Eds., Y. Murakami, K. Nakayama, S.-I. Kitamura, H. Iwata and... © by TERRAPUB, 2008.

Interdisciplinary Studies on Environmental Chemistry—Biological Responses to Chemical Pollutants,
Eds., Y. Murakami, K. Nakayama, S.-I. Kitamura, H. Iwata and S. Tanabe, pp. 311–320.
© by TERRAPUB, 2008.
Temporal Variation of PCDDs, PCDFs and PCBs
in Baikal Seals (Pusa sibirica)
Daisuke IMAEDA1, Tatsuya K UNISUE1, Yoko OCHI1, Hisato IWATA1,
Oyuna TSYDENOVA1,3, Shin TAKAHASHI1, Masao AMANO2,
Evgeny A. PETROV4, Valeriy B. BATOEV3 and Shinsuke TANABE1
1
Center for Marine Environmental Studies (CMES), Ehime University,
Bunkyo-cho 2-5, Matsuyama 790-8577, Japan
2
Department of Animal Sciences, Teikyo University of Science and Technology,
2525 Yatsusawa, Uenohara-shi, Yamanashi 409-0193, Japan
3
Baikal Institute of Nature Management, Siberian Branch of Russian Academy of
Sciences, Ulan-Ude, Buryatia 670047, Russia
4
The Eastern-Siberian Scientific and Production Fisheries Center,
“VOSTSIBRYBCENTER”, Ulan-Ude, Buryatia 670034, Russia
(Received 16 May 2008; accepted 31 July 2008)
Abstract—This study investigated accumulation features and temporal trends
of dioxins and related compounds (DRCs), such as PCDD/Fs, dioxin-like PCBs
(DL-PCBs), and non dioxin-like PCBs (NDL-PCBs) in the blubber of Baikal
seals collected in 1992 and 2005. PCBs including DL- and NDL-congeners
were dominant. Concentrations of PCDD and PCB congeners in males were
significantly higher than in females. However, such a trend was not observed
for PCDFs. In males, age-dependent accumulations were observed for PCDD,
mono-ortho PCB and NDL-PCB congeners. PCDFs and non-ortho PCBs
showed no such trend, implying that exposure of seals to these contaminants
has been decreasing in recent years. No decreasing temporal trend was observed
for PCDDs, mono-ortho PCBs and NDL-PCBs, suggesting that Baikal seals are
still exposed to relatively high levels of PCDDs and PCBs. TEQs of PCDDs and
mono-ortho PCBs in seals collected in 2005 were within 62–77% of total
TEQs. The TEQ levels in 40% of the specimens exceeded the threshold level
for immunosuppression observed in harbor seals.
Keywords: PCDD/Fs, PCBs, temporal trend, Baikal seal (Pusa sibirica)
INTRODUCTION
Lake Baikal is exposed to considerable influx of anthropogenic pollutants,
because of the rapidly developing industrial activities since the 1960s. Especially,
input of organochlorine compounds (OCs), such as dioxins, PCBs, and DDTs,
into Lake Baikal occurred heavily during the 1990s and possibly even now. High
levels of OCs were detected in Baikal seals and water birds (Iwata et al., 1995;
Nakata et al., 1995; Kunisue et al., 2002), and hence, their toxic effects such as
311
312
D. IMAEDA et al.
immunosuppression have been of great concern.
In Russia, production and use of certain harmful chemicals were banned
since the late 1980s. However, still continuing illegal use of PCBs could be
suspected because 500 tons of Sovol, a technical PCB was produced every year
up to 1992 (Ivanov and Sandell, 1992). Furthermore, in Russia, PCB was used not
only in closed systems like transformers and capacitors but also open systems
such as plasticizers. Therefore, discharge of a large amounts of PCBs to the
environment were noticed. On the other hand, no information on the present
status of dioxins and related compounds (DRCs) such as polychlorinated dibenzop-dioxins (PCDDs), dibenzofurans (PCDFs) and dioxin-like PCBs (DL-PCBs) in
Lake Baikal is available. Previously, our study group elucidated contamination
status of DRCs in Baikal seals collected in 1992 (Iwata et al., 2004), and
demonstrated that the DRC concentrations were higher than those in other seal
species collected from various regions of the world and the TEQ levels exceeded
the estimated threshold concentrations for immunosuppression reported in harbor
seal (Ross et al., 1995). From these facts, recent contamination and toxic impacts
of PCDDs, PCDFs, and PCBs in Baikal seals are still of concern.
The objectives of this study are to understand the contamination status,
accumulation features such as gender-difference, age-dependent variation and
temporal trends of PCDDs, PCDFs and PCBs by analyzing blubber samples of
Baikal seals collected in 1992 and 2005. In addition, the possible risk by PCDDs,
PCDFs and PCBs to Baikal seals is also discussed.
MATERIALS AND METHODS
Baikal seals were collected by shooting from Lake Baikal in 1992 and 2005
under license from local government by shooting and were immediately dissected.
Blubber samples of 10 males (age: 0.5–35.5) in 1992, and 10 males (age: 0.25–
41.5) and 10 females (0.25–41.5) in 2005 were obtained and stored in
Environmental Specimen Bank for Global Monitoring (es-BANK) of Ehime
University (Tanabe, 2006) at –25°C until analysis.
The PCDD/Fs and DL-PCBs were analyzed following the method described
previously (Tanabe et al., 2004). Briefly, blubber samples (3 g) were ground with
anhydrous sodium sulfate and extracted in a Soxhlet apparatus with
dichloromethane (DCM). The extract was concentrated and an aliquot of the
extract was used for lipid determination by gravimetric method. 13C12-labeled
PCDD/Fs and DL-PCBs were spiked into the remaining extract as internal
standards (IS). Lipid in this solution was removed by gel permeation
chromatography (GPC). The first fraction containing lipid was discarded, and the
second fraction containing PCDD/Fs and DL-PCBs was collected, concentrated
and passed through activated silica-gel packed in a glass column. PCDD/Fs and
DL-PCBs were eluted with hexane. After concentration, the cleaned up extract
was spiked onto activated alumina packed in a glass column. The first fraction
eluted with hexane contained most of the mono-ortho PCBs, and the second
fraction eluted with 50% DCM in hexane contained the remaining mono-ortho
PCBs, non-ortho PCBs and PCDD/Fs. Then the second fraction was passed
a
a
35
±
140
170
100
770
±
±
420
2300
±
3.7
SD
1.4
±
250
3800
850
(25−32)
32
1300
150
430
2000
25
770
12
Median
500
2100
15000
36
1300
110
Mean
(310−510)
(1700−3100)
(100−170)
(550−900)
(23−25)
(8.8−16)
Range
150
450
3300
27
730
16
Mean
Samples collected in 2005
Female
(160−360)
(2100−4200)
(480−1200)
(960−1600)
(12−40)
Range
26
Median
Immature (n = 3)
±
12
24
740
±
1100
±
Mean
350
±
98
300
±
±
14
4.0
SD
Immature (n = 3)
±
±
260
830
3400
26
30
1300
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
410
9700
2000
26
1300
73
60
180
1800
260
8.4
7.0
SD
120
380
3300
25
700
11
Median
Mature (n = 7)
300
12000
1200
570
85
26
Median
Mature (n = 7)
SD
Range
(240−760)
(980−6100)
(82−250)
(460−1100)
(19−42)
(9.8−26)
Range
(170−950)b*
(2600−35000)b,*
(640−3600)b,**
(760−2300)b,*
(18−93)
(17−230)b,*
ng/g lipid wt.
Concentrations in mature male were significantly higher than those in mature female. *p < 0.05; **p < 0.01.
b
a
∑non dioxin-like PCBsa
∑TEQ
∑mono-ortho PCBsa
∑PCDFs
∑non-ortho PCBs
∑PCDDs
∑TEQ
∑non dioxin-like PCBs
∑mono-ortho PCBs
∑PCDDs
∑PCDFs
∑non-ortho PCBs
Mean
Samples collected in 2005
Male
Table 1. Concentrations (pg/g lipid wt.) of PCDDs, PCDFs and PCBs in the blubber of Baikal seals
collected in 1992 and 2005.
Temporal Variation of PCDDs, PCDFs and PCBs in Baikal Seals (Pusa sibirica)
313
314
D. IMAEDA et al.
Table 2. Relationships between age and concentrations of dioxins and related compounds and non
dioxin-like PCBs in the blubber of Baikal seal collected in 2005.
Male (n = 10)*
a
b
r2
Female (n = 10)*
p
a
b
r2
p
Dioxins and related compounds
PCDDs
2,3,7,8-T4CDD
1,2,3,7,8-P5CDD
1,2,3,4,7,8-H6CDD
1,2,3,6,7,8-H6CDD
1,2,3,7,8,9-H6CDD
0.99
3.1
0.065
0.35
0.041
1.8
0.74
1.1
1.5
0.42
0.86
0.85
0.8
0.83
0.81
<0.001
<0.001
<0.001
<0.001
<0.001
0.0035
0.069
0.0253
0.052
0.0072
2.8
6.7
0.88
1.6
0.32
0.0023
0.090
0.51
0.40
0.35
0.89
0.40
<0.05
<0.05
0.071
PCDFs
2,3,7,8-T4CDF
1,2,3,7,8-P5CDF
0.27
0.22
12
7.6
0.23
0.12
0.16
0.33
0.068
−0.021
14
8.0
0.059
0.018
0.50
0.71
0.065
5.1
0.060
0.50
−0.011
4.0
0.019
0.70
Non-ortho PCBs
3,3′,4,4′-T4CB (#77)
1.7
88
0.16
0.26
0.43
20
0.38
0.057
3,4,4′,5-T4CB (#81)
1.8
100
0.32
0.091
−0.017
66
0.00021
0.97
3,3′,4,4′,5-P5CB (#126)
11
860
0.13
0.30
−2.0
640
0.020
0.70
3,3′,4,4′,5,5′-H6CB (#169)
0.63
21
0.48
<0.05
0.31
20
0.29
0.11
1700
99000
0.90
<0.0001
180
88000
0.0059
0.83
1600
44000
15000
350000
0.90
0.91
<0.0001
<0.0001
31
340
12000
260000
0.014
0.0034
0.74
0.87
2,3,4,7,8-P5CDF
Mono- ortho PCBs
2,3,3′,4,4′-P5CB (#105)
2,3,4,4′,5-P5CB (#114)
2,3′,4,4′,5-P5CB (#118)
2′,3,4,4′,5-P5CB (#123)
110
6900
0.57
<0.05
100
4100
0.15
0.26
2,3,3′,4,4′,5-H6CB (#156)
4300
39000
0.87
<0.0001
600
31000
0.19
0.20
2,3,3′,4,4′,5′-H6CB (#157)
2300
6800
0.91
<0.0001
210
9000
0.26
0.13
2,3′,4,4′,5,5′-H6CB (#167)
1500
11000
0.92
<0.0001
190
8400
0.23
0.16
2,3,3′,4,4′,5,5′-H7CB (#189)
190
1600
0.87
<0.0001
69
1400
0.32
0.090
through activated carbon-dispersed silica gel packed in a glass column. The first
fraction was eluted with 25% DCM in hexane to obtain the remaining mono-ortho
PCBs and combined with the first fraction separated by alumina column. Nonortho PCBs and PCDD/Fs were eluted with toluene as the second fraction. Both
fractions were concentrated to near dryness. 13C12-labeled CB-157 prepared in
decane was added in the combined first fraction, and 13C12-labeled 1234-T4CDD
and 123789-H6CDD with decane were added in the second fraction. Identification
and quantification were performed using a gas chromatograph (GC: Agilent 6890
series) with an auto injection system and a bench-topped double-focusing mass
selective detector (MS: JEOL GC-Mate II) for mono-ortho PCBs and a high
resolution MS (JEOL JMS-800D) for non-ortho PCBs and PCDD/Fs.
NDL-PCBs were analyzed as follow the method. Briefly, blubber samples
(2 g) were ground with anhydrous sodium sulfate and extracted in a Soxhlet
apparatus with diethyl ether/hexane (3:1). The extract was concentrated and
13
C12-labeled PCBs were spiked into an extract as internal standard. Lipid in this
extract was removed by GPC. The second fraction of GPC including PCBs was
concentrated and passed through the activated silica gel packed in a glass column.
PCBs were eluted with 5% DCM in hexane, and this fraction was concentrated to
Temporal Variation of PCDDs, PCDFs and PCBs in Baikal Seals (Pusa sibirica)
315
Table 2. (continued).
Male (n = 10)*
a
Non dioxin-like PCBs
2,4,4′-T3CB (#28)
2,2′5,5′-T4CB (#52)
2,2′4′,5-T4CB (#49)
2,4,4′,5-T4CB (#74)
2,2′,3,5′,6-P5CB (#95)
2,2′,4,5,5′-P5CB (#101)
2,2′,4,4′,5-P5CB (#99)
2,3′,4,4′,6-P5CB (#119)
2,2′,3,4,5′-P5CB (#87)
2,3,3′,4′,6-P5CB (#110)
2,2′,3′,4,5,6′-H6CB (#149)
2,2′,4,4′,5,5′-H6CB (#153)
2,2′,3′,4,4′,5-H6CB (#138)
2,3,3′,4,4′,6-H6CB (#158)
2,2′,3,3′,4,4′-H6CB (#128)
2,2′,3,3′,5,5′,6-H7CB (#178)
2,2′,3,4′,5,5′,6-H7CB (#187)
2,2′,3,4,4′,5′,6-H7CB (#183)
2,2′,3,3′,4′,5,6-H7CB (#177)
2,2′,3,3′,4,4′,6-H7CB (#171)
2,2′,3,4,4′,5,5′-H7CB (#180)
2,2′,3,3′,4,4′,5-H7CB (#170)
2,2′,3,3′,5,5′,6,6′-O8CB (#202)
2,2′,3,3′,4′,5,5′,6-O8CB (#199)
2,2′,3,3′,4,4′,5,5′-O8CB (#194)
2,3,3′,4,4′,5,5′,6-O8CB (#205)
2,2′,3,3′,4,5,5′,6,6′-N9CB (#208)
2,2′,3,3′,4,4′,5,5′,6-N9CB (#206)
2,2′,3,3′,4,4′,5,5′,6,6′-D10CB (#209)
b
Female (n = 10)*
r2
p
a
b
r2
p
0.042
0.21
12
18
0.052
0.19
0.53
0.21
−0.078
0.0055
11
15
0.43
0.000095
<0.05
0.98
0.052
3.5
0.23
11
67
2.5
1.5
2.4
6.1
300
73
3.8
0.90
4.5
92
8.2
240
87
11
61
110
45
−170
260
9.3
6.3
0.18
0.67
0.27
0.51
0.73
0.68
0.62
0.26
0.57
0.85
0.63
0.52
0.33
0.22
<0.01
0.13
<0.05
<0.01
<0.01
<0.01
0.13
<0.05
<0.001
<0.01
<0.05
0.085
0.00055
0.081
0.041
0.27
0.067
0.0052
0.068
−0.30
0.32
12
4.3
0.17
0.035
3.9
67
7.3
190
220
5.0
43
80
50
600
360
16
7.6
0.000016
0.0020
0.012
0.0014
0.00011
0.00093
0.0017
0.018
0.018
0.19
0.091
0.058
0.0076
0.99
0.90
0.76
0.92
0.98
0.93
0.91
0.71
0.71
0.21
0.40
0.50
0.81
6.4
11
13
0.77
2.7
70
27
2.3
7.4
13
1.3
1.3
7.6
2.1
−2.2
3.4
−7.3
1.8
−1.6
−31
4.9
−5.0
−14
−26
−1.9
−3.1
−15
−4.7
0.87
0.68
0.83
0.48
0.85
0.85
0.83
0.82
0.82
0.75
0.71
0.69
0.63
0.55
<0.0001
<0.01
<0.001
<0.05
<0.001
<0.001
<0.001
<0.001
<0.001
<0.01
<0.01
<0.01
<0.01
<0.05
0.66
1.6
1.7
0.11
0.26
8.7
2.4
0.36
1.3
2.0
0.19
0.25
1.5
0.51
14
30
25
3.2
4.9
120
42
3.0
7.4
8.9
1.0
1.1
4.0
0.69
0.31
0.29
0.42
0.14
0.39
0.42
0.39
0.49
0.55
0.52
0.49
0.55
0.56
0.71
0.096
0.11
<0.05
0.29
0.052
<0.05
0.055
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.01
*Concentration (pg/g lipid wt.) = a × age (year) + b.
H7–O8CDDs and H 6–O8CDFs were not examined because concentrations of these congeners
were below detection limit values in all the samples.
near dryness. Identification and quantification were performed using a GC
(Agilent 6890 series)-MS (Agilent 5973N).
TEQs were calculated using the mammalian TEFs proposed by WHO in
1998 (Van den Berg et al., 1998).
The decline of DRC and PCB levels in the blubber of Baikal seals were
calculated using the following equation:
Ct = C0 × e–kt
where C 0 and C t are the concentrations of the first (1992) and the last (2005)
investigation, respectively. k is the constant and t is the time interval (13 years)
between the investigations. Half-life times (t dec1/2) was defined as the duration in
316
D. IMAEDA et al.
Table 3. Comparison of DRCs concentrations (pg/g lipid wt.) in male blubber of Baikal seals
collected in 1992 and 2005 and estimated half-lives of DRCs.
Congener
Samples collected in 2005
Dioxins and related compounds
PCDDs
2,3,7,8-T4CDD
Mean
±
SD
Range
Samples collected in 1992
Mean
±
SD
Range
Half-life
k
t1/2 (year)
18
±
17
(3.1−51)
26
±
19
(3.4−64)
0.0430
16.1
1,2,3,7,8-P5CDD
1,2,3,4,7,8-H6CDD
1,2,3,6,7,8-H6CDD
53
2.2
7.2
±
±
±
55
1.2
6.0
(6.8−160)
(0.6−3.9)
(1.4−19)
65
4.1
13
±
±
±
51
2.3
9.4
(9.3−170)
(1.6−8.1)b,*
(3.2−31)
0.0419
0.0496
0.0643
16.5
14.0
10.8
1,2,3,7,8,9-H6CDD
1.1
±
0.73
(0.36−2.3)
2.0
±
1.3
(0.67−4)
0.0487
14.2
PCDFs
2,3,7,8-T4CDF
1,2,3,7,8-P5CDF
2,3,4,7,8-P5CDF
Non-ortho PCBs
3,3′,4,4′-T4CB (#77)
3,4,4′,5-T4CB (#81)
3,3′,4,4′,5-P5CB (#126)
3,3′,4,4′,5,5′-H6CB (#169)
17
±
8.9
(8−37)
49
±
27
(13−84)b,**
0.0812
8.50
11
6.1
±
±
10
4.1
(3.7−39)
(2.6−16)
63
30
±
±
36
15
(27−130)b,***
(12−56)b,***
0.135
0.139
5.12
4.99
120
130
1000
±
±
±
68
52
460
(24−220)
(54−220)
(530−2100)
220
350
2300
±
±
±
440
220
1100
(12−1500)
(110−730)b,**
(920−4600)b,**
0.0801
0.0578
8.70
12.0
32
±
15
(13−62)
55
±
28
(17−110) *
0.0336
20.6
380
41
±
±
290
27
(110−840)
(13−91)
420
49
±
±
280
28
(72−900)
(11−87)
0.0221
0.0210
31.4
33.0
1100
8.8
±
±
740
2.3
(300−2300)
(6.1−12)
1100
13
±
±
730
6.7
(230−2200)
(4.4−24)
0.0139
0.0189
49.9
36.7
110
45
36
4.8
±
±
±
±
71
38
25
3.4
(29−240)
(8.2−120)
(9.4−79)
(1.4−11)
140
46
52
9.2
±
±
±
±
86
33
36
6.6
(32−300)
(8.3−100)
(10−120)
(2.0−22)
0.0217
0.0209
0.0277
0.0418
31.9
33.2
25.0
16.6
b,
NCc
a
Mono-ortho PCBs
2,3,3′,4,4′-P5CB (#105)
2,3,4,4′,5-P5CB (#114)
2,3′,4,4′,5-P5CB (#118)
2′,3,4,4′,5-P5CB (#123)
2,3,3′,4,4′,5-H6CB (#156)
2,3,3′,4,4′,5′-H6CB (#157)
2,3′,4,4′,5,5′-H6CB (#167)
2,3,3′,4,4′,5,5′-H 7 CB (#189)
which initial concentrations decrease to half.
Mann-Whitney U test was used for gender-differences and temporal trends
analysis. Regression analysis was carried out to examine the relationships
between age and concentrations of PCDD/Fs and PCBs. A p value of less than
0.05 was considered to indicate statistical significance. These analyses were
executed using Statcel 97 for Excel.
RESULTS AND DISCUSSION
Contamination status and gender difference
DRCs, except H6-H7CDFs and O8CDD/Fs, were detected in all the blubber
samples (Table 1). In the specimens collected during 2005, mono-ortho PCBs
were dominant followed by non-ortho PCBs > PCDDs > PCDFs in males and in
females the pattern was non-ortho PCBs > PCDFs > PCDDs. Concentrations of
DL-PCBs were 4–5 orders of magnitude higher than those of PCDD/Fs.
Concentrations of almost all the PCDD and DL-PCB congeners in male were
significantly higher than those in females, suggesting excretion of these
contaminants by parturition and lactation. On the other hand, no gender-difference
was observed for PCDFs. This could be due to the lower transfer potency of PCDF
congeners to pup by parturition and lactation compared with PCDDs and DL-
Temporal Variation of PCDDs, PCDFs and PCBs in Baikal Seals (Pusa sibirica)
317
Table 3. (continued).
Congener
Non dioxin-like PCBsa
2,4,4′-T3CB (#28)
2,2′5,5′-T4CB (#52)
2,2′4′,5-T4CB (#49)
2,4,4′,5-T4CB (#74)
2,2′,3,5′,6-P5CB (#95)
2,2′,4,5,5′-P5CB (#101)
2,2′,4,4′,5-P5CB (#99)
2,3′,4,4′,6-P5CB (#119)
2,2′,3,4,5′-P5CB (#87)
2,3,3′,4′,6-P5CB (#110)
2,2′,3′,4,5,6′-H6CB (#149)
2,2′,4,4′,5,5′-H6CB (#153)
2,2′,3′,4,4′,5-H6CB (#138)
2,3,3′,4,4′,6-H6CB (#158)
2,2′,3,3′,4,4′-H6CB (#128)
2,2′,3,3′,5,5′,6-H7CB (#178)
2,2′,3,4′,5,5′,6-H7CB (#187)
2,2′,3,4,4′,5′,6-H7CB (#183)
2,2′,3,3′,4′,5,6-H7CB (#177)
2,2′,3,3′,4,4′,6-H7CB (#171)
2,2′,3,4,4′,5,5′-H7CB (#180)
2,2′,3,3′,4,4′,5-H7CB (#170)
2,2′,3,3′,5,5′,6,6′-O8CB (#202)
2,2′,3,3′,4′,5,5′,6-O8CB (#199)
2,2′,3,3′,4,4′,5,5′-O8CB (#194)
2,3,3′,4,4′,5,5′,6-O8CB (#205)
2,2′,3,3′,4,5,5′,6,6′-N9CB (#208)
2,2′,3,3′,4,4′,5,5′,6-N9CB (#206)
2,2′,3,3′,4,4′,5,5′,6,6′-D10CB (#209)
Samples collected in 2005
Mean
±
SD
Range
13
21
5.4
150
12
430
1200
53
86
150
150
4800
1500
73
21
100
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
2.7
7.9
2.0
68
7
260
1200
49
31
76
130
5100
1500
85
25
110
180
220
15
44
1100
450
33
110
190
19
±
±
±
±
±
±
±
±
±
±
19
110
31
±
±
±
Samples collected in 1992
Mean
±
SD
(7.7−16)
(11−41)
(2.8−10)
(70−250)
(5.5−31)
(190−1100)
(250−4200)
(14−170)
(43−140)
(67−350)
(42−490)
(550−15000)
(380−5300)
(18−300)
(6.3−92)
(14−320)
21
27
6.6
240
18
600
1200
63
200
220
210
3800
2000
110
40
100
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
9.5
7.6
1.8
130
8.6
400
1200
61
180
130
190
3800
2000
130
49
100
200
240
18
48
1200
460
41
130
240
24
(35−700)
(25−730)
(3.4−63)
(4.7−140)
(100−3300)
(36−1300)
(2.7−120)
(6.8−370)
(7.1−610)
(0.71−63)
250
260
25
45
1200
390
31
110
180
17
±
±
±
±
±
±
±
±
±
±
25
150
47
(0.62−73)
(2.4−380)
(0.45−120)
19
120
31
±
±
±
Range
Half-life
k
t1/2 (year)
(9.6−40)
(16−40)b,*
(4.1−9.3)
(62−410)
(8.2−38)
(160−1500)
(160−4200)
(11−210)
(39−650)b,*
(80−530)
(42−680)
(370−12000)
(260−6900)
(16−460)
(7.4−170)b,*
(8.7−310)
0.0353
0.0172
0.0197
0.0312
0.0408
0.0200
0.0096
0.0116
0.0373
0.0369
0.0119
0.00670
0.0148
0.0248
0.0476
0.0202
19.6
40.3
35.2
22.2
17.0
34.7
72.2
59.7
18.6
18.8
58.2
103
46.8
27.9
14.6
34.3
290
270
33
47
1200
410
35
120
210
18
(22−980)
(21−900)
(2.6−110)
(3.8−150)
(86−3700)
(28−1300)
(1.9−110)
(5.6−370)
(8.6−650)
(0.9−56)
0.0172
0.0206
0.0129
0.0146
0.0218
0.00670
0.0292
0.0266
0.0404
0.0415
40.3
33.7
53.7
47.5
31.8
103
23.7
26.1
17.2
16.7
23
140
40
(0.84−72)
(4.5−430)
(1.1−110)
0.0308
0.0523
0.0428
22.5
13.3
16.2
a
ng/g lipid wt.
Concentration in Baikal seals collected in 1992 was higher than those collected in 2005. *p
< 0.05; **p < 0.01; ***p < 0.001.
c
Not calculated because of higher median concentration in 2005 than in 1992 samples.
1,2,3,4,6,7,8-H 7CDD, O 8CDD, 1,2,3,4,7,8-, 1,2,3,6,7,8-, 1,2,3,7,8,9-, 2,3,4,6,7,8-H6CDF,
1,2,3,4,6,7,8-, 1,2,3,4,7,8,9-H7CDF, and O8CDF were not shown due to concentrations below
detection limits.
b
PCBs and/or decline of recent exposure to PCDF congeners.
NDL-PCB levels were in the range of 2100–35000 ng/g lipid wt. in males and
980–6100 ng/g lipid wt. in females (Table 1). Concentrations of almost all the
NDL-PCB congeners in males were significantly higher than those in females,
suggesting elimination of these contaminants via lactation. However, no genderdifference was observed for high chlorinated congeners such as Cl8–Cl 10,
suggesting possible lower transfer rates of these contaminants to milk due to their
large molecular size.
Age-dependent accumulation
When the relationships between age and concentrations of DRC congeners
were examined in Baikal seals collected in 2005, no age-dependent accumulation
318
(A)
D. IMAEDA et al.
(B)
Ringed seal
(Arctic)
Harp seal (USA)
Grey seal (USA)
Ringed seal
(Greenland)
Hooded seal (USA)
Grey seal
(Sable Island)
Harbor seal (USA)
Harbor seal
(Puget Sound)
Harbor seal (UK)
Harbor seal
(Strait of Georgia)
Ringed seal (Russia)
This study (2005)
This study (2005)
0
100
200
300
TEQ (pg/g lipid wt.)
400
500
0
10
20
30
40
Concentration (µg/g lipid wt.)
Fig. 1. Comparison of TEQ (A) and NDL-PCB (B) concentration in pinnipeds.
was observed for females (Table 2), suggesting that these contaminants are
transferred from mother to pup via placenta and milk. On the other hand,
significant age-dependent accumulation of all PCDD and mono-ortho PCB
congeners was found for males (Table 2). However, concentrations of PCDFs and
non-ortho PCBs in males did not increase with age (Table 2). This may indicate
that the exposure of Baikal seals to PCDFs and non-ortho PCBs has been
decreasing in recent years and/or these contaminants are more easily metabolized
by Baikal seals than PCDDs and mono-ortho PCBs.
Significant age-dependent accumulation of almost all NDL-PCB congeners
was found for males. However concentrations of CB-28, 49, 52, 95 and 128 in
males did not increase with age, suggesting that these contaminants are more
easily metabolized by Baikal seals. On the other hand, significant age-dependent
accumulation of 8-10 chlorinated congeners was found in both males and females
which may be due to their lower transfer rates to milk because of their large
molecular size.
Temporal trend
Comparison of the data between 1992 and 2005 showed a significant
decreasing trend of PCDFs and non-ortho PCBs except for CB-77 (Table 3),
suggesting a decline of exposure to these compounds. But no such significant
difference was observed for PCDDs, mono-ortho PCBs and NDL-PCBs (Table
3). When the half-lives of DRCs and NDL-PCBs were calculated using the data
of 1992 and 2005 samples, longer half-lives for PCDDs, mono-ortho PCBs and
NDL-PCBs than PCDFs and non-ortho PCBs were found, implying the presence
of higher sources of the former compounds in and around Lake Baikal. It is likely
that the sources of mono-ortho PCBs and NDL-PCBs are derived from Sovol, a
technical PCB used in the Soviet Union, in which these compounds are abundant,
but PCDD sources can not be clearly explained. As another possible reason why
no decline of PCDD levels was noticed between 1992 and 2005 samples, it can
be assumed that PCDD congeners may be more persistent than PCDF congeners
Temporal Variation of PCDDs, PCDFs and PCBs in Baikal Seals (Pusa sibirica)
319
in Baikal seals. Considering these observations, continuous investigations on
DRCs in Baikal seals are needed to comprehend temporal trends and assessment
of their risk.
Risk assessment
TEQ levels were significantly higher in males with the range of 160–950 pg
TEQ/g lipid wt. in males and 82–250 pg TEQ/g lipid wt. in females (Table 1). DLPCBs made the largest contribution to TEQs. TEQ and NDL-PCB levels observed
in Baikal seals were relatively higher than those in seals from other areas (Fig. 1)
(Nakata et al., 1998; Addison et al., 1999, 2005a, 2005b; Hobbs et al., 2002; Ross
et al., 2004; Riget et al., 2005; Hall and Thomas, 2007). In addition, TEQ levels
in 40% of the specimens and NDL-PCBs in 10% of the specimens exceeded the
immunosuppression value (TEQ: 209 pg/g lipid wt.; NDL-PCB: 16 µg/g lipid
wt.) observed in harbor seals (Ross et al., 1995; De Swart et al., 1995). These
results indicate that high levels of DRCs and NDL-PCBs present in Baikal seals
may cause adverse effect such as immunosuppression. Especially, it can be
expected that risk by PCBs are still at high.
Acknowledgments—We thank Dr. A. Subramanian (Ehime University) for the critical
reading of this manuscript. This study was supported by the “Global COE Program” from
the Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) and
Japan Society for the Promotion of Science (JSPS) and Grants-in-Aid for Scientific
Research (S) (No. 20221003) from JSPS.
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