Persistent Organochlorine Contaminants in Ringed Seals (phoca Hispida) from the Kara Sea, Russian Arctic

Ringed seals collected from the Kara Sea in the Russian Arctic during 1995 were analyzed for persistent organochlorines (OCs) such as DDTs, polychlorinated biphenyls (PCBs), chlordane compounds (CHLs), hexachlorocyclohexanes (HCHs), and hexachlorobenzene to understand the present status of contamination. Noticeably higher levels of DDTs and PCBs were detected in ringed seals from the Russian Arctic when the values compared with same species from the Canadian Arctic and the Norwegian Arctic. This suggests the presence of significant local sources of DDTs and PCBs in Russia or nearby areas. Concentrations of CHLs and HCHs in ringed seals were comparable with those in this species elsewhere in circumpolar regions, probably as a consequence of uniform distribution of CHLs and HCHs due to the atmospheric transport of these compounds to the Arctic region. Larga seals collected from the Sea of Okhotsk were also analyzed for OCs to compare residue levels and accumulation patterns with those in ringed seals. In larga seals, the prominent residues were DDTs and PCBs, with levels comparable or slightly lower than those in ringed seals. Lactational transfer of PCBs, DDTs, and CHLs was evident in ringed seals based on increasing concentrations with age in males but not in females. The transfer rates were estimated to be 38% for DDTs, 25% for PCBs, and 30% for CHLs of the whole body burden in the mature female. Comparison of the PCB congener pattern accumulated in seals suggested that ringed seals have an greater capacity to degrade toxic non-ortho (IUPAC 126) and mono-ortho (IUPAC 105 and 118) coplanar congeners than did Baikal seals, but a lower capacity than found in larga seals. Keywords—Organochlorines Coplanar polychlorinated biphenyls Russian Arctic Ringed seal Larga seal INTRODUCTION Monitoring of persistent organochlorine (OC) contamination in Arctic ecosystems was initiated in 1970 [1] and these contaminants were examined in a wide variety of biota [2,3]. These investigations were conducted in the Canadian and the Norwegian Arctic, Alaska, and Greenland, and documented the widespread occurrence of OCs in these remote areas. Recently, growing evidence indicates that the Russian Arctic environment is far more contaminated than the other parts of Arctic [4]; however, information on the OC levels in this region is very limited. The major objective of this study was to elucidate the present status of contamination by persistent OCs such as DDTs, polychlorinated biphenyls (PCBs), chlordane compounds (CHLs), hexachlorocyclohexane isomers (HCHs), and hexachlorobenzene (HCB) in the Russian Arctic, using ringed seals (Phoca hispida) collected from the Kara Sea. Because the ringed seal is a higher trophic predator in the ecosystem and is known as the most abundant, widespread, and sedentary species of seal in the Arctic [5], it was selected as an useful indicator to use in understanding local contamination by OCs. The OC concentrations in ringed seals were compared with concentrations determined in other studies from throughout the circumpolar region in order to elucidate recent input of OC compounds in this region. Larga seals (Phoca largha) * To whom correspondence may be addressed ([email protected]). collected during 1996 from the Sea of Okhotsk were also analyzed in order to compare the residue levels and accumulation pattern of OCs with those in the ringed seal. To assess possible toxic impact of PCBs, levels of non-, mono-, and di-ortho chlorine-substituted congeners were determined in the ringed seal and larga seal. These congeners are known to show toxic syndromes typical of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) such as carcinogenicity, immunotoxicity, and reproductive abnormalities [6]. Considering the greater contribution of coplanar PCBs to TCDD equivalents (TEqs) than of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in aquatic mammals [7,8], the role of coplanar congeners in exerting toxic impacts might be of great concern. The biodegradation capacity of ringed seal was examined based on PCB profiles in seals and their stomach contents, and these capacities were compared with those from the Baikal seal (Phoca sibirica) and larga seal to evaluate speciesspecific accumulation and risk. MATERIALS AND METHODS Samples Male and female ringed seals were collected in April 1995 from the Yenisei River estuary in the Kara Sea (73830–409N, 80823–329E, near Dikson, Russia; Fig. 1) under a cooperative project with the Russian Academy of Science. At the collection site, animals were dissected, and blubber and other tissues were packed in polyethylene bags. Stomach contents were also obtained from two specimens of ringed seal. Larga seals were 1746 Environ. Toxicol. Chem. 17, 1998 H. Nakata et al. Fig. 1. Map showing the sampling locations of ringed seals and larga seals. collected from the Sea of Okhotsk (northeastern Hokkaido, near Rausu, Japan) (Fig. 1) during February and March 1996. Fish diets (Theragra chalocogramma and Pleurogrammus ozonus) of larga seals were also collected from the same region. Blubber samples of 38 ringed seals (29 males, 9 females) and 13 larga seals (8 males, 5 females) were frozen and shipped to the laboratory, and stored at 2208C until analysis. The age of ringed seals was determined by counting dentinal and cemental growth layer groups of lower canine teeth following the method of Kasuya [9]; no age data were available for larga seals. Some biometric details of seals are given in Table 1. Chemical analysis Analyses of DDTs, PCBs, CHLs, HCHs, and HCB followed the method of Tanabe et al. [10]. Briefly, blubber (3–4 g) and fish samples (approximately 15 g) were homogenized with anhydrous Na2SO4 and extracted with diethyl ether and hexane (4:1) in a Soxhlet extractor (Matsuyama, Japan). After concentrating the extracted solvents, lipid content was determined gravimetrically using an aliquot of the lipid extract. A portion of extracts was added to dry Florisil-packed (Wako Pure Chemical, Osaka, Japan) glass column to separate OCs from lipids, and then fractionated on a wet Florisil-packed glass column. Fraction 1 eluted with hexane contained PCBs, p,p9-DDE, trans-nonachlor, and HCB, and fraction 2 eluted with hexane: dichloromethane (4:1 v/v) contained HCHs, DDTs, and CHLs. Each fraction was concentrated and injected into a Hewlett Packard 5890 Series II (Hewlett-Packard, Avondale, PA, USA) equipped with a fused silica capillary column (30 m 3 0.25mm inner diameter [i.d.]) coated with DB-1 (J&W Scientific, Folsom, CA, USA; 100% dimethyl-polysiloxane, 0.25-mm bonded phase). Concentrations of OC pesticides were quantified in comparison with the corresponding external standard. An equivalent mixture of Kanechlors 300, 400, 500, and 600 (Shinjuku, Tokyo, Japan) was used as an external standard for quantification of PCBs. Concentration of total PCBs was the sum of all congeners detected. Identification of individual PCB congeners has been described by a previous report [11]. An aliquot from the Soxhlet extracts of the three adult ringed seals, three adult larga seals, and the seal diet was analyzed for PCB congeners, including coplanar homologues by following a previously reported procedure [12,13] with some modifications. Quantification was made using a gas chromatograph–mass spectrometer (GC coupled with a 5972 Series Hewlett Packard MS) operated in the electron impact (EI) mode at 70 eV. A fused silica capillary column (30 m 3 0.25mm i.d.) coated with DB-1 was used for the determination of PCB congeners. Helium was used as carrier gas. The column oven was programmed from 1608C (10-min hold) to 2508C (20-min hold) at a rate of 28C/min. Injector and ion-source temperatures were kept at 2508C and 2808C, respectively. The M and (M 2)1 ions from each ion cluster were monitored, including an m/z of 254 and 256 for trichlorobiphenyls, 290 and 292 for tetrachlorobiphenyls, 324 and 326 for pentachlorobiphenyls, 358 and 360 for hexachlorobiphenyls, 392 and 394 for heptachlorobiphenyls, 428 and 430 for octachlorobiphenyls, respectively. Recoveries of OC pesticides and total PCBs through the analytical procedure were examined by spiking 50 ng of pesticide standards and 3.0 mg of PCB standard into corn oil. The results were 91 6 7.6% for OC pesticides and 90 6 6.0% for PCBs. For non-ortho chlorinated coplanar congeners, 90.2 ng for International Union for Pure and Applied Chemistry (IUPAC) 77, 91.0 ng for IUPAC 126, and 30.4 ng for IUPAC 169 were spiked for the recovery test, and 113, 114, and 88% were recovered for IUPAC 77, IUPAC 126, and IUPAC 169, respectively. Detection limits which were three times the value of blank, are given in Table 1. In this study, OC concentrations were not corrected for recovery efficiencies. RESULTS AND DISCUSSION Residue levels Polychlorinated biphenyls, DDTs, CHLs, HCHs, and HCB were detected in all the seals and the fish diet of the larga seal, both from the Kara Sea and from the Sea of Okhotsk (Table 1). Polychlorinated biphenyls and DDTs were the dominant contaminants in ringed seals, ranging from 1,900 to 11,000 ng/g lipid weight (mean 6 SD: 4,200 6 1,900 ng/g) in male and 1,100 to 14,000 ng/g lipid weight (mean 6 SD: 3,600 6 2,400 ng/g) in female. Residue levels of CHLs, HCHs, and HCB were one to two orders of magnitude lower than those of PCBs and DDTs. Polychlorinated biphenyls were most prominent in stomach contents of ringed seals, followed by DDTs, CHLs, HCHs, and HCB. Similarly, PCBs and DDTs were the major contaminants in larga seals from the Sea of Okhotsk. The residue levels were comparable to or slightly lower than those of ringed seal, averaging 3,200 6 1,800 ng/ g lipid weight for PCBs and 2,800 6 1,300 ng/g for DDTs in male larga seals. Mean DDT concentrations in ringed seals from the Kara Sea were comparable to or slightly lower than those in other species of seals from the North Sea and the western Atlantic reported in the 1980s and the early 1990s [14,15]. Levels of DDTs in ringed seals were approximately one order of magnitude lower than those in Baikal seals in Lake Baikal [16] and various species the Baltic Sea [17], but were several times greater than those in the same species in the Canadian Arctic [2] (Fig. 2). Production of DDTs was banned in the former USSR in the 1980s [18]; however, the use of DDT stock for Organochlorines in ringed seals from the Russian Arctic Environ. Toxicol. Chem. 17, 1998 1747 insect control is expected to continue in Siberia [19]. High residue levels of DDTs indicated the presence of local sources of DDT in Russia, and a significant input to the watershed of the Yenisei River and Kara Sea. The mean ratio of p,p9-DDE to DDTs in the ringed seal was 0.85 6 0.04 in males and 0.84 6 0.05 in females. Similar values were observed in larga seals from the Sea of Okhotsk (0.81 6 0.03 in males and 0.83 6 0.05 in females; Table 1) and ringed seals (0.75 6 0.07 in males, 0.79 6 0.09 in females) and walruses (Odobenus rosmarus) (0.82 6 0.11 in males, 0.82 6 0.089 in females) from the Canadian Arctic [20]. On the other hand, relatively lower ratios have been found in Baikal seals (0.56 6 0.14) [16]. The mean ratio of p,p9-DDE to DDTs in stomach contents of ringed seals was 0.62, which was higher than those of fish from some Asian and Oceanian countries (less than 0.40) [21] and Lake Baikal (0.32 6 0.08) [16], where the continuing use of DDTs has been documented. Because p,p9-DDE is a major metabolite of technical DDT, higher p,p9-DDE to DDTs ratios found in ringed seals and their diets from the Kara Sea suggest the past extensive use of DDT in the watershed of the Yenisei River and its tributaries. In addition, the constancy of the ratio among Arctic seals, including ringed seals from the Kara Sea, might suggest that the atmospheric input or the bioavailability of DDT is relatively constant across the Arctic region. Concentrations of PCBs in ringed seals were lower than those in seals from the North Sea [14], and Lake Baikal [16], but were apparently higher than those in the same species from the Canadian Arctic [2] and the Norwegian Arctic [22] (Fig. 3). Noticeably high levels of PCBs were also detected in beluga whales (Delphinapterus leucas) from the White Sea, Russia [23], and harp seals (Phoca groelandica) from the Russian sector outside of the White Sea [24]. In the former USSR, at least 125,000 tons of technical PCBs were produced from the 1940s to the 1990s [25], which is comparable to the quantity produced in Germany, and greater than the quantities produced in the United Kingdom, Japan, and Italy [26]. Elevated concentrations of PCBs found in ringed seals from the Kara Sea imply the presence of significant pollution sources around the Yenisei River and nearby areas. Concentrations of chlorinated biphenyl (CB) 77 in ringed seals were the most prominent among the non-ortho coplanar congeners followed by those of CB 126 and 169 (Table 2). The values were approximately four orders of magnitude lower than the concentrations of total PCBs. This pattern was in accordance with the relative concentrations in Dall porpoise (Phocoenoides dalli), Baird’s beaked whale (Berardius bairdii), killer whale (Orcinus orca), and finless porpoise (Neophocaena phocaenoides) [7]; striped dolphin (Stenella coerulealba) [27]; harbor porpoise (Phocoena phocoena) [28]; and Baikal seals [29], but differed from the pattern in ringed seals in the Canadian Arctic [20] and Svalbard [30], which showed a predominance of CB 126. This variation may be due to different PCBs sources. Levels of coplanar PCBs in larga seals from the Sea of Okhotsk were slightly lower than those in ringed seals from the Kara Sea. Concentrations of CB 77 and CB 126 were similar in larga seals. Unlike PCBs and DDTs, spatial variation in CHL and HCH concentrations were rather small among ringed seals from the Russian Arctic (present study), the Canadian Arctic [2], and the Norwegian Arctic [22] (Fig. 3). Muir et al. [2] reported that CHL and HCH levels in beluga whales were comparable between animals from the Canadian Arctic and from the St. Lawrence River. Nevertheless, PCB and DDT concentrations were much lower in the former region, suggesting long-range atmospheric transport of CHLs and HCHs to the Arctic. It is well known that semivolatile HCHs are transported to Arctic environments via the atmosphere [31]. Limited data are available for HCH levels in terrestrial mammals in the Russian Arctic; however, the concentrations of HCHs seemed less variable across the Arctic than those of DDTs and PCBs [4]. Such an uniform distribution of HCHs in Arctic seawater may provide a plausible explanation for the comparable residue levels found among Arctic seals. In terms of HCH composition, the relatively more biodegradable a-HCH was prominent in ringed seals from the Kara Sea, whereas b-HCH had the highest levels in larga seals from the Sea of Okhotsk. Considerably higher residues of a-HCH rather than g-HCH in marine mammals as well as in water and air from the Arctic and nearby regions have also been reported [18]. Chemical transformation of g-HCH to a-HCH in the environment by ultraviolet radiation [32] and selective removal of g-HCH due to its lower Henry’s law constant [33] are suggested as possible reasons for higher a-HCH concentrations in the Arctic. Enrichment of a-HCH in Arctic water may reflect on the prominent residues of a-HCHs found in marine mammals. Among CHL compounds, oxychlordane was dominant in ringed seals (Table 1). Oxychlordane is one of the major metabolites of chlordane compounds and is not contained in the technical mixture. Because the ratio of oxychlordane to total CHLs is less variable in lower trophic animals [34], the oxychlordane to CHL ratio is an useful indicator for understanding the metabolic capacity of higher animals. The mean oxychlordane to CHLs ratio in ringed seals was 0.51 6 0.09 in males and 0.52 6 0.13 in females. These values were higher than those of cetaceans and some species of pinnipeds [35], such as Weddell seals (Leptonychotes weddelli) (0.19), ribbon seals (Phoca fasciata) (0.24), and harbor seals (0.38), and comparable with those of Baikal seals (0.62 in males, 0.52 in females) [16], suggesting a higher metabolic capacity in ringed seals to CHL compounds. Concentrations of HCB were the lowest among OCs analyzed in ringed seals and larga seals. Residue levels of HCB in female ringed seals from the Kara Sea were comparable to those of seals in the Sea of Okhotsk, the Canadian Arctic (14 ng/g) [20], and the Norwegian Arctic (16–35 ng/g) [22]. Because of high mobility, atmospheric concentrations of HCB are known to be rather uniform over the world. As evidence, HCB residues on plants were dependent on temperature, with greater amounts on samples from colder regions [36]. Similar trends have also been observed in biological samples; higher levels of HCB were detected in some odontoceti species from temperate and cold waters than from those inhabiting tropical regions [37]. Noticeable levels of HCB were also reported in minke whales (Balaenoptera acutorostrata) from higher latitudes such as the Antarctic and the North Pacific [38]. Considering these observations, our results may support the dispersible nature and preferential deposition of HCB in cold water regions. Age trend and sex difference Significant age-dependent accumulations of PCBs, DDTs, and CHLs were found in male ringed seals ( p , 0.05; Mann– Whitney U test), in contrast to those trends observed in females (Fig. 4). A similar pattern has also been recorded in other aquatic mammals [16,39], although older females tend to show 1748 Environ. Toxicol. Chem. 17, 1998 H. Nakata et al. T ab le 1. O rg an oc hl or in e co nc en tr at io ns (n g/ g li pi d w ei gh t) in th e bl ub be r of ri ng ed se al s fr om th e K ar a S ea , la rg a se al s fr om th e S ea of O kh ot sk , an d in th ei r di et s a n B od y le ng th (c m ) B od y w ei gh t (k g) A ge (y ea rs ) L ip id (% ) a -H C H b -H C H g -H C H S H C H H C B O xy ch lo rd an e tr an sC hl or da ne