Article pubs.acs.org/est
Hydroxylated, Methoxylated, and Parent Polybrominated Diphenyl Ethers (PBDEs) in the Inland Environment, Korea, and Potential OHand MeO-BDE Source Un-Jung Kim, Nguyen Thi Hoang Yen, and Jeong-Eun Oh* Department of Civil and Environmental Engineering, Pusan National University, Busandaehak-ro 63beon-gil, Geumjeong-gu, Busan 609-735, Republic of Korea S Supporting Information *
ABSTRACT: The concentrations, congener profiles, and phase-specific distribution profiles of 27 polybrominated diphenyl ethers and 10 hydroxylated and 18 methoxylated brominated diphenyl ethers (OH- and MeO-BDEs; later called structural analogues of PBDEs) were determined in surface soil, water, air, and vegetation from the southeastern city of Busan, Korea for 2010−2011. The total PBDE concentrations were 0.18−7.7 ng/g in soil, 6.3−87 ng/L in water, 5.3−16 pg/m3 in air, and 0.06−0.22 ng/g in vegetation. The OH- and MeO-BDE concentrations were lower than the parent PBDE concentrations in soil samples but OH-BDEs were much greater in the water samples and MeO-BDEs were much greater in the air samples. The relative concentrations of the PBDEs and their structural analogues varied depending on the type and homologue of the degradation product, the substituent position, and the characteristics of the environmental medium. In particular, the OH-BDEs were not found in air samples and the OH-penta BDEs were not detected in any of the matrices. The dominance of the ortho-substituted structural analogues found in water and vegetation suggested that they may have natural sources, but different substituent patterns were found in the air and soil samples, suggesting that the structural analogues had different formation mechanisms in these media. PBDEs.4−9 OH- and MeO-BDEs can also be retransformed to even more toxic compounds such as the polybrominated dibenzo-p-dioxins (e.g., 1,3,7-triBDD and 1,3,8-triBDD) through diverse possible transforming pathways such as photochemical reaction and biological metabolism.10−15 It is, therefore, very important (but also very difficult) to investigate the transformation products, metabolites, and reaction byproducts of PBDEs in the environment. There have been many studies of PBDEs in different environmental compartments, but the structural analogues and transformation products of PBDEs have rarely been included in such studies. Only a small number of studies of the structural analogues and transformation products of PBDEs have been performed, and most of these have been focused on the marine environment, particularly on biota such as algae, fish, marine sponges, mussels, polar bears, and seals.8,15 Most of these studies have been aimed at determining the bioaccumulation potentials and biological metabolism mechanisms of the structural analogues and transformation products of PBDEs in relation to those of the abundant natural halogenated organic compounds that are found in marine water. An important
1. INTRODUCTION Polybrominated diphenyl ethers (PBDEs), popular additive brominated flame retardants notorious for their persistency, bioaccumulation, and negative effects, have been regulated as persistent organic pollutants (POPs) since 2009 by the Stockholm Convention. Like all other POPs, PBDEs remain in the environment for a long time once they have been emitted. Parent PBDEs have stable structures that are not easily transformed, but it is possible for them to be transformed, degraded, or metabolized under specific conditions. Such transformations lead to various types of products that are related to PBDEs being found in the environment, including hydroxylated and methoxylated brominated diphenyl ethers (OH- and MeO-BDEs; later called structural analogues of PBDEs), and debrominated PBDE congeners, including diphenyl ether.1−3 Of the known structural analogues of PBDEs, the OH- and MeO-BDEs are of particular interest. These compounds have never been purposefully synthesized for industrial use, so their occurrence in the environment can only be explained by the transformation of parent PBDEs or the presence of natural sources. OH- and MeO-BDEs (e.g., 6-OH and MeO-BDE47) can be taken up by plants such as maize (Zea mays L.) and other biota such as glaucous gulls and polar bears much more easily than PBDEs, and sometimes they have even higher toxicities and/or bioaccumulation potentials than the © XXXX American Chemical Society
Received: February 10, 2014 Revised: June 5, 2014 Accepted: June 9, 2014
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dx.doi.org/10.1021/es5006972 | Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Figure 1. Study area and sampling points. (A) Location of Busan in Korea. (B) circles = air, triangles = water, and squares = soil and vegetation sampling points).
finding in previous work was that it is possible for orthopositioned OH- and MeO-BDEs to be formed, in the absence of parent PBDEs, through the metabolic activity of marine sponges,4,15 although this was found only in a limited number of types of biota that live in the marine environment. Very few studies of structural analogues of PBDEs in the environment have been performed, and no studies of the atmospheric fates of these compounds have been performed. The occurrence of OH- and MeO-BDEs in other environmental media has only rarely been reported, and these reports have included studies of these chemicals in surface water and precipitation, in sewage sludge, and in sediment cores.16−18 There has not yet been a large-scale study aimed at understanding the occurrence of structural analogues of PBDEs related to the fate of PBDEs in the ambient environment, and certainly this has not been done in Korea. Because most PBDEs analogues studies were performed in the marine environment focusing on marine organisms, different research on diverse environmental media such as inland environment is required to expand the knowledge about presence and behavior of structural analogues of PBDEs.8,15 In the study presented here, we analyzed the parent mono- to deca-brominated diphenyl ethers and the tri- to pentabrominated OH- and MeO-BDEs in various inland environment compartments (air, water, soil, and vegetation (Pinus thunbergii Parl.)). The Pinus thunbergii Parl. was selected as representative vegetation as it is expected to well accumulate POPs compounds and widely distributed in Korea.19,20 Our aim was to improve our understanding of the occurrence, distribution, and fates of the PBDEs and the OH- and MeOBDEs in each environmental matrix. We determined the concentrations and relative contributions of the parent PBDEs and their degradation products to attempt to determine the possible origins and formation mechanisms of the structural analogues, focusing on the possibility of them being formed by the transformation of PBDEs. This is the first case study aimed
at understanding the distribution and fate of PBDEs and their structural analogues in the inland environment.
2. MATERIALS AND METHODS 2.1. Study Area. The study area was in Busan, which is a metropolitan city in southeastern South Korea. Samples of four inland environmental media, soil (samples S 1−20), air (both gaseous and particulate phases; samples A 1−5), surface river water (dissolved phase; samples W 1−14), and pine (Pinus thunbergii Parl.) needles (samples L 1−12), were collected between December 2010 and January 2011. The sampling points were selected to represent the whole area of the city and to reflect different land uses (industrial, commercial, agricultural, and residential areas). In total, 5 ambient air sampling points, 20 surface soil sampling points, 18 surface river water sampling points, and 12 pine needle sampling points were selected, and these are shown in Figure 1. Detailed information about the sampling sites is given in the Supporting Information (S1). 2.2. Sampling Methods. Ambient air samples were collected using Hi-Vol samplers (HV-100F; Sibata, Saitama, Japan), which were operated for 24 h at each of the sites in December 2010. A flow rate of 700 L/min was used, and the total collected volume for each sample was 1008 m3. One glass fiber filter and two polyurethane foam plugs were used to collect the particulate and gaseous-phase target compounds, respectively. At least 500 g of undisturbed surface soil was collected from less than 5 cm deep, using a shovel, at each soil sampling site. Two-year-old pine needles (150−200 g) were collected higher than 2 m above the ground from Pinus thunbergii Parl. trees that were not near structures that would impede air flow and were not affected by stack gas emissions. The soil and pine needle samples were collected in December 2010. Surface river water samples of at least 10−12 L were collected from each sampling point in December 2010, and background data (water pH, temperature, conductivity, and turbidity) were measured in the field. B
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2.6. Derivatization Method. The OH- and MeO-BDEs were acetylated in pyridine, following a previously published method with minor modifications.21,23 An extractant for PBDEs from previous multicolumn procedure was transferred in 500 μL of toluene. The transferred PBDE extract was homogenized for 1 min, then 100 μL of pyridine and acetic anhydride were added, then the mixture was vortexed for 2 min and heated to 60 °C for 30 min. The mixture was cooled to 25 °C for 5 min, and then washed with 700 μL of Milli-Q water (Millipore, Billerica, MA, USA) and twice with toluene to remove any remaining reactants and byproducts. Each sample was then passed through a 6-cm3 syringe filled with sodium sulfate to remove the water. The eluted sample was evaporated to 100 μL under a gentle stream of nitrogen, then transferred into a vial and exposed to the air until it almost reached dryness. Each sample was then reconstituted in 100 μL of dichloromethane and analyzed for OH- and MeO-BDEs by GC-HRMS. 2.7. Instrumental Analysis. Parent Compounds. The 27 parent PBDEs were analyzed by GC/HRMS using a JMS-800D instrument (JEOL, Tokyo, Japan), with separation achieved using a 5% phenyl 95% methylpolysiloxane capillary column (15 m long, 0.25 mm id, 0.10 μm film thickness; Phenomenex, Torrance, CA, USA). The oven temperature program was 100 °C for 5 min, increased at 40 °C min−1 to 200 °C, which was held for 5.5 min, then increased at 10 °C min−1 to 320 °C, which was held for 5 min. The octa- to deca-brominated PBDEs were separately reanalyzed using a different oven program, starting at 100 °C for 1 min, then increased at 25 °C min−1 to 320 °C, which was held for 5 min, to obtain better sensitivity. OH- and MeO-BDEs. The OH- and MeO-BDEs were analyzed using a GC/low-resolution MS instrument (Agilent 6890 GC and HP 5973 MS; Agilent Technologies, Santa Clara, CA, USA), with separation achieved using a DB-XLB capillary column (15 m long, 0.25 mm id, 0.10 μm film thickness; J&W Scientific, Agilent Technologies). The mass spectrometer was operated in full scan mode to obtain the retention times of the analytes and to determine the ions to monitor for quantifying and confirming the identities of the analytes in the subsequent quantitative analysis. Once the qualitative analysis had been performed, the OH- and MeO-BDEs were quantitatively analyzed using the JMS-800D GC/HRMS instrument, fitted with the same capillary column described above. 2.8. Quality Assurance and Quality Control. Field and travel blank samples were collected, and procedural blanks (pure solvent or distilled water instead of a real sample) were included in every batch of 10−15 samples to check for contamination occurring during the sampling and experimental procedures. The parent PBDE and structural analogue concentrations were lower than the limits of quantitation (LOQs) in all of the blanks. The 10 quality control samples of pure solvents spiked with structural analogues of the PBDEs were analyzed prior to analysis of actual samples and got accuracy over 90%. None of the blank samples that were used to check for contamination of the instrument and methods contained concentrations of more than 5% of the lowest concentrations found in the samples. Multilevel calibration curves, covering the whole concentration ranges found in the samples, were used to quantify the analytes, and R2 values higher than 0.999 were found for all of the analytes. The PBDE recoveries were 38.2−128.7% in all of the sample types, and this satisfied the requirements of U.S. EPA Method 1614 (air: 46.5−128.7%; water: 54.8−117.6%; soil: 38.2−113.6%; vegeta-
2.3. Target Compounds. The target compounds were 27 PBDEs, from mono- to deca-brominated (BDEs 3, 7, 15, 17, 27, 47, 49, 66, 71, 77, 85, 99, 100, 119, 126, 138, 153, 154, 156, 183, 184, 191, 196, 197, 206, 207, and 209), 18 MeO-BDEs, from tri- to penta-brominated (3′-MeO-BDE28, 5-MeOBDE47, 6-MeO-BDE47, 4-MeO-BDE49, 2-MeO-BDE68, 5′MeO-BDE99, 5-MeO-BDE100, 4′-MeO-BDE101, 4-MeOBDE103, eight tri- to penta-brominated MeO-BDEs that were identified from their relative retention times, and one unidentified tribrominated MeO-BDE), and 10 OH-BDEs, from tri- to penta-brominated (3′-OH-BDE28, 6-OH-BDE47, 6-OH-BDE100, six tri- to penta-brominated OH-BDEs identified from their relative retention times, and one unidentified tribrominated OH-BDE). Detailed information on the target compounds and on the identification of the structural analogues and their substituent positions are given in the SI (S2). There is a lack of labeled and native standards to match and identify all of the MeO- and OH-BDEs, so some of the MeO- and OH-BDEs were analyzed even though they were unidentified or could be identified only from their relative retention times. The OH- and MeO-BDEs were identified following the Larcorte et al.’s method and quantified by GC/ HRMS with EI-SIM mode.21 The structural analogues of the PBDEs were identified from the relative retention times suggested in a previous study, and quantified using the GCHRMS chromatogram for the appropriate m/z ratio and the mean relative response factor that has previously been reported for the same homologue.21 2.4. Standards and Reagents. The 13C12-labeled BDEs 3, 15, 28, 47, 100, 99, 154, 153, 183, 197, 207, and 209 (obtained already mixed; MBDE-MXE; Wellington Laboratories, Guelph, Canada) were used as internal standards in the PBDE analysis, and 13C12-labeled BDE 138 (Wellington Laboratories) was used as a recovery standard. The 13C12-labeled OH-BDEs 6hydroxylated-2,2′,4,4′-tetrabromodiphenyl ether (6-OHBDE47) and 6-hydroxylated-2,2′,4,4′,6-pentabromodiphenyl ether (6-OH-BDE100) and the 13C12-labeled MeO-BDEs 6methoxylated-2,2′,4,4′-tetrabromodiphenyl ether (6-MeOBDE47) and 6-methoxylated-2,2′,4,4′,6-pentabromodiphenyl ether (6-MeO-BDE100), all from Wellington Laboratories, were used as internal standards for the analysis of the hydroxylated and methoxylated PBDEs, as appropriate. 2.5. Analytical Methods. The extraction and cleanup methods for the PBDEs in the air, soil, and pine needle samples followed the U.S. Environmental Protection Agency (U.S. EPA) Method 1614. U.S. EPA Method 527 and the European Union standard method were used to analyze the PBDEs in the water samples, but with modifications to ensure that the parent compounds were recovered well. In brief, the air samples were extracted with a 3:1 mixture of dichloromethane and hexane for 18 h in a Soxhlet apparatus, and then the extracts were concentrated and cleaned-up using multilayer silica gel columns. Homogenized surface soil samples (10 g) or pine needle samples (15 g) were extracted with a 3:1 mixture of dichloromethane and hexane in an accelerated solvent extractor (ASE-300; Dionex, Sunnyvale, CA, USA), then the extracts were concentrated and cleaned up using multilayer silica gel columns.22 Further cleanup of the extracts using Florisil or alumina was performed as necessary. Surface river water samples (1 L) were extracted using an SPE-DEX 4790 solidphase extraction system fitted with 50 mm Atlantic C18 extraction disks (Horizon, Salem, NH, USA). C
dx.doi.org/10.1021/es5006972 | Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Table 1. Occurrence and Distribution of Polybrominated Diphenyl Ethers (PBDEs) and Their Hydroxylated and Methoxylated Structural Analogues hydroxylated BDEs
meana min max SDb DFc meana min max SDb DFc
tribromo (n = 4)
tetrabromo (n = 4)
1.1
