Environ. Sci. Techno/. 1995, 29, 2877-2885

Persistent Organochlorine Residues and Their Accumulation Kinetics in Baikal Seal (Phoca sibirica) from Lake Baikal,

H A R U H I K O N A K A T A , t S H I N S U K E T A N A B E , * " R Y O T A T S U K A W A , t M A S A O A M A N O , * N O B U Y U K I M I Y A Z A K I , * A N D E V G E N Y A . P E T R O V S 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 028-1 1 , 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 bi- phenyls), CHLs (chlordane compounds), and HCHs (hexachlorocyclohexanes) were determined in the blub- ber 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 contami- nants 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 re- productive 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 ac- cumulation between 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 in- habiting 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 cemental growth 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 oxy- chlordane). 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 Soxhlet extraction thesameasabove. Fxtracts were concentrated in volume to 10 mL, and the aliquots (2 mL) were added to 20 g of dry Florisil (Wako Pure Chemical Co. Ltd.) packed in a glass column and then dried bypassing through nitrogen gas. OCs adsorbed on Florisil were 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-non- achlor, and the second fraction eluted with 20% dichlo- romethane (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 needle- type injection port (splitless and solvent cut mode, Shi- madzu. 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 (60 mllmin) gases, respectively.

Dataon the chromatogramfromHRGC-ECDwere collected with a Hewlett Packard 3396Aintegrator. The concentration of individual OCs was quantified from the peak area on the sample to that of the corresponding external 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 concentra- tions 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 fol- lowing 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 1 h 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 (Hewlett- Packard5890, GCcoupledwith5970massselectivedetector) employing E1 at 70 eV. A Hewlett-Packard 5970C data system was used to aid the quantification of congeners. For the quantification of 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 octachlorobi- phenyls.

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 this SNdy, OC concentrations were 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, rangingfrom4.9 to lCiOpg/gonalipidweight basis, followed by PCBs (3.5-64pglgh CHIS (0.22-1.9pg/ @, andHCHs (0.028-0.14pg/g). OC residuesinmales were

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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

Baikal seal Baikal seal

ringed seal ringed seal harp seal harp seal

harbour seal grey seal ringed seal harbour seal harbour seal harbour seal harbour seal grey seal grey seal

harp seal harp seal grey seal grey seal harp seal

Weddel seal Weddel seal

location

Lake Baikal Lake Baikal

Barrow Strait Barrow Strait Hudson Strait Hudson Strait

Skagerrak (Sweden) Baltic Sea Baltic Sea Wadden Sea Wash (England) M. Firth (Scotland) W. Coast (Scotland) Blakeney (England) Fahne Island (England)

Newfoundland-Labrador Newfoundland-Labrador Sable Island (Canada) Sable Island (Canada) St. Lawrence

Showa station Showa station

year

1992 1992

1984 1984 1989 1989

1988 1982-88 1981-86 1975-76 1989 1989 1989 1988 1988

1970 1970 1976 1985 1989

1981 1981

n age (year) sex

16 8.5-35.5 M 25 6.5-24.5 F

Arctic 19 10.3 M 14 9.4 F 1 15 M 1 13 F

Europe 4 10-22 M 5 9-20 M 5 20-40 M 8 adult U 1 13 M 3 6.1 F 1 9.0 M 1 12 F 1 27 F

North America 1 adult M

13 adult F 6 6.8 F 9 10.6 F

13 10.7 M

Antarctic 1 1 3 o r 1 4 M 1 1 3 o r 1 4 M

fat (YO) 87 87

90 90 U U

84 90 89 U 78 70 67 71 86

85 97 82 94 U

88 88

ZDDT CPCB

64 31 22 13

0.79 0.63 0.53 0.42 2.3 1.9 0.14 0.40

7.0 84 33 110 340 320 47 700 4.6 25 3.8 39 2.4 28 7.1 41 1.2 6.6

50 26 7.1 4.7 16 14 3.7 30 2.1 2.5

0.19 0.043 na na

CCHL

1 .o 0.47

0.51 0.40 na na

na na na na na na na na na

na na na na na

na 0.069

CHCH

0.089 0.055

0.30 0.34 na na

na na na 0.40 na na na 0.030 <0.003

na na na na na

na na

ref

this study this study

23 23 24 24

25,26 25,26 25,26 27 28 28 28 29 29

30 30 31 32 24

33 34

a It is difficult to compare the OC levels in higher trophic animals since biological parameters such as age, sex, and nutritional condition strongly influence OC residue levels. Therefore, data on adult or approximate adult animals were given in this table. U, unknown; na, no data available.

significantly higher than those in females (P < 0.05, Mann- Whitney U-test). This can be due to the transfer of OCs from female to pup through gestation and lactation as documented for other pinnipeds (22). In fishes collected from Lake Baikal, PCBs and DDTs were the dominant components ranging from 0.82 to 3.2 pglg and from 0.47 to 2.0 pglg, respectively (Table 1). CHL and HCH levels were about 1-3 orders of magnitude lower than those of PCBs and DDTs.

Residue levels of OCs found in Baikal seals were compared with those reported for pinnipeds collected from various waters (Table 2). The mean concentration of DDTs in adult Baikal seals was 64 pglg in males and 22 pglg in females, which was about 1 order of magnitude higher than those of seals in the North Sea (28,291 and comparable to harbour seals in the Wadden Sea (27) and grey seals (Hulichoerus grypus) in the Baltic Sea (25, 26) (Table 2). Baltic Sea and Wadden Sea are known as highly contami- nated areas, and previous studies have pointed out the association of the presence of high levels of OCs in seals and diseases such as uterine occlusion and consequently reproductive failure (10, 11).

Among DDT metabolites, p,p’-DDE was the stable compound occupying a major proportion in Baikal seal, while p,p’-DDT was dominant in fishes (Table 1). A ratio of the concentration of p,p’-DDE to total DDTs (p,p’-DDEl DDTs) can be used to know whether it was past or present inputs of technical DDT into the ecosystem. The percentage composition of p,p’-DDEIDDTs in Baikal seal was 61 & 14% in males and 52 f 12% in females, respectively (the average of males and females was 56 f 14%; Table 1). These ratios in Baikal seals were lower than those observed for harbour seals affected by a phocine distemper epizootic

from 1988 in the North Sea around the U.K. coast, recording 66 f 20% (28),66 f 5.7% (291, and 64 & 19% (35). A similar pattern was also observed in fishes from Lake Baikal when p,p’-DDEIDDTs ratios were compared with those in the North Sea (36,37). In the former USSR, agricultural usage of technical DDT and its production were banned in the 1970s and 1980% respectively (38). However, higher concentrations of DDTs and lower p,p’-DDEIDDTs ratios in Baikal seals and their fish diet imply the recent input of technical DDT in the watershed of Lake Baikal. Larger variations of DDT compound compositions in air, water, sediment, and soil samples collected around Lake Baikal also indicated the current usage of technical DDTs nearby this lake (39).

PCB residue levels in adult Baikal seals were 31 pglg in males and 13 pglg in females, which was about half the concentrations of DDTs (Table 2). The observedlevels were comparable to those reported for harbour seals from the North Sea (28,291 and grey seals from Canadian east coast (321, but several times lower than those of ringed seals (Phocu hispida) and grey seals from the Baltic Sea (21,22). In Russia, it was estimated that the technical PCBs, Sovol and trichlorodiphenyls (TCD), were produced at ap- proximately 100 and 25 thousand tons, respectively (40). Relatively higher levels of PCB residues in Baikal seals may suggest its usage or leakage comparable to that of developed nations in this region. Five adult male Baikal seals and their fish diets were subjected to isomer-specific analysis in order to understand the pattern of PCB compositions. The mean profile of representative isomers and congeners is shown in Figure 2. Tri- tetra-, and penta-chlorinated congeners in seals were relativelylower than those observed in fishes, indicating that Baikal seals could metabolize some

2880 ENVIRONMENTAL SCIENCE &TECHNOLOGY / VOL. 29, NO. 11, 1995

3 4 5 6 7 8 Cln

FIGURE 2. PCB isomer and congener compositions in Baikal seal and their fish diet. Relative concentration means the ratio of individual PCB concentrations to that of the maximum peak (IUPAC No. 153) which was treated as 1.

TABLE 3

Percentage Compositions of PCB Congeners in Aquatic Mammals and Their Fish Diets in Lake Baikal, Canandian Arctic, and Ganges River

PCB congeners 2CI 3CI 4CI 5CI 6CI 7CI 8CI

fish 1.4 7.3 45 37 9.3 Baikal seal 1.5 29 53 14 2.5 Arctic cod musclea 3 18 32 29 16 2 ringed seala 1 11 30 45 12 1 fishb 6 20 20 26 20 7 1 GangesRiverdolphinb < I 4 12 35 36 12 1

a Cited from Muir et al. (23). IUPAC Nos. 66/95, 156/171, 157/200, and 172/197 were omitted for calculation because two congeners were mixed. Cited from Kannan et al. (47) .

of the lower chlorinated congeners present in their diet. Hexachlorinated congeners were the dominant ones in Baikal seals, followed by penta-, hepta-, octa-, and tetra- chlorinated homologues (Table 3). The percentage com- position of tetrachlorinated congeners to total PCBs in Baikal seals was 1.5%, considerablylower than that observed for ringed seals from the Canadian Arctic (23) and Ganges River dolphin from India (41 ) . This fact may suggest that Baikal seals may have a higher metabolic capacity to degrade lower chlorinated biphenyls than ringed seals and Ganges River dolphins.

The mean concentrations of CHLs in Baikal seals were 1.0 pglg in adult males and 0.47 pglg in adult females, which was several times lower than those of PCBs and DDTs (Table 2). These levels were comparable to ringed seals from the Canadian Arctic (23) and harbour seals from Hokkaido (421, the northern coast of Japan, which are known as relatively pristine areas. CHL concentrations in Baikal fish (wet wt basis) were also similar to those found in the Canadian Arctic (43). Lower levels of CHLs in Baikal seals and fish support less usage of this insecticide nearby Lake Baikal, as pointed out by Iwata et al. (39) using monitoring data from abiotic samples in this lake. Oxychlordane and trans-nonachlor were the major components of chlordane compounds in Baikal seals, whereas trans- and cis-chlor- dane and trans- and cis-nonachlor were abundant in fishes (Table 1). In higher trophic organisms, chlordane com- pounds are metabolized to two persistent epoxides, such as heptachlor epoxide and oxychlordane (44) . Therefore, the ratio of the concentration of these compounds to total CHLs is a useful indicator in understanding the capacity of animals for metabolizing these compounds. The percent- age composition of CHLs residues in various biota at different trophic levels is given in Figure 3. Plankton,

nekton, and fish have a low proportion of oxychlordane as well as cetaceans compared to pinnipeds, birds, and terrestrial mammals with some exceptions. Baikal seals revealed a higher percentage of oxychlordane among aquatic mammals. Furthermore, the percentage of trans- chlordane was much smaller in Baikal seals (Figure 3) than those of other marine mammals. Kawano (42) indicated that the transformation of chlordane compounds is actively facilitated in higher trophic organisms. Considering these observations, lower residue levels of CHLs in Baikal seals are likely to be attributed to a higher degradation capacity in Baikal seal than other marine mammals as well as less usage of this insecticides in the Lake Baikal region.

The mean HCH concentrations were 0.089pglg in adult males and 0.055 pglg in adult females, 2-3 orders of magnitude lower than those of PCBs and DDTs (Table 2). These levels were approximately 1 order of magnitude lower than those of harp seals (Phoca groenlandica) and ringed seal in the Canadian Arctic (23). Lower HCH concentration in fish was also observed from Lake Baikal when the levels were compared with those in the Canadian Arctic. In the composition of HCH isomers, a-HCH was dominant in fish, whereasp-HCH was the major component and y-HCH was not detected in Baikal seals. Technical HCHs had been used extensively in the former USSR until 1986 (38), and lindane (purified form of 90% y-isomer) is used currently (45). However, low concentrations of HCHs as well as nondetectable levels of y-HCH in Baikal seals suggest less usage of technical HCHs and lindane around Lake Baikal.

Age and Sex Dependent Accumulation. The residue levels of OCs varied with age and sex in Baikal seals. In both the sexes, concentrations of PCBs, DDTs, and CHLs increased until 7-8 years old, which is the maturity age of the Baikal seal (46) . Even after maturity, male animals sequently revealed the positive correlations of OC levels with age, whereas the levels in females remained constant (Figure 4). This pattern is common in cetaceans and pinnipeds, indicating that the uptake of OCs excesses the excretion in animals and appreciable quantities of OCs transfer from mother to her pup during the period of gestation and lactation (47-49). In the case of HCHs, age- dependent accumulation of residue levels was less pro- nounced. Asimilar observation was shown in harbour seal, grey seal (501, and northern fur seal (491, attributing to the biodegradable and less persistent nature of HCHs (49).

In grey seal, about 15% of PCB burden and 30% of DDT burden in the mother were transferred to her pup during the reproductive process (31). To estimate the transfer rates in Baikal seals, we attempted to calculate the body burdens of PCBs and DDTs in mature male and female animals [18.0 yr in males and 26.0 yr in females (46)l . In adult marine mammals, more than 90% of PCB and DDT body burdens was present in the blubber (33,51). Based on this information, the present study tried to estimate the body burdens based on the blubber concentrations and the total weight of this tissue measured for each animal at the time of dissection on-board. The relationship between age and PCB burden in both the sexes is shown in Figure 5. An intersecting point obtained from male and female regression lines indicates the first reproductive year, at 8.4 yr, contained 298 mg of PCBs. It has been reported that 88% of adult female Baikal seals breed every spring (52). Considering this, the body burden of PCBs would be 349 mg in males and 301 mg in females in the next reproductive year. This suggests that 48 mg of PCBs is transferred from the mother

VOL. 29, NO. 11,1995 /ENVIRONMENTAL SCIENCE &TECHNOLOGY 2881

Melon-hcadcd whale

1,500-

5)

9 E e 1,000-

500.

298

. . . . . . . .. - - L Tsrrrrrrinl .- . . mamrnolx

0 20 40 60 80 100

percentage ("a)

FIGURE 3. Comparison nfihe composition of chlordane compounds in various animals. Data were cited from Kawano (42) except Baikal seal and fish.

0 10 20 30 40 0 10 20 M 49

Age (year)

FIGURE 4. Age trends of organochlorine residue levels in male (a) and female IO) Baikal seals.

to her pup in every reproductive season. Then, the elimination rate of PCBs was calculated from the following formula:

female burden = male burden (1-0.01 4

wherepis the transfer rate (%). Consequently, 14% oftotal PCBs in the mother seal was estimated to be transfered to her pup. When the same approach was used for DDTs, 20% of the transfer rate (135 mg of burden) was obtained. PCB and DDT body burdens in four Baikal seals (50.5 yr) were 62 i 22 and 127 * 83 mg. respectively. These d u e s were rather close to the transfer quantities from the mother to her pup (48 mg of PCBs and 135 mg of DDTs). The estimated transfer rates in Baikal seals were comparable to thosereponedingreyseals (31). but apparentlylowerthan those ofstripeddolpbins (53). ThelactationperiodofBaikal and grey seals are known to be 2.5 and 0.5-0.7 months

I IO 20 30 40

8.4 ' o J 0

Age (year)

FIGURE 5. Estimated body burdens of PCBs in adult male (0) and female (0) Baikal seals.

(43, respectively, whereas that of striped dolphin is 18 months (54). Smaller transfer rates of OCs in seals rather than dolphin may reflect the shorter lactation period.

CapadtyandModeofPCB Metabobm As mentioned earlier, the concentration ratio of lower chlorinated PCBs in fish to Baikal seals was considerably lower than those in Ganges River dolphin, suggesting a higher metabolic capacityof Baikalsealthan river dolphin. Inorder to assess further details of metabolic capacity in both species, MI values of PCB isomers and congeners were calculated according to the following model proposed by Tanabe et al. (55):

metabolic index (MIJ = log CR,,,/CR,

where CRleo is the concentration ratio of PCB isomer 180 (IUPAC No.) in fish diets to those in mammals, and CRi is

2882 rn ENVIRONMENTAL SCIENCE &TECHNOLOGY I VOL. 29. NO. 11,1995

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3 4 5 6 7 8 Cln

FIGURE 6. Comparison of the metabolic indices of PCB isomers and congeners in Baikal seal (0) with those of Ganges River dolphin (0). PCB isomers and congeners with asterisk and cross show the lower limits of metabolic index of PCB components that were not detected in seal but were found in fish and were not detected in fish but were found in seal, respectively. larger circles indicate the isomers with both non-met% and para-chlorine substitution. Data for Ganges River dolphin were cited from Kannan et a/. (41).

the concentration ratio of other isomers. PCB isomerswith higher values of MI indicate a more biodegraqable nature than those with lower MI values near zero. The MI values obtained for Baikal seal and Ganges River dolphin (41) are described in Figure 6. It is worthwhile to note that relatively higher values with awider range of MI were found in Baikal seal as compared with those of Ganges River dolphin. Particularly, PCB isomers such as 52 (2,2’,5,5’-tetra-), 49/ 69 (2,2‘,4,5’-tetra-/2,3’,4,6-tetra-), 70 (2,3’,4‘,5-tetra-), 91/ 95 (2,2’,3,4’,6-penta-/2,2’,3,5‘,6-penta-I, 971 113 (2,2’,3’,4,5,- penta-/2,3,3’,5’,6-penta-), and 151 (2,2’,3,5,5’,6-hexa-I showed higher MI values in Baikal seal. All these nine congeners are characterized with the vicinal nonchlorinated metu and para carbons in either ring of biphenyls. Concentrations of PCB isomers and congeners with vicinal H atoms at either metu-pura position or at ortho-metu position with mono-ortho-chlorine were noted to be low in harbour seals (56). In addition, Duinker ul ul. (57) indicated that congeners with vicinal H atoms in metu- para positions were rapidly metabolized more in seals than in cetaceans. Based on these observations, it can be assumed that Baikal seals have a higher metabolic capacity to these PCBs isomers and congeners than those of Ganges River dolphin. On the other hand, MIvalues of PCB isomers 66 (2,3’,4,4’-tetra-), 60 (2,3,4,4’-tetra-), 99 (2,2’,4,4’,5-tetra-), 118 (2,3’,4,4’,5-tetra-), 132 (2,2’,3,3’,4,6’-hexa-), and 138 (2,2’,3,4,4’,5-hexa-) with adjacent ortho and metu carbons

Dall’s porpoise (Bering Sea) Dall‘s porpoise (N. N. Pacific)

Striped dolphin Melon-headed whale Ganges river dolphin

mammals Aquatic 1 Harbour Ribbon Larg h a s e a r seal seal

Baikal seal Black-eared kite

Birds Tufted puffin Black-tailed gull I

Mink L r-

1 Terrestrial mammals

Japanese long-fingered bat

unsubstituted with chlorine atoms were similar between Baikal seal and Ganges River dolphin.

The metabolism of PCB isomers and congeners was associated with hepatic mixed function oxidase such as cytochrome P-450 (58-601, and those having the vicinal nonchlorinated rnetu-para carbons and ortho-metu ones are metabolized by phenobarbital (PB-type) and 3-meth- ylcholanthrene (MC-type) induced microsomal enzymes, respectively (61-64). Considering these observations, it is likely that the Baikal seal has higher PB-type enzyme activities than Ganges River dolphin but comparable activities of MC-type enzymes in both the species.

To assess representative enzyme activities in Baikal seal, MI values of specific PCB isomers in different species of higher animals (55) were compared (Figure 7). Interestingly, MIvalues for PCB isomers metabolized by PB-type enzyme (PCB 52) were higher in Baikal seal as compared to marine mammals but apparently lower than in terrestrial mammals. On the other hand, MI values for PCB isomers metabolized by MC-type enzymes (PCB 66) were lower in Baikal seal, which was comparable to those in cetaceans. Earlier studies demonstrated that cetaceans have a smaller capacity to degrade toxic contaminants due to a poor function both PB- and MC-type enzymes. Therefore, cetaceans are recognized as one of the animal groups receiving high concentrations of persistent OCs (55,65). Baikal seals have a higher capacity to degrade OCs than cetaceans, but on the whole, still lower than other terrestrial mammals (Figure 7). This may be linked to the high accumulation natue of OC residue levels in Baikal seal.

Comparing MI values among pinnipeds, Baikal seals were estimated to have ahigher activity of PB-type enzymes than marine species while apparently having alower activity of MC-type enzymes (Figure 7). This pattern of differences in MIvalues implies the different type of drug-metabolizing enzyme systems in the degradation of xenobiotics and also suggests the occurrence of different types of toxic effects between seals inhabiting freshwater and marine water bodies. Due to the paucity of information on Baikal seals, further studies are needed to confirm the existence of such specific enzyme systems.

Conclusions Persistent OCs such as DDTs, PCBs, CHLs, and HCHs were determined in Baikal seals and five species of fish collected

PB-type MC-type

3 2 1 0 1 2 3 FIGURE 7. Estimated PB-type and MC-type enzyme activities in higher trophic animals by metabolic indices of 2,2’,5,5- and 23.4.4‘- tetrachlorobiphenyls. Data for animals except Baikal seal were cited from Tanabe et a/. (59 and Kannan et a/. (41).

VOL. 29, NO. 11, 1995 / ENVIRONMENTAL SCIENCE S! TECHNOLOGY 2883

from Lake Baikal. Although the contaminations by OCs in air, water, and sediments of Lake Baikal were not so prominent on global terms (391, noticeably high concen- trations of DDTs and PCBs were detected in Baikal seals comparable to those in some species of pinnipeds from the polluted waters such as the North Sea, the Baltic Sea and the Canadian east coast. In this context, it can be concluded that the problem of OCs pollution in Lake Baikal lies on seals that retain them with unexpected high residue levels; nevertheless, the water quality is relatively clean. Based on the results of remarkable accumulation of persistent OCs in Baikal seals due to the lower drug-metabolizing capacity and partly by their reproductive transfer, long- term contamination and concomitant toxic effects over generations are of great concern in this region. Although the decisive linkage between high levels of OC accumulation and mass mortality in Baikal seal is still unclear, the noticeable levels of OC residues might disturb the function of cytochrome P450 monooxygenase and depress the immune system in this animal. Additional research of OCs monitoring including dioxins and related compounds in association with drug-metabolizing enzyme systems are needed to understand comprehensive toxic effects to Baikal seals.

Acknowledgments The authors wish to acknowledge Dr. M. Grachev (Lim- nological Institute of the Siberian Division of the Academy of Sciences of Russia) for directing the present project supported by BICER (Baikal International Center for Ecological Research) and JABIRP (Japan Association for Baikal International Research Program). We gratefully thank the seal hunting team, the captain and crew of the R/V BaZkhash during our sampling in Lake Baikal, and scientists and secretaries of the Limnological Institute of the Siberian Division for their invaluable help and support. Our thanks are also due to Dr. T. Kawai (National Institute for Environmental Study) and Prof. K. Numachi (Faculty of Marine Biology & Fishery Technology, Tokai University, Japan) for arranging and supporting the research and to Dr. K. Kannan (Skidaway Institute of Oceanography) for critical reading of this manuscript. The helpful comments and suggestions of Dr. H. Iwata (Faculty of Veterinary Medicine, Hokkaido University, Japan) and Mr. T. Iida (Takuma Manufacturing Co. Ltd., Japan) are also greatly appreciated. The present study was supported by a grant- in-aid from the International Scientific Research Pro- grammes (Project 04041035 and 07041130) of the Ministry of Eduction, Science and Culture of Japan and from the Nissan Science Foundation.

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Received for review April 3, 1995. Revised manuscript re- ceived June 29, 1995. Accepted June 29, 1995.@

ES950230R

@Abstract published in Advance ACS Abstracts, August 15, 1995.

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