Environ. Sci. Techno/. 1995,29, 2877-2885
Persistent Organochlorine Residues and Their Accumulation Kinetics in Baikal Seal (Phoca sibirica) from Lake Baikal, HARUHIKO NAKATA,t SHINSUKE TANABE,*" RYO TATSUKAWA,t MASAO AMANO,* NOBUYUKI MIYAZAKI,* AND EVGENY A. PETROVS Department of Life Environment Conservation, Ehime University, Tarumi 3-5-7, Matsuyama 790,Japan, Otsuchi Marine Research Center, Ocean Research Institute, The University of Tokyo, Akahama, Otsuchi-cho, Iwate 028-11, Japan, and Limnological Institute of the Siberian Division of the Academy of Science of Russia, 664033 Irkutsk, Uran-Batorskaya 3, Russia
Organochlorine compounds (OCs) such as DDTs (DDT and its metabolites), PCBs (polychlorinated biphenyls), CHLs (chlordane compounds), and HCHs (hexachlorocyclohexanes) were determined in the blubber of Baikal seal (Phoca sibirica) and their fish diet collected from Lake Baikal in 1992. Residue levels of DDTs and PCBs were in the ranges of 4.9-160 pg/g and 3.5-64pglg on a lipid weight basis, respectively. The concentrations of CHLs and HCHs were approximately 1 or 3 orders of magnitude lower than those of DDTs and PCBs. Comparison of OC residue levels with those reported for other pinnipeds suggests that Baikal seal is highly contaminated species vulnerable to OC toxicity. A positive age-dependent accumulation of DDTs, PCBs, and CHLs was found in males, while a steady state observed in females suggested the transfer of these chemicals from mother to pup through gestation and lactation. On the basis of contaminant burdens in adult seals, it was estimated that an adult female Baikal seal transfers about 20% of its total DDTs and 14% of its total PCBs to the pup during a reproductive process. Based on the data from isomer-specific analysis of PCBs, it can be suggested that Baikal seals have a higher or comparable capacity to metabolize toxic contaminants than marine mammals, but it is apparently lower than terrestrial mammals, which seems to be a causative factor for the higher accumulation of OC residues in this species.
lntroduetion Lake Baikal, located in eastern Siberia, Russia, (Figure l), is known for many superlatives: the deepest (1632m1,the largest volume of freshwater (one-fif&h of the world's deposits of liquid freshwater), and geologically the most ancient (over 25 million years). Among many unique and endemic animals and plants in this lake, one of the most concern is the Baikal seal, which is a species inhabiting freshwater. They occupy the highest niche in the food chain of Lake Baikal. In 1987 and 1988, an acute disease struck the Baikal seal, and several thousands of animals died (1). Although the direct cause for this outbreak was a morbillivirus infection (1, 21, the potential factors behind the sudden infection by this virus have not been ascertained. Such mass mortalities in marine mammals have frequently been found worldwide in the latter half of this century (3).Since these disasters have mostly occurred nearby industrialized coastal areas (41, it is suspected that some stressors such as chronic exposures to toxic man-made chemicals might have played a role in triggering serious symptoms in epizootics by immunosuppression in mammals (4-6). Previous investigations reported the presence of high levels of OC residues in marine mammals (7,8), and some of them were discussed in association with the occurrence of several abnormalities (8-111, Adverse effects on reproductive and immunological functions were also noted in captive seals fed with high levels of persistent OCs (12, 13). Nevertheless, in contrast to that in marine species, very few investigations are available for freshwater species inhabiting the river and lake. To our knowledge, only four reports are available on OC contamination in Baikal seal (14-17). Studies on the comparative basis for OC accumulationbetween marine and freshwater mammals may explore new clues for understanding the mechanism of toxic action of xenobiotics in the ecosystem. On the basis of these backgrounds,the objectives of the present study are to evaluate the status of OC contamination such as DDTs, PCBs, CHLs, and HCHs in Baikal seal by comparing with those reported for other pinnipeds inhabiting various coastal waters. Furthermore, in order to understand OC accumulation kinetics in Baikal seal, the variations in the levels with sex and age and the specific feature of OC metabolism were assessed in comparison with those of aquatic and terrestrial mammals.
Experimental Section Sample Collection. Baikal seals were collected during May-June 1992 in the southern half of Lake Baikal. All the animals were shot and immediately dissected on-board. Blubber tissues of 27 male and 31 female animals were wrapped in clean polyethylene bags and frozen. The age of the Baikal seals was determined by counting dentinal and cementalgrowth layer groups in decalcified and stained thin sections of lower canine teeth prepared following the method commonly used for small odontocetes (18).Five * To whom correspondence should be addressed. +
Ehime University.
* The University of Tokyo.
Limnological Institute of the Siberian Division of the Academy of Science of Russia.
OOl3-936W95/0929-2877$09.00/0 0 1995 American Chemical Society
VOL. 29, NO. 11, 1995 I ENVIRONMENTAL SCIENCE & TECHNOLOGY
2877
FIGURE 1. Map showing lake Baikal and the locations (open square in closed circle) for collecting Baikal seals,
species of 35 fresh fish samples were also collected from Lake Baikal in 1993. These species are pelagic and known asthemaindiet ofBaikalsealforalltheyear,withexception of an unknown one. AU samples were stored at -20 O C until OC analysis. Chemical Anplysis. DDTs (p,p'-DDE, p.p'-DDD. p,p'DDT, o,p'-DDD,and 0.p'-DDT), PCBs, CHIS (cis-chlordane. trans-chlordane, cis-nonachlor, tmns-nonachlor, and oxychlordane).and HCHs (a, @, and y isomers)were analyzed following the method described by Tanabe et al. (19). A 4-5 g sample of seal blubber was ground with 100 g of Na2S04 using a glass bowl and extracted by Soxhlet apparatus for 8 h with 400 mL of a diethyl ether:hexane (31)solventmkhue. Wholefishsamples(2-loindividuals) from each species and about 15 g of subsamples were employed for Soxhletextraction thesameasabove. Fxtracts were concentrated in volume to 10 mL, and the aliquots (2 mL) were added to 20 g of dry Florisil (WakoPure Chemical Co. Ltd.) packed in a glass column and then dried bypassing through nitrogen gas. OCs adsorbed on Florisilwere eluted with 150 mL of 20% hexane-washed water in acetonitrile and transferred to a separatory funnel containing 600 mL of hexane-washed water and 100 mL of hexane. After partitioning, the hexane layer was concentrated, cleaned up with sulfuric acid, and passed through a 12-g Florisil packedglass columnfor separation The Erstfractioneluted with hexane contained PCBs, p,p'-DDE, and trans-nonachlor, and the second fraction eluted with 20% dichloromethane (DCM) in hexane contained HCHs. p,p'-DDD, o,p'-DDD, o,p'-DDT, p.p'-DDT, and CHIS. Each fraction was concentrated and injected into a RHGC-ECD (Hewlett Packard 5890 Series 11) equipped with moving needletype injection port (splitless and solvent cut mode, Shimadzu. Co. Ltd., Japan)for identification and quantification. TheGCcolumnusedwas fusedsilicacapillarycolumn(0.25 pm i.d. x 30 m length) coated with DB-1 U&W Scientific Co. Ltd., Folson CA,100%dimethyl polysiloxane, 0.25 pm bonded phase). The column oven was programmed from an initial temperature of 160 'C (10 min hold) to a final of 250 "C (20 min hold) at a rate of 2 "Chin. Injector and detector temperatures were maintained at 250 and 300 "C, respectively. Helium and nitrogen were used as canier (20-30 cmh) andmakeup (60mllmin)gases, respectively. 2878. ENVIRONMENTAL SCIENCE &TECHNOLOGY I VOL. 29.
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Dataon the chromatogramfromHRGC-ECDwerecollected with a Hewlett Packard 3396Aintegrator. The concentration of individual OCs was quantifiedfrom the peak area on the sample to that of the correspondingexternal standard. The PCB standard used for quantification was an equivalent mixture of Kanechlors 300,400,500, and 600. Total PCB concentrations were calculated by adding the concentrations of individual resolved peaks. Peak identification of PCB isomers and congeners was followed by a previous report (20). Isomer-specific analysis of PCBs was performed following the alkaline-alcohol digestion method (21). An aliquot of Soxhlet extracts for five adult males and fish samples was analyzed by this method. A 2-mL sample of extracts was refluxed for 1h in 1 N KOH-ethanol solution, followedbyatransferinhexane,andshakeninaseparatory funnel. Further steps of the analysis were similar to those reported by Tanabe et al. (20). Quantification was made using a gas chromatographyhass spectrometer (HewlettPackard5890, GCcoupledwith5970massselectivedetector) employing E1 at 70 eV. A Hewlett-Packard 5970C data system was used to aid the quantification of congeners. For the quantificationof PCB congeners, cluster ions were monitored at m / z 222,256,292,326,360,394,and 430 for di-, tri-. tetra-, penta-, hexa-, hepta-, and octachlorobiphenyls. Recoveries of OCs in the whole analytical procedures were checked three times by spiking 50 ng of pesticides and 3 pg of PCBs to oil. The recoveries were 91 5 7.6% for pesticidesand90f 6.096forPCBs. Thedetectionlimitwas designated to bethreetimesthevalueofblank. Thedetails of recoveries and the detection limit of each compounds are given in Table 1. In thisSNdy, OC concentrationswere not corrected for recovely efficiencies.
Results and Discussion Statusof~ntamlnatlon.OCsweredetectedinallsamples of seal and fishes from Lake Baikal (Table 1). In Baikal seals, DDT compounds were detected at the highest concentration,rangingfrom4.9to lCiOpg/gonalipidweight basis, followed by PCBs (3.5-64pglgh CHIS (0.22-1.9pg/ @, andHCHs (0.028-0.14pg/g). OC residuesinmales were
0
u!
0
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TABLE 2
Comparison of OC Concentrations (Mean, pg/g Lipid Wt) in Adult Baikal Seals with Those of Other Pinneipeds Collected from Varions Watersa species
location
year
n
age (year)
sex
8.5-35.5 6.5-24.5
F
Baikal seal Baikal seal
Lake Baikal Lake Baikal
1992 1992
16 25
ringed seal ringed seal harp seal harp seal
Barrow Strait Barrow Strait Hudson Strait Hudson Strait
1984 1984 1989 1989
Arctic 19 10.3 14 9.4 1 15 1 13
harbour seal grey seal ringed seal harbour seal harbour seal harbour seal harbour seal grey seal grey seal
Skagerrak (Sweden) Baltic Sea Baltic Sea Wadden Sea Wash (England) M. Firth (Scotland) W. Coast (Scotland) Blakeney (England) Fahne Island (England)
1988 1982-88 1981-86 1975-76 1989 1989 1989 1988 1988
harp seal harp seal grey seal grey seal harp seal
Newfoundland-Labrador Newfoundland-Labrador Sable Island (Canada) Sable Island (Canada) St. Lawrence
1970 1970 1976 1985 1989
Weddel seal Weddel seal
Showa station Showa station
1981 1981
4 5 5 8 1 3 1 1 1
CHCH
ref
31 13
1.o 0.47
0.089 0.055
this study this study
M F M F
90 90
U U
0.79 0.53 2.3 0.14
0.63 0.42 1.9 0.40
0.51 0.40 na na
0.30 0.34 na na
23 23 24 24
M M M
84 90 89 U 78 70 67 71 86
7.0 33 340 47 4.6 3.8 2.4 7.1 1.2
84 110 320 700 25 39 28 41 6.6
na na na na na na na na na
na na na 0.40 na na na 0.030
