Comparison of Toxaphene Congeners Levels in Five Seal Species

Jan 29, 2005 - Institut des Sciences de la Mer, Université du Québec à Rimouski, 310 Allée des Ursulines, Rimouski, Quebec, Canada G5L 3A1, Depart...
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Environ. Sci. Technol. 2005, 39, 1448-1454

Comparison of Toxaphene Congeners Levels in Five Seal Species from Eastern Canada: What Is the Importance of Biological Factors? B R U N O G O U T E U X , †,‡ M I C H E L L E B E U F , * ,§ MIKE O. HAMMILL,§ D E R E K C . G . M U I R , || A N D J E A N - P I E R R E G A G N EÄ † Institut des Sciences de la Mer, Universite´ du Que´bec a` Rimouski, 310 Alle´e des Ursulines, Rimouski, Quebec, Canada G5L 3A1, Department of Fisheries and Oceans, Maurice Lamontagne Institute, P.O. Box 1000, Mont-Joli, Quebec, Canada G5H 3Z4, and National Water Research Institute, Environment Canada, Burlington, Ontario, Canada L7R 4A6

Environmentally relevant chlorobornanes (CHBs) were measured in blubber samples of harbor (Phoca vitulina), gray (Halichoerus grypus), harp (Phoca groenlandica), and hooded seals (Cystophora cristata) sampled in different part of the St. Lawrence marine ecosystem (SLME) and ringed seals (Phoca hispida) sampled in the eastern Canadian Arctic waters. The purpose of this study was to compare the levels of six CHBs (Parlar-26, -40/-41, -44, -50, and -62) among the five seal species. Seal species could be separated into three groups based on their respective ΣCHB mean concentrations ((standard error): gray (49 ( 3.9 ng/g lipid weight) and harbor (80 ( 20 ng/g lipid weight) seals were more contaminated than ringed seals (18 ( 7.6 ng/g lipid weight) but less contaminated than harp (370 ( 87 ng/g lipid weight) and hooded (680 ( 310 ng/g lipid weight) seals. These differences are not expected to be related to different sources of toxaphene contamination, since both the SLME and the eastern Canadian Arctic environments are thought to be mainly contaminated via atmospheric transport from the southeastern part of the United States. Thus, biological factors such as sex, age, nutritive condition, metabolism capacity, and diet of the animals collected were considered. Results reported in this study indicated that the diet is likely the main factor accounting for interspecies variations in toxaphene contamination in seals from eastern Canada.

Introduction The chlorinated pesticide, toxaphene, was first produced in the United States by Hercules Inc. during the mid 1940s and was used primarily on cotton farms in the southern United * Corresponding author phone: (418)775-0690; fax: (418)775-0718; e-mail: [email protected]. † Universite ´ du Que´bec a` Rimouski. ‡ Present address: National Water research Institute, Environment Canada, Burlington, ON, Canada L7R 4A6. § Maurice Lamontagne Institute. || Environment Canada. 1448

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Sates (1). Historically, the United States was the main producer and user of this product until 1982, when concerns about its toxicity led the U.S. Environmental Protection Agency to progressively ban this contaminant (1). Toxaphene is considered as an organochlorine (OC) contaminant of concern for human health and the environment because of its considerable use in the past, persistence, bioaccumulation, inherent toxicity, and long-range transport potential (2). As a result, toxaphene is among the OCs targeted for a global ban on the production, import, export, and use by the Stockholm Convention on Persistent Organic Pollutants (2). In contrast to other OCs, such as polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) related compounds, local or riverine inputs of toxaphene to the St. Lawrence marine ecosystem (SLME) can be considered as minor (3). Local toxaphene usage, estimated by atmospheric transport and deposition modeling, accounted for less than 0.5% of the total input of toxaphene to the SLME, between 1945 and 2000 (4). During the same time period, estimated riverine inputs from the Great Lakes region, the drainage basin of the SLME, represented less than 10% of the total input of toxaphene to the SLME (4). Despite negligible local input of toxaphene, relatively high levels have been measured in beluga whales (Delphinapterus leucas) from the SLME, indicating that there is another source contributing to toxaphene levels (3, 5, 6). Toxaphene concentrations in SLME male belugas were in the range of those reported for animals living in the Canadian Arctic (7). In that region, toxaphene has never been used and atmospheric deposition, through long-range transport, represents the main source (8). The atmosphere may also be the source of toxaphene contamination of the SLME. This hypothesis is supported by several studies revealing that toxaphene is likely distributed from the south and southeast of the United States to nonsource regions such as the Great Lakes or Arctic in Canada via atmospheric long-range transport (8-10). The contamination of the SMLE by toxaphene became a topic of concern when high toxaphene levels were reported in SLME belugas, which have been listed as “threatened” under the Canadian Species at Risk Act in 2004 (11). Concentrations of total toxaphene for males were up to about 36 and 90 µg/g lipid weight in blubber samples from stranded and biopsied animals, respectively (5, 6). Furthermore, concentrations of the two predominant toxaphene congeners or chlorobornanes (CHBs), i.e., Parlar-26 and Parlar-50, in male belugas have not declined during the 1988-1999 time period (7). Surprisingly, except for studies on belugas that are permanent residents of the SLME, the dispersion of toxaphene in eastern Canada is largely unknown. Most marine mammals can serve as indicators of the dispersion of the toxaphene contamination since, occupying elevated trophic levels, high levels of recalcitrant OCs accumulate in their fat tissues (12, 13). The SLME that includes the St. Lawrence Estuary and the Gulf of St. Lawrence is inhabited by four species of seals. These include several populations of harbor seals (Phoca vitulina), of which one is a permanent resident of the St. Lawrence Estuary (14). Gray seals (Halichoerus grypus) summer in the St. Lawrence Estuary, but winter over in the Gulf of St. Lawrence or off the Atlantic coast of Canada (15). Harp (Phoca groenlandica) and hooded (Cystophora cristata) seals winter in the SLME, but migrate north to Arctic waters in summer (16, 17). Two other species, the ringed seal (Phoca hispida) and the bearded seal (Erignatus barbatus), also occur in the SLME, but their presence is limited to the northeastern portion of the SLME, since they are normally found in Arctic waters (18). 10.1021/es048886k CCC: $30.25

 2005 American Chemical Society Published on Web 01/29/2005

FIGURE 1. Location of capture sites for seals sampled in the St. Lawrence Estuary (SLE), the Gulf of St. Lawrence, and the eastern Canadian Arctic waters. The objective of this research was to compare levels of environmentally relevant toxaphene congeners among the four seal species regularly found in the SLME waters. Since two of those species spent at least several months of the year in Arctic waters, ringed seal, which can be considered as permanent resident of this environment, was also included in the comparison.

Materials and Methods Chemicals. All high-resolution gas chromatography grade solvents used were provided by EM Science (Gibbstown, NJ). Anhydrous sodium sulfate (BDH, Toronto, ON), alumina oxide (Bio-Rad Laboratories, Hercules, CA), and silica gel (EM Science, Gibbstown, NJ) were extracted three times with dichloromethane (DCM) and n-hexane prior to their use. Bio-Beads SX-3 used in the gel permeation chromatography (GPC) were obtained from Bio-Rad Laboratories (Hercules, CA). A mixture of 22 individual toxaphene congeners was purchased from EQ Laboratories (Atlanta, GA). Only the six following CHBs were analyzed: 2-endo,3-exo,5-endo,6exo,8,8,10,10-octachlorobornane (Parlar-26 or P26), 2-endo,3exo,5-endo,6-exo,8,9,10,10-octachlorobornane (Parlar-40 or P40), 2-exo,3-endo,5-exo,8,9,9,10,10-octachlorobornane (Parlar-41 or P41), 2-exo,5,5,8,9,9,10,10-octachlorobornane (Parlar-44 or P44), 2-endo,3-exo,5-endo,6-exo,8,8,9,10,10-nonachlorobornane (Parlar-50 or P50), and 2,2,5,5,8,9,9,10,10nonachlorobornane (Parlar-62 or P62). For simplicity, the Parlar nomenclature is used in the text (19). d8-4,4′-DDD, used as quantification standard, and 13C12-PCB 101, used for the instrument performance control, were obtained from Cambridge Isotope Laboratories (Andover, MA). Samples. CHBs were measured in blubber samples of five different seal species from eastern Canada (Figure 1). Four live adult male harbor seals were captured near the Bic Islands, in the St. Lawrence Estuary, in October and

November 1999 and in March 2000. Five male gray seals were sampled at Amet Island, in the southern Gulf of St. Lawrence, in June 1997. Five male harp and three male hooded seals were caught near the Magdalen Islands in March 1995 and 1996, and March 1990, respectively. Finally, five male ringed seals were sampled at Quaqtaq, Salluit, and Kangirsuk (Nunavik) in the Hudson Strait and the Ungava Bay waters in May and June 1998. All seals studied were taken under a scientific permit by Canadian Department of Fisheries and Oceans researchers, by licensed sealers, or by Inuit subsistence hunters. Animals were weighed and measured, and a tooth was extracted from each seal to determine the age by counting growth layer groups on tooth sections (20). Chemical Analysis. Details on the CHB congener extraction, cleanup, and analyze, done at the Maurice Lamontagne Institute (Mont-Joli, Qc, Canada), have been recently presented elsewhere (7, 21). Briefly, samples were chemically dried with clean anhydrous sodium sulfate. Lipids and contaminants were extracted with dichloromethane. Then, lipids were removed by GPC. A first purification step with a silica/alumina column was performed to collect PCBs and OCs and a second purification step with a silica column was realized to further isolate the CHBs of interest. Gas chromatography analyses were made using a Varian 3400CX (Varian, Walnut Creek, CA) equipped with a Varian 8200 autosampler and a programmable split/splitless injector operated in splitless mode. A DB-5MS column (30 m × 0.25 mm i.d. × 0.25 µm film thickness, J&W Scientific, Folson, CA) was used to do the chromatographic separations. P40 and P41 will be presented as P40/41, since they were not chromatographically separated. The GC was coupled to a Varian Saturn 2000 ion trap mass spectrometer. The ionization was performed by electron impact and the ion trap was operated in MS/MS mode (21). Concentrations of P26, P40, P41, P44, P50, and P62 were determined in all seal blubber VOL. 39, NO. 6, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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samples. The concentration of the sum of these individual CHBs was reported as ΣCHBs. QA/QC. One procedural blank and one Standard Reference Material (SRM) were included with every 10-sample analysis. A pilot whale (Globicephala sp.) blubber sample (SRM 1945) was obtained from the National Institute of Standards and Technology (NIST). Repeated analysis of SRM 1945 (n ) 5) indicating that the precision of the method was satisfactory, since coefficients of variation for all CHBs were within 15% of the average values. The accuracy and the precision of the toxaphene analytical method were confirmed through the Northern Contaminant Program Interlaboratory study NCP II-4 on toxaphene in a standard solution and in a lipid-free burbot liver extract (21, 22). No signal was detected in blanks, indicating that the procedural contamination was lower than the sample detection limits, which ranged from 0.1 to 13 ng/g wet weight. The limits of detection varied with sample size and the signal-to-noise ratio occurring at the retention time of the target CHB. The CHBs were quantified relative to the internal standard added at extraction, and all reported concentrations were corrected for procedural losses. The mean recovery of the internal standard in samples was 96 ( 27%. Statistical Analysis. All statistical analyses were performed from the original formulas (23) using Microsoft Excel 97 software, with a significance level of p < 0.05. ΣCHB concentrations were logarithmically transformed to reduce skewness and kurtosis. Differences of ΣCHB concentrations between seal species were estimated using an analysis of variance (ANOVA) (23). A multiple comparison procedure, using the Tukey test, was applied to determine which specific seal species differed from the others (23). Interspecies differences in age of animals were also assessed by an ANOVA (23). Since relative concentration ratios were normally distributed, one-tailed t tests were used to determine if relative concentration ratio means were close to unity, in fact, greater than 0.8 and lower than 1.2 (23).

FIGURE 2. Mean concentrations (ng/g lipid weight) of ΣCHBs ((standard error) in male seals from eastern Canada. Different letters indicate significant differences between seal species (multiple comparison Tukey test, p < 0.05).

Results and Discussion Concentrations of CHBs in Seals from Eastern Canada and the Rest of the Northern Hemisphere. Most previous reports of toxaphene concentrations in seals were based on total toxaphene determined using the technical mixture as a reference solution. To the best of our knowledge, this is the first study to report CHB congener levels in hooded and harbor seals. ΣCHB mean concentrations varied by more than an order of magnitude from about 20 ng/g lipid weight (l wt) in ringed seals to about 700 ng/g l wt in hooded seals (Figure 2). Differences in interspecies ΣCHB levels were highly significant (ANOVA; p < 0.0005). A multiple comparison revealed that seals could be separated into three groups based on their respective ΣCHB mean concentrations ((standard error): gray (49 ( 3.9 ng/g l wt) and harbor (80 ( 20 ng/g l wt) seals being more contaminated than ringed seals (18 ( 7.6 ng/g l wt) but less contaminated than harp (370 ( 87 ng/g l wt) and hooded (680 ( 310 ng/g l wt) seals (Figure 2). P26, P40/41, P44, and P50 were detected in all samples, whereas P62 concentration was below the detection limit for only one ringed seal sample (Supporting Information). P26 and P50 were the predominant CHBs in all seal species, except ringed seals, which were more contaminated by P40/41 relative to P26 (Figure 3). Nevertheless, the sum of P26 and P50 accounted for more than 55% of ΣCHBs in ringed seals and 70% and more for other seal species (Figure 3). P40/41, P44, and P62 contributed individually for less than 15% of ΣCHBs, except for P40/41, which accounted for about 25% in ringed seals (Figure 3). These results are similar to the previously reported predominance of P26 and P50 in marine mammals in general (24) and in belugas from the SLME in particular (3, 5, 7). 1450

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FIGURE 3. Mean contributions of individual CHBs relative to ΣCHB concentrations in male seal species from eastern Canada. P26 and P50 mean concentrations measured in blubber of ringed seals from the Hudson Strait and the Ungava Bay waters were on the same order of magnitude as those reported for animals living in other Arctic environments, such as Greenland and Svalbard areas (Table 1). Similarly, P26 and P50 mean concentrations for gray and harp seals were comparable to those reported for animals from Iceland and Svalbard (Table 1). Assuming that animals from a given seal species inhabiting different areas are representative of their environments, this suggests that the toxaphene contamination of these distinct areas is relatively similar. The contamination by toxaphene of the eastern part of Canada, including both SLME and Arctic areas, is thought to be mainly due to atmospheric transport from south and southeast United States (8, 10). So, it might be assumed that this source has mainly determined the global distribution of toxaphene contamination in North Atlantic waters. Levels of P26 and P50 reported in gray and harp seals collected in the North Sea and the Baltic Sea were about 10-20 and 3-5 times higher, respectively, than for animals of the same species inhabiting North Atlantic waters (Table 1). However, these results should be interpreted with caution, since only one animal from northern Europe environments was analyzed for each of these two seal species (Table 1). Furthermore, the harp seal is not normally considered a

TABLE 1. Mean Concentrations ( Standard Deviation (ng/g wet weight) of Two Major CHBs, P26 and P50, in Blubber of Seal Species from Northern Hemisphere seal species hooded harbor gray gray gray harp harpd harp ringed ringedd ringedd ringed ringed ringed ringed ringedd ringedd ringedd ringed ringed

sampling location Gulf of St. Lawrence St. Lawrence Estuary Gulf of St. Lawrence west Iceland Baltic Sea Gulf of St. Lawrence Svalbard North Sea Nunavik Svalbard Svalbard east Greenland south Greenland west Greenland northwest Greenland Svalbard Svalbard Svalbard Ellesmere Island Ellesmere Island

period 1990 1999-2000 1997 before 2001 before 2001 1995-1996 Aug 1997 before 2001 1998 May 1992 May 1992 1994 1994 1994 1994 before 1998 before 1998 before 1998 before 1997 before 1997

sex M M M nac na M na na M F M F+M F+M F+M F+M na F M M F

n 3 4 5 6 1 5 13 1 5 5 5 25 25 25 25 14 7 7 9 10

a Mean age was estimated using the weight of the animals (cf. text). means.

resident of the North Sea (25). This animal probably came from the White Sea/West Greenland populations which summer in the Barents Sea and occasionally invade the Norwegian coast (26). Nevertheless, such a difference in P26 and P50 contamination between northern Europe and North Atlantic waters animals may result from different sources of toxaphene contamination. A recent study based on the determination of toxaphene in sediments suggests that a European source of toxaphene may be predominant in Europe since the early 1990s (27). Table 1 shows that the toxaphene contamination of several seal species inhabiting a given environment is different. For instance, harp seals from northern Europe exhibit higher concentrations of P26 and P50 than gray seals from the same environment (Table 1). In addition, harbor and gray seals were more contaminated than ringed seals but less than harp and hooded seals in North Atlantic waters (Figure 2 and Table 1). This suggests that biological characteristics of the animals collected must be considered to make a meaningful comparison of ΣCHB concentrations among seals from eastern Canada. Biological Factors Explaining the Difference of ΣCHB Levels among Seals from Eastern Canada. Several biological factors such as sex, age, nutritive condition, metabolism capacity, and diet of the animals can affect the variability of OC levels in marine mammals (12, 13). Sex. OC concentrations are usually lower in female than in male marine mammals because they are transferred from females to the fetus and neonates via lipid rich tissues or milk, respectively, leading to a depuration of reproductively active females relative to males (12). To simplify the interspecies CHB levels comparison among seals from eastern Canada, only male animals were considered in this study. Age. In adult male marine mammals, OC concentrations increase with age (12, 28). In this study there was no significant difference between the mean age of the four seal species for which the age of the animals was available (Table 1; ANOVA, p > 0.10). The age of hooded seals was unfortunately not determined. However, the body mass of male hooded seals captured in March during the breeding season in the Gulf of St. Lawrence for the 1989-1995 time period was logarithmically related to the age of animals (29). The mean weight

age (yr)

lipids (%)

P26

P50

ref

10a

87 ( 2 92 ( 2 83 ( 2 na na 92 ( 1 na na 90 ( 2 98 ( 1 96 ( 3 91 ( 6 93 ( 5 94 ( 14 92 ( 8 na na na 91 91

155 ( 155 30 ( 18 10 ( 2.5 10 222 136 ( 82 75e 381 2.4 ( 1.5 1.8 ( 0.4 2.6 ( 1.1 9.6 ( 6.5 7.0 ( 4.1 9.8 ( 7.1 11 ( 13 4.0 ( 1.8 6.3 ( 4.2 7.7 ( 4.2 34 32

283 ( 204 30 ( 16 18 ( 3.3 13 221 160 ( 82 90e 697 5.6 ( 5.0 3.1 ( 0.5 4.9 ( 2.4 10 ( 6.8 9.9 ( 5.9 12 ( 9.8 11 ( 16 5.2 ( 2.7 7.5 ( 5.2 9.0 ( 5.4 86 75

this study this study this study 50 50 this study 51 50 this study 52 52 53 53 53 53 54 54 54 55 55

ca. 8.7 ( 3.1b 5.6 ( 0.5 na na 11 ( 4.5 e4 na 9.2 ( 4.0 na na 4.7 ( 3.2 1.4 ( 0.6 2.6 ( 2.4 4.6 ( 5.3 e4 >4 >4 na na b

n ) 3. c Not available. d Concentrations in ng/g lipid weight. e Geometric

of 266 kg determined for hooded seals sampled in this study (Supporting Information) was used according to this relationship to estimate a mean age of about 10 years. This was in the range of the ages determined for other seal species (Table 1). Since the mean age of animals was similar for all species, this biological cofactor is not likely to be responsible for the difference in ΣCHB levels among seals from eastern Canada. Body Condition. The seasonal fluctuation of body mass or, more specifically, of fat mass can result in the concentration or dilution of OCs in the body of marine mammals (12). Consequently, the sampling period needs to be considered, because male seals are known to lose weight during the breeding and molting periods, when the animals reduce their food intake (29, 30), or during the migration, when the animals have a high energetic demand (31). Ringed and gray seals were sampled during the period of molting and just after the breeding periods, which range from mid April to early May and from January to February, respectively (32, 33). At this time of year, animals are believed to be the thinnest in their annual condition cycle (34). Harp seals from the Northwest Atlantic population were sampled early in the breeding season, just after having attained their maxima in mass and blubber thickness (35). Hooded seal samples were obtained early in the breeding period in 1990, when condition levels were also expected to be high (29). Harbor seals from the St. Lawrence Estuary seemed to have a higher condition index (axillary girth divided by standard length) between September and May (28). Harbor seals from the St. Lawrence Estuary were captured during this time period. According to this information, the concentration of CHBs in the body of ringed and gray seals was maximal, because these animals were leanest during the sampling period. In contrast, the dilution of CHBs in the body of harbor, harp, and hooded seals was maximal, since these animals were fattest during the sampling period. Therefore, the impact of the sampling period within the year will reinforce the distribution of ΣCHB levels observed for the seals examined in this study. Sampling Year. Another factor to consider is the impact of the sampling year on the level of toxaphene in seals. Within the SLME, a general exponential decline of CHB concentrations in male and female beluga whales was observed during VOL. 39, NO. 6, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 2. Biological Parameters and Mean Concentrations (ng/g lipid weight) of ΣCHBs ((standard deviation) in Preys of Seals from the SLME (data from 38, 39, and Lebeuf, Unpublished Data) species

sampling year

n

length (mm)

weight (g)

tissue

sample (na)

lipids (%)

∑CHBs (ng/g l wt)

amphipod shrimp sand lance atlantic herring capelin Greenland halibut Greenland halibut

2001 1997 2001 2000 2001 1999 1999

3 3 3 3 3 3 3

nab 28 ( 0.8 122 ( 1.1 246 ( 4.9 130 ( 1.8 428 ( 20 428 ( 20

na 12 ( 0.7 6.8 ( 0.9 107 ( 8.7 16 ( 1.1 740 ( 83 740 ( 83

whole muscle whole liver whole liver muscle

pool (≈15) pool (7-8) pool (7-8) pool (6-8) pool (3) individual individual

1.3 ( 0.8 0.9 ( 0.1 6.5 ( 0.3 3.4 ( 0.2 1.4 ( 0.2 28 ( 4.4 7.3 ( 3.6

13c 6.6c 26 ( 1.0 37 ( 29 90 ( 14 150 ( 110 150 ( 110

a

Number of individuals in each pool.

b

Not available. c CHBs detected in only one sample.

the 1988-1999 time period (7). This suggests that animals sampled in 1990, such as hooded seals, would be more contaminated than other animals collected between 1995 and 2000. However, for male belugas, the reported decline for P26 and P50 was not statistically significant, and the corresponding time to half the concentrations was estimated to be about 20 and 28 years, respectively (7). Since, P26 and P50 were preponderant in all seal species (Figure 3), and assuming a similar temporal trend of the toxaphene contamination in seals to that in SLME belugas, the sampling year was not expected to drastically change the interspecies variations of ΣCHB levels. Biotransformation. Marine mammals can eliminate some of their OC load via elimination mechanisms such as metabolism (36, 37). The potential biotransformation of CHB congeners was investigated by evaluating the accumulation of CHBs in seals relative to their diet. This approach was originally designed to assess the capacity of marine mammals to metabolize PCBs (36). The relative concentration ratios (RRP50) of CHBs were calculated for individual seals in relation to individual prey samples as follows:

RRP50 ) ([Px]/[P50])seal/([Px]/[P50])diet

(1)

where Px and P50 represent the concentrations of a specific CHB and P50, respectively. P50 was chosen as the reference CHB because of its predominance in biological matrixes and since its structural configuration, which is characterized by only one chlorine atom in an alternating 2,3,5,6-endo-exo position at each carbon atom of the structure ring, suggests a high resistance to biotransformation, such as PCB 153 for PCBs (24). Recently, CHB levels were reported in a wide range of fish and invertebrates that are known to be preferential preys of the seal species examined in this study (38, 39, Lebeuf, unpublished data). Animals were sampled in the SLME during the 1997-2001 time period and analyzed using the same analytical method as described previously (Table 2). These prey include Greenland halibut (Reinhardtius hippoglossoides) for hooded seals (40); capelin (Mallotus villosus) for harp seals (31, 41); Atlantic herring (Clupea harengus harengus), capelin, and sand lance (Ammodytes sp.) for harbor seals (42); Atlantic herring and sand lance for gray seals in the southern SLME (43, 44); and crustaceans such as shrimps or amphipods for ringed seals (30, 32). In all seal species, the calculated mean RRP50 for P26 and P44 were statistically close to unity (Figure 4), suggesting little or no biotransformation of these CHBs (36, 45). This result for P26 was expected, because its structural configuration is similar to that of P50. Furthermore, previously reported in vitro results indicated that several marine mammals, including seals, were unable to metabolize either P26 or P50 (37, 46, 47). In addition to P26 and P44, the mean RRP50 for P40/41 in ringed seals was also close to unity. This contrasts with the other seal species, for which mean RRP50 for P40/41 were significantly lower than 0.8 (Figure 4). 1452

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FIGURE 4. Relative concentration ratios (RRP50) of CHBs in seal species to their preferential prey: (A) hooded seal to Greenland halibut; (B) harp seal to capelin; (C) harbor seal to capelin, Atlantic herring, and sand lance; (D) gray seal to Atlantic herring and sand lance; and (E) ringed seal to shrimp and amphipod. Each prey item was assumed to account for the same proportion in the diet composition of seals. *RRP50 g 0.8 (one-tailed t test, p < 0.05). **RRP50 < 0.8 (one-tailed t test, p < 0.05). nc indicates no RRP50 was calculated because CHB concentrations in prey items were below detection limits. Interestingly, the mean RRP50 values for P62 were significantly lower than 0.8 in all seal species, suggesting potential biotransformation of this CHB by seals (Figure 4). Previous in vitro studies have shown that harbor and gray seal species were able to partially metabolize enzymatically this specific CHB to its hydroxylated metabolite (37, 47). Since P26 and P50 were by far the most preponderant CHBs in all species from the SLME and P40/41 was also a preponderant CHB in ringed seals (Figure 3), it is reasonable to think that the metabolism of CHB congeners has only a minor impact on interspecies variations of ΣCHB levels in seals from eastern Canada. Diet. The diet of seals may be a good predictor of their contamination by OCs, because these compounds usually persist in the environment and are highly lipophilic, leading to bioaccumulation in food webs (48). Levels of ΣCHBs in the potential prey of seals are summarized in Table 2. ΣCHB

concentrations ((standard deviation) on a lipid weight basis were about 5 times higher in demersal fish such as Greenland halibut (150 ( 110 ng/g) than in pelagic fish such as herring (37 ( 29 ng/g) or sand lance (26 ( 1.0 ng/g). Capelin contamination was intermediate at 90 ( 14 ng/g. These results indicate that hooded and harp seals, which presented the highest ΣCHBs concentrations in their blubber among the seal species from the SLME (Figure 2), feed on the most contaminated prey items (Table 2). On the other hand, many prey species of harbor and gray seals, which are the least contaminated SMLE phocids (Figure 2), are characterized by low levels of ΣCHBs (Table 2). Finally, the very low ΣCHB levels observed in ringed seals could also be related to part of the diet of these animals in the Arctic environment. The contamination of such noncarnivorous invertebrates is not expected to be as high as that of fish, since they usually have a shorter life span and consequently accumulate less OCs (49). Results in animals from the SLME support this hypothesis, since ΣCHB levels in amphipods or shrimps are about 10 ng/g l wt, which is at least 3 times lower than the lowest concentration observed in fish (Table 2). Moreover, total toxaphene concentrations, in the Canadian Arctic marine ecosystem, were about 5-6 times lower in pelagic amphipods than in fish (49). Results reported in this study indicated that, among the several factors examined, the diet appears to be the main factor to account for interspecies variations in toxaphene contamination in seals from eastern Canada.

Acknowledgments We thank J.-F. Gosselin (DFO-QC); P. Carter (DFO-QC); hunters from the Salluit, Quaqtaq, and Kangirsuk communities; and Dr. M. Kwan (Nunavik Research Center, QC, Canada) for providing seal samples. The assistance of M. Noe¨l (DFOQC) and J. Le´vesque (DFO-QC) for the cleanup of samples was greatly appreciated. Financial support was provided to J.-P.G. and M.L. by the Toxic Substances Research Initiative (TSRI) program conducted by Health Canada, Environment Canada and the Department of Fisheries and Oceans. This work is in partial fulfillment of the Ph.D. requirement (B.G.) of the oceanography program at the University of Que´bec at Rimouski.

Supporting Information Available Table of mean CHB concentrations, lengths, and weights for each seal species. This material is available free of charge via the Internet at http://pubs.acs.org.

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Received for review July 18, 2004. Revised manuscript received November 25, 2004. Accepted November 30, 2004. ES048886K