red horizontal line represents the mean. The box represents the 25th−75th percentiles, and the whiskers represent the 10th−90th percentiles. Numbers in parentheses are the number of detections.

PCN67, and sampling sites with outlier or missing values were rejected prior to PMF analysis. The analysis was repeated 20 times from 20 random starting points for all samples, and the source profiles and percentage of species were represented as the mean and standard deviation of 20 extracted results. Statistical Analysis. We used a Kolmogorov−Smirnov test to check the normality of the data. We report mean values (with one standard deviation) for normally distributed data, and median values (with range) for non-normally distributed data. We used Student’s t-test to compare normally and log normally distributed data, and a Mann−Whitney U-test for other data. All statistical analyses were conducted using the SPSS software package 18.0 (SPSS Inc., Chicago, IL, USA).

quantified all analytes with MS operated with an ECNI ion source. Concentrations and descriptive statistics are listed in Tables S1 and S2 in the Supporting Information. All species were detected in all samples except for PBEB, which was detected in 88 of the 89 samples, and 2,4,5-TrBT, which was noted in 85 of 89 samples. Among these pollutants, PBT was the most abundant one with a median concentration of 144 pg/ sample (range 16.6−15,700 pg/sample), followed by HBB (median 130 pg/sample, range 25.8−4870 pg/sample), 1,2,4,5TeBB (median 119 pg/sample, range 17.2−1950 pg/sample), PeBB (median 98.8 pg/sample; range 14.4−5550 pg/sample), 1,2,3,5-TeBB (median 94.9 pg/sample, range 10.0−2770 pg/ sample), 2,4,5-TrBT (median 72.8 pg/sample, range not detected to 2360 pg/sample), and PBEB (median 20.0 pg/ sample; range not detected to 4700 pg/sample). In general, commercially produced polybromobenzenes had higher concentrations, except for PBEB, which was recorded at low atmospheric concentrations, perhaps due to lack of known production in North China. To compare pollutant levels with those observed elsewhere, we derived volumetric concentrations with a two-film model, which has been widely applied to PBDEs, PCBs, PCNs, and pesticides in previous studies.25,33−35 Derivation details and comparison results are shown in the Supporting Information. The sampling rate ranged from 0.7 to 3.3 m3/day, respectively. The volumetric concentrations of seven polybromobenzenes are shown in Figure 1. Briefly, the levels of PBEB in this study (median 0.07 pg/m3; range not detected to 16.1 pg/m3) were generally low, and levels of PeBB (median 0.37 pg/m3; range 0.05 to 20.6 pg/m3), PBT (median 0.50 pg/m3; range 0.06 to 54.9 pg/m3), and HBB (median 0.44 pg/m3; range 0.09 to 16.5 pg/m3) were moderate. Relative higher levels of 1,2,3,5-TeBB (median 0.93 pg/m3; range 0.10 to 27.0 pg/m3), 1,2,4,5-TeBB (median 1.16 pg/m3; range 0.17 to 19.0 pg/m3), and 2,4,5TrBT (median 1.14 pg/m3; range not detected to 37.0 pg/m3) were observed due to their higher vapor pressures. Concentrations of PBEB in North China were lower than those observed in the Great Lake basin11 and in South China, 24 but slightly higher than in remote areas such as Egbert.3 This result is consistent with the fact that PBEB is not mass produced in this region. In contrast, levels of HBB in North China were

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RESULTS AND DISCUSSION Identification of Polybromobenzenes in Air Samples. When analyzing PBDEs in air samples by GC-MS with an ECNI ion source, we observed many unidentified but significant peaks with equal response of m/z 79 and 81, indicating organic bromides. These pollutants were detected in most field samples, suggesting they are widespread in the atmosphere. We suspected that some of these peaks were polybromobenzenes. To verify this supposition, we monitored the molecular ion couples of polybromobenzene compounds, including hexabromobenzene (HBB), pentabromotoluene (PBT), pentabromoethylbenzene (PBEB), pentabromobenzene (PeBB), tetrabromobenzenes (TeBBs), tetrabromotoluenes (TeBTs), and tribromotoluenes (TrBTs) with MS operated with an EI ion source. The results indicated the possible presence of polybromobenzenes (Figure S1 in the Supporting Information). To confirm the presence of these potential pollutants, we used commercially available authentic standards and validated both the molecular ion couples and retention times. We identified seven polybromobenzene pollutants: HBB, PBT, PBEB, PeBB, 1,2,3,5-TeBB, 1,2,4,5TeBB, and 2,4,5-TrBT. This is the first atmospheric detection of the latter three species. The suspected TeBTs could not be confirmed due to the lack of authentic standards, and 2,3,6TrBT was not detected in most field samples. Levels of Polybromobenzene Pollutants in the Atmosphere of North China. After identification, we 12763

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Figure 2. Comparison of seven polybromobenzene pollutants among different functional areas.

higher than those in the Great Lake basin,11 Egbert, or oceanic areas,13,14,36−38 but lower than those in the Taihu Lake basin,39 South China,24 or Japan.40 The comparison showed that HBB level in China and Japan was generally higher than other countries, which is consistent with the fact that China and Japan are the two major manufacturers of HBB in the world.11 Levels of PBT found in North China were relatively high compared with those in the Great Lake basin,11 Egbert,3 and oceanic areas.13,14,36−38 The highest concentration of PBT in this study (54.9 pg m−3) was much higher than that in other regions except South China (125 pg m−3),24 where a significant source exists,24 indicating a potential source in North China. Concentrations of PeBB were slightly higher than those in the Great Lake region but lower than that in South China.11,24 These comparisons suggest that North China as a whole is not severely polluted by polybromobenzenes; however, they are widespread in the region, and high concentrations were observed at some sites. This is the first report on atmospheric polybromobenzenes observed with a passive air sampler. Although polybromobenzenes tend to exist primarily in a gaseous phase in the high temperatures of summer,13 the volumetric concentrations reported here may be an underestimate due to the low sampling efficiency for particulate-bound fractions. Hence, the following discussion is based on the original concentrations. Spatial Analysis of Polybromobenzene Pollutants. Although median levels of polybromobenzene pollutants were moderate or low in North China, high concentrations were observed at some sites. Ratios of the highest to lowest concentrations (H/L values) were relatively high (range: 113 to 947; Table S2 in the Supporting Information), suggesting point sources of release near the highest concentration sites.41 Pollutants from the point sources may spread to other sites via atmospheric diffusion. We used Moran’s Index (eq 1) to explore the spatial autocorrelation of atmospheric transport. Strong autocorrelation would indicate the predominance of atmospheric transport, while low autocorrelation would indicate local emission.29,30 All analytes were significantly correlated in space (p < 0.01) with a range of values of Moran’s I (from 0.25 to 0.69; Figure S2 in the Supporting Information). The relatively low values of Moran’s I for PeBB (0.36), PBT (0.25), PBEB (0.32), and HBB (0.35) indicate significant local

nonpoint emissions. PBT, PBEB, and HBB are commercial chemicals that may be released into the atmosphere during usage and disposal of products to which they are added. The relatively higher Moran’s I values of 2,4,5-TrBT (0.39), and especially 1,2,3,5-TeBB (0.69) and 1,2,4,5-TeBB (0.63), suggests that these pollutants are more likely to be dispersed from point sources. We used ordinary Kriging to interpolate the spatial distribution of BFRs from the log-transformed concentration data (Figures S3 and S4 in the Supporting Information). All of the BFRs showed similar spatial distributions, indicating two heavily polluted areas: a region of BFR manufacturing around the Laizhou Bay of Shandong Province, and an e-waste recycling site in the south of Tianjin. Exceptionally high concentrations of BFRs, such as BDE209, have been observed in both regions, 26 and we suspect that sources of polybromobenzene pollutants are linked with the production of BFRs or disposal of e-waste containing BFRs. Sources of Polybromobenzene Pollutants. To test our hypothesis that polybromobenzene pollutants are linked with BFR production and disposal, we grouped the sampling sites into four categories: (1) regions near BFR manufacturing facilities, where the primary BFRs produced are Deca-BDE, DBDPE, TBBPA, and HBCD; (2) regions with intensive BFR consumption, mainly high population density areas (i.e., >4000 km−2); (3) regions with BFR disposal sites, specifically the ewaste recycling site in southern Tianjin; and (4) noncharacteristic regions, including all sites not included in any of the previous groups. We used a two-tailed p-value of 0.01 for statistical significance in all groups except the disposal group, in which we used p < 0.1 due to the small sample size. Levels of HBB, PBT, and PeBB were significantly higher in manufacturing, consumption, and disposal regions, indicating these chemicals could be released into the atmosphere during the life cycle of respective commercial products (Figure 2). PBEB, another commercial BFR, was significantly higher only in consumption and disposal regions, which corresponds to the lack of reported manufacture of this compound in North China. The other three pollutants (i.e., 1,2,3,5-TeBB, 1,2,4,5-TeBB, and 2,4,5-TrBT) had significantly higher levels in manufacturing and disposal regions. Relatively low levels of these pollutants in areas of high population density indicate that 12764

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Figure 3. Profiles of sources determined by the PMF model and their contribution to target chemicals. Source #1 represents commercial production, source #2 represents byproducts from BFR manufacturing, and source #3 represents release from thermal processes.

emissions. The source of atmospheric PeBB was previously unknown,11 but the present study provides evidence that PeBB may enter the atmosphere in a similar manner to HBB, PBT, and PBEB. In our previous study, manufacturing activities around Laizhou Bay was the major source of BDE209 and DBDPE in North China.26 The dominance of these two pollutants in source #2 indicates that this source is due to BFR manufacturing. Unexpectedly, source #2 was also the dominant source for 1,2,3,5-TeBB, 1,2,4,5-TeBB, and 2,4,5-TrBT. This is an important finding because it provides evidence for the origin of these pollutants, but further studies are warranted to confirm the formation of these pollutants in manufacturing processes. The dominant chemical in source #3 was PCN67. Our previous study showed that ∼90% of the PCN67 observed in North China was from thermal processes;25 therefore, source #3 likely reflects thermal processes such as the incineration of solid waste. This source had a low contribution to polybromobenzenes, indicating that thermal processes are not a major source of these pollutants in North China. We developed a compositional profile of the intensity of each source at each site, and Figure 4 shows these profiles for three typical regions. In Shanxi Province, where no BFR manufacturing or e-waste recycling occurs, consumption of BFR-

they are unlikely to come from commercial products. They could, however, be released in the incineration of e-waste,27,28 and might be formed as byproducts during the manufacture of BFRs such as BDE209 and DBDPE, which are synthesized through bromination of aromatic hydrocarbons. These byproducts can be formed if benzene or toluene is present as impurities in the raw materials. To further investigate the sources of polybromobenzenes, we used PMF analysis, which is described in the Supporting Information. The best-fit model indicated three sources with an average R2 of 0.82 between predicted and measured values, indicating a good model fit. PMF-based source apportionment results are shown in Figure 3. Source #1 reflects the daily use of products containing BFRs because the dominant pollutants HBB, PBEB, PBT, and PeBB were all higher in BFRs consumption regions with high population density (Figure 2). Source #1 contributed ∼30% of BDE209 and DBDPE, which was consistent with our previous study based on a diffusion model.26 In contrast, ∼70% of HBB, PBEB, PBT, and PeBB observed in this study were from the use of products containing BFRs, indicating that BFR consumption is the dominant source of these pollutants. This is in agreement with the weak spatial autocorrelation observed for HBB, PBEB, and PBT, given that BFRs consumption mainly acted as local 12765

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Figure 4. Relative sources of polybromobenzene pollutants in Shanxi Province (panel A), Beijing−Tianjin, which includes the e-waste site, and neighboring regions (panel B), and Shandong Province (panel C). The area of the circles represents the total abundance of polybromobenzene pollutants at each site.

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containing products (source #1) was the major source. In the Beijing−Tianjin region (Jing-Jin), where two megacities and an e-waste recycling site are located, consumption of BFRcontaining products (source #1) and byproduct sources (source #3) were dominant. In Shandong Province, manufacturing of BFRs (source #2) was the dominant source at most sites. In conclusion, this study provides information on polybromobenzene pollutants and their sources. We found that two different processes contributed to atmospheric polybromobenzene pollution in North China. The major source of 1,2,3,5TeBB, 1,2,4,5-TeBB, and 2,4,5-TrBT were linked with the manufacturing activities of BFRs, while HBB, PBT, PBEB, and PeBB were mainly from the consumption of products containing BFRs. These findings could enable better understanding of polybromobenzene pollutants in this important region, and thus help formulate policy and regulations for control.

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AUTHOR INFORMATION

Corresponding Author

*Telephone: 86-10-6275 3184. Fax: 86-10-6276 0755. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by National Natural Science Foundation of China (21077004, 21322705, 41121004, and 21190051) and by special fund of State Key Joint Laboratory of E n v i r o n m e n t Si m ul a t io n a n d Po l lu t io n C o n t r o l (11Y01ESPCP). The authors are indebted to all the people who helped with the sampling.

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REFERENCES

(1) Alaee, M.; Arias, P.; Sjödin, A.; Bergman, A. An overview of commercially used brominated flame retardants, their applications, their use patterns in different countries/regions and possible modes of release. Environ. Int. 2003, 29 (6), 683−689. (2) Mikula, P.; Svobodova, Z. Brominated flame retardants in the environment: Their sources and effects (a review). Acta Vet. Brno 2006, 75 (4), 587−599. (3) Gouteux, B.; Alaee, M.; Mabury, S. A.; Pacepavicius, G.; Muir, D. C. Polymeric brominated flame retardants: Are they a relevant source of emerging brominated aromatic compounds in the environment? Environ. Sci. Technol. 2008, 42 (24), 9039−9044.

ASSOCIATED CONTENT

* Supporting Information S

Additional information noted in the text is available. This material is available free of charge via the Internet at http:// pubs.acs.org. 12766

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dx.doi.org/10.1021/es403854d | Environ. Sci. Technol. 2013, 47, 12761−12767