ARTICLE pubs.acs.org/est
Identification of Monochloro-Nonabromodiphenyl Ethers in the Air and Soil Samples from South China Zhiqiang Yu,†,* Kewen Zheng,‡ Guofa Ren,‡ Decheng Wang,‡ Shengtao Ma,†,§ Pingan Peng,† Minghong Wu,‡ Guoying Sheng,† and Jiamo Fu†,‡ †
State Key Laboratory of Organic Geochemistry, Guangdong Key Laboratory of Environment Protection and Resource Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China ‡ Institute of Environmental Pollution and Health, School of Environment and Chemical Engineering, Shanghai University, Shanghai 200072, China § Graduate School of the Chinese Academy of Sciences, Beijing 100039, China
bS Supporting Information ABSTRACT: Several studies have indicated that mixed brominated/chlorinated organic compounds could be formed during the thermal process such as the incineration of municipal solid waste and open burning of unregulated e-waste at recycling areas. In this study, air particles and soils from e-waste recycling areas, as well as outdoor and indoor air particles from urban Guangzhou, were collected and pooled for the identification of mixed chlorinated/brominated diphenyl ethers (PXDEs). Three monochlorononabromo diphenyl ethers (Cl-nonaBDEs), including 60 -Cl-BDE-206, 50 Cl-BDE-207, and/or 40 -Cl-BDE-208, were first structurally identified in these air and soil samples. The identification was done by comparison of retention times in chromatograms of pure reference compounds and environmental samples, as well as by comparison with full-scan mass spectra data in electron capture negative ionization mode. Because of their similar physicalchemical properties, 40 -Cl-BDE-208 and 50 -Cl-BDE-207 absolutely coeluted, even on a nonpolar DB-5 column. Further investigation is still needed to clarify these findings. Nevertheless, the results indicated that Cl-nonaBDEs would occur in various environmental matrices. Because the replacement of Br by Cl will change the physicalchemical properties of PBDE analogues, environmental occurrence, fate, and transport, the potential toxicity of PXDEs should be investigated.
’ INTRODUCTION Polybrominated diphenyl ethers (PBDEs) are a class of additive flame retardants used in textiles, furniture, electronic appliances, and electrical goods.1 There are three major PBDE commercial formulations in the global market: penta-BDEs, octa-BDEs, and decaBDEs. Because PBDEs are not chemically bound to the polymers, they might be released into the environment during their life cycle (e.g., production, use, disposal, or recycling).2 To date, a large number of studies have been conducted to investigate the environmental fate, toxicity, and exposure to PBDEs.24 The results of these studies have indicated that PBDEs are ubiquitous contaminants in the global environment. Additionally, they can bioaccumulate in aquatic and terrestrial food webs, as well as humans, and they have potential liver toxicity, thyroid toxicity, developmental toxicity, and developmental neurotoxicity to animals or humans.2,48 Therefore, the European Union initiated regulations to phase out the production and use of penta-BDEs and octa-BDEs commercial formulations. And, in the United States, there was a voluntary phase out of penta-BDEs and octa-BDEs commercial formulations, and this voluntary ban has recently been extended to include deca-BDEs commercial formulations. The Stockholm Convention also recently r 2011 American Chemical Society
designated penta-BDEs and octa-BDEs commercial formulations as persistent organic pollutants. Many studies have focused on biotic and abiotic transformation of PBDEs, especially biodegradation, biotransformation, and photolysis.2,3,613 Debromination transformation was the major degradation pathway for both biotic and abiotic processes, whereas oxidative transformation and hydroxyl radical reaction were also suggested for biotic and abiotic processes, respectively. The thermolytic transformation of halogenerated flame retardants has raised concern due to the formation of chlorinated- and brominated dioxins/furans (PCDD/ DFs, PBDD/DFs).1417 Most studies investigated areas near the incineration of municipal solid waste and open burning of e-waste at recycling facilities.1820 In addition, mixed brominated/chlorinated dioxins/furans (PXDD/DFs) and brominated/chlorinated biphenyl (PXB) have also been detected in environmental matrices (fly ash, sediment, soil) and biota samples.2025 Moreover, PXDD/DFs were Received: November 8, 2010 Accepted: March 2, 2011 Revised: March 1, 2011 Published: March 14, 2011 2619
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Figure 1. Synthetic schemes for 60 -Cl-BDE-206, 50 -Cl-BDE-207, and 40 -Cl-BDE-208.
observed in biota samples from the background environment.26 These results suggest that mixed brominated/chlorinated organic compounds could be formed when both chlorinated substances and brominated substances were present during the thermal process. It should be noted that PXDD/DFs have a far larger group of substances compared with PCDD/DFs and PBDD/DFs.20,27 Furthermore, PXDD/DFs have similar and, for some congeners, possibly greater toxicity than PCDD/DFs and PBDD/DFs.24 To the best of our knowledge, mixed brominated/chlorinated diphenyl ethers (PXDEs) have never been reported in environmental matrices and biota samples. Christiansson et al. investigated the occurrence of 40 -Cl-BDE-208 in the environmental samples.28 However, they did not find it and used it as an internal standard for determination of higher brominated BDEs.29 However, PXDEs might be formed if both PBDEs and chlorine exist during the thermal process according to the result of lab-simulating thermolysis experiments of 2,20 ,4,40 -tetrabromo diphenyl ether (BDE-47) and 2,20 ,4,40 ,5,50 -hexabromo diphenyl ether (BDE-153) in the presence of tetrachloromethane.30 This study was conducted to identify the structure of PXDEs in pooled air particles and soil samples from an e-waste recycling area in Guiyu, as well as outdoor and indoor air particles collected in the typical urban city, Guangzhou. Both study areas have elevated PBDE concentrations in environmental matrices, and e-waste recycling area has been found to have extremely high concentrations of PCDD/DFs and PBDD/DFs in the air.3133 The identification was done by comparison of retention times in chromatograms of pure reference compounds and environmental samples. This is the first found PXDEs in the environmental samples.
’ EXPERIMENTAL SECTION 13
C-labeled decabromodiphenyl ether ( C-BDE-209) was obtained from Cambridge Isotope Laboratories (Andover, MA, USA). All solvents used for the extraction and cleanup were of analytical grade and were redistilled Chemicals and Materials. 13
using a glass system. Prior to use, neutral silica gel (80100 mesh) and alumina (100200 mesh) were Soxhlet extracted with methanol and methylene chloride for 48 h, respectively. Sodium sulfate was stored in sealed desiccators after baking at 450 °C. Synthesis of 60 -Cl-BDE-206, 50 -Cl-BDE-207, and 40 -Cl-BDE-208. Three monochloro-nonabromodiphenyl ethers including 60 -chloro2,20 ,3,30 ,4,40 ,5,50 ,6-nonabromodiphenyl ether (60 -Cl-BDE-206), 50 -chloro-2,20 ,3,30 ,4,40 ,5,6,60 -nonabromodiphenyl ether (50 -Cl-BDE207), and 40 -chloro-2,20 ,3,30 ,4,5,50 ,6,60 -nonabromodiphenyl ether (40 -Cl-BDE-208) were prepared as follows. General Procedures. The 1H (500 MHz) and 13C NMR (125 MHz) spectra were obtained on a Bruker Avance 500 spectrometer using deuterated chloroform (CDCl3) and deuterated dimethyl sulfoxide (DMSO-d6) as solvents. Tetramethylsilane (TMS) was used as the internal standard. Electron ionization mass spectra (EIMS) were obtained using a quadrupole Agilent 5975B mass spectrometer connected to an Agilent 6890N gas chromatograph equipped with a DB-5 ms capillary column (12 m 250 μm internal diameter (i.d.); 0.25 μm film thickness; J&W Scientific, Folsom, CA) using helium as the carrier gas and an electron energy of 70 eV. The starting materials, 1-fluoro-4-nitrobenzene, 2-chlorophenol, and 3-chlorophenol, were purchased from Alfa Aesar (Tianjin, China), whereas 4-chlorodiphenyl ether was obtained from Meryer (Shenzhen, China). Iron powder was obtained from China National Medicines Corporation Ltd. (Shanghai, China). All solvents and other chemicals were of analytical grade. Silica gel column chromatography was conducted using 100200 mesh silica. All organic phases were dried with anhydrous sodium sulfate prior to being concentrated in a rotary evaporator. The final products used as authentic reference standards, 60 -Cl-BDE-206, 50 -Cl-BDE-207, and 40 -Cl-BDE-208, were simply purified through recrystallization. Synthetic Procedure. Preparation of 60 -Cl-BDE-206 and 50 -ClBDE-207 (Figure 1) was initiated by coupling 1-fluoro-4-nitrobenzene with 2-chlorophenol and 3-chlorophenol, respectively, in 2620
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Figure 2. GC/MS chromatogram of monchloro-nonaBDEs in the air, soil samples in South China in ECNI mode, recorded by ion m/z: 79, 81, and 488.6, 494.7 peak d: 40 -Cl-BDE-208 and/or 50 -Cl-BDE-207; peak c: 60 -Cl-BDE-206.
dimethylacetamide (DMAC) using potassium carbonate as a base. Similarly to Marsh’s methods,34 the coupling yielded 4-(2-chlorophenoxy)-nitrobenzene 1 and 4-(3-chlorophenoxy)-nitrobenzene 2. Then the reduction of nitro groups in the two compounds with iron produced 4-(2-chlorophenoxy)-aniline 3 and 4-(3chlorophenoxy)-aniline 4 in good yields, respectively.35 Thereafter, the generated amino groups were converted to bromine atoms to give 20 -chloro-4-bromo-diphenyl ether 5 and 30 -chloro-4-bromodiphenyl ether 6 by diazotiation with HBr/NaNO2 and the Sandmeyer reaction using CuBr according to a method reported by Kubiczak et al., with slight modification.36 The bromniated chlorodiphenyl ether 5 and 6 were perbrominated in an excess of bromine and aluminum tribromide28 to give nonabromodiphenyl ether 60 -ClBDE206 and 50 -Cl-BDE207, respectively. Some octa- and nonaBDEs have been successfully synthesized using this method.28,36 40 -Chloro-nonabromodiphenyl ether (40 -Cl-BDE-208), which was used as an internal standard during the analysis of highly brominated diphenyl ethers (octa- to nona-BDEs), was synthesized by Christiansson et al.28 This compound was prepared by the perbromination of 4-chlorodiphenyl ether using an excess of bromine and aluminum tribromide. The details of the reaction conditions for each step, as well as nuclear magnetic resonance (NMR) and mass spectra data for the intermediate products and final Cl-BDEs are listed in the Supporting Information. Samples, Extraction, and Cleanup. The outdoor and indoor air particle samples in Guangzhou,33 and the air particle31 and soil samples37 from an e-waste recycling area, were collected between October 2004 and April 2008. These samples were then used for the determination of halogenated organic contaminants. Details regarding collection of these samples are provided in the references.31,33,37 The procedures used for sample extraction and cleanup have been described previously.32,37 Briefly, glass fiber filters (GFFs),
and soil samples were Soxhlet extracted with a mixture of acetone/ n-hexane (1:1, v/v) for 72 h. Activated copper was added to the extraction flasks during the extraction to remove elemental sulfur. The extracts were then concentrated using a rotary evaporator and cleaned on multilayer silica/alumina columns (1 cm internal diameter) that had been wet-loaded sequentially with 6 cm aluminum, 2 cm silica gel, 5 cm basic silica gel (3:1 silica gel/1 M NaOH, w/w), 2 cm silica gel, 8 cm acid silica gel (1:1 silica gel/ sulfuric acid, w/w) and 2 cm anhydrous Na2SO4 from the bottom to the top. The column was eluted with 70 mL of methylene chloride/n-hexane (1:1), after which the eluates were concentrated to 200 μL under a gentle nitrogen stream and a known amount of internal standard (13C-BDE-209) was added for GC/ MS analysis. Instrument Analysis. Air and soil samples were analyzed using an Agilent 7890 series gas chromatograph coupled to an Agilent 5975C mass spectrometer (GC/MS). Electron ionization (EI) and electron capture negative ionization (ECNI) modes were used for full scan analysis. The mass spectrometer was scanned from 70 to 1000 m/z. ECNI selected ion monitoring was simultaneously used, and the following ions were monitored: m/z 79 and 81 for Br, m/z 442.6 and 494.7 for Cl-nonaBDEs, and 13C-labeled BDE-209, respectively. Three different types of columns were used for identification: DB-5-HT MS (15 m 250 μm i.d.; 0.10 μm film thickness; J&W Scientific), DB-17 MS (15 m 250 μm i.d.; 0.25 μm film thickness; J&W Scientific), SP-2331 (15 m 250 μm i.d.; 0.20 μm film thickness; Supelco, Bellefonte, USA). Manual injection (1 μL) was performed in the pulse splitless mode with a purge time of 2.0 min. The GC oven temperature program on DB-5 and DB-17 column was as follows: held at 110 °C for 5 min, 20 °C/min to 200 °C, held for 4.5 min, and then 7.5 °C/min to 305 °C, held for 16 min; For SP-2331 column, GC oven temperature program: held at 110 °C for 5 min, 20 °C/min to 200 °C, held for 4.5 min, and then 7.5 °C/min to 270 °C. 2621
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Figure 3. Mass spectra of the monochloro-nonabromodiphenyl ethers in the soil sample from e-waste recycling area in ECNI mode. peak d: mixture of 40 -Cl-BDE-208 and 50 -Cl0 -BDE-207; peak c: 60 -Cl-BDE-206.
’ RESULTS When we did screening analysis for brominated flame retardants of the pooled air particle and soil from e-waste recycling area using GCMS in ECNI mode, two significant novel peaks containing bromine were found in both samples (parts 1 and 2 of Figure 2). The retention times of these two peaks were between those of nona-BDEs (including BDE-206, 207, and 208) and BDE-209. To identify these novel brominated compounds, full-scan analysis was performed in both ECNI and EI modes. The concentrations of these two compounds in both samples were not sufficient to allow full-scan analysis by EI-MS. However, some information could be obtained from the fragment ions based on the full-scan ECNI mass spectra (Figure 3). As shown in Figure 3, three dominant fragment ions for both novel GC peaks at m/z 407.6, 442.6, and 486.6 were observed. This characteristic fragment process has been found in the ECNI mass spectra of methoxylated octa- and nona-BDEs.38 The fragment ions cluster at m/z 442.6 and 407.6 might correspond to the molecular ions C6Br4ClO and C6Br4O, m/z 35, which were present between two fragment ions, indicated the loss of one chlorine atom. The fragment ion at m/z 486.6 could correspond to C6Br5O, which is usually observed in the ECNI mass spectra of nona-, and deca-BDEs. On the basis of our analysis, we assumed that these two peaks were Cl-nonaBDEs. Prior to the final confirmation of these novel brominated compounds, two control experiments were conducted to see if the sample treatment procedures produced any Cl-nonaBDEs or Cl-nonaBDEs as a result of laboratory matrix contamination. A total of 50 ng BDE-209 was spiked into clean GFF and pre-extracted soil, after that the sample extractions, cleanup procedures and, determination methods were conducted as described in the Experimental Section. No Cl-nonaBDEs were produced during the sample cleanup procedures. Laboratory procedure blanks were also treated and analyzed. Cl-nonaBDEs were not detected, except for a minor amount of BDE-209 (
