Article pubs.acs.org/est
Newly Discovered Methoxylated Polybrominated Diphenoxybenzenes Have Been Contaminants in the Great Lakes Herring Gull Eggs for Thirty Years Da Chen,†,‡ Robert J. Letcher,*,†,‡ Lewis T. Gauthier,† Shaogang Chu,† and Robert McCrindle§,∥ †
Wildlife and Landscape Directorate, Science and Technology Branch, Environment Canada, National Wildlife Research Centre, Carleton University, Ottawa, ON, K1A 0H3, Canada ‡ Department of Chemistry, Carleton University, Ottawa, ON, K1S 5B6, Canada § Department of Chemistry, University of Guelph, Guelph, ON, N1G 2W1, Canada ∥ Wellington Laboratories, Research Division, Guelph, ON, N1G 3M5, Canada S Supporting Information *
ABSTRACT: We recently reported the discovery and identification of novel methoxylated polybrominated diphenoxybenzenes (MeO-PBDPBs) in herring gulls eggs from the Laurentian Great Lakes of North America. We presently investigated the temporal changes (1982−2010) in MeO-PBDPB concentrations and congener patterns, as well as chemical tracers of diet (ratios of carbon and nitrogen stable isotopes), in egg pool homogenates from five selected colony sites across the Great Lakes. Egg pool homogenates from the Channel-Shelter (C−S) Island (Lake Huron) contained ∑MeO-PBDPB concentrations orders of magnitude greater than those from other colonies, suggesting potential point contamination sources nearby. In the C−S Island egg pools, concentrations increased from the initial study year (31 ng/g wet weight) and peaked around the late 1990s, followed by a general decline until 2010. Over the period, concentrations generally increased in eggs from Fighting Island (Lake Erie), Toronto Harbour (Lake Ontario) and Big Sister Island (Lake Michigan) colonies, whereas the levels in Agawa Rock (Lake Superior) declined. Although other factors likely exist, changes over time in the carbon and nitrogen isotope tracers reflected a shift of the gull diet from aquatic to more terrestrial origins, and suggested this diet shift partially accounted for the temporal changes of ∑MeO-PBDPB levels in eggs from most colonies. The ratio of Br6- to Br5-MeO-PBDPB congeners generally decreased over time in the colonies at Channel-Shelter Island, Fighting Island and Agawa Rock. This suggested that Br5- versus Br6-MeO-PBDPB congeners and/or possibly their nonmethoxylated and higher brominated precursors may have been more abundant in diets of terrestrial origin. Notably, these MeO-PBDPB congeners are not “emerging” brominated substances, but rather “recently discovered” contaminants since, as of 2011, ∑MeO-PBDPB concentrations have been constantly in the range of 30−100 ng/g ww for at least the last 30 years.
■
INTRODUCTION A recent review identified a list of the principal 610 commercially produced substances of probable persistence and bioaccumulation (P&B) relevance to the environment.1 Of these 610 substances, 13% (80 compounds) were brominated compounds, a majority of which are brominated flame retardants (BFRs). BFRs are a broad class of additive and reactive substances and technical mixtures used in commercial polymeric materials. Covaci et al. estimated that at least 75 different BFRs have been commercially produced.2 Most BFR chemicals are not chemically bound to the finished products that contain them. Hence a fraction will escape during production, use, disposal and/or recycling processes, and ultimately enter the environment. Of the approximately 80 brominated compounds considered to have potential P&B properties in the environment,1 all substances have log Kow values of > 3. However, substances with log Kow values > 8 can still be considered to be potential bioaccumulative chemicals, unless perhaps they have very high molecular weights. One highly brominated BFR in the top 10 brominated priority compounds listed by Howard and Muir1 is decabromodiphenylethane (DBDPE; CAS No. 84852-53-9). © 2012 American Chemical Society
DBDPE has relatively low bioavailability (Bioconcentration Factor = 3) but high persistence.1 It can also debrominate to more bioavailable compounds.1 Similarly, the analogous BDE209 (CAS No. 001163-19-5) has a high logKow of 12.11,1 but has been detected in various wildlife species, particularly in terrestrial predators.3 BDE-209 can also be degraded into less brominated, more bioavailable PBDE congeners via photochemical or metabolizing pathways.4−6 Very recently, we discovered and identified a novel class of brominated contaminants, methoxylated tetra- to hexa-bromodiphenoxybenzenes (MeO-PBDPBs), in eggs of the herring gull (Larus argentatus; HG), a bioindicator of contamination in the Laurentian Great Lakes ecosystem.7 Three of the six MeOPBDPB congeners discovered, containing five or six bromine atoms, were detected in pooled gull egg homogenates collected in 2009 from a majority of monitored colony sites spanning the Great Lakes. These MeO-PBDPBs have the same brominated Received: Revised: Accepted: Published: 9456
May 11, 2012 August 4, 2012 August 13, 2012 August 13, 2012 dx.doi.org/10.1021/es3018978 | Environ. Sci. Technol. 2012, 46, 9456−9463
Environmental Science & Technology
Article
diphenoxybenzene base structure of tetradecabromodiphenoxybenzene (TDBDPB; CAS No. 58965-66-5), which is also listed as a potential P&B chemical.1 TDBDPB was the major component of SAYTEX 120, a commercial flame retardant product manufactured by Albemarle Corporation prior to 2003 or earlier,8 but discontinued some time ago according to Hardy et al.9 A number of suppliers from around the world (particularly in Asia) are still marketing the TDBDPB or TDBDPB-containing products.10 Nitrogen (N) and carbon (C) stable isotope ratios (δ15N, 13 δ C) are used as chemical tracers of food web pathways and structure, for example in elucidating the spatial and temporal differences in the diet of Great Lakes HGs.11,12 Relative trophic positions of species within food webs have been estimated using δ15N, whereas δ13C differentiates feeding strategies, for example, nearshore/offshore, benthic/pelagic, freshwater/marine and terrestrial/aquatic. As reported in Chen et al.,13 for four gull species, including the herring gull, within colony sites from across Canada, the stable isotope data provided insights into the influence of diet on BFR (e.g., PBDE) exposure sources and contamination patterns of gulls. Prior to our very recent report,7 absolutely nothing had been published with respect to MeO-PBDPBs in the environment. As part of our ongoing efforts to investigate comprehensively the sources, transport, fate and ecotoxicological effects of MeOPBDPBs and their potential precursors in herring gulls and the Great Lakes ecosystem, the present study aims to (1) elucidate temporal changes of MeO-PBDPB concentrations and congener patterns in herring gull egg pool homogenates from selected colony sites; and (2) investigate the influences of within-colony variations over time of the diet sources on the temporal changes of bioaccumulative MeO-PBDPBs.
Figure 1. Locations of the five herring gull colony sites in the Laurentian Great Lakes of North America: (1) Agawa Rock; (2) Big Sister Island; (3) Channel-Shelter Island; (4) Fighting Island; and (5) Toronto Harbour.
2005, 2007, and 2009, except in Fighting Island where the collection ends in 2008. The n = 10 − 13 eggs per colony site per year were subsequently pooled on an equal wet weight (ww) basis and the pooled homogenates were stored at −40 °C prior to chemical analysis. In addition, the 13 gull eggs collected in 1999 from the C−S Island were analyzed individually for chemical contaminants, as well as δ15N and δ13C. For egg pools from all other years, the δ15N and δ13C data reported in Hebert et al.15 were used. Egg Sample Preparation. Approximately 1 g of pooled or individual egg homogenates was ground with DE, spiked with 20 ng of 6-MeO-BDE-137 (internal standard; IS), and then subjected to accelerated solvent extraction (ASE) (Dionex ASE 200, Sunnyvale, CA) with 50:50 dichloromethane:hexane (DCM:HEX). A method blank (DE only) and a Standard Reference Material (SRM) (NIST SRM 1947; Lake Michigan Fish Tissue) sample were extracted along with every batch of 10 egg samples. The extract was purified by gel permeation chromatography (GPC) (OI Analytical, TX) after a 10% portion of the extract was removed for gravimetric lipid determination, followed by cleanup on a Bakerbond SPE cartridge.7 After prewashing with 6 mL HEX, target analytes were eluted from the cartridge with 8 mL 20:80 DCM:HEX. The final extract was concentrated to 250 μL for gas chromatography-mass spectrometry (GC-MS) analyses. GC-MS Analytical Methods. The MeO-PBDPB congeners and internal standard were analyzed using an Agilent 6890 GC (Agilent Tech., Palo Alto, CA) coupled to a single quadrupole mass analyzer (Agilent 5973 MS) working in electron capture negative ionization (ECNI) mode. The analytical column was a 15-m DB-5 HT column (0.25 mm i.d., 0.1 μm, J&W Scientific, Agilent Tech.). Each sample was introduced into a programmable temperature vaporization (PTV) inlet operated in the solvent vent mode at the initial temperature of 60 °C (holding for 0.8 min). A total of 15 μL was injected with three rapid injections of 3 × 5 μL and 10 s intervals in between. The split vent was kept open until 0.70 min with the flow rate of 100 mL/min. After the injections were completed, the PTV inlet temperature was increased from 60 to 240 at 600 °C/min. The purge flow of 50 mL/min was applied from 2.00 min until 10 min, and then gas saver flow of 20 mL/min was used until the end of the run. The initial oven temperature was held at 100 °C
■
EXPERIMENTAL SECTION Standards and Chemicals. To our knowledge, there are currently no pure standards commercially available for MeOPBDPBs. The standard solutions of 6-MeO-BDE-137 and 4′MeO-BDE-201 were purchased from AccuStandards Inc. (New Haven, CT). The BDE-194 standard was obtained from Wellington Laboratories (Guelph, ON, Canada). Diatomaceous earth (DE) was purchased from J.T. Baker (Mallinckrodt Baker, NJ) and treated at 600 °C overnight (>12 h) prior to use. Bakerbond SPE silica gel (SiOH), solid phase extraction (SPE) columns (6 mL, 500 mg, 47−60 μm) were purchased from VWR (Mississauga, ON, Canada). Solvents used were HPLC grade (Caledon Laboratories, Georgetown, ON, Canada). Samples. HG eggs (n = 10 − 13 per site per year) were collected in multiple years from Agawa Rock (Lake Superior), Big Sister Island (Island) (Lake Michigan), Channel-Shelter (C−S) Island (Lake Huron), Fighting Island (Lake Erie), and Toronto Harbour (Lake Ontario) (Figure 1). The Great Lakes egg samples were collected as part of Environment Canada’s Great Lakes Herring Gull Monitoring Program.14 The selection of these five colonies, instead of examining all 14 colonies investigated by Chen et al.,7 was largely based on the availability of historical egg samples. The selection also considered including point sources- versus nonpoint source-influenced colonies, as well as urban versus remote site colonies. From the C−S Island, eggs were collected in 19 separate years commencing in 1982 (specifically 1982, 1987, 1992, 1994, 1995, 1996, and 1998−2010). For other colonies, eggs were collected in 1982, 1987, 1992, 1995, 1997, 1999, 2001, 2003, 9457
dx.doi.org/10.1021/es3018978 | Environ. Sci. Technol. 2012, 46, 9456−9463
Environmental Science & Technology
■
for 2 min, increased to 250 at 25 °C/min, then to 260 at 1.5 °C/min, and finally to 325 at 25 °C/min (held for 7 min). The heated transfer line temperature was 280 °C and the quadrupole temperature was 150 °C. Methane was used as reagent gas for ECNI-MS. Under the same GC-MS analytical conditions, the peaks of two major Br5-MeO-PBDPB congeners (referred as Br5(a) and Br5(b)) had retention times (RTs) close to that of BDE-194 and an additional Br6-MeO-PBDPB (referred as Br6) had a comparable RT with BDE-206 or 4′-MeO-BDE-201 (Figure S1).7 In the absence of commercial MeO-PBDPB standards, our previous study demonstrated that BDE-194 can be used as the semiquantification standard for Br5(a) and Br5(b), since they have comparable molecular structures and close RTs on nonpolar GC column, and are equitably cleaned up and isolated from egg homogenate.7 Similarly, Br6-MeO-PBDPB can be semiquantified based on the calibration curve for 4′-MeO-BDE201. Stable Isotope Analysis. Approximately 1 g of homogenized material from each of the 13 individual C−S Island eggs (collected in 1999) was dried overnight at 80 °C. After the dried samples were ground to powder, they were spiked with 20 mL chloroform/methanol (2:1 v/v), and then vortexted and sonicated and let to stand overnight. Subsequently the samples were centrifuged at 3000 rpm for 20 min and the supernatant was discarded. After 20 mL of water was added, the samples were vortexted, sonicated and centrifuged. After the supernatant was discarded, the lipid-extracted samples were dried overnight at 80 °C, and then sent to the Environmental Isotope Laboratory (EIL) at the University of Waterloo (Ontario, Canada) for the δ15N and δ13C analysis. More details on the stable isotope analysis are provided elsewhere13 and also in the Supporting Information (SI). QA/QC and Data Analysis. The precision and accuracy of the MeO-PBDPB analytical method was assessed by matrix spiking experiments and SRM samples. In the analysis of commercial chicken eggs (n = 6) spiked with 20 ng each of BDE-194, BDE-206 and internal standard 6-MeO-BDE-137, the mean (±standard deviation) recoveries were 91(±8.6)% and 93(±7.5)% for BDE-194 and -206, respectively, and 91(±15)% for the internal standard. The analyses of NIST SRM 1947 samples (n = 6 in total) processed with every batch of gull egg samples revealed recovery efficiencies of 87(±10)% for 6-MeO-BDE-137 and between 82(±11)% and 96(±13)% for the major PBDE congeners (BDE-47, -99, -66, -99, -100, -153, and -154). The relative standard deviations (RSDs) of determined concentrations were all within 11% for individual PBDE congeners and internal standard in SRM samples. Based on 6-MeO-BDE-137, the method limits of quantification (MLOQs) of the MeO-PBDPBs, estimated as an analyte response 10 times the standard deviation of the noise, were 0.3 ng/g ww, assuming that a 1 g egg homogenate is extracted and the MeO-PBDPBs have the same ECNI responses as 6-MeOBDE-137. MeO-PBDPBs were below the limit of detection (LOD: signal/noise
