Environ. Sci. Technol. 2000, 34, 2431-2438
Circumpolar Trends of PCBs and Organochlorine Pesticides in the Arctic Marine Environment Inferred from Levels in Ringed Seals D E R E K M U I R , * ,† F R A N K R I G E T , ‡ MARIANNE CLEEMANN,§ JANNECHE SKAARE,| LARS KLEIVANE,| HARUHIKO NAKATA,⊥ RUNE DIETZ,‡ TORBJØRN SEVERINSEN,# AND SHINSUKE TANABE@ Environment Canada, National Water Research Institute, Burlington, Ontario, L7R 4A6 Canada, Departments of Arctic Environment and Environmental Chemistry, National Environmental Research Institute, Frederiksborgvej 399, DK-4000, Denmark, Department of Pharmacology and Toxicology, Norwegian College of Veterinary Medicine, N-0033 Oslo, Norway, Department of Environmental Sciences, Kumamoto University, 2-39-1 Kurokami, Kumamoto, 860-8555 Japan, Norwegian Polar Institute, N-9296 Tromso, Norway, and Center for Marine Environmental Studies, Ehime University, Tarumi 3-5-7, Matsuyama 790-8566, Japan
Geographical trends in levels of ΣPCB10 (sum of 10 major congeners), hexachlorocyclohexanes (HCH), ΣDDT (sum of DDT-related compounds), and other persistent organochlorines (OCs) in ringed seal blubber were examined at 13 sampling locations in the Arctic over 175 deg longitude from northern Canada to the South Kara Sea (Yenisey Gulf) in Russia. Concentrations of OCs were adjusted, using analysis of covariance, for effects of the covariates, sex, age, and blubber thickness. Adjusted mean concentrations of ΣPCB10 and ΣDDT were significantly higher in the samples from the Yenisey Gulf in the Russian Arctic, Svalbard, and East Greenland than in west Greenland or the Canadian Arctic. ΣPCB10 and ΣDDT in Yenisey Gulf samples were 8× and 6× higher, respectively, than the average in levels from four Canadian locations. ΣPCB10 and ΣDDT means declined significantly with increasing westerly longitude (r 2 ) 0.75 and 0.73, respectively). ΣHCH levels for sites in the Canadian Arctic were significantly higher than those from west Greenland (Qeqertarsuaq), east Greenland (Ittoqqortoormiit), and Svalbard and increased significantly from east to west. The geographical trend ΣHCH is in general agreement with observed trends of HCH in seawater where higher levels have been found in the Canadian Arctic. Higher proportions of more recalcitrant hexa- and pentachloro-PCB congeners were observed in seal blubber samples in the European/Russian Arctic. The continued use of PCBs in electrical equipment and other applications in Russia is a likely source of the more highly chlorinated congeners.
10.1021/es991245i CCC: $19.00 Published on Web 05/18/2000
2000 American Chemical Society
Introduction A recent assessment of contaminants in Arctic marine mammals and seabirds by the Arctic Monitoring and Assessment Program (AMAP) found generally higher mean concentrations of PCBs in ringed seal (Phoca hispida), polar bear (Ursus maritimus), harp seal (Phoca groenlandica), glaucous gull (Larus hyperboreus), and black-legged kittiwake (Rissa tridactyla) in the European Arctic, i.e., northeast Greenland, Svalbard, and northern Norway and Russia, compared to the North American Arctic (1). With the exception of polar bear results, the AMAP assessment involved only sum of PCBs (ΣPCBs) and sums of other organochlorine (OC) pesticides and did not take into account differences in age and male/female ratios and other factors known to influence contaminant levels. In polar bears, Norstrom et al. (2) found significant trends of ΣPCBs, total chlordane (ΣCHL), dieldrin, and p,p′-DDE in adult polar bears, after statistically adjusting for sex and age, along a very large circumpolar transect from Wrangel Island (Chukotka Penninsula, Russia) to Svalbard (Norway). One of the largest circumpolar datasets for OCs in the AMAP report was for ringed seals. However, unlike the work on polar bears, these measurements were made independently by several groups, and no attempt was made to adjust for the effects of age or sex on the apparent geographical trends in contaminant levels or for number of PCB congeners analyzed (1). The ringed seal is the most abundant Arctic pinniped with a circumpolar distribution, making this species an ideal candidate for examining spatial trends of persistent organic pollutants (POPs) in the Arctic. As a top predator in nearshore pelagic food webs, the ringed seal prefers land fast ice or multiyear ice. The ringed seal diet consists of fish, mainly Arctic cod (Boreogadus saida), polar cod (Arctocadus glacialis), and crustaceans (amphipods, mysids, and euphausids). Ringed seals are relatively sedentary, and male ringed seals may occupy the same under ice habitat for up to 9 months (3). Some regional movements, e.g. from the western Canadian Arctic islands to the East Cape of Siberia (3) and between Greenland and Canadian waters (4), have been reported. Concentrations of persistent OCs are known to increase with age in male ringed seals (5) and to be influenced by blubber thickness (6, 7). In this study the research groups that generated the OC data used in the AMAP assessment have combined their original congener specific data for PCBs and other individual OC pesticides to create the first “circumpolar” dataset for ringed seals. The dataset, representing seal populations located over 175 deg longitude from Canada to the South Kara Sea (Yenisey Gulf) in Russia, also includes information on age, sex, and blubber thickness of most samples. Our objectives were to evaluate circumpolar trends in levels and proportions of persistent OCs after adjusting for important covariates and, where possible, to link this information to prevailing levels in seawater and information on sources of these contaminants. * Corresponding author phone: (905)319-6921; fax: (905)336-6430; e-mail:
[email protected]. † Environment Canada, National Water Research Institute. ‡ Department of Arctic Environment, National Environmental Research Institute. § Department of Environmental Chemistry, National Environmental Research Institute. | Norwegian College of Veterinary Medicine. ⊥ Kumamoto University. # Norwegian Polar Institute. @ Ehime University. VOL. 34, NO. 12, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Circumpolar map of the Arctic showing sampling locations of ringed seals.
Materials and Methods Sample Collection. Results for 278 ringed seals from Canada, Greenland, Svalbard, northern Norway, and northwestern Russia were available for this study (Figure 1). Collections were made between 1990 and 1997 at 13 locations, with most samples collected between 1993 and 1995. In the Canadian Arctic archipelago, 80 ringed seal blubber samples were obtained from Pangnirtung, Grise Fiord, Eureka, Arctic Bay, and Resolute during the period 1993-1995 (8). In Greenland, 100 samples were obtained from Avanersuaq (Thule), Ittoqqortoormiit (Scoresbysund), Nanortalik, and Qeqertarsuaq (Disko) in 1994 (9). At Svalbard, 36 samples from western Svalbard and 12 from eastern Svalbard collected in 1995 and 1997, respectively, were available (10, 11). Samples from 12 predominately pups or young-of-the-year ringed seals were available from Jarfjord (N. Norway) collected in 1990 (10). Thirty-eight samples were available from the north Yenisey Gulf near the South Kara Sea collected in 1995 (12). In all cases samples were collected from hunted animals, usually as part of the local subsistence spring hunt (AprilJune). In most cases, samples consisted of both young of the year and adult animals. Sex, weight, and blubber thickness (at the sternum) were determined in the field and were available for almost all animals. A tooth or lower jaw piece was taken for age determination. Ages were determined by longitudinal thin sectioning a lower canine tooth and counting the annual growth layers in the dentine using transmitted light (13, 14) or counting of the cemental layers in decalcified and stained (toluene blue) thin sections (14µ) (15). Samples were shipped frozen to each analytical laboratory. All laboratories stored the samples at -20 to -40 °C and conducted the analysis within about 1 year of sample collection. Chemical Analysis. Each research group extracted and analyzed their blubber samples using established procedures 2432
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(16-19). Lipid was determined gravimetrically on a portion of the extract. Lipid was removed by a sulfuric acid-silica/ alumina multicolumn chromatography (15), chromatography on Florisil (12, 8), or with sulfuric acid wash (17). Separation of PCBs from most OC pesticides was performed on Florisil or silica columns except for samples from Greenland, Svalbard, and N. Norway which were analyzed without preseparation (16, 17). In three of the four labs, OC pesticides and PCB congeners were quantified by GC-ECD using 30 or 60 m fused silica capillary columns. In samples from the Kara Sea, PCB congeners were quantified by GC-MS using selected ion monitoring for tri- to octa-PCBs (12). The number of PCB congeners determined by each group varied. Results for 34 PCB congeners were available for samples from Canada, Norway/Svalbard, and Yenisey Gulf; however, only 10 congeners were determined in the samples from Greenland. A PCB suite common to all locations was obtained using 10 major congeners (CB 28, 31, 52, 101, 105, 118, 138, 153, 156, 180). On average these 10 congeners made up 55% of total PCB congeners in Canadian Arctic ringed seals (sum of 100 congener including coelutions) and 73% of total PCB reported for samples from Svalbard and Jarfjord (sum of 34 congeners). Hereinafter ΣPCB10 refers to the sum of these 10 congeners. Three of the four laboratories (results for Canada, Greenland, and Norway) participated in an international PCB congener interlaboratory comparison (20, 21) on the above 10 congeners during the time the work on samples in this study was conducted. Results for each lab are available (lab # 7, 10, and 69) in a report on the interlab comparison (20). The three laboratories had results (expressed as a relative percent difference) averaging within 9% of the target value for standard solutions of the 10 PCBs and within 15% of target values for CB 28, 52, 101, 105, 118, 138, 153, 156, and 180 for seal oil (21). The laboratory at Ehime University participated successfully in PCB intercomparisons
run by the National Institute of Standards and Technology and the Marine Mammal Health and Stranding Response Program of the National Oceanic Atmospheric Administration, National Marine Fishery Service. Statistical Analysis. Univariate and multivariate statistical analyses were performed using SAS (22). Preliminary work showed that percent lipid differed significantly between locations even though only blubber was analyzed (range of means ) 86.6-95.4%). Based on this, concentrations were expressed on a lipid weight instead of wet weight (lipid weight ) wet weight/fraction lipid). ΣPCB10, ΣDDT (sum of p,p′DDE, DDD, and DDT), ΣHCH (sum of R-, Β-, and γ-HCH), HCB, and trans-nonachlor, were selected for univariate analysis based on the availability of data for all locations. Concentrations were loge-transformed data to reduce skewness. Following log transformation, data for ΣPCB10, ΣDDT, ΣHCH, and t-nonachlor at each location did not statistically deviate from normality. Preliminary analyses also showed that blubber thickness (BT) was an important covariate. Age was also an important covariate and was very different among locations. To adjust mean concentrations of each organochlorine at each location for these covariates we developed an ANCOVA model including location (LOC) and sex as main effects, and age (yrs) and blubber thickness (BT; cm) as covariates and all first-order interaction effects. The first ANCOVA model used was
loge-concentration ) µ + LOC + SEX + Age + BT + LOC*SEX + LOC*Age + LOC*BT + SEX*Age + SEX*BT + Age*BT + (1) where µ is a constant and is an error term and main effects are capitalized. This ANCOVA was then successively reduced for factors not significant at the 5%-level according to Type III Sum of Squares test. The reduced (final) model then only included significant factors. The final model (dependent on contaminant) was used to estimate normalized or adjusted means (22). Results were normalized to a male of 7 years old and with a BT of 3.9 cm (overall mean) in cases where these covariates were included in the final model. Geometric means were obtained by back-transformation of arithmetric means of log-transformed data, and 95% confidence intervals (CI) were calculated as t0.05,df (vs2/n), where s2 is the error mean square derived from the ANCOVA. For principal component analysis (PCA), lipid normalized, untransformed concentration data were used. Prior to PCA, the data for OC pesticides and PCB congeners or for PCB congeners alone were normalized to sum of total OCs or ΣPCBs, respectively. This was done in order to describe patterns rather than the general levels of organochlorines. PCA was performed on the correlation matrix and not the covariance matrix because of the order of magnitude differences in concentrations of some analytes.
Results and Discussion Table 1 gives geometric mean concentrations (unadjusted for age and BT) and ranges for major OC analytes in blubber of male and female ringed seals at all 13 locations along with mean age and BT. Highest concentrations of p,p′-DDE, ΣDDT, CB52, CB153, and ΣPCB10 were present in samples from Yenisey Gulf and Jarfjord in Northern Norway. Lowest levels of these OCs were found in samples from NW Greenland and Arctic Bay (N. Baffin Is.). In the case of R-HCH and ΣHCH, highest levels were found in samples from the Canadian Arctic except for the set of young animals from Jarfjord. The mean ages of animals ranged widely from 28 yrs for males from Grise Fiord to
