Environ. Sci. Technol. 2004, 38, 2779-2784
Temporal Trends and Spatial Distributions of Brominated Flame Retardants in Archived Fishes from the Great Lakes LING YAN ZHU AND RONALD A. HITES* School of Public and Environmental Affairs, Indiana University, Bloomington, Indiana 47405
To explore the geographical distribution and temporal trends of polybrominated diphenyl ethers (PBDEs) in the Great Lakes, lake trout from Lakes Superior, Michigan, Huron, and Ontario and walleye from Lake Erie, collected during the period of 1980-2000, were analyzed. The concentrations of fifteen PBDE congeners and one polybrominated biphenyl (PBB-153) were determined in each fish sample. Lake trout from Lakes Michigan and Ontario had the highest ∑PBDE concentrations during the years investigated. The ∑PBDE concentrations in fishes from the five lakes increased exponentially with time, doubling every 3-4 years. The relative proportion of BDEs-47, -99, and -100 compared to BDEs-153 and -154 increased significantly as a function of time. Over the period 1980-2000, the concentrations of PBB153, which was a component of a flame retardant banned in the 1970s, generally remained the same in these Great Lakes fishes, except for lake trout from Lake Huron, where the PBB-153 concentrations decreased significantly, but slowly.
Introduction Polybrominated diphenyl ethers (PBDEs) are used to retard the flammability of plastics, textiles, electronic circuitry, and other materials (1), and perhaps because of their widespread use, these compounds are now ubiquitous environmental contaminants (2). PBDEs may be toxic; for example, they may interfere with endocrine system function and have neurotoxic effects during neonatal brain development in mice (3, 4). PBDEs are now found in air (5-7), water, sediment (8, 9), biota (10-12), and people (13). Furthermore, PBDE concentrations in most of these environmental compartments are increasing exponentially as a function of time. Hites has summarized the concentrations of PBDEs measured in several environmental media and has determined PBDE concentration trends (14). The PBDE levels in human blood, milk, and tissue have increased exponentially with a doubling time of ∼5 years all over the world. PBDE concentrations in marine mammals from the Canadian Arctic also are increasing exponentially, in this case with a doubling time of ∼7 years, even though the current concentrations are very low (∼5 ng/g of lipid). PBDE concentrations in marine mammals from the rest of the world are doubling every ∼5 years. PBDE concentrations have doubled every ∼6 years in Swedish bird’s eggs and every ∼3 years in Great Lakes herring gull eggs. In general, the distribution of PBDEs in the European environ* Corresponding author e-mail:
[email protected]. 10.1021/es035288h CCC: $27.50 Published on Web 04/09/2004
2004 American Chemical Society
ment has been studied systematically for several years. However, such studies in North America have only recently started, despite relatively high PBDE consumption rates in North America (15). Our focus in this paper is the North American Great Lakes. These five lakes are a particularly important part of North America’s physical and cultural heritage. The Great Lakes basin is home to 10% of the U.S. and 25% of the Canadian population and accounts for 18% of these two nation’s gross domestic products (16). One measure of the environmental health of the Great Lakes has been pollutant concentrations in lake trout, a top salmonid predator, measured as a function of time. These fish are collected from all of the lakes biannually by the U.S. Geological Survey (USGS), composites are ground together, and the resulting puree is frozen and archived. Past studies of these samples have focused on classic chlorinated organic compounds, such as DDT and PCBs, and it is now known that the concentrations of these compounds decreased by a factor of ∼10 between 1970 and 1990 (17). In this paper, we use these archived fish samples to explore the historical and geographical distribution of PBDEs in fishes from the Great Lakes.
Experimental Section Sample Information. Table 1 lists the information on the archived fish samples analyzed in this study. We used fish collected in 1980, 1984, 1990, 1992, 1994, 1996, 1998, and 2000. All the samples from each lake were taken from the same locations each year, except in 1984 from Lake Erie, where that year’s fish were from a different site. All of these locations were selected to be remote from urban areas. All of the fish sampled were about the same length, thus avoiding the effect of age. Each sample that we analyzed was a composite made by grinding and regrinding five fish together. The composites were stored at -30 °C in amber glassware. For 1980 and 1984, we analyzed one composite for each lake. For other years, we analyzed three composites for each lake, except for Lake Huron in 2000 (see Table 1). Lake trout (Salvelinus namaycush) were used for all lakes for all years except for Lake Erie, where only walleye (Stizostedion vitreum vitreum) were available. There are few lake trout in Lake Erie, presumably because of its relatively high water temperature. In this case, walleye were used because they are at approximately the same trophic level as lake trout. One sample in 1994 from Lake Superior and three samples in 1998 from Lakes Michigan, Erie, and Ontario were not available in the archive. Materials. The 15 PBDE congeners investigated in this study were 2,2′,4-TrBDE (BDE-17), 2,4,4′-TrBDE (BDE-28), 2,2′,4,4′-TeBDE (BDE-47), 2,2′,4,5′-TeBDE (BDE-49), 2,3′,4,4′TeBDE (BDE-66), 2,3′,4′,6-TeBDE (BDE-71), 2,2′,3,4,4′-PeBDE (BDE-85), 2,2′,4,4′,5-PeBDE (BDE-99), 2,2′,4,4′,6-PeBDE (BDE100), 2,2′,3,4,4′,5′-HxBDE (BDE-138), 2,2′,4,4′,5,5′-HxBDE (BDE-153), 2,2′,4,4′,5,6′-HxBDE (BDE-154), 2,2′,3,4,4′,5′,6HpBDE (BDE-183), 2,3,3′,4,4′,5,6-HpBDE (BDE-190), and decabromodiphenyl ether (BDE-209). All of these compounds were purchased in nonane solution from Cambridge Isotope Laboratories (Cambridge, MA). In addition, we investigated an abundant polybrominated biphenyl (PBB) congener, 2,2′,4,4′,5,5′-polybrominated biphenyl (PBB-153), a standard of which was purchased from Ultra Scientific (North Kingstown, RI). The recovery standard, 2,3′,4,4′,5-PeBDE (BDE118), was donated to us by Cambridge Isotope Laboratories. This compound is not present in the ambient environment. All the solvents used for the extraction and cleanup procedures were residue-analysis grade. VOL. 38, NO. 10, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Information on the Archived Fish Samples 1980 1984 1990 1992 1994 1996 1998 2000
site species no. of replicates site species no. of replicates site species no. of replicates site species no. of replicates site species no. of replicates site species no. of replicates site species no. of replicates site species no. of replicates
Lake Superior
Lake Michigan
Lake Huron
Lake Erie
Lake Ontario
Apostle Island lake trout 1 Apostle Island lake trout 1 Apostle Island lake trout 3 Apostle Island lake trout 3
Saugatuck lake trout 1 Saugatuck lake trout 1 Saugatuck lake trout 3 Saugatuck lake trout 3 Saugatuck lake trout 3 Saugatuck lake trout 3
Rockport lake trout 1 Rockport lake trout 1 Rockport lake trout 3 Rockport lake trout 3 Rockport lake trout 3 Rockport lake trout 3 Rockport lake trout 3 Rockport lake trout 2
Middle Bass Island walleye 1 Dunkirk walleye 1 Middle Bass Island walleye 3 Middle Bass Island walleye 3 Middle Bass Island walleye 3 Middle Bass Island walleye 3
Oswego lake trout 1 Oswego lake trout 1 Oswego lake trout 3 Oswego lake trout 3 Oswego lake trout 3 Oswego lake trout 3
Middle Bass Island walleye 3
Oswego lake trout 3
Apostle Island lake trout 3 Apostle Island lake trout 3 Apostle Island lake trout 3
Saugatuck lake trout 3
Sample Preparation. The extraction, isolation, and analytical procedures were similar to those we have used previously for PBDEs (10, 18). Generally, a portion (5-10 g wet mass) of the wet ground fish tissue was well-mixed with ∼60 g of precleaned, anhydrous Na2SO4. After being spiked with a known amount of the internal standards [13C12]2,3,3′,4,4′,5-hexachlorodiphenyl ether ([13C12]CDE-156) and [13C12]-2,2′,3,3′,4,4′,5,5′-octachlorodiphenyl ether ([13C12]CDE194) (Cambridge Isotope Laboratories), the samples were Soxhlet extracted for 24 h with 50% acetone in hexane. Throughout the extraction and analysis procedure, the analytes were protected from light by wrapping the containers with aluminum foil or by using amber glassware. The lipid concentration was determined gravimetrically. The majority of the lipids were removed by adding approximately 8 mL of concentrated H2SO4 (EM Science, Gibbstown, NJ) to each extract in 10 mL of hexane and shaking the mixture for 5 min. After centrifugation for 10 min, the upper hexane layer was recovered and combined with 5 mL of hexane used to wash the sulfuric acid residue. After reduction of the volume to ∼1 mL under N2 flow, the samples were loaded onto a 3% water deactivated silica (Grace Davison, Columbia, MD) column (20 cm × 1.9 cm i.d.). One fraction of 150 mL of dichloromethane was collected. The solvent was blown down with N2 to 500 µL, and the samples were fractioned on an alumina (ICN Biomedicals GmbH, Eschwege, Germany) column (6 cm × 0.6 cm i.d.). The column was first eluted by 8 mL of hexane followed by 8 mL of 40% dichloromethane in hexane. The PBDEs eluted in the second fraction. After solvent exchange to hexane, BDE-118 was added as a recovery standard, and the samples were analyzed by GC/MS. Instrumental Parameters. The samples were analyzed on an Agilent 6890 series gas chromatograph coupled to an Agilent 5973 mass spectrometer (GC/MS) with helium as the carrier gas. The 2 µL injections were made in the pulse splitless mode, with a purge time of 2.0 min. The injection port was held at 285 °C. For the determination of all PBDEs and PBB, except for BDE-209, the GC column used was a 60 m × 250 µm (i.d.) fused silica capillary tube coated with DB-5-MS (0.25 µm film thickness; J&W Scientific, Folsom, CA). A 60 m column was used to ensure separation of BDE-154 from PBB153. The GC oven temperature program was as follows: 2780
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isothermal at 110 °C for 1.90 min, 15 °C/min to 180 °C, 1.85 °C/min to 300 °C, and held at 300 °C for 45 min. The GC to MS transfer line was held at 285 °C. The mass spectrometer was operated in the electron capture negative ionization mode using methane as the reagent gas, and the ion source temperature was 150 °C. Selected ion monitoring of the two bromide ions at m/z 79 and 81 was used to detect the PBDEs. The ions at m/z 351.9 and 349.9 due to (M - HCl + 2)- and (M - HCl)- were used to detect CDE-156, and ions at m/z 457.8 and 455.8 due to (M + 4)- and (M + 2)- were used to detect CDE-194. The response factors for all compounds were determined using quantitation standards with known amounts of all the target compounds, internal standards, and recovery standards. The internal standard, [13C12]CDE156, was used as a retention time reference, and [13C12]CDE194 was used as the internal standard to quantitate all the PBDE congeners. BDE-118 was used as a recovery standard. All of the samples were screened for BDE-209 separately on a shorter DB-5-MS column (15 m × 250 µm i.d.; 0.25 µm film thickness; J&W Scientific) with the following temperature program: 110 °C for 1 min, 15 °C/min to 300 °C, and held at 300 °C for 17 min. Selected ion monitoring of the two bromide ions at m/z 79 and 81 was also used to detect BDE209. [13C12]CDE-194 was used as the internal standard to quantitate BDE-209. Quality Control. Three quality control criteria were used to ensure the correct identification of the target compounds: (a) The GC retention times matched those of the standard compounds. (b) The signal-to-noise ratio was greater than 3:1. Under these conditions, the detection limits were in the range of 0.0086-0.15 ng/g of wet mass depending on the individual congener. (c) The isotopic ratio between the ion pairs was within (15% of the theoretical value. The recoveries of the internal standard were greater than 65% for all the samples. The measurements were all corrected for recovery by using the chlorinated diphenyl ether internal standard, which had been added to the samples before extraction. Each batch of eight samples included one method blank to ensure the method was responding properly. The method blank consisted of 60 g of precleaned Na2SO4, which had been spiked with the same amount of internal standard as the samples. Method blanks were all below the detection limits except for BDE-47 (0.43-2.4 ng), BDE-99 (0.33-1.8 ng), and BDE-209
TABLE 2. Total PBDEs and PBB-153 Concentrations (ng/g of lipid) in Fishes from the Great Lakes in 1980-2000 Superior
a
Michigan
1980 1984 1990 1992 1994 1996 1998 2000
6.33 16.6 57.6 ( 12.7a 76.2 ( 25.4
1980 1984 1990 1992 1994 1996 1998 2000
7.65 4.91 5.55 ( 3.43 9.56 ( 1.82
454 ( 57 426 ( 22 989 ( 132
13.9 81.2 176 ( 29 420 ( 60 210 ( 34 1355 ( 310 1395 ( 56 26.0 13.0 17.0 ( 2.1 14.2 ( 6.2 6.12 ( 2.43 15.7 ( 3.0
11.8 ( 5.6 8.13 ( 1.86 18.9 ( 5.4
13.5 ( 1.8
Huron
Erie
Total PBDE 11.0 32.8 119 ( 19 166 ( 29 195 ( 43 301 ( 27 434 ( 58 369 ( 15 PBB-153 39.4 27.7 18.4 ( 2.5 23.5 ( 6.2 18.1 ( 5.1 16.9 ( 3.7 20.8 ( 6.7 17.7 ( 6.2
Ontario
6.51 19.5 77.9 ( 20.8 181 ( 71 210 ( 41 262 ( 65
10.0 97.0 143 ( 24 297 ( 5 589 ( 13 543 ( 62
600 ( 102
546 ( 23
10.0 5.98 5.47 ( 0.74 10.6 ( 6.7 4.44 ( 0.86 3.90 ( 0.92
18.6 92.4 12.5 ( 2.6 14.5 ( 2.6 17.2 ( 0.62 9.01 ( 1.74
7.67 ( 1.35
4.62 ( 0.58
Standard deviations of usually three replicates.
TABLE 3. Summary of the Total of the Major PBDEa Concentrations (ng/g of lipid) in Fishes from the Great Lakes others’ data
our data
location
year
species
∑PBDE
year
species
∑PBDE
Superiorb Ontariob Ontarioc Superiorc Huronc Eriec Michigand Michigane Michiganf
1994 1994 1997 1997 1997 1997 1996 1996 1997
smelt smelt lake trout lake trout lake trout lake trout salmon steelhead trout lake trout
150 240 ( 30 375 ( 96 281 ( 109 204 ( 73 93 ( 25 1970 2970 1030 ( 39
1996 1994 1996 1996 1996 1996 1996 1996
lake trout lake trout lake trout lake trout lake trout walleye lake trout lake trout
428 ( 54 553 ( 12 503 ( 58 428 ( 54 279 ( 26 231 ( 61 1254 ( 277 1254 ( 277
a BDE-47, -99, -100, -153, and -154. ref 21. f Data from ref 18.
b
Data from ref 10. c Data from ref 19. BDE-154 was not included in this study.
(1.4-3.4 ng). The levels of BDE-47 and BDE-99 in the method blank were well below 5% of the levels found in the fish samples. The amounts of BDE-209 found in all fish samples were in the range of “undetectable” to 3.6 ng, which was the same level as in blanks; thus, we could not conclude that BDE-209 was present in any of these samples.
Results and Discussion The lipid-normalized concentrations of total PBDEs (∑PBDE) in the fishes we analyzed are given in Table 2 as a function of the year and lake sampled; full data on the lipid concentrations and on the wet mass normalized ∑PBDE concentrations of each congener and replicates are given in the Supporting Information. For those years and locations where we had two or three composite samples, the averages and standard deviations are reported in Table 2. Our results are comparable to PBDE concentrations measured in fishes from the Great Lakes by other laboratories; see Table 3. Different numbers of congeners were reported in the literature; thus, to make consistent comparisons, only the sum of the major congeners, BDEs-47, -99, -100, -153, and -154, are listed and compared here. The concentrations we measured in lake trout in 1996 are ∼25% higher than those measured by Luross et al. (19) for the same species in Lakes Ontario, Superior, and Huron in 1997. For Lake Erie, we measured PBDE in walleye, but Luross et al. (19) used lake trout; perhaps as a result, our concentrations are about twice those of Luross et al. for this lake in 1996/1997. Our concentrations of PBDE in lake trout from Lake Michigan in 1996 are about half of those measured by Manchester-Neesvig
d
Data from ref 20. e Data from
et al. (20) and Asplund et al. (21) in salmon and in steelhead trout, respectively. The PBDE concentrations reported here are also close to those we reported in Lake Michigan lake trout, a composite of which is available as a NIST Standard Reference Material (SRM-1947) (18). Smelt from Lakes Superior and Ontario in 1994-1996 had much lower ∑PBDE levels than our lake trout from the same years. These differences of a factor of 2 or so are not unexpected given the differences in uptake efficiencies, trophic levels, and ages of the different species of fish used in these various studies. The ∑PBDE concentrations we measured in these Great Lakes fishes are on the order of 500-800 ng/g of lipid for the years 1996-2000. These values are similar to average ∑PBDE concentrations in other fishes from various other locations in North America, but these levels are about 5 times higher than average ∑PBDE concentrations measured in fishes from Europe (14). This difference is smaller but in the same direction as the difference between ∑PBDE concentrations in humans in North America and Europe. In people, North Americans have about 20 times more PBDE in their blood as do Europeans (14). Spatial Distribution of PBDE. The year 2000 ∑PBDE concentrations (ng/g of lipid) in the five lakes (see Table 2) are (Michigan) 1400, (Superior) 990, (Erie) 600, (Ontario) 550, and (Huron) 370. Lakes Michigan and Superior had the highest year 2000 ∑PBDE concentrations, which is surprising given that Lake Superior is generally thought of as the most pristine of the Great Lakes. Perhaps the relatively high PBDE concentrations in Lake Superior are a result of the slow contaminant removal processes at work in the very cold water VOL. 38, NO. 10, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Temporal trend of ∑PBDE concentrations in fishes from the Great Lakes. The fitted exponential curves are shown, the slope of which was used to calculate the doubling time (t 2 ( 1 standard error) for each lake.
FIGURE 2. Percent contributions of the various PBDE congeners to ∑PBDE for the years 1984 and 1996. of this lake. For lake trout collected in 1997, Luross observed that the ∑PBDE concentrations ranked Ontario > Superior > Huron > Erie (19), which is the same as our results for 1996. Our finding that trout from Lakes Michigan and Ontario are generally the most contaminated with PBDE is expected, given the large population residing on the shores of these lakes and given the intense industrial processes associated with these large urban regions. Like PBDEs, PCBs are also associated with human and industrial activity, and like PBDEs, PCB concentrations are also highest in fish from Lake Michigan (22). Temporal Trends of PBDE. The rate at which PBDE concentrations have increased in the environment and in humans has been of considerable interest. Temporal trend studies from Europe (23) have indicated that PBDE levels in human milk increased markedly from 1972 to 1997, doubling every ∼5 years. After that, the PBDE levels in human milk 2782
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decreased somewhat (23, 24). A similar rate of increasing PBDE concentrations was also observed in the Japanese population (13, 25). The PBDE levels in Japanese sea bass and gray mullet showed an increasing trend from 1986 to 1989 and then a decreasing trend after 1990 (25). These recent decreases may be the result of changes in industrial practices in Europe and Japan. The European Commission, for example, is phasing out the use of the commercial pentaBDE product due to concerns regarding the potential adverse human health effects of this substance (25-27). Now >95% of the current global demand for the penta-BDE product is in North America; see Table 4. This suggests that the North American Great Lakes could be receiving a relatively higher proportion of the less brominated homologues than the rest of the world. In this study, we found that the ∑PBDE levels in the fishes from all five of the Great Lakes increased exponentially as
FIGURE 3. Temporal trends of the ratio of the sum of concentrations of BDE-47 + BDE-99 + BDE-100 to the sum of the concentrations of BDE-153 + BDE-154 in fishes from the Great Lakes. The fitted lines have the following correlation coefficients (r 2): Superior, 0.797; Huron, 0.714; Michigan, 0.757; Erie, 0.674; Ontario, 0.855. All of these correlations are significant; two outliers from 1980 were omitted.
FIGURE 4. Temporal trend of PBB-153 concentrations in fishes from the Great Lakes. The fitted exponential curves are shown; the fitted lines have the following correlation coefficients (r 2): Superior, 0.481; Huron, 0.739; Michigan, 0.236; Erie, 0.128; Ontario, 0.527. Only the Lake Huron regression is significant.
TABLE 4. Estimated Global and North American Demands for the Major PBDE Commercial Products (t)
year
type
1990a
total deca octa penta total deca octa penta total deca octa penta
1999b
2001b
a
North North American ratio of penta global American % of global to octa global demand demand demand demand 40000 30000 6000 4000 67125 54800 3825 8500 67390 56100 3790 7500
Data from ref 32.
b
c c c c 33965 24300 1375 8290 33100 24500 1500 7100
c c c c 51 44 36 98 49 44 40 95
0.66
2.2
2.0 c
Data from www.bsef.com. Not available.
a function of time, doubling every 3-4 years; see Figure 1. There are some preliminary indications that the ∑PBDE concentrations have leveled off in Lakes Huron and Michigan since 1998 and in Lake Ontario since 1994. These temporal
trend results are in general agreement with the findings by Luross et al. (28), who reported that PBDE concentrations in lake trout from Lake Ontario have increased 300-fold over the past 20 years, which is a doubling time of 2.4 years. Similar trends were observed for herring gull eggs studied by Norstrom et al. (29), who reported that ∑PBDE levels increased exponentially in eggs collected from colonies on Lakes Michigan, Huron, and Ontario and that the doubling times were ∼3 years. Norstrom et al. also observed the leveling off of ∑PBDE concentrations in herring gull eggs from Lake Michigan after 1998 and from Lake Ontario after 1999. It is not yet clear what has caused this leveling in recent years. Other studies have found that PBDE levels in biota and humans from North America have increased with doubling times of 4-6 years (30). The differences in doubling times among all of these results are not statistically significant. Suffice it to say that the concentrations of ∑PBDE in the Great Lakes environment have rapidly increased since 1980, but there are some signs that these increases have slowed. Continued study of fishes from the Great Lakes is needed to verify this recent trend. Contributions to the PBDE Congener Pattern. We measured 14 PBDE congeners individually before summing them to get ∑PBDE. The ratios of these individual congener VOL. 38, NO. 10, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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concentrations to ∑PBDE (expressed as a percent) are the so-called congener patterns. In this case, the PBDE congener patterns in lake trout and walleye from all five Great Lakes were similar to each other, even though their absolute concentrations were different. However, these congener patterns changed with time. Figure 2 illustrates these congener patterns for the years 1984 and 1996. The proportion of BDE-47 was usually smaller in 1984 than in 1996, and the opposite was true for BDE-153. To explore this observation systematically, we have defined the following ratio:
R)
[47] + [99] + [100] [153] + [154]
where [x] refers to the concentration of congener x in any units. These ratios are plotted as a function of fish sampling year in Figure 3. The regressions are all statistically significant with a confidence limit of 97%, on average. Clearly, the congener patterns have changed systematically over time. Similar results were observed by Norstrom in herring eggs from the Great Lakes (29). Differences in the production and use of the penta-BDE product vs the octaBDE product may account for these differences. Table 4 lists the demand for the three major PBDE commercial products in the global and North American markets. In 1990, the ratio of the penta-BDE product to the octa-BDE product demand was ∼0.7, but this ratio increased to ∼2 in 1999 and 2001. In other words, more of the octa-BDE product, which is relatively high in BDEs-153 and -154, was used in the 1980s relative to the penta-BDE product, which is high in BDE-47, but now the opposite is true. This shift toward more of the penta-BDE product in the marketplace is mirrored by an increase in the ratios (R; see eq 1) over the same time period. The R values for the lake trout were 3-10 times higher than the ratio of the penta to octa global demand at the same time. This difference may be explained by differences in the bioavailability of the less-brominated congeners compared with the more-brominated congeners. Polybrominated Biphenyls. PBBs were introduced as flame retardants in the early 1970s, but their production was banned in the United States in 1976 because of an industrial accident: In 1973, Firemaster BP-6 and FF-1 (both PBB commercial products) were unintentionally mixed into cattle feed at a production facility in Michigan, and the resulting feed was widely distributed and used all over Michigan. This accident caused many human and animal health problems in Michigan and quickly lead to the ban of PBB flame retardants in the United States (31). In fact, it may have been this ban that led to the increased use of PBDE starting in the 1980s. Given that PBBs were banned over 20 years ago, it is likely that their levels in Great Lakes fishes would have decreased over time while at the same time ∑PBDE levels would have increased. Our concentration data for PBB-153 (see Figure 4) indicate that concentrations of this compound have not significantly changed in fishes from the Great Lakes over the period 1980-2000, with the exception of Lake Huron, where the concentrations have decreased with a half-life of 19 ( 5 years. Among the five lakes, lake trout from Lakes Superior and Huron had the highest concentrations of PBB-153 in 2000. This tendency was also observed by Luross et al. (19). This observation may indicate that there are still PBB sources to these lakes.
Acknowledgments We thank the U.S. Geological Survey, Great Lakes Science Center, and R. T. Quintal for providing the archived fish sampled from 1980 to 1998, D. L. Swackhamer for providing
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fish samples from 2000, and the U.S. Environmental Protection Agency for providing support (Grant R-83039701).
Supporting Information Available Excel spreadsheet providing data from various years. This material is available free of charge via the Internet at http://pubs.acs.org.
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Received for review November 18, 2003. Revised manuscript received January 26, 2004. Accepted February 9, 2004. ES035288H
