Environ. Sci. Technol. 2007, 41, 3877-3883
Spatial and Temporal Trends of Chiral Organochlorine Signatures in Great Lakes Air Using Passive Air Samplers T. GOUIN,† L. JANTUNEN,‡ T . H A R N E R , * ,§ P . B L A N C H A R D , § A N D T. BIDLEMAN‡ University of Toronto at Scarborough, Department of Physical and Environmental Sciences, 1265 Military Trail, Toronto, Ontario, M1C 1A4, Canada, Centre for Atmospheric Research Experiments, Science and Technology Branch, Environment Canada, 6248 Eighth Line, Egbert, Ontario L0L 1N0, Canada, and Science and Technology Branch, Environment Canada, 4905 Dufferin Street, Toronto, ON, M3H 5T4, Canada
Passive air samples (PAS) were collected and analyzed to assess the spatial and temporal trends of chiral organochlorine signatures in the Laurentian Great Lakes. Samples were collected from 15 sites and analyzed for the concentrations and enantiomer signature of chlordanes and R-hexachlorocyclohexane (R-HCH). Levels of the chlordanes were typically 4 times higher in urban areas than what were observed at rural and remote locations, exhibiting strong urban-rural gradients. Near racemic residues were seen for the chlordane enantiomers in samples collected from sites located in Toronto and Chicago, which can be attributed to continued emissions of historical use of the technical chlordane mixture, while the chiral signature observed at sites located in rural and remote locations was indicative of an aged source. Knowledge of the spatial and temporal distribution of the enantiomer signatures of chlordane and R-HCH in air is useful for distinguishing sources of these compounds to ambient air. Results suggest that potential sources, such as those associated with Toronto and Chicago, have limited influence over the levels at rural and remote sites within the Great Lakes. Sources that are relatively close to sample sites, however, have a strong influence on levels observed at those sites. For instance, results indicate that Lake Superior continues to act as a source of R-HCH to sites located on its shores. Generally, it appears that during the warmer months, local enhanced surface-air exchange influences air concentrations and that during the cooler periods of the year, levels in the atmosphere are more strongly influenced by advective transport from source regions.
Introduction Organochlorine pesticides (OCPs) were widely used in agriculture during the latter half of the 20th century to control a variety of unwanted pests. A number of these compounds, * Corresponding author e-mail:
[email protected]. † University of Toronto at Scarborough. ‡ Centre for Atmospheric Research Experiments, Science and Technology Branch, Environment Canada. § Environment Canada, Science and Technology Branch. 10.1021/es063015r CCC: $37.00 Published on Web 05/01/2007
2007 American Chemical Society
including DDT, chlordane, and toxaphene, have since become synonymous with a group of chemicals commonly referred to as persistent organic pollutants (POPs). These are chemicals that persist in the environment, have the potential to bioaccumulate, and that can cause a toxic effect on nontarget organisms. Concern regarding the use of OCPs, with POP-like characteristics, prompted a number of regulatory bodies to introduce restrictions on their use and manufacture. Most notably are the UNECE (United Nations Economic Commission for Europe) and UNEP (United Nations Environmental Program) POPs Protocols (1, 2). Although the usage of banned OCPs has decreased over the last few decades as a direct result of effective regulatory activity, residues of OCPs in agricultural soils continue to influence levels in the atmosphere (3-7). While a number of studies have demonstrated this phenomenon by measuring concentration gradients in air above soils (5, 6), others have used enantiomers of chiral pesticides as an indicator of the relative importance of soil-air exchange (6-12). Because microbial degradation can be enantioselective, causing residues in soils and water to become nonracemic, and since abiotic degradation, deposition, and volatilization affect each enantiomer identically, this latter technique has proven to be an effective method in assessing the source origin of OCPs to the atmosphere (9, 10). Therefore, racemic chiral signatures observed in the atmosphere are likely indicative of a fresh primary source or one that has not been subjected to microbial degradation, and nonracemic chiral signatures indicate an aged or secondary source. In a recent study, Bidleman et al. (7) assessed the chiral signatures of chlordane over the last 30 years in the atmosphere and demonstrated that components of the chlordane mixture were racemic in the past but that recent observations indicate a shift toward nonracemic signatures. This suggests that the relative influence of secondary sources to the atmosphere originating from soils may be more important than primary sources of chlordane, particularly for areas located far from source regions. These results are consistent with observations reported for samples collected in the Arctic (12), across North America (13), and in the Great Lakes region (8). Atmospheric monitoring programs, such as the Integrated Atmospheric Deposition Network (IADN) (14), which monitor the loadings of organic pollutants to the Great Lakes to assess spatial and temporal trends, can benefit from information about the chiral signatures of OCPs to better understand their environmental fate and behavior, as well as to assess the effectiveness of regulatory instruments. While these monitoring programs have generally relied on the collection of active high volume air samples to assess the spatial and temporal variability of OCPs in air, it has recently been demonstrated that passive air samplers (PAS) complement this traditional method and can be feasibly used as part of any successful atmospheric monitoring program (15). The effectiveness of PAS has also been demonstrated at various geographic scales, from regional to continental (16-24), with current studies investigating their feasibility as part of a global monitoring program (25, 26). In this study, PAS, using polyurethane foam (PUF) disks as sampling media, were deployed at 15 sites across the Great Lakes region (including 13 sites operated under IADN) on a quarterly basis between July 2002 and June 2003. Previous studies have reported air concentrations of a variety of POPs from these samples, including the polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and selected OCPs (15), as well as for the polychlorinated naphVOL. 41, NO. 11, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Location of sampling sites (yellow circles) in relation to population density. Background sites at Burnt Island (BNT) (45°,50′ N; 82°,57′ W) and Eagle Harbor (EGH) (47°,28′ N; 88°,09′ W) are more than 200 km from densely populated urban centers. Rural sites at Egbert (EGB) (44°,13′ N; 79°,46′ W), Grand Bend (GDB) (43°,20′ N; 81°,44′ W), Point Pelee (PPL) (41°,58′ N; 82°,31′ W), Rock Point (RPT) (42°,51′ N; 79°,33′ W), Sleeping Bear Dunes (SBD) (44°,46′ N; 86°,04′ W), Point Petre (PPT) (43°,50′ N; 77°,09′ W), Sturgeon Point (STP) (42°,41′ N; 79°,04′ W), St. Clair (STC) (42°,23′ N; 82°,24′ W), and Trent University (TNT) (44°,33′ N; 78°,30′ W) are located within agricultural areas, less than 200 km away from urban centers. Urban sites at Chicago (CHI) (41°,50′ N; 87°,37′ W), Burlington (BUR) (43°,22′ N; 79°,52′ W), and Toronto (TOR) and Downsview (DOW) (43°,41′ N; 79°,25′ W) are located within large urban centers. thalenes (PCNs) (27). This study investigates the spatial and temporal trends of chiral OCPs, specifically the chlordanes and R-hexachlorocyclohexane (R-HCH).
Experimental Procedures PAS were deployed at several sites in the Laurentian Great Lakes, including five IADN master stations and seven satellite stations (Figure 1). The samples were deployed on a seasonal basis, period 1: summer, July to September 2002; period 2: autumn, October to December 2002; period 3: winter, January to March 2003; and period 4: spring, April to June 2003. Details relating to sampler design, theory, and sampling rates have been reported elsewhere (15, 27). Briefly, PUF disks were used as PAS, which were shown to sample air at a rate of approximately 3 m3 day-1, which is referred to as the linear sampling rate. Sampling Procedure. PUF disks were cleaned prior to deployment with water, followed by 24 h Soxhlet extraction with acetone and 2 × 24 h with petroleum ether (PE). All solvents used were chromatographic grade. The PUF disks were dried by vacuum desiccation before being spiked with a suite of depuration compounds (DCs). The following DCs were used: 2,4,6-trichlorobiphenyl (PCB-30), deuterated γ-HCH (d6γ-HCH), 2,3,3′,4,5-pentachlorobiphenyl (PCB-107), and 2,2′3,3′,4,5,5′6-octachlorobiphenyl (PCB-198). DCs were diluted in 20 mL of PE, applied evenly to both sides of the disk using a Pasteur pipet, and left to dry (approximately 10 min) before storing in clean jars with Teflon lined lids. This was done to each PUF disk prior to deployment to assess the kinetics of the sampling rates of individual PAS (15). The PUF disks were shipped to each of the sampling sites, where 3878
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a single sample was deployed, with the exception of GAG, EGB, DOW, and PPT, where duplicate PUF disk samples were deployed. Sample Extraction and Quantification. Details regarding sample extraction are given elsewhere (15). Briefly, PUF disk samples were Soxhlet extracted for 18 h with 250 mL of PE. Extracts were volume reduced by rotary evaporation and under a gentle stream of nitrogen and cleaned up on a 1 g alumina column, which was eluted with 20 mL of 5% dichloromethane in PE. Extracts were volume reduced to 500 µL and solvent exchanged to isooctane. Mirex was added as an internal standard just prior to injection on the gas chromatograph--mass spectrometer (GC-MS) (HewlettPackard 6890 GC-5973 MSD). Samples were analyzed for 19 OCPs, including the chlordanes trans-chlordane (TC), cis-chlordane (CC), and trans-nonachlor (TN), using electron capture negative ion (ECNI) mass spectrometry, with methane as the reagent gas (15). Following analysis of the OCPs, the sample extracts were split, where half of the sample was archived and the other half was saved for chiral analysis. The compounds sought by chiral analysis were R-HCH, TC, and CC, two major constituents of technical chlordane. TC and CC are racemic in the technical mixture and thus have equal proportions of the (+) and (-) enantiomers. Soils around the Great Lakes show preferential degradation of the (+)TC and (-)CC, leading to enantiomer fractions (EF ) (+)/((-) + (+))) that are 0.500 for CC (3, 5-7). Extracts required an acid cleanup prior to chiral analysis to remove endosulfan, which interferes with (-)CC on the β-DEX-120 chiral column. Endosulfan is a currently used
TABLE 1. Average EF Values and PAS Concentrations in Air for r-HCH and Chlordanes between July 2002 and June 2003a EF ((+)/[(-) + (+)])
concentration (pg m-3)
site
description
r-HCH
CC
TC
BNT: Burnt Island BUR: Burlington CHI: Chicago DOW: Downsview EGB: Egbert EGH: Eagle Harbor TOR: Toronto GDB: Grand Bend PPT: Pt. Petre PPL: Pt. Pelee RPT: Rock Point SBD: Sleeping Bear Dunes STC: St. Clair STP: Sturgeon Point Trent Univ. Field Site
background semi-urban urban/industrial urban/industrial rural background urban/industrial rural rural rural rural rural rural rural rural
0.488 ( 0.013 0.497 ( 0.003 0.492 ( 0.005 0.494 ( 0.005 0.497 ( 0.003 0.475 ( 0.008 0.493 ( 0.003 0.492 ( 0.002 0.495 ( 0.003 0.491 ( 0.005 0.497 ( 0.003 0.494 ( 0.005 0.495 ( 0.004 0.496 ( 0.003 0.501 ( 0.003
0.514 ( 0.003 0.517 ( 0.007 0.510 ( 0.004 0.515 ( 0.002 0.516 ( 0.002 0.509 ( 0.004 0.507 ( 0.001 0.516 ( 0.002 0.512 ( 0.001 0.510 ( 0.003 0.513 ( 0.005 0.512 ( 0.001 0.512 ( 0.010 0.513 ( 0.003 0.512 ( 0.004
0.469 ( 0.006 0.472 ( 0.005 0.485 ( 0.002 0.477 ( 0.008 0.473 ( 0.009 0.467 ( 0.006 0.490 ( 0.003 0.458 ( 0.014 0.472 ( 0.004 0.477 ( 0.008 0.473 ( 0.008 0.466 ( 0.004 0.470 ( 0.017 0.478 ( 0.007 0.475 ( 0.002
r-HC
Hb
30 ( 6.9 22 ( 7.0 24 ( 8.6 20 ( 9.0 15 ( 2.2 73 ( 17 23 ( 9.4 30 ( 8.0 21 ( 8.7 20 ( 11 23 ( 7.2 34 ( 22 36 ( 13 30 ( 8.4 27 ( 8.7
TN
CC
TC
4.0 ( 1.6 8.8 ( 6.0 31 ( 16 6.7 ( 2.4 7.0 ( 1.9 4.6 ( 1.0 25 ( 25 13 ( 4.6 11 ( 4.3 5.1 ( 2.3 8.0 ( 2.3 10 ( 5.8 41 ( 34 12 ( 8.1 5.3 ( 1.1
3.9 ( 1.2 9.4 ( 6.7 40 ( 19 7.0 ( 1.7 6.2 ( 0.4 4.6 ( 1.2 37 ( 33 12 ( 4.3 10 ( 2.0 5.8 ( 3.0 9.3 ( 2.5 9.0 ( 4.1 36 ( 21 13 ( 7.8 6.4 ( 1.6
3.1 ( 1.0 8.5 ( 4.5 47 ( 18 6.9 ( 1.5 5.6 ( 0.9 3.3 ( 0.7 39 ( 31 9.7 ( 1.5 11 ( 3.6 5.6 ( 3.0 8.5 ( 2.2 7.8 ( 3.8 35 ( 20 12 ( 6.2 4.6 ( 0.5
a Further information for sites operated under IADN can be found at http://www.msc-smc.ec.gc.ca/iadn/stations/station_master_e.html. et al. (15).
pesticide that was present in all samples (see ref 15). Split extracts (200 µL) were diluted to 3 mL with PE, to which 1 mL of 15% fuming sulfuric acid was added. The mixture was vortexed for 1 min, followed by centrifuging for 10 min. The acid layer was washed 3 times with PE, and any acid residue in the organic layer was removed by washing with distilled water and then dried by passing through anhydrous sodium sulfate. Samples were volume reduced under a gentle stream of nitrogen and solvent exchanged to isooctane to 200 µL for chiral analysis. Instruments used for chiral analysis were a HewlettPackard 5890 GC-5989B MS Engine or Agilent 6890 GC-5973 MSD, both operated in ECNI with methane reagent gas (nominal pressure of 1.0 Torr for the MS Engine and 2.2 mL min-1 for the MSD). The ions monitored (target/qualifying) were for R-HCH (255/257) and for TC and CC (410/412). Sample volumes of 2 µL were injected splitless (split opened after 1.0 min). Three chiral columns were used for enantiomeric analysis: β-DEX-120 (BDX, 20% permethylated β-cyclodextrin in polydimethylsiloxane, 30 m × 0.25 mm i.d., 0.25 µm film thickness, Supelco), BGB-172 (BGB, 20% tert-butyldimethylsilylated β-cyclodextrin in OV-1701, 30 m × 0.25 mm i.d., 0.25 µm film thickness, BGB Analytik AG), and β-DEXcst (BDXcst, 30 m × 0.25 mm i.d., 0.25 µm film thickness, Restek). The three columns were required to eliminate interferences in the chiral analysis, whereby the BGB and BDX columns separate enantiomers of R-HCH, TC, and CC, and the BDXcst column separates enantiomers of R-HCH and CC (11, 28). QA/QC. Levels of TC, CC, and TN based on the collection and analysis of 21 field and 13 method blanks (i.e., solvent blanks) were below the instrument quantification limit (0.32 pg µL-1). Consequently, samples were not blank corrected. Details regarding recoveries and duplicates are given elsewhere (15). Briefly, recoveries were found to be >75% (n ) 75), with duplicates (n ) 11) showing a coefficient of variance that was
