Environ. Sci. Technol. 2008, 42, 4739–4744
Temporal Trends of Perfluoroalkyl Compounds with Isomer Analysis in Lake Trout from Lake Ontario (1979-2004) V A S I L E I F U R D U I , * ,†,‡ P A U L A . H E L M , ‡ PATRICK W. CROZIER,‡ CORINA LUCACIU,‡ ERIC J. REINER,‡ CHRIS H. MARVIN,§ D. MICHAEL WHITTLE,† SCOTT A. MABURY,† AND GREGG T. TOMY⊥ Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON, M5S 3H6, Ontario Ministry of the Environment, 125 Resources Road, Toronto, ON, M9P 3V6, Environment Canada, 867 Lakeshore Road, Burlington, ON, L7R 4A6, Fisheries and Oceans Canada, 867 Lakeshore Road, Burlington, ON, L7R 4A6, and Fisheries and Oceans Canada, 501 University Crescent, Winnipeg, MB, R3T 2N6
Received December 24, 2007. Revised manuscript received March 14, 2008. Accepted April 10, 2008.
carboxylates (PFCAs), emerged as new widespread, bioaccumulative contaminants (2). These chemicals have been identified worldwide in biota (3–6), including species from remote areas like the Canadian Arctic (7, 8). Two primary processes have been used to synthesize PFCs; electrochemical fluorination (ECF) and telomerization (9). The ECF products are constitutional isomeric mixtures, with the majority as linear isomers, containing also shorter and longer carbon chain homologues. The telomerization products are straight-chain arrangements without branched isomers, with an even number of carbon atoms (9) and are produced by a polymerization reaction between a perfluoroalkyl iodide (telogen) and a taxogen olefin, usually tetrafluoroethylene (CF2dCF2): CF3-CF2-I (telogen) +nCF2 ) CF2 f CF3-CF2-(CF2-CF2)n-I (1) As previously discussed (10), branched isomers can be synthesized by telomerization when a branched telogen is used, since this process conserves the geometry of the starting material. A mixture containing only isopropyl branched isomers with an odd number of carbon atoms can be obtained by using heptafluoroisopropyl iodide as telogen: (CF3)2CF-I (telogen) +nCF2 ) CF2 f (CF3)2CF-(CF2-CF2)n-I (2)
The temporal trends of perfluoroalkyl compounds (PFCs), including C7-C15 perfluorocarboxylates (PFCAs), perfluorosulfonates (PFSAs) and heptadecafluorooctane sulfonamide (PFOSA), were determined in lake trout collected between 1979 and 2004 from Lake Ontario. The average concentrations of total PFSAs ((standard error of the mean; range) increased from 20 ng g-1 wet weight ((4; 8-26) in 1979, peaked at 70 ng g-1 ((7; 58-91) in 1993, and were 46 ng g-1 ((10; 30-83) in 2004, with perfluorooctane sulfonate (PFOS) as the most abundant PFC. The PFCAs exhibited similar temporal variation, with concentrations increasing from 1.4 ng g-1 ((0.1; 0.9-1.9) in 1979 to 9.4 ng g1 ((3.1; 3-17) in 1988, and were 6.8 ng g-1 ((1.0; 4.5-9.8) in 2004. Individual mean PFCA concentrations varied between 0.2 and 2 ng g-1 (wet weight). Perfluorodecane sulfonate (PFDS) and PFOSA were the only compounds showing a declining trend in the past decade, after reaching a peak value in 1993. Branched C11 and C13 PFCA isomers were detected in the lake trout and confirmed in Niagara River suspended sediments, with trends in both matrices suggesting that declining emissions or use of products containing these isomers in part account for the observed PFCA trends in the mid-1990s. However, the most recent samples, comprised almost exclusively of linear isomers, indicate that current PFCA sources to Lake Ontario result from the telomerization process of linear telogens.
Introduction Following a first report of perfluorooctane sulfonate (PFOS) in biota (1) in 2001, the perfluoroalkyl compounds (PFCs), particularly the perfluorosulfonates (PFSAs) and perfluoro* Corresponding author e-mail:
[email protected]. † University of Toronto. ‡ Ontario Ministry of the Environment. § Environment Canada. † Fisheries and Oceans Canada, Burlington, ON. ⊥ Fisheries and Oceans Canada, Winnipeg, MB. 10.1021/es7032372 CCC: $40.75
Published on Web 06/03/2008
2008 American Chemical Society
A patent detailing the preparation of heptafluoroisopropyl iodide was filed in 1972 and suggested that the compound is used solely as a telogen for the telomerization of the tetrafluoroethylene to obtain long-chain perfluoroalkyl iodides (11). Products of reaction 2 were considered as starting materials for synthesizing branched-chain PFCAs with an isopropyl terminal group, as described in a different patent (12). These isomers would be expected to undergo the same atmospheric (13) and metabolic processes (14) that the linear materials go through. The relative proportion of even and odd chain length PFCAs produced would depend on the overall chain length of the starting materials and the dominant environmental transformation in the respective matrix. Branched PFCAs were identified as surfactants more effective in lowering surface tension of aqueous solutions than their corresponding linear-chain PFCAs (15). This tendency was later confirmed only for low concentrations of PFCAs, but not for higher concentrations of PFCAs (16), suggesting that linear-chain PFCAs would be preferred in technical mixture requiring them in concentrations higher than 0.01%, and branched-chain PFCAs in mixture requiring them in lower concentrations. Isomers of the PFCAs have been isolated in environmental samples from polar bears (10) and human blood (17). The ECF PFOA, a known source of branched isomers, was used until 2002 as a processing aid (17). There is little available information about the production of branched isomers with longer chain PFCAs, and few reports of nonlinear, longerchain PFCAs isolated from biota. It is recognized that isomer discrimination may occur during the uptake or depuration of mixed isomers of PFCAs (18) and that this may confound the elucidation of the source of contamination (17). Lake trout (Salvelinus namaycush) is a sentinel indicator species in monitoring programs in Canada and the United States for persistent organic pollutants (POPs) in the Laurentian Great Lakes. Temporal trends of contaminants such as polychlorinated biphenyls (PCBs) in lake trout have been VOL. 42, NO. 13, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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used to indicate the effectiveness of management programs to control or eliminate emissions of criteria pollutants and progress in the recovery of lakes from historical POPs contamination. More recently, analysis of archived tissues from such programs have illustrated the increased occurrence in the environment of compounds such as polybrominated diphenylether (PBDE) flame retardants (19) and PFCs like PFOS (20). The objective of this study was to examine the temporal trends of PFCs using archived lake trout collected from Lake Ontario between 1979 and 2004. A suite of 20 PFCs, including PFSAs, PFCAs, and fluorotelomer carboxylic acids (FTCAs), were quantified. The stable isotopes of nitrogen (expressed as δ15N) were determined to indicate whether changes in the Lake Ontario food web influence observed trends. During the analyses, additional isomers were observed, leading to an investigation of the isomer patterns of long-chain PFCAs, particularly perfluoroundecanoic acid (PFUnA) and perfluorotridecanoic acid (PFTrA). This is the first report of temporal variation of branched isomers in biota. Suspended sediments collected between 1980 and 2003 from the Niagara River, which represents the bulk of the water discharge to Lake Ontario, were also analyzed to confirm the trends in branched isomers.
Experimental Section Standards and Chemicals. The analytes considered in this study are the commercially available PFSAs and PFCAs: perfluorohexane sulfonate (PFHxS), PFOS, perfluorodecane sulfonate (PFDS), and heptadecafluorooctane sulfonamide (PFOSA), perfluoroheptanoic acid (PFHpA), PFOA, perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), PFUnA, perfluorododecanoic acid (PFDoA), perfluorotetradecanoic acid (PFTeA), and fluorotelomer acids (6:2, 8:2, and 10:2). Details about the standard purity, other chemicals used and providers can be found in our recently published study (21). Mass-labeled (13C) perfluorocarboxylic acids (13C4-PFOA, 13C5-PFNA, 13C2-PFDA and 13C2-PFDoA), unsaturated fluorotelomer acids (13C2-6:2 FTUCA, 13C2-8:2 FTUCA and 13C2-10:2 FTUCA) and one sulfonate (13C4-PFOS) were obtained from Wellington Laboratories (Guelph, ON, Canada); 13C2-PFOA was obtained from Perkin-Elmer Life Sciences (Boston, MA). Sample Preparation. Lake trout samples (aged 4-5 years) were collected from Lake Ontario from the same location (Eastern basin) and archived in the Great Lakes Fisheries Specimen Bank as part of the Department of Fisheries and Oceans long-term monitoring program in the Great Lakes. Analyses were conducted on four to five samples from each of 1979, 1983, 1988, 1993, 1998, and 2004 for fish that ranged between 55-70 cm length and 1810-4700 g weight (Table S1, Supporting Information (SI)). All lake trout samples were processed as individual whole fish homogenates, stored at -80 °C in sealed glass containers prior to subsampling into polyethylene vials for analysis. Approximately 0.4 g of each homogenate were extracted following the Hansen procedure (22) with an additional fluorophilicity cleanup step (21) and the residues containing the target analytes were reconstituted in 0.5 mL of 100% methanol (MeOH) containing 13C4-PFOA (2 ng) control standard. Procedural blanks (n ) 9) were prepared by replacing the fish homogenate with 0.5 mL HPLC grade water and extracted simultaneously with all other samples. Five samples were spiked with 1 ng of each analyte for recovery calculation. The final extracts were filtered through 0.2 µm nylon filters and stored in polypropylene vials at -20 °C until analysis, when they were diluted 1:10 by mixing with MeOH, internal standards (13C2-PFOA, 13C -PFNA, 13C -PFDA, 13C -PFOS, 13C - 6:2, 8:2, and 10:2 5 2 4 2 FTUCA) in MeOH, and HPLC grade water for a 1:1 MeOH/ water final composition. The sample/MeOH injection mix4740
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tures were filtered using Mini-UniPrepTM syringeless filter devices having 0.2 µm polypropylene (PP) filter media and PP housings (Whatman, Forham Park, NJ). Instrumental Analysis by LC/MS/MS. Analysis of target analytes was performed using a high performance liquid chromatograph-tandem mass spectrometer system (HPLCMS/MS), consisting of an unmodified Agilent 1100 Series HPLC coupled with a 4000 QTRAP triple quadrupole mass spectrometer (Applied BiosystemssMDS Sciex, Concord, ON, Canada). Water and MeOH solvents (0.01 M ammonium acetate) were delivered at a total flow rate of 250 µL/min. One hundred microliter aliquots of the sample/MeOH mixtures were injected through a C18 guard column (2 mm i.d. × 4 mm, Phenomenex, Torrance, CA) with chromatographic separation performed on a Genesis C18 column (2.1 mm i.d. × 50 mm, 4 µm; Chromatographic Specialties, Brockville, ON, Canada). Target analyte separation was obtained in 8 min under gradient conditions, with 75:25 MeOH/water initial mobile phase, followed by a 3 min ramp to 90:10 MeOH/water, a 3 min hold and reverting to initial conditions at 7 min (Method A) (21). The mass spectrometer was operated in negative electrospray ionization multiple reaction monitoring (MRM) mode, using previously published parameters (21). MRM transition-related parameters were optimized for each analyte, monitoring SO3F- (m/z ) 99) for sulfonates, SO2N- (m/z ) 78) for PFOSA, a loss of CO2 for carboxylates, and a loss of CO2 + HF for the unsaturated fluorotelomer acids. Additional transitions were selected for some PFCAs, monitoring C3F7- (m/z ) 169), C4F9- (m/z ) 219) and C5F11- (m/z ) 269) (Table S2, SI). Two additional separation methods were also optimized to separate the isomers observed for PFUnA and PFTrA. One method (Method B) was based on the same MeOH/water mobile phase and gradient conditions as for Method A, but used a different type of column (Allure PFP Propyl, 2.1 mm i.d. × 100 mm, 3 µm, Restek, Bellefonte, PA). The other method (Method C) used acetonitrile (ACN) instead of MeOH in the mobile phase and a longer C18 column (2.1 mm i.d. × 100 mm, 3 µm; Restek), having smaller particles than the C18 column used for Method A. Target analyte separation was obtained in 10 min under gradient conditions, with 60: 40 ACN/water initial mobile phase, followed by a 3 min ramp to 65:35 ACN/water, a 4 min ramp to 75:25 ACN/water, then reverting to initial conditions at 8 min. Water (0.01 M ammonium acetate) and ACN solvents were delivered at a total flow rate of 250 µL/min. One hundred microliter aliquots of the sample/MeOH were also injected in methods B and C. Quantification was performed using the internal standard method with multipoint calibration curves for each analyte. Isotope dilution was used to quantify PFOS (13C4-PFOS), PFOA (13C2-PFOA), PFNA (13C5-PFNA), PFDA (13C2-PFDA), PFDoA (13C2-PFDoA), 8:2 FTUCA (13C2-8:2 FTUCA), and 10:2 FTUCA (13C2-10:2 FTUCA). For the other analytes the internal standard was selected based on the chromatographic retention times, with 13C2-PFOA for PFHxS and PFHpA, and 13C -PFDA for PFOSA, PFUnA, PFDoA, PFTrA, PFTeA, and 2 perfluoropentadecanoic acid (PFPA). Concentrations were adjusted for standard purities. Since no standard was available for PFTrA, a calibration curve was obtained by averaging the peak areas of PFDoA and PFTeA obtained for each calibration level. Also PFPA was quantified using the calibration curve obtained for PFTeA. Ten percent of the samples were analyzed in duplicate and differences were 16% or lower. The average recovery for 13C4-PFOA was 88% (standard error (SE) of the mean ) 3%). Mean recoveries of each analyte, calculated based on the spiked samples, were higher than 68% for all reported analytes (Table S3, SI).
FIGURE 1. Mean Concentrations of the perfluorooctane sulfonate (PFOS), perfluorodecane sulfonate (PFDS), and heptadecafluorooctane sulfonamide (PFOSA) in lake trout from Lake Ontario (ng g-1 wet weight ( standard error (SE); wet weight). Method detection limits (MDL) were defined as the mean concentration of nine procedural blanks plus three times the standard deviation of the blank response and varied between 1 and 16 pg g-1 (normalized to 0.4 g of fish homogenate) (Table S3, SI). Mean concentrations were calculated only for the analytes detected in more than 75% of the samples, after assigning randomly generated values between zero and the compound-specific instrument detection limit (IDL) for nondetected responses (S/N < 3).
Results and Discussions Temporal Trends of PFSAs. Concentration trends of PFOS, PFDS, and PFOSA are shown in Figure 1 for each of the years sampled. Although monitored, PFHxS was not detected in any of the samples. PFOS concentrations were the highest of all PFCs, consistent with previous observations (20, 21), ranging from 6-96 ng g-1 (wet weight [ww]). The PFOS concentrations in this study (Figures 1 and S1, SI) tended to be lower than those reported previously for Lake Ontario lake trout as part of a PFOS temporal trend (20), but given the analytical challenges associated with earlier environmental analyses (23), and the number of mass-labeled internal standards now available and used here, significant differences are not unexpected. This study used different samples, processing, separation, and quantitation methods. The concentrations of PFOS increased with a doubling time of 8 years until 1993 (p < 0.005; N ) 19; Figure S1, SI). Analysis of variance (ANOVA) tests on log-transformed data indicated that PFOS concentrations were significantly higher in 1988 and 1993 than in 1979 (p < 0.005; Bonferroni test), and that a weak decline occurred between 1993 and 1998 (p < 0.1; Bonferroni test), but that 2004 concentrations were not statistically different than those in the 1980s and 1990s. The ANOVA for PFDS and PFOSA indicated that concentrations in 2004 were significantly lower than in 1993 (p < 0.05 and p < 0.001, respectively; Bonferroni tests). Although declines in PFOS concentrations in Arctic ringed seals have been indicated where atmospheric contributions to that environment are thought to be the major source (24), similar findings were not observed in Lake Ontario. Sources such as wastewater inputs contribute PFCs to the lake (25), and are likely to moderate changes in atmospheric contributions. Martin et al. also observed a decline in PFOS concentrations in Lake Ontario lake trout in the mid-1990s, suggesting it may be related to impacts on the food web by the Dreissenid mussel invasion occurring in the lake at that time (20). Stable nitrogen isotope analysis can provide information about changes in a food web, as the heavy 15N isotope is enriched relative to the lighter 14N isotope resulting in an increase in
FIGURE 2. Mean concentrations of the C8-C15 perfluorocarboxylic acids (PFCAs) in lake trout from Lake Ontario (ng g-1 ( SE; wet weight). The numbers in brackets represent the carbon chain length. δ15N (where δ15N ) [(15N/14Nsample/15N/14Nstandard)-1] × 1000) values by 3-4‰ from one trophic level to the next (26). δ15N values for the fish used in this study are reported in ref 27 and were constant after 1979 through the 1980s and 1990s, but lowered significantly only in the 2004 samples (ANOVA, p < 0.005; Bonferroni test; Table S1, SI) . This suggests that the trophic level at which trout were feeding did not change during the period of the observed drop in PFOS concentrations in the 1990s, and thus food web changes as indicated by δ15N do not explain the decline observed by Martin et al. (20). However, changes in prey species occupying similar trophic levels but having varying body-burdens could impact contaminant trends without changes in δ15N. Temporal changes in trophic position have been found to impact contaminant trends when concentrations are adjusted for trophic changes (28). Using the approach of Hebert and Weseloh (28), log-normalized concentrations of PFOS, PFDS, and PFOSA were regressed with δ15N. No significant correlations were found, and subsequent adjustment of concentrations for δ15N did not substantially alter the concentration trend. However, interpretations of PFC results with respect to stable nitrogen isotope relationships should be undertaken with caution, as accumulation of PFCs from the water column may be as important or more important than from diet in some cases (29, 30). Temporal Trends of PFCAs. The concentration trends for the PFCAs are presented in Figure 2 and represent the only non-Arctic temporal measurements of PFCAs in North America that we are aware of. The PFCA concentrations exhibited similar trends to that observed for PFOS. PFCA concentrations were generally low (nd to 3 ng g-1 ww) with PFOA and PFPA having the lowest observed concentrations, whereas PFUnA, PFDoA, and PFTrA had the greatest PFCA concentrations. This general increase with chain length up to PFTrA is consistent with previous reports in biota (8). Although monitored, PFHpA was not detected in any samples. VOL. 42, NO. 13, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 3. (a) Multiple reaction monitoring (MRM) transitions for 50 ppt standards of linear and isopropyl perfluorononanoic acid (PFNA) separated using Method A. (b) Isomer pattern for perfluoroundecanoic acid (PFUnA) observed for suspended sediment from Niagara River (A), a 50 ppt standard containing only the linear isomer (B) and a lake trout extract from Lake Ontario (C) separated using Method C (see text). ANOVA tests of the log-transformed data indicated that there were no significant differences between years for PFOA concentrations (p > 0.05), and most PFCAs had concentrations in 1988 and/or 1993 which were significantly higher than 1979 (p < 0.05; Bonferroni test), followed by a leveling or apparent decrease in concentrations. For instance, 1998 concentrations of PFDoA were lower than peak concentrations in 1988 (p < 0.05; Bonferroni test). Regression analyses for individual PFCA compounds were not of sufficient significance to indicate declines in recent years since peaks in 1988 or 1993. In general, the trends after the initial increases from 1979 are less clear for both PFCAs and PFSAs over the study period and, as was the case for PFOS above, the apparent decline in concentrations, particularly in 1998, are not explained by changes in the food web as indicated by stable isotopes of nitrogen. Regressions of δ15N with log PFCA concentrations did not show significant correlations. Branched and Linear Isomers of PFUnA and PFTrA. Additional chromatographic peaks were observed during the analysis of PFUnA and PFTrA, prompting further investigations to confirm the suspected presence of branched isomers. Since PFNA is the only PFCA for which a pure branched isomer standard is available (Wellington Laboratories, Guelph, Canada), PFNA was used to elucidate characteristic MRM transitions for branched and linear constitutional isomers, whereas previous detection of PFCA isomers was achieved using a GC-MS technique (10, 17) and recently by LC-MS (31). The method was optimized to determine possible isomer patterns simultaneously for all PFCAs, with minimal separation obtained for PFNA (Figure 3a). The PFSAs contain the 4742
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FIGURE 4. (a) Change in perfluoroundecanoic acid (PFUnA) isomer ratios observed between 1979 and 2004 (separation with Method A). (b) Concentrations of linear PFUnA (ng g-1) and peak area for branched PFUnA (number of counts) in whole body homogenates of Lake Ontario lake trout. 0-series of fragments, consisting of [CmF2mSO3]-, as observed particularly for PFOS, as well as the 9-series of fragments, [CnF2n+1]-, with constitutional isomers for PFOS easily identified based on both series (32). In comparison, the PFCAs lack the 0-series of fragments, and the 9-series alone does not allow the identification of structural isomers. The only MRM transition able to differentiate between isopropyl and linear PFNA is m/z ) 269 (C5F11-) (Figure 3a). Since no single MRM transition was found to identify only the isopropyl (nonlinear) PFNA, its presence can be confirmed in LC/MS/ MS only by considering multiple MRM transitions from the 9-series: 69, 119, 169, 219, 269, 319, 369, and 419. The most intense transitions were observed for m/z ) 169, 219, and 419. This approach was applied to monitoring the other PFCAs, since no standards are available for their branched isomers. Each PFCA was monitored using 3-4 MRM transitions and separations were optimized using methods B and C to evaluate for possible interferences. Although the C8-C15 PFCAs were scanned for the possible presence of branched isomers, only PFUnA and PFTrA showed detectable amounts. Examples of the transitions and peak resolution for PFUnA are depicted in Figure 3b, using method C to separate the isomers. Variations in the amounts of branched isomers are expressed on a peak area basis, and relative to the linear isomers using a linear to branched peak area ratio. Standard additions to the extracts with linear PFUnA affected only the second peak observed on the chromatograms presented in Figure 4a, and dilutions of the same extract at different dilution factors (1:10, 1:50) did not affect the peak area ratios. Consistent results were obtained using all three methods as the slopes of the peak area ratios with year did not differ statistically (p > 0.1, t test; Figure S2, SI). The standard additions, dilutions, and separation experiments strongly
FIGURE 5. Temporal trends of perfluoroundecanoic acid (PFUnA) using peak area ratios of linear to branched isomers (squares) and concentration of linear isomer (diamonds) from (a) Lake Ontario lake trout and (b) Niagara River suspended sediments. Separation was performed using Method A. indicate that both branched and linear isomers of PFUnA, and by analogy PFTrA, were present in lake trout extracts. Consistent results were obtained using all three methods as the slopes of the peak area ratios with year did not differ statistically (p > 0.1, t test; Figure S2, SI). The branched isomers could not be quantified as standards are not available, and differences in relative responses between the branched and linear isomers could not be determined. The approach was applied to the Lake Ontario lake trout samples to examine trends of both the linear and the branched isomers of PFUnA and PFTrA. The trends of the PFUnA linear and branched isomers are shown in Figure 4a as a sequence of chromatograms and expressed in concentration (linear PFUnA) and peak area (branched PFUnA) in Figure 4b. The trends of the linear and branched PFUnA were comparable in early samples, showing an increase from 1979 to 1983, but by 1988 the branched isomer trend deviated from the linear, decreasing to only small amounts by 2004. A similar trend was observed for PFTrA concentrations (linear) and peak areas (branched) (Figure S3, SI). Additional temporal samples were analyzed using this approach to confirm the observed trend in the lake trout. Extracts of archived suspended sediments collected from the Niagara River during the same period (1980-2002) and previously analyzed for PFCs (33) were reexamined for branched and linear isomers. The same isomer pattern was observed for PFUnA on the suspended sediments as in the lake trout, and the increasing prevalence of the linear isomer with time, expressed as the linear to branched peak area ratio, is apparent in both the Lake Ontario Lake trout and the Niagara River suspended sediments (Figure 5). The increases in this ratio with time were not significantly different between the trout and the suspended sediments (p > 0.25; t test), which is not surprising as the Niagara River provides more than 80% of the fresh water for Lake Ontario. Although
the linear to branched isomer ratios increased over the time period for PFTrA (Figures S3 and S4, SI), the rate of increase differed significantly (p < 0.05; t test) between the lake trout and the suspended sediments. Though the data indicate that the apparent single isomer of PFUnA and PFTrA varied significantly over time, it is impossible to ascertain whether biodiscrimination influenced the isomer pattern observed in the fish. Furthermore, since the fish are the same species and the same age, it is likely that biodiscrimination would be similar through time. The fact that there was little difference between the isomer pattern on suspended sediments and in the fish suggests biological differentiation of isomers was minor at best. The leveling concentration trend in the mid- to late-1990s indicates that source inputs of PFCs to the environment have changed or been reduced. It is interesting to note that the decline of branched isomers occurs before 2000-2002 when ECF production of PFCs in North America was halted. This, along with the detected presence of a limited number of branched isomers only for C11 and C13, suggests the possibility of an alternative source of these isomers to the Great Lakes environment, particularly products obtained by telomerization of branched telogens. However, C11 and C13 compounds are also more bioaccumulative than the shorterchained PFCAs such as PFOA (21). Accumulation processes in the lake trout and their food web, and similarly with the organic carbon in suspended sediments, render it difficult to rule out contributions of branched isomers from the ECF process even though branched PFOA and PFNA were not detected. The patterns detected in both suspended sediment and biota indicate that environmental sources of PFCs manufactured either by the ECF process or by telomerization of branched telogens, had been significantly reduced by the time ECF production in North America ceased. The decline in branched PFUnA and PFTrA isomers from 1993 to current times (2004), whereas the relative proportions and concentrations of linear isomers continues to increase in 2004 samples, implies that the source of PFUnA and PFTrA to biota in 2004 was almost exclusively from linear products manufactured using the telomerization process. Furthermore, the dip in the overall PFCA concentration trends in the 1990s may have been impacted by reductions in ECF and/or telomerization of branched telogens. The most recent measurements of PFUnA in Niagara River suspended sediments (2000-2002) were among the highest measured in the data set (Figure 5b), suggesting continued increases in linear PFUnA inputs. It remains to be seen if this increase continues and if the trend will be reflected in fish from Lake Ontario through continued monitoring, especially as agreements have been reached on the phase-out of PFOA and related compounds (34). However, it is worth cautioning that interpretations of the time trends of concentrations in biota should be undertaken with care, especially as the impacts of food web and other processes contribute to interannual variation. The influences of these processes are less known for compounds such as PFCs which tend to behave differently from nonpolar halogenated organic compounds, especially in a demonstrably changing system such as Lake Ontario.
Acknowledgments We thank M. J. Keir (Fisheries and Oceans Canada), technical operations staff, and the crews of the Canadian Coast Guard vessels involved in the collection, preparation, and archiving of fish tissues. Thanks also to Gilles Arsenault and Wellington Laboratories for providing the mass-labeled PFCAs, saturated and unsaturated telomer acids, and perfluorooctane sulfonate, and to the Water Quality Monitoring and Surveillance Division of Environment Canada for access to the Niagara River suspended sediment samples. At the time of publicaVOL. 42, NO. 13, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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tion, operation of the Great Lakes fish tissue archive has been transferred from Fisheries and Oceans Canada to the Water Quality Monitoring and Surveillance Division of Environment Canada.
Supporting Information Available Details about the fish samples, mass spectrometer MRM acquisition parameters, and quality control data are included, as well as HPLC method comparisons, and PFTrA data. This material is available free of charge via the Internet at http:// pubs.acs.org.
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